Simultaneous Dehalogenation and Hydrogenation in Sonogashira Coupling

We herein report a simultaneous dehalogenation and hydrogenation (DHH) reaction in Sonogashira coupling involving hexahalogenobenzene C6X6 (X = I, Br), in which a halogen on the aryl polyhalide substrate was substituted by a hydrogen atom. First, a steric bulky terminal alkyne 5 was designed and synthesized to study the influence of the reaction conditions (e.g., catalyst, solvent, temperature) and the halogens on the substrates C6X6 on the DHH reaction. Moreover, based on the optimized conditions, a terminal alkyne 6 with less steric hindrance was further synthesized to investigate the influence of alkyne on the DHH reaction. As a result, two aromatic polyynes 7 and 8 were obtained in the DHH process, and their photophysical properties were further studied and compared. The influence produced by the alkynes and aryl polyhalides substrate provide insights into Sonogashira coupling involving terminal alkyne with huge steric hindrance and polyhalogenated aromatic hydrocarbons.