Mechanism cobalt catalysis

Burdo and Seitz reported in 1975 the mechanism of the formation of a cobalt peroxide complex as the important intermediate leading to luminescence in the cobalt catalysis of the luminol CL reaction [116]. Delumyea and Hartkopf reported metal catalysis of the luminol reaction in chromatographic solvent systems in 1976 [117], while Yurow and Sass [118] reported on the structure-CL correlation for various organic compounds in the luminol-peroxide reaction. 

Cobalt bromide is used as a catalyst in the technology of production of arylcarboxylic acids by the oxidation of methylaromatic hydrocarbons (toluene, p-xylene, o-xylene, polymethyl-benzenes). A cobalt bromide catalyst is a mixture of cobaltous and bromide salts in the presence of which hydrocarbons are oxidized with dioxygen. Acetic acid or a mixture of carboxylic acids serves as the solvent. The catalyst was discovered as early as in the 1950s, and the mechanism of catalysis was studied by many researchers [195-214],... 

M(CxC) matrix, 32 290-291, 311-313 Measurements, interpretation of, in experimental catalysis, 2 251 Mechanism see also specific types cobalt catalysis, 32 342-349 dehydrocyclization, 29 279-283 rhodium catalysis, 32 369-375 ruthenium catalysis, 32 381-387 space, 32 280... 

The formation of arylzinc reagents can also be accomplished by using electrochemical methods. With a sacrificial zinc anode and in the presence of nickel 2,2-bipyridyl, polyfunctional zinc reagents of type 36 can be prepared in excellent yields (Scheme 14) . An electrochemical conversion of aryl halides to arylzinc compounds can also be achieved by a cobalt catalysis in DMF/pyridine mixture . The mechanism of this reaction has been carefully studied . This method can also be applied to heterocyclic compounds such as 2- or 3-chloropyridine and 2- or 3-bromothiophenes . Zinc can also be elec-trochemically activated and a mixture of zinc metal and small amounts of zinc formed by electroreduction of zinc halides are very reactive toward a-bromoesters and allylic or benzylic bromides . ... 

Noyori and colleagues investigated the ring opening of unsaturated mono- and bicyclic endoperoxides catalyzed by 5-10 mol% of Pd(PPh3)4 [226, 227]. Similarly to the cobalt-catalyzed reactions, (Z)-4-hydroxy enones resulted as the main products, which were accompanied by (Z)-2-ene-l, 4-diols and diepoxides. The latter are formed as the major products under either ruthenium or cobalt catalysis (see Part 2, Sects. 3.5 and 5.8). Both two-electron and radical mechanisms were considered for this transformation. Saturated bicyclic endoperoxides gave mixtures of cyclic 4-hydroxy ketones and 1,4-diols and their formation may be a result of a radical process [227, 228]. 

The properties of polyurethanes derived from the hydroformylation of fatty acid derivatives, subsequent hydrogenation, and reaction with isocyanates such as toluene diisocyanate (TDl), methylene diphenyl-4,4-diisocyanate (MDI), and 1,6-hexamethylenediisocyanate (HDI) may be strongly dependent on the metal used for the hydroformylation [12a, 62]. At high conversion rates with a rhodium catalyst, a rigid polyurethane A is formed, whereas under the conditions of cobalt catalysis and low conversion a hard rubber or rigid plastic (polyurethane B) with lower mechanical strength results (Scheme 6.100). 

Reactions 33 and 35 constitute the two principal reactions of alkyl hydroperoxides with metal complexes and are the most common pathway for catalysis of LPOs (2). Both manganese and cobalt are especially effective in these reactions. There is extensive evidence that the oxidation of intermediate ketones is enhanced by a manganese catalyst, probably through an enol mechanism (34,96,183—185). 

Several differences between the cobalt- and rhodium-catalyzed processes are noteworthy with regard to mechanism. Although there is a strong dependence in the cobalt system of the ethylene glycol/methanol ratio on temperature, CO partial pressure, and H2 partial pressure, these dependences are much lower for the rhodium catalyst. Details of the product-forming steps are therefore perhaps quite different in the two systems. It is postulated for the cobalt system that the same catalyst produces all of the primary products, but there seems to be no indication of such behavior for the rhodium system. Indeed, the multiplicity of rhodium species possibly present during catalysis and the complex dependence on promoters make it... 

An alternative interpretation of some features of the hydroformylation reaction (including the inverse CO dependence), in terms of heterogeneous catalysis by an (unidentified) insoluble cobalt component, has recently been advanced by Aldridge, Fasce and Jonassen (49a). The universal validity of this seems doubtful in the light of the considerable evidence favoring a homogeneous mechanism. 

We are still further from being able to explain the anodic activity of the CoTAA complex. The cobalt phthalocyanine, which is structurally identical with CoTAA in the inner coordination sphere, is completely inactive in the catalysis of anodic reactions. It therefore looks as if the central region is not exclusively responsible for the anodic activity. On the other hand, the fact that CoTAA is inactive for the oxidation of H2 points to n orbitals of the fuel participating in the formation of the chelate-fuel complex. A redox mechanism (cf. Section 5.2) can be ruled out because anodic oxidation proceeds only in the region below the redox potential of CoTAA (i.e. at about 600—650 mV). 

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