Metallathiacrown Ethers: Synthesis and Characterization of Transition-Metal Complexes Containing α,ω-Bis(phosphite)-Polythioether Ligands and an Evaluation of Their Soft Metal Binding Capabilities

Academic Article

Abstract

  • © 2015 American Chemical Society. The metallathiacrown ethers cis-Mo(CO)4{2,2′-(C12H8O2)PO(CH2CH2S)nCH2CH2OP(2,2′-(O2H8C12))} (n = 2, 3) and cis-Mo(CO)4{2,2′-(C12H8O2)POCH2CH2S-1-(C6H4)-2-SCH2CH2OP(2,2′-(O2H8C12))} have been prepared as soft metal selective molecular receptors. Multinuclear NMR spectroscopy and X-ray crystallography have been used to show that byproducts formed during the syntheses of the metallathiacrown ethers cis-Mo(CO)4{2,2′-(C12H8O2)PO(CH2CH2S)nCH2CH2OP(2,2′-(O2H8C12))} (n = 2, 3) are homobinuclear complexes with cis-Mo(CO)4(P-donor)(S-donor) centers. The abilities of the metallathiacrown ethers to bind PdCl2 and PtCl2 have been assessed using 31P{1H} NMR spectroscopy and X-ray crystallography. The complexes showed null results with PdCl2; however, the PtCl2 experiments showed that the complexes cis-Mo(CO)4{2,2′-(C12H8O2)PO(CH2CH2S)nCH2CH2OP(2,2′-(O2H8C12))} (n = 2, 3) formed heterobinuclear cis,cis-{[Mo(CO)4{2,2′-(C12H8O2)PO(CH2CH2S)nCH2CH2OP(2,2′-(O2H8C12))}]PtCl2} (n = 2, 3) complexes. The 31P{1H} NMR spectra of these complexes suggest a cis-PtS2Cl2 coordination environment in each, which leads to asymmetric binding in the latter complex. Binding of HgCl2 by the complexes cis-Mo(CO)4{2,2′-(C12H8O2)PO(CH2CH2S)nCH2CH2OP(2,2′-(O2H8C12))} (n = 2, 3) has been studied using 31P{1H} NMR spectroscopy. Each complex was titrated with HgCl2, and the quantitative shifts in the 31P{1H} NMR spectra were fit to a binding mechanism. The n = 2 metallathiacrown ether binds HgCl2 to form a 1:1 complex with Ka = 12.0(0.2) M-1. In contrast, interaction of HgCl2 with the n = 3 metallathiacrown ether results in isomerization to the trans complex, and HgCl2 binds to both isomers. A model has been adapted to fit the titration data of this complex and to extract equilibrium constants for each step in the cycle: the cis-trans equilibrium of the free, Kfree (0.570 (0.004)), and bound, Kbound (0.16 (0.03)), metallathiacrown ethers, as well as the association binding constants for the cis, Kcis ([4.1(0.3)] × 102 M-1) and trans, Ktrans ([1.1(0.2)] × 102 M-1), metallathiacrown ethers. The equilibrium constants demonstrate that the cis metallathiacrown ether binds more strongly to the HgCl2 than does the trans metallathiacrown ether and that the cis-trans equilibrium favors the cis metallathiacrown ether.
  • Published In

  • Organometallics  Journal
  • Digital Object Identifier (doi)

    Author List

  • Martin JR; Lucius AL; Gray GM
  • Start Page

  • 4605
  • End Page

  • 4617
  • Volume

  • 34
  • Issue

  • 18