Low-valent titanocene products from attempted syntheses of titanocene bearing dimethyl(3,3,3-trifluoropropyl)silyl groups
Abstract
Reduction-induced titanocene reactions. Reduction of silyl-substituted titanocene dichloride [TiCl2{eta(5)-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{(eta(5)-C5Me4(SiMe2CH2CH2CF3)}(2)].
The presence of isolable monochloride [TiCl{eta(5)-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 I with excess magnesium. Those include the trinuclear Ti-III-Mg-II-Ti-III hydride-bridged complex [Ti{eta(5)-C5Me4(SiMe2CH2CH2CF3)}(2)(mu-H)(2)](2)Mg (3) and a dimeric dinuclear Ti-Mg complex 4 containing the [Ti-III(mu-H)(2)Mg(mu-X)](2) core where, however, the nature of the bridging moiety X remains unknown.
The reduction of I with excess magnesium in the presence of bis(trimethylsilyl)ethyne afforded the product of C-H activation [Ti(eta(5)-C4Me4(SiMe2CH2CH2CF3))-{eta(5:eta 1)-C5Me3(CH2)(SiMe2CH2CH2CF3)}] (5) in 47% yield. This compound reacted rapidly with tert-butylethyne to give the Ti-III-acetylide complex [Ti(eta(1)-C=CCMe3)eta(5)-C5Me4(SiMe2CH2CH2CF3))(2)] (6).
All the reductions of I 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.