Synthesis of liquid crystals using Suzuki–Miyaura coupling reactions using mesoporous, ligand-free Pd/Si₃N₄ catalysts in aqueous media

Abstract

We report a ligand-free Pd/Si₃N₄ catalysed Suzuki–Miyaura aryl–aryl cross-coupling reaction using mixtures of water-miscible solvents, such as dimethoxyethane, ethanol and isopropanol with water and several bases, such as sodium carbonate and potassium phosphate. The reaction time and catalyst concentration were optimised and the heterogeneous nature of the reaction was investigated. The optimised reaction conditions were used to synthesise a standard liquid crystal using environmentally friendly solvents and a Pd/Si₃N₄ catalyst. This reaction is scalable to produce larger quantities.

Keywords:

• synthesis
• nematics
• heterogeneous catalysis
• mesoporous silicon nitride

Acknowledgements

We thank the EPSRC for the award of a postdoctoral Fellowship to Dr S.P. Kitney. We express our thanks to Dr R. Lewis (¹H NMR) and Dr K. Welham (MS) for spectroscopic measurements and Mrs J. Haley for the DSC measurement.