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Complexes salen

In order to make these oxidative reactions of 1,3-dienes catalytic, several reoxidants are used. In general, a stoichiometric amount of benzoquinone is used. Furthermore, Fe-phthalocyanine complex or Co-salen complex is used to reoxidize hydroquinone to benzoquinone. Also, it was found that the reaction is faster and stereoselectivity is higher when (phenylsulflnyl)benzoquinone (383) is used owing to coordination of the sulfinyl group to Pd, Thus the reaction can be carried out using catalytic amounts of PdfOAcji and (arylsulfinyl)benzoquinone in the presence of the Fe or Co complex under an oxygen atmosphere[320]. Oxidative dicyanation of butadiene takes place to give l,4-dicyano-2-butene(384) (40%) and l,2-dicyano-3-butene (385)[32l]. [Pg.73]

The Jacobsen-Katsuki epoxidation reaction is an efficient and highly selective method for the preparation of a wide variety of structurally and electronically diverse chiral epoxides from olefins. The reaction involves the use of a catalytic amount of a chiral Mn(III)salen complex 1 (salen refers to ligands composed of the N,N -ethylenebis(salicylideneaminato) core), a stoichiometric amount of a terminal oxidant, and the substrate olefin 2 in the appropriate solvent (Scheme 1.4.1). The reaction protocol is straightforward and does not require any special handling techniques. [Pg.29]

To date, a wide variety of structurally different chiral Mn(III)salen complexes have been prepared, of which only a handful have emerged as synthetically useful catalysts. By far the most widely used Mn(III)salen catalyst is the commercially available Jacobsen catalyst wherein R= -C4H8- and R = = i-Bu (Scheme 1.4.1). In... [Pg.29]

In 1990, Jacobsen and subsequently Katsuki independently communicated that chiral Mn(III)salen complexes are effective catalysts for the enantioselective epoxidation of unfunctionalized olefins. For the first time, high enantioselectivities were attainable for the epoxidation of unfunctionalized olefins using a readily available and inexpensive chiral catalyst. In addition, the reaction was one of the first transition metal-catalyzed... [Pg.29]

A concerted [2 + 2] cycloaddition pathway in which an oxametallocycle intermediate is generated upon reaction of the substrate olefin with the Mn(V)oxo salen complex 8 has also been proposed (Scheme 1.4.5). Indeed, early computational calculations coupled with initial results from radical clock experiments supported the notion.More recently, however, experimental and computational evidence dismissing the oxametallocycle as a viable intermediate have emerged. In addition, epoxidation of highly substituted olefins in the presence of an axial ligand would require a seven-coordinate Mn(salen) intermediate, which, in turn, would incur severe steric interactions. " The presence of an oxametallocycle intermediate would also require an extra bond breaking and bond making step to rationalize the observation of trans-epoxides from dy-olefms (Scheme 1.4.5). [Pg.32]

In most of the successful Diels-Alder reactions reported, dienes containing no heteroatom have been employed, and enantioselective Diels-Alder reactions of multiply heteroatom-substituted dienes, e.g. Danishefsky s diene, are rare, despite their tremendous potential usefulness in complex molecular synthesis. Rawal and coworkers have reported that the Cr(III)-salen complex 15 is a suitable catalyst for the reaction of a-substituted a,/ -unsubstituted aldehydes with l-amino-3-siloxy dienes [21] (Scheme 1.28, Table 1.12). The counter-ion of the catalyst is important and good results are obtained in the reaction using the catalyst paired with the SbFg anion. [Pg.21]

Table 1.12 Asymmetric Diels-Alder reactions catalyzed by the Cr-salen complex 15 [21]... Table 1.12 Asymmetric Diels-Alder reactions catalyzed by the Cr-salen complex 15 [21]...
Song and Roh investigated the epoxidation of compounds such as 2,2-dimethylchromene with a chiral Mn (salen) complex (Jacobsen catalyst) in a mixture of [BMIM][PFg] and CH2CI2 (1 4 v/v), using NaOCl as the oxidant (Scheme 5.2-12) [62]. [Pg.233]

A breakthrough in the area of asymmetric epoxidation came at the beginning of the 1990s, when the groups of Jacobsen and Katsuki more or less simultaneously discovered that chiral Mn-salen complexes (15) catalyzed the enantioselective formation of epoxides [71, 72, 73], The discovery that simple achiral Mn-salen complexes could be used as catalysts for olefin epoxidation had already been made... [Pg.204]

Table 6.8 Enantioselective epoxidation of 1,2-dihydronaphtha-lene with Mnm salen complexes. Table 6.8 Enantioselective epoxidation of 1,2-dihydronaphtha-lene with Mnm salen complexes.
Ordinary alkenes (without an allylic OH group) have been enantioselectively epoxidized with sodium hypochlorite (commercial bleach) and an optically active manganese-complex catalyst. Variations of this oxidation use a manganese-salen complex with various oxidizing agents, in what is called the Jacobsen-Katsuki... [Pg.1053]

In the case of BAE and salen complexes with simple alkyl ligands these different configurations can usually be distinguished by their color and... [Pg.343]

Catalytic hydrogenation with platinum liberates the hydrocarbon from methylcobalamin (57) and from alkyl-Co-DMG complexes (161), but not from pentacyanides with primary alkyl, vinyl, or benzyl ligands, though the cr-allyl complex yields propylene (109). Sodium sand gives mixtures of hydrocarbons with the alkyl-Co-salen complexes (64). Dithioerythritol will liberate methane from a variety of methyl complexes [cobalamin, DMG, DMG-BF2, G, DPG, CHD, salen, and (DO)(DOH)pn] (156), as will 1,4-butanedithiol from the DMG complex (157), and certain unspecified thiols will reduce DMG complexes with substituted alkyl ligands (e.g., C0-CH2COOH ->CH3C00H) (163, 164). Reaction with thiols can also lead to the formation of thioethers (see Section C,3). [Pg.432]

Only a few years after the development of the homogeneous chiral Mn(salen) complexes by Jacobsen and Katsuki, several research groups began to study different immobiUzation methods in both liquid and soUd phases. Fluorinated organic solvents were the first type of Uquid supports studied for this purpose. The main problem in the appUcation of this methodology is the low solubility of the catalytic complex in the fluorous phase. Several papers were pubUshed by Pozzi and coworkers, who prepared a variety of salen ligands with perfluorinated chains in positions 3 and 5 of the saUcyUdene moiety (Fig. 2). [Pg.153]

The first application of ionic hquids for salen complexes dealt with the epoxidation of alkenes [14]. Jacobsen s Mn complex was immobilized in [bmimjlPFe] and different alkenes were epoxidized with aqueous NaOCl solution at 0 °C. As the ionic solvent sohdified at this temperature, dichloromethane was used as a cosolvent. The recychng procedure consisted of washing with water, evaporation of dichloromethane, and product extraction with hexane. The results (Table 3) were excellent and only a slow decay in activity and enantioselectivity was detected after several cycles. [Pg.157]

Although these examples show the possible immobilization on clays and mesoporous zeolites, the most widely used support for salen complexes has... [Pg.164]

Asymmetric Ring Opening of Some Terminal Epoxides Catalyzed by Dimeric Type Novel Chiral Co(Salen) Complexes... [Pg.205]

Chiral aluminum SALEN complexes have been used by Kee for asymmetric addition of dimethyl phosphite to benzaldehyde derivatives (Scheme 5-43). [Pg.164]

The Al-Me complexes 28a-b were catalyst precursors for the reaction, which was not affected by air or water and did not require dry or degassed reagents. This system gave high yields but ees ranged only from 10 to 54% with 28a. In contrast, the t-Bu-substituted SALEN complex 28b gave racemic products at a slower rate [32]. [Pg.164]

Scheme 5.13 Electropolymerised Cr-salen-complexes for hetero-Diels-Alder reactions. Scheme 5.13 Electropolymerised Cr-salen-complexes for hetero-Diels-Alder reactions.

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Aluminium chiral salenAl complexes

Aluminium complexes salen-type

Aluminium salen complex

Bimetallic-salen complexes

Chiral Co-salen complex

Chiral indium salen complexes

Chiral salen complexes

Chiral salen-manganese complex

Chromium -salen complexes

Chromium-salen complexes, asymmetric

Co-salen complexes

Complex, Ruthenium-salene

Copper salen complexes

Cr-salen complex

Electropolymerized Films of Salen Complexes

Epoxidation with Metal(salen) Complexes

Ethers, Taddol, Nobin and Metal(salen) Complexes as Chiral Phase-Transfer Catalysts for Asymmetric Synthesis

Group 7 metal-promoted oxidations epoxidation by salen manganese complexes

Homogeneous epoxidation salen complexes

III) Salen Complexes

Iron salen complexes

Katsuki manganese -salen complex

Kinetic metal Salen complexes

Manganese catalysts salen complexes

Manganese salen complexes, alkene

Manganese salen complexes, alkene epoxidation

Manganese-salen complex

Mn-salen complex

Nickel salen complex

Organocobalt compounds Co -salen complex

Oxidation chiral salen complexes

Oxidation with metal salen complexes

Palladium salen)complexes

Porphyrin and salen complexes

Salen

Salen complex catalyst

Salen complex, immobilised

Salen ligands complexes

Salen ligands, manganese complexes

Salen-based manganese complexes

Salen-cobalt complex

Salen-metal complexes

Salen. aluminum complexes

Salene complexes, electrooxidation

Salens

Salens cobalt complex

Salens nickel complex

Supported catalysts manganese-salen complexes

Vanadyl salen complexes

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