Complexes of the imine/thioether mixed-donor ligand 8-methylthioquinoline with d-configurated transition metal centers: synthesis, structures and comparison with complexes of 1-methyl-2-(methylthiomethyl)-1H-benzimidazole

Coordination compounds of chelating 8-methylthioquinoline (MTQ) with the complex fragments Re^I(CO)₃Cl, Ru^II(bpy)₂]²⁺, Rh^III(C₅Me₅)Cl]⁺, Ir^III(C₅Me₅)Cl]⁺, and Pt^IVMe₄ were synthesized and structurally characterized. Whereas the ruthenium(II) complex displays the strongest preference of bonding to N versus S, the compound (MTQ)PtMe₄ shows the most balanced metal-donor bonding within the chelate ring due to a relatively short bond to S (2.319 Å) versus N (2.150 Å). The complex fac-(MTQ)Re(CO)₃Cl exhibits a particularly long metal-sulfur bond at 2.472 Å. Cyclic voltammetry of (MTQ)Ru(bpy)₂](PF₆)₂ reveals one reversible oxidation to Ru^III and three closely spaced reduction waves for the coordinated ligands. In comparison with the imine/thioether chelate ligand 1-methyl-2-(methylthiomethyl)-1H-benzimidazole (mmb) the MTQ ligand with its more rigid chelate setting N(sp²)-C(sp²)-C(sp²)-S forms generally shorter M-S bonds and displays stronger π acceptor behaviour.