Manganese complexes salen-based

Outside of the category of manganese porphyrins, one report indicates nuclease activity of a Schiff base manganese complex [Mn (salen)] when activated by magnesium monoperphthalate. Singlestrand breaks are observed at micromolar concentrations of the complex 163). 

An early model for the active site was found in the manganese salen class of compounds. The active sites of the enzyme and model are shown in Fig. 4.13. The Schiff base model complexes are unusual in that they are able to maintain manganese in the highly reactive +3 oxidation state, ready to catalyse the oxidation of superoxide, yet still be flexible enough to bind the larger manganese(II) ion. 

Irradiation of manganese azides derived from Mn(III) porphyrin, cyclam, and polyamide complexes represents one of the earliest methods reported for the preparation of nitrido manganese complexes (Eq. (40)) [50], Additional methods have become available for the synthesis of manganese nitrides that utilize ammonia in combination with oxidants such as Cl2, PhIO, NaCIO, and NBS (Eq. (41)) [51-53]. Employing these methods, the manganese nitrides incorporating porphyrin, phath-locyanine, cyclam, salen, and bidentate Schiff base complexes have been documen-... 

One of the most important aspects of those listed above is catalysis. A great deal of research has been carried out in the investigation of catalysts for the epoxidation of alkenes. The oxidation of a-pinene to a-pinene epoxide (Equation 1) is one of the standard trial reactions for catalyst identification. The Jacobsen manganese complex catalyst, based on a salen derivative, shows brilliant enantioselectivity, whereas the use of related indole derivatives provides greater structural variety and powerful catalysis, but so far shows poorer enantioselectivity (Figure 2). Such catalysts can sometimes be effectively embedded in zeolites. ... 

Another interesting asymmetric catalyst for epoxidation of simple olefins such as cis-PhCH=CHMe was reported by Jacobsen and coworkers. In this example the catalyst was a chiral manganese salen-based complex (3.54) (Figure 3.22), and the oxidant used was NaOCl high yields and ee of > 90% were achieved. 

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]). 

A new stereoselective epoxidation catalyst based on a novel chiral sulfonato-salen manganese(III) complex intercalated in Zn/Al LDH was used successfully by Bhattacharjee et al. [125]. The catalyst gave high conversion, selectivity, and enantiomeric excess in the oxidation of (i )-limonene using elevated pressures of molecular oxygen. Details of the catalytic activities with other alkenes using both molecular oxygen and other oxidants have also been reported [126]. 

Manganese(V) complexes of the Schiff base ligand salen and its derivatives have been the focus of intense study. These complexes have one additional ligand, either an 0x0, 0 , or a nitrido, group and much of the interest arises because these oxygen or nitrogen atoms are readily... 

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