Photochemistry of some (η5-cyclopentadienyl)carbonylchloro complexes of molybdenum, tungsten, iron, and ruthenium in frozen gas matrices at ca. 12 K and in poly(vinyl chloride) films at ca. 12–298 K

Abstract

Infrared spectroscopic evidence including ¹³CO substitution and energy-factored force-field fitting is presented to show that photolysis of [M(η⁵-C₅H₅)(CO)₃Cl] complexes (M = Mo or W) in argon, methane, nitrogen, carbon monoxide, and 5% C₂H₄–CH₄ matrices at ca. 12 K yields ejection of CO and formation of the 16-electron species [M(η⁵-C₅H₅)(CO)₂Cl] as the primary process. This process is reversible. In nitrogen and 5% C₂H₄–CH₄ matrices the [M(η⁵-C₅H₅)(CO)₂Cl] species react with N₂ and C₂H₄ to give cis-[Mo(η⁵-C₅H₅)(CO)₂(N₂)Cl] and cis-[M(η⁵-C₅H₅)(CO)₂(C₂H₄)Cl](M = Mo or W) respectively. In carbon monoxide matrices the ejection of CO is suppressed and the photolysis products are proposed to be the species [M(η⁵-C₅H₅)(CO)₃]⁺Cl^–(M = Mo or W), indicative of metal–chlorine bond heterolysis. Irradiation of [M(η⁵-C₅H₅)(CO)₂Cl] complexes (M = Fe or Ru) in methane, nitrogen, and carbon monoxide matrices and in poly(vinyl chloride) films at ca. 12 K produced only the 16-electron species [M(η⁵-C₅H₅)(CO)Cl] and CO indicating that dissociation, rather than cleavage of the metal–chlorine bond, is the principal reaction pathway. The primary process can be reversed thermally in the polymer films by virtue of their wider working temperature range (ca. 12–298 K). For the iron complex reversal occurred by ca. 60 K, whereas the ruthenium complex needed a higher temperature of annealing (ca. 80 K). The results of the low-temperature studies are discussed in relation to the thermal and photochemical reactions of complexes of Mo, W, Fe, and Ru in solution at ambient temperatures.