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 × 10-11 cm3 molecule-1 s-1. A second olefin can add to Fe(CO)3(C2Cl4) with a rate constant of 1.9 ± 0.3 × 10-13 cm3 molecule-1 s-1 to form the novel bisolefin complex Fe(CO)3(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 × 10-13 cm3 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 Ea = 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, ΔG for the isomerization of Fe(CO)3(C2Cl4) to ClFe(CO)3(C2Cl3) is estimated to be ≥4 kcal/mol at 297 K.
ASJC Scopus subject areas
- Physical and Theoretical Chemistry