Complexes of the imine/thioether mixed-donor ligand 8-methylthioquinoline with d6-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 ReI(CO)3Cl, [RuII(bpy)2]2+, [RhIII(C5Me5)Cl]+, [IrIII(C5Me5)Cl]+, and PtIVMe4 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 RuIII 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.