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

• Heteroscorpionate 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 31P NMR spectroscopy.
• The OAT reactivity of the cis isomer of (L10O)MoO2Cl demonstrated a dramatic solvent dependence and is much lower than for the trans complex.
• The catalytic oxidation of PPh3 to OPPh3 by trans-[(L10O)MoO2Cl] and cis-[(L3S)MoO2Cl] complexes using DMSO as an oxygen donor was monitored by 31P NMR.

Heteroscorpionate-based [(L10O)MoO2Cl] and [(L3S)MoO2Cl] 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 31P NMR spectroscopy. The OAT reactivity of the metal complexes toward PPh3 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)MoO2Cl] allowing investigation into the role of geometry on OAT reactivity. The OAT reactivity of the cis isomer of (L10O)MoO2Cl 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 PPh3 to OPPh3 by trans-[(L10O)MoO2Cl] and cis-[(L3S)MoO2Cl] complexes using DMSO as an oxygen donor was monitored by 31P NMR in DMF at 30 °C with rates, kcat = 4.26 × 10−5 s−1 and 5.28 × 10−5 s−1, respectively.

The effects of stereochemistry (cis and trans) on OAT between heteroscorpionate dioxo Mo(VI) complexes and triphenylphosphine are examined.Figure optionsDownload as PowerPoint slide