Is Mn(I) more promising than Fe(II) – A comparison of Mn vs. Fe complexes 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 Fe. 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 study, we have investigated the prospective capabilities of Mn complexes for cycloaddition and reversion reactions, using density functional theory. Therefore, we have initially compared literature known iron model systems and their isoelectronic Mn counterparts regarding reactivity and electronic structure. Next, we constructed potential Mn complexes derived from synthetically accessible species including carbonyl ligands and obeying octahedral geometry. Based on thermodynamic parameters and the calculation of electronic descriptors, we were able to validate the isodiagonal relationship. Our study serves as guidance for the experimental chemist.