Sheldon complex

Key Words Ethylene oxide, Propylene oxide. Epoxybutene, Market, Isoamylene oxide. Cyclohexene oxide. Styrene oxide, Norbornene oxide. Epichlorohydrin, Epoxy resins, Carbamazepine, Terpenes, Limonene, a-Pinene, Fatty acid epoxides, Allyl epoxides, Sharpless epoxidation. Turnover frequency, Space time yield. Hydrogen peroxide, Polyoxometallates, Phase-transfer reagents, Methyltrioxorhenium (MTO), Fluorinated acetone, Alkylmetaborate esters. Alumina, Iminium salts, Porphyrins, Jacobsen-Katsuki oxidation, Salen, Peroxoacetic acid, P450 BM-3, Escherichia coli, lodosylbenzene, Oxometallacycle, DFT, Lewis acid mechanism, Metalladioxolane, Mimoun complex, Sheldon complex, Michaelis-Menten, Schiff bases. Redox mechanism. Oxygen-rebound mechanism, Spiro structure. 2008 Elsevier B.V. 

FIGURE 1.11 Mo complexes involved in epoxidation, (a) Mimoun peroxo complex and (b) Sheldon complex. 

Sheldon et al. have combined a KR catalyzed by CALB with a racemization catalyzed by a Ru(II) complex in combination with TEMPO (2,2,6,6-tetramethylpi-peridine 1-oxyl free radical) [28]. They proposed that racemization involved initial ruthenium-catalyzed oxidation of the alcohol to the corresponding ketone, with TEMPO acting as a stoichiometric oxidant. The ketone was then reduced to racemic alcohol by ruthenium hydrides, which were proposed to be formed under the reaction conditions. Under these conditions, they obtained 76% yield of enantiopure 1-phenylethanol acetate at 70° after 48 hours. 

Green Oxidation of Alcohols using Biominetic Cu Complexes and Cu Enzymes as Catalysts Isabel W.C.E Arends, Patrick Gamez and Roger A. Sheldon... 

An extended series of primary oxidants of TEMPO was investigated by Sheldon and coworkers , but we do not report on all of them suffice it to observe that the selectivity of oxidation of primary vs. secondary alcohols varies substantially among the procedures, as well as the efficiency of oxidation of primary aliphatic alcohols, thereby concurring to make the matter complex. 

Sheldon RA, Arends IWCE (2003) In Simandi LI (ed) Advances in catalytic deactivation of dioxygen by metal complexes. Kluwer, Dordrecht, pp 123-155... 

Sheldon, R. A. Biocatalytic and biomimetic oxidations from an industrial perspective, Biomimetic Oxidations Catalyzed by Transition Metal Complexes , Ed. Meunier, B. Imperial College Press London, 2000, pp. 613-662. 

Cai, W.J., Wiebe, W.J., Wang, Y., and Sheldon, J.E. (2000) Intertidal marsh as a source of dissolved inorganic carbon and a sink of nitrate in the Satilla River estuarine complex in the southeastern U.S. Lirnnol. Oceanogr. 45, 1743-1752. 

Molecular hydrogen can reduce cyclic peroxo complexes, for example Reaction 30 (111), and Sheldon and Van Doom (33) had envisaged epoxide production via a similar process, Reaction 31. A mechanism based on such reactivity (with subsequent epoxide isomerization) is a possibility for our catalysis using H2/02, although Reaction 31 did not occur under mild conditions (33). Isolation of a related peroxometallocyclic rhodium complex, (Ph3As)2Rh[02C2(CN)4] + (92), allows for a testing of Reaction 31 at a Rh center. 

Sheldon and co-workers have circumvented this problem to some extent by three approaches 46 the use of sulfuric acid to reduce the pH, by addition of ammonium fluoride and by addition of ammonia. Ammonia stabilizes monomeric chromium(III) species via the formation of amine complexes, and the fluoride effects dissolution of the silica at near-neutral pH. The three catalysts that were synthesized were evaluated in the oxidative cleavage of styrene with 35% m/m hydrogen peroxide in 1,2-dichloroethane at 70 °C (Table 4.4). The... 

A number of systems consist of a palladium salt, typically PdCb or Pd(OAc)2, with abase. For example, PdCb-NaOAc catalyzes the aerobic oxidation of secondary alcohols in ethylene carbonate under nuld conditions. Sheldon has carried out mechanistic investigations on a number of related Pd systems and shown that water-soluble complexes of Pd(II) with phenanthrohnes are stable, recyclable catalysts for the selective aerobic oxidation of a wide range of alcohols to aldehydes, ketones, and carboxylic acids in a biphasic liquid liquid system. The active catalyst is a dihydroxy-bridged palladium dimer. 

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