Due to their availability, price and biological relevance, the use of catalysts based on 3d transition metals is of substantial importance for the synthesis of industrial chemicals, but also for organic synthesis in general. Hence in recent years, especially in homogeneous catalysis, the use of such Earth-abundant, biocompatible metals has become a major area of interest. However, to achieve reactivity comparable to that of noble-metal catalysts, generally sophisticated ligands—typically expensive phosphorus derivatives—have to be used. Here, we report the chemoselective reduction of quinolines and related N-heterocycles by molecular hydrogen, using a simple Mn(i) complex [Mn(CO)₅Br]. Under very mild reaction conditions this catalytic system is able to reduce a wide range of quinolines, affording high yields of the corresponding tetrahydroquinolines, a scaffold present in many bioactive compounds, including marketed pharmaceuticals. Mechanistic studies reveal the formation of the active catalyst and also show the important role of a concomitantly formed Mn(ii) species and HBr for the hydrogenation of the heterocyclic substrates.

由于它们的可获得性，价格和生物学相关性，基于3d过渡金属的催化剂的使用对于工业化学品的合成，以及一般而言对于有机合成而言，都至关重要。因此，近年来，特别是在均相催化中，使用这种富含地球的生物相容性金属已成为人们关注的主要领域。但是，为了获得可与贵金属催化剂媲美的反应性，通常必须使用复杂的配体（通常是昂贵的磷衍生物）。在这里，我们报告了使用简单的Mn（i）配合物[Mn（CO）₅来通过分子氢对喹啉和相关N杂环进行化学选择性还原Br]。在非常温和的反应条件下，该催化系统能够还原范围广泛的喹啉，从而提供高产率的相应四氢喹啉，这是许多生物活性化合物（包括市售药品）中存在的支架。机理研究揭示了活性催化剂的形成，并且还显示了伴随形成的Mn（ii）物种和HBr对于杂环底物氢化的重要作用。