Alkene complexes cobalt porphyrins

The corresponding reactions of transient Co(OEP)H with alkyl halides and epoxides in DMF has been proposed to proceed by an ionic rather than a radical mechanism, with loss of from Co(OEP)H to give [Co(TAP), and products arising from nucleophilic attack on the substrates. " " Overall, a general kinetic model for the reaction of cobalt porphyrins with alkenes under free radical conditions has been developed." Cobalt porphyrin hydride complexes are also important as intermediates in the cobalt porphyrin-catalyzed chain transfer polymerization of alkenes (see below). 

The epoxidation of alkenes by 02 is catalyzed by polydentate iron and by cobalt porphyrin complexes the latter also operate in a perfluoroalkane/MeCN biphasic system.166 Ruthenium complexes, such as (22-XL), catalyze alkene epoxidations with bis(acetoxy)iodobenzene.167... 

Epoxidation of Alkenes Catalyzed by Porphyrin Cobalt Complexes... 

A fluorous version of the cobalt-porphyrin-catalyzed aerobic epoxidation of alkenes was examined in the presence of 2-methylpropanal (Scheme 9). A fluorous porphyrin ring containing four 3,5-diperfluorooctylphenyl groups was prepared and complexed with Co(OAc)2 to form the cobalt catalyst 6. The reaction was carried out with vigorous stirring at room temperature in a biphasic system comprising... 

In some cases where a reaction involving a radical species occurred within cobalt porphyrin complexes, it has been possible to trap transient cobalt porphyrin hydride species. This was indeed observed during the synthesis of organocobalt porphyrin that resulted from the reaction of cobalt(n) porphyrin and dialkylcyanomethylradicals with alkenes, alkynes, alkyl halides, and epoxide. A transient hydride porphyrin complex was also involved in the cobalt porphyrin-catalyzed chain transfer in the free-radical polymerization of methacrylate. The catalytic chain transfer in free-radical polymerizations using cobalt porphyrin systems has been extensively investigated and will not be treated in this section. Gridnev and Ittel have published a comprehensive overview of the catalytic chain transfer in free-radical polymerizations. ... 

Since the work of Cenini and coworkers the aziridination reaction of alkenes with azide using various types of metal-loporphyrin-based catalyst has been broadly studied. Zhang and coworkers developed the Co(TPP)-catalyzed aziridination of styrenes with diphenylphosphoryl azide (DPPA) (Scheme 2.9) [14a]. In continuing their work on the cobalt-porphyrin catalyst, the asymmetric alkene aziridinations with DPPA catalyzed by the cobalt(ll) complexes with D2-sym-metric chiral porphyrin ligands were also reported [14b]. 

A Co(II) Schiff-base complex converts 1- and 2-alkenes into methyl ketones and the corresponding secondary alcohols in the presence of oxygen or H2O2 in primary alcohol solvent.543 A radical oxidation with cobalt hydroperoxide through the formation and subsequent decomposition of alkyl hydroperoxide was suggested.543 An efficient conversion of alkenylarenes to ketones was achieved by the use of molecular oxygen and EtjSiH in the presence of a catalytic amount of Co(II) porphyrin in 2-propanol.544... 

Cobalt(iii) diketonate complexes generate alkyl peroxo adducts that can oxidize alkenes to oxiranes <1999IC1603>. 0-Phenylenebis(oxamate)-Iigated square-planar cobalt(iii) complexes catalyze high-yield epoxida-tions of unfunctionalized tri- and disubstituted alkenes <1997TL2377>. Low yields are obtained with terminal alkenes. Terminal alkenes can be converted smoothly to aldehydes using an epoxidation-isomerization with ruthenium(ii) porphyrin catalysts <2004AGE4950>. 

Apart from the commonly used NaOCl, urea—H2O2 has been used/ With this reaction, simple alkenes can be epoxi-dized with high enantioselectivity. The mechanism of this reaction has been examined.Radical intermediates have been suggested for this reaction, polymer-bound Mn -salen complex, in conjunction with NaOCl, has been used for asymmetric epoxidation. Chromium-salen complexes and ruthenium-salen complexes have been used for epoxidation. Manganese porphyrin complexes have also been used. Cobalt complexes give similar results. A related epoxidation reaction used an iron complex with molecular oxygen and isopropanal. Nonracemic epoxides can be prepared from racemic epoxides with salen-cobalt(II) catalysts following a modified procedure for kinetic resolution. 

Similarly, ra 5-cyclopropanes were obtained from alkenes, such as styrene and 2,5-dimethyl-hexa-2,4-diene, with relative yields > 90% when a diazoacetate bearing a bulky ester group was decomposed by a copper catalyst with bulky salicylaldimato ligands. Several metal complexes with bulky Cj-symmetrlc chiral chelating ligands are also suitable for this purpose, e.g. (metal/ligand type) copper/bis(4,5-dihydro-l,3-oxazol-2-yl)methane copper/ethyl-enediamine ruthenium(II)/l,6-bis(4,5-dihydro-l, 3-oxazol-2-yl)pyridine cobalt(III)/ salen. The same catalysts are also suited for enantioselective reactions vide infra). For the anti selectivity obtained with an osmium-porphyrin complex, see Section 1.2.1.2.4.2.6.3.1. 

Metal complexes of fluorous tetraarylporphyrins (1-5) have been used as catalysts in the epoxidation of alkenes under FB [9] or more traditional conditions [10], depending on their affinity for perfluorocarbons. Free base porphyrins 1-5 were readily metaUated with transition metal cations under standard conditions normally employed for their nonffuorous coimterparts. In particular, porphyrins 1-4 were metalated with Mn(OAc)2 4 H2O in boiling DMF to give their respective Mn(III) complexes Mn-l-Mn-4 [10], whereas the perffuorocarbon-soluble porphyrin 5 was similarly converted into the cobalt(II) complex Co-5 by treatment with Co(OAc)2 -4H20 [9],... 

It has been shown that this catalyst is selective in epoxidation of linear alkenes the linear epoxide yield was two to four times higher than in catalysis by ordinary porphyrin. It was also demonstrated that, in catalysis by the dendrimers, cyclic alkenes are oxidized three times more rapidly than similar linear 1-alkenes are. The catalyst activity decreases only by 10% at a turnover number (TON) of 1000, which is much higher than that for the monomolecular analogue. A cobalt complex with dendrimer phthalocyanine was much more stable, while remaining active, in... 

The dechlorination of chlorinated alkenes could also be performed by porphyrin cobalt complex such as 5,10,15,20-tetrakis(4-carboxyphenyl)porphyrin cobalt ((TCPP)-Co). This cobalt complex, structurally similar to vitamin B12, was found to have superior aqueous-phase dechlorination activity on chlorinated ethylenes relative to vitamin Bi2. Based on fully detailed parameters dependence, the authors suggest the catalytic cycle below.This methodology has been used to synthesize C-labeled air-DCE from TCE (Scheme 33). ... 

Metal-catalysts that enable the direct transfer of an Ni-moiety from chloramine-T to alkenes with moderate efficiencies include metalloporphyrinoids. For example, in 2001, Simkhovich and Gross reported that iron (IV) corrole 21 (Scheme 2.29) catalyzed olefin aziridination with chloramine-T [44]. The use of porphyrine complexes of iron [Fe(TPP)Cl] and cobalt [Co(TDClPP)] in the presence of bromamine-T also allows for aziridinating a wide variety of alkenes [45,46]. A recyclable polymer-supported manganese (II) complex, which is readily prepared from chloromethy-lated poly(styrene-divinylbenzene) (PS-DVB) in two steps, transfers an Ni unit from bromamine-T to aliphatic alkenes in a heterogeneous system [47]. 

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