Synthetic routes to homoleptic and heteroleptic ruthenium(II) complexes incorporating bidentate imine ligands

Ruthenium(II) complexes are finding applications in a variety of fields and, in particular, as photo-sensitisers in the conversion of solar energy into chemical or electrical energy where a major achievement has been the development of a dye sensitised solar cell (DSSC) by the Gratzel group. In order to optimise the performance of such devices there is a need to prepare complexes with tunable spectral and physico-chemical properties. Synthetic approaches have been developed which enable the rational synthesis of heteroleptic tris(diimine)ruthenium(II) complexes with the desired properties. In this review we focus on contributions made by our group which have led to the development of two approaches to such heteroleptic complexes both of which use [Ru(CO)(2)Cl-2](n) polymer as a key precursor. These approaches differ in that one requires conversion of [Ru(L)(CO)(2)(Cl)(2)] into a triflate complex, [Ru(L)(CO)(2)(CF3SO3)(2)] followed by substitution of the triflate by a second diimine ligand (L-1) to form [Ru(L)(L-1)(CO)(2)](2+) and chemical decarbonylation in the presence of a further diimine ligand (L-2) to [Ru(L)(L-1)(L-2)](2+) while the other involves photodecarbonylation of [Ru(LO)(C)(2)(Cl)(2)] to produce [Ru(L)(CO)(Cl)(2)](2), which on sequential addition of two further diiinine ligands finally yields [Ru(L)(L-1)(L-2)](2+). These versatile methods, together with those developed by others, provide the synthetic tools needed to produce Ru(II) complexes with properties required for a particular application. (C) 2004 Elsevier B.V. All rights reserved.