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 η1,η2-diimine complexes 2 (R = tBu) and 3 (R = 1-adamantyl). Cp*­(Cl)­Ti­(N,N-di-tBu-η1,η2-diimine) (2), in the presence
of pyridine, fragments to Cp*­(Cl)­Ti­(NtBu)­(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.