Reductive Al−B σ‐Bond Formation in Alumaboranes: Facile Scission of Polar Multiple Bonds

Abstract

We present facile access to an alumaborane species with electron precise AlÀ B σ-bond. The reductive rearrangement of 1-(AlI 2 ), 8-(BMes 2 ) naphthalene (Mes = 2,4,6-Me 3 C 6 H 2 ) affords the alumaborane species cyclo-(1,8-C 10 H 6 )-[1-Al(Mes)(OEt 2 )-8-B(Mes)] with a covalent AlÀ B σ-bond. The AlÀ B σ-bond performs the reductive scission of multiple bonds: S=C(NiPrCMe) 2 affords the naphthalene bridged motif BÀ SÀ Al(NHC), NHC = N-heterocyclic carbene, while O=CPh 2 is deoxygenated to afford an BÀ OÀ Al bridged species with incorporation of the remaining �CPh 2 fragment into the naphthalene scaffold. The reaction with isonitrile Xyl-N�C (Xyl = 2,6-Me 2 C 6 H 4 ) proceeds via a proposed (amino boryl) carbene species; which adds a second equivalent of isonitrile to ultimately form the AlÀ NÀ B bridged species cyclo-(1,8-C 10 H 6 )-[1-Al(Mes)-N(Xyl)-8-B{C(Mes)=CÀ NÀ Xyl}] with complete scission of the C�N triple bond. The latter reaction is supported with isolated intermediates and by DFT calculations.

Cobalt(I)-Catalyzed Transformation of Si–H Bonds: H/D Exchange in Hydrosilanes and Hydrosilylation of Olefins

“…In this context, we present cobalt complex 7 , which allows for a systematic comparison to Holland’s catalyst 3 containing a two-coordinate monoanionic β-diketiminate scaffold. Complex 7 is composed of the previously reported monoanionic amido-imidazolin-2-imine ligand (AmIm), which was recently demonstrated to be a stronger N , N ′-donor ligand compared to β-diketiminate due to (i) the formation of five-membered versus six-membered chelates and (ii) the incorporation of a strongly electron-releasing imidazolin-2-imine entity (Scheme ). A comparison of the parent forms of β-diketimine (HNacNac) and aminoimidazolin-2-imine ligands ( 4 , HAmIm) shows that the imine nitrogen atom in 4 is a much stronger σ/π donor due to the resonance stabilization of the pendant NHC unit.…”

Evidence for Carbene Intermediates in Isocyanide Homologation by Aluminium(I)

“…Through comparing the 1 H NMR spectra of 4 and 13 C‐labeled 4 , the proton on the azaallenyl ligand ( H C=C=N) was located at 1.35 ppm ( 1 J C−H =136.0 Hz; see Figure S34 and S38). Note that although deoxygenative homocoupling of CO with the formation of a ketene group (C=C=O) has been documented using low valent Ta, [46] Mo, [47,48] or Si [49] complexes, the overall denitrogenative homocoupling of isocyanides is largely elusive and was only recently achieved using a silylene‐bridged nickel cluster [50] and an alumaborane featuring an electron‐precise Al−B bond [51] …”

“…Note that although deoxygenative homocoupling of CO with the formation of a ketene group (C=C=O) has been documented using low valent Ta, [46] Mo, [47,48] or Si [49] complexes, the overall denitrogenative homocoupling of isocyanides is largely elusive and was only recently achieved using a silylene-bridged nickel cluster [50] and an alumaborane featuring an electron-precise AlÀ B bond. [51]…”

Über Carbenintermediate in der AlI vermittelten Homologisierung von Isocyaniden

“…Der Vergleich der 1 H NMR‐Spektren von 4 und 13 C markiertem 4 zeigt das Proton des Azaallenylliganden ( H C=C=N) bei einer chemischen Verschiebung von 1.35 ppm ( 1 J C−H =136.0 Hz; siehe Abbildung S34 und S38) an. Während die deoxygenative Homokupplung von CO zur Bildung einer Ketengruppe (C=C=O) für niedervalente Ta, [46] Mo [47,48] und auch Si [49] Komplexe beschrieben ist, so ist die denitrogenierende Homokupplung von Isocyaniden nur schwer realisierbar und wurde bisher lediglich für einen silylenverbrückten Nickelcluster [50] sowie ein Aluminaboren mit elektronenpräziser Al−B Bindung beschrieben [51] …”

“…Während die deoxygenative Homokupplung von CO zur Bildung einer Ketengruppe (C=C=O) für niedervalente Ta, [46] Mo [47,48] und auch Si [49] Komplexe beschrieben ist, so ist die denitrogenierende Homokupplung von Isocyaniden nur schwer realisierbar und wurde bisher lediglich für einen silylenverbrückten Nickelcluster [50] sowie ein Aluminaboren mit elektronenpräziser AlÀ B Bindung beschrieben. [51] Die [37] verläuft, während der Bildungsmechanismus von 4 Intermediat C [52] beinhaltet (Abbildung 3c und S41). In der Tat zeigt eine Analyse der relativen Energien von B und C mittels quantenchemischer Methoden, dass beide Verbindungen in Lösung koexistieren (siehe unten).…”