Reactions of Fe(CO)3 and Fe(CO)4 with C2Cl4 in the gas phase monitored by transient infrared spectroscopy:: Formation of Fe(CO)4(C2Cl4), Fe(CO)3(C2Cl4)2, and novel chloride complexes resulting from the oxidative addition of C2Cl4

The gas-phase reactions of Fe(CO)(3) and Fe(CO)(4) with perchloroethylene (C2Cl4) have been investigated using transient infrared spectroscopy. The addition of C2Cl4 to Fe(CO)(3) produces Fe(CO)(3)(C2Cl4) with a rate constant of (3.0 +/- 0.8) x 10(-11) cm(3) molecule(-1) s(-1). A second olefin can add to Fe(CO)(3)(C2Cl4) with a rate constant of (1.9 +/- 0.3) x 10(-13) cm(3) molecule(-1) s(-1) to form the novel bisolefin complex Fe(CO)(2)(C2Cl4)(2). Absorptions of this complex were identified at 2084 and 2057 cm(-1). C2Cl4 reacts with Fe(CO)(4) with a rate constant of (1.2 +/- 0.3) x 10(-13) cm(3) molecule(-1) s(-1) to produce Fe(CO)(4)(C2Cl4), which is identified by its absorptions at 2125, 2069, and 2039 cm(-1). This product isomerizes to a novel chloride complex via an oxidative addition process, with Arrhenius parameters E-a = 21 +/- 2 kcal/mol and in A = 28 +/- 2 in the 297-315 K temperature range. The chloride complex is best assigned as ClFe(CO)(4)(C2Cl3), and possible mechanisms for this isomerization reaction are discussed. ClFe(CO)(4)(C2Cl3) can also be produced by the photolysis of Fe(CO)(4)(C2Cl4), and a mechanism for this process is proposed. Absorptions of ClFe(CO)(4)(C2Cl3) were identified at 2166, 2109, and 2089 cm(-1). Where possible, the measured rate constants and the observed infrared absorptions are compared to those for analogous C2H4 and C2F4 complexes. Finally, simulations of a "global" mechanism for the kinetics of this system are in good agreement with experimental data. From these simulations, Delta G for the isomerization of Fe(CO)(3)(C2Cl4) to ClFe(CO)(3)(C2Cl3) is estimated to be greater than or equal to 4 kcal/mol at 297 K.