Metalloporphyrins chiral

Binding of organic nitroso compounds to metalloporphyrins 99ACR529. Design and applications of chiral porphyrins 98YGK201. 

The above-described structures are the main representatives of the family of nitrogen ligands, which cover a wide spectrum of activity and efficiency for catalytic C - C bond formations. To a lesser extent, amines or imines, associated with copper salts, and metalloporphyrins led to good catalysts for cyclo-propanation. Interestingly, sulfinylimine ligands, with the chirality provided solely by the sulfoxide moieties, have been also used as copper-chelates for the asymmetric Diels-Alder reaction. Amide derivatives (or pyridylamides) also proved their efficiency for the Tsuji-Trost reaction. 

These reports sparked off an extensive study of metalloporphyrin-catalyzed asymmetric epoxidation, and various optically active porphyrin ligands have been synthesized. Although porphyrin ligands can make complexes with many metal ions, mainly iron, manganese, and ruthenium complexes have been examined as the epoxidation catalysts. These chiral metallopor-phyrins are classified into four groups, on the basis of the shape and the location of the chiral auxiliary. Class 1 are C2-symmetric metalloporphyrins bearing the chiral auxiliary at the... 

Table 1 Some examples of chiral metalloporphyrin-catalyzed epoxidation.

Kobayashi K, Tominaga M, Asakawa Y, Aoyama Y (1993) Tetrahedron Lett 34 5121. For chiral recognition of iV-protect l amino acids by a metalloporphyrin, see Konishi K, Yahara K, Toshishige H, Aida T, Inoue S (1994) J Am Chem Soc 116 1337... 

Highly enantioselective epoxidation of unfunctionalized alkenes was developed by using chiral metalloporphyrin catalysts.1214-1218 Remarkable anion axial ligand effects were observed with [Fe(TPFPP)X] complexes (X = triflate, perchlorate, nitrate).1219 Hexafluoroacetone was found to be an efficient cocatalyst with H202,1220 and alkenes could be epoxidized by ozone at ambient temperature.1221... 

Huang, X., Nakanishi, K., and Berova, N. 2000. Porphyrins and metalloporphyrins Versatile circular dichroic reporter groups for structural studies. Chirality 12 237-255. 

A chiral Ru porphyrin complex based, in part, on the Kodadek design for Rh has recently been reported to give good-to-high (80-91% ee) enantiocontrol for the cyclopropanation of styrenes and 1,1 -disubstituted alkenes [83]. The advantage here is the high trans. cis ratio, which seems to be characteristic of Ru, and, like other metalloporphyrin catalysts, turnover numbers are large. 

In the wake of this report, many chiral iron(III)- and Mn(III)-porphyrin complexes have been synthesized and applied to the epoxidation of styrene derivatives [20]. Because these asymmetric epoxidations are discussed in the first edition of this book [21], the discussion on metalloporphyrin-catalyzed epoxidation here is limited to some recent examples. Most chiral metallopor-phyrins bear chiral auxi Maries such as the one derived from a-amino acid or binapthol. Differing from these complexes is complex 6, which has no chiral auxiliary but is endowed with facial chirality by introducing a strap and has been reported by Inoue et al. [20f]. Epoxidation of styrene by using only 6 as the catalyst shows low enantioselectivity, but the selectivity is remarkably enhanced when the reaction is performed in the presence of imidazole (Scheme 6B.11). This result can be explained by assuming that imidazole coordinates to the unhindered face of the complex and the reaction occur on the strapped face [20f. ... 

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. 

Oxometalloporphyrins were taken as models of intermediates in the catalytic cycle of cytochrome P-450 and peroxidases. The oxygen transfer from iodosyl aromatics to sulfides with metalloporphyrins Fe(III) or Mn(III) as catalysts is very clean, giving sulfoxides, The first examples of asymmetric oxidation of sulfides to sulfoxides with significant enantioselectivity were published in 1990 by Naruta et al, who used chiral twin coronet iron porphyrin 27 as the catalyst (Figure 6C.2) [79], This C2 symmetric complex efficiently catalyzed the oxidation... 

Finally, it is very important to note that more sophisticated catalysts have been prepared either by introducing bulky and/or chiral substituent on the meso-aryl or pyrrole rings [for recent reviews see, for instance, 36,56e,56f,63] or by inserting the metalloporphyrin into various polymeric materials [64-75, for recent reviews see also 76], These results have shown that this was a good strategy not only toward asymmetric oxidation catalysts, but also toward more regioselec-tive and/or efficient and stable catalysts. 

Whilst the chiral manganese complexes can epoxidize alkenes with high enantioselectivity (> 90% e.e.), they are not particularly stable. This instability is probably due to the easily oxidizable imine and phenoxide ligands on the complex. Attempts are currently being made to immobilize Schiff-bases in order to increase their stability in a similar manner to the metalloporphyrins discussed earlier. 

Rose E, Andrioletti B, Zrig S, Quelquejeu-Etheve, M. Enantioselective epoxidation of olefins with chiral metalloporphyrin catalysts. Chem. Soc. Rev. 2005 34 573-583. 

Y. Ferrand, R. Daviaud, P. Le Maux, G. Simonneaux, Catalytic asymmetric oxidation of sulfide and styrene derivatives using macroporous resins containing chiral metalloporphyrins (Fe, Ru), Tetrahedron Asymmetry 17 (2006) 952. 

Konishi K., Yahara K. A novel anion-binding chiral receptor based on a metalloporphyrin with molecular asymmetry. Highly enantioselective recognition of amino acid derivatives. J Am Chem Soc 1994 116 1337-44. 

Cytochrome P-450s carrying an iron-porphyrin complex at their active sites are representative oxidizing enzymes that catalyze the oxidation of C-H and C=C bonds. To reproduce these stereoselective biological reactions in a flask, various chiral metalloporphyrin complexes have been prepared as model compounds of the active site of P-450 [3] and used as catalysts for C-H and C=C oxidation in the... 

Groves, J.T. and K.V. Shalyaev (1998). Paramagnetic H-NMR relaxation probes of stereoselectivity in metalloporphyrin catalyzed olefin epoxidation. Chirality 10, 106-119. 

Epoxidation of alkenes with iodosylbenzene can be effectively catalyzed by the analogous salen or chiral Schiff base complexes of manganese(in), ruthenium(II), or ruthenium(III). For example, the oxidation of indene with iodosylbenzene in the presence of (/ ,5)-Mn-salen complexes as catalysts affords the respective (15,2/ )-epoxyindane in good yield with 91-96% ee [704]. Additional examples include epoxidation of alkenes with iodosylbenzene catalyzed by various metalloporphyrins [705-709], corrole metal complexes, ruthenium-pyridinedicarboxylate complexes of terpyridine and chiral bis(oxazoUnyl)pyridine [710,711]. 

Various oxidations with [bis(acyloxy)iodo]arenes are also effectively catalyzed by transition metal salts and complexes [726]. (Diacetoxyiodo)benzene is occasionally used instead of iodosylbenzene as the terminal oxidant in biomimetic oxygenations catalyzed by metalloporphyrins and other transition metal complexes [727-729]. Primary and secondary alcohols can be selectively oxidized to the corresponding carbonyl compounds by PhI(OAc)2 in the presence of transition metal catalysts, such as RuCls [730-732], Ru(Pybox)(Pydic) complex [733], polymer-micelle incarcerated ruthenium catalysts [734], chiral-Mn(salen)-complexes [735,736], Mn(TPP)CN/Im catalytic system [737] and (salen)Cr(III) complexes [738]. The epox-idation of alkenes, such as stilbenes, indene and 1-methylcyclohexene, using (diacetoxyiodo)benzene in the presence of chiral binaphthyl ruthenium(III) catalysts (5 mol%) has also been reported however, the enantioselectivity of this reaction was low (4% ee) [739]. 

Recent work has improved enantiomeric excess of epoxida-tion reaction by use of metalloporphyrins having two chiral naphthyl groups, one above and one below the porphyrin plane. This asymmetric reaction seems to arise from chiral interaction between the chiral element of the catalyst and the achiral substrate in the transition state. Doubly strapped chiral porphyrins 17 are obtainable from the coupling of a,) ,a,) -tetralds-(2-aminophenyl)porphyrin and amino-acid derivative.- " Chiral space above and below the porphyrin plane results in moderately enantio selective epoxidation. Since then, various kinds of chiral porphyrins have been synthesized as catalysts for the oxygenation of organic substrates. 

Metal complexes of dimers linked with flexible spacers give rise to polymeric complexes at a higher concentration of diamine. Two metalloporphyrins with C2 symmetry linked with a rigid chiral amine spacer (Troger s base) show diastereomeric recognition for optically active, basic amino acids.- - Chiral diamine derivatives such as basic amino-acid esters are tightly bound with moderate enantioselec-tivity to the zinc porphyrin tweezers in the inner-homochiral cavity of the host (Figure 7). It is noted that... 

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