Reactivity of SiMe2H substituents in permethylated titanocene complexes: Dehydrocoupling and ethene hydrosilylation
Abstract
The complex [TiCl2{eta(5)-C5Me4(SiMe2H)}(2)] (3) was prepared by reacting the lithium salt of 2,3,4,5-tetramethyl-1-(dimethylsilyl)cyclopenta-2,4-diene (1) with [TiCl3(THF)(3)] followed by chlorination of the formed [TiCl{eta(5)-C5Me4(SiMe2H)}(2)] (2) with PbCl2. The reduction of 3 with excess magnesium in THF in the presence of excess bis(trimethylsilyl)ethyne (btmse) afforded the bivalent metal ansa disilylene complex with pi-coordinated btmse [Ti{eta(5)-C5Me4(SiMe2)}(2)(eta(2)-btmse)] (4).
The dehydrocoupling of the SiMe2H groups was accompanied by hydrogen transfer to the free btmse. Analogous reduction of 3 with magnesium in the presence of ethene gave a mixture of titanocene [Ti{eta(5)-C5Me4(SiMe2Et)}(2)] (5) and its ethene complex [Ti{eta(5)-C5Me4(SiMe2Et)}(2)(eta(2)-C2H4)] (6).
The latter complex is however unstable in this mixture and rearranges with evolution of ethane to [Ti{eta(5)-C5Me4(SiMe2Et)} {eta(5):eta(2)-C5Me4(SiMe2CH=CH2)}] (7), which has its vinyl group attached by pi-coordination to Ti(II). The chlorination of 4 by PbCl2 yields ansa-[TiCl2{eta(5)-C5Me4(SiMe2)}(2)] (8), liberating the btmse ligand.
Complex 8 is reduced with a half-equivalent of Mg to give ansa-[TiCl2{eta(5)-C5Me4(SiMe2)}(2)] (9). Compounds 5, 6, and 7 were identified by H-1, C-13, and Si-29 NMR spectra.
The crystal structures of complexes 3, 4, and 9 have been determined by X-ray crystallography.