Keep it singlet – Towards in silico design of manganese catalysts for olefin metathesis

Olefin metathesis is one of the most significant transformations in organic chemistry and an excellent example for efficient homogeneous catalysis. Although most currently used catalysts are primarily based on 4d and 5d metals, cycloaddition and cycloreversion reactions can also be attributed to first-row transition metals, such as iron. Surprisingly, the potential of Mn(I) based catalysts for olefin metathesis has been unexplored, despite its prominence in homogeneous catalysis and its diagonal relationship to Ru(II). In the present paper, we have investigated the prospective capabilities of rationally designed Mn complexes for cycloaddition and reversion reactions, using density functional theory. To keep our model complexes as synthetically feasible as possible, we included CO as co-ligands and imposed octahedral coordination. Like iron systems, a singlet ground state is required for Mn based catalysts to facilitate olefin metathesis and to prevent undesired cyclopropanation. However, the stabilization of the singlet state requires a careful selection of σ-donor and π-acceptor properties. Our results show that bidentate ligands in conjunction with CO work best. Our findings support the isodiagonal relationship and show the viability of Mn(I) complexes as catalysts for olefin metathesis.