Kinetics of Carbon Monoxide Exchange in Chloro and Bromo Carbonyl Complexes of Palladium(II) and Platinum(II)

Carbonyl exchange between [MX3(13CO)]–(MX = PdCl, PtCl or PtBr) and 12CO has been studied by IR and 13C NMR spectroscopies as a function of temperature. The exchange is first-order in both CO and complex concentration, and the activation entropies are negative, suggesting an associative reaction mechanism. There is a small solvent effect, but no chloride dependence. Activation parameters and rate constants, in the order ΔH‡/kJ mol–1, ΔS‡/J K–1 mol–1kes298/dm3 mol–1 s–1, are for [PdCl3(CO)]– 60 ± 8, –47 ± 30, 0.57 ± 0.07; for [PtCl3(CO)]– 60 ± 7, –91 ± 22, (3.3 ± 0.3)× 10–3 and for [PtBr3(CO)]– 49 ± 6, –104 ± 19, (6.0 + 0.2)× 10 –2(95% confidence interval). This is three to six orders of magnitude slower than ethene exchange in analogous ethene halide complexes.