Inexpensive, Operationally Simple Flow Reactor for Rapid, Chromatography Free Synthesis of Siloxane Based Liquid Crystals

We report on the hydrosilylation of terminal alkenes in flow using a “Karstedt-like” platinum-on-silica catalyst. A solution of alkene and siloxane in toluene was passed through the catalyst bed using a low pressure pump; the use of a high catalyst loading delivers quantitative β-addition of the siloxane to the alkene, hence the only purification required is removal of volatiles (toluene and siloxane). Following optimisation we synthesise a family of liquid crystalline siloxane terminated cyanobiphenyls, finding their properties to compare favourably to literature examples. The system and catalyst described is inexpensive, reusable, and chromatography free and thus prominently sustainable.