Visible-light-driven Hydroamination of Alkynes over a New Type of Activated Carbon Immobilized Cu 2+ Photocatalyst
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doi: 10.1007/s40242-020-0166-3
Article
Visible-light-driven Hydroamination of Alkynes over a New Type of Activated Carbon Immobilized Cu2+ Photocatalyst GU Xianmo1, MA Pengwei1, LIU Pei1, WANG Ruiyi1, LI Xincheng1,2 and ZHENG Zhanfeng1,2* 1. State Key Laboratory of Coal Conversion, Institute of Coal Chemistry, Chinese Academy of Sciences, Taiyuan 030001, P. R. China; 2. Center of Materials Science and Optoelectronics Engineering, University of Chinese Academy of Sciences, Beijing 100049, P. R. China Abstract A new type of activated carbon immobilized copper(Cu/AC) photocatalyst was prepared by a facile impregnation-adsorption method, where Cu 2+ is chemically adsorbed by abundant oxygenated functional groups on large-surface-area activated carbon surface. Cu/AC exhibited good activity and selectivity to imine for the hydro amination of alkynes at 60 °C under visible light irradiation. The reaction is initialized by the activation of alkynes molecules at Cu active sites with the aid of light as evidenced by the solid-state NMR and laser photolysis measurements and the control experiments. This strategy for catalyst design is potentially extended to the immobilization of other metal homogeneous catalysts for various heterogeneous catalytic systems. Keywords Activated carbon; Copper; Hydroamination; Photocatalysis
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Introduction
The hydroamination of alkynes, that is to say, the direct addition of an N―H bond to a C≡C bond, plays a fundamental role in synthetic chemistry. This reaction can offer a convenient route for the synthesis of important fine chemicals and synthetic intermediates as an atom-economical reaction. However, the reaction is kinetically difficult due to the strong electrostatic repulsion between the N lone pair electrons of nucleophile and the π-electrons of alkynes, which makes it almost indispensable for a catalyst to involve[1,2]. Among various catalysts, the copper-based homogeneous catalysts have been widely used to catalyze the hydroamination of alkenes or alkynes[3―5]. Whereas homogeneous systems often have the problems of difficult recovery and product separation, so the application cost of homogeneous catalysts is expensive. Additionally, the residual catalysts in the products could result in low-quality products and environmental pollution. Therefore, it is desirable to heterogenize homogeneous catalysts in order to recycle catalyst and avoid contaminating reaction mixtures[6,7]. Although Cu2+ catalysts immobilized on various supports, such as molecular sieve have also been used as heterogeneous catalysts for the hydroamination of alkynes[8,9], high reaction temperature is needed. Recently, it is reported that the direct hydroamination of alkynes could be driven by visible light at ambient temperature over supported notable metal Au/TiO2[10]. Therefore, it is highly desirable to develop inexpensive copper heterogeneous photocatalyst for hydroamination reaction
working under mild condition. Activated carbon is widely applied as the support in heterogeneous systems, because of its low c
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