Kinetics of the Addition of Tetracyanoethylene to Bis(Tertiary Phosphine)Bis(Isocyanide)Rhodium(I) Perchlorates
[Rh(RNC)2L2]C1O4 (R=p-ClC6H4, p-CH3OC6H4, cyclo-C6H11, and L = PPh3; R = p-CH3OC6H4 and L = P(OPh)3 react with tetracyanoethylene (TCNE) to give [Rh(RNC)2L2(TCNE)C1O4. The IR and PMR spectra suggest that the adducts have a trigonal bipyramidal configuration with the TCNE coordinated rigidly, if TCNE is assumed to occupy one coordination site. The kinetic study of the reactions was carried out in various organic solvents by the use of a stopped-flow photometer; the reactions are first order with respect to both the Rh(I) substrates and TCNE, and the rate of reactions increases with increasing polarity of the solvents, and with increasing electron donating power of the R groups. The activation parameters of the reactions are discussed in terms of the reaction mechanism.