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:η5′-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:η5′-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.