Reaction of Cp*(Cl)M(Diene) (M = Ti, Hf) with Isonitriles.

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 η(1),η(2)-diimine complexes 2 (R = (t)Bu) and 3 (R = 1-adamantyl). Cp*(Cl)Ti(N,N-di-(t)Bu-η(1),η(2)-diimine) (2), in the presence of pyridine, fragments to Cp*(Cl)Ti(N(t)Bu)(NC5H5) (10) and an α-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 σ-interaction between the C-C bond of a cyclopropane ring and the Hf.