Titanocene – 1,4,6-tris(trimethylsilyl)hex-3-ene-1,5-diyne-3-yl complexes – crystal structures and their retro reaction

Paramagnetic titanocene complexes containing the unsaturated carbyl group which consists of one and half molecule of 1,4-bis(trimethylsilyl)buta-1,3-diyne (BSD) are formed by the reduction of titanocene dichlorides with one molar equivalent of magnesium in the presence of 1.5 molar equivalent BSD in tetrahydrofuran (THF) for titanocene moieties Ti(η5-C5H5 − nMen)2 (n = 5 (1), 4 (2), and 3 (3)) and Ti{Me2Si(η5-C5Me4)2} (4). The non-methylated titanocene moiety affords under identical conditions known diamagnetic bis(η5-cyclopentadienyl)-2,4-bis(trimethylsilylethynyl)-3,5-bis(trimethylsilyl)titanacyclopenta-2,4-diene (5) as the major product. Crystal structures of 3 and 4 show the same bonding scheme for the 1,4,6-tris(trimethylsilyl)hex-3-ene-1,5-diyne-3-yl ligand as previously found for compound 1 [P.-M. Pellny, F.G. Kirchbauer, V.V. Burlakov, A. Spannenberg, K. Mach, U. Rosenthal, Chem. Commun. (1999) 2505]. Compound 1 is stable against weak proton donors like methanol or alk-1-ynes even at 90 °C, however, it undergoes retroreaction when oxidized by PbCl2 in THF, yielding nearly quantitatively BSD and [TiCl2(η5-C5Me5)2].