Equilibrium and kinetic study of the reaction between phthalocyaninatoiron(II) and carbon monoxide in dimethyl sulphoxide in the presence of pyridine. Evidence for the formation of a transient

The equlibrium and the rate constants for axial substitution of [Fe(pc) (demo)X] [pc = phathalocyaninate, dmso = dimethyl sulphoxide, X = pyridine (py) or carbon monoxide] by CO and py, respectively, have been measured at 20 ± 0.5°C in dmso so solvent. These data confirm the low stability and the high lability of the metal-dmso bond. Also metal-to-dmso ?-back bonding seems to operate. Solvent effect are of minor importance. The rate data suggest that the five-co-ordinate intermidate of the dissociative substitution process discimionates to a limited degree between the incoming nucleophiles. Evidence for the formation of a long-lived transient containing two pyridine and one carbon monoxide molecule is given and discussed.