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

Abstract

The novel ruthenium dithiolene complexes [(arene)Ru{S 2C 2(COOMe) 2}] (arene = C 6H 6 ( 1a), C 6H 4(Me)( iPr) ( 1b), C 6Me 6 ( 1c)) were synthesized. The equilibrium between complex 1a and the corresponding dimer [(C 6H 6)Ru{S 2C 2(COOMe) 2}] 2 ( 1a′) was confirmed in solution. The reaction of complex 1a with dimethyl- or diethylacetylene dicaboxylate gave the alkene-bridged adducts [(C 6H 6)Ru{S 2C 2(COOMe) 2}{C 2(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 [(C 6H 6)Ru{S 2C 2(COOMe) 2}(CHR)] (R = H ( 4a), SiMe 3 ( 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.