Ring-opening reactions of tetrahydrofuran versus alkyne complexation by group 4 metallocene complexes leading to general consequences for synthesis and reactions of metallocene complexes

The reduction of certain group 4 metallocene dichlorides by magnesium or lithium in the presence or absence of Me3SiC2SiMe3 in THF or toluene was investigated, giving in the case of titanium the dinuclear Ti(III) complex [rac-(ebthi)Ti(mu-Cl)](2) (1). For zirconium the 1-oxa-2-zirconacyclohexane 2 was formed by ring-opening reaction of rac-(ebthi)Zr(eta(2)-Me3SiC2SiMe3) with THF. As a byproduct from the synthesis of Cp*Zr-2(eta(2)-Me3SiC2SiMe3) starting from Cp*2ZrCl2 another 1-oxa-2-zirconacyclohexane (3) was obtained by ring-opening reaction of THF via the dinuclear complex Cp*Zr-2(Cl)-(CH2)(4)O-Zr(Cl)Cp*(2) (4). In the case of hafnium the analogous dinuclear complex Cp*Hf-2(Cl)-(CH2)(4)O-Hf(Cl)Cp*(2) (5) and 1-oxa-2-hafnacyclohexane (6) were the main products of the reaction, inhibiting the synthesis of Cp*Hf-2(eta(2)-Me3SiC2SiMe3) (7). The tendency for ring opening of THF initiated by metallocenes increases in the series Ti, Zr, Hf, thus leading to consequences for the synthesis of metallocene complexes.