KINETICS AND MECHANISM OF OXIDATIVE ADDITION OF ARYL IODIDES TO IRIDIUM(I) COMPLEXES

The kinetics of oxidative addition of aryl iodides to trans-IrCl(CO)L2 (L=tertiary phosphine) are governed by a two-term rate law, R={k1+k2[ArI]}[Ir], similar in form to the equation describing substitution reactions of square-planar complexes. The second-order path is decreased by added phosphine. Electron-withdrawing groups in either the aryl halide or the complex enhance the rate of reaction. Linear free energy relationships were found between k2 and the Hammett σp for substituents in the aryl iodide (p=+0.6) and between k2 and the Kabachnik Σσph for substituents on the phosphine (p=+0.4). A two-step mechanism is suggested for the second-order path involving predissociation of the phosphine ligand. These data are compared with prevailing ideas concerning the mechanisms of oxidative addition reactions of d8 square-planar complexes. © 1979, American Chemical Society. All rights reserved.