Cobalt complexes allylic oxidation

Acyclic /V-alkylimines, asymmetric hydrogenation, 10, 56 Acyclic ( j3-allyl)cobalt complexes, oxidation reactions, 7, 58 Acyclic allylic esters, alkylation, 11, 76 Acyclic aromatic imines, asymmetric hydrogenation, 10, 56 Acyclic 1-buly l-( )5-pencadienyl) iron cations, preparation and reactivity, 6, 156... 

Allyl complexes of cobalt in the oxidation states III and I have been identified as stmcturally defined catalysts for stereospecific butadiene polymerization. 

The two-electron reductions of [Fe(CO)2(NO)(>/3-C3H4R)] (R = Cl, Br, or Me) (248) and [Co(CO)2L(>/3-allyl)] (L = phosphine or phosphite) (249) result in metal-allyl bond cleavage. For the cobalt complexes there is a linear correlation between Elj2 and the half neutralization potential of L. The rhodium complex [Rh P(OMe)3 2(fj3-allyl)] reacts with AgPF6 to give [Rh P(OMe)3 2(f 4-C6Hi0)] in which the two C3 fragments have been oxidatively coupled (250). 

Cobalt tetraarylporphyrins with fluorine-containing substituents were active in epoxidation of alkenes using fluorous catalysis in the presence of oxygen and 2-methylpropanal [167,170-171]. Manganese and cobalt complexes of perfluorinated tetraazocyclonone catalyzed allylic oxidation of alkenes with r-BuOOH/Oa [172]. The complex with the salen ligand 57 was active in alkene epoxidation under Mikayama s conditions, and indene was epoxidated at a high stereospecificity [173]. 

Equations 3.64-3.66 illustrate routes to allyl complexes from dienes, diene complexes, and olefins. Allyl complexes have been prepared by the insertion of a conjugated diene into a metal hydride, alkyl, or acyl linkage, as illustrated for the cobalt complexes in Equation 3.64. ° Alternatively, allyl complexes have been prepared by nucleophilic or electrophilic attack on a coordinated diene. Equation 3.65 shows the formation of allyl complexes by the addition of carbanions to a cationic diene complex, and Equation 3.66 shows the formation of a cationic diene complex by the protonation of a neutral 1,3-diene complex. Allyl complexes have also been formed by the abstraction of an allylic proton from a metal-olefin complex, either by a base or by the metal itself. This reaction has been proposed as a step in the isomerization of olefins (Equation 3.67) and in the allylic oxidation of olefins (Equation 3.68). - ... 

There are few reports of oxidative addition to zerovalent transition metals under mild conditions three reports involving group 10 elements have appeared. Fischer and Burger reported the preparation of aTT -allylpalladium complex by the reaction of palladium sponge with allyl bromide(63). The Grignard-type addition of allyl halides to aldehydes has been carried out by reacting allylic halides with cobalt or nickel metal prepared by reduction of cobalt or nickel halides with manganese/iron alloy-thiourea(64). 

Cobalt chloride in diglyme is a useful catalyst for benzylic [22a] and allylic [22b] oxidation under mild conditions. The addition of sodium azide to oxidations catalyzed by transition metal acetylacetonates, heteropolyacids, phtha-locyanines, bis-(pyridylimino)isoindolines, porphyrins and Schiff bases significantly enhances the rates of the low-temperature catalytic oxidation of alkanes [22c]. Ethylbenzene is slowly oxidized by air in MeCN in the presence of catalytic amount of chromium trioxide [23]. Complexes of Fe(III) and Co(II)... 

Gaudemer, A., Nguyen-van-duong. K., Shahkarami, N. Achi. S.S., Frostin-rio, M. and Pujol, D. (1985). Allylation and oxidation reactions promoted by cobalt (II) complexes. Tetrahedron, 41,4095-4106. 

It has long been known that metal salts and complexes promote the reaction of olefins with oxygen in the liquid phase. Early work ([429] and references cited therein) established that during olefin oxidation in the presence of various copper, cobalt and manganese salts, free radicals arise via decomposition of a catalyst-hydroperoxide complex formed from allylic hydroperoxide generated in situ. Although the metal modifies the nature of the observed products in many cases, most homogeneous metal-catalyzed oxidations exhibit characteristics of free radical initiated autoxidations. 

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