Synthesis and electrochemical behaviour of σ,η2-acetylide-bridged early-late complexes;: The solid-state structure of [(η5-C5H4SiMe3)2Ti(C≡C-SiMe3)2]Pd(PPh3)

Based on the bis(alkinyl) titanocene [Ti](CdropCSiMe(3))(2) (1) a series of mixed early-late metal complexes of the general type {[Ti]-(CdropCSiMe(3))(2)} ML {[Ti] = (eta(5)-C5H4SiMe3)(2)Ti; M = Ni, Pd; L = PPh3, P(OMe)(3), P(OPh)(3)} was prepared. The solid-state structure of {[Ti](CdropCSiMe(3))(2)} Pd(PPh3) (2) is reported. Complex 2 exhibits typical features of early-late heterobimetallic tweezer complexes: (i) a pseudo-tetrahedrally coordinated Ti(IV) centre; (ii) a trigonal-planar coordination sphere around the Pd(0) centre, comprised of the two eta(2)-coordinated Me(3)SiCdropC entities and the datively-bound PPh3 ligand; (iii) a lengthening of the CdropC triple bonds upon their eta(2)-coordination to Pd(0); and (iv) a trans -deformation of the Ti-CdropC-SiMe3 units due to the tweezer effect. Cyclic voltammetric studies on 2 and {[Ti](CdropCSiMe(3))(2)}NiL [3, L = CO; 4a, L = P(OCH3)(3)] reveal an electron donating character of the coordinated M(0) centres, which is demonstrated by the shift of the Ti(IV)/Ti(III) reduction to a more negative potential. This reductive process also exhibits a dependence on the pi-acidity of the respective Lewis-base L. (C) 2002 Elsevier Science B.V. All rights reserved.