Inorganic Seminar
"A Tale of Two Metals: ET-induced Reactivity of Half-sandwich Ru and Rh Complexes "
Abstract: Half-sandwich complexes of Group 8 and 9 transition metals have long attracted significant interest due to their numerous applications in catalysis. For example, ruthenium-arene complexes are competent catalysts for a diverse set of addition reactions with organic substrates, while half-sandwich rhodium complexes supported by bidentate ligands (e.g., 2,2’ bipyridine, bpy) are well-known electrocatalysts for H2 evolution. Complexes of these types often display rich electron-transfer (ET) profiles, yet in many cases the chemical reactivity linked to these ET processes has not been fully elucidated.
Over the past two years, our group has investigated how ET can induce different modes of ligand substitution reactions in half-sandwich Ru and Rh complexes and how these processes are influenced by the structural and electronic features of the ligands involved. We have found that electrochemical oxidation of [(arene)Ru2+] complexes featuring P- or N-donor ligands can lead to ligand exchange reactions; our group has probed the identity of the products of these processes via chemical and electrochemical methods to determine how both ET itself and the subsequent reactivity are modulated by these supporting ligands. On the other hand, complexes of the form [Cp*Rh(bpy)X]n+ (Cp* = pentamethylcyclopentadienyl) are well-known to undergo sequential electron transfers via an ECE mechanism involving the dissociation monodentate ligands (X) at the substitutionally labile Rh2+ oxidation state. Our group has found that dissociation processes involving bidentate platforms are also operative in these systems; in particular, ET-induced crossover between different bidentate ligands and interconversion between mono- and dirhodium species supported by multinucleating frameworks suggest richer ligand substitution manifolds in these compounds, including processes that may be relevant to catalytic mechanisms. The results of our investigations into the electrochemical profiles of various series of Ru and Rh half-sandwich complexes and the chemical reactivity induced by ET in these systems will be discussed.