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

Reactions of the Al-III and Ga-III bases Al((NPr2)-Pr-i)(3) and E(NMe2)(3) (E = Al, Ga) with the amine-boranes [(Pr2NHBH3)-Pr-i] and [(BuNH2BH3)-Bu-t] give the amino-borane monomer [(Pr2N)-Pr-i = BH2] (4) and the borazine [(BuNBH)-Bu-t](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(mu-(NPr2)-Pr-i)](2) (7) in the formation of 4 from Al((NPr2)-Pr-i)(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(Me-2) 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.