Farrell Jeffrey M, Posaratnanathan Roy T, Stephan Douglas W
Department of Chemistry , University of Toronto , 80 St. George St. , Toronto , ON M5H3H6 , Canada . Email:
Department of Chemistry , Faculty of Science , King Abdulaziz University , Jeddah , Saudi Arabia.
Chem Sci. 2015 Mar 1;6(3):2010-2015. doi: 10.1039/c4sc03675a. Epub 2015 Jan 26.
This manuscript probes the steric and electronic attributes that lead to "frustrated Lewis pair" (FLP)-type catalysis of imine hydrogenation by borenium ions. Hydride abstraction from (IBu)HB(CF) prompts intramolecular C-H bond activation to give (CHN)(Bu) (CMeCH)CB(CF), defining an upper limit of Lewis acidity for FLP hydrogenation catalysis. A series of seven N-heterocyclic carbene-borane (NHC-borane) adducts ((R'CNR)C)(HBCH) (R' = H, R = dipp , Mes , Me ; R = Me R' = Me , Cl, ) and ((HC)(NMe)(NR)C)(HBCH) (R = Bu, , Ph ) are prepared and converted to corresponding borenium salts. These species are evaluated as catalysts for metal-free imine hydrogenation at room temperature. Systematic tuning of the carbene donor for the hydrogenation of archetypal substrate -benzylidene--butylamine achieves the highest reported turn-over frequencies for FLP-catalyzed hydrogenation at amongst the lowest reported catalyst loadings. The most active NHC-borenium catalyst of this series, derived from , is readily isolable, crystallographically characterized and shown to be effective in the hydrogenation catalysis of functional group-containing imines and N-heterocycles.
本手稿探究了导致硼正离子对亚胺氢化进行“受阻路易斯对”（FLP）型催化的空间和电子属性。从(IBu)HB(CF)中提取氢化物促使分子内C-H键活化，生成(CHN)(Bu)(CMeCH)CB(CF)，确定了FLP氢化催化路易斯酸度的上限。制备了一系列七种氮杂环卡宾-硼烷（NHC-硼烷）加合物（(R'CNR)C)(HBCH)（R' = H，R = dipp、Mes、Me；R = Me，R' = Me、Cl等）和((HC)(NMe)(NR)C)(HBCH)（R = Bu、等、Ph），并将其转化为相应的硼正盐。这些物种被评估为室温下无金属亚胺氢化的催化剂。通过对典型底物苄叉丁胺氢化的卡宾供体进行系统调节，在最低报道的催化剂负载量下实现了FLP催化氢化中报道的最高周转频率。该系列中最具活性的NHC-硼正催化剂，源自，易于分离，经晶体学表征，并显示对含官能团的亚胺和氮杂环的氢化催化有效。
