Mn Porphyrins complex

The observation that addition of imidazoles and carboxylic acids significantly improved the epoxidation reaction resulted in the development of Mn-porphyrin complexes containing these groups covalently linked to the porphyrin platform as attached pendant arms (11) [63]. When these catalysts were employed in the epoxidation of simple olefins with hydrogen peroxide, enhanced oxidation rates were obtained in combination with perfect product selectivity (Table 6.6, Entry 3). In contrast with epoxidations catalyzed by other metals, the Mn-porphyrin system yields products with scrambled stereochemistry the epoxidation of cis-stilbene with Mn(TPP)Cl (TPP = tetraphenylporphyrin) and iodosylbenzene, for example, generated cis- and trans-stilbene oxide in a ratio of 35 65. The low stereospecificity was improved by use of heterocyclic additives such as pyridines or imidazoles. The epoxidation system, with hydrogen peroxide as terminal oxidant, was reported to be stereospecific for ris-olefins, whereas trans-olefins are poor substrates with these catalysts. 

C jimHPFs] Mn(porphyrin) complex PhI(OAc)2 Epoxidation of styrene CH2C12 as co-solvent better results in presence of an ionic liquid effect of ionic liquid concentration and oxidant concentration studied products extracted with hexane catalyst active for at least 10 runs without significant decrease in activity MnTPPS4 is more active than MnTPPCl. [34] [35]... 

FIGURE 1.25 Proposed intermediates in epoxidation by hypervalent Fe and Mn porphyrin complexes. 

Scheme XL 18. The selective hydroxyiaticm of an androstandiot derivative by PhIO catalyzed by P-cyclodcxtrin-containing Mn porphyrin complex Xl-11.

Many other small molecules are reported to staek with G-quadruplexes and have recently been reviewed in detail. Similarly, metal complexes with planar ligands also like to bind to G-quaduplexes via end-stacking. " A typical example is Mn porphyrin complexes, whieh exhibited both high affinity and excellent selectivity for G-quadruplexes. This is possibly contributed by the metal ions, which are necessary for G-quadruplex stabilization. 

Cobalt complexes with pyridine ligands, for example, catalyzed the oxidation of neat ethylbenzene to acetophenone in 70% conversion and 90% selectivity [35]. Mn porphyrin complex catalyzes the ethylbenzene oxidation with dioxygen to 3 14 mixture of methylphenylcarbinole and acetophenone in the presence of acetaldehyde [36]. The system CUCI2-crown ether in the presence of acetaldehyde is efficient as catalyst of oxidation of ethylbenzene, indane, and tetralin by dioxygen (70°C) into the corresponding alcohols and ketones with high TON [37]. The oxidations were established to occur via a radical pathway and not by a metal-oxo... 

Dioxiranes generated from Oxone have recently been shown to undergo C-H insertion reactions with activated and unactivated C-H bonds. This strategy has been used in an intramolecular fashion for the oxidation of hydrocarbons (eq 49) and steroids. Fructose-derived ketone (5) has also been used for this purpose in an intermolecular reaction for the desymmetrization and kinetic resolution of 1,2-diols to a-hydroxy ketones (eq 50). There has also been a report of the direct oxidation of hydrocarbons to ketones and lactones by Mn-porphyrin complexes with Oxone. ... 

Figure 6 SEM (a and b) and AFM (c) images of vesicles of a Mn +-porphyrin complex in a mixture of chloroform and methanol. (Reproduced from Ref. 41. Royal Society of Chemistry, 2009.)...

Enhanced epoxidation rates were observed using a Mn-porphyrin complex 8 in which the carboxylic acid and imidazole groups are both linked to the ligand... 

Table 11.2 Oxidation of alkenes with Mn" -porphyrin complex 7 [57].

Scheme 11.6 Mn-porphyrin complex 6 with tethered carboxylate and imidazole groups and their proposed role in catalyzed oxidation [63].

In addition, all conceivable intermediates proposed for the oxygen activation mechanism by P-450 were prepared by employing Mn porphyrin complexes [156]. Especially, X-ray structure of peroxo-Mn (TPP) served to understand a possible structure of the corresponding Fe(III) complexes [35]. 

In 1983, Groves and Watanabe succeeded in transforming all conceivable intermediates proposed for P-450 reaction by employing Mn(TMP) [178]. In the work, the use of acylating reagent such as acid halides allowed to be formed a common intermediate in both peroxidase reaction and P-450 reaction, i.e., an acylperoxo-Mn porphyrin complex. The... 

Mn porphyrin complexes as useful oxygen activation catalysts were also demonstrated. Mansuy et al. investigated sodium ascorbate [183,184] and Zn/imidazole/acetic acid [185, 186] as electron sources and showed that the systems effectively oxidized hydrocarbons... 

A tetracationic Mn porphyrin complex immobilized on monmorillonite was found to be efficient for alkene epoxidation and alkane hydroxylation by PhIO, with a higher ability than the corresponding homogeneous or silica-supported Mn porphyrin complexes... 

Similar current-voltage-potential sweep rate trends were observed for NMnTPP, NMn(o-OCH3)TPP and NMn(p-0CH3)TPP. Table 1 lists the potentials observed for the electrode reactions of the nitrido Mn porphyrin complexes investigated. The increased potential separation between the E1/2 values of the first and second oxidations (as compared to the unhindered porphyrins) reflects the influence of the cap in inhibiting the formation... 

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