Journal of Molecular Catalysis A: Chemical最新文献

A phosphorous-modified γ-Al₂O₃ (P-Al₂O₃), where γ-Al₂O₃ support was prepared by sol-gel method with a high surface area of ∼350 m²/g, has been applied for a preparation of cobalt-supported Co/P-Al₂O₃ catalysts. The Co/P-Al₂O₃ catalysts having a different P/Al molar ratio were investigated to elucidate the roles of phosphorous species on the γ-Al₂O₃ to the catalytic stability and product distribution for CO hydrogenation to hydrocarbons. The γ-Al₂O₃ surface was partially transformed to aluminum phosphates after phosphorous modification, and the newly formed aluminum phosphate phases simultaneously altered the surface hydrophilicity and cobalt dispersion as well. The partial formation of tridymite aluminum phosphate (AlPO₄) phases on the P-Al₂O₃ support eventually enhanced the dispersion of the supported cobalt crystallites and suppressed the aggregation of cobalt nanoparticles by forming the strongly interacted cobalt crystallites on the P-Al₂O₃ surfaces. The phosphorous-modified Fischer-Tropsch synthesis (FTS) catalyst also significantly suppressed heavy hydrocarbon depositions due to an increased surface hydrophilicity originated from partially formed SiO₂-like tridymite AlPO₄ surfaces. A higher stability of the Co/P-Al₂O₃ catalyst at an optimal phosphorous content in the range of 0.5–1.0 mol% was attributed to homogeneously distributed cobalt crystallites and less deposition of heavy hydrocarbons by forming macro-emulsion droplets with the help of trace amount of alcohols formed during FTS reaction. This was confirmed by in-situ analysis of adsorbed intermediates with surface hydrophilicity and some surface characterizations such as crystallite size, reducibility, and electronic state of the supported cobalt nanoparticles.

Four cobalt (III) corroles bearing different number of pentafluorophenyl and phenyl groups were synthesized and characterized by elemental analysis, HR-MS, UV–vis, NMR, XPS as well as cyclic voltammetry. The first investigation of cobalt corrole catalyzed oxidation of alkene was conducted by using styrene as substrate. The best yield was obtained in acetonitrile solvent in the air with TBHP oxidant (96% yield based on oxidant, up to 96 TON). Benzaldehyde was detected as the main product by using PhI(OAc)₂, TBHP, KHSO₅, PhIO as oxidants. In contrast, styrene oxide was found to be the major product when using m-CPBA oxidant. Nearly no products could be found by using H₂O₂ oxidant. Possible catalytic oxidation pathway was also discussed based on the obsewrvations of UV–vis changes of the ctatalytic system in the absence of substrate and in-situ HR-MS.

The review describes catalytic properties of a unique class of metal complexes—polycyclic cage-like metallasilsesquioxanes. Article is composed in retrospective manner and reflects the progress of the investigations in the field: from classic applications to recently discovered perspectives of cage-like metallasilsesquioxanes in catalysis of oxidation of С–H compounds.

The results on the investigation of alkane activation kinetics and mechanisms in aqueous and acidic media, including theoretical and experimental approaches to the problem, proposed by the author are summarized. The new concepts are introduced: a “direct kinetic study of CH activation”, “visible and hidden reagent preactivation”, the “strongest reactant and earliest transition state” (ETS), the “5/6 effect” (the ratio of CH bonds splitting constant rates in the с-C₅H₁₀/с-C₆H₁₂ couple), “single-factor compensation effect” (SCE), and a “refined compensation temperature”. The compensation effect (CE) exists in reality, but it is necessary to exclude the influence side factors, for example, to go from rate constants to the 5/6 effect to observe its purest form. The 5/6-CE combination as an example SCE is a new instrument for studying CH-activation mechanisms. Temperature dependences of (5/6) values for the reagents in aqueous solution (Pt^II, MnO₄⁻, HMnO₄, HOCl, HOONO, HVO₂ – Ru^IV, OH, SO₄⁻) and sulfuric acid (Pd^II, Hg^II, CrO₃, Mn^III, Co^III, NO₂⁺, OH⁺, 1-adamantyl cation, C₁₄H₁₁⁺, СН₂OH⁺, SO₃H⁺) are found. The only influencing factor on the (5/6) value is conformational strain difference in the C₅ and C₆ rings, which in a series of one-type reactions decreases with increasing the reagent activity. Four mechanisms are revealed: H-atom abstraction by anionic (I⁻), uncharged (I⁰) and cationic (I⁺) oxygen-centered “O-reactants”, and a bifunctional incorporation into CH bond of electrophilic cation – base adduct (II⁺). Various SCE lines (the entropy change versus enthalpy changing) for these groups are found. They converge in a “SCE pole” (the first example of ETS). Features of these mechanisms, differences of Pt^II, Pd^II, Hg^II acidocomplexes as the reagents and a surprising similarity between the Shilov reactant Pt^IICl₃(H₂O) and OH radicals in the water are discussed. The probable general cause of CEs in various processes is compensation effects in thermodynamics of interparticle interactions.

Three new water-soluble copper(II) complexes [Cu(HL)(H₂O){(CH₃)₂NCHO}] (1), [Cu(H₂L)₂(im)₄]·CH₃OH (2) and [Cu(HL)(CH₃OH)]₂(μ₂-py) (3) were synthesized from copper(II) nitrate and sodium (Z)-2-(2-(1,3-dioxo-1-(phenylamino)butan-2-ylidene)hydrazinyl)benzene-sulfonate (NaH₂L), in the absence (for 1) and presence of imidazole (im) (for 2) or pyrazine (py) (for 3), and fully characterized. The complexes 1–3 have been tested as stereoselective CH activating catalysts for the model nitroaldol (Henry) condensation of nitroethane with various aldehydes in water. 1 was the most active catalyst affording 64−87% yields with syn/anti diasteroselectivities up to 77:23.

Reaction of dimethylamine adduct of 1-methyl-3-borolene with [(C₂H₄)₂RhCl]₂ gives the triple-decker complex (η-C₄H₄BMe)Rh(μ-η:η-C₄H₄BMe)Rh(η-C₄H₄BMe) (1a) in 62% yield and trace amount (<1%) of the hybrid rhodacyclopentadienyl/borole triple-decker complex (η-C₄H₄BMe)Rh(μ-η:η-C₄H₄Rh{(μ-η:η-C₄H₄BMe)Rh(η-C₄H₄BMe)})Rh(η-C₄H₄BMe) (2). The structure of 2 was determined by X-ray diffraction. In the presence of Cu(OAc)₂, 1a and (η-C₄H₄BPh)Rh(μ-η:η-C₄H₄BPh)Rh(η-C₄H₄BPh) (1b) catalyze the oxidative coupling of benzoic acid with diphenylacetylene selectively giving 1,2,3,4-tetraphenylnaphtalene in 50–90% yields. Analogous reactions of benzoic acid with 1-phenyl-1-butyne catalyzed by 1a and [CpRhI₂]₂ regioselectively give 1,4-diethyl-2,3-diphenylnaphthalene. The related dicationic triple-decker complexes [(9-SMe₂-7,8-C₂B₉H₁₀)Rh(μ-η:η-C₄H₄BPh)Rh(9-SMe₂-7,8-C₂B₉H₁₀)]²⁺ (3) and [Cp*Rh(μ-η:η-C₄H₄BPh)IrCp*]²⁺ (4) were also tested as catalysts.

An isolated CH bond in a molecule has a very low reactivity owing to the large kinetic barrier associated to the CH bond cleavage and the apolar nature of this bond. For this reason, the selective reactivity of such a non-functional group is under active study since several decades and is still regarded as the Holy Grail in chemistry. Metal-catalyzed CH activation/functionalization chemistry allows the step-economical and original construction of CC as well as CO and CN bonds starting from hydrocarbons (or hydrocarbon fragments) without the need of prior non catalytic oxidation steps. Furthermore, it can be of utmost importance in the domain of multistep syntheses, and also in transformations of societal significance such as the conversion of methane into methanol. This tutorial review addresses to students and researchers who would like to become acquainted with this fascinating topic. After a brief historical introduction, the main mechanistic fundaments of metal-catalyzed CH activation are exposed. Then, a selection of seminal advances and conceptual breakthroughs are presented.

The effective functionalization of CH bond in methane, the main hydrocarbon component in Earth's crust and the most real source of energy for mankind in the nearest observable future, is undoubtedly can be regarded nowadays as one of the most important scientific and technological tasks. However, the usual practice of considering catalytic and gas-phase processes as independent technological branches seriously restricts the possibilities for a deeper understanding and technological optimization of real processes. The development of more effective technologies to convert methane and other gas-phase hydrocarbons into more valuable and demanded chemicals needs a complex approach based on the combined heterogeneous–homogeneous chemistry of these processes. A number of examples are used to illustrate the interconnection between heterogeneous catalytic and gas-phase processes in oxidative functionalization of methane. A number of potential possibilities for the optimization of the real heterogeneous–homogeneous chemistry of these processes are discussed.

Catalytic efficiency of tetrabutylammonium salts of sandwich tungstophosphates B‐α‐[M₄(H₂O)₂(PW₉O₃₄)₂]ⁿ⁻, M = Co^II, Mn^II, Fe^III, was studied in the oxidation of (R)-(+)-limonene, geraniol, linalool, linalyl acetate, carveol, and cis-cyclooctene with hydrogen peroxide, in acetonitrile. Oxidation of (R)-(+)-limonene gave limonene-1,2-diol as main product. Epoxidation of linalool takes place preferentially at the more substituted 6,7-double bond, the corresponding 6,7-epoxide reacting further, yielding furano- and pyrano-oxides, via intramolecular cyclization. Oxidation of linalyl acetate occurred preferentially at the more substituted 6,7-double bond for Mn₄(PW₉)₂, affording 6,7-epoxide at 82% selectivity. Linalyl acetate 1,2-epoxide was the major product with 51% and 77% selectivity for Co₄(PW₉)₂ and Fe₄(PW₉)₂, respectively. Oxidation of carveol occurred with very good conversions in the presence of Mn₄(PW₉)₂, Co₄(PW₉)₂ and Fe₄(PW₉)₂, yielding carvone and carveol 1,2-epoxide in similar amounts. Oxidation of cis-cyclooctene gave only the epoxide, while oxidation of geraniol at room temperature afforded 2,3-epoxygeraniol as the major product.

A facile and efficient method to introduce alkyne groups to the C-1 position of biologically interesting 1,2,3,4-tetrahydroisoquinolines via direct CH-functionalization is reported. Various alkynylated N-substituted 1,2,3,4-tetrahydroisoquinolines could be obtained by using copper(I)-chloride as catalyst, alkynoic acids as alkyne source and t-BuOOH as oxidant, in a one-pot two-step decarboxylation- alkynylation reaction in moderate to high yields. Furthermore, a one-pot protocol of a three-step decarboxylation-alkynylation-1,3-dipolar cycloaddition reaction leading to 1-triazolyl-tetrahydroisoquinolines was developed, a hitherto unknown reaction cascade.