Electrochemical behaviour of cobalta-dicarbollide sandwich complexes with different capping units.

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]