Manganese proposed reaction scheme

Buhler and Mason (1961) postulate the production of perhydroxyl radicals in a chain reaction similar to that of Fig. 2. The orientation of the aromatic hydroxylations (o- and -substitution of phenols, m-sub-stitution of nitro-compounds) is characteristic of a free radical process. Manganese is presumed to catalyze a reaction analogous to that of Eq. (22). The chemical evidence of the hydroxylations thus lends further support to the reaction scheme of Eq. (15) and (22), and Fig. 2. Buhler and Mason do not propose a role for compound III in the catalytic reaction. 

Other metal oxide catalysts studied for the SCR-NH3 reaction include iron, copper, chromium and manganese oxides supported on various oxides, introduced into zeolite cavities or added to pillared-type clays. Copper catalysts and copper-nickel catalysts, in particular, show some advantages when NO—N02 mixtures are present in the feed and S02 is absent [31b], such as in the case of nitric acid plant tail emissions. The mechanism of NO reduction over copper- and manganese-based catalysts is different from that over vanadia—titania based catalysts. Scheme 1.1 reports the proposed mechanism of SCR-NH3 over Cu-alumina catalysts [31b],... 

Metalloporphyrin complexes serve as catalysts for aziridination in the presence of PhI=NTs [73], Che et al. have reported the chiral version of metalloporphyrin-catalyzed aziridination (Scheme 6B.36) [81], The reaction of styrene derivatives with a D4-manganese(III) porphyrin complex 34 proceeds with fairly good enantioselectivity, up to 68% ee. This reaction is proposed to proceed through a Mn(IV)-PhINTs adduct 35 on the basis of EPR analysis. 

The cis-trans alkene isomerization observed in the transformation of conjugated alkenes gave rise to proposals of several different reaction mechanisms. Four different pathways for the epoxidation of alkenes by the manganese metal-oxo species have been proposed (Scheme 9) in order to explain the experimental results. The two concerted pathways (b,c) involve formation of a three-membered or four-membered transition state that involves the alkene and either the transferring oxygen or the Mn=0, respectively, of the formal Mn(V) species. The other pathways are stepwise mechanisms one proceeds via bond formation between the alkene and the... 

Formic acid salts can also be prepared by the reaction of CO2 and II2 with an alkali metal manganese pcntacarbonyK such as NaMn(CO). in an inert solvent [164]. Magnesium format was synthesized directly from CO2, II3 and Mg under mild conditions 165], The catalytic fixation of Hj and CO2 was carried out in the TiCU 2THF/Mg/THF system and the following mechanism has been proposed (Scheme 4). 

Taken together, the various reactions and interconversions of these manganese porphyrin complexes have allowed the examination of each step in the activation of molecular oxygen by the mechanism suggested for P-450. Detailed mechanistic studies of the 0-0 bond cleavage event in 29 by kinetics, substituent effects, and product analysis showed that the reaction proceeds via heterolysis to produce 27 when acid is present, whereas homolysis is predominant in the absence of acid but in the presence of hydroxide ion (95). Under basic conditions, homo-lytic cleavage of the 0-0 bond of 29 forms Mn (=0)TMP (28) and an acyl-oxyl radical. Thus, when an alkyl peroxy acid is employed, decarboxylation competes with electron transfer, as shown in Scheme IX, to afford a mixture of 27 and 28. Yuan and Bruice have proposed a similar heterolysis mechanism based on the kinetic analysis for the reaction of mCPBA with catalytic amounts ofMn TPP(/(W). 

The proposed mechanism involves initial transfer of the silyl group from manganese to the ketal (Scheme 4). This view is supported by the fact that the reaction is slowed considerably in less polar solvents208. 

Although it has been reported that this reaction involves a radical intermediate, nonradical mechanisms are proposed here, including a stoichiometric Nozaki-Hiyama-Kishi reaction in Scheme 1, and a catalytic version of such reaction in the presence of manganese and trimethylchlorosilane in Scheme 2. 

The reaction between manganese(n) and terpy in DMSO has been shown to occur in two stages the rapid formation of a dinuclear intermediate is followed by a very slow reaction, which is attributed to final chelate-ring closure. The proposed mechanism is shown in Scheme 3. Analysis of the rate behaviour yielded the following rate constants ki — 1.64x 10 lmol s and k i = 46.1 s (both at 292.1 K) it3 = 2.58 xl0- s- (at 314.1 K). 

Reactions with alkynes may lead to the formation of cyclized products. The reaction of iodobenzenes with two equivalents of an alkyne has been shown to give naphthalene derivatives in the presence of cobalt catalyst with a manganese reduc-tant. The process, shown in Scheme 15, is thought to involve oxidative addition of the aryliodide to cobalt followed by double alkyne insertion. The cobalt-catalysed annulation step probably involves an pathway. The cyclopentadienyl-rhodium-catalysed annulation of benzoic acids with alkynes has been used to form isocoumarin derivatives, such as (126). The process is thought to involve cyclorhodation at the ortho-position of a rhodium benzoate intermediate, followed by alkyne insertion to form a seven-membered rhodacycle and reductive elimination The silver-catalysed annulations of diphenylphosphine oxides with alkynes proceed in the absence of rhodium. Benzophosphole oxides such as (127), formed with diphenylethyne, are produced. Here, the proposed mechanism involves homolytic cleavage of the phosphorus-hydrogen bond to give a radical which can add to the alkyne and subsequently cyclize. ... 

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