Mechanism of Linkage Isomerization in (η¹-5-Chloropentene)pentacarbonylchromium(0)

(η¹-5-Chloropentene)pentacarbonylchromium(0), (η¹-ol−Cl)Cr(CO)₅, 1, and (η²-5-chloropentene)pentacarbonylchromium(0), (η²−Cl−ol)Cr(CO)₅, 2, respectively, in which 5-chlorobenzene is bonded to Cr via a lone pair on chlorine or through the olefinic linkage, respectively, are produced via pulsed laser flash photolysis of Cr(CO)₆/Cl−ol solutions. Compound 1 then isomerizes to 2 on the submillisecond time scale. This process has been monitored both by IR and visible spectrophotometry by employing fluorobenzene (FB) as an inert diluent. Parallel studies of flash photolysis of Cr(CO)₆ in solutions containing 1-chlorobutane and 1-hexene, both neat and diluted with FB, where the Cl and ol functional groups are not linked, also were carried out. The data support a dissociative isomerization mechanism involving rate-determining Cr−Cl bond breaking. Activation parameters for this process have been obtained. The accessibility of a proposed low-energy pathway involving “agostic” C−H−Cr interactions in the transition state is evaluated.