TY - JOUR
A1 - Arrowsmith, Merle
A1 - Endres, Sara
A1 - Heinz, Myron
A1 - Nestler, Vincent
A1 - Holthausen, Max C.
A1 - Braunschweig, Holger
T1 - Probing the Boundaries between Lewis-Basic and Redox Behavior of a Parent Borylene
JF - Chemistry—A European Journal
N2 - The parent borylene (CAAC)(Me\(_{3}\)P)BH, 1 (CAAC=cyclic alkyl(amino)carbene), acts both as a Lewis base and one-electron reducing agent towards group 13 trichlorides (ECl\(_{3}\), E=B, Al, Ga, In), yielding the adducts 1-ECl\(_{3}\) and increasing proportions of the radical cation [1]\(^{•+}\) for the heavier group 13 analogues. With boron trihalides (BX\(_{3}\), X=F, Cl, Br, I) 1 undergoes sequential adduct formation and halide abstraction reactions to yield borylboronium cations and shows an increasing tendency towards redox processes for the heavier halides. Calculations confirm that 1 acts as a strong Lewis base towards EX3 and show a marked increase in the B−E bond dissociation energies down both group 13 and the halide group.
KW - redox processes
KW - bond dissociation energies
KW - borylene
KW - group 13
KW - Lewis adducts
Y1 - 2021
U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:bvb:20-opus-257154
VL - 27
IS - 70
ER -
TY - JOUR
A1 - Ban, Željka
A1 - Karačić, Zrinka
A1 - Tomić, Sanja
A1 - Amini, Hashem
A1 - Marder, Todd B.
A1 - Piantanida, Ivo
T1 - Triarylborane dyes as a novel non-covalent and non-inhibitive fluorimetric markers for DPP III enzyme
JF - Molecules
N2 - Novel dyes were prepared by simple “click CuAAC” attachment of a triarylborane–alkyne to the azide side chain of an amino acid yielding triarylborane dye 1 which was conjugated with pyrene (dye 2) forming a triarylborane–pyrene FRET pair. In contrast to previous cationic triarylboranes, the novel neutral dyes interact only with proteins, while their affinity to DNA/RNA is completely abolished. Both the reference triarylborane amino acid and triarylborane–pyrene conjugate bind to BSA and the hDPP III enzyme with high affinities, exhibiting a strong (up to 100-fold) fluorescence increase, whereby the triarylborane–pyrene conjugate additionally retained FRET upon binding to the protein. Furthermore, the triarylborane dyes, upon binding to the hDPP III enzyme, did not impair its enzymatic activity under a wide range of experimental conditions, thus being the first non-covalent fluorimetric markers for hDPP III, also applicable during enzymatic reactions with hDPP III substrates.
KW - triarylborane
KW - pyrene
KW - click CuAAC synthesis
KW - DPP III enzyme
KW - BSA
KW - fluorescence
Y1 - 2021
U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:bvb:20-opus-245046
SN - 1420-3049
VL - 26
IS - 16
ER -
TY - JOUR
A1 - Berger, Sarina M.
A1 - Ferger, Matthias
A1 - Marder, Todd B.
T1 - Synthetic Approaches to Triarylboranes from 1885 to 2020
JF - Chemistry – A European Journal
N2 - In recent years, research in the fields of optoelectronics, anion sensors and bioimaging agents have been greatly influenced by novel compounds containing triarylborane motifs. Such compounds possess an empty p‐orbital at boron which results in useful optical and electronic properties. Such a diversity of applications was not expected when the first triarylborane was reported in 1885. Synthetic approaches to triarylboranes underwent various changes over the following century, some of which are still used in the present day, such as the generally applicable routes developed by Krause et al. in 1922, or by Grisdale et al. in 1972 at Eastman Kodak. Some other developments were not pursued further after their initial reports, such as the synthesis of two triarylboranes bearing three different aromatic groups by Mikhailov et al. in 1958. This review summarizes the development of synthetic approaches to triarylboranes from their first report nearly 135 years ago to the present.
KW - arylmetalate
KW - boranes
KW - chromophore
KW - Lewis acid
KW - synthetic methods
Y1 - 2021
U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:bvb:20-opus-238952
VL - 27
IS - 24
SP - 7043
EP - 7058
ER -
TY - JOUR
A1 - Berger, Sarina M.
A1 - Rühe, Jessica
A1 - Schwarzmann, Johannes
A1 - Phillipps, Alexandra
A1 - Richard, Ann-Katrin
A1 - Ferger, Matthias
A1 - Krummenacher, Ivo
A1 - Tumir, Lidija-Marija
A1 - Ban, Željka
A1 - Crnolatac, Ivo
A1 - Majhen, Dragomira
A1 - Barišić, Ivan
A1 - Piantanida, Ivo
A1 - Schleier, Domenik
A1 - Griesbeck, Stefanie
A1 - Friedrich, Alexandra
A1 - Braunschweig, Holger
A1 - Marder, Todd B.
T1 - Bithiophene-Cored, mono-, bis-, and tris-(Trimethylammonium)-Substituted, bis-Triarylborane Chromophores: Effect of the Number and Position of Charges on Cell Imaging and DNA/RNA Sensing
JF - Chemistry—A European Journal
N2 - The synthesis, photophysical, and electrochemical properties of selectively mono-, bis- and tris-dimethylamino- and trimethylammonium-substituted bis-triarylborane bithiophene chromophores are presented along with the water solubility and singlet oxygen sensitizing efficiency of the cationic compounds Cat\(^{1+}\), Cat\(^{2+}\), Cat(i)\(^{2+}\), and Cat\(^{3+}\). Comparison with the mono-triarylboranes reveals the large influence of the bridging unit on the properties of the bis-triarylboranes, especially those of the cationic compounds. Based on these preliminary investigations, the interactions of Cat\(^{1+}\), Cat\(^{2+}\), Cat(i)\(^{2+}\), and Cat\(^{3+}\) with DNA, RNA, and DNApore were investigated in buffered solutions. The same compounds were investigated for their ability to enter and localize within organelles of human lung carcinoma (A549) and normal lung (WI38) cells showing that not only the number of charges but also their distribution over the chromophore influences interactions and staining properties.
KW - singlet oxygen
KW - boron
KW - bioimaging
KW - luminescence
KW - nucleic acid
Y1 - 2021
U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:bvb:20-opus-256963
VL - 27
IS - 56
ER -
TY - JOUR
A1 - Brückner, Tobias
A1 - Fantuzzi, Felipe
A1 - Stennett, Tom E.
A1 - Krummenacher, Ivo
A1 - Dewhurst, Rian D.
A1 - Engels, Bernd
A1 - Braunschweig, Holger
T1 - Isolation of neutral, mono-, and dicationic B\(_2\)P\(_2\) rings by diphosphorus addition to a boron-boron triple bond
JF - Angewandte Chemie International Edition
N2 - The NHC-stabilised diboryne (B\(_2\)(SIDep)\(_2\); SIDep=1,3-bis(2,6-diethylphenyl)imidazolin-2-ylidene) undergoes a high-yielding P−P bond activation with tetraethyldiphosphine at room temperature to form a B\(_2\)P\(_2\) heterocycle via a diphosphoryldiborene by 1,2-diphosphination. The heterocycle can be oxidised to a radical cation and a dication, respectively, depending on the oxidant used and its counterion. Starting from the planar, neutral 1,3-bis(alkylidene)-1,3-diborata-2,4-diphosphoniocyclobutane, each oxidation step leads to decreased B−B distances and loss of planarity by cationisation. X-ray analyses in conjunction with DFT and CASSCF/NEVPT2 calculations reveal closed-shell singlet, butterfly-shaped structures for the NHC-stabilised dicationic B\(_2\)P\(_2\) rings, with their diradicaloid, planar-ring isomers lying close in energy.
KW - inorganic chemistry
KW - radicals
KW - boron
KW - density functional calculations
KW - oxidation
KW - phosphorus heterocycles
Y1 - 2021
U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:bvb:20-opus-256451
VL - 60
IS - 24
ER -
TY - JOUR
A1 - Brückner, Tobias
A1 - Heß, Merlin
A1 - Stennett, Tom E.
A1 - Rempel, Anna
A1 - Braunschweig, Holger
T1 - Synthesis of Boron Analogues of Enamines via Hydroamination of a Boron-Boron Triple Bond
BT - Dedicated to Professor Wolfgang Kaim on the occasion of his 70th birthday
JF - Angewandte Chemie, International Edition
N2 - An N-heterocyclic-carbene-stabilized diboryne undergoes rapid, high-yielding and catalyst-free hydroamina- tion reactions with primary amines, yielding 1-amino-2-hydro- diborenes, which can be considered boron analogues of enamines. The electronics of the organic substituent at nitrogen influence the structure and further reactivity of the diborene product. With electron-rich anilines, a second hydroamination can occur at the diborene to generate 1,1-diamino-2,2-dihy- drodiboranes. With isopropylamine, the electronic influence of the alkyl substituent upon the diborene leads to an unprece- dented boron-mediated intramolecular N-dearylation reaction of an N-heterocyclic carbene unit.
KW - boron
KW - diborynes
KW - diborenes
KW - DFT
KW - enamines
KW - hydroamination
KW - multiple bonds
Y1 - 2021
U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:bvb:20-opus-240669
VL - 60
IS - 2
ER -
TY - JOUR
A1 - Budiman, Yudha P.
A1 - Lorenzen, Sabine
A1 - Liu, Zhiqiang
A1 - Radius, Udo
A1 - Marder, Todd B.
T1 - Base‐Free Pd‐Catalyzed C−Cl Borylation of Fluorinated Aryl Chlorides
JF - Chemistry – A European Journal
N2 - Catalytic C−X borylation of aryl halides containing two ortho‐fluorines has been found to be challenging, as most previous methods require stoichiometric amounts of base and the polyfluorinated aryl boronates suffer from protodeboronation, which is accelerated by ortho‐fluorine substituents. Herein, we report that a combination of Pd(dba)2 (dba=dibenzylideneacetone) with SPhos (2‐dicyclohexylphosphino‐2’,6’‐dimethoxybiphenyl) as a ligand is efficient to catalyze the C‐Cl borylation of aryl chlorides containing two ortho‐fluorine substituents. This method, conducted under base‐free conditions, is compatible with the resulting di‐ortho‐fluorinated aryl boronate products which are sensitive to base.
KW - boronate ester
KW - borylation
KW - cross-coupling
KW - fluoroarene
KW - palladium-catalyzed
Y1 - 2021
U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:bvb:20-opus-225687
VL - 27
IS - 11
SP - 3869
EP - 3874
ER -
TY - JOUR
A1 - Budiman, Yudha P.
A1 - Westcott, Stephen A.
A1 - Radius, Udo
A1 - Marder, Todd B.
T1 - Fluorinated Aryl Boronates as Building Blocks in Organic Synthesis
JF - Advanced Synthesis & Catalysis
N2 - Organoboron compounds are well known building blocks for many organic reactions. However, under basic conditions, polyfluorinated aryl boronic acid derivatives suffer from instability issues that are accelerated in compounds containing an ortho‐fluorine group, which result in the formation of the corresponding protodeboronation products. Therefore, a considerable amount of research has focused on novel methodologies to synthesize these valuable compounds while avoiding the protodeboronation issue. This review summarizes the latest developments in the synthesis of fluorinated aryl boronic acid derivatives and their applications in cross‐coupling reactions and other transformations.
image
KW - homogeneous catalysis
KW - boron reagents
KW - boronates
KW - fluorine
KW - fluoroarene
Y1 - 2021
U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:bvb:20-opus-225908
VL - 363
IS - 9
SP - 2224
EP - 2255
ER -
TY - JOUR
A1 - Chen, Xing
A1 - Meng, Guoyun
A1 - Liao, Guanming
A1 - Rauch, Florian
A1 - He, Jiang
A1 - Friedrich, Alexandra
A1 - Marder, Todd B.
A1 - Wang, Nan
A1 - Chen, Pangkuan
A1 - Wang, Suning
A1 - Yin, Xiaodong
T1 - Highly Emissive 9-Borafluorene Derivatives: Synthesis, Photophysical Properties and Device Fabrication
JF - Chemistry—A European Journal
N2 - A series of 9-borafluorene derivatives, functionalised with electron-donating groups, have been prepared. Some of these 9-borafluorene compounds exhibit strong yellowish emission in solution and in the solid state with relatively high quantum yields (up to 73.6 % for FMesB-Cz as a neat film). The results suggest that the highly twisted donor groups suppress charge transfer, but the intrinsic photophysical properties of the 9-borafluorene systems remain. The new compounds showed enhanced stability towards the atmosphere, and exhibited excellent thermal stability, revealing their potential for application in materials science. Organic light-emitting diode (OLED) devices were fabricated with two of the highly emissive compounds, and they exhibited strong yellow-greenish electroluminescence, with a maximum luminance intensity of >22 000 cd m\(^{-2}\). These are the first two examples of 9-borafluorene derivatives being used as light-emitting materials in OLED devices, and they have enabled us to achieve a balance between maintaining their intrinsic properties while improving their stability.
KW - boron heterocycles
KW - photophysics
KW - organic light-emitting diodes
KW - luminescence
KW - density functional calculations
Y1 - 2021
U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:bvb:20-opus-256738
VL - 27
IS - 20
ER -
TY - THES
A1 - Crumbach, Merian
T1 - Modifying the Optoelectronic Properties of Polycyclic Aromatic Hydrocarbons and Linear Oligomers by Doping with Boron and Further Heteroatoms
T1 - Modifizierung der Optoelektronischen Eigenschaften von Polyzyklischen Aromatischen Kohlenwasserstoffen und Linearen Oligomeren durch Dotierung mit Bor und weiteren Heteroatomen
N2 - Der Austausch ausgewählter CC-Einheiten durch ihre isoelektronischen und isosteren BN-Einheiten in π-konjugierten organischen Verbindungen (BN/CC-Isosterie), insbesondere in polyzyklischen aromatischen Kohlenwasserstoffen (PAKs), hat sich als erfolgreiche Strategie zur Herstellung neuartiger organisch-anorganischer Hybridmaterialien erwiesen, die strukturelle Ähnlichkeiten mit ihren reinen Kohlenstoff Analoga aufweisen, aber in vielen Fällen mit veränderten faszinierenden Eigenschaften und Funktionen.
In den ersten beiden Kapiteln werden die Synthese und Eigenschaften von neuartigen BNB-dotierten Phenalenylen, Dithienoazadiborepinen und Dithienooxadiborepinen vorgestellt. Die optoelektronischen Eigenschaften dieser neuen Bauelemente können durch Variation der eingebauten Ar- (Mes, Tip, FMes) und R-Gruppen (H, Me, i-Pr, t-Bu, Ph) effektiv eingestellt werden. Theoretische Untersuchungen, einschließlich NICS (Nucleus Independent Chemical Shift) Scans und AICD (Anisotropy of the Induced Current Density)-Berechnungen, wurden durchgeführt und geben Einblick in ihren aromatischen oder antiaromatischen Charakter.
Der Einbau von BP-Einheiten, welche mit BN und CC valenz-isoelektronisch sind, in ungesättigte organische Verbindungen ist dagegen bisher kaum untersucht worden, obwohl das Potenzial der resultierenden BCP-Hybridmaterialien für elektronische Anwendungen erst kürzlich erkannt wurde. Konjugierte Hauptkettenpolymere mit BP-Fragmenten im Rückgrat sind bisher unbekannt. Die ersten molekularen Modellverbindungen für ein BP-Analogon des konjugierten Polymers Poly(p-phenylen-vinylen) (PPV) werden in Kapitel 3 vorgestellt. Theoretische Untersuchungen ergaben, dass die Mes*-Gruppe das Phosphor-zentrum vollständig planarisiert, wodurch der B=P-Doppelbindungscharakter verstärkt und eine Konjugation über die BP-Einheit ermöglicht wird. Es wurden verschiedene synthetische Ansätze zu diesen molekularen Modellverbindungen untersucht und eine erfolgreiche synthetische Strategie gefunden.
N2 - The substitution of selected CC units by their isoelectronic and isosteric BN units in π−conjugated organic compounds (BN/CC isosterism), especially polycyclic aromatic hydrocarbons (PAHs), has emerged as a viable strategy to produce novel organic–inorganic hybrid materials with structural similarities to their all-carbon congeners, but in many cases with intriguing properties and functions.
In the first two chapters the synthesis and properties of novel BNB-doped phenalenyls, dithienoazadiborepins and dithienooxadiborepins are presented. The optoelectronic properties of these new building blocks can be effectively tuned by variation of the incorporated Ar (Mes, Tip, FMes) and R groups (H, Me, i-Pr, t-Bu, Ph). Theoretical investigations, including NICS (Nucleus Independent Chemical Shift) scans and AICD (Anisotropy of the Induced Current Density) calculations, have been performed which provide insight into their aromatic or antiaromatic character, respectively.
The incorporation of BP units, on the other hand, which are valence isoelectronic with BN and CC, into unsaturated organic compounds, has been scarcely studied, though the potential of the resulting BCP hybrid materials for electronic applications has been recognized quite recently. Main chain conjugated polymers featuring BP fragments in the backbone are unknown so far. The first molecular model compounds for a BP analogue of the conjugated polymer poly(p-phenylene vinylene) (PPV) are presented in chapter 3. Theoretical investigations revealed that the Mes* group to fully planarizes the phosphorus center, increasing the B=P double bond character and enabling conjugation over the BP unit. Different synthetic approaches to the molecular model compounds have been investigated and a viable synthetic strategy was found.
KW - Aromatizität
KW - Isoelektronisches Prinzip
KW - Polycyclische Aromaten
KW - Oligomere
KW - Bor
KW - BN compounds
KW - boron
KW - BP compounds
KW - polycycles
KW - oligomers
KW - Bor-Stickstoff-Verbindungen
KW - Bor
KW - Bor-Phosphor-Verbindungen
KW - Polyzyklen
KW - Oligomere
Y1 - 2021
U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:bvb:20-opus-242845
ER -
TY - JOUR
A1 - Crumbach, Merian
A1 - Bachmann, Jonas
A1 - Fritze, Lars
A1 - Helbig, Andreas
A1 - Krummenacher, Ivo
A1 - Braunschweig, Holger
A1 - Helten, Holger
T1 - Dithiophene‐Fused Oxadiborepins and Azadiborepins: A New Class of Highly Fluorescent Heteroaromatics
JF - Angewandte Chemie International Edition
N2 - Access to dithiophene‐fused oxadiborepins and the first azadiborepins attained via a modular synthesis route are presented. The new compounds emit intense blue light, some of which demonstrate fluorescence quantum yields close to unity. Cyclic voltammetry (CV) revealed electrochemically reversible one‐electron reduction processes. The weak aromatic character of the novel 1,2,7‐azadiborepin ring is demonstrated with in‐depth theoretical investigations using nucleus‐independent chemical shift (NICS) scans and anisotropy of the induced current density (ACID) calculations.
KW - aromaticity
KW - BN compounds
KW - boron
KW - isoelectronic analogues
KW - polycycles
Y1 - 2021
U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:bvb:20-opus-238996
VL - 60
IS - 17
SP - 9290
EP - 9295
ER -
TY - JOUR
A1 - Cui, Jingjing
A1 - Dietz, Maximilian
A1 - Härterich, Marcel
A1 - Fantuzzi, Felipe
A1 - Lu, Wei
A1 - Dewhurst, Rian D.
A1 - Braunschweig, Holger
T1 - Diphosphino-Functionalized 1,8-Naphthyridines: a Multifaceted Ligand Platform for Boranes and Diboranes
JF - Chemistry—A European Journal
N2 - A 1,8-naphthyridine diphosphine (NDP) reacts with boron-containing Lewis acids to generate complexes featuring a number of different naphthyridine bonding modes. When exposed to diborane B\(_{2}\)Br\(_{4}\), NDP underwent self-deprotonation to afford [NDP-B\(_{2}\)Br\(_{3}\)]Br, an unsymmetrical diborane comprised of four fused rings. The reaction of two equivalents of monoborane BBr\(_{3}\) and NDP in a non-polar solvent provided the simple phosphine-borane adduct [NDP(BBr\(_{3}\))\(_{2}\)], which then underwent intramolecular halide abstraction to furnish the salt [NDP-BBr\(_{2}\)][BBr\(_{4}\)], featuring a different coordination mode from that of [NDP-B\(_{2}\)Br\(_{3}\)]Br. Direct deprotonation of NDP by KHMDS or PhCH2K generates mono- and dipotassium reagents, respectively. The monopotassium reagent reacts with one or half an equivalent of B\(_{2}\)(NMe\(_{2}\))\(_{2}\)Cl\(_{2}\) to afford NDP-based diboranes with three or four amino substituents.
KW - pincer ligand
KW - potassium reagent
KW - diborane
KW - naphthyridine
KW - boron
Y1 - 2021
U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:bvb:20-opus-256994
VL - 27
IS - 63
ER -
TY - JOUR
A1 - Czernetzki, Corinna
A1 - Arrowsmith, Merle
A1 - Fantuzzi, Felipe
A1 - Gärtner, Annalena
A1 - Tröster, Tobias
A1 - Krummenacher, Ivo
A1 - Schorr, Fabian
A1 - Braunschweig, Holger
T1 - A neutral beryllium(I) radical
JF - Angewandte Chemie International Edition
N2 - The reduction of a cyclic alkyl(amino)carbene (CAAC)-stabilized organoberyllium chloride yields the first neutral beryllium radical, which was characterized by EPR, IR, UV/Vis spectroscopy and X-ray crystallography. DFT calculations show significant spin density at beryllium and confirm donor–acceptor bonding between an alkylberyllium radical fragment and a neutral CAAC ligand.
KW - inorganic chemistry
KW - X-ray crystallography
KW - Beryllium
KW - cyclic alkyl(amino)carbene
KW - EDA-NOCV
KW - radical
Y1 - 2021
U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:bvb:20-opus-256529
VL - 60
IS - 38
ER -
TY - JOUR
A1 - Ferger, Matthias
A1 - Ban, Željka
A1 - Krošl, Ivona
A1 - Tomić, Sanja
A1 - Dietrich, Lena
A1 - Lorenzen, Sabine
A1 - Rauch, Florian
A1 - Sieh, Daniel
A1 - Friedrich, Alexandra
A1 - Griesbeck, Stefanie
A1 - Kenđel, Adriana
A1 - Miljanić, Snežana
A1 - Piantanida, Ivo
A1 - Marder, Todd B.
T1 - Bis(phenylethynyl)arene Linkers in Tetracationic Bis-triarylborane Chromophores Control Fluorimetric and Raman Sensing of Various DNAs and RNAs
JF - Chemistry-A European Journal
N2 - We report four new luminescent tetracationic bis-triarylborane DNA and RNA sensors that show high binding affinities, in several cases even in the nanomolar range. Three of the compounds contain substituted, highly emissive and structurally flexible bis(2,6-dimethylphenyl-4-ethynyl)arene linkers (3: arene=5,5′-2,2′-bithiophene; 4: arene=1,4-benzene; 5: arene=9,10-anthracene) between the two boryl moieties and serve as efficient dual Raman and fluorescence chromophores. The shorter analogue 6 employs 9,10-anthracene as the linker and demonstrates the importance of an adequate linker length with a certain level of flexibility by exhibiting generally lower binding affinities than 3–5. Pronounced aggregation–deaggregation processes are observed in fluorimetric titration experiments with DNA for compounds 3 and 5. Molecular modelling of complexes of 5 with AT-DNA, suggest the minor groove as the dominant binding site for monomeric 5, but demonstrate that dimers of 5 can also be accommodated. Strong SERS responses for 3–5 versus a very weak response for 6, particularly the strong signals from anthracene itself observed for 5 but not for 6, demonstrate the importance of triple bonds for strong Raman activity in molecules of this compound class. The energy of the characteristic stretching vibration of the C≡C bonds is significantly dependent on the aromatic moiety between the triple bonds. The insertion of aromatic moieties between two C≡C bonds thus offers an alternative design for dual Raman and fluorescence chromophores, applicable in multiplex biological Raman imaging.
KW - boranes
KW - Raman probes
KW - molecular modelling
KW - fluorescent probes
KW - DNA/RNA sensors
Y1 - 2021
U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:bvb:20-opus-256717
VL - 27
IS - 16
ER -
TY - JOUR
A1 - Ferger, Matthias
A1 - Berger, Sarina M.
A1 - Rauch, Florian
A1 - Schönitz, Markus
A1 - Rühe, Jessica
A1 - Krebs, Johannes
A1 - Friedrich, Alexandra
A1 - Marder, Todd B.
T1 - Synthesis of Highly Functionalizable Symmetrically and Unsymmetrically Substituted Triarylboranes from Bench-Stable Boron Precursors
JF - Chemistry—A European Journal
N2 - A novel and convenient methodology for the one-pot synthesis of sterically congested triarylboranes by using bench-stable aryltrifluoroborates as the boron source is reported. This procedure gives systematic access to symmetrically and unsymmetrically substituted triarylboranes of the types BAr\(_{2}\)Ar’ and BArAr'Ar’’, respectively. Three unsymmetrically substituted triarylboranes as well as their iridium-catalyzed C−H borylation products are reported. These borylated triarylboranes contain one to three positions that can subsequently be orthogonally functionalized in follow-up reactions, such as Suzuki-Miyaura cross-couplings or Sonogashira couplings.
KW - synthetic methods
KW - boranes
KW - borylation
KW - chromophore
KW - functionalization
Y1 - 2021
U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:bvb:20-opus-256827
VL - 27
IS - 35
ER -
TY - JOUR
A1 - Franzsico, Marcos A. S.
A1 - Fantuzzi, Felipe
A1 - Cardozo, Thiago M.
A1 - Esteves, Pierre M.
A1 - Engels, Bernd
A1 - Oliveira, Ricardo R.
T1 - Taming the Antiferromagnetic Beast: Computational Design of Ultrashort Mn-Mn Bonds Stabilized by N-Heterocyclic Carbenes
JF - Chemistry—A European Journal
N2 - The development of complexes featuring low-valent, multiply bonded metal centers is an exciting field with several potential applications. In this work, we describe the design principles and extensive computational investigation of new organometallic platforms featuring the elusive manganese-manganese bond stabilized by experimentally realized N-heterocyclic carbenes (NHCs). By using DFT computations benchmarked against multireference calculations, as well as MO- and VB-based bonding analyses, we could disentangle the various electronic and structural effects contributing to the thermodynamic and kinetic stability, as well as the experimental feasibility, of the systems. In particular, we explored the nature of the metal-carbene interaction and the role of the ancillary η\(^{6}\) coordination to the generation of Mn\(_{2}\) systems featuring ultrashort metal-metal bonds, closed-shell singlet multiplicities, and positive adiabatic singlet-triplet gaps. Our analysis identifies two distinct classes of viable synthetic targets, whose electrostructural properties are thoroughly investigated.
KW - metal-metal interactions
KW - ab initio calculations
KW - carbene ligands
KW - density functional calculations
KW - manganese
Y1 - 2021
U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:bvb:20-opus-256874
VL - 27
IS - 47
ER -
TY - THES
A1 - Fritze, Lars
T1 - Ways to Novel Inorganic-Organic Hybrid Materials Applying New B–C Bond Formation Strategies
T1 - Wege zu neuartigen anorganisch-organischen Hybridmaterialien durch Anwendung von neuen B–C Kupplungsstrategien
N2 - π-Conjugated oligomers and polymers with tricoordinate boron centers incorporated into the main chain have attracted considerable attention as the interaction of the vacant p orbital on boron with an adjacent π system of the chain leads to conjugated materials with intriguing optical and electronic properties. This enables applicability in organic electronics and optoelectronics (OLEDs, OFETs, photovoltaics) or as sensory materials.
The potential of our B–C coupling protocol using metal-free catalytic Si/B exchange condensation is demonstrated by the synthesis of a series of π-conjugated monodisperse (het)aryl oligoboranes. Variation of the (het)aryl moieties allowed for tunability of the optoelectronic properties of the materials. Additionally, catalytic C–C cross-coupling strategies were applied to synthesize oligofuryl-based mono- and bisboranes, as well as polymers. These studies led to very robust and highly emissive compounds (f up to 97 %), which allow for tuning of their emission color from blue to orange. Furthermore, this work includes investigations of reaction routes to a kinetically stabilized tetraoxaporphyrinogen.
Being a key aspect of this work, a full investigation of the mechanism of the catalytic Si/B exchange was carried out. Additionally, this work presents the use of borenium cations to perform B–C coupling via intermolecular electrophilic borylation. Similar to the Si/B exchange, this route is capable of giving access to diaryl(bromo)boranes.
N2 - π-konjugierte Oligomere und Polymere mit dreifach koordinierten Bor-Zentren, die in die Hauptkette eingebaut sind, haben große Aufmerksamkeit erregt, da die Wechselwirkung des vakanten p-Orbitals am Bor mit dem π-System der Kette zu konjugierten Materialien mit faszinierenden optischen und elektronischen Eigenschaften führt. Dies ermöglicht die Anwendbarkeit in organischer Elektronik und Optoelektronik (OLEDs, OFETs, Photovoltaik) oder als sensorische Materialien.
Das Potenzial unseres B–C-Kupplungsprotokolls unter Verwendung der metallfreien katalytischen Si/B-Austauschskondensation wird durch die Synthese einer Reihe von π-konjugierten monodispersen (Het)aryl-Oligoboranen demonstriert. Durch Variation der (Het)aryl-Anteile konnten die optoelektronischen Eigenschaften der Materialien eingestellt werden. Zusätzlich wurden katalytische C–C-Kreuzkupplungsstrategien angewandt, um Oligofuryl-basierte Mono- und Bisborane sowie Polymere zu synthetisieren. Diese Untersuchungen führten zu sehr robusten und stark emittierenden Verbindungen (f bis zu 97 %), die die Einstellung ihrer Emissionsfarbe von blau bis orange ermöglichen. Weiterhin beinhaltet diese Arbeit Untersuchungen von Reaktionswegen zu einem kinetisch stabilisierten Tetraoxaporphyrinogen.
Als ein Schlüsselaspekt dieser Arbeit wurde eine vollständige Untersuchung des Mechanismus des katalytischen Si/B-Austauschs durchgeführt. Zusätzlich wird in dieser Arbeit die Verwendung von Borenium-Kationen zur Durchführung von B–C-Kupplungen über intermolekulare elektrophile Borylierungen vorgestellt. Ähnlich wie beim Si/B-Austausch kann dieser Weg genutzt werden, um Zugang zu Diaryl(bromo)boranen zu geben.
KW - Konjugierte Polymere
KW - Borverbindungen
KW - Kation
KW - Furanderivate
KW - Silizium-Bor-Austausch
KW - B–C-Kupplung
KW - C–C-Kupplung
KW - Furylborane
KW - C–H Aktivierung
KW - Silicon-Boron exchange
KW - B–C coupling
KW - C–C coupling
KW - Furylboranes
KW - C–H activation
Y1 - 2021
U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:bvb:20-opus-242173
ER -
TY - JOUR
A1 - Full, Julian
A1 - Panchal, Santosh P.
A1 - Götz, Julian
A1 - Krause, Ana‐Maria
A1 - Nowak‐Król, Agnieszka
T1 - Modular Synthesis of Organoboron Helically Chiral Compounds: Cutouts from Extended Helices
JF - Angewandte Chemie International Edition
N2 - Two types of helically chiral compounds bearing one and two boron atoms were synthesized by a modular approach. Formation of the helical scaffolds was executed by the introduction of boron to flexible biaryl and triaryl derived from small achiral building blocks. All‐ortho‐fused azabora[7]helicenes feature exceptional configurational stability, blue or green fluorescence with quantum yields (Φ\(_{fl}\)) of 18–24 % in solution, green or yellow solid‐state emission (Φ\(_{fl}\) up to 23 %), and strong chiroptical response with large dissymmetry factors of up to 1.12×10\(^{-2}\). Azabora[9]helicenes consisting of angularly and linearly fused rings are blue emitters exhibiting Φ\(_{fl}\) of up to 47 % in CH\(_{2}\)Cl\(_{2}\) and 25 % in the solid state. As revealed by the DFT calculations, their P–M interconversion pathway is more complex than that of H1. Single‐crystal X‐ray analysis shows clear differences in the packing arrangement of methyl and phenyl derivatives. These molecules are proposed as primary structures of extended helices.
KW - chirality
KW - circular dichroism
KW - fluorescence
KW - helicene
KW - organoboron
Y1 - 2021
U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:bvb:20-opus-225775
VL - 60
IS - 8
SP - 4350
EP - 4357
ER -
TY - JOUR
A1 - Föhrenbacher, Steffen A.
A1 - Krahfuss, Mirjam J.
A1 - Zapf, Ludwig
A1 - Friedrich, Alexandra
A1 - Ignat'ev, Nikolai V.
A1 - Finze, Maik
A1 - Radius, Udo
T1 - Tris(pentafluoroethyl)difluorophosphorane: a versatile fluoride acceptor for transition metal chemistry
JF - Chemistry Europe
N2 - Fluoride abstraction from different types of transition metal fluoride complexes [L\(_n\)MF] (M=Ti, Ni, Cu) by the Lewis acid tris(pentafluoroethyl)difluorophosphorane (C\(_2\)F\(_5\))\(_3\)PF\(_2\) to yield cationic transition metal complexes with the tris(pentafluoroethyl)trifluorophosphate counterion (FAP anion, [(C\(_2\)F\(_5\))\(_3\)PF\(_3\)]\(^-\)) is reported. (C\(_2\)F\(_5\))\(_3\)PF\(_2\) reacted with trans-[Ni(iPr\(_2\)Im)\(_2\)(Ar\(^F\))F] (iPr2Im=1,3-diisopropylimidazolin-2-ylidene; Ar\(^F\)=C\(_6\)F\(_5\), 1 a; 4-CF\(_3\)-C\(_6\)F\(_4\), 1 b; 4-C\(_6\)F\(_5\)-C\(_6\)F\(_4\), 1 c) through fluoride transfer to form the complex salts trans-[Ni(iPr\(_2\)Im)\(_2\)(solv)(Ar\(^F\))]FAP (2 a-c[solv]; solv=Et\(_2\)O, CH\(_2\)Cl\(_2\), THF) depending on the reaction medium. In the presence of stronger Lewis bases such as carbenes or PPh\(_3\), solvent coordination was suppressed and the complexes trans-[Ni(iPr\(_2\)Im)\(_2\)(PPh\(_3\))(C\(_6\)F\(_5\))]FAP (trans-2 a[PPh\(_3\)]) and cis-[Ni(iPr\(_2\)Im)\(_2\)(Dipp\(_2\)Im)(C\(_6\)F\(_5\))]FAP (cis-2 a[Dipp\(_2\)Im]) (Dipp\(_2\)Im=1,3-bis(2,6-diisopropylphenyl)imidazolin-2-ylidene) were isolated. Fluoride abstraction from [(Dipp\(_2\)Im)CuF] (3) in CH\(_2\)Cl\(_2\) or 1,2-difluorobenzene led to the isolation of [{(Dipp\(_2\)Im)Cu}\(_2\)]\(^2\)\(^+\)2 FAP\(^-\) (4). Subsequent reaction of 4 with PPh\(_3\) and different carbenes resulted in the complexes [(Dipp\(_2\)Im)Cu(LB)]FAP (5 a–e, LB=Lewis base). In the presence of C6Me6, fluoride transfer afforded [(Dipp\(_2\)Im)Cu(C\(_6\)Me\(_6\))]FAP (5 f), which serves as a source of [(Dipp\(_2\)Im)Cu)]\(^+\). Fluoride abstraction of [Cp\(_2\)TiF\(_2\)] (7) resulted in the formation of dinuclear [FCp\(_2\)Ti(μ-F)TiCp\(_2\)F]FAP (8) (Cp=η\(^5\)-C\(_5\)H\(_5\)) with one terminal fluoride ligand at each titanium atom and an additional bridging fluoride ligand.
KW - inorganic chemistry
KW - copper
KW - nickel
KW - phosphoranes
KW - titanium
KW - weakly coordinating anions
Y1 - 2021
U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:bvb:20-opus-256665
VL - 27
IS - 10
ER -
TY - JOUR
A1 - Föhrenbacher, Steffen A.
A1 - Zeh, Vivien
A1 - Krahfuss, Mirjam J.
A1 - Ignat'ev, Nikolai V.
A1 - Finze, Maik
A1 - Radius, Udo
T1 - Tris(pentafluoroethyl)difluorophosphorane and N‐Heterocyclic Carbenes: Adduct Formation and Frustrated Lewis Pair Reactivity
JF - European Journal of Inorganic Chemistry
N2 - The synthesis and characterization of Lewis acid/base adducts between tris(pentafluoroethyl)difluorophosphorane PF\(_{2}\)(C\(_{2}\)F\(_{5}\))\(_{3}\) and selected N-heterocyclic carbenes (NHCs) R\(_{2}\)Im (1,3-di-organyl-imidazolin-2-ylidene) and phosphines are reported. For NHCs with small alkyl substituents at nitrogen (R=Me, nPr, iPr) the adducts NHC ⋅ PF\(_{2}\)(C\(_{2}\)F\(_{5}\))\(_{3}\) (2 a–h) were isolated. The reaction with the sterically more demanding NHCs Dipp\(_{2}\)Im (1,3-bis-(2,6-di-iso-propylphenyl)-imidazolin-2-ylidene) (1 i) and tBu\(_{2}\)Im (1,3-di-tert-butyl-imidazolin-2-ylidene) (1 j) afforded the aNHC adducts 3 i and 3 j (a denotes “abnormal” NHC coordination via a backbone carbon atom). The use of tBuMeIm (1-tert-butyl-3-methyl-imidazolin-2-ylidene) (1 m) led to partial decomposition of the NHC and formation of the salt [tBuMeIm−H][MeIm ⋅ PF\(_{2}\)(C\(_{2}\)F\(_{5}\))\(_{3}\)] (4 m). The phosphorane PF\(_{2}\)(C\(_{2}\)F\(_{5}\))\(_{3}\) forms adducts with PMe\(_{3}\) but does not react with PPh\(_{3}\) or PCy\(_{3}\). The mer-cis isomer of literature-known Me\(_{3}\)P ⋅ PF\(_{2}\)(C\(_{2}\)F\(_{5}\))\(_{3}\) (5 a) was structurally characterized. Mixtures of the phosphorane PF\(_{2}\)(C\(_{2}\)F\(_{5}\))\(_{3}\) and the sterically encumbered NHCs tBu\(_{2}\)Im, Dipp\(_{2}\)Im, and Dipp\(_{2}\)Im\(^{H2}\) (1,3-bis-(2,6-di-iso-propylphenyl)-imidazolidin-2-ylidene) (1 k) showed properties of FLPs (Frustrated Lewis Pairs) as these mixtures were able to open the ring of THF (tetrahydrofuran) to yield NHC−(CH\(_{2}\))\(_{4}\)O−PF\(_{2}\)(C\(_{2}\)F\(_{5}\))\(_{3}\) 6 i–k. Furthermore, the deprotonation of the weak C−H acids CH\(_{3}\)CN, acetone, and ethyl acetate was achieved, which led to the formation of the corresponding imidazolium salts and the phosphates [PF\(_{2}\)(C\(_{2}\)F\(_{5}\))\(_{3}\)(CH\(_{2}\)CN)]\(^{-}\) (7), [PF\(_{2}\)(C\(_{2}\)F\(_{5}\))\(_{3}\)(OC(=CH\(_{2}\))CH\(_{3}\))]\(^{-}\) (8) and [PF\(_{2}\)(C\(_{2}\)F\(_{5}\))\(_{3}\)(CH\(_{2}\)CO\(_{2}\)Et)]\(^{-}\) (9).
KW - C-H activation
KW - N-Heterocyclic Carbene Adducts
KW - N-Heterocyclic Carbenes
KW - Frustrated Lewis Pairs
KW - Fluoro(perfluoroalkyl) phosphoranes
Y1 - 2021
U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:bvb:20-opus-257386
VL - 2021
IS - 20
ER -
TY - JOUR
A1 - Gerlach, Marius
A1 - Monninger, Sophie
A1 - Schleier, Domenik
A1 - Hemberger, Patrick
A1 - Goettel, James T.
A1 - Braunschweig, Holger
A1 - Fischer, Ingo
T1 - Photoelectron Photoion Coincidence Spectroscopy of NCl\(_{3}\) and NCl\(_{2}\)
JF - ChemPhysChem
N2 - We investigate NCl\(_{3}\) and the NCl\(_{2}\) radical by photoelectron-photoion coincidence spectroscopy using synchrotron radiation. The mass selected threshold photoelectron spectrum (ms-TPES) of NCl\(_{3}\) is broad and unstructured due to the large geometry change. An ionization energy of 9.7±0.1 eV is estimated from the spectrum and supported by computations. NCl2 is generated by photolysis at 213 nm from NCl\(_{3}\) and its ms-TPES shows an extended vibrational progression with a 90 meV spacing that is assigned to the symmetric N−Cl stretching mode in the cation. An adiabatic ionization energy of 9.94 ± 0.02 eV is determined.
KW - radicals
KW - photoelectron spectroscopy
KW - synchrotron radiation
KW - nitrogen trichloride
KW - photolysis
Y1 - 2021
U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:bvb:20-opus-257322
VL - 22
IS - 21
ER -
TY - JOUR
A1 - Gärtner, Annalena
A1 - Marek, Matthäus
A1 - Arrowsmith, Merle
A1 - Auerhammer, Dominic
A1 - Radacki, Krzysztof
A1 - Prieschl, Dominic
A1 - Dewhurst, Rian D.
A1 - Braunschweig, Holger
T1 - Boron- versus Nitrogen-Centered Nucleophilic Reactivity of (Cyano)hydroboryl Anions: Synthesis of Cyano(hydro)organoboranes and 2-Aza-1,4-diborabutatrienes
JF - Chemistry—A European Journal
N2 - Cyclic alkyl(amino)carbene-stabilized (cyano)hydroboryl anions were synthesized by deprotonation of (cyano)dihydroborane precursors. While they display boron-centered nucleophilic reactivity towards organohalides, generating fully unsymmetrically substituted cyano(hydro)organoboranes, they show cyano-nitrogen-centered nucleophilic reactivity towards haloboranes, resulting in the formation of hitherto unknown linear 2-aza-1,4-diborabutatrienes.
KW - nucleophile
KW - boron
KW - boryl anion
KW - cumulene
Y1 - 2021
U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:bvb:20-opus-256853
VL - 27
IS - 37
ER -
TY - JOUR
A1 - Hagspiel, Stephan
A1 - Arrowsmith, Merle
A1 - Fantuzzi, Felipe
A1 - Vargas, Alfredo
A1 - Rempel, Anna
A1 - Hermann, Alexander
A1 - Brückner, Tobias
A1 - Braunschweig, Holger
T1 - Highly colored boron-doped thiazolothiazoles from the reductive dimerization of boron isothiocyanates
JF - Angewandte Chemie International Edition
N2 - Reduction of (CAAC)BBr\(_2\)(NCS) (CAAC=cyclic alkyl(amino)carbene) in the presence of a Lewis base L yields tricoordinate (CAAC)LB(NCS) borylenes which undergo reversible E/Z-isomerization. The same reduction in the absence of L yields deep blue, bis(CAAC)-stabilized, boron-doped, aromatic thiazolothiazoles resulting from the dimerization of dicoordinate (CAAC)B(NCS) borylene intermediates.
KW - inorganic chemistry
KW - aromaticity
KW - reduction
KW - fused thiazaboroles
KW - DFT
KW - borylenes
Y1 - 2021
U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:bvb:20-opus-256432
VL - 60
IS - 12
ER -
TY - JOUR
A1 - Hagspiel, Stephan
A1 - Fantuzzi, Felipe
A1 - Dewhurst, Rian D.
A1 - Gärtner, Annalena
A1 - Lindl, Felix
A1 - Lamprecht, Anna
A1 - Braunschweig, Holger
T1 - Adducts of the parent boraphosphaketene H\(_2\)BPCO and their decarbonylative insertion chemistry
JF - Angewandte Chemie International Edition
N2 - The first examples of Lewis base adducts of the parent boraphosphaketene (H\(_2\)B-PCO) and their cyclodimers are prepared. One of these adducts is shown to undergo mild decarbonylation and phosphinidene insertion into a B−C bond of a borole, forming very rare examples of 1,2-phosphaborinines, B/P isosteres of benzene. The strong donor properties of these 1,2-phosphaborinines are confirmed by the synthesis of their π complexes with the Group 6 metals.
KW - inorganic chemistry
KW - phosphorus
KW - boron
KW - decarbonylation
KW - heterocycles
KW - ketenes
Y1 - 2021
U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:bvb:20-opus-256470
VL - 60
IS - 24
ER -
TY - JOUR
A1 - Hanft, Anna
A1 - Radacki, Krzysztof
A1 - Lichtenberg, Crispin
T1 - Cationic Bismuth Aminotroponiminates: Charge Controls Redox Properties
JF - Chemistry – A European Journal
N2 - The behavior of the redox‐active aminotroponiminate (ATI) ligand in the coordination sphere of bismuth has been investigated in neutral and cationic compounds, [Bi(ATI)\(_{3}\)] and [Bi(ATI)\(_{2}\)L\(_{n}\)][A] (L=neutral ligand; n=0, 1; A=counteranion). Their coordination chemistry in solution and in the solid state has been analyzed through (variable‐temperature) NMR spectroscopy, line‐shape analysis, and single‐crystal X‐ray diffraction analyses, and their Lewis acidity has been evaluated by using the Gutmann–Beckett method (and modifications thereof). Cyclic voltammetry, in combination with DFT calculations, indicates that switching between ligand‐ and metal‐centered redox events is possible by altering the charge of the compounds from 0 in neutral species to +1 in cationic compounds. This adds important facets to the rich redox chemistry of ATIs and to the redox chemistry of bismuth compounds, which is, so far, largely unexplored.
KW - aminotroponiminates
KW - bismuth
KW - cationic species
KW - redox chemistry
KW - redox-active ligands
Y1 - 2021
U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:bvb:20-opus-225669
VL - 27
IS - 20
SP - 6230
EP - 6239
ER -
TY - JOUR
A1 - Hanft, Anna
A1 - Rottschäfer, Dennis
A1 - Wieprecht, Nele
A1 - Geist, Felix
A1 - Radacki, Krzysztof
A1 - Lichtenberg, Crispin
T1 - Aminotroponiminates: Impact of the NO\(_{2}\) Functional Group on Coordination, Isomerisation, and Backbone Substitution
JF - Chemistry—A European Journal
N2 - Aminotroponiminate (ATI) ligands are a versatile class of redox-active and potentially cooperative ligands with a rich coordination chemistry that have consequently found a wide range of applications in synthesis and catalysis. While backbone substitution of these ligands has been investigated in some detail, the impact of electron-withdrawing groups on the coordination chemistry and reactivity of ATIs has been little investigated. We report here Li, Na, and K salts of an ATI ligand with a nitro-substituent in the backbone. It is demonstrated that the NO2 group actively contributes to the coordination chemistry of these complexes, effectively competing with the N,N-binding pocket as a coordination site. This results in an unprecedented E/Z isomerisation of an ATI imino group and culminates in the isolation of the first “naked” (i. e., without directional bonding to a metal atom) ATI anion. Reactions of sodium ATIs with silver(I) and tritylium salts gave the first N,N-coordinated silver ATI complexes and unprecedented backbone substitution reactions. Analytical techniques applied in this work include multinuclear (VT-)NMR spectroscopy, single-crystal X-ray diffraction analysis, and DFT calculations.
KW - aminotroponiminates
KW - non-coordinate anionic ligand
KW - isomerisation
KW - electrophilic substitution
KW - alkali metal
Y1 - 2021
U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:bvb:20-opus-256988
VL - 27
IS - 57
ER -
TY - JOUR
A1 - He, Jiang
A1 - Rauch, Florian
A1 - Friedrich, Alexandra
A1 - Krebs, Johannes
A1 - Krummenacher, Ivo
A1 - Bertermann, Rüdiger
A1 - Nitsch, Jörn
A1 - Braunschweig, Holger
A1 - Finze, Maik
A1 - Marder, Todd B.
T1 - Phenylpyridyl-fused boroles: a unique coordination mode and weak B-N coordination-induced dual fluorescence
JF - Angewandte Chemie International Edition
N2 - Phenylpyridyl-fused boroles [TipPBB1]\(_4\) and TipPBB2 were synthesized and their properties investigated. [TipPBB1]\(_4\) forms a tetramer in both the solid state and solution. TipPBB2 contains a 4-coordinate boron atom in the solid state but dissociates to give a 3-coordinate boron species in solution. TipPBB2 shows interesting temperature-dependent dual fluorescence in solution because of the equilibrium between 3- and 4-coordinate boron species due to weak N⋅⋅⋅B intermolecular coordination.
KW - inorganic chemistry
KW - weak intermolecular coordination
KW - boroles
KW - dual fluorescence
KW - equilibrium
KW - tetramers
Y1 - 2021
U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:bvb:20-opus-256423
VL - 60
IS - 9
ER -
TY - JOUR
A1 - Heß, Merlin
A1 - Krummenacher, Ivo
A1 - Dellermann, Theresa
A1 - Braunschweig, Holger
T1 - Rhodium-Mediated Stoichiometric Synthesis of Mono-, Bi-, and Bis-1,2-Azaborinines: 1-Rhoda-3,2-azaboroles as Reactive Precursors
JF - Chemistry—A European Journal
N2 - A series of highly substituted 1,2-azaborinines, including a phenylene-bridged bis-1,2-azaborinine, was synthesized from the reaction of 1,2-azaborete rhodium complexes with variously substituted alkynes. 1-Rhoda-3,2-azaborole complexes, which are accessible by phosphine addition to the corresponding 1,2-azaborete complexes, were also found to be suitable precursors for the synthesis of 1,2-azaborinines and readily reacted with alkynyl-substituted 1,2-azaborinines to generate new regioisomers of bi-1,2-azaborinines, which feature directly connected aromatic rings. Their molecular structures, which can be viewed as boron-nitrogen isosteres of biphenyls, show nearly perpendicular 1,2-azaborinine rings. The new method using rhodacycles instead of 1,2-azaborete complexes as precursors is shown to be more effective, allowing the synthesis of a wider range of 1,2-azaborinines.
KW - structure elucidation
KW - azaborinines
KW - nitrogen heterocycles
KW - cyclization
KW - metallacycles
Y1 - 2021
U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:bvb:20-opus-256830
VL - 27
IS - 37
ER -
TY - THES
A1 - Hock, Andreas
T1 - NHC-stabilized Alanes and Gallanes
T1 - NHC-stabilisierte Alane und Gallane
N2 - This thesis describes the synthesis and reactivity of NHC-stabilized Lewis-acid/Lewis-base adducts of alanes and gallanes (NHC = Me2ImMe, iPr2Im, iPr2ImMe, Dipp2Im, Dipp2ImH). As this field of research has developed tremendously, especially in the last five years, the first chapter provides an overview of the current state of knowledge.
The influence of electronegative π-donor-substituents on the stability of the NHC alane adducts is examined in chapter 2. For this purpose, the carbene stabilized alanes (NHC)∙AlH3 (NHC = iPr2Im, Dipp2Im) were reacted with secondary amines of different steric demand and with phenols. The π-donor substituents saturate the Lewis acidic aluminium center and coordination of a second NHC-ligand was not observed. The strongly electronegative N and O substituents increase the Lewis acidity of the aluminium atom, which leads to stronger Al-CNHC as well as Al-H bonds, which inhibits the insertion of the carbene into the Al-H bond.
In Chapter 3 the development of the synthesis and reactivity of carbene-stabilized gallanes is presented. The synthesis of NHC gallane adducts (NHC)∙GaH3, (NHC)∙GaH2Cl and (NHC)∙GaHCl2 and their reactivity towards NHCs and cAACMe were investigated in detail. The reaction of the mono- and dichlorogallanes (NHC)∙GaH2Cl and (NHC)∙GaHCl2 (NHC = iPr2ImMe, Dipp2Im) with cAACMe led to insertion of the cAACMe with formation of chiral and achiral compounds depending on the sterically demand of the used NHC. Furthermore, the formation of bis-alkylgallanes was observed for the insertion of two equivalents of cAACMe with release of the NHC ligand.
Chapter 4 describes investigations concerning the synthesis and reactivity of NHC-stabilized iodoalanes and iodogallanes, which are suitable for the formation of cationic aluminium and gallium dihydrides. The reaction of (NHC)∙EH2I (E = Al, Ga) stabilized by the sterically less demanding NHCs (NHC = Me2ImMe, iPr2Im, iPr2ImMe) with an additional equivalent of the NHC led to the formation of the cationic bis-NHC aluminium and gallium dihydrides [(NHC)2∙AlH2]+I- and [(NHC)2∙GaH2]+I-. Furthermore, the influence of the steric demand of the used NHC was investigated. The adduct (Dipp2Im)∙GaH2I was reacted with an additional equivalent of Dipp2Im. Due to the bulk of the NHC used, rearrangement of one of the NHC ligands from normal to abnormal coordination occurred and the cationic gallium dihydride [(Dipp2Im)∙GaH2(aDipp2Im)] was isolated.
Chapter 5 of this thesis reports investigations concerning the reduction of cyclopentadienyl-substituted alanes and gallanes with singlet carbenes. NHC stabilized pentamethylcyclopentadienyl aluminium and gallium dihydrides (NHC)∙Cp*MH2 (E = Al, Ga) were prepared by the reaction of (AlH2Cp*)3 with the corresponding NHCs or by the salt elimination of (NHC)∙GaH2I with KCp*. The gallane adducts decompose at higher temperatures with reductive elimination of Cp*H and formation of Cp*GaI. . The reductive elimination is preferred for sterically demanding NHCs (Dipp2Im > iPr2ImMe > Me2ImMe). In addition, NHC ring expansion of the backbone saturated carbene Dipp2ImH was observed for the reaction of the NHC with (AlH2Cp*)3, which led to (RER-Dipp2ImHH2)AlCp*. Furthermore, the reactivity of the adducts (NHC)∙Cp*EH2 (E = Al, Ga) towards cAACMe was investigated. The reaction of the alane adducts stabilized by the sterically more demanding NHCs iPr2ImMe and Dipp2Im afforded the exceptionally stable insertion product (cAACMeH)Cp*AlH V-10 with liberation of the NHC. The reaction of the gallium hydrides (NHC)∙Cp*GaH2 with cAACMe led to the reductive elimination of cAACMeH2 and formation of Cp*GaI.
A variety of neutral and cationic carbene-stabilized alanes and gallanes are presented in this work. The introduction of electronegative π-donor substituents (Cl-, I-, OR-, NR2-) and the investigations on the thermal stability of these compounds led to the conclusion that the stability of alanes and gallanes increased significantly by such a substitution. Investigations on the reactivity of the NHC adducts towards cAACMe resulted in various insertion products of the carbene into the Al-H or Ga-H bonds and the first cAACMe stabilized dichlorogallane was isolated. Furthermore, a first proof was provided that carbenes can be used specifically for the (formal) reduction of group 13 hydrides of the higher homologues. Thus, the synthesis of Cp*GaI from the reaction of (NHC)∙Cp*GaH2 with cAACMe was developed. In the future, this reaction pathway could be of interest for the preparation of other low-valent compounds of aluminium and gallium.
N2 - Die vorliegende Arbeit befasst sich mit der Synthese und Reaktivität NHC stabilisierter Lewis-Säuren/Lewis-Basen Addukte von Alanen und Galanen. Da sich dieses Forschungsgebiet insbesondere in den letzten fünf Jahren rasant entwickelt hat, wird im ersten Kapitel dieser Arbeit eine Übersicht über den gegenwärtigen Kenntnisstand gegeben. Nachdem in vorangegangenen Arbeiten in der Gruppe gezeigt werden konnte, dass NHC-substituierte Alane (NHC)∙AlH3 eine begrenzte Stabilität bezüglich einer möglichen Eliminierung von Dihydroaminal NHC-H2 bzw. der Ringerweiterung oder Ringöffnung des NHC-Liganden aufweisen, wird in Kapitel 2 der Arbeit der Einfluss elektronegativer π-Donor-Substituenten am Aluminium auf die Stabilität der dargestellten NHC-Alan-Addukte untersucht. Dazu wurden die Carben stabilisierten Alane (NHC)∙AlH3 (NHC = iPr2Im, Dipp2Im) mit sekundären Aminen unterschiedlichen sterischen Anspruchs und Phenolen umgesetzt. Die π-Donor Substituenten sättigen das Lewis-saure Aluminiumzentrum ab, sodass eine Koordination eines zweiten NHC-Liganden nicht möglich ist. Ferner erhöhen die stark elektronegativen N- und O-Substituenten die Lewis-Acidität des Aluminiumatoms, das zu stärkeren Al-CNHC, aber auch Al-H-Bindungen führt und vermutlich deshalb die Insertion des Carbens in diese Bindung erschwert ist. Kapitel 3 beschreibt die Entwicklung der Synthese von Carben-stabilisierten Gallanen und Untersuchungen zu deren Reaktivität. Es wurde die Darstellung der NHC-Gallan-Addukte und ihre Reaktivität gegenüber NHCs und cAACMe im Detail untersucht. Durch die Substitution der Hydrid-Substituenten durch Chloride konnte mit zunehmendem Chlorierungsgrad eine erhöhte Stabilität der Addukte festgestellt werden. Die Reaktion von cAACMe mit den NHC-stabilisierten Gallanen führt zur Insertion des cAACMe in die Ga-H-Bindung unter Ausbildung chiraler und achiraler Insertionsprodukten, sowie der zweifachen Insertion von cAACMe unter Abspaltung des NHC-Liganden und Bildung von Bisalkylgallanen. Kapitel 4 beschreibt Untersuchungen zur Synthese und Reaktivität Carben-stabilisierter Iodtriele, welche zur Darstellung kationischer Aluminium- und Galliumdihydride geeignet sind. Die Reaktion der NHC-Iodotriele (NHC)∙EH2I (E = Al, Ga), welche durch weniger sterisch anspruchsvollen NHCs stabilisiert werden, mit einem zusätzlichen Äquivalent des entsprechenden NHCs führt zur Bildung der kationischen bis-NHC-Aluminium- und Galliumdihydride [(NHC)∙MH2]+I. Um den Einfluss des sterischen Anspruchs des NHCs zu untersuchen, wurde das Addukt (Dipp2Im)∙GaH2I mit einem zusätzlichen Äquivalent Dipp2Im umgesetzt. Aufgrund der Sterik der verwendeten Carbene führte dies zur Umlagerung eines NHCs von normaler zu abnormaler Koordination unter Bildung von [(Dipp2Im)∙GaH2(aDipp2Im)]I. Im fünften Kapitel der Arbeit werden Untersuchungen zur Reduktion Cp*-substituierter Triele mit Carbenen beschrieben. Die Darstellung NHC-stabilisierter Cp* -Alane- und Gallane (NHC)∙Cp*MH2 (M = Al, Ga) erfolgte durch die direkte Umsetzung von (AlH2Cp*)3 mit den entsprechenden NHCs, bzw. durch Salzeliminierung ausgehend von (NHC)∙GaH2I mit KCp*. Die Gallan-Addukte zersetzen sich bei höheren Temperaturen unter reduktiver Eliminierung von Cp*H und Bildung von Cp*GaI. Die reduktive Eliminierung findet bevorzugt für sterisch anspruchsvolle NHCs statt. Darüber hinaus wurde eine NHC Ringerweiterungsreaktion des im Rückgrat gesättigten Carbens Dipp2ImH bei der Reaktion mit (AlH2Cp*)3 unter Ausbildung von (RER-Dipp2ImHH2)AlCp*. Darüber hinaus wurde die Reaktivität der Addukte (NHC)∙Cp*EH2 (E = Al. Ga) gegenüber cAACMe untersucht. Die Reaktion der durch die sterisch anspruchsvolleren NHCs iPr2ImMe und Dipp2Im stabilisierten Addukte mit cAACMe führte zur Bildung des außergewöhnlich stabilen Insertionsproduktes (cAACMeH)Cp*AlH unter Abspaltung des NHC-Liganden. Die Reaktion der Galliumhydride (NHC)∙Cp*GaH2 mit cAACMe führte stattdessen direkt zur reduktiven Eliminierung von cAACMeH2 unter Ausbildung von Cp*GaI.Im Rahmen dieser Arbeit wurden neutrale und kationische Carben-stabilisierte Alane und Gallane eingehend untersucht. Durch das Einführen elektronegativer π-Donor-Substituenten und Untersuchungen zur thermischen Belastbarkeit dieser Verbindungen wurde nachgewiesen, dass sich die Stabilität der Alane bzw. Gallane durch eine derartige Substitution deutlich erhöht. Untersuchungen zur Reaktivität der NHC-Addukte gegenüber cAACMe brachte diverse Insertionsprodukte des Carbens in Al-H bzw. Ga-H-Bindungen hervor. Ferner konnte das erste cAACMe-stabilisierte Dichlorogalliumhydrid dargestellt werden. Darüber hinaus wurde ein erster Nachweis erbracht, dass Carbene gezielt zur (formalen) Reduktion von Hydriden der höheren Homologen der Gruppe 13 verwendet werden können. So wurde die Synthese von Cp*GaI aus der Reaktion von (NHC)∙Cp*GaH2 mit cAACMe entwickelt. In Zukunft könnte dieser Reaktionspfad zur Darstellung niedervalenter Verbindungen der Triele Aluminium und Gallium von Interesse sein.
KW - Aluminiumhydridderivate
KW - Gallium
KW - Heterocyclische Carbene <-N>
KW - Aluminium
KW - Carbene
Y1 - 2021
U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:bvb:20-opus-212525
ER -
TY - JOUR
A1 - Huang, Mingming
A1 - Wu, Zhu
A1 - Krebs, Johannes
A1 - Friedrich, Alexandra
A1 - Luo, Xiaoling
A1 - Westcott, Stephen A.
A1 - Radius, Udo
A1 - Marder, Todd B.
T1 - Ni-Catalyzed Borylation of Aryl Sulfoxides
JF - Chemistry—A European Journal
N2 - A nickel/N-heterocyclic carbene (NHC) catalytic system has been developed for the borylation of aryl sulfoxides with B\(_{2}\)(neop)\(_{2}\) (neop=neopentyl glycolato). A wide range of aryl sulfoxides with different electronic and steric properties were converted into the corresponding arylboronic esters in good yields. The regioselective borylation of unsymmetric diaryl sulfoxides was also feasible leading to borylation of the sterically less encumbered aryl substituent. Competition experiments demonstrated that an electron-deficient aryl moiety reacts preferentially. The origin of the selectivity in the Ni-catalyzed borylation of electronically biased unsymmetrical diaryl sulfoxide lies in the oxidative addition step of the catalytic cycle, as oxidative addition of methoxyphenyl 4-(trifluoromethyl)phenyl sulfoxide to the Ni(0) complex occurs selectively to give the structurally characterized complex trans-[Ni(ICy)\(_{2}\)(4-CF\(_{3}\)-C\(_{6}\)H\(_{4}\)){(SO)-4-MeO-C\(_{6}\)H\(_{4}\)}] 4. For complex 5, the isomer trans-[Ni(ICy)\(_{2}\)(C\(_{6}\)H\(_{5}\))(OSC\(_{6}\)H\(_{5}\))] 5-I was structurally characterized in which the phenyl sulfinyl ligand is bound via the oxygen atom to nickel. In solution, the complex trans-[Ni(ICy)\(_{2}\)(C\(_{6}\)H\(_{5}\))(OSC\(_{6}\)H\(_{5}\))] 5-I is in equilibrium with the S-bonded isomer trans-[Ni(ICy)\(_{2}\)(C\(_{6}\)H\(_{5}\))(SOC\(_{6}\)H\(_{5}\))] 5, as shown by NMR spectroscopy. DFT calculations reveal that these isomers are separated by a mere 0.3 kJ/mol (M06/def2-TZVP-level of theory) and connected via a transition state trans-[Ni(ICy)\(_{2}\)(C\(_{6}\)H\(_{5}\))(η\(^{2}\)-{SO}-C\(_{6}\)H\(_{5}\))], which lies only 10.8 kcal/mol above 5.
KW - Boron
KW - cross-coupling
KW - N-heterocyclic carbenes
KW - nickel
KW - borylation
Y1 - 2021
U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:bvb:20-opus-256778
VL - 27
IS - 31
ER -
TY - THES
A1 - Kerner, Florian Tobias
T1 - Reactions of rhodium(I) with diynes and studies of the photophysical behavior of the luminescent products
T1 - Reaktionen von Rhodium(I) mit Diinen und Untersuchung der photophysikalischen Eigenschaften der lumineszenten Produkte
N2 - Chapter 1 deals with the reaction of [Rh(acac)(PMe3)2] with para-substituted 1,4-diphenylbuta-1,3-diynes at room temperature, in which a complex containing a bidentate organic fulvene moiety, composed of two diynes, σ-bound to the rhodium center is formed in an all-carbon [3+2] type cyclization reaction. In addition, a complex containing an organic indene moiety, composed of three diynes, attached to the rhodium center in a bis-σ-manner is formed in a [3+2+3] cyclization process.
Reactions at 100 °C reveal that the third diyne inserts between the rhodium center and the bis-σ-bound organic fulvene moiety. Furthermore, the formation of a 2,5- and a 2,4-bis(arylethynyl)rhodacyclopentadiene is observed. The unique [3+2] cyclization product was used for the synthesis of a highly conjugated organic molecule, which is hard to access or even inaccessible by conventional methods. Thus, at elevated temperatures, reaction of the [3+2] product with para-tolyl isocyanate led to the formation of a purple organic compound containing the organic fulvene structure and one equivalent of para-tolyl isocyanate.
The blue and green [3+2+3] complexes show an unusually broad absorption from 500 – 1000 nm with extinction coefficients ε of up to 11000 M-1 cm-1. The purple organic molecule shows an absorption spectrum similar to those of known diketopyrrolopyrroles.
Additionally, the reaction of [Rh(acac)(PMe3)2] with para-tolyl isocyanate was investigated. A cis-phosphine complex of the form cis-[Rh(acac)(PMe3)2(isocyanate)2] with an isocyanate dimer bound to the rhodium center by one carbon and one oxygen atom was isolated.
Replacing the trimethylphosphine ligands in [Rh(acac)(PMe3)2] with the stronger σ-donating NHC ligand Me2Im (1,3-dimethylimidazolin-2-ylidene), again, drastically alters the reaction. Similar [3+2] and [3+2+3] products to those discussed above could not be unambiguously assigned, but cis- and trans-π-complexes, which are in an equilibrium with the two starting materials, were formed.
Chapters 2 is about the influence of the backbone of the α,ω-diynes on the formation and photophysical properties of 2,5-bis(aryl)rhodacyclopentadienes. Therefore, different α,ω-diynes were reacted with [Rh(acac)(PMe3)2] and [Rh(acac)(P(p-tolyl)3)2] in equimolar amounts. In general, a faster consumption of the rhodium(I) starting material is observed while using preorganized α,ω-diynes with electron withdrawing substituents in the backbone. The isolated PMe3-substituted rhodacyclopentadienes exhibit fluorescence, despite the presence of the heavy atom rhodium, with lifetimes τF of < 1 ns and photoluminescence quantum yields Φ of < 0.01 as in previously reported P(p-tolyl)-substituted 2,5-bis(arylethynyl)rhodacyclopentadienes. However, an isolated P(p-tolyl)-substituted 2,5-bis(aryl)rhodacyclopentadiene shows multiple lifetimes and different absorption and excitation spectra leading to the conclusion that different species may be present.
Reaction of [Rh(acac)(Me2Im)2] with dimethyl 4,4'-(naphthalene-1,8-diylbis(ethyne-2,1-diyl))dibenzoate, results in the formation of a mixture trans- and cis-NHC-substituted 2,5-bis(aryl)rhodacyclopentadienes.
In chapter 3 the reaction of various acac- and diethyldithiocarbamate-substituted rhodium(I) catalysts bearing (chelating)phosphines with α,ω-bis(arylethynyl)alkanes (α,ω-diynes), yielding luminescent dimers and trimers, is described. The photophysical properties of dimers and trimers of the α,ω-diynes were investigated and compared to para-terphenyl, showing a lower quantum yield and a larger apparent Stokes shift.
Furthermore, a bimetallic rhodium(I) complex of the form [Rh2(ox)(P(p-tolyl)3)4] (ox: oxalate) was reacted with a CO2Me-substituted α,ω-tetrayne forming a complex in which only one rhodium(I) center reacts with the α,ω-tetrayne. The photophysical properties of this mixed rhodium(I)/(III) species shows only negligible differences compared to the P(p-tolyl)- and CO2Me-substituted 2,5-bis(arylethynyl)rhodacyclopentadiene, previously synthesized by Marder and co-workers.
N2 - Kapitel 1 beschäftigt sich mit der Umsetzung von [Rh(acac)(PMe3)2] mit zwei Äquivalenten para-substituierten 1,4-Diphenylbuta-1,3-diins bei Raumtemperatur. Dabei bildete sich ein Komplex, welcher eine organische Fulveneinheit, bestehend aus zwei Diinen und verbunden über zwei σ-Bindungen mit dem Rhodiumzentralatom, besitzt. Diese Verbindung bildet sich in einer „all-carbon“ [3+2] ähnlichen Zyklisierungsreaktion. Ebenso konnte aus derselben Reaktion ein Komplex mit einer Indeneinheit, bestehend aus drei Diinen, welche durch zwei σ-Bindungen mit dem Rhodiumzentralatom verbunden sind, isoliert und charakterisiert werden. Diese Verbindung bildet sich in einer „all-carbon“ [3+2+3] ähnlichen Zyklisierungsreaktion. Experimente bei 100 °C zeigen, dass sich das zusätzliche dritte Diin zwischen dem Rhodiumzentralatom und der organischen Fulveneinheit einfügt. Zusätzlich konnte die Bildung von 2,4- und 2,5-Bis(arylethinyl)rhodazyklopentadienen bei 100°C beobachtet werden. Diese seltene [3+2] Zyklisierungsreaktion kann benutzt werden um konjugierte, organische Moleküle darzustellen, welche sonst nur schwer oder gar nicht mit bisher bekannten Synthesemethoden zugänglich sind. In der Umsetzung des [3+2] Komplexes mit para-Tolylisocyanat bei 80 °C konnte ein violetter, rein organischer Feststoff erhalten werden, bestehend aus der organischen Fulveneinheit und einem Äquivalent para-Tolylisocyanat. Die blauen und grünen [3+2+3] Komplexe zeigen unter anderem eine ungewöhnliche breite Absorption von 500 – 1000 nm mit einem Extinktionskoeffizienten von bis zu 11000 M-1 cm-1. Die violette, rein organische Verbindung zeigt ein Absorptionsspektrum ähnlich zu bereits bekannten Diketopyrrolopyrrolen. Auch wurde die Reaktion von [Rh(acac)(PMe3)2] mit para-Tolylisocyanat untersucht. Es konnte ein cis-phosphan Komplex, bei dem ein para-Tolylisocyanat-Dimer über ein Kohlenstoff- und ein Sauerstoffatom an das Rhodiumzentralatom koordiniert, isoliert und charakterisiert werden. Substitution des Trimethylphosphans im Rh(I)-Präkursors durch einen NHC Liganden, nämlich Me2Im (1,3-dimethylimidazolin-2-yliden) führt zu einem unterschiedlichen Reaktionsverlauf. Ähnliche [3+2] und [3+2+3] Komplexe konnten nicht zweifelsfrei bestätigt werden, dafür konnte aber gezeigt werden, dass sich in der Reaktion bildende cis- und trans-Komplexe im Gleichgewicht mit den verwendeten Startmaterialien befinden.
Im zweiten Kapitel dieser Arbeite wurde der Einfluss des Rückgrats von α,ω-bis(arylethynyl)alkanen (α,ω-Diine) auf die Bildung und die photophysikalischen Eigenschaften von 2,5-Bis(aryl)rhodazyklopentadienen untersucht. Dazu wurden mehrere α,ω-Diine mit unterschiedlichem Rückgrat synthetisiert und diese mit [Rh(acac)(PMe3)2] und [Rh(acac)(P(p-tolyl)3)2] in äquimolaren Mengen reagiert. Es konnte ein schnellerer Verbrauch des Rh(I)-Präkursors bei der Verwendung von vororganisierten α,ω-Diinen mit elektronenziehenden Substituenten am Rückgrat festgestellt werden. Die PMe3-substituierten Rhodazyklopentadiene zeigen Fluoreszenz, trotz der Anwesenheit eines Schwermetalls. Lebenszeiten von τF < 1 ns und Quantenausbeuten von Φ < 0.01, ähnlich wie in P(p-tolyl)-substituierten 2,5-Bis(arylethynyl)rhodazyklopentadienen wurden beobachtet. Bei einem isolierten P(p-tolyl)-substituierten 2,5-Bis(aryl)rhodazyklopentadien konnten mehrere Lebenszeiten, wie auch unterschiedliche Absorptions- und Anregungsspektren detektiert werden, was zu der Schlussfolgerung führt, dass in Lösung mehrere Spezies vorhanden sind. Die Reaktion von [Rh(acac)(Me2Im)2] mit Dimethyl 4,4'-(naphthalen-1,8-diylbis(ethyn-2,1-diyl))dibenzoat führt zur Bildung einer Mischung aus trans- und cis-NHC-substituierter 2,5-Bis(aryl)rhodazyklopentadienen.
Im dritten Kapitel, wurde die Bildung lumineszenter Dimere und Trimere aus der Umsetzung von verschiedenen α,ω-Diinen mit katalytischen Mengen verschiedener acac- und diethyldithiocarbamat-substituierter Rhodium(I)-Katalysatoren mit (chelatisierenden) phosphanen untersucht. Anschließend wurden die photophysikalischen Eigenschaften der Dimere und Trimere untersucht und mit para-Terphenyl verglichen. Dabei wurden ähnliche Lebenszeiten, eine geringere Quantenausbeute wie auch größere Stokes-Verschiebungen der Dimere und Trimere im Vergleich zu para-Terphenyl gefunden. Auch wurde die Reaktion zwischen einem bimetallischen Rhodium Komplex [Rh2(ox)(P(p-tolyl)3)4] (ox: oxalat) und einem CO2Me-substituiertem α,ω-bis(arylbutadiynyl)alkan (α,ω-Tetrain) untersucht. In dieser Umsetzung reagierte nur eine der beiden möglichen Rhodium(I)-zentren mit dem α,ω-Tetrain unter Bildung eines 2,5-Bis(arylethynyl)rhodazyklopentadiens. Die photophysikalischen Eigenschaften dieser gemischten Rhodium(I)/(III)-Spezies zeigt nur marginale unterschiede, verglichen mit einem mononuklearen P(p-tolyl)- und CO2Me-substituiertem 2,5-Bis(arylethynyl)rhodazyklopentadiens, welches zuvor im Arbeitskreis Marder schon synthetisiert wurde.
KW - Übergangsmetallkomplexe
KW - Rhodium
KW - Übergangsmetallkomplex
KW - Zyklisierung
KW - Transitionmetal
KW - Cyclization
Y1 - 2021
U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:bvb:20-opus-209107
ER -
TY - JOUR
A1 - Kole, Goutam Kumar
A1 - Merz, Julia
A1 - Amar, Anissa
A1 - Fontaine, Bruno
A1 - Boucekkine, Abdou
A1 - Nitsch, Jörn
A1 - Lorenzen, Sabine
A1 - Friedrich, Alexandra
A1 - Krummenacher, Ivo
A1 - Košćak, Marta
A1 - Braunschweig, Holger
A1 - Piantanida, Ivo
A1 - Halet, Jean-François
A1 - Müller-Buschbaum, Klaus
A1 - Marder, Todd B.
T1 - 2- and 2,7-substituted para-N-methylpyridinium pyrenes: syntheses, molecular and electronic structures, photophysical, electrochemical, and spectroelectrochemical properties and binding to double-stranded (ds) DNA
JF - Chemistry - A European Journal
N2 - Two N-methylpyridinium compounds and analogous N-protonated salts of 2- and 2,7-substituted 4-pyridyl-pyrene compounds were synthesised and their crystal structures, photophysical properties both in solution and in the solid state, electrochemical and spectroelectrochemical properties were studied. Upon methylation or protonation, the emission maxima are significantly bathochromically shifted compared to the neutral compounds, although the absorption maxima remain almost unchanged. As a result, the cationic compounds show very large apparent Stokes shifts of up to 7200 cm\(^{-1}\). The N-methylpyridinium compounds have a single reduction at ca. −1.5 V vs. Fc/Fc\(^+\) in MeCN. While the reduction process was reversible for the 2,7-disubstituted compound, it was irreversible for the mono-substituted one. Experimental findings are complemented by DFT and TD-DFT calculations. Furthermore, the N-methylpyridinium compounds show strong interactions with calf thymus (ct)-DNA, presumably by intercalation, which paves the way for further applications of these multi-functional compounds as potential DNA-bioactive agents.
KW - inorganic chemistry
KW - viologens
KW - chromophores
KW - luminescent
KW - pyrenes
KW - pyridinium
Y1 - 2021
U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:bvb:20-opus-256642
VL - 27
IS - 8
ER -
TY - JOUR
A1 - Krahfuss, Mirjam J.
A1 - Radius, Udo
T1 - N‐Heterocyclic Silylene Main Group Element Chemistry: Adduct Formation, Insertion into E−X Bonds and Cyclization of Organoazides
JF - European Journal of Inorganic Chemistry
N2 - Investigations concerning the reactivity of the N‐heterocyclic silylene Dipp\(_{2}\)NHSi (1, 1,3‐bis(2,6‐diisopropylphenyl)‐1,3‐diaza‐2‐silacyclopent‐4‐en‐2‐ylidene) towards selected alanes and boranes, elemental halides X\(_{2}\) (X=Br, I), selected halide containing substrates such as tin chlorides and halocarbons, as well as organoazides are presented. The NHSi adducts Dipp\(_{2}\)NHSi⋅AlI\(_{3}\) (2), Dipp\(_{2}\)NHSi⋅Al(C\(_{6}\)F\(_{5}\))\(_{3}\) (3), and Dipp\(_{2}\)NHSi⋅B(C\(_{6}\)F\(_{5}\))\(_{3}\) (4) were formed by the reaction of Dipp\(_{2}\)NHSi with the corresponding Lewis acids AlI\(_{3}\), Al(C\(_{6}\)F\(_{6}\))\(_{3}\) and B(C\(_{6}\)F\(_{5}\))\(_{3}\). Adducts 3 and 4 were tested with respect to their ability to activate small organic molecules, but no frustrated Lewis pair reactivity was observed. Reactions of Dipp\(_{2}\)NHSi with Br\(_{2}\), I\(_{2}\), Ph\(_{2}\)SnCl\(_{2}\) and Me\(_{3}\)SnCl led to formation of Dipp\(_{2}\)NHSiBr\(_{2}\) (5), Dipp\(_{2}\)NHSiI\(_{2}\) (6), Dipp\(_{2}\)NHSiCl\(_{2}\) (7) and {(Me\(_{3}\)Sn)N(Dipp)CH}\(_{2}\) (8), respectively. The reaction with the halocarbons methyl iodide, benzyl chloride, and benzyl bromide afforded the insertion products Dipp\(_{2}\)NHSi(I)(CH\(_{3}\)) (9), Dipp\(_{2}\)NHSi(Cl)(CH\(_{2}\)Ph) (10) and Dipp\(_{2}\)NHSi(Br)(CH\(_{2}\)Ph) (11). Reaction of Dipp\(_{2}\)NHSi with the organoazides Ad‐N\(_{3}\) (Ad=adamantyl) and TMS‐N\(_{3}\) (TMS=trimethylsilyl) led to the formation of 1‐Dipp\(_{2}\)NHSi‐2,5‐bis(adamantyl)‐tetrazoline (12) and bis(trimethylsilyl)amido azido silane (13), respectively. For 2,6‐(diphenyl)phenyl‐N\(_{3}\) C−H activation occurs and a cyclosilamine 14 was isolated.
KW - arbenes
KW - E−X bond activation
KW - acid/base adducts
KW - Organoazides
KW - Silylenes
Y1 - 2021
U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:bvb:20-opus-224507
VL - 2021
IS - 6
SP - 548
EP - 561
ER -
TY - JOUR
A1 - Krebs, Johannes
A1 - Haehnel, Martin
A1 - Krummenacher, Ivo
A1 - Friedrich, Alexandra
A1 - Braunschweig, Holger
A1 - Finze, Maik
A1 - Ji, Lei
A1 - Marder, Todd B.
T1 - Synthesis and Structure of an o-Carboranyl-Substituted Three-Coordinate Borane Radical Anion
JF - Chemistry—A European Journal
N2 - Bis(1-(4-tolyl)-carboran-2-yl)-(4-tolyl)-borane [(1-(4-MeC\(_{6}\)H\(_{4}\))-closo-1,2-C\(_{2}\)B\(_{10}\)H\(_{10}\)-2-)\(_{2}\)(4-MeC\(_{6}\)H\(_{4}\))B] (1), a new bis(o-carboranyl)-(R)-borane was synthesised by lithiation of the o-carboranyl precursor and subsequent salt metathesis reaction with (4-tolyl)BBr\(_{2}\). Cyclic voltammetry experiments on 1 show multiple distinct reduction events with a one-electron first reduction. In a selective reduction experiment the corresponding paramagnetic radical anion 1\(^{.−}\) was isolated and characterized. Single-crystal structure analyses allow an in-depth comparison of 1, 1\(^{.−}\), their calculated geometries, and the S\(_{1}\) excited state of 1. Photophysical studies of 1 show a charge transfer (CT) emission with low quantum yield in solution but a strong increase in the solid state. TD-DFT calculations were used to identify transition-relevant orbitals.
KW - Wade’s rules
KW - carborane
KW - charge transfer
KW - radical
KW - threecoordinate boron
Y1 - 2021
U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:bvb:20-opus-256841
VL - 27
IS - 31
ER -
TY - JOUR
A1 - Lindl, Felix
A1 - Guo, Xueying
A1 - Krummenacher, Ivo
A1 - Rauch, Florian
A1 - Rempel, Anna
A1 - Paprocki, Valerie
A1 - Dellermann, Theresa
A1 - Stennett, Tom E.
A1 - Lamprecht, Anna
A1 - Brückner, Tobias
A1 - Radacki, Krzysztof
A1 - Bélanger-Chabot, Guillaume
A1 - Marder, Todd B.
A1 - Lin, Zhenyang
A1 - Braunschweig, Holger
T1 - Rethinking Borole Cycloaddition Reactivity
JF - Chemistry—A European Journal
N2 - Boroles are attracting broad interest for their myriad and diverse applications, including in synthesis, small molecule activation and functional materials. Their properties and reactivity are closely linked to the cyclic conjugated diene system, which has been shown to participate in cycloaddition reactions, such as the Diels-Alder reaction with alkynes. The reaction steps leading to boranorbornadienes, borepins and tricyclic boracyclohexenes from the thermal reaction of boroles with alkynes are seemingly well understood as judged from the literature. Herein, we question the long-established mechanistic picture of pericyclic rearrangements by demonstrating that seven-membered borepins (i. e., heptaphenylborepin and two derivatives substituted with a thienyl and chloride substituent on boron) exist in a dynamic equilibrium with the corresponding bicyclic boranorbornadienes, the direct Diels-Alder products, but are not isolable products from the reactions. Heating gradually converts the isomeric mixtures into fluorescent tricyclic boracyclohexenes, the most stable isomers in the series. Results from mechanistic DFT calculations reveal that the tricyclic compounds derive from the boranorbornadienes and not the borepins, which were previously believed to be intermediates in purely pericyclic processes.
KW - pericyclic reaction
KW - Boron
KW - computational chemistry
KW - isomer
KW - isomerization
Y1 - 2021
U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:bvb:20-opus-256888
VL - 27
IS - 43
ER -
TY - THES
A1 - Liu, Zhiqiang
T1 - Fluorinated Aryl Boronates as Units in Organic Synthesis
T1 - Fluorierte Arylboronate als Einheiten in organischer Synthese
N2 - It is generally acknowledged that polyfluoroarenes are important fluorinated structural units for various organic molecules, such as pharmaceuticals, agrochemicals, and organic materials. Polyfluorinated aryl alkynes and alcohols are also powerful building blocks in chemical synthesis because of their versatility to be transformed into various useful molecules and also their ubiquity in natural product synthesis. Efficient methods for the synthesis of polyfluorinated aryl alkynes and alcohols are presented in Chapter 2 and Chapter 3. In addition, 3-amino-indoles have found a broad applications in medicinal chemistry as effective anticancer agents, compounds with analgesic properties and can function as potent inhibitors of tubulin polymerization, and agents for the prevention of type II diabetes. A simple method for the synthesis of 3-amino-indoles via the annulation reaction of polyfluorophenylboronates with DMF is reported in Chapter 4.
Chapter 2
In Chapter 2, a mild process for the copper-catalyzed oxidative cross-coupling of electron-deficient polyfluorophenylboronate esters with terminal alkynes (Scheme S-1) is reported. This method displays good functional group tolerance and broad substrate scope, generating cross-coupled alkynyl(fluoro)arene products in moderate to excellent yields. This copper-catalyzed reaction was conducted on a gram scale to generate the corresponding product in good yield (72%).
Scheme S-1. Copper-catalyzed oxidative cross-coupling of terminal alkynes with polyfluorophenylboronate esters.
Based on previous reports and the aforementioned observations, a plausible catalytic cycle for this oxidative cross-coupling reaction is shown in Scheme S-2. The first step involves the addition of an alkynyl anion to Cu leading to the formation of alkynylcopper(II) species B. Subsequent transmetalation between ArFBpin and intermediate B occurs to form intermediate C. The desired product 3a is generated by eductive elimination. Finally, the oxidation of Cu(0) to Cu(II) with DDQ and Ag2O regenerates A to complete the catalytic cycle.
Scheme S-2. Proposed mechanism of copper(II)-catalyzed oxidative cross-coupling between terminal alkynes and polyfluorophenylboronate esters.
Chapter 3
In Chapter 3, A convenient and efficient protocol for the transition metal-free 1,2-addition of polyfluoroaryl boronate esters to aldehydes and ketones is reported, which provides secondary alcohols, tertiary alcohols, and ketones (Scheme S-3). The distinguishing features of this procedure include the employment of commercially available starting materials and the broad scope of the reaction with a wide variety of carbonyl compounds giving moderate to excellent yields.
Scheme S-3. Base-promoted 1,2-addition of polyfluorophenylboronates to aldehydes and ketones.
Control experiments were carried out to gain insight into the reaction mechanism. The reaction of 2a with pentafluorobenzene 5 under standard conditions was examined, yet 3a was not formed in any detectable amounts (Scheme S-4a), indicating that the C-Bpin moiety is essential and deprotonation of the fluoroarene or nucleophilic attack at the fluoroarene by the base is not a plausible pathway. Interestingly, for the standard reaction between 1a and 2a, the yield dropped dramatically if 18-crown-6 ether and K2CO3 were added (Scheme S-4b). This experimental result indicates that the presence of the potassium ion plays a crucial role for the outcome of the reaction. Furthermore, if the reaction of 1a and 2a was performed in the presence of only a catalytic amount of K2CO3 (20 mol%) (Scheme S-4c), reaction rates were reduced, and a week was required to produce 3a in good yield. This finding again indicates that the potassium ion (or the base) plays an important role in the reaction. Substituting ortho-fluorines by ortho-chlorines, using either C6Cl5Bpin 2,6-dichlorophenyl-1-Bpin as substrates, did not yield any product as shown by in situ GCMS studies.
Scheme S-4. Control experiments.
Based on DFT calculations, a mechanism for the 1,2-addition of polyfluorophenylboronates to aryl aldehydes in the presence of K2CO3 as base is proposed, as shown in Scheme S-5. K2CO3 interacts with the Lewis-acidic Bpin moiety of substrate 1 to generate base adduct A, which weakens the carbon-boron bond and ultimately cleaves the BC bond along with attachment of a potassium cation to the aryl group. The resulting ArF- anion adduct B undergoes nucleophilic attack at the aldehyde carbon atom of substrate 2 to generate methanolate C. The methanolate oxygen atom then attacks the electrophilic Bpin group to obtain compound D. Transfer of K2CO3 from intermediate D to the boron atom of the more Lewis-acidic polyfluorophenyl-Bpin 1 finally closes the cycle and regenerates complex A. Thus, the primary reaction product is the O-borylated addition product E, which was detected by HRMS and NMR spectroscopy for the perfluorinated derivative.
Scheme S-5. Proposed mechanism of the 1,2-addition of polyfluorophenylboronates to aldehydes and ketones.
Chapter 4
Chapter 4 presents a novel protocol for the transition metal-free addition and annulation of polyfluoroarylboronate esters to DMF, which provides 3-aminoindoles and tertiary amines in moderate to excellent yields (Scheme S-6).
Scheme S-6. Annulation and addition reactions of polyfluorophenylboronates with DMF.
While exploring the application of this strategy in synthesis, perfluorophenylBpin reacted smoothly with ethynylarenes and DMF to afford propargylamines with moderate to excellent yields (Scheme S-7).
Scheme S-7. Three-component cross-coupling reaction for the synthesis of propargylamines.
N2 - Polyfluorarene sind wichtige fluorierte Schlüsselstruktureinheiten für verschiedene organische Moleküle, wie z. B. Pharmazeutika, Agrochemikalien und organische Materialien. Auch polyfluorierte Arylalkine und -alkohole sind aufgrund ihrer vielseitigen Möglichkeiten, in verschiedene nützliche Moleküle umgewandelt zu werden als auch wegen ihrer Allgegenwart in der Naturstoffsynthese, leistungsfähige Bausteine. Effiziente Methoden zur Synthese polyfluorierter Arylalkine und -alkohole werden in Kapitel 2 und Kapitel 3 vorgestellt. Darüber hinaus haben 3-Amino-Indole eine breite Anwendung in der medizinischen Chemie als wirksame Antikrebsmittel, Verbindungen mit analgetischen Eigenschaften und als potente Inhibitoren der Tubulinpolymerisation sowie als Mittel zur Prävention von Typ-II-Diabetes gefunden. Eine einfache Methode zur Synthese von 3-Amino-Indolen über die Annulierungssreaktion von Polyfluorphenylboronaten mit DMF wird in Kapitel 4 berichtet.
Kapitel 2
In Kapitel 2 wird über ein mildes Verfahren zur kupferkatalysierten oxidativen Kreuzkupplung von elektronenarmen Polyfluorphenylboronatestern mit terminalen Alkinen (Schema S-1) berichtet. Diese Methode zeichnet sich durch eine gute Toleranz gegenüber funktionellen Gruppen und eine große Bandbreite an Substraten aus und erzeugt kreuzgekoppelte Alkinyl(fluor)aren-Produkte in moderaten bis exzellenten Ausbeuten. Diese kupferkatalysierte Reaktion wurde im Gramm-Maßstab durchgeführt, und erzeugt das entsprechende Produkt in guter Ausbeute (72 %).
Schema S-1. Kupfer-katalysierte oxidative Kreuzkupplung terminaler Alkine mit Polyfluorphenylboronatestern.
Basierend auf früheren Arbeiten und den oben erwähnten Beobachtungen ist ein plausibler katalytischer Zyklus für diese oxidative Kreuzkupplungsreaktion in Schema S-2 dargestellt. Der erste Schritt beinhaltet die Addition eines Alkinylanions, was zur Bildung des Alkinylkupfer(II)-Komplexes B führen sollte. Anschließend erfolgt eine Transmetallierung zwischen ArFBpin und dem Zwischenprodukt B zur Bildung des Zwischenproduktes C. Das gewünschte Produkt 3a wirde dann daraus durch reduktive Eliminierung erzeugt. Durch eine Oxidation des dabei entstehenden Cu(0)-Komplexes mit DDQ und Ag2O wird Komplex A regeneriert und der katalytische Zyklus schließt sich.
Schema S-2. Vorgeschlagener Mechanismus der Kupfer(II)-katalysierten oxidativen Kreuzkupplung terminaler Alkine und Polyfluorphenylboronatestern.
Kapitel 3
In Kapitel 3 wird ein praktisches und effizientes Protokoll für die übergangsmetallfreie 1,2-Addition von Polyfluorarylboronatestern an Aldehyde und Ketone vorgestellt, welches sekundäre Alkohole, tertiäre Alkohole und Ketone liefert (Schema S-3). Die besonderen Merkmale dieses Verfahrens sind die Verwendung kommerziell erhältlicher Ausgangsmaterialien und die große Bandbreite der Reaktion mit einer Vielzahl von Carbonylverbindungen, die mäßige bis exzellente Ausbeuten erbringen.
Schema S-3. Basen-unterstützte 1,2-Addition von Polyfluorphenylboronaten an Aldehyde und Ketone.
Um einen Einblick in den Reaktionsmechanismus zu erhalten, wurden Kontrollexperimente durchgeführt. Die Reaktion von 2a mit Pentafluorbenzol 5 unter Standardbedingungen wurde untersucht, jedoch wurde 3a nicht in nachweisbaren Mengen gebildet (Schema S-4a). Dies deudet darauf hin, dass der C-Bpin Anteil essenziell ist und eine Deprotonierung des Fluorarens oder ein nukleophiler Angriff am Fluoraren durch die Base kein plausibler Weg ist. Interessanterweise sank bei der Standardreaktion zwischen 1a und 2a die Ausbeute dramatisch, wenn 18-Kronen-6-Ether und K2CO3 zugesetzt wurden (Schema S-4b). Dieses experimentelle Ergebnis belegt, dass die Anwesenheit des Kalium-Ions eine entscheidende Rolle für den Ausgang der Reaktion spielt. Wenn die Reaktion von 1a und 2a in Gegenwart von nur einer katalytischen Menge K2CO3 (20 mol%) durchgeführt wurde (Schema S-4c), waren die Reaktionsgeschwindigkeiten geringer und es war eine Woche erforderlich, um 3a in guter Ausbeute zu erlangen. Dieser Befund weist erneut darauf hin, dass das Kalium-Ion (oder die Base) eine wichtige Rolle bei der Reaktion spielt. Die Substitution von ortho-Fluorsubstituenten durch ortho-Chlorsubstituenten, wobei entweder C6Cl5Bpin oder 2,6-Dichlorphenyl-Bpin als Substrate verwendet wurden, lieferte kein Produkt, wie in situ GCMS-Studien zeigten.
Schema S-4. Kontrollexperimente.
Ein Vorschlag zum Mechanismus der 1,2-Addition von Polyfluorphenylboronaten an Arylaldehyde in Gegenwart von K2CO3 als Base wird in Schema S-5 vorgeschlagen. Dabei wechselwirkt die Base K2CO3 mit der Lewis-sauren Bpin-Einheit des Substrats 1 unter Ausbildung des Basenadduktes A, in welchem die Kohlenstoff-Bor-Bindung geschwächt ist und schließlich die B-C Bindung gespalteen wird, wobei sich ein Kaliumkation an die Arylgruppe anlagert. Das resultierende ArF- Anion im Addukt B greift nukleophil am Aldehyd-Kohlenstoffatom von Substrat 2 an, um Methanolat C zu erzeugen. Das Methanolat-Sauerstoffatom reagiert dann mit der elektrophilen Bpin-Gruppe, um Verbindung D zu erhalten. Die Übertragung von K2CO3 vom Zwischenprodukt D auf das Boratom des Lewis-acideren Polyfluorphenyl-Bpin 1 schließt schließlich den Zyklus und regeneriert den Komplex A. Das primäre Reaktionsprodukt ist also das O-borylierte Additionsprodukt E, das mittels HRMS und NMR-Spektroskopie für das perfluorierte Derivat nachgewiesen wurde.
Schema S-5. Vorgeschlagener Mechanismus der 1,2-Addition von Polyfluorphenylboronaten an Aldehyden und Ketonen.
Kapitel 4
In Kapitel 4 wird ein neuartiges Protokoll für die übergangsmetallfreie Addition und Annulierungsreaktion von Polyfluorarylboronatestern an DMF vorgestellt, das 3-Aminoindole und tertiäre Amine in mäßigen bis ausgezeichneten Ausbeuten liefert(Schema S-6).
Schema S-6. Annulierungs- und Additionsreaktion von Polyfluorphenylboronaten mit DMF.
Bei der Erkundung der Anwendung dieser Strategie in der Synthese konnten Propargylamine mit mäßigen bis ausgezeichneten Ausbeuten hergestellt werden (Schema S-7).
Schema S-7. Kreuzkupplungsreaktion für die Synthese von Propargylaminen.
KW - Fluorinated Aryl Boronates
KW - Fluorierte Arylboronate
Y1 - 2021
U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:bvb:20-opus-245769
ER -
TY - JOUR
A1 - Liu, Zhiqiang
A1 - Kole, Goutam Kumar
A1 - Budiman, Yudha P.
A1 - Tian, Ya-Ming
A1 - Friedrich, Alexandra
A1 - Luo, Xiaoling
A1 - Westcott, Stephen A.
A1 - Radius, Udo
A1 - Marder, Todd B.
T1 - Transition metal catalyst-free, base-promoted 1,2-additions of polyfluorophenylboronates to aldehydes and ketones
JF - Angewandte Chemie International Edition
N2 - A novel protocol for the transition metal-free 1,2-addition of polyfluoroaryl boronate esters to aldehydes and ketones is reported, which provides secondary alcohols, tertiary alcohols, and ketones. Control experiments and DFT calculations indicate that both the ortho-F substituents on the polyfluorophenyl boronates and the counterion K\(^+\) in the carbonate base are critical. The distinguishing features of this procedure include the employment of commercially available starting materials and the broad scope of the reaction with a wide variety of carbonyl compounds giving moderate to excellent yields. Intriguing structural features involving O−H⋅⋅⋅O and O−H⋅⋅⋅N hydrogen bonding, as well as arene-perfluoroarene interactions, in this series of racemic polyfluoroaryl carbinols have also been addressed.
KW - inorganic chemistry
KW - transition metal-free
KW - alcohol
KW - 1,2-additionreaction
KW - boronateesters
KW - fluoroarene
Y1 - 2021
U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:bvb:20-opus-256487
VL - 60
IS - 30
ER -
TY - THES
A1 - Lorenz, Thomas
T1 - Conjugated Polymers with BN Units in the Main Chain
T1 - Konjugierte Polymere mit BN-Einheiten in der Hauptkette
N2 - In recent years PI-conjugated organoboron polymers and BN-doped polycyclic aromatic hydrocarbons have attracted a lot of interest due to their great potential in organic electronics. However, there are only few known examples of conjugated polymers with BN units in their main chain. Within this work silazane cleavage with silicon-boron (Si/B) exchange for the synthesis of a novel class of inorganic-organic hybrid polymers is demonstrated. These polymers consist of alternating NBN and para-phenylene units in the main chain. Photophysical studies and TD-DFT calculations for the polymer and molecular model systems were carried out, revealing a low extent of PI-conjugation across the NBN units. The new polymers can be used as macromolecular polyligands by a cross-linking reaction with a ZrIV compound. In the next chapter the synthesis and characterization of the first poly(p-phenylene iminoborane) is presented. This novel inorganic–organic hybrid polymer can be described as a BN analogue of the well-known poly(p-phenylene vinylene) (PPV) and is also accessible using the previously described Si/B exchange as synthetic strategy. Photophysical investigations and TD-DFT calculations on the polymer and corresponding model oligomers provide clear evidence for PI-conjugation across the B=N units and extension of the conjugation path with increasing chain length. Furthermore, a possible application of Si/B exchange for the synthesis of polysulfoximines was explored. Herein, diaryl sulfoximines and a p-phenylene bisborane serve as building blocks for new BN- and BO-doped alternating inorganic–organic hybrid copolymers. While the BN-linked polymers were accessible by a facile silicon/boron exchange protocol, the synthesis of polymers with B–O linkages in the main chain is achieved by salt elimination. In the last chapter the concept of Si/B exchange was investigated for the synthesis of BP-linked oligomers. Herein oligomers with sterically less demanding substituents (substituents: 2,4,6-trimethylphenyl or 2,4,6-tri-iso-propylphenyl) at the phosphorus are accessible using Si/B exchange, but the oligomer with Mes* (2,4,6-tri-tert-butylphenyl) as substituent needed a salt elimination pathway to give the desired product. Experimental data and theoretical investigations indicate, that the P-substituent has a high influence on the geometry of the phosphorus center and therefore on the possible conjugation over the BP units.
N2 - In den letzten Jahren haben PI-konjugierte Organoborpolymere und BN-dotierte polyzyklische aromatische Kohlenwasserstoffe aufgrund ihres großen Potenzials in organischer Elektronik großes Interesse auf sich gezogen. In der Literatur sind jedoch nur wenige Beispiele für konjugierte Polymere mit BN-Einheiten in ihrer Hauptkette bekannt. In dieser Arbeit wird die Silazanspaltung mit Silizium-Bor (Si/B)-Austausch zur Synthese einer neuen Klasse von anorganisch-organischen Hybridpolymeren vorgestellt. Diese Polymere bestehen aus alternierenden NBN- und para-Phenylen-Einheiten in der Hauptkette. Es wurden photophysikalische Untersuchungen und TD-DFT-Berechnungen für das Polymer und molekulare Modellsysteme durchgeführt, welche auf ein geringes Ausmaß an PI-Konjugation über die NBN-Einheiten deuten. Durch eine Vernetzungsreaktion über ZrIV-Verbindungen besteht die Möglichkeit diese neuen Polymere als makromolekulare Polyliganden einzusetzen. Im nächsten Kapitel wird die Synthese und Charakterisierung des ersten Poly(p-phenyleniminoborans) vorgestellt. Dieses neue anorganisch-organische Hybridpolymer kann als ein BN-Analogon des bekannten Poly(p-phenylenvinylen) (PPV) beschrieben werden und ist auch über den zuvor beschriebenen Si/B-Austausch als Synthesestrategie zugänglich. Photophysikalische Untersuchungen und TD-DFT-Berechnungen an dem Polymer und an entsprechenden Oligomeren als Modellsystem liefern deutliche Hinweise auf eine PI-Konjugation über die B=N-Einheiten und eine Erweiterung der Konjugationslänge mit wachsender Kettenlänge. Weiterhin wurde die Anwendungsmöglichkeit des Si/B-Austausches für die Synthese von Polysulfoximinen untersucht. Dabei dienen Diarylsulfoximine und p-Phenylenbisboran als Bausteine für neue BN- und BO-dotierte alternierende anorganisch-organische Hybridkopolymere. Während die BN-verknüpften Polymere über den Silizium/Bor-Austausch als Synthesestrategie zugänglich waren, wird die Synthese der Polymere mit B-O-Bindungen in der Hauptkette durch eine Salzeliminierung erreicht. Im letzten Kapitel wurde das Konzept des Si/B-Austausches für die Synthese von BP-verknüpften Oligomeren untersucht. Dabei sind Oligomere mit sterisch weniger anspruchsvollen Substituenten (Substituenten: 2,4,6-trimethylphenyl oder 2,4,6-tri-iso-propylphenyl) am Phosphor mittels Si/B-Austausch zugänglich, während für die Synthese des Oligomers mit Mes* (2,4,6-tri-tert-Butylphenyl) als Substituent eine Salzeliminierung notwendig war um das gewünschte Produkt zu erhalten. Experimentelle Daten und theoretische Untersuchungen deuten darauf hin, dass der P-Substituent einen großen Einfluss auf die Geometrie des Phosphorzentrums und damit auf die mögliche Konjugation über die BP-Einheit hat.
KW - Polyphenylenvinylenanaloga
KW - Iminoborane
KW - Sulfoximin
KW - Konjugierte Polymere
KW - Silizium-Boraustausch
KW - silicon-boron exchange
KW - diimidoborane
Y1 - 2021
U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:bvb:20-opus-219230
ER -
TY - JOUR
A1 - Luis, Werner
A1 - Horrer, Günther
A1 - Philipp, Michael
A1 - Lubitz, Katharina
A1 - Kuntze‐Fechner, Maximilian W.
A1 - Radius, Udo
T1 - A General Synthetic Route to NHC‐Phosphinidenes: NHC‐mediated Dehydrogenation of Primary Phosphines
JF - Zeitschrift für anorganische und allgemeine Chemie
N2 - The dehydrocoupling of primary phosphines with N-heterocyclic carbenes (NHCs) to yield NHC-phosphinidenes is reported. The reaction of two equivalents of the NHCs Me\(_2\)Im (1,3-dimethylimidazolin-2-ylidene), Me\(_4\)Im (1,3,4,5-tetramethylimidazolin-2-ylidene), iPr\(_2\)Im (1,3-di-iso-propylimidazolin-2-ylidene) and Mes\(_2\)Im (2,4,6-trimethylphenylimidazolin-2-ylidene) with PhPH\(_2\) and MesPH\(_2\) led to the NHC stabilized phosphinidenes (NHC)PAr: (iPr\(_2\)Im)PPh (1), (Mes\(_2\)Im)PPh (2), (Me\(_4\)Im)PPh (3), (Mes\(_2\)Im)PMes (4), (Me\(_2\)Im)PMes (5), (Me\(_4\)Im)PMes (6) and (iPr\(_2\)Im)PMes (7). The reaction of tBuPH\(_2\) with two equivalents of the NHCs afforded the corresponding NHC stabilized parent phosphinidenes (NHC)PH: (iPr\(_2\)Im)PH (8), (Mes\(_2\)Im)PH (9) and (Me\(_4\)Im)PH (10). Reaction of 1 with oxygen and sulfur led to isolation of iPr\(_2\)Im-P(O)\(_2\)Ph (11) and iPr\(_2\)Im-P(S)\(_2\)Ph (12), whereas the reaction with elemental selenium and tellurium gave (NHC)PPh cleavage with formation of (iPr\(_2\)Im)Se (13), iPr\(_2\)ImTe (14) and different cyclo-oligophosphines. Furthermore, the complexes [{(iPr\(_2\)Im)PPh}W(CO)\(_5\)] (15), [Co(CO)\(_2\)(NO){(iPr\(_2\)Im)PPh}] (16) and [(η\(^5\)-C\(_5\)Me\(_2\))Co(η\(^2\)-C\(_2\)H\(_4\)){(iPr\(_2\)Im)PPh}] (17) have been prepared starting from 1 and a suitable transition metal complex precursor. The complexes 16 and 17 decompose in solution upon heating to ca. 80 °C to yield the NHC complexes [Co(iPr\(_2\)Im)(CO)\(_2\)(NO)] and [(η\(^5\)-C\(_5\)Me\(_5\))Co(iPr\(_2\)Im)(η\(^2\)-C\(_2\)H\(_4\))] with formation of cyclo-oligophosphines. The reaction of 1 with [Ni(COD)\(_2\)] afforded the diphosphene complex [Ni(iPr\(_2\)Im)\(_2\)(trans-PhP=PPh)] 18.
KW - transition metal complexes
KW - N-heterocyclic carbenes
KW - phosphinidenes
KW - dehydrocoupling
Y1 - 2021
U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:bvb:20-opus-258016
VL - 647
IS - 8
ER -
TY - JOUR
A1 - Maier, Jan
A1 - Marder, Todd B.
T1 - Mechanistic and Kinetic Factors of ortho‐Benzyne Formation in Hexadehydro‐Diels‐Alder (HDDA) Reactions
JF - Chemistry – A European Journal
N2 - With the rapid development of the hexadehydro‐Diels‐Alder reaction (HDDA) from its first discovery in 1997, the question of whether a concerted or stepwise mechanism better describes the thermally activated formation of ortho‐benzyne from a diyne and a diynophile has been debated. Mechanistic and kinetic investigations were able to show that this is not a black or white situation, as minor changes can tip the balance. For that reason, especially, linked yne‐diynes were studied to examine steric, electronic, and radical‐stabilizing effects of their terminal substituents on the reaction mechanism and kinetics. Furthermore, the influence of the nature of the linker on the HDDA reaction was explored. The more recently discovered photochemical HDDA reaction also gives ortho‐arynes, which display the same reactivity as the thermally generated ones, but their formation might not proceed by the same mechanism. This minireview summarizes the current state of mechanistic understanding of the HDDA reaction.
KW - Alkyne
KW - Benzyne
KW - Cyclization
KW - Hexadehydro-Diels-Alder
KW - reaction mechanism
Y1 - 2021
U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:bvb:20-opus-239006
VL - 27
IS - 30
SP - 7978
EP - 7991
ER -
TY - THES
A1 - Maier, Jan Richard
T1 - Investigations of Metal-free Cannibalistic Hexadehydro-Diels-Alder and Pt-catalyzed Dimerization Reactions of Linked Aryl Bisdiynes
T1 - Untersuchungen von metallfreien kannibalistischen Hexadehydro-Diels-Alder und Pt-katalysierten Dimerisierungsreaktionen von verbrückten Arylbisdiinen
N2 - The introductory chapter reviews the current state of mechanistic understanding of the hexadehydro-Diels-Alder (HDDA) reaction. With the rapid development of the HDDA reaction from its first discovery in 1997, the question of whether a concerted or stepwise mechanism better describes the thermally activated formation of ortho-benzyne from a diyne and a diynophile has been debated. Mechanistic and kinetic investigations were able to show that this is not a black or white situation, as minor changes can tip the balance. In chapter 2 of this thesis, the catalytic process leading from 1,11-bis(p-tolyl)undeca-1,3,8,10-tetrayne to fully-substituted naphthalene and azulene derivatives, by two different platinum-catalyzed dimerization pathways, was investigated. In chapter 3, the cannibalistic self-trapping reaction of an ortho-benzyne derivative generated from 1,11-bis(p-tolyl)undeca-1,3,8,10-tetrayne in an HDDA reaction was investigated. Without adding any specific trapping agent, the highly reactive benzyne is trapped by another bisdiyne molecule in at least three different modes. In chapter 4 direct UV/VIS spectroscopic evidence for the existence of an o-benzyne in solution is reported, and the dynamics of its formation in a photo-induced reaction are established. For this purpose, 1,11-bis(p-tolyl)undeca-1,3,8,10-tetrayne was investigated, using femtosecond transient absorption spectroscopy in the ultraviolet/visible region. In chapter 5, following the isolation and characterization of the reaction products discussed in chapter 3, further species resulting from reactions of the highly reactive ortho-benzyne derivative were identified.
N2 - Das einleitende Kapitel gibt einen Überblick über den aktuellen Stand des mechanistischen Verständnisses der Hexadehydro-Diels-Alder (HDDA)-Reaktion. Mit der rasanten Entwicklung der HDDA-Reaktion seit ihrer ersten Entdeckung im Jahr 1997 wurde die Frage diskutiert, ob ein konzertierter oder ein schrittweiser Mechanismus die thermisch aktivierte Bildung von ortho-Benzin aus einem Diin und einem Diinophil besser beschreibt. Mechanistische und kinetische Untersuchungen konnten zeigen, dass es sich hierbei nicht um eine Schwarz-Weiß-Situation handelt, da schon kleine Änderungen das Gleichgewicht verändern können. In Kapitel 2 dieser Arbeit wurde der katalytische Prozess, der von 1,11-Bis(p-tolyl)undeca-1,3,8,10-tetrain zu vollständig substituierten Naphthalin- und Azulen-Derivaten führt, über zwei verschiedene platinkatalysierte Dimerisierungspfade untersucht. In Kapitel 3 wurde die kannibalistische Selbsteinfangreaktion eines ortho-Benzin-Derivats untersucht, das aus 1,11-Bis(p-tolyl)undeca-1,3,8,10-tetrain in einer HDDA-Reaktion erzeugt wurde. Ohne Zugabe eines spezifischen Einfangmittels wird das hochreaktive Benzin von einem anderen Bisdiin-Molekül in mindestens drei verschiedenen Modi eingefangen. In Kapitel 4 wird der direkte UV/VIS-spektroskopische Nachweis für die Existenz eines o-Benzins in Lösung berichtet und die Dynamik seiner Bildung in einer photoinduzierten Reaktion aufgezeigt. Zu diesem Zweck wurde 1,11-Bis(p-tolyl)undeca-1,3,8,10-tetrayne mittels Femtosekunden-Transienter-Absorptionsspektroskopie im ultravioletten/sichtbaren Bereich untersucht. In Kapitel 5 wurden nach der Isolierung und Charakterisierung der in Kapitel 3 diskutierten Reaktionsprodukte weitere Spezies identifiziert, die aus Reaktionen des hochreaktiven ortho-Benzin-Derivats resultieren.
KW - Diels-Alder-Reaktion
KW - Reaktivität
KW - hexadehydro-Diels-Alder
KW - Dimerization
KW - Reaction mechanism
KW - Reaktionsmechanismus
KW - Transient absorption
KW - Transiente Absorption
Y1 - 2021
U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:bvb:20-opus-240411
ER -
TY - JOUR
A1 - Matler, Alexander
A1 - Arrowsmith, Merle
A1 - Schorr, Fabian
A1 - Hermann, Alexander
A1 - Hofmann, Alexander
A1 - Lenczyk, Carsten
A1 - Braunschweig, Holger
T1 - Reactivity of Terminal Iron Borylenes and Bis(borylenes) with Carbodiimides: Cycloaddition, Metathesis, Insertion and C−H Activation Pathways
JF - European Journal of Inorganic Chemistry
N2 - The reactions of carbodiimides with the iron arylborylene complex [Fe=BDur(CO)\(_{3}\)(PMe\(_{3}\))] (Dur=2,3,5,6-Me\(_{4}\)C\(_{6}\)H) and the iron bis(borylene) complex [Fe{=BDur}{=BN(SiMe\(_{3}\))\(_{2}\)}(CO)\(_{3}\)] yield a wide variety of temperature-dependent products, including known FeBNC and novel FeBNB metallacycles, complexes of N-heterocyclic boracarbene and spiro-boracarbene ligands and a unique 1,3,2,4-diazadiborolyl pianostool complex, characterized by NMR spectroscopy and X-ray crystallography. The product distributions can be rationalized by considering sequences of cycloaddition, metathesis, insertion, and C−H activation pathways mainly governed by sterics.
KW - structure elucidation
KW - borylene complexes
KW - cycloaddition
KW - metathesis
KW - reaction mechanisms
Y1 - 2021
U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:bvb:20-opus-257397
VL - 2021
IS - 45
ER -
TY - JOUR
A1 - Merz, Viktor
A1 - Merz, Julia
A1 - Kirchner, Maximilian
A1 - Lenhart, Julian
A1 - Marder, Todd B.
A1 - Krueger, Anke
T1 - Pyrene-Based "Turn-Off" Probe with Broad Detection Range for Cu\(^{2+}\), Pb\(^{2+}\) and Hg\(^{2+}\) Ions
JF - Chemistry—A European Journal
N2 - Detection of metals in different environments with high selectivity and specificity is one of the prerequisites of the fight against environmental pollution with these elements. Pyrenes are well suited for the fluorescence sensing in different media. The applied sensing principle typically relies on the formation of intra- and intermolecular excimers, which is however limiting the sensitivity range due to masking of e. g. quenching effects by the excimer emission. Herein we report a highly selective, structurally rigid chemical sensor based on the monomer fluorescence of pyrene moieties bearing triazole groups. This sensor can quantitatively detect Cu\(^{2+}\), Pb\(^{2+}\) and Hg\(^{2+}\) in organic solvents over a broad concentrations range, even in the presence of ubiquitous ions such as Na\(^{+}\), K\(^{+}\), Ca\(^{2+}\) and Mg\(^{2+}\). The strongly emissive sensor's fluorescence with a long lifetime of 165 ns is quenched by a 1 : 1 complex formation upon addition of metal ions in acetonitrile. Upon addition of a tenfold excess of the metal ion to the sensor, agglomerates with a diameter of about 3 nm are formed. Due to complex interactions in the system, conventional linear correlations are not observed for all concentrations. Therefore, a critical comparison between the conventional Job plot interpretation, the method of Benesi-Hildebrand, and a non-linear fit is presented. The reported system enables the specific and robust sensing of medically and environmentally relevant ions in the health-relevant nM range and could be used e. g. for the monitoring of the respective ions in waste streams.
KW - probes
KW - fluorescence spectroscopy
KW - pyrene
KW - heavy metals
KW - luminescence
Y1 - 2021
U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:bvb:20-opus-256803
VL - 27
IS - 31
ER -
TY - THES
A1 - Ming, Wenbo
T1 - Synthesis of α‑Aminoboronates and PBP Pincer Palladium Boryl Complexes
T1 - Synthese von α-Aminoboronaten und PBP-Pincer-Palladium-Boryl-Komplexen
N2 - The first Borono-Strecker reaction has been developed to synthesize α-aminoboronates via a multicomponent reaction of readily available carbonyl compounds (aldehydes and ketones), amines and B2pin2. The preparation of α-amino cyclic boronates can be achieved via multicomponent coupling of salicylaldehydes, amines, and B2(OH)4. In addition, the diazaborole-based PBP pincer palladium chloride and the diazaborole-based PBP pincer palladium trifluoromethanesulfonate complexes were synthesized and fully characterized for the first time, and used as catalysts for Suzuki-Miyaura cross-coupling reactions.
N2 - Wurde die erste Borono-Strecker Reaktion zur Synthese von α-Aminoboronaten, mittels einer Multikomponenten-Reaktion aus leicht zugänglichen Carbonylverbindungen (Aldehyde und Ketone), Aminen und B2pin2, entwickelt. Außerdem gelang die Darstellung von zyklischen α-Aminoboronaten durch Multikomponenten-Kupplung von leicht zugänglichen Salicylaldehyden, Aminen und B2(OH)4. Des Weiteren wurde der Diazaborol-basierte PBP Pincer Palladium Chlorid Komplex und der Diazaborol-basierte PBP Pincer Palladium Trifluoromethylsulfonat Komplex erstmalig synthetisiert, vollständig charakterisiert und als Katalysator für Suzuki-Miyaura Kreuzkupplungen eingesetzt.
KW - borylation
KW - α-aminoboronates
KW - PBP pincer palladium complexes
KW - cross-coupling
Y1 - 2021
U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:bvb:20-opus-198323
ER -
TY - JOUR
A1 - Oberdorf, Kai
A1 - Hanft, Anna
A1 - Ramler, Jacqueline
A1 - Krummenacher, Ivo
A1 - Bickelhaupt, Matthias
A1 - Poater, Jordi
A1 - Lichtenberg, Crispin
T1 - Bismuth Amides Mediate Facile and Highly Selective Pn–Pn Radical‐Coupling Reactions (Pn=N, P, As)
JF - Angewandte Chemie, International Edition
N2 - The controlled release of well‐defined radical species under mild conditions for subsequent use in selective reactions is an important and challenging task in synthetic chemistry. We show here that simple bismuth amide species [Bi(NAr\(_2\))\(_3\)] readily release aminyl radicals [NAr\(_2\)]. at ambient temperature in solution. These reactions yield the corresponding hydrazines, Ar\(_2\)N−NAr\(_2\), as a result of highly selective N−N coupling. The exploitation of facile homolytic Bi−Pn bond cleavage for Pn−Pn bond formation was extended to higher homologues of the pnictogens (Pn=N–As): homoleptic bismuth amides mediate the highly selective dehydrocoupling of HPnR\(_2\) to give R\(_2\)Pn−PnR\(_2\). Analyses by NMR and EPR spectroscopy, single‐crystal X‐ray diffraction, and DFT calculations reveal low Bi−N homolytic bond‐dissociation energies, suggest radical coupling in the coordination sphere of bismuth, and reveal electronic and steric parameters as effective tools to control these reactions.
KW - bismuth amides
KW - radical species
KW - pnictogen coupling
KW - aminyl radicals
KW - diphosphanes
KW - heavier pnictogens
KW - radical coupling
Y1 - 2021
U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:bvb:20-opus-236582
VL - 60
IS - 12
ER -
TY - JOUR
A1 - Philipp, Michael S. M.
A1 - Krahfuss, Mirjam J.
A1 - Radacki, Krzysztof
A1 - Radius, Udo
T1 - N‐Heterocyclic Carbene and Cyclic (Alkyl)(amino)carbene Adducts of Antimony(III)
JF - European Journal of Inorganic Chemistry
N2 - A systematic study on Lewis-acid/base adducts of N-heterocyclic carbenes (NHCs) and the cyclic (alkyl)(amino)carbene cAAC\(^{Me}\) (1-(2,6-di-iso-propylphenyl)-3,3,5,5-tetramethyl-pyrrolidin-2-ylidene) with antimony(III) chlorides of the general formula SbCl\(_{2}\)R (R=Cl, Ph, Mes) is presented. The reaction of the NHCs Me\(_{2}\)Im\(^{Me}\) (1,3,4,5-tetra-methyl-imidazolin-2-ylidene), iPr\(_{2}\)Im\(^{Me}\) (1,3-di-isopropyl-4,5-dimethyl-imidazolin-2-ylidene), Mes\(_{2}\)Im, Dipp\(_{2}\)Im (R\(_{2}\)Im=1,3-di-organyl-imidazolin-2-ylidene; Mes=2,4,6-trimethylphenyl, Dipp=2,6-di-isopropylphenyl) and cAAC\(^{Me}\) with antimony(III) compounds SbCl\(_{2}\)R (R=Cl (1), Ph (2) and Mes (3)) yields the adducts NHC ⋅ SbCl\(_{2}\)R (R=Cl (4), Ph (5) and Mes (6); NHC=Me\(_{2}\)Im\(^{Me}\) (a), iPr\(_{2}\)Im\(^{Me}\) (b), Dipp\(_{2}\)Im (c) and Mes\(_{2}\)Im (d)) and cAAC\(^{Me}\) ⋅ SbCl\(_{2}\)R (R=Cl (4 e) and Ph (5 e)). Thermal treatment of (Dipp\(_{2}\)Im) ⋅ SbCl\(_{2}\)Ar (Ar=Ph (5 c) and Mes (6 c)) in benzene leads to isomerization to the backbone coordinated \(^{a}\)NHC-adduct \(^{a}\)Dipp\(_{2}\)Im ⋅ SbCl\(_{2}\)Ar (Ar=Mes (7) and Ph (8)) (\(^{"a"}\) denotes “abnormal” coordination mode of the NHC) in high yields. One of the chloride substituents at antimony of 7 can be abstracted by GaCl3 or Ag[BF\(_{4}\)] to obtain the imidazolium salts [\(^{a}\)Dipp\(_{2}\)Im ⋅ SbClMes][BF\(_{4}\)] (9) and [\(^{a}\)Dipp\(_{2}\)Im ⋅ SbClMes][GaCl\(_{4}\)] (10).
KW - N-Heterocyclic carbenes
KW - antimony
KW - cyclic (alkyl)(amino)carbenes
KW - Lewis acid/base adducts
KW - main group element halides
Y1 - 2021
U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:bvb:20-opus-257408
VL - 2021
IS - 38
ER -
TY - JOUR
A1 - Ramler, Jaqueline
A1 - Fantuzzi, Felipe
A1 - Geist, Felix
A1 - Hanft, Anna
A1 - Braunschweig, Holger
A1 - Engels, Bernd
A1 - Lichtenberg, Crispin
T1 - The dimethylbismuth cation: entry into dative Bi-Bi bonding and unconventional methyl exchange
JF - Angewandte Chemie International Edition
N2 - The dimethyl bismuth cation, [BiMe\(_2\)(SbF\(_6\))], has been isolated and characterized. Reaction with BiMe\(_3\) allows access to the first compound featuring Bi→Bi donor–acceptor bonding. In solution, dynamic behavior with methyl exchange via an unusual S\(_E\)2 mechanism is observed, underlining the unique properties of bismuth species as soft Lewis acids with the ability to undergo reversible Bi−C bond cleavage.
KW - inorganic chemistry
KW - methyl exchange
KW - bismuth
KW - cationic species
KW - electrophilic substitution
KW - Lewis acidity
Y1 - 2021
U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:bvb:20-opus-256543
VL - 60
ER -
TY - THES
A1 - Riensch, Nicolas Alexander
T1 - Silicon/Boron Exchange Routes to Novel Inorganic-Organic Hybrid Molecules, Oligomers, Polymers and Macrocycles
T1 - Silizium/Bor Austauschrouten zu Neuartigen Anorganisch-Organischen Hybridmolekülen, Oligomeren, Polymeren und Makrozyklen
N2 - Industrially used semiconducting materials, building blocks of modern electronics and computer industry, are mostly based on inorganic, crystalline solids, which have the drawback of relatively high production costs. As an alternative, organic pi-conjugated systems show enhanced flexibility and processability as well as the opportunity to obtain light-weight materials. They have emerged as attractive candidates, especially since elements beyond hydrogen and carbon can be used to create pi-conjugated frameworks. In recent years, pi-conjugated oligomers and polymers with tricoordinate boron centers incorporated into the main chain of such organic polymers have attracted considerable attention as the interaction of the vacant p orbital on boron with an adjacent pi system of the chain leads to extended conjugated materials. These materials show intriguing optical and electronic properties and potential applications in organic electronics and optoelectronics (OLEDs, OFETs, photovoltaics) or as sensory materials.
In this thesis, a catalytic Si/B exchange reaction protocol is used as a facile and highly effective B-C bond formation method to synthesize organoboron molecules, oligomers, polymers and macrocycles. This reaction is applied to synthesize a series of thienyl- and furylborane based materials. Special focus is on furylborane based materials, which, in general, have been only scarcely explored so far. This is mainly due to synthetic challenges since furan decomposes readily in the presence of light and oxygen. Our mild and highly selective reaction protocol in combination with sufficient kinetic protection of the boron centers gives access to a series of extended organoboranes featuring furylborane units in the main chain. Furthermore, kinetically stabilized furylboranes are established as highly robust and versatile building blocks for pi conjugated materials. The obtained materials reveal remarkable luminescence properties. The scope of potential starting materials was investigated by a catalyst screening, demonstrating that the Si/B exchange reaction can also be performed for less reactive aryldichloroboranes. Furthermore, borazine-based hybrid cyclomatrix microspheres have been synthesized via a Si/B exchange condensation reaction under precipitation polymerization conditions. Finally, synthetic routes to tetrabora- and diboraporphyrinogens were attempted in a multi-step reaction procedure. In the case for tetraboraporphyrinogens, the final macrocyclization reaction under pseudo high-dilution conditions afforded a mixture of macrocycles with different ring sizes. UV-vis and fluorescence spectroscopic analysis indicated significant differences in comparison to their linear congeners.
N2 - Industriell eingesetzte Halbleitermaterialien können als Bausteine der modernen Elektronik- und Computerindustrie beschrieben werden und basieren meist auf anorganischen, kristallinen Festkörpern, die relativ hohe Herstellungskosten als Nachteil haben. Als Alternative bieten pi-konjugierte Systeme eine höhere Flexibilität und Verarbeitbarkeit sowie die Möglichkeit, leichte Materialien zu erhalten. Sie haben sich als attraktive Kandidaten erwiesen, zumal auch Elemente jenseits von Wasserstoff und Kohlenstoff zur Herstellung von pi konjugierten Gerüsten verwendet werden können. In den letzten Jahren haben pi-konjugierte Oligomere und Polymere mit dreifach koordinierten Bor-Zentren, die in der Hauptkette solcher organischen Polymere eingebaut sind, große Aufmerksamkeit erregt, da die Wechselwirkung des vakanten p-Orbitals am Bor mit einem benachbarten pi-System der Kette zu ausgedehnten konjugierten Materialien führt. Diese Materialien zeigen faszinierende optische und elektronische Eigenschaften und potenzielle Anwendungen in der organischen Elektronik und Optoelektronik (OLEDs, OFETs, Photovoltaik) oder als Sensormaterialien.
In dieser Arbeit wird ein katalytisches Si/B-Austauschreaktionsprotokoll als einfache und hocheffektive Methode zur Bildung von B-C-Bindungen verwendet, um Organobor-Moleküle, Oligomere, Polymere und Makrozyklen zu synthetisieren. Diese Reaktion wird zur Synthese einer Reihe von Materialien auf Thienyl- und Furylboranbasis eingesetzt. Besonderes Augenmerk liegt dabei auf furylboranbasierten Materialien, die im Allgemeinen bisher nur wenig erforscht sind. Dies ist vor allem auf synthetische Herausforderungen zurückzuführen, da Furan in Gegenwart von Licht und Sauerstoff leicht zersetzt wird. Unser mildes und hochselektives Reaktionsprotokoll in Kombination mit einem ausreichenden kinetischen Schutz der Bor-Zentren ermöglicht den Zugang zu einer Reihe von ausgedehnten Organoboranen, die Furylboran-Einheiten in der Hauptkette besitzen. Darüber hinaus werden kinetisch stabilisierte Furylborane als sehr robuste und vielseitige Bausteine für konjugierte Materialien etabliert. Die erhaltenen Materialien weisen bemerkenswerte Lumineszenz-eigenschaften auf. Die Bandbreite möglicher Ausgangsmaterialien wurde durch ein Katalysator-Screening untersucht. Dabei zeigte sich, dass die Si/B-Austauschreaktion auch für weniger reaktive Aryldichlorborane durchgeführt werden kann. Weiterhin wurden Borazin-basierte Hybrid-Cyclomatrix-Mikrokugel über eine Si/B-Austauschkondensationsreaktion unter Fällungspolymerisationsbedingungen synthetisiert. Abschließend wurden Synthesewege zu Tetrabora- und Diboraporphyrinogenen in einem mehrstufigen Reaktionsverfahren untersucht. Im Falle der Tetraboraporphyrinogene ergab die abschließende Makrozyklisierungsreaktion unter Pseudo-Hochverdünnungsbedingungen ein Gemisch von Makrozyklen mit unterschiedlichen Ringgrößen. Die UV-Vis- und fluoreszenzspektroskopische Analyse zeigte signifikante Unterschiede im Vergleich zu ihren linearen Verwandten.
KW - Bororganische Verbindungen
KW - Konjugierte Polymere
KW - Borazin
KW - Silizium-Boraustausch
KW - Silicon-Boron Exchange
KW - Furylborane
KW - Organoboron
Y1 - 2021
U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:bvb:20-opus-238657
ER -
TY - JOUR
A1 - Riensch, Nicolas Alexander
A1 - Swoboda, Lukas
A1 - Lik, Artur
A1 - Krummenacher, Ivo
A1 - Braunschweig, Holger
A1 - Helten, Holger
T1 - Conjugated Bis(triarylboranes) with Disconnected Conjugation
JF - Zeitschrift für anorganische und allgemeine Chemie
N2 - A series of methylene-bridged bis(triarylboranes) has been synthesized via two complementary routes using metal-free catalytic Si/B exchange condensation under mild conditions. The title compounds comprise two borane moieties that show effective internal π-conjugation involving the respective boron centers and the adjacent hetaryl groups. Conjugation between both borane units, however, is disrupted by the aliphatic linker. Cyclic voltammetry revealed minimal electronic communication between the boron centers, as evidenced by two closely spaced reduction processes. The UV-vis spectra showed bathochromic shifted absorption bands compared to related monoboranes, which is attributed to the methylene bridge. A further red-shift results upon introduction of methyl or SiMe\(_3\) groups at the terminal thiophene rings.
KW - Boron
KW - thiophene
KW - conjugated oligomers
KW - hybrid materials
KW - boranes
Y1 - 2021
U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:bvb:20-opus-258020
VL - 647
IS - 5
ER -
TY - JOUR
A1 - Roy, Dipak Kumar
A1 - Tröster, Tobias
A1 - Fantuzzi, Felipe
A1 - Dewhurst, Rian D.
A1 - Lenczyk, Carsten
A1 - Radacki, Krzysztof
A1 - Pranckevicius, Conor
A1 - Engels, Bernd
A1 - Braunschweig, Holger
T1 - Isolation and Reactivity of an Antiaromatic s‐Block Metal Compound
JF - Angewandte Chemie International Edition
N2 - The concepts of aromaticity and antiaromaticity have a long history, and countless demonstrations of these phenomena have been made with molecules based on elements from the p, d, and f blocks of the periodic table. In contrast, the limited oxidation‐state flexibility of the s‐block metals has long stood in the way of their participation in sophisticated π‐bonding arrangements, and truly antiaromatic systems containing s‐block metals are altogether absent or remain poorly defined. Using spectroscopic, structural, and computational techniques, we present herein the synthesis and authentication of a heterocyclic compound containing the alkaline earth metal beryllium that exhibits significant antiaromaticity, and detail its chemical reduction and Lewis‐base‐coordination chemistry.
KW - antiaromaticity
KW - aromaticity
KW - beryllium
KW - heterocycles
KW - s-block metals
Y1 - 2021
U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:bvb:20-opus-224447
VL - 60
IS - 7
SP - 3812
EP - 3819
ER -