582-25-2Relevant articles and documents
Significant effect of base on the improvement of selectivity in the hydrogenation of benzoic acid over NiZrB amorphous alloy supported on γ-Al2O3
Wen, Xin,Cao, Yingying,Qiao, Xianliang,Niu, Libo,Huo, Li,Bai, Guoyi
, p. 3281 - 3287 (2015)
This study presents a facile way to improve the selectivity for cyclohexanecarboxylic acid by adding a base in the hydrogenation of benzoic acid over a non-noble metal NiZrB amorphous alloy supported on γ-Al2O3. It is found that alkali metal carbonates exhibit an excellent selectivity improvement from 50.3% to a range of 93.5-95.7%, with the conversion of benzoic acid higher than 92.3%. Even a very small amount of K2CO3 (1 mol% benzoic acid) was efficient for improving the selectivity for cyclohexanecarboxylic acid. In addition, a lower reaction temperature was beneficial to the improvement of selectivity. Based on the results of temperature programmed desorption of NH3 and inductively coupled plasma analysis, the improvement of selectivity in the presence of a base was attributed to the neutralization of the acidic sites on the surface of the catalyst by the in situ generated potassium benzoate, inhibiting the hydrodeoxygenation of carbonyl and resulting in a high selectivity for cyclohexanecarboxylic acid.
An Anionic, Chelating C(sp3)/NHC ligand from the Combination of an N-heterobicyclic Carbene and Barbituric Heterocycle
Benaissa, Idir,Gajda, Katarzyna,Vendier, Laure,Lugan, No?l,Kajetanowicz, Anna,Grela, Karol,Michelet, Véronique,César, Vincent,Bastin, Stéphanie
, p. 3223 - 3234 (2021/09/30)
The coordination chemistry of the anionic NHC1-based on an imidazo[1,5-a]pyridin-3-ylidene (IPy) platform substituted at the C5 position by an anionic barbituric heterocycle was studied with d6(Ru(II), Mn(I)) and d8(Pd(II), Rh(I), Ir(I), Au(III)) transition-metal centers. While the anionic barbituric heterocycle is planar in the zwitterionic NHC precursor 1·H, NMR spectroscopic analyses supplemented by X-ray diffraction studies evidenced the chelating behavior of ligand 1-through the carbenic and the malonic carbon atoms in all of the complexes, resulting from a deformation of the lateral barbituric heterocycle. The complexes were obtained by reaction of the free carbene with the appropriate metal precursor, except for the Au(III) complex 10, which was obtained by oxidation of the antecedent gold(I) complex [AuCl(1)]?with PhICl2as an external oxidant. During the course of the process, the kinetic gold(I) intermediate 9 resulting from the oxidation of the malonic carbon of the barbituric moiety was isolated upon crystallization from the reaction mixture. The νCOstretching frequencies recorded for complex [Rh(1)(CO)2] (5) demonstrated the strong donating character of the malonate-C(sp3)/NHC ligand 1-. The ruthenium complex [Ru(1)Cl(p-cymene)] (11) was implemented as a precatalyst in the dehydrogenative synthesis of carboxylic acid derivatives from primary alcohols and exhibited high activities at low catalyst loadings (25-250 ppm) and a large tolerance toward functional groups.
A Diaminopropane Diolefin Ru(0) Complex Catalyzes Hydrogenation and Dehydrogenation Reactions
Casas, Fernando,Trincado, Monica,Rodriguez-Lugo, Rafael,Baneerje, Dipshikha,Grützmacher, Hansj?rg
, p. 5241 - 5251 (2019/11/16)
New ruthenium (0) complexes with a cooperative diolefin diaminopropane (DAP) or the dehydrogenated iminopropenamide ligand (IPA) were synthesized for comparison with their diaminoethane (DAE)/ diazadiene (DAD) ruthenium analogues. These DAP/IPA complexes are efficient catalysts in dehydrogenation reactions of alkaline aqueous methanol which proceeds under mild conditions (T=70 °C) and of higher alcohols, forming the corresponding carbonate and carboxylates, respectively. The scope of the reaction includes an example of a 1,2-diol as model for biomass derived alcohols. Their catalytic applications are extended to the atom-efficient dehydrogenative coupling of alcohols and amines to amides. The reaction proceeds without any additives and is applicable to the synthesis of formamides from methanol. Moreover, DAP/IPA complexes catalyze the hydrogenation of a series of esters, lactone, ketone, activated olefin, aldehyde and imine substrates. The diaminopropane Ru catalyst exhibits higher activity compared to the dehydrogenated β-ketiminate (IPA) and previously studied DAD/DAE based catalysts. We present studies on their stoichiometric reactivity with relevance to their possible catalytic mechanisms and the isolation and full characterization of key reaction intermediates.
Mechanistic investigation of imine formation in ruthenium-catalyzed N-alkylation of amines with alcohols
Yu, Xiaojun,Li, Yaqiu,Fu, Haiyan,Zheng, Xueli,Chen, Hua,Li, Ruixiang
, (2018/02/09)
Imines are observed frequently in ruthenium-catalyzed N-alkylation of amines with alcohols. Herein, nitrogen–phosphine functionalized carbene ligands were developed and used in ruthenium-catalyzed N-alkylation to explore the mechanism of imine formation. The results showed that strongly electron-donating ligands were beneficial for imine formation and alcohol dehydrogenation to generate acid. In addition, with an increase of electron density of nitrogen atom in substituted amines, the yield of imines in N-alkylation was improved. At the same time, with electron-rich imines as substrates, the transfer hydrogenation of imines became difficult. It is suggested that strongly electron-donating ligands and substrates caused an increase of electron density on the ruthenium center, which resulted in the elimination of hydrogen atoms in active species [LRuH2] as hydrogen gas rather than transfer onto the imine coordinated with the ruthenium center.