Trivalent Titanocene Alkyls and Hydrides as Well-Defined, Highly Active, and Broad Scope Precatalysts for Dehydropolymerization of Amine-Boranes

We report well-defined Ti(III) metallocene complexes Cp* 2 TiMe ( 1 Me ) and Cp* 2 TiH ( 1 H ) (Cp* = η 5 -C 5 Me 5 ) as the first isolable early transition metal precatalysts for the dehydropolymerization of amine-boranes RNH 2 ·BH 3 . These earth-abundant metal catalysts combine high activity with broad substrate scope. In contrast to late transition metal catalysts, 1 Me displays reactivity toward a variety of primary amine-boranes, including those containing reactive moieties such as olefinic groups. The ability to functionalize the side chain of the resultant polyaminoborane [RNH-BH 2 ] n provides a promising method for controlling properties. Mechanistic investigation of the dehydrogenation of secondary amine-borane Me 2 NH·BH 3 supports a bond-metathesis/β-hydride elimination, redox-neutral mechanism with a Ti(III)-H resting state.