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Salen complex catalyst

The asymmetric addition of trimethylsilyl cyanide to aldehydes was accomplished in good enantioselectivities in the presence of a bimetallic alu-minium(salen) complex catalyst using triphenylphosphine oxide as the cocatalyst. ... [Pg.70]

With a similar synthetic approach, a cobalt (II) salen complex catalyst has been supported on silica and successfully employed in the aerobic oxidation of alkyl aromatics at atmospheric pressure in the presence of N-hydroxyphthalimide (NHPI). The reaction is particularly selective for the oxidation of the benzylic CH2 group and the major product obtained was ketone (Scheme 23.72). The immobilized catalyst... [Pg.749]

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]

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]

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]

Hou reported the use of a chiral (salen)titanium catalyst for the desymmetriza-tion of meso-epoxides with thiols (Scheme 7.14). The complex, fonned in situ... [Pg.236]

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]

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]

Kim et al. (19) also observed that the ee of recovered epichlorohydrin was reduced to 17% in the second hydrolysis reaction with Jacobsen s Co-OAc salen catalyst, if the catalyst was not regenerated with acetic acid in air. Although they attributed the loss of enantioselectivity to the reduction of Co(lll) to Co(ll) salen complex after the HKR reaction, no spectroscopic evidence was provided. Therefore, we probed the catalyst by UV-Vis and XANES spectroscopy before and after the HKR reaction. [Pg.392]

A dinuclear salen complex was investigated as catalyst for the aerobic oxidation of 3,5-di-ferf.-butylcatechol into 3,5-di-teri.-butylquinone in organic and aqueous organic solution. The actual catalyst composition varies in both solvent systems. Formation of a mononuclear species competes with formation of a dinuclear copper(ll) catalyst. The aerobic oxidation of 8 into 9 is 140,000-fold accelerated over background in aqueous methanol, and is about twice as fast as the same reaction in pure methanol. [Pg.476]

Metal-Catalyzed. Cyclopropanation. Carbene addition reactions can be catalyzed by several transition metal complexes. Most of the synthetic work has been done using copper or rhodium complexes and we focus on these. The copper-catalyzed decomposition of diazo compounds is a useful reaction for formation of substituted cyclopropanes.188 The reaction has been carried out with several copper salts,189 and both Cu(I) and Cu(II) triflate are useful.190 Several Cu(II)salen complexes, such as the (V-f-butyl derivative, which is called Cu(TBS)2, have become popular catalysts.191... [Pg.921]

The divalent Co(salen) complex (69a) is one of the most versatile and well-studied Co coordination compounds. It has a long and well-documented history and we shall not restate this here. Recent applications of (69a) as both a synthetic oxygen carrier and as a catalyst for organic transformations are described in Sections 6.1.3.1.2 and 6.1.4.1 respectively. Isotropic shifts in the HNMR spectrum of low-spin Co(salphn) (69b) were investigated in deuterated chloroform, DMF, DMSO, and pyridine.319 Solvent-dependent isotropic shifts indicate that the single unpaired electron, delocalized over the tetradentate 7r-electron system in CHCI3, is an intrinsic property of the planar four-coordinate complex. The high-spin/low-spin equilibrium of the... [Pg.34]

The insoluble polymer-supported Rh complexes were the first immobilized chiral catalysts.174,175 In most cases, however, the immobilization of chiral complexes caused severe reduction of the catalytic activity. Only a few investigations of possible causes have been made. The pore size of the insoluble support and the solvent may play important roles. Polymer-bound chiral Mn(III)Salen complexes were also used for asymmetric epoxidation of unfunctionalized olefins.176,177... [Pg.261]

The most well-developed recent examples of catalysis concern catalysts for oxidation reactions these are essentially achiral or chiral metal-salen complexes. Taking into account a number of results suggesting the importance of a degree of mobility of the bound complex, Sherrington et al. synthesized a series of polymer-supported complexes in which [Mn(salen)Cl] units are immobilized in a pendant fashion by only one of the aromatic rings, to polystyrene or poly(methacrylate) resin beads of various morphology (Figure 6).78,79... [Pg.452]

Spectacular achievements in catalytic asymmetric epoxidation of olefins using chiral Mnm-salen complexes have stimulated a great deal of interest in designing polymeric analogs of these complexes and in their use as recyclable chiral catalysts. Techniques of copolymerization of appropriate functional monomers have been utilized to prepare these polymers, and both organic and inorganic polymers have been used as the carriers to immobilize these metal complexes.103... [Pg.454]


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See also in sourсe #XX -- [ Pg.123 ]




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