Dinuclear dialkoxo-bridged cyclopentadienylsiloxo titanium complexes

Abstract

The dinuclear dialkoxo-bridged complexes [(TiCl)₂(μ-O₂L)(μ-{(η⁵-C₅Me₄SiMeO)₂(μ-O)})] (O₂L = 1,2-O₂C₂H₄1a, 1,2-O₂C₆H₄1b, 1,2-(OCH₂)₂C₆H₄1c, O₂SiPh₂1d) were obtained by reaction of [(TiCl₂)₂(μ-{(η⁵-C₅Me₄SiMeO)₂(μ-O)})] (A) with the corresponding dilithium salt (1a) or diol (1b, 1c, 1d). Alkylation of 1a and 1b with ClRMg afforded [(TiR)₂(μ-O₂L)(μ-{(η⁵-C₅Me₄SiMeO)₂(μ-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(μ-{(η⁵-C₅Me₄SiMeO)₂(μ-O)})] (4). Reaction of 1a with Al(C₆F₅)₃ produced the elimination of the dialkoxo ligand to give [{TiCl(C₆F₅)}₂(μ-{(η⁵-C₅Me₄SiMeO)₂(μ-O)})] (5), whereas the same reaction of 1b with Al(C₆F₅)₃ produced the oxo-alane adduct [(TiCl)₂(μ-O₂L)(μ-{(η⁵-C₅Me₄SiMeO)₂(μ-O·Al{C₆F₅}₃)})] (O₂L = 1,2-O₂C₆H₄6) which was further transformed to give a mixture of 5 and [(TiCl){Ti(C₆F₅)}(μ-O₂L)(μ-{(η⁵-C₅Me₄SiMeO)₂(μ-O)})] (O₂L = 1,2-O₂C₆H₄7). One benzyl group of complexes 3 was abstracted with E(C₆F₅)₃ (E = B, Al) to give the monoionic compounds [Ti(TiBz)(μ-O₂L)(μ-{(η⁵-C₅Me₄SiMeO)₂(μ-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(μ-Cl)(μ-{(η⁵-C₅Me₄SiMeO)₂(μ-O)})][BzAl(C₆F₅)₃] (10) was identified, and compound 9B was also unstable at ambient temperature. Polymerization of ε-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.