Kinetics study of the substitution reaction of fac-[Fe II(CN) 2(CO) 3I] − with PPh 3

Abstract

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