Time-resolved infrared spectroscopy is used to examine the reactions of the transient intermediate W(CO) 5 (CyH) (CyH ) cyclohexane), formed by photolysis of a cyclohexane solution of W(CO) 6 , with L ) pyrrole and pyrrolidine. Time-and temperature-dependent rate constants for the ligand substitution reaction to form W(CO) 5 (L) are determined. These reactions appear to go through an associative interchange mechanism. Eyring activation parameters for the ligand exchange are derived. For L ) pyrrolidine, ∆H q ) 1.8 ( 0.1 kcal mol -1 and ∆S q ) -18.9 ( 0.4 eu; for L ) pyrrole, ∆H q ) 5.1 ( 0.2 kcal mol -1 and ∆S q ) -11.6 ( 1.2 eu. Most unusually, the observed pseudo-first-order rate constant for reaction with pyrrole is not a linear function of pyrrole concentration. This deviation from simple first-order behavior is explained in terms of association of pyrrole in solution to form dimers and higher clusters that lower the ligand's effective concentration. The enthalpy of dimerization of pyrrole is estimated from the kinetic data to be approximately 4 kcal mol -1 . The results of reaction of W(CO) 5 (CyH) with pyrrole and pyrrolidine are discussed in terms of the behavior of this intermediate with other ligands.

Photolysis of a cyclohexane (CyH) solution of M(CO)6 (M = Cr, Mo, W) in the presence of excess 2,3- or 2,5-dihydrofuran (DHF) yields the complex M(CO)5(DHF). The solvated complex M(CO)5(CyH) formed upon photolysis reacts with DHF to form, with a second-order rate constant of 106−107 L mol-1 s-1, a single product, identified as the O-bound complex M(CO)5(η1-DHF). On a longer time scale (milliseconds to seconds), equilibrium is established between this kinetic product and a second product, M(CO)5(η2-DHF), in which the ligand is bound to the metal through the DHF CC double bond, via an intramolecular linkage isomerization reaction. Time-resolved infrared absorption spectroscopy (TRIR) is used to monitor the kinetics of this linkage isomerization, and activation and equilibrium parameters for the isomerization are determined. For all six systems, ΔH ⧧ ≈ 15 kcal mol-1, while the isomerization is thermoneutral or slightly exothermic (|ΔH°| ≈ 0−2 kcal mol-1). Trends in reactivity as a function of the metal and of the ligand are discussed, and the utility of TRIR as a method for investigating intramolecular linkage isomerization in carbonyl complexes is assessed.