Theoretical study of the formation of metal-oxo species of the first transition series with the ligand 14-TMC: driving factors of the Oxo Wall

Terminal metal-oxo species of the early transition metal series are well known, whereas those for the late transition series are rare, and this is related to the Oxo Wall. Here, we have undertaken a theoretical study on the formation of metal-oxo species from the metal hydroperoxo species of the 3d series (Cr, Mn, Fe, Co, Ni, and Cu) with the ligand 14-TMC (1,4,8,11-tetramethyl-1,4,8,11-tetraazacyclotetradecane) via O center dot center dot center dot O bond cleavage. DFT calculations reveal that the barrier for O center dot center dot center dot O bond cleavage is higher with the late transition metals (Co, Ni, and Cu) than the early transition metals (Cr, Mn, and Fe), and the formed late metal-oxo species are also thermodynamically less stable. The higher barrier may be due to electronic repulsion because of the pairing of d electrons. In the late transition metal series, the electron goes into an antibonding orbital, which decreases the bond order and hence decreases the possibility of metal-oxo formation. Computed structural parameters and spin densities suggest that valence tautomerism occurs in the late transition metal-oxo species which remain as a metal-oxyl. Our findings support the concept of the Oxo Wall.

Automated summary

This theoretical study on metal-oxo species of transition metals reveals that late transition metals have higher barriers and less stability in forming metal-oxo species compared to early transition metals, which may be attributed to electronic repulsion and the influence of antibonding orbitals.