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Salens

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]

To a solution of indoline (20 mM in MeOH) was added Co(salen) (0.10 equiv.) and O2 was bubbled through the suspension at 25°C. After 1 h the suspension became homogeneous and the solvent was removed in vacuo and the product purified by chromatography on silica gel. [Pg.149]

Chiral (salene)Ti(IV) complexes, TMSCN. This system is selective for aldehydes the asymmetric induction is dependent upon aldehyde struc-... [Pg.349]

Figure 14.5 (a) Reaction of Al,Al -ethylenebis(3-Bu -salicylideniminato)cobalt(II) with dioxygen and pyridine to form the superoxo complex [Co(3-Bu Salen)2(02)py] the py ligand is almost coplanar with the Co-O-O plane, the angle between the two being 18°.< (b) Reversible formation of the peroxo complex [Ir(C0)Cl(02)(PPh3)2]. The more densely shaded part of the complex is accurately coplanar. ... [Pg.617]

Complexes with mixed 0-and A -donor ligands such as edta and Schiff bases are well known and [Fe(edta)(H20)] and [Fe(salen)Cl] are examples of 7-coordinate (pentagonal bipyramidal) and 5-coordinate (square-pyramidal) stereochemistries respectively. [Pg.1090]

As in the case of Cr , oxo-bridged species with magnetic moments reduced below the spin-only value (5.9 BM in the case of high-spin Fe ) are known. [Fe(salen)]20, for instance, has a moment of 1.9 BM at 298 K which falls to 0.6 BM at 80 K and the interaction between the electron spins on the 2 metal... [Pg.1090]

Square planar complexes are also well authenticated if not particularly numerous and include [Co(phthalocyanine)] and [Co(CN)4] as well as [Co(salen)] and complexes with other Schiff bases. These are invariably low-spin with magnetic moments at room temperature in the range 2.1-2.9 BM, indicating 1 unpaired electron. They are primarily of interest because... [Pg.1132]

The difficulty of assigning a formal oxidation state is more acutely seen in the case of 5-coordinate NO adducts of the type [Co(NO)(salen)]. These are effectively diamagnetic and so have no unpaired electrons. They may therefore be formulated either as Co -NO or Co -NO+. The infrared absorptions ascribed to the N-O stretch lie in the range 1624-1724 cm which is at the lower end of the range said to be characteristic of NO+. But, as in all such cases which are really concerned with the differing polarities of covalent bonds, such formalism should not be taken literally. [Pg.1133]

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]

While generation of a Mn(V)oxo salen intermediate 8 as the active chiral oxidant is widely accepted, how the subsequent C-C bond forming events occur is the subject of some debate. The observation of frans-epoxide products from cw-olefins, as well as the observation that conjugated olefins work best support a stepwise intermediate in which a conjugated radical or cation intermediate is generated. The radical intermediate 9 is most favored based on better Hammett correlations obtained with o vs. o . " In addition, it was recently demonstrated that ring opening of vinyl cyclopropane substrates produced products that can only be derived from radical intermediates and not cationic intermediates. ... [Pg.32]

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]

To date, no effieient and general Mn(III)salen-eatalyst exists that effeets epoxidation of 1,1-disubstituted olefins with good enantioseleetivity. [Pg.37]

The Jacobsen-Katsuki epoxidation reaction has found wide synthetic utility in both academia and industrial settings. As described previously, the majority of olefin classes, when conjugated, undergo Mn(salen)-catalyzed epoxidation in good enantioselectivity. In this section, more specific synthetic utilities are presented. [Pg.38]

The first asymmetric Mn(salen)-catalyzed epoxidation of silyl enol ethers was carried out by Reddy and Thornton in 1992. Results from the epoxidation of various silyl enol ethers gave the corresponding keto-alcohols in up to 62% ee Subsequently, Adam and Katsuki " independently optimized the protocol for these substrates yielding products in excellent enantioselectivity. [Pg.39]

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]...
Chiral salen chromium and cobalt complexes have been shown by Jacobsen et al. to catalyze an enantioselective cycloaddition reaction of carbonyl compounds with dienes [22]. The cycloaddition reaction of different aldehydes 1 containing aromatic, aliphatic, and conjugated substituents with Danishefsky s diene 2a catalyzed by the chiral salen-chromium(III) complexes 14a,b proceeds in up to 98% yield and with moderate to high ee (Scheme 4.14). It was found that the presence of oven-dried powdered 4 A molecular sieves led to increased yield and enantioselectivity. The lowest ee (62% ee, catalyst 14b) was obtained for hexanal and the highest (93% ee, catalyst 14a) was obtained for cyclohexyl aldehyde. The mechanism of the cycloaddition reaction was investigated in terms of a traditional cycloaddition, or formation of the cycloaddition product via a Mukaiyama aldol-reaction path. In the presence of the chiral salen-chromium(III) catalyst system NMR spectroscopy of the crude reaction mixture of the reaction of benzaldehyde with Danishefsky s diene revealed the exclusive presence of the cycloaddition-pathway product. The Mukaiyama aldol condensation product was prepared independently and subjected to the conditions of the chiral salen-chromium(III)-catalyzed reactions. No detectable cycloaddition product could be observed. These results point towards a [2-i-4]-cydoaddition mechanism. [Pg.162]

Chiral salen-cobalt(III) complexes can also catalyze the reaction of glyoxylates with activated dienes to give the cycloaddition product in moderate yield and ee [29]. [Pg.167]

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]


See other pages where Salens is mentioned: [Pg.73]    [Pg.148]    [Pg.149]    [Pg.149]    [Pg.185]    [Pg.179]    [Pg.185]    [Pg.402]    [Pg.414]    [Pg.618]    [Pg.907]    [Pg.995]    [Pg.995]    [Pg.30]    [Pg.31]    [Pg.33]    [Pg.34]    [Pg.36]    [Pg.38]    [Pg.43]    [Pg.572]    [Pg.328]    [Pg.328]    [Pg.328]    [Pg.329]    [Pg.329]    [Pg.329]    [Pg.331]   
See also in sourсe #XX -- [ Pg.95 , Pg.294 ]

See also in sourсe #XX -- [ Pg.3 ]




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Adsorption salen ligands

Al(Salen)Cl

Al-salens

Al[ -salen

Aluminium SALEN

Aluminium chiral salenAl complexes

Aluminium complexes salen-type

Aluminium salen complex

Aluminum salen

Bifunctional catalysts salen based

Bimetallic-salen complexes

Catalyst cobalt-salen

Catalyst salen-based

Catalysts vanadium salen

Catalytic system salen

Chiral Co-salen complex

Chiral Mn salen,

Chiral Schiff-base salen

Chiral Schiff-base salen ligands

Chiral indium salen complexes

Chiral salen catalysts

Chiral salen catalysts, olefins asymmetric

Chiral salen complexes

Chiral salen ligands

Chiral salen-manganese complex

Chromium -salen complexes

Chromium salen catalyst

Chromium salen, with epoxide

Chromium-salen

Chromium-salen complexes, asymmetric

Co salen

Co-salen catalysts

Co-salen complexes

Cobalt Salen

Cobalt salen, with epoxides

Complex, Ruthenium-salene

Coordination chemistry salen

Coordination geometries salen ligands

Copper compounds salen ligands

Copper salen

Copper salen complexes

Copper salen, catalysis

Copper-salen catalyst

Cr-salen complex

Diels-Alder reaction -salen catalyst

Electrooxidation salene

Electropolymerized Films of Salen Complexes

Entrapment salen ligands

Epoxidation Cr-salen-catalysed

Epoxidation Mn-salen-catalysed

Epoxidation with Metal(salen) Complexes

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

Fluorinated salen ligands

Fluorous Salen

Group 7 metal-promoted oxidations epoxidation by salen manganese complexes

Homogeneous epoxidation salen complexes

III) Salen Complexes

Immobilized salen ligands

Ionic salen ligands

Iron salen complexes

Iron salen-type

Katsuki manganese -salen complex

Katsuki-type salen ligand

Kinetic metal Salen complexes

Ligands, salen-type

Manganese catalysts salen complexes

Manganese compounds salen ligands

Manganese salen

Manganese salen complexes, alkene

Manganese salen complexes, alkene epoxidation

Manganese salen species

Manganese-salen catalyst

Manganese-salen complex

Metal ions salen

Metal-Schiff base salen

Metalated salen ligands

Mn salen

Mn salen-catalyzed asymmetric

Mn-salen catalysts

Mn-salen complex

Nickel salen complex

Nickel-salen

Nucleic acids salen

Organocobalt compounds Co -salen complex

Oxidation chiral salen complexes

Oxidation with metal salen complexes

Palladium salen)complexes

Porphyrin and salen complexes

Ruthenium salen

Salen

Salen

Salen H2salen

Salen catalyst

Salen catalyst, epoxide

Salen chiral

Salen complex catalyst

Salen complex, immobilised

Salen complexes

Salen dendrimer-cored

Salen derivatives

Salen ligands

Salen ligands complexes

Salen ligands immobilization methods

Salen ligands reaction

Salen ligands, manganese complexes

Salen like metal binding

Salen metalated

Salen terminal ligands

Salen-based anion

Salen-based manganese complexes

Salen-based polymers

Salen-based receptor

Salen-based system

Salen-cobalt complex

Salen-containing catalysts

Salen-derived ligands

Salen-derived ligands epoxidation

Salen-metal complexes

Salen-pyrrole ligands

Salen-silicon

Salen. aluminum complexes

Salene

Salene complexes, electrooxidation

Salens cobalt complex

Salens nickel complex

Six-Coordinate Aluminum Cations Based on Salen Ligands

Solid salen ligands

Supported catalysts manganese-salen complexes

Titanium-salen catalyst

Transition metals salen ligands

Vanadyl salen

Vanadyl salen complexes

Zn salen

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