Chemistry of oxidomolybdenum(IV) and -(VI) complexes with ONS donor ligands: Synthesis, computational evaluation and oxo-transfer reactions

A series of dioxidomolybdenum(VI) complexes, [MoVIO2L1–6] (1–6) and [MoVIO2L1–6(solv)] (1a–6a) where solv (solvent) = DMSO (1a, 3a, 5a and 6a) and H2O (2a and 4a) have been synthesized using thiosemicarbazone ligands, H2L1–6. Furthermore, six monooxidomolybdenum(IV) complexes [MoIVOL1–6(N-N)] (7–12) where co-ligand (N-N) = 2,2′-bipyridine (bipy) (7, 10 and 11) and 1,10-phenanthroline (phen) (8, 9 and 12) have also been synthesized from the corresponding Mo(VI) precursors, [MoVIO2L1–6] (1–6) by oxygen atom transfer (OAT) reaction. Complexes have been characterized by conventional methods, including X-ray crystallography, and DFT (density functional theory) calculations. OAT reactivity of Mo(VI) and Mo(IV) complexes have been successfully established through the formation of OPPh3and Me2S. These OAT products have been characterized by31P NMR (OPPh3), UV–Vis spectroscopy and GC–MS (Me2S) and DFT simulations supported this finding through the prediction of ΔGtotsolfor the reaction of oxygen atom transfer. DFT methods suggested that the oxygen atom transfer from [MoVIO2L] species to PPh3to give [MoIVOL(bipy)] and from DMSO to [MoIVOL(bipy)] to yield [MoVIO2L] is strongly favored, whereas the formation of μ-oxido dimer [MoV2O3L2], is much less probable.