Group 6 carbonyl complexes of N,O,P-ligands as precursors of high-valent metal-oxo catalysts for olefin epoxidation

•Review of M(CO)6 and [MXm(CO)x(L)n] derivatives as olefin epoxidation pre-catalysts.•Tri- and tetracarbonyl complexes of N,O,P-ligands are effective catalyst precursors.•Links are made between precursor structure, ligand types, and catalytic performance.•Analysis of ligand effects on catalyst activation by oxidative decarbonylation (OD).•Structures and catalytic behavior of MoVI complexes, clusters and hybrids formed by OD.