Among the wide spectrum of CO2 chemistry, its insertion to a substrate is particularly interesting as the process has 100% atomic economy. In recent years, direct carboxylation of terminal alkynes with CO2 (CTACO2) by its insertion to the C-H is drawing wide attentions because the resulted products, propiolic acids, are very important intermediates for the chemical and pharmaceutical industries. Previously, Ag(I) complex was established to be active for the CTACO2 reaction in a homogeneous catalysis regime. Based on related understandings, heterogeneous catalysts for the process were prepared. For example, it was reported that AgI can be directly used to catalyze CTACO2, but its efficiency is only moderate. More active catalysts were then developed by anchoring Ag(I)/Cu(I) onto polymerized backbones with N-heterocyclic carbine structures. As such, synergistic activation of alkynes and CO2 was achieved on metal and NHC sites, respectively, which greatly enhanced the yield. Inspired by this, herein we report a series of novel CTACO2 catalysts by loading Ag nano-particles onto ZIF-8 framework (Ag@Z8). The catalysts could be rapidly prepared by exchanging the Zn(II) ions in ZIF-8 by Ag(I) ions in methanolic solution. Reduction of the exchanged Ag(I) enabled the formation of highly dispersed metallic nano-particles, and the crystalline structure of ZIF-8 stayed intact. This guaranteed the preservation of advantages of the parent ZIF-8, e.g. high stability and more importantly, high porosity. N2 adsorption experiments indicated that the Ag@Z8 catalysts possessed large surface areas (over 1000 m2/g), which is important for enriching CO2 on the surface and facilitate its conversion. Consequently, very good yield of 3-phenylpropiolic acid could be achieved at mild conditions (Table 1).

Carboxylation of terminal alkynes with CO2 over Ag loaded ZIF-8

2019 Spring National Meeting

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