含氮多齿配体修饰的Rh单原子催化剂在芳基乙烯氢甲酰化反应中的研究

2-Arylpropanals produced via hydroformylation of arylethenes, were considered as the key intermediates in the synthesis of antiinflammatory drugs 2-arylpropanoic acids, and the hydroformylation step was a hot problem both in homogeneous and heterogeneous catalysis all the way. Rh single atom catalyst presented high activity comparable to homogeneous Rh complex catalysts due to the extremely high utilization of Rh atoms and the intrinsic reactivity. The limitation of Rh single atom catalyst was the poor regioselectivity to 2-arylpropanals. The aim of this research is to provide a new strategy for building up a pseudo-homogeneous catalyst system: the combination of Rh single atom catalyst with multidentate nitrogenous ligands. The Rh single atom catalyst with identical active sites was preprared at first, and then multidentate nitrogenous ligands were introduced to coordinate with Rh single atoms forming an analogy of homogeneous “metal center -ligands” structure. Thus, the chemical environment of Rh single-atom active sites can be tuned by the structure change of nitrogenous ligands. To aim for an efficient catalytic system with high activity and regioselectivity, the coordination mode between nitrogenous ligands and Rh single atoms is of essential importance, and moreover, the investigation of the key factor that dominates the regioselectivity though mechanism study is strongly emphasized. We open up a new route for the reaction in which single atom catalyst is used instead of homogeneous catalyst.

芳基乙烯氢甲酰化产物2-芳基丙醛是合成非甾体抗炎药2-芳基丙酸的关键中间体，是均相和多相催化领域共同关注的热点问题之一。Rh单原子催化剂以其高原子利用率高本征反应活性的特点在芳基乙烯氢甲酰化反应中表现出与均相催化剂相媲美的活性，但对2-芳基丙醛的选择性亟待提高。对此我们提出“Rh单原子催化剂+含氮多齿配体”均多相融合的研究策略：首先制备具有均一活性中心的Rh单原子催化剂，然后利用含氮多齿配体与Rh单原子配位，在多相催化剂表面建立类似均相催化剂的“金属中心原子-配体”结构，并通过含氮配体来调控Rh单原子周围的化学环境。本项目的关键在于明确含氮配体与Rh单原子的配位作用机制，争取在反应机理层面认识影响氢甲酰化反应区域选择性的关键因素，以期在保留Rh单原子催化剂高活性的同时，达到提高2-芳基丙醛选择性的目的。本研究的实施将为今后单原子催化剂替代其它均相络合物催化剂的研究提供借鉴。

利用均多相融合的策略合成了一种P修饰的Rh单原子催化剂Rh1/PNP-ND，并将其应用于芳基乙烯氢甲酰化反应中，首先选取了可分散性纳米金刚石作为载体，利用纳米金刚石表面丰富的羧基官能团固载含氮的双膦配体，合成了表面P修饰的碳载体材料，为下一步Rh的高分散锚定提供了大量的位点。结合31P固体核磁表征结果可知在锚定Rh原子之后P的化学位移向低场区迁移，证实了Rh单原子通过Rh-P键锚定在纳米金刚石上，且电子从P转移到Rh上。同时利用球差校正透射电镜也直观的验证了单原子Rh在纳米金刚石载体上的高分散性在温和的反应条件下实现了高区域选择性的制备异构醛-2-芳基丙醛，其选择性高达94%，可与目前主流的均相Rh基络合物催化剂相媲美。对苯乙烯及其它芳基乙烯氢甲酰化反应表现出优异的区域选择性和底物普适性，优势产物为异构醛2-芳基丙醛，选择性>90%。该催化剂还显示出了良好的底物普适性和循环稳定性，利用该催化剂成功实现了两种药物分子布洛芬和芬地林的高效合成，拓展了单原子催化剂在有机合成，特别是药物分子合成的应用。

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