Facile Hydrolysis of Nickel(II) Complexes with N-Heterocyclic Carbene Ligands
摘要:
Metal complexes with N-heterocyclic carbene ligands (NHC) are ubiquitously used in catalysis, where the stability of the metal-ligand framework is a key issue. Our study shows that Ni-NHC complexes may undergo facile decomposition due to the presence of water in organic solvents (hydrolysis). The ability to hydrolyze Ni(NHC)(2)X-2 complexes decreases in the order of NHC = 1,2,4-triazolium > benzimidazolium approximate to imidazolium. Depending on the ligand and substituents, the half reaction time of the complex decomposition may change from several minutes to hours. The nature of the halogen is also an important factor, and the ability for decomposition of the studied complexes decreases in the order of Cl > Br > I. NMR and MS monitoring revealed that Ni-NHC complexes in the presence of water undergo hydrolysis with Ni-C-carbene bond cleavage, affording the corresponding N,N'-dialkylated azolium salts and nickel(II) hydroxide. These findings are of great importance for designing efficient and recyclable catalytic systems, because trace water is a common contaminant in routine synthetic applications.
atom‐economic direct amidation of alcohols with amines has been recently highlighted as an attractive and promising transformation. Among the versatile reported catalytic systems, in situ generated N‐heterocycliccarbene (NHC)/ruthenium (Ru) catalytic systems have demonstrated their advantages such as easy operation and use of commercial Ru compounds. However, the existing catalyst loadings are relatively
Mechanistic Study of a Switch in the Regioselectivity of Hydroheteroarylation of Styrene Catalyzed by Bimetallic Ni-Al through CH Activation
作者:Wen-Ching Chen、Ying-Chieh Lai、Wei-Chun Shih、Ming-Shiuan Yu、Glenn P. A. Yap、Tiow-Gan Ong
DOI:10.1002/chem.201400303
日期:2014.6.23
previously reported a highly efficient protocol for bimetallicNi–Al‐catalyzedhydroheteroarylation of styrene with benzimidazole based on CH bond activation. We have now delineated the mechanism of this process, providing a rationale for an observed switch in regioselectivity in the presence of the Lewis acid, AlMe3. The present mechanisticstudy gives insights for the rational development of catalysts
Well‐defined N‐heterocyclic carbene/ruthenium complexes for the alcohol amidation with amines: The dual role of cesium carbonate and improved activities applying an added ligand
Dehydrogenative amide bond formationfrom alcohols and amines has been regarded as an atom‐economic and sustainable process. Among various catalytic systems, N‐heterocycliccarbene (NHC)‐based Ru catalytic systems have attracted growing interest due to the outstanding properties of NHCs as ligands. Herein, an NHC/Ru complex (1) was prepared and its structure was further confirmed with X‐ray crystallography
由醇和胺形成的脱氢酰胺键被认为是原子经济且可持续的过程。在各种催化体系中,基于N杂环卡宾(NHC)的Ru催化体系由于其作为配体的NHC的出色性能吸引了越来越多的关注。本文制备了NHC / Ru络合物(1),并通过X射线晶体学进一步证实了其结构。在Cs 2 CO 3的存在下,两个基于NHC / Ru的催化体系据报道对这种酰胺合成具有活性。不包含任何添加的配体的系统A要求催化剂负载为1.00mol%。有趣的是,通过添加NHC前体(L)。L的量和其他条件的优化产生了体系B,该体系是更有效的体系,其Ru负载量低至0.25mol%。此外,从1和Cs 2 CO 3的回流甲苯中鉴定出NHC-Ru-碳酸盐络合物6,进一步研究表明6是该催化反应的重要中间体。基于以上结果,我们声称Cs 2 CO 3的作用是促进关键中间体6的形成。另一方面,它为选择性酰胺的形成提供了优化的碱性。
Imidazolium-based ionic liquids with large weakly coordinating anions
作者:William Levason、David Pugh、Gillian Reid
DOI:10.1039/c6nj03674k
日期:——
weakly-coordinating anions [BArF]− and [Al(OtC4F9)4]− ([BArF]− = tetrakis3,5-bis(trifluoromethyl)phenyl}borate) have been synthesized. Characterization by 1H NMR spectroscopy shows that the salts are fully dissociated in solution. Six examples have been further characterized by X-ray crystallography, revealing that weak hydrogen bonds do occur in the solid phase between the imidazolium cations and weakly coordinating
八种咪唑鎓盐与弱配位阴离子[BAr F ] -和[Al(O t C 4 F 9)4 ] -([BAr F ] - =四3,5-双(三氟甲基)苯基}硼酸酯)已合成。用1表征1 H NMR光谱表明盐在溶液中完全解离。X射线晶体学进一步表征了六个例子,揭示了在咪唑鎓阳离子和弱配位阴离子之间的固相中确实发生了弱氢键。与笨重的[IDiPPH]咪唑阳离子(IDiPPH = 1,3-双2,6-双(二异丙基)苯基}咪唑鎓)的比较显示,靠近咪唑鎓质子的大空间容积可阻止氢键形成。盐的差示扫描量热法显示,所有盐在高达200°C的温度下都具有热稳定性,这使其成为潜在的适合在高温下进行电化学过程的背景电解质。
Alfaia, Antonio J. I.; Calado, Antonio R. T.; Reis, Joao Carlos R., European Journal of Organic Chemistry, 2000, # 21, p. 3627 - 3631
作者:Alfaia, Antonio J. I.、Calado, Antonio R. T.、Reis, Joao Carlos R.