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.