31P{1H} NMR spectroscopic and X-ray crystallographic studies of conformational dynamics in cis-M{Ph2P(CH2CH2O)5CH2CH2PPh2-P,P'} (M = Mo(CO)4, PtCl2) metallacrown ethers

Academic Article

Abstract

  • Broad P{ H} NMR resonances are observed for cis-M{Ph P(CH CH O) CH CH PPh -P,P'} (M = Mo(CO) , 3, and PtCl , 6) metallacrown ethers at 295 K. Variable temperature P{ H} NMR studies of these metallacrown ethers have demonstrated that this is due to exchange between symmetrical and unsymmetrical conformers. Simulation of the P{ H} NMR spectra of 6 using the gNMR(TM) program yields an E(a) of 34 kJ mol , ΔH(≠) of 32 kJ mol and ΔS(≠) of 146 J mol-K for the exchange process. The relative amounts of the symmetrical and unsymmetrical conformers in solutions of 3 (90:10) and 6 (42:58) are quite different. The X-ray crystal structures of 3 (symmetrical) and 6 (unsymmetrical) are consistent with the relative amounts of conformers in solution. This suggests that the steric bulk of the metal center is determining the relatively stabilities of the symmetrical and unsymmetrical conformers. The square planar platinum center can accommodate the more crowded unsymmetrical structure while axial ligands in the octahedral molybdenum center favor the more open, symmetrical structure. (C) 2000 Elsevier Science S.A. 31 1 31 1 31 1 -1 -1 -1 2 2 2 5 2 2 2 4 2
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    Digital Object Identifier (doi)

    Author List

  • Gray GM; Smith DC; Duffey CH
  • Start Page

  • 581
  • End Page

  • 586
  • Volume

  • 300-302