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 Cp2Ti(η2-Me3SiC2SiMe3) (7) and Cp2Zr(py)(η2-Me3SiC2SiMe3) (11, Cp = η5-cyclopentadienyl, py = pyridine) with carbodiimides RNCNR (R = Cy, i-Pr, p-Tol) leads to the formation of five membered hetero-metallacycloallenes Cp2M{Me3SiCCC[N(SiMe3)(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.