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*₂TiMe (1_Me) and Cp*₂TiH (1_H) (Cp* = η⁵-C₅Me₅) as the first isolable early transition metal precatalysts for the dehydropolymerization of amine-boranes RNH₂·BH₃. 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-BH₂]_n provides a promising method for controlling properties. Mechanistic investigation of the dehydrogenation of secondary amine-borane Me₂NH·BH₃ supports a bond-metathesis/β-hydride elimination, redox-neutral mechanism with a Ti(III)-H resting state.