@article{HeRauchFriedrichetal.2019, author = {He, Jiang and Rauch, Florian and Friedrich, Alexandra and Sieh, Daniel and Ribbeck, Tatjana and Krummenacher, Ivo and Braunschweig, Holger and Finze, Maik and Marder, Todd B.}, title = {N-Heterocyclic Olefins as Electron Donors in Combination with Triarylborane Acceptors: Synthesis, Optical and Electronic Properties of D-π-A Compounds}, series = {Chemistry - A European Journal}, volume = {25}, journal = {Chemistry - A European Journal}, doi = {10.1002/chem.201903118}, url = {http://nbn-resolving.de/urn:nbn:de:bvb:20-opus-204690}, pages = {13777-13784}, year = {2019}, abstract = {N-heterocyclic olefins (NHOs), relatives of N-heterocyclic carbenes (NHCs), exhibit high nucleophilicity and soft Lewis basic character. To investigate their π-electron donating ability, NHOs were attached to triarylborane π-acceptors (A) giving donor (D)-π-A compounds 1-3. In addition, an enamine π-donor analogue (4) was synthesized for comparison. UV-visible absorption studies show a larger red shift for the NHO-containing boranes than for the enamine analogue, a relative of cyclic (alkyl)(amino) carbenes (CAACs). Solvent-dependent emission studies indicate that 1-4 have moderate intramolecular charge-transfer (ICT) behavior. Electrochemical investigations reveal that the NHO-containing boranes have extremely low reversible oxidation potentials (e.g., for 3, \(E^{ox}_{1/2}\) =-0.40 V vs. ferrocene/ferrocenium, Fc/Fc\(^+\), in THF). Time-dependent (TD) DFT calculations show that the HOMOs of 1-3 are much more destabilized than that of the enamine-containing 4, which confirms the stronger donating ability of NHOs.}, language = {en} } @article{LiuMingZhangetal.2019, author = {Liu, Xiaocui and Ming, Wenbo and Zhang, Yixiao and Friedrich, Alexandra and Marder, Todd B.}, title = {Copper-Catalyzed Triboration: Straightforward, Atom-Economical Synthesis of 1,1,1-Triborylalkanes from Terminal Alkynes and HBpin}, series = {Angewandte Chemie International Edition}, volume = {58}, journal = {Angewandte Chemie International Edition}, number = {52}, doi = {10.1002/anie.201909376}, url = {http://nbn-resolving.de/urn:nbn:de:bvb:20-opus-206185}, pages = {18923-18927}, year = {2019}, abstract = {A convenient and efficient one-step synthesis of 1,1,1-triborylalkanes was achieved via sequential dehydrogenative borylation and double hydroborations of terminal alkynes with HBpin (HBpin=pinacolborane) catalyzed by inexpensive and readily available Cu(OAc)\(_2\). This process proceeds under mild conditions, furnishing 1,1,1-tris(boronates) with wide substrate scope, excellent selectivity, and good functional-group tolerance, and is applicable to gram-scale synthesis without loss of yield. The 1,1,1-triborylalkanes can be used in the preparation of α-vinylboronates and borylated cyclic compounds, which are valuable but previously rare compounds. Different alkyl groups can be introduced stepwise via base-mediated deborylative alkylation to produce racemic tertiary alkyl boronates, which can be readily transformed into useful tertiary alcohols.}, language = {en} } @article{LiuMingZhangetal.2019, author = {Liu, Xiaocui and Ming, Wenbo and Zhang, Yixiao and Friedrich, Alexandra and Marder, Todd B.}, title = {Kupferkatalysierte Triborierung: Einfache, atom{\"o}konomische Synthese von 1,1,1-Triborylalkanen aus terminalen Alkinen und HBpin}, series = {Angewandte Chemie}, volume = {131}, journal = {Angewandte Chemie}, number = {52}, doi = {10.1002/ange.201909376}, url = {http://nbn-resolving.de/urn:nbn:de:bvb:20-opus-212189}, pages = {19099-19103}, year = {2019}, abstract = {Eine effiziente, einstufige Synthese von 1,1,1-Trialkylalkanen durch die sequenzielle, dehydrierende Borylierung und zweifache Hydroborierung von terminalen Alkinen mit Pinakolboran (HBpin) wurde unter Verwendung des kosteng{\"u}nstigen und einfach zug{\"a}nglichen Kupfersalzes Cu(OAc)2 als Katalysator realisiert. Das Verfahren zeichnet sich durch ein breites Substratspektrum, eine außerordentliche Selektivit{\"a}t und eine hohe Toleranz gegen{\"u}ber funktionellen Gruppen aus. Zudem kann die Reaktion ohne Ausbeuteverlust im Gramm-Maßstab durchgef{\"u}hrt werden. Die somit erhaltenen 1,1,1-Trialkylalkane k{\"o}nnen Anwendungen in der Herstellung von synthetisch wertvollen und bislang schwer zug{\"a}nglichen α-Vinylboronaten und zyklischen Boryl-Verbindungen finden. Verschiedene Alkylgruppen k{\"o}nnen stufenweise {\"u}ber eine basenvermittelte deborylierende Alkylierung eingef{\"u}hrt werden, um racemische, terti{\"a}re Alkylboronate herzustellen, die einfach in n{\"u}tzliche terti{\"a}re Alkohole umgewandelt werden k{\"o}nnen.}, language = {de} } @article{BudimanFriedrichRadiusetal.2019, author = {Budiman, Yudha P. and Friedrich, Alexandra and Radius, Udo and Marder, Todd B.}, title = {Copper-catalysed Suzuki-Miyaura cross-coupling of highly fluorinated aryl boronate esters with aryl iodides and bromides and fluoroarene-arene π-stacking interactions in the products}, series = {ChemCatChem}, volume = {11}, journal = {ChemCatChem}, number = {21}, doi = {10.1002/cctc.201901220}, url = {http://nbn-resolving.de/urn:nbn:de:bvb:20-opus-204839}, pages = {5387-5396}, year = {2019}, abstract = {A combination of copper iodide and phenanthroline as the ligand is an efficient catalyst for Suzuki-Miyaura cross-coupling of highly fluorinated boronate esters (aryl-Bpin) with aryl iodides and bromides to generate fluorinated biaryls in good to excellent yields. This method represents a nice alternative to traditional cross-coupling methods which require palladium catalysts and stoichiometric amounts of silver oxide. We note that π⋅⋅⋅π stacking interactions dominate the molecular packing in the partly fluorinated biaryl crystals investigated herein. They are present either between the arene and perfluoroarene, or solely between arenes or perfluoroarenes, respectively.}, language = {en} } @article{LiuBudimanTianetal.2020, author = {Liu, Zhiqiang and Budiman, Yudha P. and Tian, Ya-Ming and Friedrich, Alexandra and Huang, Mingming and Westcott, Stephen A. and Radius, Udo and Marder, Todd B.}, title = {Copper-Catalyzed Oxidative Cross-Coupling of Electron-Deficient Polyfluorophenylboronate Esters with Terminal Alkynes}, series = {Chemistry - A European Journal}, volume = {26}, journal = {Chemistry - A European Journal}, number = {71}, doi = {10.1002/chem.202002888}, url = {http://nbn-resolving.de/urn:nbn:de:bvb:20-opus-224362}, pages = {17267 -- 17274}, year = {2020}, abstract = {We report herein a mild procedure for the copper-catalyzed oxidative cross-coupling of electron-deficient polyfluorophenylboronate esters with terminal alkynes. This method displays good functional group tolerance and broad substrate scope, generating cross-coupled alkynyl(fluoro)arene products in moderate to excellent yields. Thus, it represents a simple alternative to the conventional Sonogashira reaction.}, language = {en} } @article{MerzDietzVonhausenetal.2020, author = {Merz, Julia and Dietz, Maximilian and Vonhausen, Yvonne and W{\"o}ber, Frederik and Friedrich, Alexandra and Sieh, Daniel and Krummenacher, Ivo and Braunschweig, Holger and Moos, Michael and Holzapfel, Marco and Lambert, Christoph and Marder, Todd B.}, title = {Synthesis, Photophysical and Electronic Properties of New Red-to-NIR Emitting Donor-Acceptor Pyrene Derivatives}, series = {Chemistry - A European Journal}, volume = {26}, journal = {Chemistry - A European Journal}, number = {2}, doi = {10.1002/chem.201904219}, url = {http://nbn-resolving.de/urn:nbn:de:bvb:20-opus-207486}, pages = {438-453}, year = {2020}, abstract = {We synthesized new pyrene derivatives with strong bis(para -methoxyphenyl)amine donors at the 2,7-positions and n -azaacene acceptors at the K-region of pyrene. The compounds possess a strong intramolecular charge transfer, leading to unusual properties such as emission in the red to NIR region (700 nm), which has not been reported before for monomeric pyrenes. Detailed photophysical studies reveal very long intrinsic lifetimes of >100 ns for the new compounds, which is typical for 2,7-substituted pyrenes but not for K-region substituted pyrenes. The incorporation of strong donors and acceptors leads to very low reduction and oxidation potentials, and spectroelectrochemical studies show that the compounds are on the borderline between localized Robin-Day class-II and delocalized Robin-Day class-III species.}, language = {en} } @article{LiuMingFriedrichetal.2020, author = {Liu, Xiaocui and Ming, Wenbo and Friedrich, Alexandra and Kerner, Florian and Marder, Todd B.}, title = {Copper-Catalyzed Triboration of Terminal Alkynes Using B\(_2\)pin\(_2\): Efficient Synthesis of 1,1,2-Triborylalkenes}, series = {Angewandte Chemie International Edition}, volume = {59}, journal = {Angewandte Chemie International Edition}, number = {1}, doi = {10.1002/anie.201908466}, url = {http://nbn-resolving.de/urn:nbn:de:bvb:20-opus-206694}, pages = {304-309}, year = {2020}, abstract = {We report herein the catalytic triboration of terminal alkynes with B\(_2\)pin\(_2\) (bis(pinacolato)diboron) using readily available Cu(OAc)\(_2\) and P\(^n\)Bu\(_3\). Various 1,1,2-triborylalkenes, a class of compounds that have been demonstrated to be potential matrix metalloproteinase (MMP-2) inhibitors, were obtained directly in moderate to good yields. The process features mild reaction conditions, a broad substrate scope, and good functional group tolerance. This copper-catalyzed reaction can be conducted on a gram scale to produce the corresponding 1,1,2-triborylalkenes in modest yields. The utility of these products was demonstrated by further transformations of the C-B bonds to prepare gem -dihaloborylalkenes (F, Cl, Br), monohaloborylalkenes (Cl, Br), and trans -diaryldiborylalkenes, which serve as important synthons and have previously been challenging to prepare.}, language = {en} } @article{LiuMingFriedrichetal.2020, author = {Liu, Xiaocui and Ming, Wenbo and Friedrich, Alexandra and Marder, Todd B.}, title = {Kupfer-katalysierte Triborierung terminaler Alkine mit B2pin2: Effiziente Synthese von 1,1,2-Triborylalkenen}, series = {Angewandte Chemie}, volume = {132}, journal = {Angewandte Chemie}, number = {1}, doi = {10.1002/ange.201908466}, url = {http://nbn-resolving.de/urn:nbn:de:bvb:20-opus-219699}, pages = {311-316}, year = {2020}, abstract = {Wir berichten {\"u}ber die katalytische Triborierung terminaler Alkine mit B\(_2\)pin\(_2\) (Bis-(pinakolato)-dibor) unter Verwendung von einfach zug{\"a}nglichem Cu(OAc)\(_2\) und P\(^n\)Bu\(_3\). Verschiedene 1,1,2-Triborylalkene, eine Verbindungsklasse mit potentieller Funktion als Matrix-Metallo-Proteinase(MMP-2)-Inhibitor, werden direkt in m{\"a}ßigen bis guten Ausbeuten erhalten. Das Verfahren zeichnet sich durch milde Reaktionsbedingungen, ein breites Substratspektrum und eine gute Vertr{\"a}glichkeit gegen{\"u}ber funktionellen Gruppen aus. Diese Cu-katalysierte Reaktion kann im Gramm-Maßstab durchgef{\"u}hrt werden und liefert die entsprechenden 1,1,2-Triborylalkene in m{\"a}ßigen Ausbeuten. Die Verwendung solcher Verbindungen wird anhand weiterer Transformationen der C-B-Bindungen zur Darstellung eines geminalen Dihalogenborylalkens (F, Cl, Br), eines Monohalogendiborylalkens (Cl, Br) und eines trans-Diaryldiborylalkens demonstriert, welche bedeutende Synthesebausteine darstellen und bisher nur schwer zug{\"a}nglich waren.}, language = {de} } @article{LiuMingLuoetal.2020, author = {Liu, Xiaocui and Ming, Wenbo and Luo, Xiaoling and Friedrich, Alexandra and Maier, Jan and Radius, Udo and Santos, Webster L. and Marder, Todd B.}, title = {Regio- and Stereoselective Synthesis of 1,1-Diborylalkenes via Br{\o}nsted Base-Catalyzed Mixed Diboration of Alkynyl Esters and Amides with BpinBdan}, series = {European Journal of Organic Chemistry}, volume = {2020}, journal = {European Journal of Organic Chemistry}, number = {13}, doi = {10.1002/ejoc.202000128}, url = {http://nbn-resolving.de/urn:nbn:de:bvb:20-opus-214728}, pages = {1941 -- 1946}, year = {2020}, abstract = {The NaOtBu-catalyzed mixed 1,1-diboration of terminal alkynes using the unsymmetrical diboron reagent BpinBdan (pin = pinacolato; dan = 1,8-diaminonaphthalene) proceeds in a regio- and stereoselective fashion affording moderate to high yields of 1,1-diborylalkenes bearing orthogonal boron protecting groups. It is applicable to gram-scale synthesis without loss of yield or selectivity. The mixed 1,1-diborylalkene products can be utilized in Suzuki-Miyaura cross-coupling reactions which take place selectivly at the C-B site. DFT calculations suggest the NaOtBu-catalyzed mixed 1,1-diboration of alkynes occurs through deprotonation of the terminal alkyne, stepwise addition of BpinBdan to the terminal carbon followed by protonation with tBuOH. Experimentally observed selective formation of (Z)-diborylalkenes is supported by our theoretical studies.}, language = {en} } @article{RauchEndresFriedrichetal.2020, author = {Rauch, Florian and Endres, Peter and Friedrich, Alexandra and Sieh, Daniel and H{\"a}hnel, Martin and Krummenacher, Ivo and Braunschweig, Holger and Finze, Maik and Ji, Lei and Marder, Todd B.}, title = {An Iterative Divergent Approach to Conjugated Starburst Borane Dendrimers}, series = {Chemistry - A European Journal}, volume = {26}, journal = {Chemistry - A European Journal}, number = {57}, doi = {10.1002/chem.202001985}, url = {http://nbn-resolving.de/urn:nbn:de:bvb:20-opus-218345}, pages = {12951 -- 12963}, year = {2020}, abstract = {Using a new divergent approach, conjugated triarylborane dendrimers were synthesized up to the 2nd generation. The synthetic strategy consists of three steps: 1) functionalization, via iridium catalyzed C-H borylation; 2) activation, via fluorination of the generated boronate ester with K[HF\(_{2}\)] or [N(nBu\(_{4}\))][HF\(_{2}\)]; and 3) expansion, via reaction of the trifluoroborate salts with aryl Grignard reagents. The concept was also shown to be viable for a convergent approach. All but one of the conjugated borane dendrimers exhibit multiple, distinct and reversible reduction potentials, making them potentially interesting materials for applications in molecular accumulators. Based on their photophysical properties, the 1st generation dendrimers exhibit good conjugation over the whole system. However, the conjugation does not increase further upon expansion to the 2nd generation, but the molar extinction coefficients increase linearly with the number of triarylborane subunits, suggesting a potential application as photonic antennas.}, language = {en} } @article{RauchFuchsFriedrichetal.2020, author = {Rauch, Florian and Fuchs, Sonja and Friedrich, Alexandra and Sieh, Daniel and Krummenacher, Ivo and Braunschweig, Holger and Finze, Maik and Marder, Todd B.}, title = {Highly Stable, Readily Reducible, Fluorescent, Trifluoromethylated 9-Borafluorenes}, series = {Chemistry - A European Journal}, volume = {26}, journal = {Chemistry - A European Journal}, number = {56}, doi = {10.1002/chem.201905559}, url = {http://nbn-resolving.de/urn:nbn:de:bvb:20-opus-218390}, pages = {12794 -- 12808}, year = {2020}, abstract = {Three different perfluoroalkylated borafluorenes (\(^{F}\)Bf) were prepared and their electronic and photophysical properties were investigated. The systems have four trifluoromethyl moieties on the borafluorene moiety as well as two trifluoromethyl groups at the ortho positions of their exo-aryl moieties. They differ with regard to the para substituents on their exo-aryl moieties, being a proton \(^{F}\)Xyl\(^{F}\)Bf, \(^{F}\)Xyl: 2,6-bis(trifluoromethyl)phenyl), a trifluoromethyl group (\(^{F}\)Mes\(^{F}\)Bf, \(^{F}\)Mes: 2,4,6-tris(trifluoromethyl)phenyl) or a dimethylamino group (p-NMe\(_{2}\)-\(^{F}\)Xyl\(^{F}\)Bf, p-NMe\(_{2}\)-\(^{F}\)Xyl: 4-(dimethylamino)-2,6-bis(trifluoromethyl)phenyl), respectively. All derivatives exhibit extraordinarily low reduction potentials, comparable to those of perylenediimides. The most electron-deficient derivative \(^{F}\)Mes\(^{F}\)Bf was also chemically reduced and its radical anion isolated and characterized. Furthermore, all compounds exhibit very long fluorescent lifetimes of about 250 ns up to 1.6 μs; however, the underlying mechanisms responsible for this differ. The donor-substituted derivative p-NMe\(_{2}\)-\(^{F}\)Xyl\(^{F}\)Bf exhibits thermally activated delayed fluorescence (TADF) from a charge-transfer (CT) state, whereas the \(^{F}\)Mes\(^{F}\)Bf and FXylFBf borafluorenes exhibit only weakly allowed locally excited (LE) transitions due to their symmetry and low transition-dipole moments.}, language = {en} } @article{FoehrenbacherKrahfussZapfetal.2021, author = {F{\"o}hrenbacher, Steffen A. and Krahfuss, Mirjam J. and Zapf, Ludwig and Friedrich, Alexandra and Ignat'ev, Nikolai V. and Finze, Maik and Radius, Udo}, title = {Tris(pentafluoroethyl)difluorophosphorane: a versatile fluoride acceptor for transition metal chemistry}, series = {Chemistry Europe}, volume = {27}, journal = {Chemistry Europe}, number = {10}, doi = {10.1002/chem.202004885}, url = {http://nbn-resolving.de/urn:nbn:de:bvb:20-opus-256665}, pages = {3504-3516}, year = {2021}, abstract = {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.}, language = {en} } @article{FergerBanKrošletal.2021, author = {Ferger, Matthias and Ban, Željka and Krošl, Ivona and Tomić, Sanja and Dietrich, Lena and Lorenzen, Sabine and Rauch, Florian and Sieh, Daniel and Friedrich, Alexandra and Griesbeck, Stefanie and Kenđel, Adriana and Miljanić, Snežana and Piantanida, Ivo and Marder, Todd B.}, title = {Bis(phenylethynyl)arene Linkers in Tetracationic Bis-triarylborane Chromophores Control Fluorimetric and Raman Sensing of Various DNAs and RNAs}, series = {Chemistry-A European Journal}, volume = {27}, journal = {Chemistry-A European Journal}, number = {16}, doi = {10.1002/chem.202005141}, url = {http://nbn-resolving.de/urn:nbn:de:bvb:20-opus-256717}, pages = {5142-5159}, year = {2021}, abstract = {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.}, language = {en} } @article{HeRauchFriedrichetal.2021, author = {He, Jiang and Rauch, Florian and Friedrich, Alexandra and Krebs, Johannes and Krummenacher, Ivo and Bertermann, R{\"u}diger and Nitsch, J{\"o}rn and Braunschweig, Holger and Finze, Maik and Marder, Todd B.}, title = {Phenylpyridyl-fused boroles: a unique coordination mode and weak B-N coordination-induced dual fluorescence}, series = {Angewandte Chemie International Edition}, volume = {60}, journal = {Angewandte Chemie International Edition}, number = {9}, doi = {10.1002/anie.202013692}, url = {http://nbn-resolving.de/urn:nbn:de:bvb:20-opus-256423}, pages = {4833-4840}, year = {2021}, abstract = {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.}, language = {en} } @article{KrebsHaehnelKrummenacheretal.2021, author = {Krebs, Johannes and Haehnel, Martin and Krummenacher, Ivo and Friedrich, Alexandra and Braunschweig, Holger and Finze, Maik and Ji, Lei and Marder, Todd B.}, title = {Synthesis and Structure of an o-Carboranyl-Substituted Three-Coordinate Borane Radical Anion}, series = {Chemistry—A European Journal}, volume = {27}, journal = {Chemistry—A European Journal}, number = {31}, doi = {10.1002/chem.202100938}, url = {http://nbn-resolving.de/urn:nbn:de:bvb:20-opus-256841}, pages = {8159-8167}, year = {2021}, abstract = {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.}, language = {en} } @article{HuangWuKrebsetal.2021, author = {Huang, Mingming and Wu, Zhu and Krebs, Johannes and Friedrich, Alexandra and Luo, Xiaoling and Westcott, Stephen A. and Radius, Udo and Marder, Todd B.}, title = {Ni-Catalyzed Borylation of Aryl Sulfoxides}, series = {Chemistry—A European Journal}, volume = {27}, journal = {Chemistry—A European Journal}, number = {31}, doi = {10.1002/chem.202100342}, url = {http://nbn-resolving.de/urn:nbn:de:bvb:20-opus-256778}, pages = {8149-8158}, year = {2021}, abstract = {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.}, language = {en} } @article{LiuKoleBudimanetal.2021, author = {Liu, Zhiqiang and Kole, Goutam Kumar and Budiman, Yudha P. and Tian, Ya-Ming and Friedrich, Alexandra and Luo, Xiaoling and Westcott, Stephen A. and Radius, Udo and Marder, Todd B.}, title = {Transition metal catalyst-free, base-promoted 1,2-additions of polyfluorophenylboronates to aldehydes and ketones}, series = {Angewandte Chemie International Edition}, volume = {60}, journal = {Angewandte Chemie International Edition}, number = {30}, doi = {10.1002/anie.202103686}, url = {http://nbn-resolving.de/urn:nbn:de:bvb:20-opus-256487}, pages = {16529-16538}, year = {2021}, abstract = {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.}, language = {en} } @article{ChenMengLiaoetal.2021, author = {Chen, Xing and Meng, Guoyun and Liao, Guanming and Rauch, Florian and He, Jiang and Friedrich, Alexandra and Marder, Todd B. and Wang, Nan and Chen, Pangkuan and Wang, Suning and Yin, Xiaodong}, title = {Highly Emissive 9-Borafluorene Derivatives: Synthesis, Photophysical Properties and Device Fabrication}, series = {Chemistry—A European Journal}, volume = {27}, journal = {Chemistry—A European Journal}, number = {20}, doi = {10.1002/chem.202005185}, url = {http://nbn-resolving.de/urn:nbn:de:bvb:20-opus-256738}, pages = {6274-6282}, year = {2021}, abstract = {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.}, language = {en} } @article{KoleMerzAmaretal.2021, author = {Kole, Goutam Kumar and Merz, Julia and Amar, Anissa and Fontaine, Bruno and Boucekkine, Abdou and Nitsch, J{\"o}rn and Lorenzen, Sabine and Friedrich, Alexandra and Krummenacher, Ivo and Košćak, Marta and Braunschweig, Holger and Piantanida, Ivo and Halet, Jean-Fran{\c{c}}ois and M{\"u}ller-Buschbaum, Klaus and Marder, Todd B.}, title = {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}, series = {Chemistry - A European Journal}, volume = {27}, journal = {Chemistry - A European Journal}, number = {8}, doi = {10.1002/chem.202004748}, url = {http://nbn-resolving.de/urn:nbn:de:bvb:20-opus-256642}, pages = {2837-2853}, year = {2021}, abstract = {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.}, language = {en} } @article{FergerBergerRauchetal.2021, author = {Ferger, Matthias and Berger, Sarina M. and Rauch, Florian and Sch{\"o}nitz, Markus and R{\"u}he, Jessica and Krebs, Johannes and Friedrich, Alexandra and Marder, Todd B.}, title = {Synthesis of Highly Functionalizable Symmetrically and Unsymmetrically Substituted Triarylboranes from Bench-Stable Boron Precursors}, series = {Chemistry—A European Journal}, volume = {27}, journal = {Chemistry—A European Journal}, number = {35}, doi = {10.1002/chem.202100632}, url = {http://nbn-resolving.de/urn:nbn:de:bvb:20-opus-256827}, pages = {9094-9101}, year = {2021}, abstract = {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.}, language = {en} }