Photochemistry of some dinuclear molybdenum and tungsten cyclopentadienyl carbonyl complexes in frozen gas matrices at ca. 12 K: infrared spectroscopic evidence for carbon monoxide ejection as a primary photoprocess

Abstract

Infrared spectroscopic evidence, including the use of ¹³CO-labelling, is presented to show that CO ejection is a primary process when the non-methylene-bridged and methylene-bridged dimers, [{M(η⁵-C₅H₅)(CO)₃}₂] and [M₂(µ-η⁵:η^5′-C₅H₄CH₂C₅H₄)(CO)₆](M = Mo or W), respectively, are photolysed in frozen argon, methane, carbon monoxide, and nitrogen matrices at ca. 12 K. The [M₂(η⁵-C₅H₅)₂(CO)₅](M = Mo or W) photoproduct fragments for the non-methylene bridged species are proposed to have two terminal, two bridging (2-electron) and one bridging (4-electron) CO ligands whereas in the case of the photolysis of the parent methylene bridged species, which are constrained in a cis geometry and which undergo slower photolysis, the [M₂(µ-η⁵:η^5′-C₅H₄CH₂C₅H₄)(CO)₅] photoproduct fragments are proposed to contain three terminal and two bridging (2-electron) CO ligands. Surprisingly, no secondary reactions were observed in carbon monoxide and nitrogen matrices and no ¹³CO-exchange was observed for ¹³CO-doped methane matrices. The low-temperature results are discussed in relation to solution and flash photolysis studies at ambient temperatures.