Evidence for a carbonyl-containing intermediate in the 308-nm photolysis of trans-RhCl(CO)(PMe₃)₂

Time-resolved infrared absorption spectroscopy is used to monitor the events during the first ∼100 μs following 308-nm photolysis of trans-RhCl(CO)(PMe₃)₂ (I) in a C₆D₆ or Decalin solution. Upon photolysis, the intensity of the carbonyl stretching absorption of I decreases and a new C-O stretching absorption (A) appears at 2006 cm^-1 in C₆D₆ (2013 cm^-1 in Decalin). Within ∼100 μs, A disappears concurrently with partial regeneration of I and oxidative addition of a solvent C-D (C-H) bond. Our observation of the prompt formation of a carbonyl-containing intermediate contrasts with prior observations that photolysis at longer wavelengths leads solely to dissociation of CO from I. The implications of the observation of A for the understanding of the mechanisms of photocatalytic reactions of I are discussed.