We have investigated the reaction of isonitriles (RNC) with electronically unsaturated diene complexes of Ti and Hf. Cp*(Cl)Ti(2,3-dimethylbutadiene) (1) reacts with 2 equiv of RNC to give eta(1),eta(2)-diimine complexes 2 (R = Bu-t) and 3 (R = 1-adamantyl). Cp*(Cl)Ti(N,N-di-Bu-t-eta(1),eta(2)-diimine) (2), in the presence of pyridine, fragments to Cp*(Cl)Ti((NBu)-Bu-t)(NC5H5) (10) and an alpha-methylene cyclopent-3-enimine (11). The hafnium analogue of 1, Cp*(Cl)Hf(2,3-dimethylbutadiene) (14), has been reported to give a cyclic amidine complex when treated with 2 equiv of 2,6-dimethylphenyl isonitrile. By X-ray crystallography, however, we find that 14 and 2,6-dimethylphenyl isonitrile give instead a 2,5-diazahafnacyclopentane that features a sigma-interaction between the C-C bond of a cyclopropane ring and the Hf.