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

Abstract

Reactions of the AlIII and GaIII 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 RhI 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.