Ov. Gusev et al., REDUCTION OF RUTHENIUM ARENECYCLOPENTADIENYL COMPLEXES - REACTIONS INDUCED BY ELECTRON-TRANSFER, Journal of organometallic chemistry, 534(1-2), 1997, pp. 57-66
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.