Département de chimie moléculaire

A series of [OsII(NN)(CO)2Cl2] complexes where NN is a 2,2'-bipyridine ligand substituted in the 4,4' positions by H (C1), CH3 (C2), C(CH3)3 (C3), or C(O)OCH(CH3)2 (C4) has been studied as catalysts for the redn. of CO2. Electrocatalysis shows that the selectivity of the reaction can be switched toward the prodn. of CO or HCOO- with an electron-donating (C2, C3) or -withdrawing (C4) substituent, resp. The electrocatalytic process is a result of the formation of an Os0-bonded polymer, which was characterized by electrochem., UV/Visible and EPR spectroscopies. Photolysis of the complexes under CO2 in DMF+TEOA produces CO as a major product with a remarkably stable turnover frequency during 14 h of irradn. Our results suggest that electrocatalysis and photocatalysis occur through two distinct processes, starting mainly from an OsI dimer precatalyst if the redn. is performed by an electrode and an OsI mononuclear species in case of a photoredn. process. [on SciFinder(R)]