Copper(I) catalyzed CO2 transformation: A density functional theory investigation

https://doi.org/10.1016/j.comptc.2020.112745Get rights and content

Highlights

  • A new strategy of CO2 transformation catalyzed by Cu(I) is presented.

  • The reaction of CO2 with the negative ions H/OH is investigated.

  • Transformation configurations of intermediates play an important role on obtaining the products.

Abstract

A new Cu(I) catalyzed CO2 transformation is investigated by using density functional theory. The new copper-catalyzed CO2 transformation utilizes the negative ions H/OH of the complex CuH/CuOH with the ligand 6,6′’-bis(2,4,6-trimethylanilido) terpyridine (H2TpyNMes), unlike the conventional coordination of CO2 to Cu. We find that the inactive CO2 can react with negative ions H/OH through a nucleophilic reaction to obtain respective product HCOOH/H2CO3, and the predicted rate-determining free energy barriers are 8.38 and 24.31 kcal/mol for negative ions H and OH, respectively. We expect that this work can provide an alternative of the CO2 transformation.

Introduction

Since carbon dioxide is an abundant, renewable carbon source and an environmentally friendly chemical reagent [1], [2], [3], [4], [5], [6], significant efforts have been devoted toward exploring new methods for CO2 transformation. A broad range of transition metals, such as middle − late 3d metals iron [7], cobalt [8], and copper [9], have been employed as catalysts in the reduction of CO2 to formic acid [10], [11], formaldehyde [12], methanol [13], methane [14], [15], and acetals [16]. Moreover, the key of performing the reductions is the activation of CO2, which is through the coordination of CO2 to transition metals. Of course, there are other methods without transition metals to reduce CO2, for example, Maeda et al reported the hydrogenation of carbon dioxide catalyzed by the pincer-type phosphorus, which provided an alternative of CO2 transformation [17].

In recent years, Cu-catalyzed CO2 transformation has gained increasing attention, due to the abundance and low cost of copper and the availability of well established syntheses for many types of copper-based metal–organic complexes [18], [19], [20], [21]. For example, Zhang reported a copper-catalyzed transformation of CO2 to carboxylic acids via Csingle bondH bond activation of terminal alkynes [22]. Nolan et al. have demonstrated the ability of NHC copper(I) hydroxide complexes to enable the regioselective carboxylation of Nsingle bondH and Csingle bondH bonds [23].

Herein, we are very interested in the work reported by Szymczak [24], where the square-planar coordination geometry of l-copper(I) complexes (L = 6,6′’-bis(2,4,6-trimethylanilido) terpyridine (H2TpyNMes)) with compensation halide ion (Cl, Br and I), have provide long Cu-halide bond, due to the NH-halide hydrogen bond interaction. The long Cu-halide bond with an active halide anion caught our attentions, as the active halide anion may provide a potential target for CO2 transformation.

In this work, we are further concerned with copper-based catalyzed CO2 reduction, and we would like to investigate the reaction of CO2 transformations catalyzed by the Cu(I) complex with ligand H2TpyNMes. Because the C-halide bond is unstable in acyl chloride, we do not intend to investigate the complexes of compensation halide ion. Instead, compensation ions H and OH are employed. From the application point of view, it is not economic for obtaining CuH/CuOH by using CuCl, but our investigation aims at developing new potential routes of CO2 transformation.

In H2TpyNMes-copper(I)-H (IIH) and H2TpyNMes-copper(I)–OH (IIOH)complexes, there is highly activated Cu-H and Cu-O bond, respectively, due to the action of the ligand, respectively. Therefore, it is expected that negative ion H/OH reacts with the C atom of CO2 to form Csingle bondH or Csingle bondO(H) bond, which promotes the CO2 transformation. The proposed reaction route is shown in Scheme 1. As far as we know, this way of CO2 transformation has not been reported, which is greatly different from the conventional copper-catalyzed CO2 transformations through CO2 activation.

Computational studies have helped to better understand and predict the mechanisms of CO2 transformations. For example, Lin et al. reported the reaction mechanisms for carboxylative-coupling reactions among terminal alkynes, allylic chlorides, and CO2 catalyzed by N-heterocyclic carbene copper(I) complex (IPr)CuCl [25]. Herein, with the aid of DFT calculations, we report our computational study on the reaction of CO2 transformations catalyzed by the Cu complex with ligands H2TpyNMes, and aim to provide a new feasible routes of CO2 transformation.

Section snippets

Computational details

Molecular geometries of all the model complexes were fully optimized without constraints via DFT calculations using the Becke3LYP (B3LYP) functional [26], [27] with 6-31G(d, p) basis set for all atoms. The reason why we chose DFT method B3LYP was that this method has been shown to be a good choice for studying Cu-catalyzed organic reactions [28], [29]. Moreover, B3LYP functional is tested to be reliable for our studied system though comparing with the results from B3LYP density functional

The active site in the complexes IIH and IIOH

First, the complexes H2TpyNMes-copper(I)-H (IIH) and H2TpyNMes-copper(I)–OH (IIoH) with the decrease of 29.24 and 32.16 kcal/mol in Gibbs energy are obtained through using H2TpyNMes-copper(I)-Cl as a precursor. Their structures are shown in Fig. 1. In IIH, the Cu-H bond length is longer by 0.13 Å than that of single CuH, and in IIOH, the Cu-O bond length is longer by 0.20 Å than that of single CuOH. Then, it suggests that the Cu-H bond and the Cu-O bond are activated. The distance of H-H1/H2 is

Conclusions

In summary, our computational study reports a new strategy of Cu catalyzed CO2 transformation. Two routes of the reactions CO2 with CuH and CuOH (with the ligand 6,6′’-bis(2,4,6-trimethylanilido) terpyridine (H2TpyNMes)) are depicted, respectively. The new copper-catalyzed CO2 transformation utilizes the negative ions H/OH to react CO2, which is different from the conventional CO2 transformations. Calculation results show that the Csingle bondH bond formation process (TSC-H) is the rate-determining step

CRediT authorship contribution statement

Mengyu Qi: Investigation, Data curation, Writing - original draft, Conceptualization, Methodology, Formal analysis. Chuankai Tang: Data curation, Writing - original draft, Conceptualization, Methodology, Formal analysis. Zhong-jun Zhou: Investigation, Resources, Writing - review & editing, Visualization, Project administration. Fang Ma: Conceptualization, Methodology, Investigation, Resources, Writing - review & editing, Project administration, Funding acquisition.

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.

Acknowledgements

This work was supported by the National Natural Science Foundation of China (No. 21303065), Anhui University Natural Science Research Project (No. KJ2017A388) and innovation and pioneering projects in Anhui Province (201610373043).

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