Heterogeneous catalysis by ultra-small bimetallic nanoparticles surpassing homogeneous catalysis for carbon–carbon bond forming reactions
Heterogeneous catalysis by ultra-small bimetallic nanoparticles surpassing homogeneous catalysis for carbon–carbon bond forming reactions
复制标题
超小双金属纳米粒子的多相催化超越均相催化的碳-碳键形成反应
DOI：
10.1039/d0nr04105j
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发表时间：
2020
期刊：
影响因子：
6.7
通讯作者：
El-Shall, M. Samy
中科院分区：
文献类型：
--
作者：
Norouzi, Nazgol;Das, Mrinmoy K.;Richard, Alexander J.;Ibrahim, Amr A.;El-Kaderi, Hani M.;El-Shall, M. Samy
钯催化的交叉偶联反应代表了当代有机合成的一个重大进展，因为这些反应在药物发现和开发领域具有战略重要性。负载型钯基催化剂在碳-碳键形成催化工艺中非常受欢迎，以确保催化剂的回收和再利用，同时防止产品污染。本文报道了以气相二氧化硅为载体的多相Pd基催化剂的开发，该催化剂具有与均相催化剂相匹配的高活性和选择性，消除了催化剂的浸出和烧结，并允许催化剂的有效回收。使用强静电吸附（SEA）将小于1.0重量%负载量的钯和贱金属（Cu、Ni或Co）含量沉积在中孔气相二氧化硅载体（表面积SABET = 350 m2 g-1）上，产生平均尺寸为1.3 nm的均匀合金化纳米颗粒。发现所有的CuPd/SiO2催化剂对Suzuki交叉偶联（SCC）反应具有高活性，其中CuPd/SiO2催化剂具有上级活性和稳定性。低CuPd/SiO2负载量（Pd：0.3mol%）在环境条件下在水/乙醇溶剂中在30分钟内完成溴苯和苯基硼酸向联苯的转化。相比之下，单Pd/SiO2（Pd：0.3mol%）在相同条件下在3小时内完成相同的反应。Pd与贱金属的组合有助于通过从贱金属向Pd的电荷捐赠来保持Pd 0状态，从而降低芳基卤化物氧化加成步骤的活化能。沿着其卓越的活性，CuPd/SiO2在60 °C的微波反应条件下具有280 000 h−1的周转频率（TOF），表现出优异的回收性能。 我们的研究表明，SEA是一个很好的合成策略，用于沉积超小的Pd基纳米粒子的多孔二氧化硅SCC。该途径不仅提供了高活性和耐烧结的催化剂，而且显著降低了催化剂中的Pd含量而不损害催化活性，使得催化剂对于大规模应用非常实用。
Palladium catalyzed cross-coupling reactions represent a significant advancement in contemporary organic synthesis as these reactions are of strategic importance in the area of pharmaceutical drug discovery and development. Supported palladium-based catalysts are highly sought-after in carbon–carbon bond forming catalytic processes to ensure catalyst recovery and reuse while preventing product contamination. This paper reports the development of heterogeneous Pd-based bimetallic catalysts supported on fumed silica that have high activity and selectivity matching those of homogeneous catalysts, eliminating the catalyst's leaching and sintering and allowing efficient recycling of the catalysts. Palladium and base metal (Cu, Ni or Co) contents of less than 1.0 wt% loading are deposited on a mesoporous fumed silica support (surface area SABET = 350 m2 g−1) using strong electrostatic adsorption (SEA) yielding homogeneously alloyed nanoparticles with an average size of 1.3 nm. All bimetallic catalysts were found to be highly active toward Suzuki cross-coupling (SCC) reactions with superior activity and stability for the CuPd/SiO2 catalyst. A low CuPd/SiO2 loading (Pd: 0.3 mol%) completes the conversion of bromobenzene and phenylboronic acid to biphenyl in 30 minutes under ambient conditions in water/ethanol solvent. In contrast, monometallic Pd/SiO2 (Pd: 0.3 mol%) completes the same reaction in three hours under the same conditions. The combination of Pd with the base metals helps in retaining the Pd0 status by charge donation from the base metals to Pd, thus lowering the activation energy of the aryl halide oxidative addition step. Along with its exceptional activity, CuPd/SiO2 exhibits excellent recycling performance with a turnover frequency (TOF) of 280 000 h−1 under microwave reaction conditions at 60 °C. Our study demonstrates that SEA is an excellent synthetic strategy for depositing ultra-small Pd-based bimetallic nanoparticles on porous silica for SCC. This avenue not only provides highly active and sintering-resistant catalysts but also significantly lowers Pd contents in the catalysts without compromising catalytic activity, making the catalysts very practical for large-scale applications.