Time-Resolved Infrared Spectral Studies of Photochemically Induced Oxidative Addition of Benzene to trans-RhCl(CO)(PMe₃)₂

Time-resolved infrared and time-resolved optical spectroscopy were used to examine the pathway(s) by which 355 nm photolysis of the rhodium(I) species trans-RhCl(CO)(PMe 3 ) 2 ( 1 ) in benzene leads to the C−H oxidative-addition product (Ph)(H)RhCl(CO)(PMe 3 ) 2 ( 2 ). Two reaction pathways to the formation of 2 were found. One of these was the “prompt” formation (<150 ns) of 2, the apparent result of a direct reaction of the electronic excited state of the four-coordinate species 1 with the C 6 H 6 solvent. The second route was more a convoluted stepwise process, involving CO photodissociation to give the “tricoordinate” intermediate RhCl(PMe 3 ) 2 followed by benzene oxidative addition then CO addition to give 2 .