Rare Gas-Metal Carbonyl Complexes: Bonding of Rare Gas Atoms to the Group VI Pentacarbonyls

Transient infrared spectroscopy has been used to study reactions of M(CO)₅ generated by 355-nm photolysis of M(CO)₆ where M = Cr, Mo, and W. At 298 K, M(CO)₅ reacts with CO with bimolecular rate constants of (1.4 ± 0.2) × 10⁻¹⁰, (1.5 ± 0.1) × 10⁻¹⁰, and (1.4 ± 0.1) × 10⁻¹⁰ cm³ molecule⁻¹ s⁻¹ for Cr, Mo, and W, respectively. M(CO)₅ also reacts with Xe with bimolecular rate constants of (0.9 ± 0.4) × 10⁻¹⁰, (0.9 ± 0.4) × 10⁻¹⁰, and (2.6 ± 0.2) × 10⁻¹⁰ cm³ molecule⁻¹ s⁻¹ for Cr, Mo, and W, respectively. Infrared absorptions attributed to M(CO)₅Xe and W(CO)₅Kr were observed. The rate of dissociative loss of the Xe atom from the M(CO)₅Xe complexes was determined by the observation of the rate of regeneration of M(CO)₆ in a reaction mixture consisting of M(CO)₅, CO, and Xe. The bond dissociation energy for the loss of the Xe atom from M(CO)₅Xe for all three metals is the same within experimental error and has an average value of 8.5 kcal/mol. A bond dissociation energy was estimated for the loss of Kr from W(CO)₅Kr, and an upper limit can be estimated for the bond dissociation energy for loss of Ar from W(CO)₅Ar.