Dinuclear dicyclopentadienyl titanium complexes with bridging cyclopentadienylsiloxo ligands

Lorena Postigo, Luca Bellarosa, Javier Sánchez-Nieves, Pascual Royo, Agustí Lledós, Marta E.G. Mosquera

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Addition of 1 equiv of T1Cp to compound [(TiCl2) 2(μ-{(η5-C5Me4SiMeO) 2(μ-O)})] (A) at 80°C gave a mixture with different molar ratios of the two possible isomers of [(TiClCp)(TiCl 2)(μ-{(η5C5Me4SiMeO) 2(μ-O)})] (1). Reaction of compound A with 2 equiv of TlC p at 80°C afforded [(TiClCp)2(μ- {(η5-C5Me4SiMeO)2(μ-O)})] (2as) as the unique reaction product. Each Cp ligand of 2as is located in different positions anti and syn with respect to the Si-O-Si bridge. However, a mixture of two isomers of [(TiClCp)2(μ-{(η5-C 5Me4SiMeO)2(μ-O)})], 2as ( > 95% by NMR) and 2aa ( < 5% by NMR), was obtained when the reaction was carried out at 60 °C; the two Cp ligands of 2aa were located at anti positions. Alkylation of isomer 2as with LiMe gave a mixture of the three possible isomers [(TiMeCp) 2(μ-{(η5-C5Me4SiMeO) 2(μ-O)})] (3as, 3aa, 3ss). The proportion of each was dependent on the reaction temperature. Isomer 2as reacted with Lewis acids E(C 6Fs)3 (E = B, Al) and with Li[B(C6F 5)4] to give the chloro-bridged dititanium compounds [(TiCp)2(μ-{(η5-C5Me4SiMeO) 2(μ-O)})μ-Cl)][Q] (Q = ClB(C6F5) 3, 4B; C1A1(C6F5)3, 4Al; Q = B(C6F5)4, 4C) as the unique reaction products. Addition of [Ph3C][B(CgF5)4] to the mixture of isomers in 3 gave a mixture of complexes [(TiCpMe)(TiCp)(μ- {(η5-C5Me4SiMeO)2(μ-O)})][Q] (5aC and 5sC; Q = B(C6F5)4), with the remaining methyl ligand located at anti or syn positions depending on the methyl group being abstracted. DFT studies were carried out to determine the stability of the isomers of 2 and 3, to determine which chlorine atom in compound 2as was more easily eliminated, and also to clarify the transformation of isomer 2as into the mixture of isomers 3as, 3aa, and 3ss during the alkylation reaction. © 2010 American Chemical Society.
Original languageEnglish
Pages (from-to)642-655
Issue number3
Publication statusPublished - 8 Feb 2010

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