A kinetic investigation of the oxidative addition reactions of the dimeric Bu4N[Ir2(μ-Dcbp)(cod)2] complex with iodomethane

The kinetic results of the oxidative addition of iodomethane to Bu4N[Ir2(μ-Dcbp)(cod)2] (Dcbp = 3,5-dicarboxylatepyrazolate anion) show that oxidative addition can occur via a direct equilibrium pathway (K1 = 88(22) acetone, 51(3) 1,2-dichloroethane, 55(4) dichloromethane, 52(12) acetonitrile and 43(5) M−1 chloroform) or a solvent-assisted pathway (k2, k3). Oxidative addition occurs mainly along the direct pathway, which is a factor 10–40 faster than the solvent-assisted pathway. The observed solvent effect cannot be attributed to the donosity or polarity of the solvents. The fairly negative ΔS≠ value (−110(7) J K−1 mol−1) and the positive ΔH≠ value (+47(2) kJ mol−1) for the oxidative addition step are indicative of an associative process.