Abstract

The electrochemical behaviour of a series of neutral and cationic N-C and N-N-C cyclometallated gold(III) species: ([Au(py¹)(Cl)₂], Hpy¹=2-benzylpyridine; [Au(bipyⁿ)(Cl)][PF₆], Hbipy¹=6-benzyl-2,2′-bipyridine, Hbipy²=6-(1-methylbenzyl)-2,2′-bipyridine, Hbipy³=6-(1,1-dimethylbenzyl)-2,2′-bipyridine, Hbipy⁴=6-phenyl-2,2′-bipyridine) has been investigated in different solvent systems using cyclic voltammetry and controlled-potential coulometry. All the species considered show, in cyclic voltammetry, an irreversible one-electron reduction in the potential range -0.9/-1.2 V versus Fc^+/0, using a Pt electrode. On the other hand, exhaustive coulometries have shown the consumption of a number of Faraday per mole within the range 1-2. The very complex decomposition of the electrogenerated species affords elemental gold and significant amounts of different gold by-products. In some situations (e.g. reduction of [Au(bipy⁴)(Cl)][PF₆]), working with 0.1 mol dm^-3 Na[PF₆], CH₃CN solvent system, it has been possible to characterise the most abundant gold(III) compound, by NMR, FAB-MS, and elemental analysis. The analytical and spectroscopic data provide evidence for the N-C bis-cyclometallated gold(III) derivative (e.g. [Au(bipy⁴)₂][PF₆]); the result entails quite an unusual transcyclometallation process. The same compound can also be obtained, albeit in very minor yield, by chemical reduction of [Au(bipy⁴)(Cl)][PF₆].

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