A series of easily prepared Lewis basic ionic liquids were developed for cyclic carbonate synthesis from epoxide and carbon dioxide at low pressure without utilization of any organic solvents or additives. Notably, quantitative yields together with excellent selectivity were attained whenCl) was used as a catalyst. Furthermore, the catalyst could be recycled over five times without appreciable loss of catalytic activity. The effects of the catalyst structure and various reaction parameters on the catalytic performance were investigated in detail. This protocol was found to be applicable to a variety of epoxides producing the corresponding cyclic carbonates in high yields and selectivity. Therefore, this solvent-free process thus represents an environmentally friendly example for the catalytic conversion of carbon dioxide into value-added chemicals by employing Lewis basic ionic liquids as catalyst. A possible catalytic cycle for the hydrogen bond-assisted ring-opening of epoxide and activation of carbon dioxide induced by the nucleophilic tertiary nitrogen of the ionic liquid was also proposed.

A bifunctional cobalt-salen complex containing a Lewis acidic metal center and a quaternary phosphonium salt unit anchored on the ligand effectively catalyzes the synthesis of cyclic carbonates from CO2 and epoxides under mild conditions without the utilization of additional organic solvents or co-catalysts. The effects of various reaction variables on the catalytic performance were studied in detail and indicate an optimized reaction temperature of about I00 degrees C and CO2 pressure of around 4 MPa, although the reaction proceeds smoothly even at pressures as low as 2 MPa. The catalyst is applicable to a variety of epoxides, producing the corresponding cyclic carbonates in good yields in most cases. Furthermore, the catalyst can be easily recovered and reused several times without significant loss of its catalytic activity. This process thus represents a greener pathway for the environmentally benign chemical fixation of CO2 to produce cyclic carbonates.

A benzimidazole-based nonheme manganese complex efficiently catalyzes benzylic, aliphatic C-H as well as tertiary C-H oxidation with hydrogen peroxide as the oxidant in the presence of acetic acid as additive. (18)O labeling experiments suggest the reaction may proceed via a high-valent manganese-oxo intermediate.

We report a remarkable Brønsted acid effect in the epoxidation of olefins by nonheme manganese catalysts and aqueous hydrogen peroxide. More specifically, a mononuclear nonheme manganese complex bearing a tetradentate N4 ligand, Mn(II)(Dbp-MCP)(OTf)2 (Dbp-MCP = (1R,2R)-N,N'-dimethyl-N,N'-bis((R)-(3,5-di-tert-butyl-phenyl)-2-pyridinylmethyl)cyclohexane-1,2-diamine; OTf(-) = CF3SO3(-)), is a highly efficient catalyst in the epoxidation of olefins by aqueous H2O2 in the presence of H2SO4 (1-3 mol %). The yields of epoxide products as well as the chemo- and enantioselectivities increase dramatically in the presence of H2SO4; no formation of epoxides is observed in the absence of H2SO4. In addition, the product yields and enantioselectivities are dependent significantly on the manganese catalysts and Brønsted acids. The catalytic epoxidation of olefins by other oxidants, such as peracids, alkyl hydroperoxides, and iodosylbenzene, is also affected by the presence of H2SO4; product yields and enantioselectivities are high and similar irrespective of the oxidants in the presence of H2SO4, suggesting that a common epoxidizing intermediate is generated in the reactions of [Mn(II)(Dbp-MCP)](2+) and the oxidants. Mechanistic studies, performed with (18)O-labeled water (H2(18)O) and cumyl hydroperoxide, reveal that a high-valent manganese-oxo species is formed as an epoxidizing intermediate via O-O bond heterolysis of Mn-OOH(R) species. The role of H2SO4 is proposed to facilitate the formation of a high-valent Mn-oxo species and to increase the oxidizing power and enantioselectivity of the Mn-oxo oxidant in olefin epoxidation reactions. Density functional theory (DFT) calculations support experimental results such as the formation of a Mn(V)-oxo species as an epoxidizing intermediate.

Die Stetter‐Reaktion nutzt eine umgepolte Reaktivität zur katalytischen Bildung 1,4‐difunktionalisierter Produkte. Bei der vorgestellten ersten enzymatischen 1,4‐Addition ermöglicht das ThDP‐abhängige Enzym PigD eine anspruchsvolle asymmetrische intermolekulare Stetter‐Reaktion (siehe Schema).

Chiral bioinspired iron complexes of N 4 ligands based on the ethylenediamine backbone display remarkable levels of enantioselectivity for the first time in the asymmetric epoxidation of a,b-unsaturated ketones using hydrogen peroxide (up to 87% ee) or peracetic acid as oxidant, respectively. Notablely, isotopic labeling with H 2 18O strongly demonstrated that there is a reversible water binding step prior to generation of the significant intermediate.usually derived from the decay of the LFe(IV)=O species or thermodynamic sinks for a number of iron complexes was identified by HR-MS. In addition, the possible mechanisms were proposed and LFe(V)=O species may be the main active intermediate in the catalytic system.

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Bioinspired manganese and iron complexes bearing nonporphyrinic tetradentate N4 ligands are highly efficient catalysts in asymmetric oxidation reactions by hydrogen peroxide (H2O2), in which carboxylic acid is employed as an essential additive to improve product yields and stereo-, regio-, and enantioselectivities. The metal catalysts should possess two cis-binding sites for oxidant (e.g., H2O2) and carboxylic acid to generate high-valent metal-oxo species as active oxidants via a “carboxylic acid-assisted” mechanism. In the present study, we have investigated the role(s) of carboxylic acid and the nature of reactive intermediate(s) in the manganese complex-catalyzed enantioselective epoxidation of olefins, by employing non-heme manganese catalysts, such as 1 bearing a tetradentate N4 ligand (LN4) and 2 bearing a pentadentate N5 ligand (LN5), and using various oxidants, such as H2O2, alkyl hydroperoxides, and iodosylbenzene (PhIO). As expected, 1 possessing two cis-binding sites is an effective catalyst irrespective of the oxidants in the presence of carboxylic acid. In contrast, 2 possessing only one binding site is not an effective catalyst in the reactions of H2O2 and alkyl hydroperoxides even in the presence of carboxylic acid. However, unexpectedly, 2 turns out to be an effective catalyst in the asymmetric epoxidation of olefins by PhIO in the presence of carboxylic acid. The latter result indicates that a manganese complex, which cannot bind carboxylic acid as an auxiliary ligand, can afford a high enantioselectivity, probably through a second-sphere coordination interaction between carboxylic acid and the oxo group of a presumed manganese-oxo oxidant. We have also provided indirect evidence supporting that a high-valent Mn­(V)-oxo species is the active oxidant in the catalytic asymmetric epoxidation reactions.