Journal of Molecular Catalysis A: Chemical最新文献

Counteranion-catalysis represents an appealing but challenging approach for the development of enantioselective oxidative CH bond functionalization reactions. In this work, a new family of 3,3′-triazolyl BINOL-derived phosphoric acids was synthesized and employed in the intramolecular asymmetric CH bond functionalization of N-aryl substituted tetrahydroisoquinolines. As previously reported with related structures, the presence of the triazole groups on the catalysts was key to attain enantioselectivity. Our study also shows the importance of choosing the appropriate regioisomeric triazole groups at the BINOL backbone to achieve a more efficient chirality transfer. Moderate enantiomeric ratios were obtained with the N-benzamide substrates, whereas the change of the nature of the nucleophile fragment was translated to a dramatic loss of the enantioselectivity. Therefore, it can be foreseen that there is a need for designing further superior catalyst structures to develop future counter-anion organocatalyzed asymmetric CH bond functionalization reactions.

A dinuclear complex [(Me₃P)₃Ru(μ-OH)₃Ru(PMe₃)₃]⁺[OPh]⁻ (1) (0.5 mol%) catalyzes E-selective dimerization of phenylacetylene, which involves the C–H bond cleavage of phenylacetylene and resulting stereospecific C–C bond forming reaction, at 100 °C for 2 h to give (E)-1,4-diphenylbut-3-en-1-yne in quantitative yield (E/Z = 91/9). Similar reactions using 4-nitro-, 4-cyano-, 4-trifluoromethyl-, 4-acetyl-, and 4-methylphenylacetylene give the corresponding enynes. The kinetic study for dimerization of phenylacetylene shows the second-order and first-order reactions with regard to the phenylacetylene and 1 concentrations, respectively, suggesting this reaction to be catalyzed by a dinuclear ruthenium complex. Addition of PMe₃ to the catalytic system strongly discourages the dimerization. These features are consistent with the scenario, where dissociation of a PMe₃ ligand from 1 gives a coordinatively unsaturated diruthenium species and one of the ruthenium centers performs as a reaction site for the enyne formation and the other ruthenium center behaves as a spectator in the catalysis.

The complexes of copper [Cu(κONN’-HL)(NO₃)(DMF)](NO₃)∙H₂O (1) and [Cu(κONN’-HL)Cl₂]∙½DMSO (2), and of manganese [Mn(κON-HL)₂Cl₂]Cl (3) and [Mn(κON-HL)₂(NO₃)₂](NO₃)∙H₂O (4) were synthesized by reactions of the respective chloride or nitrate salt with a non-aqueous solutions of the Schiff base aminoalcohol HL (product of condensation of salicylic aldehyde and aminoethylpiperazine) and characterized by X-ray diffraction analysis. The catalytic investigations disclosed a prominent activity of the copper compounds 1 and 2 towards oxidation of cyclohexane with hydrogen peroxide in the presence of various promoters (nitric, hydrochloric, oxalic acids and pyridine), under mild conditions. The unusual promoting effect of pyridine on the catalytic activity of the copper catalysts allowed to achieve yields up to 21% based on cyclohexane. Chromatographic studies revealed that cyclohexyl hydroperoxide is a main reaction product and chlorocyclohexane (in the presence of HCl as promoter) was also detected, suggesting a free radical reaction pathway with hydroxyl radicals as attacking species. Complexes 1 and 2 act also as catalysts in the oxidation of 1-phenylethanol with tert-butylhydroperoxide, showing acetophenone yields up to 62% and TON (turnover numbers) up to 620 in the presence of the K₂CO₃ promoter.

Acceleration of palladium catalyzed CH activation by various Lewis Acids was demonstrated on the directed ortho-alkenylation and acylation of acetanilide and urea derivatives. The universality of this effect was investigated by the study of different palladium catalysts, directing groups in the aromatic substrates and versatile Lewis acids. Experiments were carried out to monitor the reactions and to compare the behavior and activity of different types of Lewis acids. Kinetic investigation revealed a rate determining CH activation step, and DFT studies were performed for the explanation of Lewis acid effect on CH activation.

Direct activation of CH₄ to oxygenates and unsaturated light hydrocarbons was investigated using Fe-modified ZSM-5 and Ferrierite (FER) for a partial oxidation of CH₄ with N₂O oxidant. The amount of active α-oxygen sites and number of Bronsted acid sites on the Fe-modified zeolites were well correlated with CH₄ conversion rate and product distributions. The amount of α-oxygen sites was largely changed according to preparation method such as wet impregnation or ion-exchange of iron precursor and types of zeolites. A large number of Bronsted acid sites and α-oxygen sites on the Fe-modified FER revealed a higher oxygenate formation such as methanol and dimethyl ether (DME) with COx, and a larger number of strong acid sites on Fe-modified ZSM-5 was also responsible for a higher selectivity to light hydrocarbons by a successive dehydration of oxygenates formed. The different catalytic performances were verified through proper measurements of the amount and type of acidic sites as well as the α-oxygen sites measured by N₂O pulse chemisorption. The Fe-modified FER prepared by impregnation method possessed a larger amount of α-oxygen sites due to abundant Bronsted acid sites, which was responsible for a higher rate of CH₄ conversion to oxygenates with the help of N₂O decomposition on the α-oxygen sites originated from iron oxide nanoparticles.

3d metal (Cu, Fe, Co, V) containing composite catalysts for the solvent-free microwave-assisted transformation of 1-phenylethanol to acetophenone with tert-butyl hydroperoxide (TBHP) as oxidant were prepared by ball milling. The influence of multiwalled carbon nanotubes (CNTs) and graphene oxide (GO) additives on the catalytic activity of the catalysts was studied. CNTs or GO were mixed by ball milling with the metal salts (CoCl₂), oxides (CuO, Fe₂O₃, V₂O₅) or binary systems (Fe₂O₃-CoCl_2, CoCl₂-V₂O₅, CuO-Fe₂O₃). For CoCl₂-based catalytic systems, addition of small amounts (0.1–5%) of CNTs or GO leads to significant improvement in catalytic activity, e.g. 1% of the CNTs additive allows to rise yields from 28 to 77%, under the same catalytic conditions. The CoCl₂-5%CNTs composite is the most active among the studied ones with 85% yield and TON of 43 after 1 h.

Herein, nickel-based metal-organic framework, Ni-MOF-74, was synthesized by a solvothermal method and its properties was characterized by a host of techniques. Ni-MOF-74 exhibited exceptional catalytic activity toward the direct arylation of azoles via CH activation while other Ni-MOFs, nickel-based heterogeneous systems, and homogeneous counter parts displayed lower activity. Optimal conditions involved the use of Li₂CO₃ or KCl salts in diglyme solvent in 18 h and no additional ligand is required. This is the first and unprecedented report using KCl salt as promoter for arylation of heterocycles. By avoiding the use of strong bases and oxidants, optimized conditions are compatible with wide range of functional groups and heterocycles. Furthermore, by taking advantage of large aperture size of Ni-MOF-74, we are able to utilize optimized conditions to successfully synthesize several bioactive arylated azole derivatives. Previous studies using heterogeneous catalysts to approach these bioactive compounds are not performed in the literature. Leaching tests indicated that homogeneous catalysis via leached active nickel species is unlikely. Thus, the catalyst was facilely separated from the reaction mixture and reused several times without significant degradation of the catalytic reactivity.

Lewis base, N-methylmorpholine (NMM) accelerated Pd-catalyzed Sonogashira coupling of steric hindered super active esters, 1a–1e, and terminal alkynes. This approach provided an efficient synthetic protocol for a broad array of acylated o-alkynoylphenols compounds, 3a–3e, under moderate conditions. The mechanistic study clearly demonstrated that NNM stabilized the catalytic palladium species, and accelerated the leaving of triazine moiety during the catalytic cycle of the cross-coupling reactions. In addition, piperazine was found to efficiently catalyze the 6-endo cyclization of acylated o-alkynoylphenols, which achieved the diversity oriented synthesis of γ-benzopyranones, 4aa–4eg, with 93–99% yields.

Different inorganic acids were used to activate sepiolite, and the acid-activated sepiolites supported nickel and potassium bimetallic catalysts were prepared. Nitrogen adsorption-desorption, hydrogen chemisorption, ammonia temperature programmed desorption (NH₃-TPD), temperature programmed reduction (TPR), powder X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), Fourier Transform Infrared Spectroscopy (FTIR) and energy dispersive X-ray (EDX) were used to characterize the catalysts. The catalytic performance of the acid-activated sepiolite supported K-Ni bimetallic catalysts were investigated in 1,6-hexanedinitrile (HDN) hydrogenation in liquid phase. It was revealed that the potassium could increase the alkalinity of the catalyst with the aim of inhibiting the formation of the 1-azacycloheptane (ACH). And the addition of potassium reduces the particle size of nickel and improves its dispersion. Compared with hydrochloric acid and sulfuric acid, nitric acid treatment increases more silanol groups (SiOH) on the sepiolite surface, which is helpful to nickel particles adsorption and dispersion. Nitric acid activated sepiolite supported nickel and potassium bimetallic catalysts (K-Ni/NASEP) present the best catalytic performance, the conversion of HDN comes up to 92.0% under moderate conditions of lower temperature and pressure, the selectivity to 6-aminocapronitrile (ACN) and 1,6-hexanediamine (HDA) is up to 95.2%.

In this work, the catalytic activity of ruthenium II and III complexes containing chloride, pyridine, phosphine and CO ligands was investigated in the hydroformylation – hydrogenation and hydroformylation – acetalization reactions. The complexes mer-[RuCl₃(dppb)(H₂O)](1), mer-[RuCl₃(dppb)(4-Vpy)](2), mer-[RuCl₃(dppb)(4-tBupy)](3), mer-[RuCl₃(dppb)(py)](4), mer-[RuCl₃(dppb)(4-Phpy)](5), mer-[RuCl₃(dppb)(4-Mepy)](6), cis-[RuCl₂(CO)₂(dppb)](7), trans-[RuCl₂(CO)₂(dppb)](8), RuCl₃·xH₂O(9), [RuCl₂(PPh₃)₃](10) and [RuCl₂(PPh₃)₂(dppb)](11) were used as supplied or synthesized as previously described in the literature {Where PPh₃ = triphenylphosphine, dppb = 1,4-bis(diphenylphosphino)butane, py = pyridine, 4-Mepy = 4-methylpyridine, 4-Vpy = 4-vinylpyridine, 4-tBupy = 4-tert-butylpyridine and 4-Phpy = 4-phenylpyridine}. These complexes were used as a pre-catalysts in a hydroformylation catalytic system to produce CC, CO and CO bonds, where 1-decene resulted in a formation of respective alcohol and dimethyl acetals. Several reactions were performed in order to find the best reaction conditions presenting the best conversion (64% after 24 h). The 1-decene was also used as a substrate in two type tandem reactions labeled as: hydroformylation – hydrogenation (HH) and hydroformylation – acetalization (HA) reactions. The relationship between Ru – catalyst/substrate was 1:100, without free ligands or additives, in a controlled temperature and pressure. All the products of catalytic reactions HH and HA were analyzed by CG-FID with good yields.