Synthesis and reactions of 1,10-phenanthroline-2(1H)-thione: a facile synthesis of 2,2′-thiobis-1,10-phenanthroline

Treatment of 2-chloro-1,10-phenanthroline with NaSH hydrate in DMF, Na2S nonahydrate in DMF or thiourea in refluxing ethanol readily afforded 1,10-phenanthroline-2(1H)-thione. This thione undergoes reaction with 1,2-dibromoethane to yield a thiazole bromide salt. Upon heating the thione in diphenyl ether with 2-chloro-1,10-phenanthroline, the hydrochloride salt of 2,2′-thiobis-1,10-phenanthroline precipitated and could be converted into the corresponding free base on treatment with aqueous base. Heteroaryl substituted sulfides could be prepared by treatment of 2-chloro-1,10-phenanthroline with pyridine-2-thione or pyrimidine-1-thione with potassium carbonate in DMF.