Reactions of group 4 metallocene alkyne complexes with carbodiimides: experimental and theoretical studies of the structure and bonding of five-membered hetero-metallacycloallenes.

The reaction of the low-valent metallocene(II) sources Cp(2)Ti(η(2)-Me(3)SiC(2)SiMe(3)) (7) and Cp(2)Zr(py)(η(2)-Me(3)SiC(2)SiMe(3)) (11, Cp = η(5)-cyclopentadienyl, py = pyridine) with carbodiimides RN═C═NR (R = Cy, i-Pr, p-Tol) leads to the formation of five membered hetero-metallacycloallenes Cp(2)M{Me(3)SiC═C═C[N(SiMe(3))(R)]-N(R)} (9M-R) (M = Ti, R = i-Pr; M = Zr, R = Cy, i-Pr, p-Tol). Elimination of the alkyne (as the hitherto known reactivity of titanocene and zirconocene alkyne complexes would suggest) was not observed. The molecular structures of the obtained complexes were confirmed by X-ray studies. Moreover, the structure and bonding of the complexes 9Zr-Cy and 9Zr-p-Tol was investigated by DFT calculations.