Synthesis and crystal structures of thermally stable titanocenes

Reduction of fully substituted titanocene dichlorides [TiCl2(η5-C5Me4R)2] (R=SiMe2CH2CH2Ph, 3; SiMe2Ph, 4; and SiMePh2, 5) with magnesium in THF proceeds via the formation of titanocene monochlorides [TiCl(η5-C5Me4R)2] 6–8 to afford monomeric titanocenes, [Ti(η5-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 °C 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 °C). 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(1) and 14.4(2)°, 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(η5-C5Me4R)2(η2-Me3SiCCSiMe3)] complexes. On the other hand, titanocene 11 does not observably react with btmse.