The use of supporting ligands that can store either protons or electrons has emerged as a powerful strategy in catalysis. While these strategies are potent individually, natural systems mediate remarkable transformations by combining the storage of both protons and electrons in the secondary coordination sphere. As such, there has been recent interest in using this strategy to enable fundamentally different transformations. Furthermore, outsourcing H-atom or hydrogen storage to ancillary ligands can also enable alternative mechanistic pathways and thereby selectivity. Here, we describe the application of this strategy to facilitate radical reactivity in Co-based hydrogenation catalysis. Metalation of previously reported dihydrazonopyrrole ligands with Co results in paramagnetic complexes, which are best described as having Co(II) oxidation states. These complexes catalytically hydrogenate olefins with low catalyst loadings under mild conditions (1 atm H₂, 23 °C). Mechanistic, spectroscopic, and computational investigations indicate that this system goes through a radical hydrogen-atom transfer (HAT) type pathway that is distinct from classic organometallic mechanisms and is supported by the ability of the ligand to store H₂. These results show how ancillary ligands can facilitate efficient catalysis, and furthermore how classic organometallic mechanisms for catalysis can be altered by the secondary coordination sphere.

中文翻译：

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通过基于配体的二氢储存实现钴催化的氢化反应

使用可以存储质子或电子的支持配体已成为催化中的一种强大策略。虽然这些策略单独使用是有效的，但自然系统通过在二级配位层中结合质子和电子的存储来调解显着的转变。因此，最近人们对使用这种策略来实现根本不同的转变产生了兴趣。此外，将氢原子或储氢外包给辅助配体也可以实现替代机制途径，从而实现选择性。在这里，我们描述了这种策略在钴基加氢催化中促进自由基反应的应用。先前报道的二亚肼基吡咯配体与 Co 的金属化导致顺磁性配合物，最好描述为具有 Co(II) 氧化态。₂ , 23°C)。机械、光谱和计算研究表明，该系统通过自由基氢原子转移 (HAT) 型途径，该途径不同于经典的有机金属机制，并得到配体储存 H 2 能力的_支持。这些结果显示了辅助配体如何促进有效催化，以及二次配位球如何改变经典的有机金属催化机制。