Selective Hydrogenation of Cyclic Imides to Diols and Amines and Its Application in the Development of a Liquid Organic Hydrogen Carrier.
ABSTRACT: Direct hydrogenation of a broad variety of cyclic imides to diols and amines using a ruthenium catalyst is reported here. We have applied this strategy toward the development of a new liquid organic hydrogen carrier system based on the hydrogenation of bis-cyclic imide that is formed by the dehydrogenative coupling of 1,4-butanediol and ethylenediamine using a new ruthenium catalyst. The rechargeable system has a maximum gravimetric hydrogen storage capacity of 6.66 wt%.
Project description:A sustainable, new synthesis of oxalamides, by acceptorless dehydrogenative coupling of ethylene glycol with amines, generating H<sub>2</sub>, homogeneously catalyzed by a ruthenium pincer complex, is presented. The reverse hydrogenation reaction is also accomplished using the same catalyst. A plausible reaction mechanism is proposed based on stoichiometric reactions, NMR studies, X-ray crystallography as well as observation of plausible intermediates.
Project description:Formic acid and its salts are an alternative source for hydrogen generation. In this study, we store hydrogen using the formate-bicarbonate cycle. Aqueous sodium bicarbonate is hydrogenated to form sodium formate, which can then be decomposed to release hydrogen and sodium bicarbonate. The hydrogenation step is carried out under mild conditions in the presence of a homogeneous ruthenium catalyst. Hydrogen charge is realized at 70 °C under a hydrogen pressure of 20 bar, achieving yields > 80% and turnover number > 610. The catalyst is stable and robust through numerous cycles of the hydrogenation reaction. The formate ion formed during the bicarbonate hydrogenation is assayed and quantified by ion chromatography.
Project description:Herein, we report a one-step peroxide mediated heterogeneous catalytic oxidation of amides to imides utilizing a series of manganese oxides. Among them, Cs/Mn2O3 was found to be the most active catalyst for the selective partial oxidation of N-benzylbenzamide to diphenyl imide. We have been able to apply an optimized oxidation method to other aromatic substrates. The feasibility of using air as an oxidant, the heterogeneous nature, inexpensive catalytic materials, respectable turnover numbers, and chemoselectivity to imides make this methodology an attractive choice for functional group transformations of amides to imides.
Project description:Dehydrogenative annulation reactions are among the most straightforward and efficient approach for the preparation of cyclic structures. However, the applications of this strategy for the synthesis of saturated heterocycles have been rare. In addition, reported dehydrogenative bond-forming reactions commonly employ stoichiometric chemical oxidants, the use of which reduces the sustainability of the synthesis and brings safety and environmental issues. Herein, we report an organocatalyzed electrochemical dehydrogenative annulation reaction of alkenes with 1,2- and 1,3-diols for the synthesis of 1,4-dioxane and 1,4-dioxepane derivatives. The combination of electrochemistry and redox catalysis using an organic catalyst allows the electrosynthesis to proceed under transition metal- and oxidizing reagent-free conditions. In addition, the electrolytic method has a broad substrate scope and is compatible with many common functional groups, providing an efficient and straightforward access to functionalized 1,4-dioxane and 1,4-dioxepane products with diverse substitution patterns.
Project description:A nonenzymatic dynamic kinetic resolution of acyclic and cyclic benzylic alcohols is reported. The approach merges rapid transition-metal-catalyzed alcohol racemization and enantioselective Cu-H-catalyzed dehydrogenative Si-O coupling of alcohols and hydrosilanes. The catalytic processes are orthogonal, and the racemization catalyst does not promote any background reactions such as the racemization of the silyl ether and its unselective formation. Often-used ruthenium half-sandwich complexes are not suitable but a bifunctional ruthenium pincer complex perfectly fulfills this purpose. By this, enantioselective silylation of racemic alcohol mixtures is achieved in high yields and with good levels of enantioselection.
Project description:The first general and efficient non-noble metal-catalysed reductive C2-alkoxylation of cyclic imides (phthalimides and succinimides) is presented. Crucial for the success is the use of [Co(BF<sub>4</sub>)<sub>2</sub>·6H<sub>2</sub>O/triphos (<b>L1</b>)] combination and no external additives are required. Using the optimal cobalt-system, the hydrogenation of the aromatic ring of the parent phthalimide is avoided and only one of the carbonyl groups is selectively functionalized. The resulting products, <i>N</i>- and aryl-ring substituted 3-alkoxy-2,3-dihydro-1<i>H</i>-isoindolin-1-one and <i>N</i>-substituted 3-alkoxy-pyrrolidin-2-one derivatives, are prepared under mild conditions in good to excellent isolated yields. Intramolecular reductive couplings can also be performed affording tricyclic compounds in a one-step process. The present protocol opens the way to the development of new base-metal processes for the straightforward synthesis of functionalized <i>N</i>-heterocyclic compounds of pharmaceutical and biological interest.
Project description:Development of a simple and easy handing process for preparation of multifunctional heterogenous catalysts and exploration of their applications in sequential organic transformation are of great significance in heterogeneous asymmetric catalysis. Herein, through the utilization of a BF4- anion-bonding strategy, we anchor conveniently both organic bases and chiral ruthenium complex into the nanopores of Me-FDU-12, fabricating a Lewis base/Ru bifunctional heterogeneous catalyst. As we envisaged, cyclic amine as a Lewis base promotes an intermolecular aza-Michael addition between enones and arylamines, affording ?-secondary amino ketones featuring with aryl motif, whereas ruthenium/diamine species as catalytic promoter boosts an asymmetric transfer hydrogenation of ?-secondary amino ketones to ?-secondary amino alcohols. As expected, both enhance synergistically the aza-Michael addition/asymmetric transfer hydrogenation one-pot enantioselective organic transformation, producing chiral ?-secondary amino alcohols with up to 98% enantioselectivity. Unique features, such as operationally simple one-step synthesis of heterogeneous catalyst, homo-like catalytic environment as well as green sustainable process make this heterogeneous catalyst an attracting in a practical preparation of optically pure pharmaceutical intermediates of antidepressants.
Project description:The synthesis and antiviral activity of a series of novel polycyclic analogues of the orthopoxvirus egress inhibitor tecovirimat (ST-246) is presented. Several of these compounds display sub-micromolar activity against vaccinia virus, and were more potent than cidofovir (CDV). The more active compounds were about 10-fold more active than CDV, with minimum cytotoxic concentrations above 100 μM. Chemical manipulations of the two carbon-carbon double bonds present in the compounds were carried out to further explore the structure-activity relationships of these new polycyclic imides. Hydrogenation of the two carbon-carbon double bonds decreases antiviral activity, whereas either cyclopropanation or epoxidation of the double bonds fully eliminates the antiviral activity.
Project description:The bis(trimethylsilyl)-substituted hydroxycyclopentadienyl ruthenium hydride [2,5-(SiMe(3))(2)-3,4-(CH(2)OCH(2))(?(5)-C(4)COH)]Ru(CO)(2)H (10) is an efficient catalyst for hydrogenation of aldehydes and ketones. Because 10 transfers hydrogen rapidly to aldehydes and ketones and because it does not form an inactive bridging hydride during reaction, hydrogenation of aldehydes and ketones can be performed at room temperature under relatively low hydrogen pressure (3 atm); this is a significant improvement compared with previously developed Shvo type catalysts. Kinetic and (2)H NMR spectroscopic studies of the stoichiometric reduction of aldehydes and ketones by 10 established a two-step process for the hydrogen transfer: (1) rapid and reversible hydrogen bond formation between OH of 10 and the oxygen of the aldehyde or ketone, (2) followed by slow transfer of both proton and hydride from 10 to the aldehyde or ketone. The stoichiometric and catalytic activities of complex 10 are compared to those of other Shvo type ruthenium hydrides and related iron hydrides.
Project description:A green process for the hydrogenation of sugars to sugar alcohols was designed in aqueous medium using hydrous ruthenium oxide (HRO) as a pre-catalyst supported on Na-? zeolite. Under optimized reaction conditions, sugars such as xylose, glucose, and mannose converted completely to the corresponding sugar alcohols xylitol, sorbitol, and mannitol with 100% selectivity. The pre-catalyst (HRO) is converted <i>in situ</i> to active Ru(0) species during the reaction under H<sub>2</sub>, which is responsible for the hydrogenation. The catalyst was recyclable up to five cycles with no loss in activity. The reduction of HRO to the active Ru(0) species is dependent on the reaction temperature and H<sub>2</sub> pressure. Ru(0) formation increased and consequently an increased hydrogenation of sugars was observed with an increase in reaction temperature and hydrogen pressure. Further, <i>in situ</i> generation of Ru(0) from HRO was assessed in different solvents such as water, methanol, and tetrahydrofuran; aqueous medium was found to be the most efficient in reducing HRO. This work further demonstrates the use of supported HRO as an efficient pre-catalyst for biomass-based hydrogenation reactions.