• 主题
高级搜索  >
历史搜索 清空历史
首页> 外文期刊>Chemistry: A European journal >A biomimetic pathway for vanadium-catalyzed aerobic oxidation of alcohols: Evidence for a base-assisted dehydrogenation mechanism
【24h】

A biomimetic pathway for vanadium-catalyzed aerobic oxidation of alcohols: Evidence for a base-assisted dehydrogenation mechanism

机译：钒催化的酒精好氧氧化的仿生途径：碱辅助脱氢机理的证据

获取原文
获取原文并翻译 | 示例
           
页面导航
  • 摘要
  • 著录项
  • 相似文献
  • 相关主题

摘要

The first step in the catalytic oxidation of alcohols by molecular O _2, mediated by homogeneous vanadium(V) complexes [LV ~V(O)(OR)], is ligand exchange. The unusual mechanism of the subsequent intramolecular oxidation of benzyl alcoholate ligands in the 8-hydroxyquinolinato (HQ) complexes [(HQ)_2V~V(O)(OCH _2C_6H_4-p-X)] involves intermolecular deprotonation. In the presence of triethylamine, complex 3 (X=H) reacts within an hour at room temperature to generate, quantitatively, [(HQ)_2V ~(IV)(O)], benzaldehyde (0.5 equivalents), and benzyl alcohol (0.5 equivalents). The base plays a key role in the reaction: in its absence, less than 12 % conversion was observed after 72 hours. The reaction is first order in both 3 and NEt_3, with activation parameters δH ~+=(28±4) kJ mol~(-1) and δS~+=(- 169±4) J K~(-1) mol~(-1). A large kinetic isotope effect, 10.2±0.6, was observed when the benzylic hydrogen atoms were replaced by deuterium atoms. The effect of the para substituent of the benzyl alcoholate ligand on the reaction rate was investigated using a Hammett plot, which was constructed using σ_p. From the slope of the Hammett plot, ρ=+(1.34±0.18), a significant buildup of negative charge on the benzylic carbon atom in the transition state is inferred. These experimental findings, in combination with computational studies, support an unusual bimolecular pathway for the intramolecular redox reaction, in which the rate-limiting step is deprotonation at the benzylic position. This mechanism, that is, base-assisted dehydrogenation (BAD), represents a biomimetic pathway for transition-metal-mediated alcohol oxidations, differing from the previously identified hydride-transfer and radical pathways. It suggests a new way to enhance the activity and selectivity of vanadium catalysts in a wide range of redox reactions, through control of the outer coordination sphere.
机译：由均相钒（V）络合物[LV〜V（O）（OR）]介导的分子O _2催化醇氧化的第一步是配体交换。随后在8-羟基喹啉（HQ）配合物[（HQ）_2V〜V（O）（OCH _2C_6H_4-p-X）]中进行苯甲醇苄基配体分子内氧化的异常机制涉及分子间去质子化。在三乙胺的存在下，配合物3（X = H）在室温下在一小时内反应，定量生成[（HQ）_2V〜（IV）（O）]，苯甲醛（0.5当量）和苯甲醇（0.5等价物）。该碱在反应中起关键作用：在不存在该碱的情况下，在72小时后观察到转化率低于12％。反应在3和NEt_3中均为一阶反应，活化参数为δH〜+ =（28±4）kJ mol〜（-1）和δS〜+ =（-169±4）JK〜（-1）mol〜（ -1）。当苄基氢原子被氘原子取代时，观察到很大的动力学同位素效应，为10.2±0.6。使用Hammett图研究了苄醇酯配体的对位取代基对反应速率的影响，该图使用σ_p构建。从哈米特曲线的斜率ρ= +（1.34±0.18），可以推断出过渡态苄基碳原子上的负电荷显着增加。这些实验发现与计算研究相结合，为分子内氧化还原反应提供了一条不寻常的双分子途径，其中限速步骤是苄基位置的去质子化。这种机制，即碱辅助脱氢（BAD），代表了过渡金属介导的醇氧化的仿生途径，不同于先前确定的氢化物转移和自由基途径。它提出了通过控制外部配位域来提高钒催化剂在广泛的氧化还原反应中的活性和选择性的新方法。

著录项

相似文献

  • 外文文献
  • 中文文献
  • 专利
获取原文

客服邮箱：kefu@zhangqiaokeyan.com

京公网安备：11010802029741号 ICP备案号：京ICP备15016152号-6 六维联合信息科技 (北京) 有限公司©版权所有

  • 客服微信

  • 服务号