Transient infrared spectroscopy has been used to study reactions of Cr(CO)5 generated by UV (351 or 355 nm) photolysis of Cr(CO)6 in the gas phase. At 298 K Cr(CO)5 reacts with H2, C2H4, C2F4, and C6H6 with bimolecular rate constants of (9.0 ± 2.9), (19.0 ± 2.0), (1.8 ± 0.2), and (26.0 ± 1.0) × 10-11 cm3 molecule-1 s-1, respectively, where the rate constants reported are for the high-pressure limit. Infrared absorptions attributed to Cr(CO)5L where L = H2, C2H4, C2F4, and C6H6 were observed. The rate of dissociative loss of L from the Cr(CO)5L complexes was determined by the observation of the rate of regeneration of Cr(CO)6 and/or the rate of disappearance of Cr(CO)5L in a reaction mixture consisting of Cr(CO)5, CO, and L. The rate of dissociative loss of a ligand can be directly related to the bond dissociation energy for the loss of L from Cr(CO)5L which has been determined as 15.0 ± 1.3, 24.7 ± 2.4, 19.7 ± 1.4, and 13.7 ± 0.8 kcal/mol for H2, C2H4, C2F4, and C6H6, respectively. Data were also obtained which pertain to the magnitudes of the bonding interaction between C6F6 and CH4 and Cr(CO)5. The nature of the bonding between Cr(CO)5 and L is discussed. Implications of these measurements for reactions of coordinatively unsaturated species in solution are also considered.
ASJC Scopus subject areas
- Physical and Theoretical Chemistry