Nitriles cobalt catalysts

Eatty amines are made by dehydration of amides to nitriles at 280—330°C, followed by hydrogenation of the nitrile over nickel or cobalt catalysts ... 

In a related reaction, heating ketones in the presence of TlClsOTf leads to 1,3,5-trisubstituted arenes. " Nitriles react with 2 mol of acetylene, in the presence of a cobalt catalyst, to give 2-substituted pyridines. " Triketones fix nitrogen gas in the presence of TiCU and lithium metal to form bicyclic pyrrole derivatives. " ... 

Alkyne-nitrile cyclotrimerization is a powerful synthetic methodology for the synthesis of complex heterocyclic aromatic molecules.118 Recently, Fatland et al. developed an aqueous alkyne-nitrile cyclotrimerization of one nitrile with two alkynes for the synthesis of highly functionalized pyridines by a water-soluble cobalt catalyst (Eq. 4.62). The reaction was chemospecific and several different functional groups such as unprotected alcohols, ketones, and amines were compatible with the reaction.119 In addition, photocatalyzed [2+2+2] alkyne or alkyne-nitrile cyclotrimerization in water120 and cyclotrimerization in supercritical H2O110121 have been reported in recent years. 

Much recent work has been done on the synthesis of pyridines from alkynes and nitriles over cobalt catalysts. For example, 2-vtnylpyndine has heen obtained in good yield from acetylene and acrylonitrile using a cyclopentadienyl-cobalt catalyst. Pyridine has also been obtained from cyclopentadiene and ammonia over a sihca/alumina catalyst. 

There have been many known cases where high yields of primary amines were obtained over cobalt catalysts in the hydrogenation of nitriles. Hydrogenation of 3,4-... 

Cobalt catalysts are reasonably active for hydrogenation reactions but they are particularly useful for the hydrogenation of nitriles and aldoximes to primary amines.2. 22 Other than for these reactions cobalt has not been generally used as a hydrogenation catalyst even though there is a similarity between the catalytic activity of cobalt and nickel. Raney cobalt, which is prepared from a commercially available aluminum-cobalt alloy,2 -23 was found to be somewhat less active than Raney nickel and more sensitive to variations in the reaction procedure and catalyst age than the nickel catalyst.22,23... 

In contrast to carbocyclic alkyne cyclotrimerizations, the catalytic pyridine synthesis from alkynes and nitriles relies exclusively on cobalt catalysts with a few exceptions where rhodium [16] and iron complexes [17] could be applied. The cobalt-catalyzed pyridine synthesis can even be carried out in a one-potreac-tion generating the catalyst from C0CI2 6 H20/NaBH4 -1- nitrile/alkyne in situ [18]. 

The homogeneous catalytic [2+2+2]-cycloaddition of alkynes and nitriles was first discovered by Yamazaki and Wakatsuki [3] using the phosphine-stabilized cobalt(III) complex (Stmcture 5). At the same time, Bdnnemann and co-workers [5] observed the co-cyclization (eq. (2)) at cobalt catalysts prepared in situ, as well as using phosphine-free organocobalt(I) diolefm complexes. 

The cobalt-catalyzed co-cyclization of alkynes with heterofunctional substrates is not limited to nitriles. / -Cp-cobalt half-sandwich complexes are capable of co-oligomerizing alkynes with a number of C=C, C=N, C=0, or C=S bonds in a Diels-Alder-type reaction. Chen has observed that these cycloadditions are best performed in the presence of a small amount of ketones or esters [48]. This modified cycloaddition may be used for the formation of dihydroindole systems at the 7 -Cp-cobalt catalyst (eq. (17)). 

The nitrile can be converted to hexamethylene diamine by reduction in the presence of liquid ammonia at 125 C under 600 to 625 atmospheres pressure together with a copper-cobalt catalyst. 

Pyridine was first isolated, like pyrrole, from bone pyrolysates the name is constrncted from the Greek for fire, pyr , and the suffix idine , which was at the time being used for all aromatic bases - phenetidine, toluidine, etc. Pyridine and its simple alkyl derivatives were for a long time produced by isolation from coal tar, in which they occur in quantity. In recent years this source has been displaced by synthetic processes pyridine itself, for example, can be produced on a commercial scale in 60-70% yields by the gas-phase high-temperatnre interaction of crotonaldehyde, formaldehyde, steam, air and ammonia over a silica-alumina catalyst. Processes for the manufacture of alkyl-pyridines involve reaction of acetylenes and nitriles over a cobalt catalyst. 

In the presence of Co(I)-catalysts alkynes and nitriles can be co-trimerized in organic solvents to yield substituted pyridines under rather harsh conditions. The reaction is biased by formation of large quantities of benzene derivatives and with acetylene gas as much as 30 % of all products may arise from homotrimerization. It has been found recently, that with cobalt catalysts heterotrimerization of various nitriles and C2H2 could be achieved under ambient conditions using aqueous/organic biphasic systems and irradiating the reaction mixture with visible light (Scheme 7.12) [39,40],... 

A process for coproduction of mono- and diaminoalkylated glycols has been developed which involves Michael addition of excess diethylene glycol to acrylonitrile followed by catalytic hydrogenation of the nitrile mixture over a chromium-promoted sponge cobalt catalyst. 

More recently, chromium-promoted sponge cobalt has been found to be an active catalyst for nitrile hydrogenation. Examples of nitriles which have been successfully hydrogenated using this catalyst include 2-methylglutaronitrile [6], nitrilotriacetonitrile [7], and adiponitrile [8]. Hydrogenation of the latter nitriles typically is complicated by intramolecular cyclization reactions of the feedstocks. Use of the chromium-promoted sponge cobalt catalyst results in improved selectivities to linear products. 

The reduction can be carried out in batches or continuously at about 9,000 psig and 125 C in an ammonia atmosphere, over a cobalt-copper catalyst, in yields of over 90 per cent of theory. A number of other catalysts have been described for this reaction, including Raney nickel, cobalt on silica, and cobalt-silver-magnesium. The starting nitrile must be quite pure to avoid poisoning the catalyst. It is claimed that the presence of carbon monoxide, in addition to hydrogen and ammonia, extends the life of the cobalt catalysts normally used. ... 

Acids are converted to nitriles by reaction with ammonia at atmospheric pressure at 280-360 C in the presence of catalysts such as bauxite, zinc oxide, or manganese or cobalt salts. Hydrogenation of the nitrile proceeds via the aldimine (RCH=NH) at 120-180 °C and 20-100 bar in the presence of nickel or cobalt catalysts. 

In addition to cobalt catalysts, ruthenium catalysts were applied in [2 + 2 + 2] cycloaddition reactions as well. In 2001, Itoh and coworkers reported a ruthenium-catalyzed cyclization of 1,6-diynes with dicyanides to produce the desired bicyclic pyridines in good yields [28]. By applying Cp Ru(cod)Cl (Cp = pentamethylcyclopentadienyl) as the catalyst, good yields of the products can be achieved (Scheme 3.12). Meanwhile, they explored the catalyst system in cyclization of 1,6-diynes with electron deficient nitriles as well. The desired bicyclic pyridines can be isolated in moderate to high yields [29]. Later on, in 2005, Yamamoto and coworkers performed systematic studies on this... 

In a typical process, adipic acid is converted to the nitrile in the vapour phase by treatment with ammonia at 350—450°C using boron phosphate as catalyst. The adiponitrile is separated by distillation and then hydrogenated at 100-135°C and about 670 atmospheres. Hydrogenation is carried out in the presence of a supported cobalt catalyst and ammonia (which minimizes cyclization to hexamethyleneimine). Pure hexamethylenediamine is isolated by distillation under reduced pressure. 

A direct synthesis of substituted pyridines in yields of about 50% is found in the treatment of acetylene and an alkyl nitrile in the presence of a cobalt catalyst. A general method for the synthesis of 3- and 3,4-substituted furans from ketones has been developed. A new route to various heterocycles with 2 or more heteroatoms has been presented, as well as a procedure involving 1,3- or 3,3-cyclization on difunctional nucleophiles, such as hydrazine, hydroxylamine, alkyl and aryl-diamines. 76 77... 

This procedure avoids oligomerization of the starting diyne. The nitrile is used in excess (10 equiv) and mixed directly with the derivatized resin in toluene. After addition of the cobalt catalyst, the mixture is irradiated at 300 W for 10 min. With no solid support, the product desired, 103, is obtained only as traces (R = Ph). With dissymmetrical diynes 104, the reaction proved perfectly regioselective. 

As far as catalytic properties are concerned, nickel and cobalt catalysts rank among those most often described and used in the production of primary amines from higher fatty acids via the hydrogenation of the corresponding nitriles. It was also assumed in previous papers that when nickel is deposited on a support, only the degre of nickel dispersion is affected and there is no substantial modification of the selectivity (5). 

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