13 research outputs found
Oxidation, Coordination, and Nickel-Mediated Deconstruction of a Highly Electron-Rich Diboron Analogue of 1,3,5-Hexatriene
The reductive coupling of an N-heterocyclic carbene (NHC) stabilized (dibromo)vinylborane yields a 1,2-divinyldiborene, which, although isoelectronic to a 1,3,5-triene, displays no extended Ï conjugation because of twisting of the C2B2C2 chain. While this divinyldiborene coordinates to copper(I) and platinum(0) in an η2-B2 and η4-C2B2 fashion, respectively, it undergoes a complex rearrangement to an η4-1,3-diborete upon complexation with nickel(0)
Metal-Free Intermolecular CâH Borylation of N-Heterocycles at BâB Multiple Bonds
Carbene-stabilized diborynes of the form LBBL (L = NHC or CAAC) induce rapid, high yielding, intermolecular ortho-CâH borylation at N-heterocycles at room temperature. A simple pyridyldiborene is formed when an NHC-stabilized diboryne is combined with pyridine, while a CAAC-stabilized diboryne leads to activation of two pyridine molecules to give a tricyclic alkylideneborane, which can be forced to undergo a further H-shift resulting in a zwitterionic, doubly benzo-fused 1,3,2,5-diazadiborinine by heating. Use of the extended N-heteroaromatic quinoline leads to a borylmethyleneborane under mild conditions via an unprecedented boron-carbon exchange process
Metallfreie intermolekulare C-H-Borylierung von N-Heterocyclen an B-B-Mehrfachbindungen
Carbenstabilisierte Diborine der Form LBBL (L=N-heterocyclisches Carben (NHC) oder cyclisches Alkyl(amino)carben (CAAC)) induzieren bei Raumtemperatur eine schnelle, ertragreiche, intermolekulare ortho-C-H-Borylierung an N-Heterocyclen. Ein einfaches Pyridyldiboren wird gebildet, wenn ein NHC-stabilisiertes Diborin mit Pyridin kombiniert wird, wĂ€hrend ein CAAC-stabilisiertes Diborin zur Aktivierung von zwei PyridinmolekĂŒlen fĂŒhrt, um ein tricyclisches Alkylidenboran zu bilden, das durch Erhitzen zu einem zwitterionischen, zweifach benzokondensierten 1,3,2,5-Diazadiborinin mittels einer weiteren H-Verschiebung umgelagert werden kann. Die Verwendung des verlĂ€ngerten N-heteroaromatischen Chinolins fĂŒhrt unter milden Bedingungen ĂŒber einen bisher unbekannten Bor-Kohlenstoff-Austauschprozess zu einem Borylmethylenboran
Lewis base-stabilized boron-boron multiple bonds - reactivity studies on diboracumulenes and dicyanodiborenes
Die vorliegende Arbeit umfasst im Wesentlichen Studien ĂŒber die ReaktivitĂ€t von Diboracumulenen sowie Dicyanodiborenen gegenĂŒber diversen Substraten verschiedener Substanzklassen, wie z. B. Acetylenen, Aminen, Aziden, Nitrilen, Isonitrilen und Ăbergangsmetallen. Auf diese Weise sollen zunĂ€chst Einblicke in das unterschiedliche Reaktionsverhalten der niedervalenten Borverbindungen ermöglicht sowie ein VerstĂ€ndnis fĂŒr die erhaltenen, teils neuartigen, Bindungsmodi und Substanzklassen etabliert werden. Die jeweiligen MecAAC- und CycAAC-stabilisierten Verbindungen wurden hierbei auf den Einfluss des sterischen Anspruchs der Liganden in Bezug auf die ReaktivitĂ€t untersucht. Die aufgefĂŒhrten Kapitel beziehen sich daher auf die ReaktivitĂ€t der Diboracumulene wie auch die der Dicyanodiborene gegenĂŒber Verbindungen jeweils einer bestimmten Substanzklasse. Die erhaltenen Produkte werden, soweit möglich, miteinander verglichen.The present work mainly comprises studies on the reactivity of diboracumulenes as well as dicyanodiborenes towards diverse substrates of different substance classes, such as acetylenes, amines, azides, nitriles, isonitriles and transition metals. In this way, insights into the different reaction behavior of the low-valent boron compounds of the obtained, partly novel, binding modes and substance classes should be established. In this context, the respective MecAAC- and CycAAC-stabilized compounds were examined towards the influence of the steric requirement of the ligands with respect to the reactivity. Therefore, the chapters refer to the reactivity of the diboroacumulenes as well as that of the dicyanodiborenes towards compounds of a particular substance class in each case. Where possible, the products obtained are compared with each other
Double CH Activation of a Masked Cationic Bismuth Amide
The transformation of CâH bonds into more reactive CâM bonds amenable to further functionalization is of fundamental importance in synthetic chemistry. We demonstrate here that the transformation of neutral bismuth compounds into their cationic analogues can be used as a strategy to facilitate CH activation reactions. In particular, the double CH activation of bismuth-bound diphenyl amide, (NPh2)â, is reported along with simple one-pot procedures for the functionalization of the activated positions. The organometallic products of the first and second CH activation steps were isolated in high yields. Analysis by NMR spectroscopy, single-crystal X-ray diffraction, and DFT calculations revealed unusual ground-state properties (e.g., ring strain, moderate heteroaromaticity), and provided mechanistic insight into the formation of these compounds
CatĂĄlogo de los cĂłdices latinos de la real bihlioteca del Escorial, ŃĐŸĐł el P. Guillermo AntolĂn, O. S.A. Vol. I-IV. Madrid, 1910-1916
CatĂĄlogo de los cĂłdices latinos de la real bihlioteca del Escorial, ŃĐŸĐł el P. Guillermo AntolĂn, O. S.A. Vol. I-IV. Madrid, 1910-1916. In: BibliothĂšque de l'Ă©cole des chartes. 1917, tome 78. pp. 366-368
Oxidation, Coordination, and Nickel-Mediated Deconstruction of a Highly Electron-Rich Diboron Analogue of 1,3,5-Hexatriene
The reductive coupling of an N-heterocyclic carbene (NHC) stabilized (dibromo)vinylborane yields a 1,2-divinyl- diborene, which, although isoelectronic to a 1,3,5-triene, displays no extended p conjugation because of twisting of the CBC chain. While this divinyldiborene coordinates to copper(I) and platinum(0) in an η-B and η-CB fashion, respectively, it undergoes a complex rearrangement to an η-1,3-diborete upon complexation with nickel(0)
cAACâstabilisierte 9,10âDiboraanthracene â offenschalige Singulettbiradikale
Geringe HOMO-LUMO-AbstĂ€nde und eine hohe LadungstrĂ€germobilitĂ€t prĂ€destinieren die höheren Acene fĂŒr Anwendungen im Bereich der Organoelektronik. Die LeistungsfĂ€higkeit derartiger Verbindungen steigt hierbei dramatisch mit der Anzahl anellierter Benzolringe. GröĂere Acenmengen sind synthetisch bisher jedoch nur fĂŒr Acene bis Heptacen verlĂ€sslich zugĂ€nglich. Theoretischen Studien zufolge besitzen (Oligo)acene offenschalige Singulettbiradikal- und (Poly)acene polyradikalische GrundzustĂ€nde. Eindeutige experimentelle Belege fĂŒr diese Vorhersagen sind hingegen Ă€uĂerst selten. Durch den Einbau von zwei Boratomen in das AnthracengrundgerĂŒst konnten wir den HOMO-LUMO-Abstand von Acenen dramatisch verringern und zwar ohne die Notwendigkeit einer Ausweitung des konjugierten Ï-Systems. Stabilisierung der Borzentren durch cyclische (Alkyl)(amino)carbene lieferte hierbei neutrale 9,10-Diboraanthracene mit disjunkten, offenschaligen Singulettbiradikal-GrundzustĂ€nden
cAACâStabilized 9,10âdiboraanthracenesâAcenes with OpenâShell Singlet Biradical Ground States
Narrow HOMOâLUMO gaps and high chargeâcarrier mobilities make larger acenes potentially highâefficient materials for organic electronic applications. The performance of such molecules was shown to significantly increase with increasing number of fused benzene rings. Bulk quantities, however, can only be obtained reliably for acenes up to heptacene. Theoretically, (oligo)acenes and (poly)acenes are predicted to have openâshell singlet biradical and polyradical ground states, respectively, for which experimental evidence is still scarce. We have now been able to dramatically lower the HOMOâLUMO gap of acenes without the necessity of unfavorable elongation of their conjugated Ïâ
system, by incorporating two boron atoms into the anthracene skeleton. Stabilizing the boron centers with cyclic (alkyl)(amino)carbenes gives neutral 9,10âdiboraanthracenes, which are shown to feature disjointed, openâshell singlet biradical ground states
Oxidation, Coordination, and NickelâMediated Deconstruction of a Highly ElectronâRich Diboron Analogue of 1,3,5âHexatriene
The reductive coupling of an N-heterocyclic carbene (NHC) stabilized (dibromo)vinylborane yields a 1,2-divinyl- diborene, which, although isoelectronic to a 1,3,5-triene, displays no extended p conjugation because of twisting of the CBC chain. While this divinyldiborene coordinates to copper(I) and platinum(0) in an η-B and η-CB fashion, respectively, it undergoes a complex rearrangement to an η-1,3-diborete upon complexation with nickel(0)