A Kinetic Study of the Oxidative Addition of Substituted Benzenethiols Towards trans-Halocarbonylbis(triphenylphosphine)iridium(I)

The kinetics of the oxidative addition of a series of para-substituted benzenethiols, HSC 6 H 4 Y, where Y = 4-NO 2 , 4-Br, 4-Cl, 4-F, 4-H, 4-CH 3 , or 4-CH 3 O towards the complexes, trans-IrX(CO)(Ph 3 P) 2 where X = Cl, Br, or I have been studied in benzene between 15 and 45°. These reactions follow simple second order kinetics, rate = k 2 [IrX(CO)(Ph 3 P) 2 ][HSC 6 H 4 Y]. The two principal factors which influence the rates of these reactions are the mesomeric and inductive effects of the para-substituent and the nature of the ligand, X, coordinated to iridium. The rate of reaction increases as the substituent becomes more electron withdrawing and as X varies from Cl to Br to I. The kinetic data together with spectroscopic data (i.r. and n.m.r.) suggest that oxidative addition proceeds via a three-centered activated complex to give the cis-product.