Die Beständigkeit von (η5-C5H4R)2Ti(CCR′)2 in Abhängigkeit von den elektronischen Eigenschaften der Cyclopentadienyl-Liganden. Die Festkörperstruktur von (η5-C5H5)(η5-C5H4SiMe3)Ti(CCSiMe3)2

The synthesis of the titanocene dichlorides (η5-C5H5)(η5-C5H4SiMe3)TiCl2 (3) and (η5-C5H4CO2R)2TiCl2 (8a, R=CH3; 8b, R=CH2CH3), which contain either electron-donating or electron-withdrawing substituents at the cyclopentadienyl fragments is discussed. While the reaction of 8a or 8b with LiCCR′ in different stoichiometric ratios leads only to product mixtures from which no pure components could be isolated, treatment of 3 with two equivalents of LiCCR′ (9a, R′=C6H5; 9b, R′=tBu; 9c, R′=SiMe3) selectively produces the bis(alkinyl) titanocenes (η5-C5H5)(η5-C5H4SiMe3)Ti(CCR′)2 (10a, R′=C6H5; 10b, R′=tBu; 10c, R′=SiMe3). However, it was found that when complex 10c is stirred in tetrahydrofuran solutions, Me3SiCC is eliminated and Me3SiCCCCSiMe3 (11) along with [(η5-C5H5)(η5-C5H4SiMe3)Ti(CCSiMe3)]2 (12) is formed.The solid-state structure of (η5-C5H5)(η5-C5H4SiMe3)Ti(CCSiMe3)2 (10c) is reported. Complex 10c crystallises in the monoclinic space group Pc with two independent molecules in the asymmetric unit and with the cell constants a=20.8131(6), b=10.6615(3), c=12.2543(4) Å, β=101.12(3)°, V=2668.14(14) Å3 and Z=4. 10c exhibits a pseudotetrahedrally coordination sphere around the Ti(IV) centre comprised of the two σ-bonded alkynyl ligands Me3SiCC and the η5-coordinated cyclopentadienyl moieties C5H5 as well as C5H4SiMe3.