This application discloses triphenyl carbenium NCA's as catalyst activators for a class of asymmetrically bridged hafnocene catalyst precursors. These catalsyst precursors are activated into olefin polymerization catalysts and are suitable for gas, solution, and slurry-phase polymerization reactions. The disclosed bridge is methylenyl- or silanylenyl-based and is optionally, alkyl or aryl substituted. The catalytic activity of the disclosed hafnocene catalyt precursors is substantially enhanced over identical catalysts that are activated with other activators.