苯醌助催化剂对 DAF/Pd(OAc)2 催化的好氧烯丙基乙酰氧基化在 Co(salophen) 助催化剂存在和不存在下的贡献,ACS Catalysis

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苯醌助催化剂对 DAF/Pd(OAc)2 催化的好氧烯丙基乙酰氧基化在 Co(salophen) 助催化剂存在和不存在下的贡献
ACS Catalysis ( IF 11.3 ) Pub Date : 2021-05-13 , DOI: 10.1021/acscatal.1c01074
Caitlin V Kozack ₁ , Stephen J Tereniak ₁ , Jonathan N Jaworski ₁ , Bao Li ₁ , David L Bruns ₁ , Spring M M Knapp ₁ , Clark R Landis ₁ , Shannon S Stahl ₁

Affiliation

钯 (II) 催化的烯丙基乙酰氧基化一直是广泛开发和研究的重点。使用分子氧 (O ₂ ) 作为末端氧化剂的方法通常受益于使用苯醌 (BQ) 和过渡金属 (TM) 助催化剂，例如 Co(salophen)，以在催化周转期间支持 Pd ^{0的氧化。}我们之前表明，Pd(OAc) ₂和 4,5-diazafluoren-9-one (DAF) 作为辅助配体在没有助催化剂的情况下用 O _{2催化烯丙基氧化。}在此，我们表明 BQ 增强了 DAF/Pd(OAc) ₂催化活性，几乎与包括 BQ 和 Co(salophen) 在内的反应的性能相匹配。_{这些观察得到了 DAF/Pd(OAc) 2}催化剂体系在三种不同氧化条件下的机理研究的补充：(1) O ₂单独，(2) O ₂与助催化 BQ，和 (3) O ₂与助催化 BQ 和 Co （萨洛芬）。在不存在 Co(salophen) 的情况下，BQ 的有益效果可追溯到 O ₂和 BQ 的协同作用，两者都能够将 Pd ⁰氧化为 Pd ^II。_{O 2}反应生成H ₂ O ₂作为副产物，它可以在 Pd ^II存在下将氢醌氧化为醌。然而，NMR 光谱研究表明，在不存在 Co(salophen) 的情况下，对苯二酚是醌助催化剂的主要氧化还原状态，而 Co(salophen) 的加入在整个反应过程中保持氧化醌，从而产生更好的反应性能。

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Benzoquinone Cocatalyst Contributions to DAF/Pd(OAc)2-Catalyzed Aerobic Allylic Acetoxylation in the Absence and Presence of a Co(salophen) Cocatalyst

Palladium(II)-catalyzed allylic acetoxylation has been the focus of extensive development and investigation. Methods that use molecular oxygen (O₂) as the terminal oxidant typically benefit from the use of benzoquinone (BQ) and a transition-metal (TM) cocatalyst, such as Co(salophen), to support oxidation of Pd⁰ during catalytic turnover. We previously showed that Pd(OAc)₂ and 4,5-diazafluoren-9-one (DAF) as an ancillary ligand catalyze allylic oxidation with O₂ in the absence of cocatalysts. Herein, we show that BQ enhances DAF/Pd(OAc)₂ catalytic activity, nearly matching the performance of reactions that include both BQ and Co(salophen). These observations are complemented by mechanistic studies of DAF/Pd(OAc)₂ catalyst systems under three different oxidation conditions: (1) O₂ alone, (2) O₂ with cocatalytic BQ, and (3) O₂ with cocatalytic BQ and Co(salophen). The beneficial effect of BQ in the absence of Co(salophen) is traced to the synergistic roles of O₂ and BQ, both of which are capable of oxidizing Pd⁰ to Pd^II. The reaction of O₂ generates H₂O₂ as a byproduct, which can oxidize hydroquinone to quinone in the presence of Pd^II. NMR spectroscopic studies, however, show that hydroquinone is the predominant redox state of the quinone cocatalyst in the absence of Co(salophen), while inclusion of Co(salophen) maintains oxidized quinone throughout the reaction, resulting in better reaction performance.

更新日期：2021-06-04

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