A Kinetic Study on Ligand Substitution Reaction of N-Cyclohexyl-2-pyrrolidone for Triphenylphosphine in Trichlorooxorhenium (V) Complex

The crystal structure of the ReOCl3(PPh3)(NCP) (PPh3 = triphenylphosphine and NCP = N-cyclohexyl-2pyrrolidone) complex was determined by a single-crystal X-ray diffraction method. It was found that NCP coordinates to the trans-position of the oxo group, Re = O, and that the Re(V) center is in a distorted octahedral geometry. The equilibrium reaction of ReOCl3(PPh3)2 + NCP ↔ ReOCl3(PPh3)(NCP) + PPh3 was examined, and its equilibrium constant was determined as 0.33 ± 0.1 in CH2Cl2 at 25 ˚C. Kinetic studies were carried out for the forward and backward reactions, and revealed that the rate determining steps for the both reactions are dissociation of the coordinated ligand from the Re center. Taking into account of geometrical isomers of the ReOCl3(PPh3)2 complex, a reaction mechanism was proposed.