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 (1Me) and Cp*2TiH (1H) (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, 1Me 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.