Development of a Catalytic Protocol for Alkane Dehydrogenation by C–H Activation at Iridium(III)

项目摘要 廉价而丰富的未活化烷烃是生产商品的理想前体 化学品工业过程中常见的起始材料和复杂分子中普遍存在的基序， 烯烃可以由更容易获得的烷烃通过过渡金属催化的 脱氢虽然多相催化已被证明在低碳烯烃的工业脱氢中是有用的， 烷烃，在化学合成中的应用受到限制，由于高温，对 催化剂失活焦化，以及对长链烷烃底物的低选择性。相比之下，同质 催化反应通常在较温和的条件下进行， 高级烷烃广泛的研究表明钳形连接的Ir化合物是最佳的催化剂， 最近的研究表明，Ir（III）配合物是有希望的候选物，能够避免许多 现有Ir（I）系统的局限性。 本申请描述了一种用于通过钳形催化剂催化烷烃脱氢的新方案的开发， 连接的Ir（III）配合物使用最经济的氧化剂可用，分子氧。研究策略 建立在先前证明的（NCN）Ir（III）络合物介导烷烃的能力上 脱氢和在需氧条件下再生。迄今为止，催化剂仍然难以捉摸， Ir（III）络合物在氧存在下在高温下的不稳定性， 脱氢计算研究表明，Ir（III）金属中心与贫电子 钳形配体框架将降低脱氢的能垒。根据得出的结论， 从这些实验和计算研究中，本研究计划的中心假设是， 通过策略性改性，降低反应温度，可实现催化脱氢 的钳形配体支持的Ir（III）金属中心。本申请的具体目的是：1）合成 用于烷烃脱氢的新型Ir（III）钳形配合物，2）Ir（III）催化的烷烃脱氢， 需氧条件，和3）官能化有机底物的脱氢。 开发一种在有氧条件下Ir（III）催化烷烃脱氢的方法， 提供了一种新的烯烃制备策略，其在使用时不受当前方法的许多限制的影响， 一种环保氧化剂。该项目的研究结果将对烯烃的制备产生重大影响- 含有与人类健康相关的化学品和复杂分子或其中间体。

PROJECT SUMMARY Inexpensive and abundant, unactivated alkanes are ideal precursors for the production of commodity chemicals. Common starting materials in industrial processes and ubiquitous motifs in complex molecules, alkenes can be produced from more readily available alkanes through transition-metal-catalyzed dehydrogenation. While heterogeneous catalysis has proven useful in industrial dehydrogenation of low-carbon alkanes, applications in chemical synthesis have been limited due to high temperatures, susceptibility to catalyst-deactivating coking, and low selectivity with longer-chain alkane substrates. In contrast, homogeneous catalytic reactions generally proceed under milder conditions and can be effective in the dehydrogenation of higher alkanes. Extensive research has revealed pincer-ligated Ir compounds to be the optimal catalysts, and recent studies have implicated Ir(III) complexes as promising candidates capable of circumventing many limitations of established Ir(I) systems. This application describes the development of a novel protocol for catalytic alkane dehydrogenation by pincer- ligated Ir(III) complexes using the most economical oxidant available, molecular oxygen. The research strategy builds on the previously demonstrated capabilities of a (NCN)Ir(III) complex for mediating alkane dehydrogenation and for regenerating under aerobic conditions. To date, catalysis has remained elusive due to the instability of the Ir(III) complex in the presence of oxygen at the high temperatures required for dehydrogenation. Computational studies suggest that ligation of the Ir(III) metal center with electron-poor pincer ligand frameworks will lower the energy barrier to dehydrogenation. Based on the conclusions drawn from these experimental and computational investigations, the central hypothesis of this research plan is that catalytic dehydrogenation can be realized by reducing the reaction temperature through strategic modification of the pincer ligand supporting the Ir(III) metal center. The specific aims of this application are: 1) synthesis of novel Ir(III) pincer complexes for alkane dehydrogenation, 2) Ir(III)-catalyzed alkane dehydrogenation under aerobic conditions, and 3) dehydrogenation of functionalized organic substrates. The development of a method for Ir(III)-catalyzed alkane dehydrogenation under aerobic conditions will contribute a novel olefin preparation strategy invulnerable to many limitations of current processes while using an environmentally friendly oxidant. The results of this project will greatly impact the preparation of olefin- containing commodity chemicals and complex molecules relevant to human health or intermediates thereto.