Matrix photochemistry of methyltrioxorhenium(VII), CH3ReO3: Formation of the methylidene tautomer H2C=Re(O)(2)OH and its potential relevance to olefin metathesis

IR spectroscopic measurements:have been used to chart the reactions activat ed by irradiating argon matrices doped with methyltrioxorhenium, CH3ReO3 (1 ), first with light sit wavelengths near 254 nm and subsequently with broad -band UV-visible light (200 less than or equal to lambda less than or equal to 800 nm). Assignments of the IR absorption bands are made and. their car riers identified on the basis of experiments with CD3ReO3 or (CH3ReO3)-C-13 and by comparison either with the vibrational. properties forecast by dens ity functional theory (DFT) calculations or with those of related molecules . Photoexcitation at lambda = ca. 254 nm results in tautomerization of CH3R eO3 to the methylidene derivative H2C=Re(O)(2)OH (2), the properties of whi ch have been determined, partly by experiment and partly by DFT calculation s. The mechanism of the change is discussed, as is the relevance of the tau tomeric product to the catalytic action of CH3ReO3 in olefin metathesis. Br oad-band UV-visible radiation leads to the formation of a rhenium carbonyl, 3, possibly the Re(V) compound H2Re(CO)(O)OH.