Stability of (η5-C5H4R)2Ti(CCR')2 as a function of the electronic properties of cyclopentadienyl ligands.: Solid-state structure of (η5-C5H5)(η5-C5H4SiMe3)Ti(CCSiMe3)2

The synthesis of the titanocene dichlorides (eta (5)-C5H5)(eta (5)-C5H4SiMe3)TiCl2 (3) and (eta (5)-C5H4CO2R)(2)TiCl2 (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 drop 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 drop CR' (9a, R'= C6H5; 9b, R'='Bu; 9c, R'= SiMe3) selectively produces the bis(alkinyl) titanocenes (eta (5)-C5H5)(eta (5)-C-5-C5H(4)SiMe(3))Ti(C drop CR')(2) (10a, R'= C6H5; 10b, R' =Bu; 10c, R'= SiMe3). However, it was found that when complex 10c is stirred in tetrahydrofuran solutions, Me3SiC dropC is eliminated and Me3SiC dropC-C drop CSiMe3 (11) along with [(n(5)-C5H5)(eta (5) -C5H4SiMe3)Ti(C drop CSiMe3)(2) (12) is formed. The solid-state structure of (eta (5)-C5H5)(eta (5)-C5H4SiMe3)Ti(C drop 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), e = 12.2543(4) Angstrom, beta = 101.12(3)degrees, V = 2668.14(14) Angstrom (3) and Z = 4. 10c exhibits a pseudotetrahedrally coordination sphere around the Ti(IV) centre comprised of the two sigma -bonded alkynyl ligands Me3SiC dropC and the eta (5)-coordinated cyclopentadienyl. moieties C5H5 as well as C5H4SiMe3. (C) 2001 Elsevier Science B.V. All rights reserved.