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Abstract
A mild, catalytic dehydrocoupling route to aminoboranes and borazine derivatives from either primary or secondary amine-borane adducts has been developed using late transition metal complexes as precatalysts. The dehydrocoupling of Me 2 NH·BH 3 was found to be catalyzed by 0.5 mol% [Rh(1,5-cod)(μ-Cl)] 2 in solution at 25°C to give [Me 2 N─BH 2 ] 2 (1) quantitatively after ca. 8 h. This new catalytic method was extended to other secondary adducts RR ′NH·BH 3 which afforded the dimeric [(1,4-C 4 H 8 )N─BH 2 ] 2 (2) and [PhCH 2 (Me)N─BH 2 ] 2 (3) or the monomeric aminoborane i Pr 2 N═BH 2 (4) under mild conditions. The catalytic dehydrocoupling of NH 3 ·BH 3 , MeNH 2 ·BH 3 , and PhNH 2 ·BH 3 at 45°C affords the borazine derivatives [RN─BH] 3 (5: R = H; 6: R = Me; 7:R = Ph). TEM analysis of the contents of the reaction solution for the [Rh(1,5-cod)(μ-Cl)] 2 catalyzed dehydrocoupling of Me 2 NH·BH 3 together with Hg poisoning experiments suggested a soluble heterogeneous catalyst involving Rh(0) nanoclusters.
