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.