Collect. Czech. Chem. Commun. 2005, 70, 11-33

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

Lenka Lukešováa, Michal Horáčeka, Róbert Gyepesb, Ivana Císařováb, Petr Štěpničkab, Jiří Kubištaa and Karel Macha,*

a J. Heyrovský Institute of Physical Chemistry, Academy of Sciences of the Czech Republic, Dolejškova 3, 182 23 Prague 8, Czech Republic
b Department of Inorganic Chemistry, Charles University, Hlavova 2030, 128 40 Prague 2, Czech Republic


Reduction of silyl-substituted titanocene dichloride [TiCl25-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)}- {η51-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.

Keywords: Metallocenes; Sandwich complexes; Titanium; Titanocenes; Magnesium; Silyl derivatives; (3,3,3-Trifluoropropyl)silyl group; Hydrides; ESR spectroscopy; X-Ray diffraction; Crystal structure.

References: 46 live references.