Synthesis and crystal structures of thermally stable titanocenes

Reduction of fully substituted titanocene dichlorides [TiCl2(eta(5)-C5Me4R)(2)] (R = SiMe2CH2CH2Ph, 3; SiMe2Ph, 4; and SiMePh2, 5) with magnesium in THF proceeds via the formation of titanocene monochlorides [TiCl(eta(5)-C5Me4R)(2)] 6-8 to afford monomeric titanocenes, [Ti(eta(5)-C5Me4R)(2)], 9-11. Titanocene monochlorides give the expected EPR spectra in toluene solution and glass. The structure of 7 was further corroborated by single-crystal X-ray diffraction. Titanocenes 9-11 are EPR silent down to -196 degreesC but exhibit paramagnetic broadening of the signals in solution NMR spectra. The positions of the NMR signals are temperature-dependent, obeying the Curie Law in the range investigated (0-60 degreesC). As revealed by X-ray crystallography, titanocenes 9 and 11 possess bent metallocene structures with the cyclopentadienyl rings tilted at an angle of 9.8(l) and 14.4(2)degrees, respectively. Titanocenes 9-11 are easily oxidized with PbCl2 to the parent dichloride complexes 3-5. Titanocenes 9 and 10 react with bis(trimethylsilyl)ethyne (btmse) only in large excess of the alkyne to give an equilibrium concentration of the respective [Ti(eta(5)-C5Me4R)(2)(eta(2)-Me3SiC drop CSiMe3)] complexes. On the other hand, titanocene 11 does not observably react with btmse. (C) 2002 Elsevier Science B.V. All rights reserved.