Amino acid-derived N-heterocyclic carbene palladium complexes for aqueous phase Suzuki–Miyaura couplings

Elliot Steeples,Alexandra Kelling,Uwe Schilde,Davide Esposito

doi:10.1039/c5nj03337c

Abstract

Five palladium complexes featuring N-heterocyclic carbene ligands derived from sustainable precursors have been synthesized and applied in aqueous Suzuki–Miyaura couplings.

Highlights

The current dependence of the chemical industry on petrochemically-derived solvents has sparked a recent movement in developing sustainable alternatives.[1]
Amino acid-derived N-Heterocyclic carbenes (NHCs) precursors have been documented for the synthesis of Au and Ru compounds,[34,35] but no examples of similar Pd–NHC complexes from amino-acid precursors have yet been developed to the best of our knowledge
Since initial attempts to directly complex these zwitterions to palladium were unsuccessful, conversion of these building blocks into suitable NHC precursors was performed via a simple esterification of the carboxylate arms in ethanol, using acetyl chloride as the source of both the acidic catalyst and the chloride counterion

Summary

Introduction

The current dependence of the chemical industry on petrochemically-derived solvents has sparked a recent movement in developing sustainable alternatives.[1] Water is one of the leading contenders,[2] alongside ionic liquids[3,4] and biomassderived solvents.[5,6] The drive to utilize water as a solvent is due to its large heat capacity, non-toxicity, thermal stability, and large abundance on the planet.[2,7] The issue of designing catalytic systems suitable for ‘‘in-water’’ and ‘‘on-water’’ organic synthesis still remains and has gained startling momentum within research.[8,9] The most popular approach of adapting metalcatalyzed processes for use in water is currently the coordination of water-soluble ligands to the metal centre appropriate for the reaction.[9,10] This approach facilitates simple separation of insoluble organic products from the water medium, allowing for the possible recycling of the catalytic water layer.[11] Notable examples of homogeneous catalysis in water include Ir in asymmetric hydrogenation,[12,13] Ru in olefin metathesis,[14,15] and the work on Pd catalyzed C–C coupling reactions.[16,17,18]

Methods

Results

Conclusion