Studies on gold(II) complexes with hard and soft donor ligands. Part IV. A reactivity study in solution using EPR spectroscopy

The reactions of Au(II) complexes, cis-[Au(mta)2Cl]Cl (1a), trans-[Au(mta)2Cl]Cl (1b), [Au(mta)2Cl]2Cl2 (1c), Au(pma)Cl (2a), Au(pma)Br (2b) and Au2(pma)Cl4 (2c), where mta and pma are the deprotonated ligands of o-methylthioaniline (Hmta) and N-(2-pyridylmethyl)-2-mercaptoaniline (Hpma), respectively, are reported. When these complexes are reacted with selected ligands containing nitrogen donors, the resulting EPR spectra are indicative of coordination with the nitrogen of the incoming ligand. Both compounds 2a and 2c react with cysteine (cys) in DMF solution to produce the stable reaction product [Au(pma)(cys)]2 (2e), the EPR spectrum of which indicates the presence of two interacting gold(II) ions to form a dimeric system. A radical formed during the course of the reaction of 2c with CN- in DMSO solution which exhibits a multiline EPR spectrum with a g value of 2.003 may be due to the formation of pyridine-N-oxide anion radical subsequently stabilized by either DMSO complex formation and/or σ-bond formation to the central metal atom