Manganese complexes aryls

The use of Mn-salen catalysts for asymmetric epoxidation has been reviewed.30 Oxo(salen)manganese(V) complexes, generated by the action of PhIO on the corresponding Mn(III) complexes, have been used to oxidize aryl methyl sulfides to sulfoxides.31 The first example of C—H bond oxidation by a (/r-oxo (manganese complex has been reported.32 The rate constants for the abstraction of H from dihydroanthracene correlate roughly with O—H bond strengths. 

The SjvAr reaction is another attractive method for diaryl ether synthesis, and reactions of o-nitro- and o-cyanofluorobenzenes with phenols were reported . 7r-Complexation of aryl halides with transition metals activates the aromatic nuclei toward S fAr. Segal employed a ruthenium chlorobenzene complex in the poly(aryl ether) synthesis , and the methodology was extensively studied by Pearson, Rich and their coworkers using manganese complex and later iron and ruthenium complexes in natural product synthesis " . The intramolecular substitution of an aromatic chloride with a phenylalanine derivative takes place at room temperature without racemization (equation 27). 

The main drawback in Sharpless epoxidation is that the substrate must bear a functional group to achieve the precoordination required for high enantioselec-tivity (as in the case of allyl alcohol). This restriction is not applicable to the epoxidation of alkyl- and aryl-substituted olefins with manganese complexes of chiral Schiffs bases as catalysts. Very high enantioselectivities can be obtained in these reactions (Jacobsen, 1993). The most widely used catalysts that give high enantioselectivity are those derived from the Schiff bases of chiral diamines such as [SiS] and [RR] 1,2-diphenylethylenediamine and [SS] and [RR] cyclohexyl-1,2-diamine. An example is the synthesis of cromakalim. 

Figure 7.2 Synthesis and electronic structure of reduced aryl-substituted bis(imino)pyridine manganese complexes.

More recently, Katsuki et al. [109] prepared the Salen manganese complex (50) (Figure 1.6), which is efficient in the oxidation of alkyl aryl sulfide with iodosobenzene as oxidant. With 1 mol% of catalyst, they obtained the 2-nitrophenyl methyl sulfoxide in 1 h at -20°C in acetonitrile solution with 90% ee and 88% yield. This is currently one of the best results for catalytic asymmetric sulfoxidation. 

Aryl alkyl ketones (e.g. 161) can be converted to amides (e.g. 162), with a loss of the alkyl group, by reaction with a carbodiimide. This unusual C -C arbonyi single-bond cleavage is catalysed by manganese complexes such as [HMn(CO)4l3 or Mn2(CO)io-Aryl isocyanates, Ar-N=C=0, are mechanistically implicated, as the reaction can also be carried out using such isocyanates, and indeed, two isocyanate molecules can be converted to the corresponding carbodiimide using either catalyst. ... 

Mn catalysts that show activity in alkene or alcohol oxidation with H2O2 are potentially active in the oxidation of sulfides also. The Mn-tmtacn catalysts and a number of tn-sifu-formed complexes employing ligands such as 39 are examples of such catalysts (see above). These complexes were found to be highly active in the oxidation of sulfides to sulfoxides. For example, the dinudear manganese complex based on tmtacn (6) performs efficiently in the oxidation of aryl alkyl sulfides and generally results in fiJl conversion within 1 h. Unfortunately, as is often the case, in... 

Treatment of the allyl manganese complex MnCl(CH2CR =CHMe) (R - Me, Bu) with a, unsaturated esters R CHsCHCX>2Me (R = Me, Pr) leads to and-1,4 addidon products. i The reaction of MnX2 with 0.5 equivalents of Mg(Mes)2(thf)2 in the presence of PMe3 followed by O2 oxidation results in the aryl btxnplex Mn(Mes)X2(PMe3)2. ... 

Alkyl- and aryl-cobalt tetracarbonyls also react readily with phosphines forming acyl derivatives RCOCo(CO)3PR 3. Phosphite ligands are found to replace carbon monoxides successively forming RCOCo(CO)2L2 [193]. The replacement of two carbon monoxide ligands by phosphites under conditions where phosphine ligands will only replace one carbon monoxide, is therefore found for both cobalt and manganese complexes. Both... 

No racemization occurs at the phenylglycine moiety throughout the entire sequence. With more complex arenetricarbonylmanganese complexes, such as that derived from the methyl ester of iV-acetyl-O-phenyltyrosine 5, two equivalents of the lithiated dialkoxydihydropyrazine 1 have to be used30. If not, no arylaled dialkoxydihydropyrazine is formed and the loss of tricarbonyl-manganese is observed. 

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