Copper(I)-modified covalent organic framework for CO2 insertion to terminal alkynes

DOI: 10.1016/j.mcat.2020.111319

Source and publish data:

Molecular catalysis (2021)

Update date:2022-08-28

Topics:

Authors:

Bu, Ran Bu, Ran

Zhang, Lin

Gao, Lu-Lu

Sun, Weng-Jie

Yang, Shuai-Liang

Gao, En-Qing

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Article abstract of DOI:10.1016/j.mcat.2020.111319

The carboxylation of terminal alkynes with CO₂ is an attractive route for CO₂ fixation and conversion, and various homogeneous Cu(I) catalysts have been explored for the reaction. However, it is still a challenge to develop efficient heterogeneous catalysts for the conversion under mild conditions. Considering that covalent organic frameworks (COFs) are emerging as versatile platforms for the design of functional materials, we developed a TpBpy-supported Cu(I) catalyst, where TpBpy is a stable imine-type porous COF furnished with rich N,N- and N,O-chelating sites for Cu(I) immobilization. The hybrid material can efficiently catalyze the conversion of CO₂ and terminal alkynes to propiolic acids under relatively mild conditions (1 atm CO₂, 60 ℃). The catalytic activity arises from the synergy between the organic framework of TpBpy and the Cu(I) sites. Not merely serving as a porous support to afford isolated and accessible Cu(I) sites, the organic framework itself has its own catalytic activity through the polar and basic N and O functional sites, which could activate the C–H bond and facilitate CO₂ absorption. In addition, the framework also serves as a giant ligand to shift the reversible Cu(I)-catalyzed process in favor of carboxylation. The catalyst shows somewhat reduced activity after reused for three cycles owing to the oxidation of Cu(I) to Cu(II), but it can be easily regenerated by treating with KI.

Full text of DOI:10.1016/j.mcat.2020.111319

Molecular Catalysis xxx (xxxx) xxx

Contents lists available at ScienceDirect

Molecular Catalysis

journal homepage: www.journals.elsevier.com/molecular-catalysis

Copper(I)-modiﬁed covalent organic framework for CO₂insertion to

terminal alkynes

Ran Bu, Lin Zhang, Lu-Lu Gao, Weng-Jie Sun, Shuai-Liang Yang, En-Qing Gao*

Shanghai Key Laboratory of Green Chemistry and Chemical Processes, School of Chemistry and Molecular Engineering, East China Normal University, Shanghai 200062,

China

A R T I C L E I N F O

A B S T R A C T

Keywords:

The carboxylation of terminal alkynes with CO₂is an attractive route for CO₂ﬁxation and conversion, and

various homogeneous Cu(I) catalysts have been explored for the reaction. However, it is still a challenge to

develop efﬁcient heterogeneous catalysts for the conversion under mild conditions. Considering that covalent

organic frameworks (COFs) are emerging as versatile platforms for the design of functional materials, we

developed a TpBpy-supported Cu(I) catalyst, where TpBpy is a stable imine-type porous COF furnished with rich

N,N- and N,O-chelating sites for Cu(I) immobilization. The hybrid material can efﬁciently catalyze the conver-

sion of CO₂and terminal alkynes to propiolic acids under relatively mild conditions (1 atm CO₂, 60 ℃). The

catalytic activity arises from the synergy between the organic framework of TpBpy and the Cu(I) sites. Not

merely serving as a porous support to afford isolated and accessible Cu(I) sites, the organic framework itself has

its own catalytic activity through the polar and basic N and O functional sites, which could activate the C–H bond

and facilitate CO₂absorption. In addition, the framework also serves as a giant ligand to shift the reversible Cu

(I)-catalyzed process in favor of carboxylation. The catalyst shows somewhat reduced activity after reused for

three cycles owing to the oxidation of Cu(I) to Cu(II), but it can be easily regenerated by treating with KI.

Covalent organic frameworks

Terminal alkyne

Carboxylation

Acetylenic acid

Heterogeneous catalysis

Copper

1. Introduction

actually thermodynamically unfavorable [11]. The situation can be

reversed in the presence of a base (e.g., Cs₂CO₃), but the reaction still

Carbon dioxide (CO₂) has long blamed as the main cause of global

warming with the industrialization [1,2], and it has also been deemed as

a cheap, non-toxic, abundant, and renewable C1 source for synthesis of

high value-added chemicals and fuels [3,4]. Among various methodol-

ogies for chemical ﬁxation and conversion of CO₂, direct C–H carbox-

ylation of terminal alkynes with CO₂has attracted increasing attention

in recent years. The reaction represents a straightforward approach to-

ward propiolic acids, which are important intermediates for synthesis of

ﬁne chemicals, pharmaceuticals and functional polymers [5–7].

Compared to conventional approaches toward propiolic acids (oxidation

of propargylic alcohols or propiolaldehydes [8], hydrolysis of corre-

sponding esters [9], and carboxylation of moist-/air-senstive

metal-alkylides [10]), direct carboxylation of terminal alkynes not only

provides a promising route for conversion and utilization of CO₂but also

has some other advantages such as high atom economy, saving of pre-

functionalization steps, and potential compatibility with various func-

tional groups. However, due to the high stability of CO₂, the reaction is

suffers from the sluggish kinetics. Therefore, many efforts have been

devoted to catalytic reactions under milder conditions. The efﬁcient

homogeneous catalysts thus far reported are mainly Cu(I) [12] and Ag(I)

[13] species (complexes with N-chelates [14] or N-heterocyclic carbenes

[15], and simple Ag(I) salts [16]), with sparse other examples. However,

homogeneous catalysts complicate product separation and puriﬁcation,

and they are often difﬁcult or unable to be reused, which reduces the

total atom economy. Therefore, increasing attention is being paid to the

development of heterogeneous catalysts for the reaction. While the

studies are overwhelmingly focused on silver nanoparticles composited

with various solid supports, such as organic polymers [7,17,18] and

metal-organic frameworks (MOFs) [5,19,20], very few heterogeneous

catalysts using the cheaper copper have been reported, including

MIL-101-supported Pd–Cu nano-alloy [21], ZnO-supported CuBr [22],

and Cu(I)-doped carbon nitride-based single-atom catalysts [23]. How-

ever, these catalytic systems are still not satisfactory in some aspects

such as the use of precious metal, the decaying activity in recycling, and

* Corresponding author at: Shanghai Key Laboratory of Green Chemistry and Chemical Processes, College of Chemistry and Molecular Engineering, East China

Normal University, Shanghai 200062, China.

E-mail address: eqgao@chem.ecnu.edu.cn (E.-Q. Gao).

https://doi.org/10.1016/j.mcat.2020.111319

Received 22 September 2020; Received in revised form 5 November 2020; Accepted 12 November 2020

Please cite this article as: Ran Bu, Molecular Catalysis, https://doi.org/10.1016/j.mcat.2020.111319

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Molecular Catalysis, Corrected proof, 111319. doi:10.1016/j.mcat.2020.111319

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