Regioselective Hydrogenation Research Articles

ChemInform Abstract: General Strategy for Large‐Scale Synthesis of (+)‐Rivastigmine (IV) and (+)‐NPS R‐568 (VII)

Abstractinvolving regioselective hydrogenation of diastereomerically pure amine (II) or (V) as the key step

Hydrogen migration on the C60 fullerene

We investigate the migration barriers, transition states, and optimum migration paths of hydrogen on the C60 fullerene using the ab initio density functional theory. Calculated energy barriers tend to be higher for non-local exchange-correlation functionals. We find that the migration between adsorption sites with the same energy has high migration barriers, and thus the initial stages of the H nucleation requires desorption–adsorption cycles. The migration barrier is reduced near another H adsorbate. The migration may be involved more in the later stages of the regio-selective hydrogenation of C60. We find that the migration barriers are reduced by the presence of hydrogen sources, and the hydrogenating agents in the environment are required in order to reach the regio-selective hydrogenation of the C60 fullerene.

General Strategy for Large-Scale Synthesis of (+)-Rivastigmine and (+)-NPS R-568

An economically viable strategy for the total synthesis of (+)-rivastigmine and (+)-NPS R-568 has been reported. The strategy involves regioselective hydrogenation of diastereomerically pure bis amine to realize the desired α-methyl chiral substituted benzyl amine. The route is economical, scalable, and versatile enough to be adapted to similar classes of compounds.

Hydrogenation of quinolines, alkenes, and biodiesel by palladium nanoparticles supported on magnesium oxide

A new catalyst composed of Pd nanoparticles supported on MgO has been prepared by the room temperature NaBH(4) reduction of Na(2)PdCl(4) in methanol in the presence of the support. TEM measurements reveal well-dispersed Pd particles of mean diameter 1.7 nm attached to the MgO surface. Further characterization was achieved by ICP-AES, XPS, XRD, H(2) pulse chemisorption and H(2)-TPR. The new catalyst is efficient for the regioselective hydrogenation of the heterocyclic ring of quinolines, as well as for the mild reduction of a variety of alkenes representative of fuel components, and the partial saturation of biodiesel. The new material is considerably more reactive than commercial Pd/SiO(2) and Pd/Al(2)O(3) catalysts under analogous reaction conditions.

Efficient Catalytic Interconversion between NADH and NAD+ Accompanied by Generation and Consumption of Hydrogen with a Water-Soluble Iridium Complex at Ambient Pressure and Temperature

Regioselective hydrogenation of the oxidized form of β-nicotinamide adenine dinucleotide (NAD(+)) to the reduced form (NADH) with hydrogen (H(2)) has successfully been achieved in the presence of a catalytic amount of a [C,N] cyclometalated organoiridium complex [Ir(III)(Cp*)(4-(1H-pyrazol-1-yl-κN(2))benzoic acid-κC(3))(H(2)O)](2) SO(4) [1](2)·SO(4) under an atmospheric pressure of H(2) at room temperature in weakly basic water. The structure of the corresponding benzoate complex Ir(III)(Cp*)(4-(1H-pyrazol-1-yl-κN(2))-benzoate-κC(3))(H(2)O) 2 has been revealed by X-ray single-crystal structure analysis. The corresponding iridium hydride complex formed under an atmospheric pressure of H(2) undergoes the 1,4-selective hydrogenation of NAD(+) to form 1,4-NADH. On the other hand, in weakly acidic water the complex 1 was found to catalyze the hydrogen evolution from NADH to produce NAD(+) without photoirradiation at room temperature. NAD(+) exhibited an inhibitory behavior in both catalytic hydrogenation of NAD(+) with H(2) and H(2) evolution from NADH due to the binding of NAD(+) to the catalyst. The overall catalytic mechanism of interconversion between NADH and NAD(+) accompanied by generation and consumption of H(2) was revealed on the basis of the kinetic analysis and detection of the catalytic intermediates.

Kinetics and Mechanisms of Homogeneous Catalytic Reactions. Part 11. Regioselective Hydrogenation of Quinoline Catalyzed by Rhodium Systems Containing 1,2-Bis(diphenylphosphino)ethane

The system prepared in situ by addition of two equivalents of 1,2-bis(diphenylphosphino)ethane (dppe) to Rh2Cl2(COE)4 (COE = cyclooctene) showed to be an efficient and regioselective precatalyst for the hydrogenation of quinoline (Q). This reaction showed to be independent of the Q concentration and of fractional order on H2 and catalyst concentrations (1.5 and 0.6, respectively). The fractional order on catalyst concentration indicates that several catalytic species with different activities are present in the reaction medium; however, the cationic species [Rh (dppe)2]+ was the only phosphorous-containing compound detected by 31P{1H} NMR. For the acac salt of this cationic bis(dppe) complex, a kinetic study led to the rate law r = {K1k2/(1 + K1[H2])}[M][H2]2; [M(Q)(κ2-dppe)(κ1-dppe)]+ was proposed as the catalytically active species (CAS) of the cycle. The general mechanism involves a reversible oxidative addition of H2 to generate a dihydrido complex, which transfers the hydride ligands to the coordinated Q to yield species containing a 1,2-dihydroquinoline (DHQ) ligand, followed by a second oxidative addition of H2, considered as the rate-determining step of the cycle; hydrogen transfer toward the DHQ ligand yields THQ, regenerates the CAS and restarts the catalytic cycle. The system prepared in situ by addition of two equivalents of 1,2-bis(diphenylphosphino)ethane (dppe) to Rh2Cl2(COE)4 (COE = cyclooctene) showed to be an efficient and regioselective precatalyst for the hydrogenation of quinoline (Q). This reaction proceeds through several catalytic species with different activities; the cationic species [Rh (dppe)2]+ was the only phosphorous compound detected by 31P{1H} NMR. For the acac salt of this cationic bis(dppe) complex, a kinetic study lead to the rate law r = {K1k2/(1 + K1[H2])}[M][H2]2; [M(Q)(κ2-dppe)(κ1-dppe)]+ was proposed as the catalytically active species (CAS) of the cycle. The general mechanism involves a reversible oxidative addition of H2 to generate a dihydrido complex, which transfer the hydride ligands to the coordinated Q to yield species containing a 1,2-dihydroquinoline (DHQ) ligand, followed by a second oxidative addition of H2, considered as the rate-determining step of the cycle; hydrogen transfer toward the DHQ ligand yield THQ, regenerates the CAS and restarts the catalytic cycle.

Ligand-Controlled Highly Regioselective and Asymmetric Hydrogenation of Quinoxalines

The research group of Glorius developed a ligand-controlled hydrogenation of quinoxalines. Selecting the right N-heterocyclic carbene ligand facilitates the regioselective hydro-genation of either the heterocyclic or the carbocyclic ring of a substituted quinoxaline. The hydrogenated products were generally obtained in quantitative yields and by employing chiral N-heterocyclic carbene ruthenium complexes, the 5,6,7,8-tetrahydroquinoxalines were furnished with good enantioselectivities.

ChemInform Abstract: Pd‐MCM‐48: A Novel Recyclable Heterogeneous Catalyst for Chemo‐ and Regioselective Hydrogenation of Olefins and Coupling Reactions.

AbstractA novel, heterogeneous Pd‐MCM‐48 catalyst is developed by encapsulating palladium nanoparticles into the cubic phase of mesoporous MCM‐48 matrix.

ChemInform Abstract: Rapid and Regioselective Hydrogenation of α,β‐Unsaturated Ketones and Alkylidene Malonic Diesters Using Hantzsch Ester Catalyzed by Titanium Tetrachloride.

ChemInform Abstract: Rapid and Regioselective Hydrogenation of α,β‐Unsaturated Ketones and Alkylidene Malonic Diesters Using Hantzsch Ester Catalyzed by Titanium Tetrachloride.

Hydrogenation of Quinolines Using Pd0Nanoparticles on Hydroxyapatite

The formation of Pd0 nanoparticles (Æ = 1-1.5 nm) on hydroxyapatite (HAP) and their application to regioselective hydrogenation is described. Treatment of HAP-bound PdCl2 with H2 for 30 min led to the HAP-supported Pd0 nanoparticles (Pd0HAP). Hydrogenation of quinolines using Pd0HAP gave the corresponding 1,2,3,4-tetrahydroquinolines.

Characterization of Synthetic Iron Oxides and their Performance as Support for Au Catalysts.

AbstractGold(0) catalysts supported on ferric oxide are effective catalysts, and so far, the only heterogeneous ones known for the regioselective hydrogenation of α,β‐unsaturated ketones to the corresponding α,β‐unsaturated secondary alcohols. A set of ferric oxide samples, synthesized under strictly controlled conditions and thoroughly characterized (X‐ray powder diffraction, Mössbauer spectroscopy, micro‐Raman spectroscopy, transmission electron microscopy, temperature‐programmed reduction), were employed as supports of gold(0) catalysts for this reaction. The activity and selectivity of the catalysts changed in the same direction from one catalyst to another; increasing fractions of nanostructured ferric oxide phases in the support (with nanoparticles size lower than 10 nm) increased both. With a 4 % gold catalyst supported on the ferric oxide sample containing the highest proportion of nanostructured matter, we achieved a selectivity of 66 % towards the unsaturated alcohol at more than 90 % conversion in the hydrogenation of benzalacetone (ethanol, 60 °C, 103 kPa), which is one of the best performances ever reported for this reaction.

Rapid and Regioselective Hydrogenation of α,β-Unsaturated Ketones and Alkylidene Malonic Diesters Using Hantzsch Ester Catalyzed by Titanium Tetrachloride

A regioselective hydrogenation of α,β-unsaturated ketones and alkylidene malonic diesters using Hantzsch ester as the reducing agent and titanium tetrachloride as a catalyst is described. The short reaction times and mild reaction conditions are the advantages of this method.

ChemInform Abstract: Homogeneous Catalytic Hydrogenation of Aromatic Hydrocarbons and Heteroaromatic Nitrogen Compounds: Synthetic and Mechanistic Aspects

The synthetic and mechanistic aspects of the homogeneous catalytic hydrogenation of mono and polynuclear aromatic hydrocarbons and the corresponding heteroaromatic nitrogen compounds will be reviewed. A comparison of the regioselectivities under various hydrogenation conditions for both classes of compounds will be discussed for a wide variety of transition-metal complexes with regard to substrate binding at the metal center and the role of free radical intermediates in metal carbonyl hydride reactions, where substrate does not bind to the metal center prior to hydrogen transfer. The polynuclear heteroaromatic nitrogen compounds appear to hydrogenate more readily, under similar reaction conditions, than the polynuclear aromatic hydrocarbons. The relative rates of hydrogenation of a variety of heteroaromatic nitrogen compounds as well as compounds that inhibit and enhance selective hydrogenation of the nitrogen-containing ring will be addressed. A relatively new spectroscopic technique, high pressure nuclear magnetic resonance spectroscopy, will be shown to be a powerful tool to elucidate the mechanisms of the regioselective hydrogenation of polynuclear heteroaromatic nitrogen compounds.

ChemInform Abstract: Regioselective Hydrogenation of Unsaturated Compounds Using Platinum- Zeolite Coupled with Organosilicon Alkoxide by CVD Method.

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Fine Tuning of Pd0 Nanoparticle Formation on Hydroxyapatite and Its Application for Regioselective Quinoline Hydrogenation

Abstract Fine control of the formation of Pd0 nanoparticles with diameters between 1 and 1.5 nm on hydroxyapatite (HAP) was achieved by adjusting the temperature at which the PdII species on the HAP surface (PdIIHAP) was reduced in the presence of 1 atm of molecular hydrogen. The HAP-supported Pd0 nanoparticles (Pd0HAP) having an average diameter of 1.5 nm exhibited significantly high catalytic activity for the regioselective hydrogenation of quinolines to the corresponding 1,2,3,4-tetrahydroquinolines under mild reaction conditions. Moreover, the Pd0HAP catalyst was reusable without appreciable loss of its high catalytic activity or selectivity.

A concise, phosphate-mediated approach to the total synthesis of (-)-tetrahydrolipstatin.

An efficient synthesis of (-)-tetrahydrolipstatin (THL) is reported. This method takes advantage of a phosphate tether-mediated, one-pot, sequential RCM/CM/hydrogenation protocol to deliver THL in eight total steps from a readily prepared (S,S)-triene. The strategy incorporates selective cross-metathesis, regioselective hydrogenation, regio- and diastereoselective cuprate addition, and Mitsunobu inversion for installation of the C5 formamide ester subunit.

Pd-MCM-48: a novel recyclable heterogeneous catalyst for chemo- and regioselective hydrogenation of olefins and coupling reactions

A novel, heterogeneous Pd-MCM-48 catalyst has been developed by encapsulating palladium nanoparticles into the cubic phase of mesoporous MCM-48 matrix at room temperature. The catalyst demonstrated excellent chemo- and regioselectivity for the hydrogenation of olefins at room temperature within 30-80 min. The turnover frequency for the hydrogenation is very high (4400 h(-1)). Interestingly, selectivity of the catalyst was significantly influenced by the mode of addition of palladium precursor. Moreover, the catalyst was also very effective for the coupling reactions with the formation of carbon-carbon and carbon-nitrogen bonds under ligand-free and aerobic conditions.

Kinetics and Mechanisms of Homogeneous Catalytic Reactions. Part 10. Regioselective Hydrogenation of Quinoline Catalyzed by the Systems M2Cl2(COE)4/2 Triphos [M = Rh, Ir; COE = Cyclooctene; Triphos = 1,1,1-Tris(diphenylphosphinomethyl)Ethane

The systems prepared in situ by addition of two equivalents of 1,1,1-tris(diphenylphosphinomethyl)ethane (triphos) to M2Cl2(COE)4 (M = Rh, Ir; COE = cyclooctene) showed to be efficient and regioselective precatalysts for the hydrogenation of quinoline. For both systems, kinetic studies lead to the rate laws r = {K 1 k 2/(1 + K 1[H2])}[M][H2]2; it was proposed that the catalytically active species are the cationic unsaturated complexes [M(Q)(triphos)]+. The general mechanism involves a rapid and partial hydrogenation of these species to generate complexes of the type [M(H)2(Q)(triphos)]+ (isolated and characterized for M = Ir), which transfer the hydride ligands to the coordinated Q to yield species containing a 1,2-dihydroquinoline (DHQ) ligand, followed by a second oxidative addition of H2, considered as the rate-determining step of the cycle; hydrogen transfer toward the DHQ ligand yield THQ, regenerates the active species and restarts the catalytic cycle. The systems prepared in situ by addition of two equivalents of 1,1,1-tris(diphenylphosphinomethyl)ethane (triphos) to M2Cl2(COE)4 (M = Rh, Ir; COE = cyclooctene) showed to be efficient and regioselective precatalysts for the hydrogenation of quinoline. For both systems, kinetic studies lead to the rate laws r = {K 1 k 2/(1 + K 1[H2])}[M][H2]2; it was proposed that the catalytically active species are the cationic unsaturated complexes [M(Q)(triphos)]+. The general mechanism involves a rapid and partial hydrogenation of these species to generate complexes of the type [M(H)2(Q)(triphos)]+ (isolated and characterized for M = Ir), which transfer the hydride ligands to the coordinated Q to yield species containing a 1,2-dihydroquinoline (DHQ) ligand, followed by a second oxidative addition of H2, considered as the rate-determining step of the cycle; hydrogen transfer toward the DHQ ligand yield THQ, regenerates the active species and restarts the catalytic cycle.

Regioselective Hydrogenation of α,β-Unsaturated Ketones over Wilkinson’s Catalyst

The reactivity of a variety of α,β-unsaturated acyclic and cyclic ketones towards regioselective hydrogenation in the presence of Wilkinson's catalyst was determined. Hydrogenation of sterically hindered α,β-unsaturated ketones proceeded at inefficient rates, if at all.

Silica supported silver nanoparticles from a silver(I) carboxylate: Highly active catalyst for regioselective hydrogenation

Abstract The selective hydrogenation of the α,β-unsaturated aldehyde citral (3,7-dimethyl-2,6-octadienal) was investigated with nano-sized silver particles on silica (Ag/SiO 2 ). The catalysts were synthesized from the precursors silver nitrate and silver 2-[2-(2-methoxyethoxy)ethoxy]acetate [AgO 2 C(CH 2 OCH 2 ) 3 H], respectively, and a mean particle diameter in the range of 4–8 nm could be detected via TEM. The results show that these catalysts are selective for C O hydrogenation of citral ( S UOL = 71–77% at X = 50%) even at high conversion levels. In addition, the silver carboxylate [AgO 2 C(CH 2 OCH 2 ) 3 H], soluble in water as well as in polar organic solvents, offers a straightforward preparation route for nano-sized silver particles generation.