Unusual behavior in the 308 nm flash photolysis of Vaskaʹs complex

Time-resolved IR absorption spectroscopy was used to investigate the photolysis of Vaskaʹs Complex (VC), trans-(PPh3)2Ir(CO)(Cl). Upon 308 nm photolysis, an intermediate was formed that regenerated VC on a millisecond timescale. This intermediate was not formed at the laser flash, but was generated over the course of ∼10 μs. Most unusually, there was no evidence for prompt bleach of the C–O stretch of VC upon photolysis. Evidence was presented that the intermediate from which regeneration of VC occurred was a dimeric species. Possible pathways for the generation of the dimeric intermediate are discussed.