Water-soluble SNS cationic palladium(II) complexes and their Suzuki-Miyaura cross-coupling reactions in aqueous medium.

Alphonse Fiebor,Henok H Kinfe,Richard Tia,Banothile C E Makhubela

doi:10.3762/bjoc.14.160

Abstract

Unlike their SCS analogues, SNS pincer complexes are poorly studied for their use in coupling reactions. Accordingly, a series of water soluble cationic Pd(II) SNS pincer complexes have been successfully synthesised and investigated in detail for their catalytic activity in Suzuki–Miyaura coupling reactions. By using only 0.5 mol % loading of the complexes, the coupling of inactivated aryl bromides and activated aryl chlorides with various boronic acids in water was achieved in excellent yields and the catalysts were found to be reusable for three cycles without a significant loss of activity. The investigation of the mechanism of the reaction revealed that a Pd(II) to Pd(IV) route is the more likely pathway which was further supported by computational studies.

Highlights

The Suzuki–Miyaura C–C coupling reaction is a powerful method for the synthesis of ubiquitous biaryls and has been extensively employed in the synthesis of natural products, pharmaceuticals, agrochemicals, and polymers
The commonly employed phosphorous and carbene ligand-based palladium(II) complexes are found to be in most cases sensitive to moisture and air limiting the scope of their catalytic application in aqueous reactions [32,33]
Complex 17b was synthesised and characterised successfully while ligands 19c and 19d possessing the electron-donating thioether side groups favoured the formation of the corresponding pincer complexes 17c and 17d directly without formation of an isolable bidentate intermediate observed during the synthesis of complexes 17a and 17b

Summary

Introduction

The Suzuki–Miyaura C–C coupling reaction is a powerful method for the synthesis of ubiquitous biaryls and has been extensively employed in the synthesis of natural products, pharmaceuticals, agrochemicals, and polymers. We report the synthesis of the SNS Pd(II) pincer complexes and their interesting catalytic activities in the Suzuki–Miyaura cross coupling reactions in neat water.

Results

Conclusion