Organic Matrix and Solution Photochemical Studies of (Allyl)dicarbonyl(cyclopentadienyl)molybdenum Compounds

Abstract

Photolysis of fresh samples of the η3-allyl compounds [(η5-C5H5)Mo(CO)2(η3-C3H5)] or [(η5-C5H5)Mo(CO)2(η3-C3H4CH3)] in a Nujol matrix at ca. 90 K at a wavelength greater than 400 nm was found by IR spectroscopy to cause conversion of the endo rotamer to the exo rotamer. Photolysis of exo enriched samples of [(η5-C5H5)Mo(CO)2(η3-C3H5)] at wavelengths of between 360 and 400 nm reversed the photoconversion leading to an exo to endo conversion. At higher energies photochemical CO loss was also observed. In the case of the 2-methylallyl derivative, a photoproduct believed to be [(η5-C5H5)Mo(H)(CO)(η4-C4H6)] was observed along with CO loss. Time-resolved IR studies of the flash photolysis of [(η5-C5H5)Mo(CO)2(η3-C3H5)] in n-heptane confirm both endo to exo rotamer conversion and CO loss. Under these conditions, the species formed after CO loss is probably [(η5-C5H5)Mo(CO)(n-heptane)(η3-C3H5)]. When [(η5-C5H5)Mo(CO)2(η3-C3H5)] was dissolved in supercritical ethylene and photolyzed, [(η5-C5H5)Mo(CO)(C2H4)(η3-C3H5)] was formed. A mechanism involving two distinct excited states is proposed to account for the photoreversible endo/exo transformations.