Elsevier

Molecular Catalysis

Volume 493, September 2020, 111042
Molecular Catalysis

Core-shell iron oxide@cathecol-polymer@palladium/copper nanocomposites as efficient and sustainable catalysts in cross-coupling reactions

https://doi.org/10.1016/j.mcat.2020.111042Get rights and content

Highlights

  • Magnetic core-shell Fe2O3@polymer-Pd/Cu nanocomposites.

  • Catalytically active metal nanoparticles (Pd and Cu NPs) at low metal content.

  • Highly active catalysts for Suzuki-Miyaura cross-coupling reactions (87-97%).

  • Cu-based NCs highly active (> 80%) in the synthesis of propargylamines.

  • NCs presented a good reusability.

Abstract

Magnetic core-shell Fe2O3@polymer-Pd/Cu nanocomposites (NCs) were developed as efficient and sustainable nanocatalysts for cross-coupling reactions. The designed NCs consisted of three components: i) a magnetic core (Fe2O3 nanoparticle), which allowed the recovery and reuse of the NCs, enhancing thus their attractiveness as green catalysts; ii) a catechol-based polymer coating, chosen because of its strong chelating ability towards metal ions, and its potential to be obtained from biomass (lignin depolymerization); and iii) catalytically active metal nanoparticles (Pd and Cu NPs) immobilized via in situ formation onto the polymeric shell. As-prepared Pd-based NCs successfully catalyzed Suzuki-Miyaura cross-coupling reactions, achieving yields between 87% and 97% in only 20–40 min depending on the aryl halides and boronic acid derivatives. Similarly, Cu-based NCs exhibited a quite good catalytic efficiency (> 80%) in the synthesis of propargylamines via A3 coupling reaction of phenylacetylene with various aldehydes and amines. Importantly, these NCs presented a good reusability, without significant decrease in efficiency after several cycles. However, the major advantage of the designed NCs is the lower Pd or Cu content (1.5 wt% and 2.6 wt%, respectively) as compared to most of the reported similar catalysts (between 3 – 6 wt% for Pd and > 5 wt% for Cu), which is a key challenge in view of developing cost-effective and environment-friendly catalysts while maintaining a high efficiency.

Section snippets

INTRODUCTION

Due to the increasing demand for sustainable chemical processes with improved efficiencies, minimization on the generation of waste, less energy consumption, and use of green conditions, much efforts have been focused on developing catalysts with improved activities and selectivity as well as with superior reusability and recyclability potential. In this context, the use of metal nanoparticles (NPs) as heterogeneous catalysts has emerged as a promising alternative towards a variety of chemical

Reagents and solvents

For the synthesis of Fe2O3 nanoparticles, hydrochloric acid (HCl, ACS reagent, ≥37%), ammonia (NH3, anhydrous, ≥99.95%), iron(III) chloride hexahydrate (FeCl3·6H2O) (≥98%, purified lumps), iron(II) chloride tetrahydrate (FeCl2·4H2O) (puriss. p.a., ≥99.0%), tetramethylammonium hydroxide (TMAOH, solution 25 wt.% in H2O) and ammonia solution (NH4OH, solution 25 wt.% in H2O) were obtained from Sigma-Aldrich. For the preparation of Fe2O3@CSF and Fe2O3@TCF supports, ethanol (EtOH) (anhydrous,

Design and synthesis of the NCs

The designed catalytic nanocomposites (NCs), two Pd-based NCs and one Cu-based NC, were prepared in three steps (cf., Scheme 1Scheme 1) according to the three main parts of the catalyst’s architecture: a magnetic core NP, a polymeric shell, and catalytically active metallic NPs on the support’s surface. First, superparamagnetic iron oxide NPs (Fe2O3 NPs) with a size of ca. 10 nm in diameter and maghemite structure as confirmed by XRD were synthesized via a co-precipitation method and calcined

CONCLUSIONS

A facile synthetic method to prepare core-shell magnetic Fe2O3@polymer-Pd/Cu nanocomposites with remarkable catalytic properties towards cross-coupling reactions was developed. The designed nanocomposites, Pd-based and Cu-based NCs, displayed high catalytic efficiency for Suzuki-Miyaura reactions and A3 coupling reactions, respectively, affording the desired cross-coupled products in excellent yields, even presenting lower metal loadings than commonly reported catalysts, and importantly

Declaration of Competing Interest

The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.

ACKNOWLEDGMENTS

A.R. gratefully acknowledges Sistan and Balouchestan University of Iran for the financial support, as well as Iran Nanotechnology Initiative Council for complementary financial supports. R.L. gratefully acknowledges MINECO as well as FEDER funds for funding under project CTQ2016-78289-P and financial support from the University of Cordoba (Spain). The publication has been prepared with support from RUDN University Program 5-100.

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