Low-Valent Titanocene Products from Attempted Syntheses of Titanocene Bearing Dimethyl(3,3,3-trifluoropropyl)silyl Groups

Abstract

Reduction of silyl-substituted titanocene dichloride [TiCl2{η5-C5Me4(SiMe2CH2CH2CF3)}2] (1) with one molar equivalent of magnesium afforded a mixture of products, thus precluding the isolation of the possibly formed titanocene [Ti{(η5-C5Me4(SiMe2CH2CH2CF3)}2]. The presence of isolable monochloride [TiCl{η5-C5Me4(SiMe2CH2CH2CF3)}2] (2) in the mixture indicates that the mangnesium is consumed in concurrent reactions, that produce various titanocene compounds of which some were obtained by the reduction of 1 with excess magnesium. Those include the trinuclear TiIII-MgII-TiIII hydride-bridged complex [Ti{η5-C5Me4- (SiMe2CH2CH2CF3)}2(μ-H)2]2Mg (3) and a dimeric dinuclear Ti-Mg complex 4 containing the [TiIII(μ-H)2Mg(μ-X)]2 core where, however, the nature of the bridging moiety X remains unknown. The reduction of 1 with excess magnesium in the presence of bis(trimethylsilyl)ethyne afforded the product of C-H activation [Ti{η5-C5Me4(SiMe2CH2CH2CF3)}- {η5:η1-C5Me3(CH2)(SiMe2CH2CH2CF3)}] (5) in 47% yield. This compound reacted rapidly with tert-butylethyne to give the TiIII-acetylide complex [Ti(η1-C≡CCMe3){η5-C5Me4- (SiMe2CH2CH2CF3)}2] (6). All the reductions of 1 at molar ratios Mg:Ti ≥ 1 gave mixtures, where a good deal of the reduction products remained in the mother liquors unidentified. The structures of 1, 2, 3, 5, and 6 were determined by X-ray diffraction analysis and, for 2, 3, 4, 5, and 6, further corroborated by ESR spectra.