Department of Organic Chemistry, Stockholm University, 10691 Stockholm, Sweden.
Chemistry. 2012 Nov 5;18(45):14510-9. doi: 10.1002/chem.201201845. Epub 2012 Sep 24.
A series of new iridium(III) complexes containing bidentate N-heterocyclic carbenes (NHC) functionalized with an alcohol or ether group (NHC-OR, R = H, Me) were prepared. The complexes catalyzed the alkylation of anilines with alcohols as latent electrophiles. In particular, biscationic Ir(III) complexes of the type Cp*(NHC-OH)Ir(MeCN)2[BF(4)(-)] afforded higher-order amine products with very high efficiency; up to >99% yield using a 1:1 ratio of reactants and 1-2.5 mol % of Ir, in short reaction times (2-16 h) and under base-free conditions. Quantitative yields were also obtained at 50 °C, although longer reaction times (48-60 h) were needed. A large variety of aromatic amines have been alkylated with primary and secondary alcohols. The reactivity of structurally related iridium(III) complexes was also compared to obtain insights into the mechanism and into the structure of possible catalytic intermediates. The Ir(III) complexes were stable towards oxygen and moisture, and were characterized by NMR, HRMS, single-crystal X-ray diffraction, and elemental analyses.
一系列新型铱(III)配合物，其中含有双齿 N-杂环卡宾（NHC），并带有醇或醚基团（NHC-OR，R = H，Me）。这些配合物可催化苯胺与醇作为潜在亲电试剂的烷基化反应。特别地，双阳离子 Ir(III)配合物Cp*(NHC-OH)Ir(MeCN)2[BF(4)(-)]以非常高的效率提供高一级的胺产物；在反应物比例为 1:1，使用 1-2.5 mol%的 Ir，在短反应时间（2-16 小时）和无碱条件下，最高收率可达>99%。在 50°C 下也可获得定量收率，尽管需要更长的反应时间（48-60 小时）。已用各种芳香胺对伯醇和仲醇进行了烷基化。还比较了结构相关的铱(III)配合物的反应性，以深入了解反应机理和可能的催化中间体的结构。Ir(III)配合物对氧气和水分稳定，并通过 NMR、高分辨质谱、单晶 X 射线衍射和元素分析进行了表征。
