An electrochemical investigation on the reduction path of the arene complexes [CpM(arene)] 2+ and [(η-9-SMe 2-7,8-C 2B 9H 10)M(arene)] 2+ (M=Rh, Ir)

The reduction behavior of the isoelectronic complexes [CpM III(η 6-C 6R 6)] 2+ (M=Rh, Ir; R=H, Me) and [(η-9-SMe 2-7,8-C 2B 9H 10)M III(η 6-C 6R 6)] 2+ (M=Rh, Ir; C 6R 6∈= ∈C 6H 6, C 6H 5OMe, C 6H 3Me 3) has been studied by cyclic voltammetry and controlled potential coulometry in acetonitrile and propylene carbonate at 253 and 298 K, respectively. The extent of chemical reversibility of the pertinent sequences Rh(III)/Rh(II)/Rh(I) and Ir(III)/Ir(I) is highly dependent on both the nature of the solvent and the intrinsic electronic properties of the arene substituents. The arene η 6 coordination makes the derivatives in their lower oxidation states notably short lived, even if, in some cases, the use of propylene carbonate improves their stability or causes the increase in their lifetimes before changing the arene coordination from η 6 to η 4. Cations [(η-9-SMe 2-7,8-C 2B 9H 10)M(η 6- C 6R 6)] 2+ were obtained by the bromide abstraction from [(η-9-SMe 2-7,8-C 2B 9H 10)MBr 2] 2 with Ag + in the presence of benzene and its derivatives. The structure of [(η-9-SMe 2-7,8-C 2B 9H 10)Ir(η 6- C 6H 5OMe)](BF 4) 2 was determined by X-ray diffraction. © 2007 Springer-Verlag.