Kinetics of carbon monoxide exchange in chloro and bromo carbonyl complexes of palladium(II) and platinum(II)

Abstract

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^–1k_es²⁹⁸/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.