Dinuclear dialkoxo-bridged cyclopentadienylsiloxo titanium complexes

The dinuclear dialkoxo-bridged complexes [(TiCl)(2)(mu-O2L)(mu-{(eta(5)-C5Me4SiMeO)(2)(mu-O)})] (O2L = 1,2-O2C2H4 1a, 1,2-O2C6H4 1b, 1,2-(OCH2)(2)C6H4 1c, O2SiPh2 1d) were obtained by reaction of [(TiCl2)(2)(mu-{(eta(5)-C5Me4SiMeO)(2)(mu-O)})] (A) with the corresponding dilithium salt (1a) or diol (1b, 1c, 1d). Alkylation of 1a and 1b with ClRMg afforded [(TiR)(2)(mu-O2L)(mu-{(eta(5)-C5Me4SiMeO)(2)(mu-O)})] (O2L = 1,2-O2C2H4, R = Me 2a, Bz 3a; O2L = 1,2-O2C6H4, R = Me 2b, Bz 3b). Addition of four equiv. of LiOiPr to A afforded [{Ti(OiPr)(2)}(2)(mu-{(eta(5)-C5Me4SiMeO)(2)(mu-O)})] (4). Reaction of 1a with Al(C6F5)(3) produced the elimination of the dialkoxo ligand to give [{TiCl(C6F5)}(2)(mu-{(eta(5)-C5Me4SiMeO) 2(mu-O)})] (5), whereas the same reaction of 1b with Al(C6F5)(3) produced the oxo-alane adduct [(TiCl)(2)(mu-O2L)(eta(5){(eta(5)-C5Me4SiMeO)(2)(mu-O center dot Al{C6F5}(3))})] (O2L = 1,2-O2C6H4 6) which was further transformed to give a mixture of 5 and [(TiCl){Ti(C6F5)}(mu-O2L)(mu-{(eta(5)-C5Me4SiMeO)(2)(mu-O)})] (O2L = 1,2-O2C6H4 7). One benzyl group of complexes 3 was abstracted with E(C6F5)(3) (E = B, Al) to give the monoionic compounds [Ti(TiBz)(mu-O2L)(mu-{(eta(5)-C5Me4SiMeO)(2)(mu-O)})][BzE(C6F5)(3)] (O2L = 1,2-O2C2H4, E = B 8B, Al 8Al; O2L = 1,2-O2C6H4, E = B 9B), although 8Al was unstable in CD2Cl2 evolving to a mixture of compounds where [(TiBz)(2)(mu-Cl)(mu-{(eta(5)-C5Me4SiMeO)(2)(mu-O)})][BzAl(C6F5)(3)] ( 10) was identified, and compound 9B was also unstable at ambient temperature. Polymerization of epsilon-caprolactone was only achieved with the tetraalkoxo compound 4. All of these complexes were characterized by NMR spectroscopy and 1a, 1b and 7 by X-ray diffraction studies.