Layered Double Hydroxides as Bifunctional Catalysts for the Aryl Borylation under Ligand-Free Conditions

Lorenna Silva,Luiz Malta,Raphael Silva,Alexsandro Silva,José Campos,Vitor Ramos,Vinícius Neves,Jaqueline Senra

doi:10.3390/catal9040302

Abstract

Organic derivatives of boron, such as boronic esters and acids, are important precursors for a wide range of environmental, energy, and health applications. Several catalytic methods for their synthesis have been reported, even though with the use of toxic and structurally complex ligands. Herein, we demonstrate preliminary studies envisaging the synthesis of boronic esters from an inexpensive catalytic system based on Cu/Al layered double hydroxides (LDH) in the presence of Na2PdCl4. The Cu/ Al LDHs were prepared according to coprecipitation method and characterized by X-ray diffraction (XRD) (with Rietveld refinement) to evaluate the contamination with malachite and other phases. Preliminary catalytic results suggest that pure Cu/Al LDH has potential for the borylation of aryl iodides/ bromides in the absence of base. Indeed, a synergic effect between copper and palladium is possibly related to the catalytic efficiency.

Highlights

Organoboron compounds have received great attention in last years due to significant impact in analytical [1], technological [2], and medicinal fields [3]
The key points examined here are the influence of layered double hydroxides (LDH) purity and the catalytic conditions towards the
A set of conditions were varied to accomplish the synthesis of the Cu/Al LDH

Summary

Introduction

Organoboron compounds have received great attention in last years due to significant impact in analytical [1], technological [2], and medicinal fields [3]. Low-weight compounds containing boronic acid/ester moieties have played an important role in the synthesis of new hybrid materials, sensors and complex organic molecules, through synthetic protocols such as Suzuki–Miyaura reactions. Mild and selective synthesis of boronic acids and esters still represent a challenge. The classic reactions involving the generation of organometallics (e.g., arylmagnesium or aryllithium) followed by the reaction with a borate have been substituted by catalytic protocols [4]. Most of them suffer from low reactivity/selectivity along with relatively high costs of the boron reagents. Some advantages of the catalytic protocols are the improved reaction selectivity and the possibility of the whole system reuse. Since the general steps for the catalytic synthesis of boronic acids and esters involve a sequence of oxidative addition and reductive elimination, several

Methods

Results

Conclusion