IMes(IMes=1,3-双(2,4,6-三甲基苯基)咪唑-2-亚基)和IPr(IPr=1,3-双(2,6-二异丙基苯基)咪唑-2-亚基)是迄今为止最常用的N-杂环卡宾配体在均相催化中,然而,尽管有许多优点,这些配体是有限的缺乏空间灵活性的催化口袋。我们报告了一类新的独特的不对称N-杂环卡宾配体,其特征在于咪唑-2-亚基结构中可自由旋转的N-芳族翼尖。可旋转的N-CH2Ar键与构象固定的N-Ar键的组合导致高度模块化的配体拓扑结构,输入IMes和IPr无法访问的几何范围。这些配体在Cu(I)催化的炔烃的β-硼氢化反应中具有高度反应性,对含硼化合物的合成产生了革命性影响的原型硼基铜化过程。此类中最具反应性的Cu(I)-NHC已与MilliporeSigma合作商业化,以使合成化学界能够广泛获得。配体逐渐覆盖从37.3%到52.7%的%Vbur几何形状,后者代表迄今为止为IPr类似物描述的最大%Vbur,同时保留N翼尖的全部灵活性。考虑到N-杂环卡宾催化中对新型几何空间的模块化访问,我们预计这一概念将为有机合成带来新的机遇,药物发现和活性金属中心的稳定。
IMes (IMes=1,3-bis(2,4,6-trimethylphenyl)imidazol-2-ylidene) and IPr (IPr=1,3- bis(2,6-diisopropylphenyl)imidazol-2-ylidene) represent by far the most frequently used N-heterocyclic carbene ligands in homogeneous catalysis, however, despite numerous advantages, these ligands are limited by the lack of steric flexibility of catalytic pockets. We report a new class of unique unsymmetrical N-heterocyclic carbene ligands that are characterized by freely-rotatable N-aromatic wingtips in the imidazol-2-ylidene architecture. The combination of rotatable N-CH2 Ar bond with conformationally-fixed N-Ar linkage results in a highly modular ligand topology, entering the range of geometries inaccessible to IMes and IPr. These ligands are highly reactive in Cu(I)-catalyzed β-hydroboration, an archetypal borylcupration process that has had a transformative impact on the synthesis of boron-containing compounds. The most reactive Cu(I)-NHC in this class has been commercialized in collaboration with MilliporeSigma to enable broad access of the synthetic chemistry community. The ligands gradually cover %Vbur geometries ranging from 37.3 % to 52.7 %, with the latter representing the largest %Vbur described for an IPr analogue, while retaining full flexibility of N-wingtip. Considering the modular access to novel geometrical space in N-heterocyclic carbene catalysis, we anticipate that this concept will enable new opportunities in organic synthesis, drug discovery and stabilization of reactive metal centers.