Electronic effects on carbon monoxide dissociation from iron(II) tetraphenylporhyrins

Abstract

We report the kinetics of CO binding to a series of substituted ferrous tetra(4-X-phenyl)porphyrins ( X = CF 3, Cl , H , CH 3, OCH 3) in DMSO solvent using a mixture of 1,2-DMI/1-MeIm as proximal base. The CO dissociation rate constant increases with electron donation of the substituent X; the aggregate Hammett ρ value is -0.38. Using a Swain-Lupton analysis we determine the electronic effects to be transmitted 67% by through-bond or field effect and 33% by resonance. These results indicate that there is significant conjugation between the phenyl rings and the porphyrin core of iron tetraphenylporphyrin systems.