Complexes of gold(III) with mononegative bidentate N,O-ligands

Abstract

Gold(III) complexes of a variety of deprotonatable bidentate N,OH ligands have been prepared by direct reaction with [AuX₄]^–(X = Cl or Br). Schiff-base ligands 2-HOC₆H₄CHNR, (R = Me, Et, Prⁱ, Buⁿ, CH₂Ph, or C₆H₁₁) give predominantly [Au(2-OC₆H₄CHNR)₂][AuCl₄]; the monomeric neutral form [AuCl₂(2-OC₆H₄CHNR)] is always a minor product. 2-Pyridyl-methanol and -ethanol (HL) give simple complexes [AuX₃(HL)] in the presence of excess of halide ion. These ligands and a range of substituted pyridine-2-carboxylic acids and quinolinecarboxylic acids (HL′) give mono- and bis-chelated complexes [AuX₂(L′)] and [AuL′₂]⁺. Some of the latter are capable of binding chloride ion to give five-co-ordinate complexes [AuCl(L′)₂]. When the ligand substituent is a hydroxy or carboxylic acid group another deprotonation step is possible to give neutral hydrogen-bonded polymeric [{AuL′(L′– H)}_n] or anionic [Au(L′– H)₂]^– complexes. Crystal structure data are reported for Na[Au(L′– H)₂]·4H₂O (HL′= pyridine-2,5-dicarboxylic acid) and [AuX₂(L′)](X = Cl or Br; HL′= pyridine-2-carboxylic acid: X = Cl, HL′= 3-hydroxypyridine-2-carboxylic acid), showing the expected square-planar geometry for gold with a trans arrangement for the bis(chelate).