New bipyridyl/phenanthroline ruthenium(II) and ruthenium(III) complexes possessing acetate appended thioether. Evidence for oxidative linkage isomerization

The acetate bearing dithioether, sodium di(2-carboxymethylsufanyl)maleonitrile, L1 upon reaction with [RuII(bpy)2Cl2]·2H2O, [RuII(phen)2Cl2]·2H2O, [RuIII(bpy)2Cl2]+ or [RuIII(phen)2Cl2]+ in methanol formed complexes of the type [(bpy)2Ru{S2(CH2COO)2C2(CN)2}], (1), [(phen)2Ru{S2(CH2COO)2C2(CN)2}], (2), [(bpy)2Ru{(OOCCH2)2S2C2(CN)2}]+, (5) and [(phen)2Ru{(OOCCH2)2S2C2(CN)2}]+, (6) respectively. Four other Ru(III) complexes with di(benzylsulfanyl)maleonitrile, L2, [(bpy)2Ru{S2(PhCH2)C2(CN)2}]3+, (7) and [(phen)2Ru{S2(PhCH2)2C2(CN)2}]3+, (8), and with acetate, [(bpy)2Ru(OOCCH3)2]+, (9) and [(phen)2Ru(OOCCH3)2]+, (10) were also synthesized. In the cyclic voltammetry, complexes (1) and (2) exhibited quasireversible oxidation waves at 1.01 and 1.02 V vs. Ag/AgCl over GC electrode in DMF, while the corresponding Ru(III) L1 complexes (5) and (6) exhibit reversible oxidation at E1/2 0.59 and 0.58 V, respectively, under identical conditions. This is unlike the voltammetric behavior of the Ru(II) and Ru(III) L2 complexes, wherein the complex pairs (3), (7) and (4), (8) exhibited identical voltammograms with single reversible one electron waves at E1/2 0.98 and 0.92 V, respectively under identical conditions. The voltammograms of Ru(II)-L2 complexes (3) and (4) also became irreversible in presence of nearly four molar equivalent of sodium acetate. Hence, the irreversible redox behavior of complexes (1) and (2) has been interpreted in terms of rapid linkage isomerization, i.e. shift in κ2-S,S′ to κ2-O,O′ coordination, following the Ru(II)/Ru(III) electrode process. The electronic spectra of Ru(III)-L1 complexes (5) and (6) resemble closely with that of (9) and (10) instead of Ru(III)-L2 complexes (7) and (8), further supports proposed linkage isomerization. The cationic complexes were obtained as [PF6]− salts and all compounds were characterized using analytical and spectral (IR, 1H NMR, UV–vis and mass) data.