Cervantes-Reyes Alejandro, Rominger Frank, Hashmi A Stephen K
Organisch-Chemisches Institut, Heidelberg University, Im Neuenheimer Feld 270, 69120, Heidelberg, Germany.
Chemistry Department, Faculty of Science, King Abdulaziz University, Jeddah, 21589, Saudi Arabia.
Chemistry. 2020 Apr 24;26(24):5530-5540. doi: 10.1002/chem.202000600. Epub 2020 Apr 20.
The synthesis and full characterization of new air-stable Ag and Cu complexes bearing structurally bulky expanded-ring N-heterocyclic carbene (erNHC) ligands is presented. The condensation of protonated NHC salts with Ag O afforded a collection of Ag complexes, and their first use as ligand transfer reagents led to novel isostructural Cu or Au complexes. In situ deprotonation of the NHC salts in the presence of a copper(I) source, provides a library of new Cu complexes. The solid-state structures feature large N-C -N angles (118-128°) and almost identical angles between the aryl groups on the nitrogen atoms and the plane of the N-C-N unit of the carbene (i.e. torsion angles close to 0°). Among the steric parameters, the percent buried volume (%V ) values span easily in the 50-57 % range, and that one of (9-Dipp)CuBr complex (%V =57.5) overcomes to other known erNHC-metal complexes reported to date. Preliminary catalytic experiments in the copper-catalyzed coupling between N-tosylhydrazone and phenylacetylene, afforded 76-93 % product at the 0.5-2.5 mol % catalyst loading, proving the stability of Cu erNHC complexes at elevated temperatures (100 °C).
本文介绍了带有结构庞大的扩环 N-杂环卡宾（erNHC）配体的新型空气稳定的 Ag 和 Cu 配合物的合成及全面表征。质子化 NHC 盐与 Ag₂O 的缩合反应得到了一系列 Ag 配合物，它们首次用作配体转移试剂时生成了新型同构的 Cu 或 Au 配合物。在铜（I）源存在下，NHC 盐的原位去质子化反应提供了一个新的 Cu 配合物库。固态结构的特征是具有较大的 N-C-N 键角（118-128°），并且氮原子上的芳基与卡宾的 N-C-N 单元平面之间的夹角几乎相同（即扭转角接近 0°）。在空间参数中，掩埋体积百分比（%V）值很容易在 50-57%范围内，其中（9-Dipp）CuBr 配合物的%V 值（57.5）超过了迄今为止报道的其他已知 erNHC-金属配合物。在 N-甲苯磺酰腙与苯乙炔的铜催化偶联反应中的初步催化实验表明，在 0.5-2.5 mol%的催化剂负载量下，产物产率为 76-93%，这证明了 Cu erNHC 配合物在高温（100°C）下的稳定性。
