Comparative photochemistry of tricarbonyl(η5-cyclopentadienyl)methyl- and -ethyl-molybdenum and -tungsten in poly(vinyl chloride) film matrices at 12–298 K

Abstract

The photoreactions of [M(η⁵-C₅H₅)(CO)₃(CH₃)] and [M(η⁵-C₅H₅)(CO)₃(C₂H₅)] complexes (M = Mo or W) in poly(vinyl chloride)(pvc) film matrices over a wide temperature range have been monitored using i.r. spectroscopy. At 298 K the methyl complexes dealkylate on irradiation (λ > 300 nm) to form [M(η⁵-C₅H₅)(CO)₃ Cl], [M(η⁵-C₅H₅)(CO)₃H], and [M₂(η⁵-C₅H₅)₂(CO)₆]. Photolysis at 12 K leads primarily to the formation of [M(η⁵-C₅H₅)(CO)₂(CH₃)]. In the case of molybdenum, M–CH₃ bond cleavage also occurs at 12 K and the complexes [Mo(η⁵-C₅H₅)(CO)₃Cl] and [Mo(η⁵-C₅H₅)(CO)₃H] are generated on warming the matrices. Photolysis of [M(η⁵-C₅H₅)(CO)₃(C₂H₅)] at 12 K proceeds with the formation of [M(η⁵-C₅H₅)(CO)₂(C₂H₅)] which rearranges photochemically or thermally to form trans-[M(η⁵-C₅H₅)(CO)₂(C₂H₄)H]. The cis-ethylene–hydride complex is also observed for tungsten at temperatures below ca. 50 K. At 298 K, photolysis of [W(η⁵-C₅H₅)(CO)₃(C₂H₅)] leads directly to trans-[W(η⁵-C₅H₅)(CO)₂(C₂H₄)H] which reacts further to form [W(η⁵-C₅H₅)(CO)₃H], [W(η⁵-C₅H₅)(CO)₂(C₂H₄)Cl], [W(η⁵-C₅H₅)(CO)₃Cl], and [W₂(η⁵-C₅H₅)₂(CO)₆]. However, on photolysis of [Mo(η⁵-C₅H₅)(CO)₃(C₂H₅)] at 298 K the main product observed is [Mo(CO)₆] with trace amounts of [Mo(η⁵-C₅H₅)(CO)₃H], [Mo(η⁵-C₅H₅)(CO)₃Cl], and [MO₂(η⁵-C₅H₅)₂(CO)₆].