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 Al-B σ-bond. The reductive rearrangement of 1-(AlI₂ ), 8-(BMes₂ ) naphthalene (Mes=2,4,6-Me₃ C₆ H₂ ) affords the alumaborane species cyclo-(1,8-C₁₀ H₆ )-[1-Al(Mes)(OEt₂ )-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=CPh₂ is deoxygenated to afford an B-O-Al bridged species with incorporation of the remaining ≡CPh₂ fragment into the naphthalene scaffold. The reaction with isonitrile Xyl-N≡C (Xyl=2,6-Me₂ C₆ H₄ ) 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-C₁₀ H₆ )-[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.

Keywords: Alumaborane; Bond Scission; Migration Reactions; Polarized Bonds; σ-Bonds.