Group 13 BN dehydrocoupling reagents, similar to transition metal catalysts but with unique reactivity

Abstract

Reactions of the Al^III and Ga^III bases Al(NⁱPr₂)₃ and E(NMe₂)₃ (E = Al, Ga) with the amine-boranes [ⁱPr₂NHBH₃] and [^tBuNH₂BH₃] give the amino-borane monomer [ⁱPr₂N = BH₂] (4) and the borazine [^tBuNBH]₃ (5), respectively. This is similar to the results of dehydrocoupling previously seen with single-site Rh^I catalysts and appears to occur via intermediate group 13 hydrides, as shown by the isolation of the amido-alane [H₂Al(μ-NⁱPr₂)]₂ (7) in the formation of 4 from Al(NⁱPr₂)₃. In general, the outcome of group 13 dehydrocoupling reactions show a marked dependence on the amine-borane used and on the nucleophilic and redox character of the group 13 pre-catalyst. The importance of these factors is seen in the formation of the unusual, delocalised amino-borane [B{(NHBH)N(SiMe₃)Si(Me₂)N(SiMe₃)₂}₃] (10) in the non-catalytic reaction of [Ga{N(SiMe₃)₂}₃] with [NH₃BH₃], in which coupling of B–N as well as Si–N bonds occurs along with the deposition of Ga metal.