LASER-PHOTOLYSIS STUDIES OF ISOCYANIDE COMPLEXES OF CHLOROCHROMIUM(III) TETRAPHENYLPORPHYRIN IN TOLUENE SOLUTIONS

Chloroaquachromium(III) tetraphenylporphyrin, Cl(H2O)CrIIITPP, reversibly reacts with isocyanide, CN−R, to form Cl(CN−R)CrIIITPP in toluene solutions containing 4.4 × 10-3 M H2O and CN−R. The equilibrium constant for the formation of Cl(CN−R)CrIIITPP obtained by spectroscopic measurements ranges from 10 to 102 depending on the nature of the isocyanide used. The laser-photolysis studies of the toluene solution demonstrate that CN−R is photodissociated from Cl(CN−R)CrIIITPP to produce ClCrIIITPP with a quantum yield ca. 0.1. The five-coordinate ClCrIIITPP reacts with H2O and CN−R to give Cl(H2O)CrIIITPP and Cl(CN−R)CrIIITPP, respectively. The transient product Cl(H2O)CrIIITPP further reacts with CN−R to regenerate Cl(CN−R)CrIIITPP. The rates for the decay of Cl(H2O)CrIIITPP are measured as a function of the concentration of CN−R in order to determine the rate constants of the forward and backward reactions for the formation of Cl(CN−R)CrIIITPP. The equilibrium constants obtained from the kinetic analysis fo...