We report well-defined Ti(III) metallocene complexes Cp*2TiMe (1(Me)) and Cp*2TiH ((1H)) (Cp* = eta(5)-C5Me5) as the first isolable early transition metal precatalysts for the dehydropolymerization of amine-boranes RNH2 center dot 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 center dot BH3 supports a bond-metathesis/beta-hydride elimination, redox-neutral mechanism with a Ti(III)-H resting state.