The chemistry of cyano complexes of gold(I) with emphasis on the ligand scrambling reactions

The gold(l) complexes, containing cyanide and some other ligand (L), {LAuCN} are stable in the solid state, while in solution they undergo dissociation to form ionic species. The X-ray and IR, studies show that some cyanogold(I) complexes exist as non-ionic complexes (LAuCN) and some as the ionic species {[Au(L-2)](+)[Au(CN)(2)](-)} in the solid state. In solution, the LAuCN complexes undergo ligand scrambling reactions exhibiting the equilibrium, 2[L-Au-CN]reversible arrow[AuL2](+) + [Au(CN)(2)](-). Equilibrium constants (K-eq) for the scrambling equilibria are determined by integration of the C-13 and P-31 NMR spectra. The equilibrium constant is dependent on such factors as the initial concentration of the complex, ionic strength of the solution, temperature and polarity of the solvent, with polarity of the solvent showing major influence on Keq. The order of ability of different L-Au-CN complexes undergoing disproportionation is: [>C=SeAuCN] > [R3PSeAuCN] > [>C=SAuCN] > [R3PAuCN] greater than or equal to [R3PSAuCN]. The reactions of gold drugs and their metabolites, with cyanide lead to the formation of intermediates, [RSAuCN](-) and [Et3PAuCN], which undergo disproportionation generating [Au(CN)(2)](-) that is readily taken up by red blood cells. The formation of aurocyanide is dependent on thiocyanate and occurs both by the myeloperoxidase dependent oxidation of thiocyanate and by a secondary reaction of hypochlorous acid with thiocyanate. [Au(CN)(2)](-) is a common metabolite of the gold drugs in the blood and urine of chrysotherapy patients. The oxidation of [Au(CN)(2)](-) by OCl- could lead to the formation of gold(III) metabolites. (C) 2003 Elsevier B.V. All rights reserved.