Isolation, Characterization and Reactivity of Key Intermediates Relevant to Reductive (Electro)catalysis with CpRh Complexes Containing Pyridyl-MIC (MIC=Mesoionic Carbene) Ligands

In recent years, metal complexes of pyridyl-mesoionic carbene (MIC) ligands have been reported as excellent homogeneous and molecular electrocatalysts. In combination with group 9 metals, such ligands form highly active catalysts for hydrogenation/transfer hydrogenation/hydrosilylation catalysis and electrocatalysts for dihydrogen production. Despite such progress, very little is known about the structural/electrochemical/spectroscopic properties of crucial intermediates for such catalytic reactions with these ligands: solvato complexes, reduced complexes and hydridic species. We present here a comprehensive study involving the isolation, crystallographic characterization, electrochemical/spectroelectrochemical/theoretical investigations, and in-situ reactivity studies of all the aforementioned crucial intermediates involving Cp*Rh and pyridyl-MIC ligands. A detailed mechanistic study of the precatalytic activation of [RhCp*] complexes with pyridyl-MIC ligands is presented. Intriguingly, amphiphilicity of the [RhCp*]-hydride complexes was observed, displaying the substrate dependent transfer of H+, H or H-. To the best of our knowledge, this study is the first of its kind targeting intermediates and reactive species involving metal complexes of pyridyl-MIC ligands and investigating the interconversion amongst them. The isolation and crystallographic, electrochemical, spectroelectrochemical and theoretical investigations of key intermediates relevant to reductive (electro)catalysis with Rh-pyridyl-MIC complexes are presented. Additionally, the interconversion between them and their role in pre-catalytic activation are discussed.+image