REDUCTION OF RUTHENIUM ARENECYCLOPENTADIENYL COMPLEXES - REACTIONS INDUCED BY ELECTRON-TRANSFER

Ruthenium arenecyclopentadienyl complexes [Ru(eta(5)-C5R5)(eta(6)-aren e)](+) (1, R = H, arene = C6H6; 2, R = Me, arene = C6H6; 3, R = H; are ne = C6H3Me3; 4, R = Me, arene = C6H3Me3; 5, R = H, arene = C6Me6; 6, R = Me, arene = C6Me6; 7, R = Me, arene = C10H8) and [Ru(eta(5)-C9H7)( eta(6)-C6H6)](+) (8) have been studied by cyclic voltammetry; the comp lexes are capable of both reduction and oxidation. The reduction peak potential values for 1-6 become more negative by about 31 mV for each Me-group at the arene ring and 61 mV for each Me-group at the cyclopen tadienyl ring. Reduction of naphthalene complex 7 proceeds by two one- electron processes; the first one is reversible and the second one is irreversible. Two reversible reduction peaks were observed for indenyl complex 8. The following reactions occur on reduction of benzene comp lexes 1, 2 and 8 with sodium amalgam in tetrahydrofuran (THF): hydroge n atom addition to and decoordination of benzene ligand as well as dim erization of ligand-to-ligand type. Mesitylene compounds 3 and 4 form dimers u(mu-eta(5):eta(5)-Me3H3C6C6H3Me3)Ru(eta(5)-C5R5)] (14, R = H; 15, R = Me) in both chemical and electrochemical reduction processes. Reaction of [Ru(eta(5)-C5H5)(eta(6)-C6Me6)](+) (5) With sodium amalgam in THF leads to the dimer H5)Ru(mu-eta(5):eta(5)-Me6C6C6Me6)Ru(eta(5) -C5H5)] (16) as the major. product; products of H-atom addition to bot h hexamethylbenzene and cyclopentadienyl ligands, [Ru(eta(5)-C5H5)(eta (5)-C6Me6H)] (17) and [Ru(eta(4)-C5H6)(eta(6)-C6Me6)] (18), an also fo rmed in low yields. In the case of permethylated 6 only H-atom additio n to hexamethylbenzene was observed and the mixture of endo-H and exo- H isomers [Ru(eta(5)-C5H5)(eta(5)-C6Me6H)] (19a,b) was isolated. Reduc tion of 7 gives [Ru(eta(5)-C5Me5)(eta(5)-C10H9)] (20). The modes of re action of 19-electron radicals formed by reduction of 1-8 depend on el ectronic and steric properties of ligands.