Synthesis and electrochemical behaviour of σ,η2-acetylide-bridged early–late complexes;: The solid-state structure of [(η5-C5H4SiMe3)2Ti(CCSiMe3)2]Pd(PPh3)

Based on the bis(alkinyl) titanocene [Ti](CCSiMe3)2 (1) a series of mixed early–late metal complexes of the general type {[Ti](CCSiMe3)2}ML {[Ti]=(η5-C5H4SiMe3)2Ti; M=Ni, Pd; L=PPh3, P(OMe)3, P(OPh)3} was prepared. The solid-state structure of {[Ti](CCSiMe3)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 η2-coordinated Me3SiCC entities and the datively-bound PPh3 ligand; (iii) a lengthening of the CC triple bonds upon their η2-coordination to Pd(0); and (iv) a trans-deformation of the TiCCSiMe3 units due to the tweezer effect. Cyclic voltammetric studies on 2 and {[Ti](CCSiMe3)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 π-acidity of the respective Lewis-base L.