Cobalt catalysis addition with

The elTiciency of cobalt and ruthenium catalysis is not very sensitive to the presence of promoters )21]. With cobalt, the addition of thorium and alkali promoters increases wax production and supports were incorporated to increase the active metal surface area. On the other hand, promoters and supports are essentia) for iron catalysts. 

In addition to iridium and cobalt catalysis, and following the work initiated by Cavell et al. [138] on the alkylation of azolium salts, nickel-catalyzed alkylations of various heteroarenes (i.e., indoles [139], benzimidazoles [139], benzothiazoles [139], benzoxazoles [139], 1,3,4-oxadiazoles [140]) with olefins have been reported (Scheme 19.95 and Scheme 19.96). These reactions proved complementary to other methods because they proceeded with the Markovnikov regioselectivity with respect to the olefin. 

The need for higher product specificity and milder reaction conditions (see also Section IX) has led to extensive research in hydroformylation technology. This research, as reported in technical journals, patent literature, and commercial practice has been primarily concerned with catalysis by rhodium, in addition to the traditional cobalt, and with catalyst modification by trialkyl or triaryl phosphines. These catalyst systems form the basis for the major portion of the discussion in this chapter some other catalyst systems are discussed in Section VIII. 

Fig. 4 Effect of added water on the C5 + selectivity (filled symbols) and CH4 selectivity (open symbols) as a function of CO conversion at different conditions for Co/A1203 (A), CoRe/Al203 (B), Co/Si02 (C), CoRe/Si02 (D), Co/Ti02 (E), and CoRe/Ti02 (F). Before water addition ( , ), 20% water added ( , O), 33% water added (A, A) and after water addition ( , O).19 Reprinted from Journal of Catalysis, Vol. 231, S. Storsaeter, 0. Borg, E. A. Blekkan and A. Holmen, Study of the effect of water on Fischer-Tropsch synthesis over supported cobalt catalysts, pp. 405-419. Copyright (2005), with permission from Elsevier.

The chemical reactivity of crown-ether complexes with neutral molecules has received little attention. Nakabayashi et al. (1976) have reported crown-ether catalysis in the reaction of thiols with l-chloro-2,4-dinitrobenzene. The catalytic activity was attributed to deprotonation of thiols by dicyclohexyl-18-crown-6 in acetonitrile solution. Blackmer et al. (1978) found that the rate of aquation of the cobalt(III) complex [333] increases on addition of... 

The reaction between alkenes and synthesis gas (syngas), an equimolar mixture of carbon monoxide and hydrogen, to form aldehydes was discovered in 1938 by Otto Roelen [1,2]. Originally called oxo-reaction , hydroformyla-tion is the term used today. This reflects the formal addition of formaldehyde to the olefinic double bond. Commercially, homogeneous metal complexes based on cobalt and rhodium are used as catalysts. With more than 10 million metric tons of oxo products per year, this reaction represents the most important use of homogeneous catalysis in the chemical industry. 

Metal-ion catalysis has been extensively reviewed (Martell, 1968 Bender, 1971). It appears that metal ions will not affect ester hydrolysis reactions unless there is a second co-ordination site in the molecule in addition to the carbonyl group. Hence, hydrolysis of the usual types of esters is not catadysed by metal ions, but hydrolysis of amino-acid esters is subject to catalysis, presumably by polarization of the carbonyl group (KroU, 1952). Cobalt (II), copper (II), and manganese (II) ions promote hydrolysis of glycine ethyl ester at pH 7-3-7-9 and 25°, conditions under which it is otherwise quite stable (Kroll, 1952). The rate constants have maximum values when the ratio of metal ion to ester concentration is unity. Consequently, the most active species is a 1 1 complex. The rate constant increases with the ability of the metal ion to complex with 2unines. The scheme of equation (30) was postulated. The rate of hydrolysis of glycine ethyl... 

Intermolecular addition of radicals, generated by photo-electrochemical catalysis, to activated alkenes can also be brought about. The reaction of 66 is used as a key step in one synthesis of the insect pheromone, brevicomin [219]. The reaction of a secondary radical from 67 occurs at low cathode potentials and without photochemical assistance [219]. This illustrates the equiibrium between a secondary al-kylcobalt(m) species and the radical - cobalt(ii) pair. The carbon radical is eventually captured by reaction with the alkene. Further steps in the synthesis lead to four isomers of the pheromone, multistriatin, each of which is a pure enantiomer since... 

In addition to OH , other nucleophiles such as BH4 ,318 CN-319,320 and N3-321 also add at the nitrile carbon of cobalt(III)-nitrile complexes at rates which are = 104 times those of the corresponding reactions of the free ligands. Catalysis by C032 in the hydration of [(NH3)5RuNCMe]3+,316 and of the acrylonitrile complex [(NH3)5CoNCCH=CH2]3+,322 has been observed. In the latter complex, a direct nucleophilic pathway results in the incorporation of oxygen from C032 into the amide product with elimination of C02. 

In the presence of a large excess of Co2+, both native (97) and cobalt (92) carboxypeptidase A show an approximately two-fold activity increase. The kinetics of the enzyme are very complex at moderate or high substrate concentrations and involve both apparent activation and inhibition by substrate (95). Under the standard assay conditions used in connection with the observed cobalt activation, all these complicating factors contribute significantly. The additional Co2+ possibly interferes with these secondary effects rather than being a participant in catalysis. Further experimentation is needed to clarify this detail. 

The first mechanism is. in fact, reminiscent of the well-known copper-catalyzed dimerization of acetylene viny(acetylene being the main by-product of this process. This side reaction can, however, be inhibited to some extent by the use of cobalt salts as additives [IS]. The cyanation of acetylene and of alkenyl halides is also promoted by Co and Ni cyanides and Pd catalysis. A reducing reagent, such as Zn or NaBll4, has been used in conjunction with cobalt cyanide complexes, and the formation of. succinonitrile has been reported to result from the basebase-catalyzed hydrocyanation of acrylonitrile. 

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