Reactions of [{N−,N,Cnaphthyl−}HfMe][MeB(C6F5)3] (2) precatalyst with a series of α-olefins have been investigated in order to intercept the active polymerization species generated by an in situ modification of the precursor by insertion of a single monomer unit into the Hf−CAryl bond. In all cases the first migratory insertion of monomer occurs into the Hf−CAryl bond rather than the Hf−CAlkyl bond. A low-temperature polymerization with 170 equiv of 1-hexene activated with tris(pentafluorophenyl)borane (FAB) allows for the complete NMR characterization of a Hf−CAlkylaryl methyl cation. This structure agrees with DFT studies of the kinetically favored diastereomer, although a number of other structures are more stable thermodynamically. Attempts to trap an inserted catalyst through the stoichiometric addition of 2-vinylpyridine or 3-ethoxy-1-propylene led to complicated reactions, but in both cases, experimental and computational data suggest that both processes initiate through insertion of the substrate ...