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首页> 外文期刊>Catalysis science & technology >Engineering regioselectivity in the hydrosilylation of alkynes using heterobimetallic dual-functional hybrid catalysts
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Engineering regioselectivity in the hydrosilylation of alkynes using heterobimetallic dual-functional hybrid catalysts

机译：使用异金属双功能混合催化剂的工程区域选择性

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The synthesis and characterization of carbon black supported rhodium and iridium heterobimetallic catalysts, termed hybrid catalysts, and their application in the hydrosilylation of alkynes is described. An aryl diazonium grafting procedure was applied to simultaneously immobilize Rh and Ir pyrazole–triazole complexes with tethers of varying lengths to carbon black, yielding the hybrid catalysts. The complexes differ in metal centre oxidation state and co-ligands, which are CO or Cp*Cl for the Rh complexes and Cp*Cl for the Ir complexes. The immobilization results in simultaneous surface binding and modification of the Rh complexes bearing CO-ligands. In this process, the CO ligands are removed and the overall structure of the catalytically active complex is altered. Analysis of the hybrid catalysts by XPS and SEM/EDX shows that the catalysts bear both surface bound Rh- and Ir-complexes. The Rh content is substantially higher than the Ir content. This is due to more efficient binding of the modified Rh complexes to the carbon black, as they feature two potential binding sites. Synchrotron based X-ray absorption spectroscopy (XAS) at the Rh K- and Ir L3 edges further confirms the presence of the surface bound metal complexes. There is no indication that the presence of a secondary metal affects the electronic structure of the adjacent metal in the systems under investigation, for either the long or short tether derivatives. The performance of the different catalysts was assessed for promoting the hydrosilylation of alkynes, an important industrially relevant reaction. All catalysts are highly efficient. The modified Rh sites are α-selective in the product formation on activation of terminal alkynes, while the RhCp*Cl and IrCp*Cl sites are β(Z)-selective. When operating at mild conditions with high metal loadings, the surface bound Rh catalyst is the active species, while the Ir sites are inactive. At a lower overall surface coverage or higher temperature, the Ir sites become active, which allows engineering of the regioselectivity by adjusting surface coverages and metal loadings.
机译：描述了碳黑色支持的若i支持的铑和虹膜杂金属催化剂，称为杂化催化剂，并描述了它们在炔烃的氢化硅酸化中的应用。采用了芳基的嫁接程序，以同时固定RH和IR吡唑 - 三唑络合物，其长度不同的碳黑色含量为黑色，从而产生混合催化剂。络合物在金属中心氧化态和共配体方面有所不同，RH复合物的CO或CP*CL和IR复合物的CP*Cl。固定化导致同时表面结合和带有共配体的RH复合物的修饰。在此过程中，去除了CO配体，并改变了催化活性复合物的整体结构。通过XPS和SEM/EDX对杂化催化剂的分析表明，催化剂均具有表面结合的RH-和IR-complexes。 RH含量大大高于IR含量。这是由于修饰的RH复合物与碳黑色的更有效结合，因为它们具有两个潜在的结合位点。基于同步加速器的X射线吸收光谱（XAS）在RH K-和IR L3边缘进一步证实了表面结合金属络合物的存在。没有迹象表明二级金属的存在会影响长或短的系绳衍生物中所研究系统中相邻金属的电子结构。评估了不同催化剂的性能，以促进炔烃的氢化化，这是一个重要的工业相关反应。所有催化剂均高效。修饰的RH位点在末端炔烃激活的产物形成中是α选择性的，而RHCP*Cl和IRCP*Cl位点是β（Z）的选择性。当在具有高金属载荷的轻度条件下运行时，表面结合的RH催化剂是活性物种，而IR位点不活跃。在较低的整体表面覆盖范围或更高的温度下，IR位点变得活跃，从而通过调节表面覆盖范围和金属载荷来工程区域选择性。

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