Bonding and Catalytic Application of Ruthenium N‑Heterocyclic Carbene Complexes Featuring Triazole, Triazolylidene, and Imidazolylidene Ligands

The first mixed normal/abnormal NHC ruthenium­(II) complexes bearing triazole/imidazole-based ligands are presented. The ruthenium complexes show differing coordination geometries depending on the ligand sphere and the coordination of the triazole. Two Ru­(II) monocarbene complexes have been obtained, with a 2-imidazolylidene carbene and the 1,2,3-triazoles acting as neutral nitrogen donors. In addition, a tridentate Ru­(II) complex featuring a normal 2-imidazolylidene as well as two abnormal 1,2,3-triazolylidene carbene moieties is described. Both structural motifs are evaluated in transfer hydrogenation of acetophenone, with the electron-rich Ru­(II) tri-NHC exhibiting the highest conversion.本文报道首例搭载三唑/咪唑类配体的正常/反常混合型N-杂环卡宾（N-Heterocyclic Carbene, NHC）钌(II)配合物。该系列钌配合物的配位几何构型会随配体环境以及三唑的配位方式发生变化。研究得到两种Ru(II)单卡宾配合物，分别以2-咪唑基卡宾与1,2,3-三唑作为中性氮给体参与配位。此外，还报道了一种三齿Ru(II)配合物，其配体结构包含一个正常2-咪唑基卡宾以及两个反常1,2,3-三唑卡宾单元。针对这两种结构基元在苯乙酮转移氢化反应中的催化性能开展了评估，结果显示富电子的三-N-杂环卡宾钌(II)配合物展现出最高的催化转化率。