Generally Applicable NMR Titration Methods for the Determination of Equilibrium Constants for Coordination Complexes: Syntheses and Characterizations of Metallacrown Ethers with α,ω-Bis(phosphite)-polyether Ligands and Determination of Equilibrium Binding Constants to Li+

Abstract

A new metallacrown ether, cis-PdCl2{(2,2′-C12H8O2)P(OCH2CH2)4OP(2,2′-O2H8C12)}, has been synthesized and fully characterized by NMR spectroscopy and X-ray crystallography. A new synthetic method and complete NMR characterization for the previously reported and closely related cis-Mo(CO)4(2,2′-C12H8O2)P(OCH2CH2)4OP(2,2′-O2H8C12) metallacrown ether are also reported. Both complexes are monomeric, exhibiting cis coordination geometries both in solution and in the solid state, and the cis-Mo(CO)4(2,2′-C12H8O2)P(OCH2CH2)4OP(2,2′-O2H8C12) metallacrown ether does not appear to undergo cis–trans isomerization in the presence of HgCl2. These results are surprising because the closely related PdCl2(Ph2P(CH2CH2O)nCH2CH2PPh2) (n = 3–5) metallacrown ethers exhibit both cis–trans and monomer–cyclic oligomer equilibria in solution, and cis-Mo(CO)4 (Ph2P(CH2CH2O)nCH2CH2PPh2) (n = 3–5) metallacrown ethers rapidly undergo cis–trans isomerization in the presence of HgCl2. The coordination of Li+ cations to the cis-Mo(CO)4(2...