Matrix Photochemistry of Methyltrioxorhenium(VII), CH₃ReO₃: Formation of the Methylidene Tautomer H₂CRe(O)₂OH and Its Potential Relevance to Olefin Metathesis

Abstract

IR spectroscopic measurements have been used to chart the reactions activated by irradiating argon matrices doped with methyltrioxorhenium, CH3ReO3 (1), first with light at wavelengths near 254 nm and subsequently with broad-band UV−visible light (200 ≤ λ ≤ 800 nm). Assignments of the IR absorption bands are made and their carriers identified on the basis of experiments with CD3ReO3 or 13CH3ReO3 and by comparison either with the vibrational properties forecast by density functional theory (DFT) calculations or with those of related molecules. Photoexcitation at λ = ca. 254 nm results in tautomerization of CH3ReO3 to the methylidene derivative H2CRe(O)2OH (2), the properties of which have been determined, partly by experiment and partly by DFT calculations. The mechanism of the change is discussed, as is the relevance of the tautomeric product to the catalytic action of CH3ReO3 in olefin metathesis. Broad-band UV−visible radiation leads to the formation of a rhenium carbonyl, 3, possibly the Re(V) compound H2Re(CO)(O)OH.