Metal-catalyzed nitrogen-atom transfer methods for the oxidation of aliphatic C-H bonds.
Metal-catalyzed nitrogen-atom transfer methods for the oxidation of aliphatic C-H bonds.
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DOI：
10.1021/ar200318q
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发表时间：
2012-06-19
影响因子：
18.3
通讯作者：
Du Bois J
中科院分区：
文献类型：
--
作者：
Roizen JL;Harvey ME;Du Bois J
一个多世纪以来，化学家一直致力于发现和开发能够选择性氧化碳氢化合物的反应过程。 20 世纪 70 年代，Abramovitch 和 Yamada 描述了磺酰亚氨基碘烷 (RSO2N=IPh) 的合成和亲电子反应性，证明了此类新型试剂可用作氮宾等价物。 Breslow、Mansuy 和 Müller 的后续研究表明，当与过渡金属盐或金属络合物（即 Mn、Fe 和 Rh 的盐）结合时，此类氧化剂能够实现烯烃和饱和烃的官能化。在这里，我们追溯了我们自己的研究，开发用于 C-H 和 π 键氧化的 N 原子转移技术。本报告讨论了二铑和二钌络合物介导的分子内和分子间胺化过程的进展，以及催化剂反应性和阻滞的机制基础。明确提及尚未解答的问题以及有待发现的丰富问题领域。胺化技术的一个根本性进步是认识到亚氨基碘氧化剂可以在金属催化剂存在下原位生成，从而引发随后的 N 原子转移。在这些条件下，二铑和二钌灯笼络合物均可作为与一系列氮源（例如氨基甲酸酯、氨基磺酸酯、磺酰胺等）进行C-H键氧化的有效催化剂，其中许多氮源不会形成可分离的亚氨基碘烷等价物。实用的合成方法及其应用与对有效反应机制的研究同时发展。对于分子内二铑催化过程，实验和计算数据的主体与协调的异步C-H插入途径一致，类似于Rh-卡宾转移的共识机制。其他研究表明，覆盖二铑核心的桥连四羧酸盐配体基团在标准反应条件下不稳定交换。该信息导致了螯合二羧酸双核铑配合物的生成，例如 Rh2(esp)2。该催化剂体系在分子内和分子间 C-H 胺化反应中的性能是其他二铑配合物无法比拟的。四桥混合价二钌络合物可作为氨基磺酸酯氧化环化的有效促进剂。这些催化剂可以用羧酸盐以外的配体组来制作，并且比对应的二铑催化剂更耐氧化。四-2-氧基吡啶二钌氯化物络合物[Ru2(hp)4Cl]积累的一系列实验和计算机制数据已将插入事件确定为涉及离散自由基中间体的逐步途径。这些数据对比了二铑催化的 C-H 胺化，并为理解两种催化剂类型之间观察到的不同化学选择性趋势提供了一个令人信服的模型。这项工作是朝着实现对产物选择性进行可预测的试剂水平控制的最终目标迈出的重要一步。
For more than a century, chemists have endeavored to discover and develop reaction processes that enable the selective oxidation of hydrocarbons. In the 1970s, Abramovitch and Yamada described the synthesis and electrophilic reactivity of sulfonyliminoiodinanes (RSO2N=IPh), demonstrating the utility of this new class of reagents to function as nitrene equivalents. Subsequent investigations by Breslow, Mansuy, and Müller would show such oxidants to be competent for alkene and saturated hydrocarbon functionalization when combined with transition metal salts or metal complexes, namely those of Mn, Fe, and Rh. Here, we trace our own studies to develop N-atom transfer technologies for C–H and π-bond oxidation. This Account discusses advances in both intra- and intermolecular amination processes mediated by dirhodium and diruthenium complexes, as well as the mechanistic foundations of catalyst reactivity and arrest. Explicit reference is given to questions that remain unanswered and to problem areas that are rich for discovery. A fundamental advance in amination technology has been the recognition that iminoiodinane oxidants can be generated in situ in the presence of a metal catalyst that elicits subsequent N-atom transfer. Under these conditions, both dirhodium and diruthenium lantern complexes function as competent catalysts for C–H bond oxidation with a range of nitrogen sources (e.g., carbamates, sulfamates, sulfamides, etc.), many of which will not form isolable iminoiodinane equivalents. Practical synthetic methods and applications thereof have evolved in parallel with inquiries into the operative reaction mechanism(s). For the intramolecular dirhodium-catalyzed process, the body of experimental and computational data is consistent with a concerted asynchronous C–H insertion pathway, analogous to the consensus mechanism for Rh-carbene transfer. Other studies reveal that the bridging tetracarboxylate ligand groups, which shroud the dirhodium core, are labile to exchange under standard reaction conditions. This information has led to the generation of chelating dicarboxylate dinuclear rhodium complexes, exemplified by Rh2(esp)2. The performance of this catalyst system is unmatched by other dirhodium complexes in both intra- and intermolecular C–H amination reactions. Tetra-bridged, mixed-valent diruthenium complexes function as effective promoters of sulfamate ester oxidative cyclization. These catalysts can be crafted with ligand sets other than carboxylates and are more resistant to oxidation than their dirhodium counterparts. A range of experimental and computational mechanistic data amassed with the tetra-2-oxypyridinate diruthenium chloride complex, [Ru2(hp)4Cl], has established the insertion event as a stepwise pathway involving a discrete radical intermediate. These data contrast dirhodium-catalyzed C–H amination and offer a cogent model for understanding the divergent chemoselectivity trends observed between the two catalyst types. This work constitutes an important step toward the ultimate goal of achieving predictable, reagent-level control over product selectivity.