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

Abstract

2-(3-Thienyl)pyridine (3-Hthpy) and 2-(2-thienyl)pyridine (2-Hthpy) reacted with Na[AuCl₄]·2H₂O to afford the adducts [AuCl₃(3-Hthpy)] 1a and [AuCl₃(2-Hthpy)] 1b, respectively. The cycloaurated complex [AuCl₂(3-thpy-C²,N)] [3-thpy = 3-(2-pyridyl)thiophen-2-yl] 2a was obtained by warming 1a at 80 °C in an acetonitrile–water (1∶5) mixed solvent, whereas the cycloaurated complex [AuCl₂(2-thpy-C³,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(µ-Cl)Cl[(2-thpy-C ⁵)H]}₂]Cl₂ [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-C¹,N)(PPh₃)]BF₄ 4a and [AuCl(3-thpy-C¹,N)(PPh₃)]BF₄ 4b, which were obtained by the reactions of 2a and 2b with triphenylphosphine, have been performed.