Ruthenium(II/III) bipyridine complexes incorporating thiol-based imine functions: Synthesis, spectroscopic and redox properties

Abstract

A group of five new ruthenium(II) bipyridine heterochelates of the type [Ru II(bpy) 2L] + 1a– 1e have been synthesized (bpy=2,2′-bipyridine; L=anionic form of the thiol-based imine ligands, HS–C 6H 4NC(H)C 6H 4(R) (R=OMe, Me, H, Cl, NO 2). The complexes 1a− 1e are 1:1 conducting and diamagnetic. The complexes 1a− 1e exhibit strong MLCT transitions in the visible region and intra-ligand transitions in the UV region. In acetonitrile solvent complexes show a reversible ruthenium(III)–ruthenium(II) couple in the range 0.2–0.4 V and irreversible ruthenium(III)→ruthenium(IV) oxidation in the range 1.15–1.73 V vs. SCE. Two successive bipyridine reductions are observed in the ranges −1.43 to −1.57 and −1.67 to −1.78 V vs. SCE. The complexes are susceptible to undergo stereoretentive oxidations to the trivalent ruthenium(III) congeners. The isolated one-electron paramagnetic ruthenium(III) complex, 1c + exhibits weak rhombic EPR spectrum at 77 K ( g 1=2.106, g 2=2.093, g 3=1.966) in 1:1 chloroform–toluene. The EPR spectrum of 1c + has been analyzed to furnish values of distortion parameters ( Δ=8988 cm −1; V=0.8833 cm −1) and energy of the expected ligand field transitions ( ν 1=1028 nm and ν 2=1186 nm) within the t 2 shell. One of the ligand field transitions has been experimentally observed at 1265 nm.