Electrochemistry of Au-complexes

The redox chemistry of Au(I) and Au(III) complexes PPN[AuCl2] (1), PPN[AuCl4] (2), Bu4N[Au(C6Cl5)(2)] (3), Bu4N[Au(C6F5)(2)] (4), Au(C6F5)(3)THT (5), Bu4N[Au(C6F5)(2)Cl-2] (6), Bu4N[Au(C6F5)(3)Br] (7), Bu4N[Au(C6F5)(3)I] (8), Au(PPh3)Cl (9), Au(PPh3)(acac) (10), Au(THT)Cl(11), (AuCl)(2)dppm (12), (AuCl)(2)dppe (13), and Au(AsPh3)Cl(14) was studied by cyclic voltammetry in CH2Cl2 and in part acetonitrile. Reduction of Au(III) -->Au(I) was observed for Au(III) complexes and reduction of Au(I) --> Au(0) for most of the Au(I) complexes. Anodic dissolution of an Au(0) film on Pt requires either high Cl- concentration or the presence of a stabilizing ligand such as PPh3. Peak potentials of - 0.1 and - 0.7 V versus SCE for the successive reduction of 2 are in contrast to the reduction peaks at - 2 V for 9 and < - 2.6 V for 3, the other complexes lying in between. The order of stabilization of both oxidation states is C6F5 > C6Cl5 >> Cl for anionic and PR3 >> tetrahydrothiophene (THT) for neutral ligands. Short lived intermediates in the Au(III) --> Au(I) reduction were observed in the case of 2 and 7. (C) 1999 Elsevier Science S.A. All rights reserved.