Chlorobenzene, time-resolved

Observations of the UV absorption4 attributable to benzyne in the vapor phase, evidence from time-resolved mass spectrometry,5 and more recently of the IR spectrum6 of benzyne in a matrix at very low temperature leave no doubt as to the existence of such a transient intermediate. Its lifetime in solution is extended when benzyne is supported on a polymer phase.7 Results of competitive trapping experiments, when benzyne is generated from different precursors, and the classical experiments of Roberts et al. on cine-substitution in the amination of chlorobenzene confirm the formation of benzyne as an intermediate.8,9... 

Time-resolved IR spectroscopy was used to identify cis and trans isomers [W(C0)4L(S)J, L = PPh3, P(0-i-Pr)3, or P(OEt)3 and S = heptane. These isomers were prepared by photolysis of [W(CO)5L] and cw-[W(CO)4L(pip)]. In heptane the cis isomer is shorter lived than the trans isomer there is no evidence for interconversion of the two. The two isomers react with CO with different rates, and the rate increases with the size of L. The term Token Ligand is coined to indicate that there is a specific interaction between a solvent molecule and what would otherwise be a vacant coordination site. Reactions of ds-[W(CO)4L(pip)] with L, L and V = phosphine or phosphite, proceed by reversible pip dissociation, forming square-pyramidal [W(CO)4L] in which L is equatorially coordinated. The general reaction sequence is given in Scheme 6. Dissociative loss of chlorobenzene from ci5-[W(C0)4 P(0-/-Pr)3 (PhCl)] displays activation parameters of A/Zj = 13.0 kcal mol and ASf = -f 5.6 cal K" mol". Rate constants for thermal reactions of ci5-[W(CO)4(L)(PhCl)] with P(0-f-Pr)3, given in Table 10.5, are predominantly... 

Dunbar, R.C. (1987) Time-resolved Photodissociation of Chlorobenzene Ion in the ICR Spectrometer. J. Phys. Chem. 91 2801-2804. 

---