Organogold(III) complexes derived from auration reactions of thienyl-substituted pyridine derivatives

2-(3-Thienyl)pyridine (3-Hthpy) and 2-(2-thienyl)pyridine (2-Hthpy) reacted with Na[AuCl4]. 2H(2)O to afford the adducts [AuCl3(3-Hthpy)] 1a and [AuCl3(2-Hthpy)] 1b, respectively. The cycloaurated complex [AuCl2(3-thpy-C-2,N)] [3-thpy=3-(2-pyridyl)thiophen-2-yl] 2a was obtained by warming 1a at 80 degrees C in an acetonitrile-water (1:5) mixed solvent, whereas the cycloaurated complex [AuCl2(2-thpy-C-3,N)] [2-thpy= 2-(2-pyridyl)thiophen-3-yl] 2b was produced by the reaction of 1b with silver(I) tetrafluoroborate in refluxing dichloromethane. Moreover, when 1b was heated at reflux in dichloromethane in the absence of silver(I) tetrafluoroborate, the thiophene-C(5) metallated species [{Au(mu-Cl)Cl[(2-thpy-C-5)H]}(2)]Cl-2 [2-thpy=2-(2-pyridyl)thiophen-5-yl] 3b was formed. Thermal degradation of 3b in aqueous acetonitrile yielded 2-(5-chloro-2-thienyl)pyridine and 5,5'-bis(2-pyridyl)-2,2'-bithienyl. X-Ray structural analyses of [AuCl(3-thpy-C-1,N)(PPh3)]BF4 4a and [AuCl(3-thpy-C-1,N)(PPh3)]BF4 4b, which were obtained by the reactions of 2a and 2b with triphenylphosphine, have been performed.