在这份手稿中,关于单卤素和双卤素(F,Cl,Br,和I)在4位或/和4,5位取代的咪唑-2-亚基(NHC)金属络合物进行了讨论:特别是,它们与各种金属的结构多样性(第6-13组),重要的物理化学性质,对催化和医药/生物应用进行了综述。据我们所知,没有文献报道具有这种类型的NHC配体的第4族和第5族金属络合物。卤化咪唑-2-亚基金属配合物值得特别注意,因为卤素是共轭芳族/杂芳族环系统中的经典给电子基团(介孔),而是感应吸电子。然而,它们表现出显著的吸电子诱导效应,从而提供独特的电子特性。这对于微调咪唑-2-亚烷基的“卡宾”碳的σ供体能力很重要,直接影响其金属配合物的催化性能。其他应用,优势,卤化与卤化的缺点本文对未取代的咪唑-2-亚基金属配合物进行了严格的分析和总结。
In this manuscript, literature reports on mono- and di-halogen (F, Cl, Br, and I) substituted at positions 4 or/and 4,5 imidazol-2-ylidene (NHC) metal complexes are discussed: particularly, their structural diversity with various metals (groups 6-13), important physicochemical properties, catalytic and medicinal/biological applications are reviewed. To our knowledge, there are no literature reports on group 4 and 5 metal complexes with this type of NHC ligands. Halogenated imidazol-2-ylidene metal complexes deserve special attention because halogens are the classic electron donating groups (mesomerically) in conjugated aromatic/heteroaromatic ring systems, but electron withdrawing inductively. However, they exhibit a significant electron withdrawing inductive effect, thus providing unique electronic properties. This is important for fine tuning of σ-donor abilities of the \"carbenic\" carbon of imidazol-2-ylidenes, which directly affect catalytic performance of their metal complexes. Other applications, advantages, and disadvantages of halogenated vs. unsubstituted imidazol-2-ylidene metal complexes are critically analyzed and summarized in this review.