Isolation of Mo(V)-dithiolene-radical: an elusive intermediate species relevant to catalytic cycle of molybdenum cofactor.

A pair of bis-dithiolene-molybdenum(V) complexes, [Mo(V)(O)(LE2-)(LE˙-)] [E = S (1), E = Se (2), LE = NHC-based dithiolene ligand] have been successfully isolated and fully characterised. These complexes represent a rare and well-defined structural analogue of the active sites found in molybdenum cofactor enzymes (Moco) in bacteria. They were spectroscopically characterised with IR, UV-Vis, XPS, and EPR measurements. Stability, bonding and distribution of electron densities were studied by DFT and EDA-NOCV calculations. Notably, this work constitutes the first report of a molybdenum-oxo bisdithiolene complex in which the same ligand simultaneously exists [C-C 1.411(6), 1.350(6) Å] in radical monoanionic and closed-shell dianionic forms, which was previously speculated.