Divergent Mechanistic Pathways for Copper(I) Hydrophosphination Catalysis: Understanding That Allows for Diastereoselective Hydrophosphination of a Tri-substituted Styrene
Divergent Mechanistic Pathways for Copper(I) Hydrophosphination Catalysis: Understanding That Allows for Diastereoselective Hydrophosphination of a Tri-substituted Styrene
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DOI：
10.1021/acscatal.2c05221
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发表时间：
2022-12
期刊：
影响因子：
12.9
通讯作者：
Steven G Dannenberg;Dennis M. Seth;Emma J. Finfer;R. Waterman
中科院分区：
文献类型：
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作者：
Steven G Dannenberg;Dennis M. Seth;Emma J. Finfer;R. Waterman
：易于获得且工作台稳定的Cu（acac）2（1）解决了探索性氢膦化催化中的许多挑战。进行了机理研究，以回答有关1的反应性，光在催化中的作用仍然存在的问题，并为进一步的研究提供方向。不同的Hammett图表明基于烯烃底物处的电子密度的不同机制。基于捕获反应和原位EPR实验，消除了自由基过程。同位素标记实验，两性离子捕获实验，化学计量模型反应，和催化反应，使用代理中间体表明，这两个共轭加成和插入为基础的机制的途径发生与此系统，这取决于不饱和底物。计算分析表明，最低的能量跃迁是从磷配体的配体到金属的电荷转移（LMCT），其中LUMO具有显着的Cu-P反键特性，这表明在光催化条件下，削弱的Cu-P键加速插入。该假设解释了与铜催化的氢化膦化报道相比1的更大活性，并且似乎是铜（I）催化剂的一般现象。这些结果已被用于实现迄今未知的催化氢膦化反应性，即三取代的苯乙烯底物的非对映选择性氢膦化。
: Readily available and bench-stable Cu(acac) 2 ( 1 ) addresses many challenges in exploratory hydrophosphination catalysis. Mechanistic investigations were performed to answer questions that remain about the reactivity of 1 , the role of light in the catalysis, and to provide direction for further study. A divergent Hammett plot indicates differing mechanisms based on electron density at the alkene substrate. A radical process was eliminated based on trapping reactions and in-situ EPR experiments. Isotopic labeling experiments, a zwitterionic trapping experiment, stoichiometric model reactions, and catalytic reactions using proxy intermediates indicate that both conjugate addition and insertion-based mechanistic pathways occur with this system, depending on the unsaturated substrate. Computational analysis indicates that the lowest energy transition is a ligand-to-metal charge transfer (LMCT) from the phosphido ligand where the LUMO has significant Cu–P antibonding character, suggesting that a weakened Cu–P bond accelerates insertion under photocatalytic conditions. This hypothesis explains the greater activity of 1 compared to copper-catalyzed hydrophosphination reports and appears to be a general phenomenon for copper(I) catalysts. These results have been leveraged to achieve heretofore unknown catalytic hydrophosphination reactivity, namely the diastereoselective hydrophosphination of a tri-substituted styrene substrate.