Catalysts for transfer hydrogenation (TH) reactions based on the earth abundant transition metal manganese are an emerging field of research. A common moiety found in most reported phosphine-free catalysts is a primary or secondary amine donor, which is generally considered to be crucial within an outer-sphere mechanism. Here, we investigated the role of the NH-motif in the mechanism in catalytic transfer hydrogenation of ketones. Therefore, we synthesized Mn(I) complexes with a pyridyl-pyrazole or a pyridyl-imidazole ligand, which carry an NH-motif at different positions. Subsequent investigation of their catalytic activity points towards an inner-spere mechanism in which the NH-motif of the amino ligand is deprotonated throughout the catalytic cycle. The resulting amido ligand increases the electron density at the metal which facilitates the hydride transfer to the substrate. The presented alternative inner-sphere mechanism may aid in the future development of manganese-based catalysts for hydrogen transfer reactions.

基于地球丰富的过渡金属锰的转移氢化（TH）反应催化剂是一个新兴的研究领域。在大多数报道的无膦催化剂中发现的常见部分是伯胺或仲胺供体，这通常被认为在外球机制中是至关重要的。在这里，我们研究了 NH 基序在酮催化转移氢化机理中的作用。因此，我们合成了具有吡啶基-吡唑或吡啶基-咪唑配体的 Mn(I) 配合物，它们在不同位置带有 NH 基序。随后对其催化活性的研究指向了一种内在机制，其中氨基配体的 NH 基序在整个催化循环中被​​去质子化。得到的酰胺配体增加了金属上的电子密度，这有助于氢化物转移到基材上。所提出的替代内球机制可能有助于未来开发用于氢转移反应的锰基催化剂。