Oligomerization and cis-tram isomerization equilibria in dichloropalladium(n) metallacrown ethers and a dichloropalladium(n) complex of l,12-bis(diphenylphosphino)-dodecane

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  • Quantitative 31P{1H} NMR spectroscopic studies of monomer-oligomer and cis-imns equilibria in chloroforma/ solutions of PdCl2{Ph2P(CH2CH2O) nCH2CH2PPhP,P′}n (n = 3,4, 5) metallacrown ethers and of PdCl2{Ph2P-(CH2)32PPh2-.P,.P′} are reported. The NMR data for all of the complexes can be adequately modeled using a single cis-trans isomerization equilibrium and two step-polymerization (dimerization, oligomerization) equilibria. As expected, both the dimerization and oligomerization equilibrium constants for the metallacrown ethers increase as n increases. However, the dimerization equilibrium constants of the metallacrown ethers are much smaller than are the oligomerization equilibrium constants. In contrast, the dimerization and oligomerization equilibrium constants for PdCl2{Ph2P(CH2)12PPh 2-P,P′)} are nearly identical and are significantly larger than are those of the metallacrown ethers. Kinetic studies of monomer-oligomer and cis-trans equilibria in solutions of râ-PdCl2{Ph2P(CH2CH2O) 3-CH2CH2PPh2-P,P′} indicate that the Irans monomer and trims oligomers are formed at approximately the same rates and that the reactions follow reversible first-order kinetics. The very different dimerization constants for the metallacrown ethers and PdCl2{Ph2P(CH2)12PPh2-/J,/)'}and the similar rates of formation for the trans monomer and Irans oligomers suggest that the isomerization and dimerization reactions have a common rate-determining step that involves cleavage of a palladium-phosphorus bond. © The Royal Society of Chemistry 2000.
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  • Smith DC; Gray GM
  • Start Page

  • 677
  • End Page

  • 683
  • Issue

  • 5