Exploration of Abnormal N-Heterocyclic Carbene Nickel and Copper Complexes (aNiCu)

典型的N-杂环卡宾（NHC），即1，3-咪唑-2-亚基，是非常通用的σ-供体配体，其导致了金属有机化学和催化的显著进展。NHC的广泛成功主要是由于与传统膦配体相比其更强的σ-供体能力。实验和理论数据表明，异常NHC（aNHC）（1，3-咪唑-4-亚基或1，3-咪唑-5-亚基）是比经典NHC更强的σ-供体，可能是迄今为止已知的最强的碳供体中性配体。尽管它们在催化及其他方面具有巨大的潜力，但稳定的aNHC-络合物（特别是与后3d-金属）非常稀缺，并且大多数报道的化合物都是偶然的产物。因此，开发合理的aNHC-配合物的合成方法及其探索是重要的和高度期望的。本项目旨在合成aNHC-Cu和aNHC-Ni配合物，并探索其结构、反应活性和潜在的催化应用。所提出的合成方法依赖于使用C2-芳基化的咪唑鎓盐，其容易通过NHC的催化C2-芳基化来获得。这些盐是合成aNHC和官能化aNHC的有前景的前体。将研究三组配体，即aNHC、官能化aNHC和ditopic cabanionic aNHC（dc-aNHC）。合成一系列的铜和镍的配合物，包括杂环衍生物，是战略性的。对所提出的化合物与小分子如CO2、P4和有机底物的反应性研究旨在实现对它们的“结构-反应性关系”的基本理解，这将用于揭示它们在催化合成中的潜在应用。

Classical N-heterocylic carbenes (NHCs), 1,3-imidazol-2-ylidenes, are very versatile σ-donor ligands that have led to remarkable advances in organometallic chemistry and catalysis. The widespread success of NHCs is mainly due to their stronger σ-donor ability compared to traditional phosphine ligands. Experimental and theoretical data suggest that abnormal NHCs (aNHCs) (1,3-imidazol-4-ylidenes or 1,3-imidazol-5-ylidenes) are even stronger σ-donors than classical NHCs, perhaps the strongest carbon-donor neutral ligands known till date. Despite their enormous potential in catalysis and beyond, stable aNHC-complexes (particularly with late 3d-metals) are very scarce and most of the reported compounds are serendipitous products. Therefore, the development of rational synthetic methods for aNHC-complexes and their exploration is important and highly desired. This project aims at the synthesis of aNHC-Cu and aNHC-Ni complexes and the exploration of their structure, reactivity, and potential catalytic applications. The proposed synthetic methodologies rely on the use of C2-arylated imidazolium salts, which are readily accessible by the catalytic C2-arylation of NHCs. These salts are promising precursors for the synthesis of aNHCs and functionalized aNHCs. Three sets of ligands namely aNHCs, functionalized aNHCs, and ditopic cabanionic aNHCs (dc-aNHCs) will be investigated. Syntheses of a series of Cu- and Ni-complexes, including heterobimetallic derivatives, are strategic. Reactivity studies of the proposed compounds with small molecules such as CO2, P4, and organic substrates aim to accomplish a fundamental understanding of their “structure-reactivity relationship”, which will be used to uncover their potential applications in catalytic synthesis.