C−N Coupling Reactions of Allenes and Methylacetylenes with an Imidotitanium Complex

Reaction of the imidotitanium complexes [(N2Npy-κ3 N)Ti(NtBu)(py)] (1) and [(N2Npy-κ3 N)Ti(NtBu)] (1a) (N2Npy = (2-C5H4N)C(Me)(CH2NSiMe3)2) with 2-butyne and 1-phenylpropyne led to C−N coupling with the imido ligand and yielded the four-membered titanaazetidines [(N2Npy-κ3 N)Ti{N(tBu)C(CHCH3)CH2}] (2) and [(N2Npy-κ3 N)Ti{N(tBu)C(CHC6H5)CH2}] (3), respectively. The same reaction products were obtained in 2 + 2 cycloaddition reactions of 1 and 1a with 1,2-butadiene and phenylallene. The four-membered metallacycle with an exocyclic CC double bond was established by X-ray diffraction studies of both compounds. A mechanism to explain the observed products from both types of reactions is proposed. Whereas the reactions of 1 with CO2, tBuNCO, and PhNCO were highly unspecific and did not lead to an isolable product, the conversion with the sterically encumbered isocyanate 2,6-iPr2C6H3NCO yielded the product of 2 + 2 cycloaddition to the TiN bond, namely [(N2Npy-κ3 N)Ti{N(tBu)C(N-2,6-C6H3 iPr2)O}(py)] (4), the structure of which was elucidated by NMR spectroscopy.