Reactivity and electrochemical behavior of ruthenium dithiolene complexes with coordinatively unsaturated metal centers: cycloaddition and dimerization reactions

The novel ruthenium dithiolene complexes [(arene)Ru{S2C2(COOMe)2}] (arene = C6H6 (1a), C6H4(Me)(iPr) (1b), C6Me6 (1c)) were synthesized. The equilibrium between complex 1a and the corresponding dimer [(C6H6)Ru{S2C2(COOMe)2}]2 (1a′) was confirmed in solution. The reaction of complex 1a with dimethyl- or diethylacetylene dicaboxylate gave the alkene-bridged adducts [(C6H6)Ru{S2C2(COOMe)2}{C2(COOR)2}] (R = Me (2a), Et (3a)) as [2 + 2] cycloaddition products formally. The reactions of complex 1a with diazo compounds also gave the alkylidene-bridged adducts [(C6H6)Ru{S2C2(COOMe)2}(CHR)] (R = H (4a), SiMe3 (5a), COOEt (6a)) as [2 + 1] cycloaddition products. The electrochemical behavior of complex 1a was investigated. The reductant of complex 1a was a stable species for several minutes. The oxidant of complex 1a was very unstable; the cation 1a+ formed was immediately converted to the corresponding cationic dimer 1a′+. The cationic dimer 1a′+ was stable for several minutes, and it was rapidly and quantitatively converted to the neutral complex 1a when it was reduced.