Journal of Organometallic Chemistry p. 63 - 74 (1997)
Update date:2022-08-11
Topics:
Varga, Vojtech
Hiller, Jo?rg
Gyepes, Ro?bert
Pola?s?ek, Miroslav
Sedmera, Petr
Thewalt, Ulf
Mach, Karel
Dimethylsilylene-bridged complexes Me2Si(C5Me4)2TiCl (2), Me2Si(C5Me4)2Ti[η2-C2(SiMe3)2] (3) and Me2Si(C5H4)2Ti[η2-C2(SiMe3)2] (4) have been prepared by the general methods which are known for obtaining of analogous non-bridged titanocene complexes. X-ray crystal structures of Me2Si(C5Me4)2TiCl2 (1), 2, and 3 reveal that the dihedral angle ? between the least-squares planes of cyclopentadienyl rings increases in the order 2 < 3 < 1. Comparison with the structures of analogous (C5HMe4)2Ti and (C5Me5)2Ti compounds shows that the value of ? increases in the series (C5Me5)2Ti < (C5HMe4)2Ti < Me2Si(C5Me4)2Ti, e.g. in the bis(trimethylsilyl)acetylene complexes from 41.1° for (C5Me5)2Ti[η2-C2(SiMe3)2] (9) to 50.0° for (C5HMe4)2Ti[η2-C2(SiMe3)2] (8) and to 53.5° for 3. Compounds 3, 8 and 9 induce the head-to-tail dimerization of 1-hexyne with the selectivity of 72percent, 21percent and ca. 100percent respectively. The discrepancy between the selectivities and the values of ? for 3 and 8 is accounted for by a larger flexibility of the titanocene skeleton in 8, affording a larger space for a non-specific coordination of 1-hexyne. The effects of the μ-Me2Si group in 2 and 3 on some of their properties are compared with the effects of Me and H substituents in the non-ansa compounds with controversial results. For instance, the affinity of 2 to 2-methyltetrahydrofuran approaches that of (C5H2Me3)2TiCl whereas the shift of the v(C≡C) vibration in 3 indicates a stronger metal-acetylene bond than in 9.
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