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

We present facile access to an alumaborane species with electron precise Al−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 Al−B σ‐bond. The Al−B σ‐bond performs the reductive scission of multiple bonds: S=C(NiPrCMe)(2) affords the naphthalene bridged motif B−S−Al(NHC), NHC=N‐heterocyclic carbene, while O=CPh(2) is deoxygenated to afford an B−O−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 Al−N−B bridged species cyclo‐(1,8‐C(10)H(6))‐[1‐Al(Mes)‐N(Xyl)‐8‐B{C(Mes)=C−N−Xyl}] with complete scission of the C≡N triple bond. The latter reaction is supported with isolated intermediates and by DFT calculations.