钯催化电化学烯丙位4-吡啶化反应中的配体作用研究

doi:10.61558/2993-074X.3438

摘要/Abstract

摘要：

过渡金属络合物在电化学合成中获得了广泛的应用，其中配体对于络合物在电场中稳定性、催化活性以及选择性的影响还了解有限。4-氰基-吡啶作为一种高效吡啶化试剂，在自由基化学中获得广泛应用。在前期的工作中，我们实现了电化学条件下，手性双膦配体钯络合物催化4-氰基-吡啶与烯丙基醋酸酯反应，构建了多种手性烯丙基吡啶化合物。我们发现双膦配体对反应有着关键的作用，决定着反应的活性、区域选择性和对映选择性。在本工作中，我们系统性地研究了多种双膦配体钯金属络合物，在烯丙基醋酸酯与氰基吡啶的电化学还原偶联过程中的性质。通过控制实验，电化学分析以及理论计算等方法，我们揭示了双膦配体对于络合物稳定性及反应区域选择性的影响。进而，我们发现在电场条件下存在一个非稳定价态的过渡金属络合物。这个非稳定价态的过渡金属络合物中，双膦配体可以将电荷和自旋密度分散于整个络合物之中，而不是局限于金属离子之上。这样，络合物既可以作为电子转移催化剂，也可以作为过渡金属催化剂，同时控制整个电子转移过程以及成键过程。我们认为这种配体与金属在电场条件下的非稳定价态络合物，展现了电化学条件下过渡金属催化的独特能力，这有助于发展未来的新型的电化学催化体系。同时，我们还发现锌电极至关重要，其不仅可以活化4-氰基吡啶，还可以淬灭氰根离子，展现出Lewis酸性金属离子的特殊用途。

关键词: 电化学, 钯催化, 膦配体, 吡啶化, 烯丙基

Abstract:

4-CN-pyridine is a widely applied 4-pyridinylation reagent for diverse transformations. Conventionally, the reaction proceeds via an open-shell radical cross-coupling pathway. Following our previous study, in this work, we report the Pd-catalyzed allyl 4-pyrinylation reaction under electrochemical conditions. The reaction proceeds via radical-polar crossover pathway in which the role of phosphine ligand in reactivity and selectivity was extensively investigated.

Key words: Electrochemistry, Palladium, Phosphine, Pyridinylation, Allyl

丁伟杰, 杨春晖, 冯钟涛, 陆仕荣, 程旭. 钯催化电化学烯丙位4-吡啶化反应中的配体作用研究[J]. 电化学（中英文）, 2024, 30(5): 2313003.

Wei-Jie Ding, Chun-Hui Yang, Zhong-Tao Feng, Shi-Rong Lu, Xu Cheng. Comparison of Ligands in Palladium-Catalyzed Electrochemical Allyl 4-Pyridinylation[J]. Journal of Electrochemistry, 2024, 30(5): 2313003.

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链接本文: https://electrochem.xmu.edu.cn/CN/10.61558/2993-074X.3438

https://electrochem.xmu.edu.cn/CN/Y2024/V30/I5/2313003

图/表 6

参考文献 42

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Entry	Deviation from standard conditions	Yield of 3a	B/L
1	none	64%	5:1
2	no electricity	Nd	-
3	no PdCl₂	Nd	-
4	no ligand	Nd	-
5	no H₂O	Nd	-
6	graphite felt as anode	Trace	-
7	LiClO₄instead of nBu₄NBF₄	Trace	-
8	DMF instead of MeCN	60%	2:1
9	DMSO instead of MeCN	48%	2:1
10	MeCN/MeOH (5:1, v/v)	74% (72%)^[b]	5:1
11	Cinnamyl bromide instead of 1a	Nd	-
12	Cinnamyl methyl carbonate instead of 1a	Nd	-