Examination of oxygen atom transfer reactivity of heteroscorpionate dioxo-Mo(VI) complexes: Geometric isomers, solvent effect, intermediates, and catalytic oxidation

Heteroscorpionate-based [(L10O)MoO 2 Cl] and [(L3S)MoO 2 Cl] complexes containing an interchangeable third heteroatom donor have been utilized for the systematic investigation of oxygen atom transfer (OAT) reactivity. The detection of phosphoryl intermediates and products in the reaction pathway were probed by UV–Vis, mass spectrometry, and 31 P NMR spectroscopy. The OAT reactivity of the metal complexes toward PPh 3 were monitored by UV–Vis spectroscopy under pseudo-first order conditions. The sterically encumbered (L10O) ligand gives rise to isolable trans and cis isomers of [(L10O)MoO 2 Cl] allowing investigation into the role of geometry on OAT reactivity. The OAT reactivity of the cis isomer of (L10O)MoO 2 Cl demonstrated a dramatic solvent dependence, in which the reaction proceeded at a measureable rate only in pyridine. However, the trans counterpart reacted in all solvents and at much faster rates. The catalytic oxidation of PPh 3 to OPPh 3 by trans -[(L10O)MoO 2 Cl] and cis -[(L3S)MoO 2 Cl] complexes using DMSO as an oxygen donor was monitored by 31 P NMR in DMF at 30 °C with rates, k cat = 4.26 × 10 −5 s −1 and 5.28 × 10 −5 s −1, respectively.