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Abstract  The reduction behavior of the isoelectronic complexes [CpMIII(η6-C6R6)]2 (M=Rh, Ir; R=H, Me) and [(η-9-SMe2-7,8-C2B9H10)MIII(η6-C6R6)]2 (M=Rh, Ir; C6R6 = C6H6, C6H5OMe, C6H3Me3) 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 η6 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 η6 to η4. Cations [(η-9-SMe2-7,8-C2B9H10)M(η6-C6R6)]2 were obtained by the bromide abstraction from [(η-9-SMe2-7,8-C2B9H10)MBr2]2 with Ag in the presence of benzene and its derivatives. The structure of [(η-9-SMe2-7,8-C2B9H10)Ir(η6-C6H5OMe)](BF4)2 was determined by X-ray diffraction. [ABSTRACT FROM AUTHOR]

The redox aptitude of a series of cobalt(III) or cobalt(I) sandwich complexes bearing a charge compensated dicarbollide ligand ([9-L-7,8-C2B9H10]−) as a constant unit and different counterparts (varying from classical [7,8-C2B9H11]2− to charge-compensated [9-L-7,8-C2B9H10]− dicarbollides, from cyclopentadienyl [C5R5]− (R = Me, H) to cyclobutadiene [C4Me4]0 ligands) has been studied. All the Co(III) complexes display the reversible sequence Co(III)/Co(II)/Co(I). In contrast, the Co(I) complexes (namely, those capped by tetramethylcyclobutadiene) accede reversibly only to the Co(II) oxidation state, the passage to Co(III) being irreversible. When possible, the Co(II) intermediates have been characterized by EPR spectroscopy. The molecular structures of the monocation [Co(η-9-SMe2-7,8-C2B9H10)2]+ in its DD/LL and meso diastereomeric forms as well as that of heteroleptic (η-7,8-C2B9H11)Co(η-9-SMe2-7,8-C2B9H10) have been obtained by single-crystal diffraction. [ABSTRACT FROM AUTHOR]