Titanium alpha-acetylides as building blocks for heterobimetallic transition metal complexes: synthesis and redox behaviour of pi-conjugated organometallic systems

A series of related Ti sigma-acetylides of the type {Ti}C = CR ({Ti} = (eta (5)-C5H5)(2)Ti(CH5SiMe3); 2: R = SiMe3; 3: R = C6H3(CH2NMe2)(2)-3,5; 4: R = C6H2I-4-(CH2NMe2)(2)-3,5; 5: R = C6H4CN-4; 6: R = C5H4N-4; 7: R = Fc, Fc = (eta(5)-C5H4)Fe(eta(5)C(5)H(5)); 8: R = C6H4(C = C{Ti})-4) have been prepa red by reacting the corresponding lithium acetylides with {Ti}Cl (1). The X -ray crystal structure determination of {Ti}C = CSiMe3 (2) is reported. Thi s compound exhibits a one-dimensional (1D) arrangement with respect to the Ti-C =C unit. The reaction of 2 with [CuCl](n) afforded 1 and [CuC = SiMe3] (n) (10) and is proposed to occur via prior formation of the dimeric interm ediate [(eta(2)-{Ti}C = CSiMe3)(2)Cu2Cl2]. The chemical oxidation of {Ti}C = CFc, 7, with Ag[BF4] yielded HC = CFc and an undefined Ti species. Treatm ent of 5 or 6 with {Ru}N = N{Ru} ({Ru} = mer, trans-[RuCl2(NN'N)]; NN'N = e ta(3)-C5H3N(CH2NMe2)(2)-2,6) produced intensively coloured heterodinuclear compounds, such as [{Ti}C = CC5H4N-4]{Ru} (16). In contrast, 5 and 6 react with cationic Pt compounds of the type [{Pt}. L][X]({Pt} = [Pt(C6H3{CH2NMe2 }-2,6](+); L = H2O, MeCN; X = BF4, OTf) to give product mixtures rather tha n defined compounds. Electrochemical studies on some of the bimetallic comp ounds show that the Ti(III)/Ti(IV) redox potential appears to be reversible and is shifted to a more negative value upon substitution of the Cl ligand in 1 by C = CR (compounds 2-8). Whereas the nature of R in {Ti}C = CR has an influence on the Ti(III)/Ti(IV) redox potential, the attachment of a sec ond metal onto the pi-conjugated system has only negligible effect on the e lectrochemical properties of the Ti centre. (C) 1998 Elsevier Science S.A. All rights reserved.