Manganese salen complex

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... 

A typical manganese-salen complex (27)[89] is capable of catalysing the asymmetric epoxidation of (Z)-alkenes (Scheme 18) using sodium hypochlorite (NaOCl) as the principle oxidant. Cyclic alkenes and a, (3-unsaturated esters are also excellent starting materials for example indene may be transformed into the corresponding epoxide (28) with good enantiomeric excess1901. The epoxidation of such alkenes can be improved by the addition of ammonium acetate to the catalyst system 911. 

Epoxidation using manganese salen complexes is very easy to carry out it occurs under aqueous conditions and commercial house bleach can be used as the oxidant. The results are similar to those reported in the literature Table 6.1 gives other examples of alkenes which can be epoxidized using the same procedure. This method gives good results, especially for disubstituted Z-alkenes but trisubstituted alkenes can be epoxidized as well. 

Although the Sharpless catalyst was extremely useful and efficient for allylic alcohols, the results with ordinary alkenes were very poor. Therefore the search for catalysts that would be enantioselective for non-alcoholic substrates continued. In 1990, the groups of Jacobsen and Katsuki reported on the enantioselective epoxidation of simple alkenes both using catalysts based on chiral manganese salen complexes [8,9], Since then the use of chiral salen complexes has been explored in a large number of reactions, which all utilise the Lewis acid character or the capacity of oxene, nitrene, or carbene transfer of the salen complexes (for a review see [10]). 

The successful application of manganese salen complexes is illustrated in Figure 14.11. In the catalyst used large 2-phenylnaphthyl-l substituents have... 

In Fig. 2.1.6.6, the FTIR spectra of the Jacobsen ligand (a), the Jacobsen catalyst (bj, and the immobilized manganese salen complex in the cages of dealuminated faujasite zeolite (c) are compared. While spectra a and b have been measured using the standard KBr technique, the spectrum c of the ship in a bottle catalyst has been recorded using a self-supported wafer. The bands at wavenumbers 1466 cm, 1434 cm" , 1399 cm" and 1365 cm" in spectrum c can be assigned to the... 

Fig. 2.1.6.6 FTIR spectra of a) the Jacobsen ligand, b) the Jacobsen catalyst, and c) the manganese-salen complex, in zeolite supercages.

The optically active manganese-salen complexes 230 and 231 are effective catalysts for the enantioselective epoxidation of unfunctionalized alkenes357-361. The yield of epoxide... 

In a related study, Jorgensen has examined the regio- and enantioselective catalytic epoxidation of conjugated aliphatic dienes using achiral and chiral manganese salen complexes and sodium hypochlorite or iodosylbenzene as the terminal oxidant. For most substrates, the less substituted diene is epoxidized however, in the case of isoprene, the more highly substituted double bond is the more reactive. Jorgensen proposes an intermediate of type 11, the... 

In the same year (1990) that Jacobsen reported his asymmetric epoxidation, a group led by Tsutomu Katsuki at the University of Kyushu in Japan reported a closely related asymmetric epoxidation. The chiral catalyst is also a salen and the metal manganese. The oxidant is iodosobenzene (Phl=0) but this method works best for E-alkenes. It is no coincidence that Katsuki and Jacobsen both worked for Sharpless. It is not unusual for similar discoveries to be made independently in different parts of the world, the Katsuki manganese salen complex... 

Asymmetric epoxidation The catalytic asymmetric epoxidation of alkenes has been the focus of many research efforts over the past two decades. The non-racemic epoxides are prepared either by enantioselective oxidation of a prochiral carbon-carbon double bond or by enantioselective alkylidenation of a prochiral C=0 bond (e.g. via a ylide, carbene or the Darzen reaction). The Sharpless asymmetric epoxidation (SAE) requires allylic alcohols. The Jacobsen epoxidation (using manganese-salen complex and NaOCl) works well with ds-alkenes and dioxirane method is good for some trans-alkenes (see Chapter 1, section 1.5.3). 

However, 1,2-diamino-l,2-di-(cr(-butylethane (3) holds particular interest because of its increased steric bulk and the absence of benzylic protons. Its recent ready availability should render it as attractive as the frequently used vicinal diamines 7 and 8. To our knowledge, only one application of this diamine has been previously described in the literature (eq 5), where the regio- and enantioselective epoxidation of conjugated aliphatic dienes were studied using the chiral manganese salen complex (9). 

Hydroxylamines that have an a-proton are converted to nitrones when treated with a manganese salen complex. " ... 

Manganese salen complex catalyzes C—H oxidation of organic molecules with NaOCl or PhIO, giving alcohols . Larrow and Jacobsen observed kinetic resolution in the benzylic hydroxylation . Katsuki and coworkers used the axis chiral salen manganese complexes for the benzyl hydroxylation and ether hydroxylation, and attained higher ee with the ligand possessing (/f,/f)-diamine and (R)-axis chirality (equation 84). ... 

Although asymmetric aziridination of styrenes was attempted by Burrow and Katsuki and their coworkers using manganese salen complexes in the presence of PhI=NTs, low asymmetric induction was observed ". Nishikori and Katsuki later employed a salen complex synthesized from (/ ,/f)-2,3-diaminobutane and ( i-biphenol, and found that the chirality at the 3,3 -positions is more important for the asymmetric induction (equation 85) . Carreira conducted the stoichiometric amination of enol ethers and alkenes using a manganese nitride salen complex. Komatsu extended the methodology to the catalytic process and attained 94% ee for aziridination of / -isopropylstyrene. ... 

D. Feichtinger, D. A. Plattner, Oxygen transfer to manganese-salen complexes An electrospray tandem mass spectrometric study, J. Chem. Soc. Perkin Trans. 2 (2000) 1023. 

L. Cavallo, H. Jacobsen, Manganese-salen complexes as oxygen-transfer agents in catalytic epoxidations—A density functional study of mechanistic aspects, Eur. J. Inorg. Chem. (2003) 892. 

Key Words Polymer-supported catalysts, Manganese(ll) complexes, Manganese-salen complexes, Manganese-porphyrin complexes,... 

Dendritic and nondendritic polystyrene-boimd manganese-salen complexes were described by Seebach and coworkers [30]. The supported catalysts were prepared by suspension copolymerization of styrene with the vinyl-substituted complexes and employed in the epoxidation of phenyl-substituted alkenes by m-CPBA/NMO. Activities and selectivities were similar to those obtained with the monomeric complexes. High catalyst stabilities were observed and it was demonstrated that the immobilized catalysts can be recycled up to 10 times without loss of performance. Laser ablation inductively coupled plasma mass spectrometry was used to monitor the manganese content in repeatedly used polystyrene beads and a correlation between metal leaching from the support and catalytic activity was disclosed [31]. 

Copolymerization of an acryloyl-substituted manganese-salen complex with ethylene glycol dimethacrylate and styrene [32] yielded catalysts that showed low enantioselectivity in the epoxidation of styrene by m-CPBA/NMO or iodosylben-zene (PhIO). The influence of porosity and cross-linking degree on activity was explored and the catalysts could be used repeatedly with no loss of activity for at least three cycles. 

Axial bonding of manganese-salen complexes to polystyrene containing phen-oxide or sulfonate groups yielded catalysts for the asymmetric epoxidation of styrene and styrene derivatives with NaClO/PPNO [35]. Catalyst performances were similar to the corresponding nonsupported systems and epoxide yields reached 93% with 70% ee using 1-phenylcyclohexene as substrate. Catalyst recyclability was investigated and the catalysts could be used up to three times in the epoxidation of ot-methylstyrene. 

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