Reduction of CO2 by Pyridine Monoimine Molybdenum Carbonyl Complexes: Cooperative Metal-Ligand Binding of CO2

[((PMI)-P-Ar)Mo(CO)(4)] complexes (PMI=pyridine monoimine; Ar=Ph, 2,6-di-iso-propylphenyl) were synthesized and their electrochemical properties were probed with cyclic voltammetry and infrared spectroelectrochemistry (IR-SEC). The complexes undergo a reduction at more positive potentials than the related [(bipyridine)Mo(CO)(4)] complex, which is ligand based according to IR-SEC and DFT data. To probe the reaction product in more detail, stoichiometric chemical reduction and subsequent treatment with CO2 resulted in the formation of a new product that is assigned as a ligand-bound carboxylate, [(iPr2PhPMI)Mo(CO)(3)(CO2)](2-), by NMR spectroscopic methods. The CO2 adduct [(iPr2PhPMI)Mo(CO)(3)(CO2)](2-) could not be isolated and fully characterized. However, the CC coupling between the CO2 molecule and the PDI ligand was confirmed by X-ray crystallographic characterization of one of the decomposition products of [(iPr2PhPMI)Mo(CO)(3)(CO2)](2-).