Synthesis and electrochemical properties of bis(bipyridine)ruthenium(II) complexes bearing pyridinyl- and pyridinylidene ligands induced by cyclometalation of N′-methylated bipyridinium analogs

Ruthenium complexes with bipyridine-analogous quaternized (N,C) bidentate ligands [RuL(bpy)2](PF6)2 (bpy = 2,2′-bipyridine, (1), L = L1 = N′-methyl-2,4′-bipyridinium; (2), L = L2 = N′-methyl-2,3′-bipyridinium) were synthesized and characterized. The structure of complex 2 was determined by the X-ray structure analysis. The 13C{1H} NMR spectroscopic and cyclic voltammetric studies indicate that the coordination modes of these ligands are quite different, that is, the C-coordinated rings of (N,C)-ligands in 1 and 2 are linked to ruthenium(II) with a pyridinium manner and a pyridinylidene one, respectively. The ligand-localized redox potentials of 1 and 2 also revealed the substantial difference in the electron donating ability of both ligands.