Rhenium oxo

A remarkable aspect of the rhenium oxo complex chemistry is the ability of terminal oxo functions to act as nucleophiles. This has been used to incorporate dioxo complexes such as [Re02(py)4] or [Re02(CN)4] between the negatively charged interlayers of silicates like hector-ite (pyridine complex) or between the positive layers of a hydrotalcite-like Mg/Al double hydroxide. " The same concept has been applied for the isolation of molecular units containing Re-O-M bridges where M is a Lewis acid. ... 

Analogous alkoxy and aryloxyrhenium complexes do not show the same reactivity. However, Brown and Mayer discovered soon thereafter that a different rhenium complex could mediate C—O bond formation.68 Photolysis of the Re(V) complex 13 led to C—H activation and formation of a phenyl rhenium oxo, 14. Yields were improved from 30-40% to 90% upon addition of pyridine to the photolysis mixture. The role of pyridine was unclear, because other tertiary amines provided no such improvement in yield. Substituted benzenes showed a preference for para activation over meta fluorobenzene also gave a significant amount of ortho activation. 

Although high-valent rhenium-oxo complexes such as perrhenate, Rc207, and ReOjX (X = F, Cl, Br) are widely known, their use as oxidants is rather rare. The stoichiometric oxidation of alkenes to a mixture of ketone and epoxide by Rc207 has been reported in the patent literature. For example, 2-butene is transformed to 2,3-epoxybutane and 2-butanone by Rc207 at 100 °C. A catalytic oxidation was observed in the presence of excess hydrogen peroxide but precise data on this reaction are lacking. 

S. Owens, J. Arias, M. M. Abu-Omar, Rhenium oxo complexes in catalytic oxidations, Catal. Today 55, 317-363 (2000). 

Krische MJ, Lehn JM (2000) The Utilization of Persistent H-Bonding Motifs in the Self-Assembly of Supramolecular Architectures. 96 3-30 Krumholz P (1971) Iron(II) Diimine and Related Complexes. 9 139-174 Kuhn FE, Herrmann WA (2000) Rhenium-Oxo and Rhenium-Peroxo Complexes in Catalytic Oxidations. 97 213-236 Kubas GJ, see Ryan RR (1981) 46 47-100 Kuki A (1991) Electronic Tunneling Paths in Proteins. 75 49-84... 

Scheme 5.3-14 Rhenium oxo- and peroxo-species present in the MTO-UHPepoxidation system in ionic liquids.

T. R. Cundari, S. C, Critchlow, R. R. Conry, E. Spaltenstein, K. A. Hall, S. Tahmassebi, and J. M. Mayer, Organometallics, 13, 322 (1994). Rhenium-Oxo-Bis(acetylene) Anions Structure, Properties, and Electronic Structure. Comparison of Re—O Bonding with That in Other Rhenium-Oxo Complexes. 

Rhenium-Oxo and Rhenium-Peroxo Complexes in Catalytic Oxidations... 

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