C-N coupling reactions of allenes and methylacetylenes with an imidotitanium complex

Reaction of the imidotitanium complexes [(N(2)Npy-kappa N-3)Ti(=NtBu)(py)] (1) and [(N(2)Npy-kappa N-3)Ti(=NtBu)] (1a) (N(2)Npy = (2-C5H4N)C(Me)(CH2NS iMe3)(2)) with 2-butyne and 1-phenyl-propyne led to C-N coupling with the i mido ligand and yielded the four-membered titanaazetidines [(N(2)Npy-kappa N-3)Ti{N(tBu)C(CHCH3)CH2}] (2) and [(N(2)Npy-kappa N-3)Ti{N(tBu)C(CHC6H5)CH 2}] (3), respectively. The same reaction products were obtained in 2 + 2 cy cloaddition reactions of 1 and 1a with 1,2-butadiene and phenylallene. The four-membered metallacycle with an exocyclic C=C double bond was establishe d by X-ray diffraction studies of both compounds. A mechanism to explain th e observed products from both types of reactions is proposed. Whereas the r eactions of 1 with CO2, tBuNCO, and PhNCO were highly unspecific and did no t lead to an isolable product, the conversion with the sterically encumbere d isocyanate 2,6-iPr(2)C(6)H(3)NCO yielded the product of 2 + 2 cycloadditi on to the Ti=N bond, namely [(N(2)Npy-kappa N-3)Ti{N(tBu)C(N-2,6-C(6)H(3)iP r(2))O} (py)] (4), the structure of which was elucidated by NMR spectroscop y.