Mechanistic Basis for High Reactivity of (salen)Co-OTs in the Hydrolytic Kinetic Resolution of Terminal Epoxides
Mechanistic Basis for High Reactivity of (salen)Co-OTs in the Hydrolytic Kinetic Resolution of Terminal Epoxides
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DOI：
10.1021/jo300181f
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发表时间：
2012-03-02
影响因子：
3.6
通讯作者：
Jacobsen, Eric N.
中科院分区：
文献类型：
--
作者：
Nielsen, Lars P. C.;Zuend, Stephan J.;Jacobsen, Eric N.
（salen）Co（III）催化的末端环氧化物水解动力学拆分（HKR）是一个通过在亲核（salen）Co-OH催化剂和刘易斯酸性（salen）Co-X催化剂之间分配来控制速率的水热反应过程。常用的（salen）Co-OAc和（salen）Co-Cl预催化剂在环氧化物水解反应过程中经历与环氧化物的完全和不可逆的反加成，导致定量形成弱刘易斯酸性（salen）Co-OH，并且在HKR反应的后期阶段中严重降低反应速率。相比之下，（salen）Co-OT在HKR反应的整个过程中保持高反应性。我们在这里描述了不同的（salen）Co-X预催化剂的催化剂分配的调查，并证明，在（salen）Co-OT的情况下，反式加成到环氧化物是可逆的。这种可逆的反离子添加导致亲核和刘易斯酸性催化剂物质之间的稳定分配，从而允许在整个HKR反应过程中进行高效催化。
The (salen)Co(III)-catalyzed hydrolytic kinetic resolution (HKR) of terminal epoxides is a bimetallic process with a rate controlled by partitioning between a nucleophilic (salen)Co-OH catalyst and a Lewis acidic (salen)Co-X catalyst. The commonly used (salen)Co-OAc and (salen)Co-Cl precatalysts undergo complete and irreversible counterion addition to epoxide during the course of the epoxide hydrolysis reaction, resulting in quantitative formation of weakly Lewis acidic (salen)Co-OH and severely diminished reaction rates in the late stages of HKR reactions. In contrast, (salen)Co-OTs maintains high reactivity over the entire course of HKR reactions. We describe here an investigation of catalyst partitioning with different (salen)Co-X precatalysts and demonstrate that counterion addition to epoxide is reversible in the case of the (salen)Co-OTs. This reversible counterion addition results in stable partitioning between nucleophilic and Lewis acidic catalyst species, allowing highly efficient catalysis throughout the course of the HKR reaction.