Jacobsen’s Catalyst for Hydrolytic Kinetic Resolution: Structure Elucidation of Paramagnetic Co(III) Salen Complexes in Solution via Combined NMR and Quantum Chemical Studies

NMR investigation of chiral Co(III) salen catalysts, important for enantioselective hydrolytic kinetic resolution (HKR), revealed the presence of a paramagnetic high-spin Co(III) species, which is in solvent- and temperature-dependent equilibrium with the known diamagnetic low-spin Co(III) complex. Combined with quantum chemical DFT calculations, the para- and diamagnetic chemical shifts were used to study the salen ligand conformation of the para- and diamagnetic complexes, resulting in a mechanistic proposal for the enantioselective step in catalysis.