@phdthesis{Kerner2021,
  author    = {Kerner, Florian Tobias},
  title     = {Reactions of rhodium(I) with diynes and studies of the photophysical behavior of the luminescent products},
  doi       = {10.25972/OPUS-20910},
  url       = {http://nbn-resolving.de/urn:nbn:de:bvb:20-opus-209107},
  school      = {Universit{\"a}t W{\"u}rzburg},
  year      = {2021},
  abstract  = {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.},
  subject      = {{\"U}bergangsmetallkomplexe},
  language  = {en}
}
@article{BuraBeaupreLegareetal.2018,
  author    = {Bura, Thomas and Beaupr{\´e}, Serge and L{\´e}gar{\´e}, Marc-Andr{\´e} and Ibraikulov, Olzhas A. and Leclerc, Nicolas and Leclerc, Mario},
  title     = {Theoretical calculations for highly selective Direct Heteroarylation Polymerization: new nitrile-substituted Dithienyl-Diketopyrrolopyrrole-based polymers},
  series = {Molecules},
  volume    = {23},
  journal   = {Molecules},
  number    = {9},
  issn      = {1420-3049},
  doi       = {10.3390/molecules23092324},
  url       = {http://nbn-resolving.de/urn:nbn:de:bvb:20-opus-197648},
  pages     = {2324},
  year      = {2018},
  abstract  = {Direct Heteroarylation Polymerization (DHAP) is becoming a valuable alternative to classical polymerization methods being used to synthesize π-conjugated polymers for organic electronics applications. In previous work, we showed that theoretical calculations on activation energy (Ea) of the C-H bonds were helpful to rationalize and predict the selectivity of the DHAP. For readers' convenience, we have gathered in this work all our previous theoretical calculations on Ea and performed new ones. Those theoretical calculations cover now most of the widely utilized electron-rich and electron-poor moieties studied in organic electronics like dithienyl-diketopyrrolopyrrole (DT-DPP) derivatives. Theoretical calculations reported herein show strong modulation of the Ea of C-H bond on DT-DPP when a bromine atom or strong electron withdrawing groups (such as fluorine or nitrile) are added to the thienyl moiety. Based on those theoretical calculations, new cyanated dithienyl-diketopyrrolopyrrole (CNDT-DPP) monomers and copolymers were prepared by DHAP and their electro-optical properties were compared with their non-fluorinated and fluorinated analogues.},
  language  = {en}
}
@phdthesis{Ribbeck2022,
  author    = {Ribbeck, Tatjana},
  title     = {Seltenerdmetallkomplexe mit Cyanoborat-Anionen - sowie - Synthese und Charakterisierung des Hydroxytricyanoborat-Anions},
  doi       = {10.25972/OPUS-18346},
  url       = {http://nbn-resolving.de/urn:nbn:de:bvb:20-opus-183465},
  school      = {Universit{\"a}t W{\"u}rzburg},
  year      = {2022},
  abstract  = {Im Rahmen dieser Arbeit konnten Seltenerdmetallcyanoborate mit unterschiedlich funktionalisierten Anionen, beispielsweise Hydrido-, Fluoro- oder Perfluoralkylcyanoborat-Anionen, synthetisiert und vollst{\"a}ndig charakterisiert werden. L{\"o}sungen der wasserfreien Komplexe Ln[BH2(CN)2]3 (Ln = La, Eu, Ho) in der korrespondierenden ionischen Fl{\"u}ssigkeit [EMIm][BH2(CN)2] konnten hinsichtlich Dichte Viskosit{\"a}t und Leitf{\"a}higkeit in Abh{\"a}ngigkeit der Konzentration des gel{\"o}sten Komplexes untersucht werden. Alle Europiumkomplexe wurden hinsichtlich ihrer photochemischen Eigenschaften untersucht. Weiterhin konnte im Rahmen dieser Arbeit die erste selektive Synthese des Hydroxytricyanoborat-Anions [B(OH)(CN)3]- vorgestellt werden. Ausgehend von der Br{\o}nsteds{\"a}ure dieses Anions konnte die Synthese einer ganzen Reihe von Salzen und Komplexverbindungen, sowie von ionischen Fl{\"u}ssigkeiten mit diesem Anion realisiert werden.},
  subject      = {Cyanoborate},
  language  = {de}
}
@article{AuerhammerArrowsmithBraunschweigetal.2017,
  author    = {Auerhammer, Dominic and Arrowsmith, Merle and Braunschweig, Holger and Dewhurst, Rian D. and Jim{\´e}nez-Halla, J. Oscar C. and Kupfer, Thomas},
  title     = {Nucleophilic addition and substitution at coordinatively saturated boron by facile 1,2-hydrogen shuttling onto a carbene donor},
  series = {Chemical Science},
  volume    = {8},
  journal   = {Chemical Science},
  number    = {10},
  doi       = {10.1039/c7sc03193a},
  url       = {http://nbn-resolving.de/urn:nbn:de:bvb:20-opus-170255},
  pages     = {7066-7071},
  year      = {2017},
  abstract  = {The reaction of [(cAAC\(^{Me}\))BH\(_{3}\)] (cAAC\(^{Me}\) = 1-(2,6-iPr\(_{2}\)C\(_{6}\)H\(_{3}\))-3,3,5,5-tetramethylpyrrolidin-2-ylidene) with a range of organolithium compounds led to the exclusive formation of the corresponding (dihydro)organoborates, Li\(^{+}\)[(cAAC\(^{Me}\)H)BH\(_{2}\)R]- (R = sp\(^{3}\)-, sp\(^{2}\)-, or sp-hybridised organic substituent), by migration of one boron-bound hydrogen atom to the adjacent carbene carbon of the cAAC ligand. A subsequent deprotonation/salt metathesis reaction with Me3SiCl or spontaneous LiH elimination yielded the neutral cAAC-supported mono(organo)boranes, [(cAAC\(^{Me}\)H)BH\(_{2}\)R]- (R]. Similarly the reaction of [cAAC\(^{Me}\))BH\(_{3}\)] with a neutral donor base L resulted in adduct formation by shuttling one boron-bound hydrogen to the cAAC ligand, to generate [(cAAC\(^{Me}\)H)BH\(_{2}\)L], either irreversibly (L = cAAC\(^{Me}\)) or reversibly (L = pyridine). Variable-temperature NMR data and DFT calculations on [(cAAC\(^{Me}\)H)BH\(_{2}\)(cAAC\(^{Me}\))] show that the hydrogen on the former carbene carbon atom exchanges rapidly with the boron-bound hydrides.},
  language  = {en}
}
@article{LandmannHennigIgnat'evetal.2017,
  author    = {Landmann, Johannes and Hennig, Philipp T. and Ignat'ev, Nikolai V. and Finze, Maik},
  title     = {Borylation of fluorinated arenes using the boron centred nucleophile B(CN)\(_{3}\)\(^{2-}\) - a unique entry to aryltricyanoborates},
  series = {Chemical Science},
  volume    = {8},
  journal   = {Chemical Science},
  number    = {9},
  doi       = {10.1039/c7sc02249b},
  url       = {http://nbn-resolving.de/urn:nbn:de:bvb:20-opus-170417},
  pages     = {5962-5968},
  year      = {2017},
  abstract  = {The potassium salt of the boron-centred nucleophile B(CN)\(_{3}\)\(^{2-}\)(1) readily reacts with perfluorinated arenes, such as hexafluorobenzene, decafluorobiphenyl, octafluoronaphthalene and pentafluoropyridine, which results in KF and the K\(^{+}\) salts of the respective borate anions with one {B(CN)\(_{3}\)} unit bonded to the (hetero)arene. An excess of K\(_{2}\)1 leads to the successive reaction of two or, in the case of perfluoropyridine, even three C-F moieties and the formation of di- and trianions, respectively. Moreover, all of the 11 partially fluorinated benzene derivatives, C\(_{6}\)F\(_{6-n}\)H\(_{n}\) (n = 1-5), generally react with K\(_{2}\)1 to give new tricyano(phenyl)borate anions with high chemo- and regioselectivity. A decreasing number of fluorine substituents on benzene results in a decrease in the reaction rate. In the cases of partially fluorinated benzenes, the addition of LiCl is advantageous or even necessary to facilitate the reaction. Also, pentafluorobenzenes R-C\(_{6}\)F\(_{5}\) (R = -CN, -OMe, -Me, or -CF\(_{3}\)) react via C-F/C-B exchange that mostly occurs in the para position and to a lesser extent in the meta or ortho positions. Most of the reactions proceed via an S\(_{N}\)Ar mechanism. The reaction of 1,4-F\(_{2}\)C\(_{6}\)H\(_{4}\) with K\(_{2}\)1 shows that an aryne mechanism has to be considered in some cases as well. In summary, a wealth of new stable tricyano(aryl)borates have been synthesised and fully characterized using multi-NMR spectroscopy and most of them were characterised using single-crystal X-ray diffraction.},
  language  = {en}
}
@unpublished{AuerhammerArrowsmithBissingeretal.2017,
  author    = {Auerhammer, Dominic and Arrowsmith, Merle and Bissinger, Philipp and Braunschweig, Holger and Dellermann, Theresa and Kupfer, Thomas and Lenczyk, Carsten and Roy, Dipak and Sch{\"a}fer, Marius and Schneider, Christoph},
  title     = {Increasing the Reactivity of Diborenes: Derivatization of NHC- Supported Dithienyldiborenes with Electron-Donor Groups},
  series = {Chemistry, A European Journal},
  journal   = {Chemistry, A European Journal},
  doi       = {10.1002/chem.201704669},
  url       = {http://nbn-resolving.de/urn:nbn:de:bvb:20-opus-155419},
  year      = {2017},
  abstract  = {A series of NHC-supported 1,2-dithienyldiborenes was synthesized from the corresponding (dihalo)thienylborane NHC precursors. NMR and UV-vis spectroscopic data, as well as X-ray crystallographic analyses, were used to assess the electronic and steric influences on the B=B double bond of various NHCs and electron-donating substituents on the thienyl ligands. Crystallographic data showed that the degree of coplanarity of the diborene core and thienyl groups is highly dependent on the sterics of the substituents. Furthermore, any increase in the electron- donating ability of the substituents resulted in the destabilization of the HOMO and greater instability of the resulting diborenes.},
  language  = {en}
}
@unpublished{AuerhammerArrowsmithBoehnkeetal.2018,
  author    = {Auerhammer, Dominic and Arrowsmith, Merle and B{\"o}hnke, Julian and Braunschweig, Holger and Dewhurst, Rian D. and Kupfer, Thomas},
  title     = {Brothers from Another Mother: a Borylene and its Dimer are Non-Interconvertible but Connected through Reactivity},
  series = {Chemical Science},
  journal   = {Chemical Science},
  doi       = {10.1039/C7SC04789D},
  url       = {http://nbn-resolving.de/urn:nbn:de:bvb:20-opus-157125},
  year      = {2018},
  abstract  = {The self-stabilizing, tetrameric cyanoborylene [(cAAC)B(CN)]4 (I, cAAC = 1-(2,6-diisopropylphenyl)-3,3,5,5-tetramethylpyrrolidin-2-ylidene) and its diborene relative, [(cAAC)(CN)B=B(CN)(cAAC)] (II), both react with disulfides and diselenides to yield the corresponding cAAC-supported cyanoboron bis(chalcogenides). Furthermore, reactions of I or II with elemental sulfur and selenium in various stoichiometries provided access to a variety of cAAC- stabilized cyanoboron-chalcogen heterocycles, including a unique dithiaborirane, a diboraselenirane, 1,3-dichalcogena-2,4-diboretanes, 1,3,4-trichalcogena- 2,5-diborolanes and a rare six-membered 1,2,4,5-tetrathia-3,6-diborinane. Stepwise addition reactions and solution stability studies provided insights into the mechanism of these reactions and the subtle differences in reactivity observed between I and II.},
  language  = {en}
}
@unpublished{BoehnkeBraunschweigJimenezHallaetal.2018,
  author    = {B{\"o}hnke, Julian and Braunschweig, Holger and Jim{\´e}nez-Halla, Oscar and Krummenacher, Ivo and Stennett, Tom E.},
  title     = {Half-Sandwich Complexes of an Extremely Electron-Donating, Re-dox-Active η\(^6\)-Diborabenzene Ligand},
  series = {Journal of the American Chemical Society},
  journal   = {Journal of the American Chemical Society},
  doi       = {10.1021/jacs.7b12394},
  url       = {http://nbn-resolving.de/urn:nbn:de:bvb:20-opus-156766},
  year      = {2018},
  abstract  = {The heteroarene 1,4-bis(CAAC)-1,4-diborabenzene (1; CAAC = cyclic (alkyl)(amino)carbene) reacts with [(MeCN)\(_3\)M(CO)\(_3\)] (M = Cr, Mo, W) to yield half-sandwich complexes of the form [(η\(^6\)-diborabenzene)M(CO)\(_3\)] (M = Cr (2), Mo (3), W (4)). Investigation of the new complexes with a combination of X-ray diffraction, spectroscopic methods and DFT calculations shows that ligand 1 is a remarkably strong electron donor. In particular, [(η\(^6\)-arene)M(CO)\(_3\)] complexes of this ligand display the lowest CO stretching frequencies yet observed for this class of complex. Cyclic voltammetry on complexes 2-4 revealed one reversi- ble oxidation and two reversible reduction events in each case, with no evidence of ring-slippage of the arene to the η\(^4\) binding mode. Treatment of 4 with lithium metal in THF led to identification of the paramagnetic complex [(1)W(CO)\(_3\)]Li·2THF (5). Compound 1 can also be reduced in the absence of a transition metal to its dianion 1\(^{2-}\), which possesses a quinoid-type structure.},
  language  = {en}
}
@phdthesis{Boehnke2019,
  author    = {B{\"o}hnke, Julian},
  title     = {Reaktivit{\"a}t niedervalenter, Carben-stabilisierter Bor-Bor-Mehrfachbindungssysteme},
  doi       = {10.25972/OPUS-16333},
  url       = {http://nbn-resolving.de/urn:nbn:de:bvb:20-opus-163335},
  school      = {Universit{\"a}t W{\"u}rzburg},
  year      = {2019},
  abstract  = {Im Rahmen dieser Arbeit war es m{\"o}glich, vielf{\"a}ltige Reaktivit{\"a}ten des Diborakumulens (7) und davon abgeleiteter Verbindungen zu untersuchen. H{\"a}ufig begr{\"u}ndet in den bemerkenswerten elektronischen Eigenschaften der verwendeten CAAC-Liganden, konnten neuartige und teilweise ungew{\"o}hnliche Bindungsmodi an niedervalenten Borspezies beobachtet werden. Der Einfluss der starken σ-Donor-F{\"a}higkeiten und der hohen π-Acidit{\"a}t der cyclischen (Alkyl)(amino)carbene spiegeln sich hierbei in vergleichenden Reaktivit{\"a}tsstudien mit den entsprechenden NHC-stabilisierten Bor-Bor-Mehrfachbindungssystemen wider. Zun{\"a}chst wurde jedoch auf die Synthese weiterer Diborakumulene eingegangen und am Beispiel der Bis(CAACCy)-stabilisierten B2-Einheit (12) erfolgreich durchgef{\"u}hrt. Mit vergleichbaren 11B-NMR-Verschiebungen und Bindungsl{\"a}ngen unterscheidet sich die Verbindung in ihren elektronischen Eigenschaften kaum von B2(CAAC)2 (7), welches aufgrund der besseren Zug{\"a}nglichkeit f{\"u}r die Reaktivit{\"a}tsstudien eingesetzt wurde. Grundlegende Studien zum Redoxverhalten des Diborakumulens zeigten die vollst{\"a}ndige, oxidative Spaltung der Bor-Bor-Bindung mit Chlorgas unter Ausbildung eines CAAC-stabilisierten Bortrichlorid-Fragments. Die Arbeiten zum Bis(boraketen) 17 und die Darstellung des Bis(boraketenimins) 18 durch die Umsetzung des Diborakumulens mit Kohlenstoffmonoxid bzw. geeigneten Isocyaniden, stellte einen ersten gr{\"o}ßeren Teilbereich dieser Arbeit dar. Durch die enorme π-R{\"u}ckbindung in die CAAC-Liganden und die CO-Liganden aus der elektronenreichen B2-Einheit kommt es in 17 zu einer Aufweitung der B-B-Bindung und orthogonal zueinander stehenden Molek{\"u}lh{\"a}lften. Im weiteren Verlauf konnte ein Mechanismus f{\"u}r die Addition von CO an B2(CAAC)2 gefunden werden, in dem aufgrund hoher energetischer Barrieren eine Umsetzung zum Bis(boralacton) - einer Spezies, die f{\"u}r die Reaktion von Kohlenstoffmonoxid mit NHC-stabilisierten Diborinen gefunden wurde - unterbunden wird. Die elektronischen und strukturellen Unterschiede zwischen Diborinen und dem Diborakumulen 7 konnten so erstmals anhand definierter Reaktionsbedingungen evaluiert werden. Die Reaktion von 7 mit zwei {\"A}quivalenten tert-Butylisocyanid f{\"u}hrte zur Bildung eines Bis(boraketenimins). {\"A}hnlich wie im Bis(boraketen) 17 kommt es auch hier unter anderem zu einer starken π-R{\"u}ckbindung in den Isocyanidliganden einhergehend mit der Aufweitung der B-B-Bindung und orthogonal zueinander stehenden Molek{\"u}lh{\"a}lften. Die Thermolyse der Verbindung f{\"u}hrte zu einer Abspaltung zweier tert-Butylradikale und zur Bildung des ersten, strukturell charakterisierten Dicyanodiborens 20. Das Dicyanodiboren zeigte hier eine strukturelle Besonderheit: W{\"a}hrend ein CAAC-Ligand in Konjugation mit dem π-System der B2-Einheit steht, zeigt der zweite CAAC-Ligand eine orthogonale Orientierung zu diesem, was vermutlich zu einer Polarisierung der B=B-Doppelbindung f{\"u}hrt und potentiell hochinteressante Reaktivit{\"a}ten erm{\"o}glicht. So f{\"u}hrte die Umsetzung von 20 mit Kohlenstoffmonoxid zur Spaltung der B-B-Bindung und Insertion eines µ2-gebundenen CO-Molek{\"u}ls in die BB-Einheit. Die Tatsache, dass ein {\"a}hnliches Reaktionsverhalten bisher nur vom ebenfalls CAAC-stabilisierten Dihydrodiboren 22 bekannt war (vide infra), demonstrierte an diesem Beispiel eindeutig die bemerkenswerten F{\"a}higkeiten von CAACs reaktive, niedervalente Hauptgruppenelementverbindungen zu stabilisieren. Die Reaktivit{\"a}t des Diborakumulens 7 gegen{\"u}ber Diwasserstoff stellte einen weiteren, großen Teilaspekt dieser Arbeit dar. Das R{\"u}hren von 7 unter einer H2-Atmosph{\"a}re f{\"u}hrte zur 1,2-Addition des H2-Molek{\"u}ls an die B2-Einheit unter Ausbildung eines trans-st{\"a}ndigen, Basen-stabilisierten Dihydrodiborens 22. Im Gegensatz zum Dicyanodiboren (20) handelt es sich bei 22 um eine C2-symmetrische Verbindung, dessen π-System im HOMO aufgrund der π-Acidit{\"a}t der CAAC-Liganden {\"u}ber das gesamte C-B-B-C-Grundger{\"u}st delokalisiert ist. Die Hydrierung wurde ebenfalls mit hochreinem D2 durchgef{\"u}hrt, um eine Hydridabstraktion aus dem L{\"o}sungsmittel auszuschließen. DFT-Berechnungen konnten zudem die Bor-gebundenen Wasserstoffatome als Hydride klassifizieren und den Mechanismus der Addition von Diwasserstoff an die B2-Einheit ermitteln. Mit einem berechneten, exothermen Reaktionsverlauf stellt die Umsetzung von 7 zu 22 auf diesem Weg das erste Beispiel einer nicht katalysierten Hydrierung einer homodinuklearen Mehrfachbindung der 2. Periode dar. Das CAAC-stabilisierte Dihydrodiboren 22 zeigte im Verlauf dieser Arbeit vielf{\"a}ltige Bindungsmodi aus der Umsetzung mit Kohlenstoffmonoxid. Unter anderem die Eigenschaft von CAACs, eine 1,2-Wasserstoffwanderung von angrenzenden BH-Einheiten auf das Carbenkohlenstoffatom zu beg{\"u}nstigen, f{\"u}hrte zur Ausbildung verschiedener Tautomere. W{\"a}hrend das Produkt aus der formalen Addition und Insertion von zwei CO-Molek{\"u}len (24) lediglich unter CO-Atmosph{\"a}re stabil war, konnte unter Argonatmosph{\"a}re ein Tautomerengemisch von 25 mit intakter Bor-Bor-Bindung und einer Boraketeneinheit isoliert werden. W{\"a}hrend dieser Prozess vollst{\"a}ndig reversibel war, f{\"u}hrte das Erhitzen von 25 zur Bildung eines Alkylidenborans (26), welches ebenfalls in zwei tautomeren Formen vorlag. Dar{\"u}ber hinaus konnte die Bildung einer weiteren Spezies (27) in geringen Ausbeuten beobachtet werden, die aus der vollst{\"a}ndigen Spaltung eines CO-Fragments und der Bildung einer intramolekularen C≡C-Dreifachbindung resultierte. VT-NMR- und Korrelationsexperimente, Kristallisationen unter verschiedenen Atmosph{\"a}ren, Schwingungsspektroskopie sowie die mechanistische Analyse der Umsetzungen basierend auf DFT-Berechnungen erm{\"o}glichten hier einen tiefen und detaillierten Einblick in die zugrunde liegenden Prozesse. Die thermische Umsetzung des Dihydrodiborens 22 mit Acetylen f{\"u}hrte wider Erwarten nicht zur Cycloaddition an die B=B-Doppelbindung, sondern zur Insertion in diese. Das erhaltene Produkt 28 zeigte eine C2-symmetrische Struktur und durchg{\"a}ngig sp2-hybridisierte Kohlenstoff- und Borzentren entlang der Hauptachse. Eine DFT-Studie ergab ein konjugiertes π-System, dass dem 1,3,5-Hexatrien stark {\"a}hnelte. Eine weitere Umsetzung von 22 mit zwei {\"A}quivalenten Diphenyldisulfid f{\"u}hrte ebenfalls zur Spaltung der B=B-Doppelbindung und zur Ausbildung eines CAAC-stabilisierten, sp3-hybridisierten Monoborans. Das Diborakumulen 7 konnte in zwei weiteren Reaktivit{\"a}tsstudien selektiv mit Kohlenstoffdioxid und Aceton umgesetzt werden. Die Reaktion von B2(CAAC)2 mit zwei CO2-Molek{\"u}len f{\"u}hrte zur Ausbildung einer Spezies mit einer Boraketenfunktionalit{\"a}t und einem Bors{\"a}ureesterderivat (30). F{\"u}r die Aktivierung von Kohlenstoffdioxid an unpolaren Mehrfachbindungen gab es bisher kein Beispiel in der Literatur, sodass diese mechanistisch untersucht wurde. Hier erfolgte die Reaktion {\"u}ber eine ungew{\"o}hnliche, sukzessive [2+1]-Cycloaddition an die koordinativ unges{\"a}ttigten Boratome mit einem insgesamt stark exergonen Verlauf. Die Umsetzung von 7 mit Aceton f{\"u}hrte zur Ausbildung eines f{\"u}nfgliedrigen Heterocyclus mit einer C=C-Doppelbindung und asymmetrisch verbr{\"u}ckter Bor-Bor-Bindung mit einem orthogonal zum Heterocyclus stehenden μ2-Hydrid. Interessanterweise zeigte hier eine vergleichende Studie von Tobias Br{\"u}ckner an einem SIDep-stabilisierten Diborin bei einer analogen Reaktionsf{\"u}hrung ein 1,2-Enol-Additionsprodukt, sodass der zugrunde liegende Reaktionsmechanismus ebenfalls untersucht wurde. W{\"a}hrend das 1,2-Enol-Additionsprodukt als Intermediat zur Bildung von 31 beschrieben werden konnte, f{\"u}hrten moderate Energiebarrieren und ein deutlich exergoner Reaktionsverlauf im Fall des Diborakumulens zu einer doppelten Acetonaktivierung. F{\"u}r 31 konnte dar{\"u}ber hinaus ein Isomerengemisch beobachtet werden, das nach der Bildung nicht mehr ineinander {\"u}berf{\"u}hrt werden konnte. Die Reaktion des Diborakumulens mit M{\"u}nzmetallhalogeniden ergab f{\"u}r die Umsetzung von 7 mit drei {\"A}quivalenten Kupfer-(I)-chlorid-Dimethylsulfidaddukt eine T-f{\"o}rmige Koordination von drei CuCl-Fragmenten an die B2-Einheit (33). Setzte man das Diborakumulen 7 mit einem {\"A}quivalent IMeMe um, bildete sich das heteroleptisch substituierte Mono-Basenaddukt 34. Dieses zeigte eine thermische Labilit{\"a}t, sodass sich nach einem Zeitraum von 24 Stunden bei erh{\"o}hter Temperatur selektiv das Produkt einer CH-Aktivierung isolieren ließ. Das gleiche Produkt (35) konnte ebenfalls durch die Zugabe einer Lewis-S{\"a}ure (Galliumtrichlorid) zu 34 nach kurzer Zeit bei Raumtemperatur erhalten werden. Setzte man 34 mit einem weiteren {\"A}quivalent IMeMe um, so bildete sich das Bis(IMeMe)-Addukt des Diborakumulens 36, das zun{\"a}chst an das Bis(CO)-Addukt 17 erinnerte und durch die hohe sterische Spannung im System eine stark aufgeweitete Bor-Bor-Bindung besitzt. Die Reaktion von 34 gegen{\"u}ber Kohlenstoffmonoxid lieferte das heteroleptisch substituierte Basenaddukt 37. Das elektronenreiche Boratom des Boraketenstrukturfragments f{\"u}hrt hier zu einer erheblichen π-R{\"u}ckbindung in den CO-Liganden, der die niedrigsten, zu diesem Zeitpunkt jemals beobachteten Wellenzahlen f{\"u}r die CO-Schwingung in einer derartigen Funktionalit{\"a}t aufweist. Eine abschließende Umsetzung des Mono-Basenaddukts 34 mit Diwasserstoff f{\"u}hrte zur spontanen Hydrierung beider Boratome und zur Spaltung der Bor-Bor-Bindung. Die Reaktionsmischung zeigte nach erfolgter Reaktion ein 1:1-Verh{\"a}ltnis aus einem CAAC-stabilisierten BH3-Fragment 39 und einem zweifach Basen-stabilisierten BH-Borylen 38. Die Spaltung einer Bor-Bor-(Mehrfach)-Bindung zur Synthese von heteroleptisch Lewis-Basen-stabilisierten Borylenen stellte dabei einen bisher nicht bekannten Zugang zu dieser Verbindungsklasse dar. Ein sehr großer Teilbereich dieser Arbeit besch{\"a}ftigte sich mit der Synthese und Reaktivit{\"a}t von Diborabenzol-Derivaten. Setzte man das Diborakumulen 7 mit Acetylen um, so konnte die Bildung eines CAAC-stabilisierten 1,4-Diborabenzols beobachtet werden. Das planare Grundger{\"u}st, C-C- und B-C-Bindungen im Bereich von (partiellen) Doppelbindungen, stark entschirmte Protonen des zentralen B2C4H4-Heterocyclus, Grenzorbitale, die denen des Benzols {\"a}hneln, sowie negative NICS-Werte stellen 42 als einen 6π-Aromaten dar, der mit seinem energetisch stark destabilisierten HOMO als elektronenreicher Ligand in der {\"U}bergangsmetallchemie eingesetzt werden konnte (vide infra). Die Reaktion von B2(CAAC)2 mit Propin bzw. 2-Butin lieferte hingegen 2π-aromatische, paramagnetische Verbindungen mit Schmetterlingsgeometrie aus der [2+2]-Cycloaddition an die Bor-Bor-Bindung und anschließender Umlagerung zu den thermodynamisch stabileren 1,3-Diboreten. Die weitere, thermisch induzierte Umsetzung von 40 und 41 mit Acetylen erm{\"o}glichte die Darstellung der Methyl-substituierten 1,4-Diborabenzol-Derivate 43 und 44. Um die Eigenschaften des CAAC-stabilisierten 1,4-Diborabenzols zu analysieren, wurde sowohl die Redoxchemie von 42 als auch dessen potentieller Einsatz als η6-Ligand an {\"U}bergangsmetalle der Chromtriade untersucht. Es zeigte sich, dass durch die Reduktion mit Lithium die Darstellung des zweifach reduzierten Diborabenzols 45 m{\"o}glich war. Die Ausbildung eines quinoiden Systems f{\"u}hrte hier zu einem Isomerengemisch aus cis/trans-konfigurierten CAAC-Liganden. Die Umsetzung der isolierten Verbindung mit 0.5 {\"A}quivalenten Zirkoniumtetrachlorid f{\"u}hrte quantitativ zur Bildung von 42 und demonstrierte somit das hohe Reduktionspotential der dilithiierten Spezies. Durch die Reaktion von 42 mit [(MeCN)3M(CO)3] (M = Cr, Mo, W) gelang dar{\"u}ber hinaus die Darstellung von 18-Valenzelektronen-Halbsandwichkomplexen. Die Koordination des elektronenreichen Heteroarens an die Metalltricarbonyl-Segmente lieferte die niedrigsten, zu diesem Zeitpunkt je beobachteten Carbonylschwingungen f{\"u}r [(η6-aren)M(CO)3]-Komplexe, die durch den starken, elektronendonierenden Einfluss des Liganden auf das Metall und die daraus resultierende erhebliche R{\"u}ckbindung in die antibindenden π*-Orbitale der CO-Liganden hervorgerufen werden. DFT-Analysen der Verbindungen zeigten zudem im Vergleich zu [(η6-C6H6)Cr(CO)3] signifikant h{\"o}here Bindungsenergien zwischen dem Metallfragment und dem 1,4-Diborabenzol und unterstreichten zusammen mit weiteren spektroskopischen und theoretischen Analysen die bemerkenswerten Eigenschaften von 42 als {\"u}beraus stark elektronendonierender Ligand. Letztlich gelang in einer Reaktivit{\"a}tsstudie am Wolframkomplex 48 die Darstellung eines Mono-Radikalanions (49), das vermutlich das erste Beispiel eines monoanionischen Aren-Metalltricarbonyl-Komplexes der Gruppe 6 darstellt. Ein abschließendes, großes Thema dieser Arbeit besch{\"a}ftigte sich mit der Synthese von Biradikalen aus verdrehten Doppelbindungen und dem Vergleich mit den verwandten, diamagnetischen Diborenen. Die Reaktion des Diborakumulens mit verschieden substituierten Disulfiden und einem Diselenid f{\"u}hrte zur Ausbildung von persistenten, paramagnetischen, biradikalischen Spezies durch die 1,2-Addition an die Bor-Bor-Mehrfachbindung. W{\"a}hrend die Addition der Substrate an das IDip-stabilisierte Diborin 5 geschlossenschalige, diamagnetische Diborene mit coplanarer Anordnung der Substituenten lieferte, konnte nach der Addition der Substrate an das Diborakumulen 7 stets eine Bor-Bor-Einfachbindung mit orthogonaler Ligandenorientierung festgestellt werden. ESR-spektroskopische und magnetische Messungen der Proben ergaben f{\"u}r 51e einen Triplett-Grundzustand bei Raumtemperatur und durch den captodativen-Effekt der π-Donor Stickstoffatome und der π-Akzeptor Boratome eine erhebliche Delokalisierung der ungepaarten Elektronen in die Liganden. Detaillierte theoretische Studien konnten dar{\"u}ber hinaus zeigen, dass die Singulett-Zust{\"a}nde der synthetisierten Diborene stabiler als die Triplett-Zust{\"a}nde sind und dass die Triplett-Zust{\"a}nde der paramagnetischen Verbindungen 51a,b,e stabiler als die entsprechenden Singulett-Zust{\"a}nde sind. Die Verbindungen liegen stets in ihrem Grundzustand vor und lieferten somit hochinteressante Modellsysteme zum tieferen Verst{\"a}ndnis dieser Verbindungsklasse.},
  subject      = {Bor},
  language  = {de}
}
@unpublished{StoyBoehnkeJiménezHallaetal.2018,
  author    = {Stoy, Andreas and B{\"o}hnke, Julian and Jiménez-Halla, J. Oscar C. and Dewhurst, Rian D. and Thiess, Torsten and Braunschweig, Holger},
  title     = {CO\(_2\) Binding and Splitting by Boron-Boron Multiple Bonds},
  series = {Angewandte Chemie, International Edition},
  journal   = {Angewandte Chemie, International Edition},
  doi       = {10.1002/anie.201802117},
  url       = {http://nbn-resolving.de/urn:nbn:de:bvb:20-opus-164265},
  year      = {2018},
  abstract  = {CO\(_2\) is found to undergo room-temperature, ambient- pressure reactions with two species containing boron-boron multiple bonds, leading to incorporation of either one or two CO\(_2\) molecules. In one case, a thermally-unstable intermediate was structurally characterized, indicating the operation of an initial 2+2 cycloaddition mechanism in the reaction.},
  language  = {en}
}
@unpublished{ArrowsmithMattockBoehnkeetal.2018,
  author    = {Arrowsmith, Merle and Mattock, James D. and B{\"o}hnke, Julian and Krummenacher, Ivo and Vargas, Alfredo and Braunschweig, Holger},
  title     = {Direct access to a cAAC-supported dihydrodiborene and its dianion},
  series = {Chemical Communications},
  journal   = {Chemical Communications},
  doi       = {10.1039/C8CC01580E},
  url       = {http://nbn-resolving.de/urn:nbn:de:bvb:20-opus-164276},
  year      = {2018},
  abstract  = {The two-fold reduction of (cAAC)BHX\(_2\) (cAAC = 1-(2,6-diisopropylphenyl)-3,3,5,5-tetramethylpyrrolidin-2-ylidene; X = Cl, Br) provides a facile, high-yielding route to the dihydrodiborene (cAAC)\(_2\)B\(_2\)H\(_2\). The (chloro)hydroboryl anion reduction intermediate was successfully isolated using a crown ether. Overreduction of the diborene to its dianion [(cAAC)\(_2\)B\(_2\)H\(_2\)]\(^{2-}\) causes a decrease in the B-B bond order whereas the B-C bond orders increase.},
  language  = {en}
}
@article{BoehnkeBruecknerHermannetal.2018,
  author    = {B{\"o}hnke, Julian and Br{\"u}ckner, Tobias and Hermann, Alexander and Gonz{\´a}lez-Belman, Oscar F. and Arrowsmith, Merle and Jim{\´e}nez-Halla, J. Oscar C. and Braunschweig, Holger},
  title     = {Single and double activation of acetone by isolobal B≡N and B≡B triple bonds},
  series = {Chemical Science},
  volume    = {9},
  journal   = {Chemical Science},
  doi       = {10.1039/c8sc01249k},
  url       = {http://nbn-resolving.de/urn:nbn:de:bvb:20-opus-164286},
  pages     = {5354-5359},
  year      = {2018},
  abstract  = {B≡N and B≡B triple bonds induce C-H activation of acetone to yield a (2-propenyloxy)aminoborane and an unsymmetrical 1-(2- propenyloxy)-2-hydrodiborene, respectively. DFT calculations showed that, despite their stark electronic differences, both the B≡N and B≡B triple bonds activate acetone via a similar coordination-deprotonation mechansim. In contrast, the reaction of acetone with a cAAC-supported diboracumulene yielded a unique 1,2,3-oxadiborole, which according to DFT calculations also proceeds via an unsymmetrical diborene, followed by intramolecular hydride migration and a second C-H activation of the enolate ligand.},
  language  = {en}
}
@unpublished{CidHermannRadcliffeetal.2018,
  author    = {Cid, Jessica and Hermann, Alexander and Radcliffe, James E. and Curless, Liam D. and Braunschweig, Holger and Ingleson, Michael J.},
  title     = {Synthesis of Unsymmetrical Diboron(5) Compounds and Their Conversion to Diboron(5) Cations},
  series = {Organometallics},
  journal   = {Organometallics},
  doi       = {10.1021/acs.organomet.8b00288},
  url       = {http://nbn-resolving.de/urn:nbn:de:bvb:20-opus-164299},
  year      = {2018},
  abstract  = {Reaction of bis-catecholatodiboron-NHC adducts, B\(_2\)Cat\(_2\)(NHC), (NHC = IMe (tetramethylimidazol-2-ylidene), IMes (1,3-dimesitylimidazol-2-ylidene) or IDIPP (1,3-bis(2,6-diisopropylphenyl)imidazol-2-ylidene)) with BCl3 results in the replacement of the catecholato group bound to the four coordinate boron with two chlorides to yield diboron(5) Lewis acid-base adducts of formula CatB-BCl\(_2\)(NHC). These compounds are precursors to diboron(5) monocations, accessed by adding AlCl\(_3\) or K[B(C\(_6\)F\(_5\))\(_4\)] as halide abstraction agents in the presence of a Lewis base. The substitution of the chlorides of CatB-BCl\(_2\)(NHC) for hydrides is achieved using Bu\(_3\)SnH and a halide abstracting agent to form 1,1-dihydrodiboron(5) compounds, CatB-BH\(_2\)(NHC). Attempts to generate diboron(4) monocations of formula [CatB-B(Y)(NHC)]\(^+\) (Y = Cl or H) led to the rapid formation of CatBY.},
  language  = {en}
}
@phdthesis{Mao2018,
  author    = {Mao, Lujia},
  title     = {Transition Metal-Catalyzed Construction of Benzyl/Allyl sp\(^3\) and Vinyl/Allenyl sp\(^2\) C-B Bonds},
  url       = {http://nbn-resolving.de/urn:nbn:de:bvb:20-opus-154022},
  school      = {Universit{\"a}t W{\"u}rzburg},
  year      = {2018},
  abstract  = {Organoboron compounds, such as benzyl-, allyl-, allenyl-, vinyl-, and 2-boryl allyl-boronates, have been synthesized via metal-catalyzed borylations of sp3 C-O and C-H bonds. Thus, Cu-catalyzed borylations of alcohols and their derivatives provide benzyl-, allyl-, allenyl-, vinyl-, and 2-boryl allyl-boronates via nucleophilic substitution. The employment of Ti(OiPr)4 turns the OH moiety into a good leaving group ('OTi'). The products of Pd-catalyzed oxidative borylations of allylic C-H bonds of alkenes were isolated and purified, and their application in the one-pot synthesis of stereodefined homoallyl alcohols was also investigated. Chapter 2 presents a copper-catalyzed synthesis of benzyl-, allyl-, and allenyl-boronates from benzylic, allylic, and propargylic alcohols, respectively, employing a commercially available catalyst precursor, [Cu(CH3CN)4]2+[BF4-]2, and Xantphos as the ligand. The borylation of benzylic alcohols was carried out at 100 oC with 5-10 mol \% [Cu(CH3CN)4]2+[BF4-]2, which afforded benzylic boronates in 32\%-95\% yields. With 10 mol \% [Cu(CH3CN)4]2+[BF4-]2, allylic boronates were provided in 53\%-89\% yields from the borylation of allylic alcohols at 60 or 100 oC. Secondary allylboronates were prepared in 72\%-84\% yields from the borylation of primary allylic alcohols, which also suggests that a nucleophilic substitution pathway is involved in this reaction. Allenylboronates were also synthesized in 72\%-89\% yields from the borylation of propargylic alcohols at 40 or 60 oC. This methodology can be extended to borylation of benzylic and allylic acetates. This protocol exhibits broad reaction scope (40 examples) and high efficiency (up to 95\% yield) under mild conditions, including the preparation of secondary allylic boronates. Preliminary mechanistic studies suggest that nucleophilic substitution is involved in this reaction. Chapter 3 reports an efficient methodology for the synthesis of vinyl-, allyl-, and (E)-2-boryl allylboronates from propargylic alcohols via copper-catalyzed borylation reactions under mild conditions. In the presence of a commercially available catalyst precursor (Cu(OAc)2 or Cu(acac)2) and ligand (Xantphos), the reaction affords the desired products in up to 92\% yield with a broad substrate scope (43 examples). Vinylboronates were synthesized in 50\%-83\% yields via Cu-catalyzed hydroboration of mono-substituted propargylic alcohols. With 1,1-disubstituted propargylic alcohols as the starting materials and Cu(OAc)2 as the catalyst precursor, a variety of allylboronates were synthesized in 44\%-83\% yields. The (E)-2-boryl allylboronates were synthesized in 54\%-92\% yields via the Cu-catalyzed diboration of propargylic alcohols. The stereoselectivity is different from the Pd(dba)2-catalyzed diboration of allenes that provided (Z)-2-boryl allylboronates predominantly. The isolation of an allenyl boronate as the reaction intermediate suggests that an SN2'-type reaction, followed by borylcupration, is involved in the mechanism of the diboration of propargylic alcohols. In chapter 4, a Pd-catalyzed allylic C-H borylation of alkenes is reported. The transformation exhibits high regioselectivity with a variety of linear alkenes, employing a Pd-pincer complex as the catalyst precursor, and the allylic boronate products were isolated and purified. This protocol can also be extended to one-pot carbonyl allylation reactions to provide homoallyl alcohols efficiently. An interesting mechanistic feature is that the reaction proceeds via a Pd(II)/Pd(IV) catalytic cycle. Formation of the Pd(IV) intermediate occurs by a unique combination of an NCNpincer complex and application of F-TEDA-BF4 as the oxidant. An important novelty of the present C-H borylation reaction is that all allyl-Bpin products can be isolated with usually high yields. This is probably a consequence of the application of the NCN-pincer complex as catalyst, which selectively catalyzes C-B bond formation avoiding subsequent C-B bond cleavage based side-reactions},
  subject      = {{\"U}bergangsmetall},
  language  = {en}
}
@unpublished{WangArrowsmithBraunschweigetal.2017,
  author    = {Wang, Sunewang Rixin and Arrowsmith, Merle and Braunschweig, Holger and Dewhurst, Rian and Paprocki, Valerie and Winner, Lena},
  title     = {CuOTf-mediated intramolecular diborene hydroarylation},
  series = {Chemical Communications},
  journal   = {Chemical Communications},
  doi       = {10.1039/C7CC07371B},
  url       = {http://nbn-resolving.de/urn:nbn:de:bvb:20-opus-154055},
  year      = {2017},
  abstract  = {Upon complexation to CuOTf, a PMe\(_3\)-stabilized bis(9-anthryl) diborene slowly undergoes an intramolecular hydroarylation reaction at room temperature. Subsequent triflation of the B-H bond with CuOTf, followed by a PMe\(_3\) transfer, finally yields a cyclic sp\(^2\)-sp\(^3\) boryl-substituted boronium triflate salt.},
  language  = {en}
}
@unpublished{BraunschweigBruecknerDeissenbergeretal.2017,
  author    = {Braunschweig, Holger and Br{\"u}ckner, Tobias and Deißenberger, Andrea and Dewhurst, Rian and Gackstatter, Annika and G{\"a}rtner, Annalena and Hofmann, Alexander and Kupfer, Thomas and Prieschl, Dominic and Thiess, Torsten and Wang, Sunewang Rixin},
  title     = {Reaction of Dihalodiboranes(4) with N-Heterocyclic Silylenes: Facile Construction of 1-Aryl-2-Silyl-1,2-Diboraindanes},
  series = {Chemistry, A European Journal},
  journal   = {Chemistry, A European Journal},
  doi       = {10.1002/chem.201702377},
  url       = {http://nbn-resolving.de/urn:nbn:de:bvb:20-opus-153068},
  year      = {2017},
  abstract  = {Dihalodiboranes(4) react with an N-heterocyclic silylene (NHSi) to generate NHSi-adducts of 1-aryl-2-silyl-1,2-diboraindanes as confirmed by X-ray crystallography, featuring the functionalization of both B-X (X = halogen) bonds and a C-H bond under mild conditions. Coordination of a third NHSi to the proposed 1,1-diaryl- 2,2-disilyldiborane(4) intermediates, generated by a two-fold B-X insertion, may be crucial for the C-H borylation that leads to the final products. Notably, our results demonstrate the first C-H borylation with a strong B-F bond activated by silylene insertion.},
  language  = {en}
}
@unpublished{ArrowsmithBoehnkeBraunschweigetal.2017,
  author    = {Arrowsmith, Merle and B{\"o}hnke, Julian and Braunschweig, Holger and Celik, Mehmet Ali},
  title     = {Reactivity of a Dihydrodiborene with CO: Coordination, Insertion, Cleavage and Spontaneous Cyclic Alkyne Formation},
  series = {Angewandte Chemie, International Edition},
  journal   = {Angewandte Chemie, International Edition},
  doi       = {10.1002/anie.201707907},
  url       = {http://nbn-resolving.de/urn:nbn:de:bvb:20-opus-153318},
  year      = {2017},
  abstract  = {Under a CO atmosphere the dihydrodiborene [(cAAC)HB=BH(cAAC)] underwent coordination of CO concomitant with reversible hydrogen migration from boron to the carbene carbon atom, as well as reversible CO insertion into the B=B bond. Heating of the CO-adduct resulted in two unusual cAAC ring-expansion products, one presenting a B=C bond to a six-membered 1,2-azaborinane-3-ylidene, the other an unprecedented nine-membered cyclic alkyne resulting from reductive cleavage of CO and spontaneous C≡C triple bond formation.},
  language  = {en}
}
@phdthesis{Schuster2019,
  author    = {Schuster, Julia Katharina},
  title     = {Lewis-Basen-Stabilisierte Mono- und Dinukleare Verbindungen des Galliums und Niedervalente Verbindungen des Berylliums - Darstellung und Reaktivit{\"a}tsstudien},
  doi       = {10.25972/OPUS-16638},
  url       = {http://nbn-resolving.de/urn:nbn:de:bvb:20-opus-166381},
  school      = {Universit{\"a}t W{\"u}rzburg},
  year      = {2019},
  abstract  = {The present work is divided into two parts, the first of which is concerned with the synthesis and reactivity of carbene-stabilized gallium compounds. The second part of this thesis adresses the synthesis of novel, beryllium-containing compounds, whereby, in addition to investigations into new structural motifs of linear, sp-hybridized beryllium compounds, the stabilization of low valent beryllium complexes by the use of carbene ligands is a central part of this thesis. 1 Lewis-base-stabilized gallium compounds In this chapter, two different synthetic routes towards carbene stabilized, low-valent gallium compounds were investigated. By the use of CAAC ligands, four different [GaCl3(RCAAC)]-species (R = Me, Cy, Et, Menth) were realized, and investigated in terms of their reactivity towards reducing agents. However, all experimental approaches led to either decomposition products or renewed isolation of the starting materials and the synthesis of dinuclear gallium compounds via reductive coupling of two CAAC-Ga fragments was found not to be feasible. A different approach towards low-valent gallium compounds was the chemical reduction of Lewis-base-stabilized digallanes(4), in which the two gallium atoms are already connected via a σ bond. The synthesis of such compounds by reaction of either the subhalide ´GaI` or the mixed-valent salt [Ga]+[GaCl4]- with two equivalents of the free MeCAAC did not afford the double Lewis-base-stabilized [Ga2X4(MeCAAC)2] species (X = I, Cl). However, [Ga2Cl4(MeCAAC)2] was accessible through ligand exchange reaction of [Ga2Cl4(1,4-dioxane)2] with two equivalents of MeCAAC, due to the relatively weakly-coordinating nature of 1,4-dioxane. In an analogous fashion, three additional Lewis-base-stabilized digallanes(4) could be realized when the carbenes CyCAAC, SIDep und IDipp were used. The reactivity of the Lewis-base-stabilized digalliumtetrachlorides was tested towards different reducing agents. However, none of the reactions led to a distinct product formation and the synthesis of neutral, Ga-Ga multiple bond systems could not be realized in this manner. However, treatment of [Ga2Cl4(MeCAAC)2] with two equivalents of 1,3,2 diazaborolyllithium induced Ga-Ga bond cleavage and [GaCl2{B(NDippCH)2}(MeCAAC)] was isolated as the only boron-containing compound. The halide exchange reactions of the double Lewis-base adducts of digalliumtetrachloride were also investigated. Treatment of [Ga2Cl4(MeCAAC)2] and [Ga2Cl4(CyCAAC)2] with 1.3 molar equivalents of either BBr3 or BI3, well established reagents for halide exchange at other Group 13 elements, yielded the corresponding [Ga2X4(MeCAAC)2] (X = Br, I ) and [Ga2X4(CyCAAC)2] (X = Br, I), with retention of the carbene ligands. Also, the reaction of [Ga2Br4(CyCAAC)2] with BI3 afforded the fully iodinated species. In contrast to the MeCAAC-stabilized compounds, which feature extreme insolubility in common organic solvents, the CyCAAC-stabilized compounds could be characterized by NMR spectroscopy and X-ray diffraction. 2 Lewis-base-stabilized beryllium compounds The reaction of BeCl2 with two equivalents 1,3,2-diazaborolyllithium provided the homoleptic, linear Be{B(NDippCH)2}2. In its 9Be NMR spectrum, the compound shows a chemical shift of δ = 45 ppm, significantly outside the normal range of two-coordinate beryllium compounds. The electrophilic nature of the beryllium center in Be{B(NDippCH)2}2 was calculated by quantum chemical calculations and demonstrated by its reactivity towards different substrates: methanolysis of Be{B(NDippCH)2}2 induced a Be-B bond cleavage, and, along with insoluble materials presumed to be the polymeric beryllium methanolate, cleanly afforded the protonated 1,3,2 diazaborole. The use of deuterated MeOD in the reaction confirmed methanol as the proton source. Treatment of Be{B(NDippCH)2}2 with one equivalent of the small carbene IMe effected addition at the beryllium center to yield the trigonal mixed Lewis-base adduct. The heteroleptic BeCl{B(NDippCH)2} could not be synthesized by the reaction of BeCl2 with equimolar amounts of 1,3,2-diazaborolyllithium. Therefore, [BeClCp*] was used as starting material for the synthesis of novel, heteroleptic sp-hybridized beryllium species. Treatment of [BeClCp*] with various NHCs did not lead to the expected adduct formation, but yielded, only in the case of IiPr, the metallocene [BeCp*2] and the double Lewis-base adduct [BeCl2(IiPr)2] in a ligand exchange reaction. The reaction of [BeClCp*] with equimolar amounts of 1,3,2 diazaborolyllithium formed the linear coordinated [BeCp*{B(NDippCH)2}] in a salt elimination reaction. A central part of this work was the monomerization of BeCl2 by the use of CAAC ligands. Four differerent [BeCl2(RCAAC)] species (R = Me, Cy, Et, Menth) were synthesized via reaction of the corresponding free carbenes and BeCl2. Furthermore, the reactivity of these kinds of compounds towards different substrates was investigated. Treatment of [BeCl2(MeCAAC)] with equimolar amounts of 1,3,2-diazaborolyllithium afforded the trigonal mixed Lewis-base adduct [BeCl{B(NDippCH)2}(MeCAAC)] in a salt elimination reaction. This compound showed limited stability under reduced pressure, in solution as well as in the solid state, and subsequently formed the protonated 1,3,2 diazaborole and a beryllium containing compound that could not be further identified. The reaction of [BeCl2(MeCAAC)] with Bogdanović-Magnesium ([Mg(C14H10)(thf)3]) provided the CAAC-stabilized berylliumanthracendiyl [Be(C14H10)(MeCAAC)], which was isolated as a red solid. The mechanism of this reaction might be described as a nucleophilic addition of the dianionic anthracene unit to the beryllium center with concomitant loss of MgCl2. [Be(C14H10)(MeCAAC)] shows structural similarities to the magnesium containing species [Mg(C14H10)(thf)3], as both compounds show a non-planar anthracene moiety in their solid-state structures, due to the loss of aromaticity of the substituent. None of the attempts to chemically reduce the various [BeCl2(RCAAC)] compounds with a range of one-electron reducing agents afforded a selective reaction product, and either decomposition products or starting materials were isolated. However, treatment of the Lewis-base adducts [BeCl2(MeCAAC)] and [BeCl2(CyCAAC)] with potassium graphite in the presence of an additional equivalent of RCAAC (R = Me, Cy) yielded the homoleptic and heteroleptic compounds [Be(CyCAAC)2], [Be(MeCAAC)2] and [Be(MeCAAC)(CyCAAC)]. The solid-state structures of the double Lewis-base stabilized beryllium compounds show linear geometries around the beryllium center and significant differences to their beryllium-containing starting materials. A contraction of the Be1-C1 bonds as well as an elongation of the ligand-centered C1-N1 bonds was observed, indicative of strong Be-C bonding. Whereas the beryllium atom is usually found in its +II oxidation state, the central atom in the linear [Be(CAAC)] compounds is formally in its elemental form. Therefore, these compounds represent the first neutral complexes with a formally zerovalent CAAC-stabilized s-block element. The unusual electronic structure of these compounds is emphasized by their deep violet color (λmax (THF) = 575/579 nm). Quantum chemical calculations describe the bonding situation in [Be(CAAC)2] with a combination of donor-acceptor interactions between two ground-state singlet CAAC ligands and Be(0) in a 1s22s02p2 electronic configuration, resulting in a 3c 2e- π bond stretching over the C Be C core. Furthermore, the stabilization arising from π backdonation from Be to the CAAC ligands was found to significantly predominate over that from σ-donation from CAAC to the beryllium center. The NHC-stabilized compounds [Be(IDipp)2] and [Be(IDipp)(IMes)] and the mixed NHC/CAAC-stabilized species [Be(MeCAAC)(NHC)] (NHC = IDipp, IMes, SIDep) could not be synthesized. This might be explained by the different electronic properties of the carbenes. On the one hand, the π-accepting abilities of the NHCs are likely insufficient to form a 3c 2e- π bond. On the other hand, the stability of the mixed CAAC/NHC stabilized Be(0) compounds might not be sufficient due to differences in the σ-donating and π accepting properties of the ligands, which limits the formation of a symmetrical 3c 2e- π bond across the C-Be-C unit.},
  subject      = {Beryllium},
  language  = {de}
}
@unpublished{BoehnkeDellermannCeliketal.2018,
  author    = {B{\"o}hnke, Julian and Dellermann, Theresa and Celik, Mehmet Ali and Krummenacher, Ivo and Dewhurst, Rian D. and Demeshko, Serhiy and Ewing, William C. and Hammond, Kai and Heß, Merlin and Bill, Eckhard and Welz, Eileen and R{\"o}hr, Merle I. S. and Mitric, Roland and Engels, Bernd and Meyer, Franc and Braunschweig, Holger},
  title     = {Isolation of diradical products of twisted double bonds},
  series = {Nature Communications},
  journal   = {Nature Communications},
  url       = {http://nbn-resolving.de/urn:nbn:de:bvb:20-opus-160248},
  year      = {2018},
  abstract  = {Molecules containing multiple bonds between atoms—most often in the form of olefins—are ubiquitous in nature, commerce, and science, and as such have a huge impact on everyday life. Given their prominence, over the last few decades, frequent attempts have been made to perturb the structure and reactivity of multiply-bound species through bending and twisting. However, only modest success has been achieved in the quest to completely twist double bonds in order to homolytically cleave the associated π bond. Here, we present the isolation of double-bond-containing species based on boron, as well as their fully twisted diradical congeners, by the incorporation of attached groups with different electronic properties. The compounds comprise a structurally authenticated set of diamagnetic multiply-bound and diradical singly-bound congeners of the same class of compound.},
  language  = {en}
}
@unpublished{StennettMattockVollertetal.2018,
  author    = {Stennett, Tom and Mattock, James and Vollert, Ivonne and Vargas, Alfredo and Braunschweig, Holger},
  title     = {Unsymmetrical, Cyclic Diborenes and Thermal Rearrangement to a Borylborylene},
  series = {Angewandte Chemie, International Edition},
  volume    = {57},
  journal   = {Angewandte Chemie, International Edition},
  doi       = {10.1002/anie.201800671},
  url       = {http://nbn-resolving.de/urn:nbn:de:bvb:20-opus-160258},
  pages     = {4098-4102},
  year      = {2018},
  abstract  = {Cyclic diboranes(4) based on a chelating monoanionic, benzylphosphine linker were prepared by boron-silicon exchange between arylsilanes and B\(_2\)Br\(_4\). Coordination of Lewis bases to the remaining sp\(^2\) boron atom yielded unsymmetrical sp\(^3\)-sp\(^3\) diboranes, which were reduced with KC\(_8\) to their corresponding trans-diborenes. These compounds were studied by a combination of spectroscopic methods, X-ray diffraction and DFT calculations. PMe\(_3\)-stabilized diborene 6 was found to undergo thermal rearrangement to gem- diborene 8. DFT calculations on 8 reveal a polar boron-boron bond, and indicate that the compound is best described as a borylborylene.},
  language  = {en}
}