Efficient Suzuki-Miyaura cross-coupling reaction by loading trace Pd nanoparticles onto copper-complex-derived Cu/C-700 solid support

https://doi.org/10.1016/j.jcis.2021.10.174Get rights and content

Highlight

  • The development of efficient carbon-carbon cross-coupling catalysts with low noble metal amounts.

  • The Cu/C-700/Pd nanocomposite is obtained by loading trace Pd2+ onto carbon support derived from a novel mononuclear copper complex.

  • The Cu/C-700/Pd nanocomposite shows excellent catalytic activity and selectivity in Suzuki-Miyaura cross-coupling reaction, which implied a good synergistic effect in the bimetallic composite catalyst.

  • The bimetallic composite catalyst has excellent stability and recyclability.

Abstract

The development of efficient carbon–carbon cross-coupling catalysts with low noble metal amounts attracts much attention recently. Herein, a Cu/C-700/Pd nanocomposite is obtained by loading trace Pd2+ onto carbon support derived from a novel mononuclear copper complex, {[Cu(POP)2(Phen)2]BF4}. The as-prepared nanomaterial features the facial structure of highly dispersed copper phosphide nanoparticles as well as Pd nanoparticles via neighboring Cu-Pd sites. The Cu/C-700/Pd nanocomposite shows excellent catalytic activity (99.73%) and selectivity in Suzuki-Miyaura cross-coupling reaction, at trace Pd loading (0.43 mol%). Compared with the reported palladium nano catalysts, its advantages are proved. The appealing gateway to this stable, innovative and recyclability, Cu/C-700/Pd nanostructure recommends its beneficial utilization in carbon–carbon coupling and other environmentally friendly processes.

Introduction

Carbon-based nanomaterials aroused widespread concern owing to their outstanding optical, electronic, mechanical characteristics, which were comprehensively used as absorbents, electrode materials, and catalyst supports [1], [2], [3], [4]. Extensive strategies have been devoted to preparing carbon-based nanomaterials, including chemical vapor decomposition, template synthesis, nanocasting, chemical or physical activation methods, and so on [5], [6], [7], [8], [9]. With the high specific surface area, carbon-based nanomaterials also can strongly interact with metal atoms, which could effectively inhibit the aggregation of metal nanoparticles. Meanwhile, the carbon-based support exhibit high electron mobility and a flexible surface to allow high loading of catalytic sites, which are beneficial to increase the contact area between the substrate and the active site, thus improving the catalytic activity. Over the past decade, carbon materials have been demonstrated as excellent hosts and their derivatives were applied in diverse catalytic fields, such as carbon dioxide electro/photo-reduction, organic wastewater treatment, selective hydrogenation, photocatalytic H2 production and cross-coupling reactions [10], [11], [12], [13], [14], [15], [16], [17], [18], [19]..

Suzuki-Miyaura cross-coupling (SMC) reactions representing a versatile strategy for the construction of Csingle bondC bonds in organic chemistry have made great progress, which have been widely used in the fields of material science, medicine, natural product synthesis, catalysis, and so on. Among many catalysts, homogeneous palladium catalysts (especially the palladacycles complexes) were generally considered to be the most promising candidates for SMC reaction [20], [21], [22], [23]. The homogeneous metal complexes have high selectivity due to the steric and electronic effect of ligands, but suffering from separation and recyclability difficulties and product pollution. Fortunately, heterogeneous catalysts anchoring evenly distributed well-defined metal sites on supports achieve the merits of outstanding recyclability and stability, which could provide ideal platforms for organic reaction. It has been demonstrated that heterogeneous palladium catalysts supported on carbon-based materials showed high-performance for SMC reactions [24], [25], [26]. However, this kind of catalyst inevitably consumed a large amount of precious metal palladium compounds, resulting in a great degree of environmental problems and resource waste because of its toxicity and scarcity. Therefore, it is highly desirable to reduce the amount of noble metal palladium and choose non-precious metal to substitute palladium partly or completely for SMC reactions. How to reduce the dosage of palladium or substitute non-precious metal for palladium without loss of performance is now of the greatest concern in academia.

To solve this problem, some research groups have made progress in developing non-precious metal catalysts for SMC reactions [27], [28], [29]. Among these non-precious metal catalysts, copper-based materials show great potential for SMC reactions due to their low cost and high activity. In this regard, Rothenberg and co-works for the first time corroborated that non-precious copper nanocluster catalysts could effectively catalyze SMC reactions and achieve high catalytic conversion [28]. Mingming Huang and co-workers confirmed that copper catalyst showed good catalytic performance in Heck, Sonogashira and Suzuki cross-coupling reactions, and had the ability to completely or partially replace precious metal palladium catalyst [30]. Brijesh S. Kadu system summarizes the advantages of copper as catalyst in SMC reaction, which can replace precious metal palladium catalyst [31]. Their discoveries paved the way to utilize the non-precious catalyst instead of palladium for SMC reactions. Despite great efforts, few results can achieve satisfactory catalytic performance and durability, because the intrinsic catalytic activity of non-precious metals is relatively low.

The metal complexes are a class of compounds with characteristic chemical structure, which is formed by the metal nodes and the organic ligands surrounding it completely or partially through the coordination bond. The metal-organic frameworks (MOFs) are preferable catalyst templates due to their metal centers, ordered porous structure, and functional organic linkers. Some catalysts have been obtained by using MOFs as the precursor and used in the field of catalysis [32], [33], [34]. Xu et al [35] used MOF-5 as a template to prepare nanoporous carbon materials, which exhibits excellent electrochemical performance as an electrode material for an electrochemical double-layered capacitor. Inspired by this, we consider that it is possible to use the non-precious metal complexes with the similar structure as the precursor to prepare catalysts to induce SMC reactions. The mononuclear metal complex as the precursor has the following advantages: (1) The metal particles would have small size and evenly distribution for the metal ions are surrounded with organic ligands preventing their aggregation and growth, which can effectively increase the active sites and contact area with the substrate. (2) Through pyrolysis of metal complex, organic ligands can be used as the source of carbon, leading to directly production of metal/carbon composite. The dispersion and size of the metal/carbon materials prepared by this method are better than those through post loading with metal. (3) More importantly, the good electron transport performance between the uniformly dispersed metal particles and the carbon substrate could significantly enhance the catalytic activity.

Our interest in copper-catalyzed SMC reactions prompted us to consider the possibility of taking advantage of the mononuclear copper complex as the precursor, although similar examples are rarely reported. The structure of the mononuclear copper complex is not only conducive to the formation of dispersed copper nanoparticles after high-temperature calcination, but also the preparation of copper complex is relatively simple compared with the traditional palladium complex and greatly reduces the cost. The previously reported routes for synthesizing heterogeneous catalysts for SMC reactions involve tedious fabrication process and are also difficult to achieve mass production. Herein, a simple method for preparing Cu/C composites with copper complex [Cu(POP)2(Phen)2]BF4 as the precursor is proposed and shown in Scheme 1. Due to the organic ligands (POP and Phen) coordinated with copper ions in copper complexes, the aggregation could be effectively prevented during thermal polymerization, thus copper species will be uniformly dispersed. By pyrolysis of the precursor, the organic ligand formed carbon substrate, on which copper ions were in situ reduced. The full exposure of small size copper particles could effectively contact the reaction substrate, thus improving the catalytic activity of the catalyst. Furthermore, we also tried to load a very small amount of palladium on the Cu/C composite. As expected, the results showed that a small amount of palladium was loaded on the Cu/C-700 surface to form a bimetallic synergistic effect, which greatly improved the catalytic activity of the catalyst for SMC reactions.

Section snippets

Materials

Tetrakis (acetonitrile) copper (Ⅰ) Tetrafluoroborate (98%), Bis[2-(diphenyl-phosphine)- phenyl] ether (abbreviated as POP) (98%), 1,10-phenanthroline (abbreviated as Phen), Phenylboronic acid (99%), Iodobenzene and Potassium carbonate (99.5%) were purchased from J&K SCIENTIFIC LTD. N, N-Dimethyl formamide (DMF) and Dichloromethane (DCM) were purchased from Tianjin Kermel limited company. No further purification is required for all commercially available reagents in the experimental process.

Preparation of the copper complex

Catalysts caracterization

Mononuclear copper complexes were used as precursors to synthesize copper/carbon composites. The novel the tetra-coordinated copper complex, [Cu(POP)2(Phen)2]BF4, was synthesized using [Cu(NCCH3)4]BF4, POP and Phen by facile ion-exchanging reaction at 293 K. The crystallographic structure of the complex was successfully obtained. Figs. S1 and S2 showed their ORTEP plots featuring 2D laminar stacking structure. It adopted a tetrahedral geometry around the CuI center with N–Cu–N and P–Cu–P angles

Conclusions

In summary, a Cu/C composite with uniform Cu dispersion was successfully prepared by the facile method of high-temperature calcination of copper complex. The small size of copper particles and the tight contact with the carbon support endowed a good catalytic activity in SMC reactions. Then, the Pd nanoparticles were easily introduced under photo-induced deposition, with ultralow Pd loading amounts. Remarkably, the yield and selectivity of SMC reaction were further improved in the Cu/C-700/Pd

CRediT authorship contribution statement

Longjiang Sun: Conceptualization, Methodology, Software, Investigation, Writing – original draft. Qi Li: Investigation, Visualization. Mang Zheng: Investigation, Data curation, Formal analysis. Siying Lin: Validation, Software. Changliang Guo: Writing – review & editing, Supervision. Laiyu Luo: Writing – review & editing, Supervision. Shien Guo: . Yuxin Li: Resources, Writing – review & editing, Supervision, Data curation, Funding acquisition. Cheng Wang: Resources, Writing – review & editing,

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.

Acknowledgment

This work was supported by the National Natural Science Foundation of China (51973051, 819611380, 21771061), Outstanding Youth Fund of Heilongjiang Province (JQ 2020B002), Natural Science Foundation of Jiangxi Province (20202BABL213002) and the Education Department of Jiangxi Province (No. GJJ191703).

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