Mechanistic study of oxygen atom transfer catalyzed by rhenium compounds

The investigation of oxygen atom transfer (OAT) catalyzed by transition metal complexes continues to provide chemical insight for advanced studies in bioinorganic chemistry as well as industrial applications. Unlike molybdenum(IV/VI) pairs, which received intensive interest from inorganic and bioinorganic chemists for decades, rhenium(V/VII), forming the redox loop involving two-electron or one-oxygen atom processes has only received limited attention.;A family of oxorhenium(V) complexes was synthesized from methyltrioxorhenium(VII), abbreviated as MTO, that can be reduced by phosphanes, thiols or sulfides and coordinated by suitable ligands including thiolates, phosphanes, pyridines, phenolates, carboxylates and etc. An unexpected methyl transfer from rhenium to thiolate sulfur was discovered when MTO react with 1,2-ethanedithiol without the presence of a reducing reagent.;Ligand displacement was found to be an essential step in OAT reactions catalyzed by rhenium(V) complexes. This allows the oxidant to access rhenium(V) and be activated by the metal subsequently. Kinetic studies of ligand exchange of McReO(dithiolate)Py with Py or phosphanes and ReO(kappa2-edt)(kappa 2-edtMe) with phosphanes all revealed an unique correlation behavior when series of substituted ligands were employed. Detailed investigation led us to conclude that a three-step mechanism was involved and caused this unique phenomenon.;Further study of the OAT catalytic cycle led us to investigate the geometric effect on the oxidation of rhenium(V) complexes with pyridine N-oxides. Five and six coordinated rhenium(V) complexes with tridentate ligands display an entirely different rate law. The reactions of six-coordinate compounds shows first-order dependence on the concentration of water instead of pyridine N-oxide in the rate law of the reactions of five coordinated rhenium(V) compounds. Steric demand may play the key role in this difference.;A catalytic OAT cycle with pyridine N-oxides and sulfide catalyzed by MeReO(PA)2, where PAH is 2-piclinic acid, was investigated. Mechanistic and isotope labeling studies were applied to trap the intermediate, from which a structure was postulated.