Synthesis, characterization, and cis-trans isomerization studies of cis-[PdCl2{Ph2P(CH2CH2O) 3CH2CH2PPh2-P,P′}] and trans-[PtCl2{Ph2P(CH2CH2O) 3CH2CH2PPh2-P,P′}] metallacrown ethers

Academic Article

Abstract

  • The metallacrown ether cis-[PdCl2{Ph2P(CH 2CH2O)3CH2-CH2PPh 2-P,P′}] (cis-1) has been kinetically trapped via precipitation during the reaction of PdCl2 and Ph2P(CH 2CH2O)3-CH2CH2PPh 2 in an acetonitrile/THF mixture. The kinetics of the cis-trans isomerization and oligomerization equilibria of cis-1 have been followed using quantitative 31P{1H} NMR spectroscopy. The reaction follows reversible first-order kinetics, and an Eyring analysis was carried out to yield ΔH‡f (81 ± 2 kJmol -1), ΔH‡r (46 ± 2 kJmol-1), ΔS‡f (117 ± 4 Jmol-1 K-1), and ΔS‡r (20 ± 6 Jmol-1K-1) for the isomerization reaction. The ΔH‡f is consistent with a proposed associative transition state involving partial cleavage of a Pd-P bond and partial formation of Pd-O(ether) bond to an adjacent ether oxygen. For comparison, trans-[PtCl2{Ph2P(CH2CH 2O)3CH2-CH2PPh2-P, P′}] (trans-2) was isolated from a mixture of cis and trans isomers by column chromatography. An analysis of the isomerization process of trans-2 to cis-2 using quantitative 31P{1H} NMR spectroscopy revealed that no isomerization occurs at 348 K in the absence of an acid catalyst and that the acid-catalyzed trans-cis isomerization is zero order in complex. Crystal structures of cis-1, cis-2, and trans-2 are also presented, and the conformations of the metallacrown ether rings in these structures have been related to the data presented above. © Wiley-VCH Verlag GmbH & Co. KGaA, 2008.
  • Authors

    Digital Object Identifier (doi)

    Pubmed Id

  • 15849297
  • Author List

  • Owens SB; Smith DC; Lake CH; Gray GM
  • Start Page

  • 4710
  • End Page

  • 4718
  • Issue

  • 30