Gold(III) diazonium complexes were synthesized for the first time and studied for electrochemical reductive grafting. The diazonium complex [CN-4-C6H4N N]AuCl4 was synthesized by protonating CN-4-C6H4NH2 with chloroauric acid H[AuCl4]center dot 3H(2)O to form the ammonium salt [CN-4-C6H4NH3]AuCl4, which was then oxidized by the one-electron oxidizing agent [NO]PF6 in CH3CN. The highly irreversible reduction potential of 0.1 mM [CN-4-C6H4N N]AuCl4 observed at -0.06 V versus Ag/AgCl in CH3CN/0.1 M [Bu4N]PF6 encompasses both gold(0) deposition and diazonium reduction. Repeated scans showed the absence of the reduction peak on the second run, which indicates that surface modification with a blocking gold aryl film has occurred and is largely complete.