Synthesis and structural systematics of mixed triphenylphosphine/imidazole base adducts of silver(I) oxyanion salts†

Abstract

From the interaction between imidazole-type ligands B and [Ag(PPh₃)₄]X (X = NO₃, BF₄, ClO₄ or CF₃CO₂), [Ag(PCy₃)₂(NO₃)] and [Ag(PPh₃)X)] (X = NO₂ or CH₃SO₃), new ionic mononuclear [Ag(PR₃)_4–n(B)_n]⁺[X]^– (R = Ph or Cy) and neutral mono- ([Ag(PR₃)_3–n(B)_n(X)]) and di-nuclear ([{Ag(PPh₃)(B)(µ-X)}₂]) complexes have been obtained which have been characterized through elemental analysis, IR and far-IR, conductivity, ¹H NMR and in some cases also by vaporimetric molecular weight measurements and ³¹P NMR. Stoichiometries and molecular structures are dependent on the nature of the azole (steric hindrance and basicity), of the counter ion, and on the number of the P-donor ligands in the starting reactants. Solution data are consistent with a partial dissociation of complexes, occurring through breaking of both Ag–N and Ag–P bonds. The majority of the possible Ph₃P/imidazole base combinations have been characterized structurally by room-temperature single crystal X-ray studies, thus: [Ag(PPh₃)₃(4-Ph-im)]NO₃ (4-Ph-im = 4-phenylimidazole), [Ag(PPh₃)₂B₂]NO₃ for B = imidazole (Him) or 2-methyl-imidazole (2-Me-im), [Ag(PPh₃)(2-Me-im)₃][CF₃CO₂], [Ag(PPh₃)₂(2-Me-im)(O₂NO)], [{Ag(PPh₃)(1-Me-im)(µ-OSOCH₃O)}₂] and [{Ag(PPh₃)(Him)(µ-ONO)}₂]; the latter is a mixture of isomers in which one or both oxygen atoms of the anions interact with silver atoms. In the methanesulfonate complex the interactions of the anions with the silver may be regarded as a perturbation on a proto-linear P–Ag–N array (Ag–P,N 2.3662(6), 2.189(1) Å; P–Ag–N 144.28(6)°).