Abstract Kinetics and equilibrium measurements for the reversible binding of CN to carbonylated phthalocyaninatoiron(II) ([Fe(pe)(CO)-(dmso)]) have been carried out, at 25.0°C in dimethyl sulfoxide. The rate of cynide binding to [Fe(pe)(CO)(dmso)] is limited by the rate of CO dissociation and the ultimate formation of [Fe(pe)(CN) 2 ] 2 does not occur via [Fe(pe)(CO)(CN)]. These results agree with a