N-heterocyclic phosphines (NHPs) have recently emerged as a new group of promising catalysts for metal-free reductions, owing to their unique hydridic reactivity. The excellent hydricity of NHPs, which rivals or even exceeds those of many metal-based hydrides, is the result of hyperconjugative interactions between the lone-pair electrons on N atoms and the adjacent σ*(P–H) orbital. Compared with the conventional protic reactivity of phosphines, this umpolung P–H reactivity leads to hydridic selectivity in NHP-mediated reductions. This reactivity has therefore found many applications in the catalytic reduction of polar unsaturated bonds and in the hydroboration of pyridines. This review summarizes recent progress in studies of the reactivity and synthetic applications of these phosphorus-based hydrides, with the aim of providing practical information to enable exploitation of their synthetically useful chemistry.

中文翻译：

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N-杂环氢化磷的反应性研究及合成应用新进展

N-杂环膦（NHP s）由于其独特的氢化反应性，最近成为一类新的有前途的无金属还原催化剂。NHP s的优异水合度可与许多金属基氢化物相媲美甚至超过，这是 N 原子上的孤对电子与相邻 σ*(P-H) 轨道之间超共轭相互作用的结果。与膦的常规质子反应性相比，这种 umpolung P-H 反应性导致NHP 中的氢化选择性-介导的减少。因此，这种反应性在极性不饱和键的催化还原和吡啶的硼氢化反应中有许多应用。本综述总结了这些磷基氢化物的反应性和合成应用研究的最新进展，旨在提供实用信息，以开发其合成有用的化学物质。