Cobalt catalysts complexes

The switch from the conventional cobalt complex catalyst to a new rhodium-based catalyst represents a technical advance for producing aldehydes by olefin hydroformylation with CO, ie, by the oxo process (qv) (82). A 200 t/yr CSTR pilot plant provided scale-up data for the first industrial,... 

With cobalt complex catalysts, in polar, aprotic solvents like DME it is often possible to get a-keto acids by controlled double carbonylation874-877. Alternatively, a-hydroxy acids are formed when benzyl halides are carbonylated in the presence of calcium hydroxide, in aqueous media878. Presumably the initially formed a-keto acid is reduced in the Meerwein-Ponndorf fashion to give the a-hydroxy group878. 

Okada, T. et al., A comparative study of organic cobalt complex catalysts for oxygen reduction in polymer electrolyte fuel cells, J. Inorg. Organometal. Polym., 9,199,1999. Bron, M. et al., EXAFS, XPS and electrochemical studies on oxygen reduction catalysts obtained by heat treatment of iron phenanthroline complexes supported on high surface area carbon black, J. Electroanal. Chem., 535, 113, 2002. 

One of the most significant processes that involve CO in organic industrial chemistry is the hydroformylation of alkene, or the 0x0 process, in which rhodium and cobalt complex catalysts are used. Ruthenium is a strong candidate for replacing the very expensive rhodium catalyst. Further, ruthenium complexes are excellent catalysts for the addition of formyl groups of aldehydes, formates and formamides to alkenes. 

Cobalt complex catalyst A homogeneous cobalt carbonyl complex was used in the first commercial process (developed by BASF) which requires pressures as high as 600-700 atm and a temperature of 250 C. 

The heptanuclear iron carbonyl cluster [Fe3(CO)u(/u-H)]2-Fe(DMF)4 (178) acted as an efficient catalyst in the reduction of carboxamides by l,2-bis(dimethylsilyl)benzene in toluene to the corresponding amines in high yields. Several tertiary and secondary amides including a sterically crowded amide were also reduced smoothly A review of the development of optically active cobalt complex catalysts for enan-tioselective synthetic reactions has addressed the applications of ketoiminatocobalt(II) complexes such as (5)-MPAC (179) and (5)-AMAC (180), transition-state models for borohydride reduction, halogen-free reduction by cobalt-carbene complexes. 

Turnover rates for the reduction of DBCH to cyclohexene mediated by the PLL-Co film in bicontinuous SDS microemulsions were controlled by the difference between the reduction potential of the reactant and E° of the catalyst in the film, similar to dissolved cobalt complex catalysts. High conductivity and low viscosity of the bulk microemulsion also facilitated fast catalyst turnover. 

New Steroidal derivatives of androstene and pregnene containing an a-amino moiety have been prepared in a one-pot hydroformylation-amidocarbonylation reaction using a rhodium or a rhodium-cobalt complex catalyst [157]. 

An early attempt to hydroformylate butenediol using a cobalt carbonyl catalyst gave tetrahydro-2-furanmethanol (95), presumably by aHybc rearrangement to 3-butene-l,2-diol before hydroformylation. Later, hydroformylation of butenediol diacetate with a rhodium complex as catalyst gave the acetate of 3-formyl-3-buten-l-ol (96). Hydrogenation in such a system gave 2-methyl-1,4-butanediol (97). 

When the Claus reaction is carried out in aqueous solution, the chemistry is complex and involves polythionic acid intermediates (105,211). A modification of the Claus process (by Shell) uses hydrogen or a mixture of hydrogen and carbon monoxide to reduce sulfur dioxide, carbonyl sulfide, carbon disulfide, and sulfur mixtures that occur in Claus process off-gases to hydrogen sulfide over a cobalt molybdate catalyst at ca 300°C (230). 

The nickel or cobalt catalyst causes isomerization of the double bond resulting in a mixture of C-19 isomers. The palladium complex catalyst produces only the 9-(10)-carboxystearic acid. The advantage of the hydrocarboxylation over the hydroformylation reaction is it produces the carboxyUc acids in a single step and obviates the oxidation of the aldehydes produced by hydroformylation. 

Chiral salen chromium and cobalt complexes have been shown by Jacobsen et al. to catalyze an enantioselective cycloaddition reaction of carbonyl compounds with dienes [22]. The cycloaddition reaction of different aldehydes 1 containing aromatic, aliphatic, and conjugated substituents with Danishefsky s diene 2a catalyzed by the chiral salen-chromium(III) complexes 14a,b proceeds in up to 98% yield and with moderate to high ee (Scheme 4.14). It was found that the presence of oven-dried powdered 4 A molecular sieves led to increased yield and enantioselectivity. The lowest ee (62% ee, catalyst 14b) was obtained for hexanal and the highest (93% ee, catalyst 14a) was obtained for cyclohexyl aldehyde. The mechanism of the cycloaddition reaction was investigated in terms of a traditional cycloaddition, or formation of the cycloaddition product via a Mukaiyama aldol-reaction path. In the presence of the chiral salen-chromium(III) catalyst system NMR spectroscopy of the crude reaction mixture of the reaction of benzaldehyde with Danishefsky s diene revealed the exclusive presence of the cycloaddition-pathway product. The Mukaiyama aldol condensation product was prepared independently and subjected to the conditions of the chiral salen-chromium(III)-catalyzed reactions. No detectable cycloaddition product could be observed. These results point towards a [2-i-4]-cydoaddition mechanism. 

The cationic aqua complexes prepared from traws-chelating tridentate ligand, R,R-DBFOX/Ph, and various transition metal(II) perchlorates induce absolute enantio-selectivity in the Diels-Alder reactions of cyclopentadiene with 3-alkenoyl-2-oxazoli-dinone dienophiles. Unlike other bisoxazoline type complex catalysts [38, 43-54], the J ,J -DBFOX/Ph complex of Ni(C104)2-6H20, which has an octahedral structure with three aqua ligands, is isolable and can be stored in air for months without loss of catalytic activity. Iron(II), cobalt(II), copper(II), and zinc(II) complexes are similarly active. 

Although the enantioselective intermolecular addition of aliphatic alcohols to meso-epoxides with (salen)metal systems has not been reported, intramolecular asymmetric ring-opening of meso-epoxy alcohols has been demonstrated. By use of monomeric cobalt acetate catalyst 8, several complex cyclic and bicydic products can be accessed in highly enantioenriched form from the readily available meso-epoxy alcohols (Scheme 7.17) [32]. 

The first reported chiral catalysts allowing the enantioselective addition of diethylzinc to aryl aldehydes in up to 60% cc were the palladium and cobalt complexes of 1,7,7-trimethylbicy-clo[2.2.1. ]heptane-2,3-dione dioxime (A,B)3. A number of other, even more effective catalysts, based on the camphor structure (C K, Table 26) have been developed. 

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