ETHENE-EXCHANGE KINETICS OF PALLADIUM(II) AND PLATINUM(II) CHLORO ETHENE COMPLEXES

The ethene-exchange kinetics of M2Cl4(C2H4)2 and MCl3(C2H4)-(M = Pd(II)) in thf-d8 has been studied as a function of temperature by H-1 NMR band shape analysis. The exchange is first order with respect to free ethene. The activation parameters and second-order rate constants are as follows (DELTA-H double-ended dagger/kJ mol-1, DELTA-S double-ended dagger/J K-1 mol-1, k2(298)/m-1 s-1): PdCl3(C2H4)-, 49 +/- 5, -17 +/- 18, (1.3 +/- 0.2) x 10(3; Pd2Cl4(C2H4)2; 31 +/- 4, -11 +/- 21, (4.8 +/- 0.6) x 10(6; PtCl3(C2H4)-, 43 +/- 5, -43 +/- 18, (9.0 +/- 1.1) x 10(2); Pt2Cl4(C2H4)2, 30 +/- 4, -23 +/- 20, (1.7 +/- 0.2) x 10(6). Formation of a bis(ethene) complex, PtCl2(C2H4)2, is observed in solutions of Pt2Cl4(C2H4)2 and ethene in thf-d8 at low temperatures. The chemical shift parameters and the exchange mechanism are discussed.