Structural effects in the reductive activation of (Indenyl)RhL2 complexes: the reduction of the anti and syn isomers of Cr(CO)3-Indenyl-Rh(cod).

The electrochemical reduction of anti- and syn-[Cr(CO)(3)(indenyl)Rh(cod)] complexes (cod = cyclooctadiene) has been investigated, to evaluate, in each stereochemical situation, the effects of the contemporary presence of two metals coordinated to the indenyl ligand. In contrast to the reduction of monometallic [(indenyl)Rh(cod)], which gives rise to two well separated monoelectronic waves, the reduction of both bimetallic complexes occurs at more positive potentials in a single bielectronic and chemically reversible wave. These results indicate that an ECrevE mechanism is active, in which the chemical step following the first electron transfer is the reversible structural rearrangement of the 35-electron radical anion, which allows the second electron transfer to occur at a more positive potential than the first one. This structural rearrangement is more marked when the two metals are syn, which suggests the presence of an interaction between the two metals in this configuration. Side reactions correspond to the dissociation of the mono- and dianions; yet the dianions are surprisingly less frangible than the monoanions.