Photochemistry of carbonyl(µ5-cyclopentadienyl)dihydridoiridium in frozen gas matrices at ca. 12 K: infrared evidence relating to C–H activation

Abstract

Infrared spectroscopic evidence, including deuterium and ¹³CO labelling, is presented to show that photolysis of [Ir(η⁵-C₅H₅)(CO)H₂] in a methane matrix at ca. 12 K affords [Ir(η⁵-C₅H₅)(CO)(CH₃)H] probably via initial reductive elimination of the hydride ligands as molecular H₂ to form [Ir(η⁵-C₅H₅)(CO)], which is detected in argon matrices. Photolysis of [Ir(η⁵-C₅H₅)(CO)H₂] in nitrogen and carbon monoxide matrices yields [Ir(η⁵-C₅H₅)(CO)(N₂)] and [Ir(η⁵-C₅H₅)(CO)₂], respectively. The lack of evidence for HCO˙ in CO matrices and the lack of isotopic scrambling in mixed H/D isotope experiments, e.g. studies of [Ir(η⁵-C₅H₅)(CO)H₂] in CD₄ and [Ir(η⁵-C₅H₅)(CO)D₂] in CH₄ matrices, confirms that the initial photoprocess is H₂ ejection. Surprisingly, this ejection is reversible even at 12 K using long-wavelength irradiation. Mechanisms for C–H activation processes are discussed, cf. the observation that [Ir(η⁵-C₅H₅)(¹²CO)H₂] exchanges ¹³CO for ¹²CO via a thermal reaction in the gas phase at 298 K.