Cyclic metallasiloxane compounds of TiIV and ZrIV. X-Ray crystal structures of a cis-bis(pyridine) bis(cyclosiloxy)titanate and a pyridinelithiated tris(cyclosiloxy)zirconate

Abstract

The reaction between Si₂Ph₄O(OLi)₂(1) and TiCl₄in 2 : 1 or 3 : 1 molar ratio gave on addition of pyridine (py) the titanatrisiloxane compound [[graphic omitted]}₂(py)₂]·2C₆H₅Me (2). Treatment of ZrCl₄ with (1) in 1 : 2 molar ratio gave the zirconadisiloxane system Li₂Z[graphic omitted])₃]·3py· 1.5C₆H₅Me (3). Compound (2) was also isolated from reactions employing the diol Si₂Ph₄O(OH)₂ and TiCl₄in 2 : 1 molar ratio in the presence of pyridine. Siloxane chain expansion was also observed in the product from reaction of (1) with SiMe₂Cl₂ but not from reaction with SiMe₃Cl. The formation of the cyclic titanatrisiloxane and the cyclic tetrasiloxane is presumably a consequence of the ring strain in the titanadisiloxane and trisiloxane systems respectively, rather than a tendency of the siloxanediolate species (1) to oligomerise in the presence of base or metal halides. Compounds (2) and (3) have been studied by X-ray crystallography.