Development of magnesium oxide–silver hybrid nanocatalysts for synergistic carbon dioxide activation to afford esters and heterocycles at ambient pressure,Green Chemistry

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Development of magnesium oxide–silver hybrid nanocatalysts for synergistic carbon dioxide activation to afford esters and heterocycles at ambient pressure
Green Chemistry ( IF 9.3 ) Pub Date : 2020-03-24 , DOI: 10.1039/c9gc04040d
Upasana Gulati _{1,

1,

2,

3,

4} , U. Chinna Rajesh _{1,

2,

3,

4} , Diwan S. Rawat _{1,

5,

6,

7} , Jeffrey M. Zaleski _{1,

2,

3,

4}

Affiliation

Multi-metallic hybrid nanocatalysts consisting of a porous metal oxide host and metal satellite guests serve as a scaffold for multi-step transformations of divergent and energy-challenging substrates. Here we have developed a 3D porous MgO framework (Lewis basic host) with Ag⁰ nanoparticles (noble metal guest) for ambient pressure activation and insertion of CO₂ into unsaturated alkyne substrates. The hybrid MgO@Ag-x (x = 2, 5, 7, 8 at% Ag) catalysts are synthesized by impregnating Ag⁺ ions in porous MgO cubes followed by reduction using NaBH₄. Morphological (SEM, TEM, EDX mapping) and structural (PXRD, XPS) characterization reveal that the micron-sized hybrid cubes derive from self-assembly of ∼100 nm (edge length) MgO cubes decorated with ∼5 to 25 nm Ag⁰ NPs. Detailed XPS analysis illustrates Ag⁰ is present in two forms, <10 nm NPs and ∼25 nm aggregates. The MgO@Ag-7 catalyst is effective for inserting CO₂ into aryl alkynes followed by S_N2 coupling with allylic chlorides to afford a wide range of ester and lactone heterocycles in excellent yields (61–93%) and with low E-factor (2.8). The proposed mechanism suggests a CO₂ capture and substrate assembly role for 3D porous MgO while Ag⁰ performs the key activation of alkyne and CO₂ insertion steps. The catalyst is recyclable (5×) with no significant loss of product yield. Overall, these results demonstrate viable approaches to hybrid catalyst development for challenging conversions such as CO₂ utilization in a green and sustainable manner.

中文翻译：

氧化镁-银杂化纳米催化剂的开发，用于在环境压力下协同活化二氧化碳以提供酯和杂环

由多孔金属氧化物主体和金属卫星客体组成的多金属杂化纳米催化剂用作发散性和挑战性底物的多步转化的支架。在这里，我们开发了3D多孔MgO框架（Lewis基本主体），该框架具有Ag ⁰纳米颗粒（贵金属客体），用于环境压力激活和将CO ₂插入不饱和炔烃基质中。通过将Ag ⁺离子浸渍在多孔MgO立方体中，然后使用NaBH ₄还原，可以合成MgO @ Ag- x（x = 2、5、7、8 at％Ag）杂化催化剂。形态（SEM，TEM，EDX映射）和结构（PXRD，XPS）表征表明，微米级混合立方体是由约100 nm（边缘长度）MgO立方体的自组装形成的，该立方体装饰有约5至25 nm Ag ⁰ NP。。XPS的详细分析表明，Ag ⁰以两种形式存在：<10 nm NPs和〜25 nm聚集体。MgO @ Ag-7催化剂可有效地将CO ₂插入芳基炔烃中，然后将S _N 2与烯丙基氯化物偶合，以优异的收率（61–93％）和低E因子提供广泛的酯和内酯杂环（2.8）。拟议的机制表明3D多孔MgO而Ag ^0时具有CO ₂捕获和基质组装作用执行炔烃和CO ₂插入步骤的密钥激活。催化剂是可回收的（5x），产物收率没有明显损失。总体而言，这些结果证明了开发混合催化剂的可行方法，用于以绿色和可持续的方式挑战性转化，例如CO _2的利用。

更新日期：2020-03-24

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