Substituent effects in reduction-induced synthesis of ansa-titanocenes |
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| Authors: | Jiří Pinkas Ivana Císařová Róbert Gyepes Jiří Kubišta Karel Mach Michal Horáček |
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| Affiliation: | 1.J. Heyrovsky Institute of Physical Chemistry,Academy of Sciences of the Czech Republic,Prague 8,Czech Republic;2.Department of Inorganic Chemistry, Faculty of Science,Charles University,Prague 2,Czech Republic;3.Department of Chemistry, Faculty of Education,J. Selye University,Komárno,Slovak Republic |
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| Abstract: | Bis{(diphenylvinylsilyl)tetramethylcyclopentadienyl}titanium dichloride [TiCl2{η5-C5Me4(SiPh2CH=CH2)}2] (1) is reduced with a half molar equivalent of magnesium to the monochloride ([TiCl{η5-C5Me4(SiPh2CH=CH2)}2] (2), whereas one molar equivalent of magnesium affords the titanocene [Ti{η5-C5Me4(SiPh2CH=CH2)}{η5:η2-C5Me4(SiPh2CH=CH2)}] (3) stabilized by η2-coordination of one of the two vinyl groups to titanium(II). In the presence of excess magnesium, the vinyl moieties of 3 undergo intramolecular coupling to afford the ansa-titanocene [Ti(η5:η5:η2-C5Me4SiPh2CH=CHCH2CH2SiPh2C5Me4)] (4) possessing the η2-coordinated double bond in lateral position of its ansa-chain. The symmetrical ansa-titanocene [Ti(η5:η5:η2-C5Me4SiPh2CH2CH=CHCH2SiPh2C5Me4)] (5) was not obtained although its DFT-calculated energy is only slightly higher than that of 4. It is considered that transient 5 gives rise to non-identified tar-like by-products which inherently accompany the formation of 4. |
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