Origins of Catalyst-Controlled Chemoselectivity in Transition-Metal-Catalyzed Divergent Epoxide Conversion

Transition-metal-catalyzed transformation reactions of epoxides can provide practical C2 synthons in synthetic chemistry. These reactions offer a feasible strategy for catalyst-controlled epoxide divergent transformations. Therefore, finding out the crucial factors controlling chemoselectivity is the key to the rational design of transition-metal-catalyzed divergent conversions with high selectivity. In these studies, we have selected and systematically explored the general mechanism of both Mn(CO)5–- and Co(CO)4–-catalyzed divergent epoxide transformations associated with different products, namely, alkenes and β-lactones. Our computational studies showed that the chemoselective reaction undergoes either a retro-[3 + 2] step forming an alkene or a carbonyl migration insertion step for generating a β-lactone. For the Mn-catalyzed reaction, the energy barrier of the retro-[3 + 2] step is lower than that of the carbonyl migration insertion step, but the case is reversed in the Co-catalyzed reaction. Further analysis revealed that the spatial configurations of metal complexes and Pauli repulsion controlled by the metal atomic radius could be responsible for the phenomenon. The insights obtained are not only important for understanding chemoselectivity determined by the inherent properties of transition metals but also provide a valuable case for studying transition-metal-catalyzed reactions with catalyst-controlled chemoselectivity.