Kinetics study of the substitution reaction of fac-[FeII(CN)2(CO)3I]− with PPh3

Substitution reaction of fac-[FeII(CN)2(CO)3I]− with triphenylphosphine (PPh3) produced mono phosphine substituted complex cis-cis-[FeII(CN)2(CO)2(PPh3)I]−. Crystal structure of the product showed that carbonyl positioned trans- to iodide was replaced by PPh3. The substitution reaction was monitored by quantitative infrared spectroscopic method, and the rate law for the substitution reaction was determined to be rate = k[[FeII(CN)2(CO)2(PPh3)I]−][PPh3]. Transition state enthalpy and entropy changes were obtained from Eyring equation k = (kBT/h)exp(−ΔH≠/RT + ΔS≠/R) with ΔH≠ = 119(4) kJ mol−1 and ΔS≠ = 102(10) J mol−1 K−1. Positive transition state entropy change suggests that the substitution reaction went through a dissociative pathway.