Phase-transfer catalysts (PTCs), currently, are one of the most important tools of chemists for performing organic reactions. PTCs accelerate several types of reactions in biphasic systems, giving excellent yields of the desired product. Most of the PTCs belong to the general formula NR₄⁺X^–. In the recent past, several compounds possessing a novel scaffold with the general formula NL₂⁺X^– have been reported as PTCs. In the NL₂⁺ species, a nitrogen atom with a formal positive charge accepts electron density from electron-donating ligands. Electronic structure studies reported in the literature confirmed the possibility of L → N coordination (donor–acceptor) interactions in these species, and thus, this class of compounds are known as divalent N^I compounds. These species are reported to exhibit better catalytic potential in comparison to the traditional NR₄⁺ systems. Some of the NL₂⁺ systems are found to be useful in asymmetric phase-transfer catalysis. Thus, these systems offer extensive opportunities for exploring the catalytic properties and novel mechanistic aspects associated with their unique electronic structure. In this paper, the synthesis, electronic, and structural properties and the applications in catalysis of the NL₂⁺-based PTCs are reviewed with their bright future scope in catalytic organic chemistry.

中文翻译：

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NL ₂ ⁺系统作为新一代相转移催化剂

目前，相转移催化剂（PTC）是化学家进行有机反应的最重要工具之一。PTC可以加速双相系统中的几种类型的反应，从而获得所需产物的优异收率。大多数PTC属于通式NR ₄ ⁺ X ^–。在最近的过去，若干化合物具有与通式NL的新型支架₂ ⁺ X ^-已报道的PTC。在NL ₂ ⁺物种中，带有形式正电荷的氮原子接受供电子配体的电子密度。文献中报道的电子结构研究证实了这些物种中L→N配位（供体-受体）相互作用的可能性，因此这类化合物被称为二价N ^I化合物。据报道，与传统的NR ₄ ⁺系统相比，这些物质具有更好的催化潜力。一些NL ₂ ⁺发现该体系可用于不对称相转移催化中。因此，这些系统提供了广泛的机会来探索与其独特的电子结构相关的催化性能和新颖的机械方面。本文综述了NL ₂ ⁺基PTC的合成，电子和结构性质及其在催化中的应用，并展望了它们在催化有机化学领域的广阔前景。