Organic matrix and solution photochemical studies of (allyl)dicarbonyl(cyclopentadienyl)molybdenum compounds

Photolysis of fresh samples of the eta (3)-allyl compounds [(eta (5)-C5H5)M o(CO)(2)(eta (3)-C3H5)] or [(eta (5)-C5H5)Mo(CO)(2)(eta (3)-C3H4CH3)] in a Nujol matrix at ca. 90K at a wavelength greater than 400 nm was found by IR spectroscopy to cause conversion of the endo rotamer to the exo rotamer. P hotolysis of exo enriched samples of [(eta (5)-C5H5)Mo(CO)(2)(eta (3)-C3H5) ] at wavelengths of between 360 and 400 nm reversed the photoconversion lea ding to an exo to endo conversion. At higher energies photochemical CO loss was also observed. In the case of the 2-methylallyl derivative, a photopro duct believed to be [(eta (5)-C5H5)Mo(H)(CO)(eta (4)-C4H6)] was observed al ong with CO loss. Time-resolved IR studies of the flash photolysis of [(eta (5)-C5H5)Mo(CO)(2)(eta (3)-C3H5)] in n-heptane confirm both endo to exo ro tamer conversion and CO loss. Under these conditions, the species formed af ter CO loss is probably [(eta (5)-C5H5)Mo(CO)(n-heptane)(eta (3)-C3H5)]. Wh en [(eta (5)-C5H5)Mo(CO)(2)(eta (3)-C3H5)] was dissolved in supercritical e thylene and photolyzed, [(eta (5)-C5H5)Mo(CO)(C2H4)(eta (3)-C3H5)] was form ed. A mechanism involving two distinct excited states is proposed to accoun t for the photoreversible endo/exo transformations.