Cobalt isomerizations

Isomerization of [Co(en)(NH3)3(OH)] + and of [Co(en)(NH3)2(OH)2]+ has been extensively studied by spectrophotometry in dilute aqueous solution. Recent kinetic results for the former isomerization obtained by the use of Co n.m.r. spectroscopy, in concentrated solutions, are consistent with the early spectrophotometric results. The [Co(en)(NH3)2(OH)2]+ cation exists in three isomeric forms. The observed isomerization paths and their respective rate constants, also obtained by Co n.m.r. spectroscopy, are shown in Table 27. The proposed mechanism for these isomerizations involves reversible dissociation of one end of the ethylenediamine ligand from the cobalt. Isomerization of mer- or yhc-[Co(en)(NH3)3(OH)] + was not detected, even after... 

The 3.8-nonadienoate 91, obtained by dimerization-carbonylation, has been converted into several natural products. The synthesis of brevicomin is described in Chapter 3, Section 2.3. Another royal jelly acid [2-decenedioic acid (149)] was prepared by cobalt carbonyl-catalyzed carbonylation of the terminal double bond, followed by isomerization of the double bond to the conjugated position to afford 149[122], Hexadecane-2,15-dione (150) can be prepared by Pd-catalyzed oxidation of the terminal double bond, hydrogenation of the internal double bond, and coupling by Kolbe electrolysis. Aldol condensation mediated by an organoaluminum reagent gave the unsaturated cyclic ketone 151 in 65% yield. Finally, the reduction of 151 afforded muscone (152)[123]. n-Octanol is produced commercially as described beforc[32]. 

The first identified complexes of unsubstituted thiazole were described by Erlenmeyer and Schmid (461) they were obtained by dissolution in absolute alcohol of both thiazole and an anhydrous cobalt(II) salt (Table 1-62). Heating the a-CoCri 2Th complex in chloroform gives the 0 isomer, which on standirtg at room temperature reverses back to the a form. According to Hant2sch (462), these isomers correspond to a cis-trans isomerism. Several complexes of 2,2 -(183) and 4,4 -dithiazolyl (184) were also prepared and found similar to pyridyl analogs (185) (Table 1-63). Zn(II), Fe(II), Co(II), Ni(II) and Cu(II) chelates of 2.4-/>is(2-pyridyl)thiazole (186) and (2-pyridylamino)-4-(2-pyridy])thiazole (187) have been investigated. The formation constants for species MLr, and ML -" (L = 186 or 187) have been calculated from data obtained by potentiometric, spectrophotometric, and partition techniques. 

In contrast to triphenylphosphine-modified rhodium catalysis, a high aldehyde product isomer ratio via cobalt-catalyzed hydroformylation requires high CO partial pressures, eg, 9 MPa (1305 psi) and 110°C. Under such conditions alkyl isomerization is almost completely suppressed, and the 4.4 1 isomer ratio reflects the precursor mixture which contains principally the kinetically favored -butyryl to isobutyryl cobalt tetracarbonyl. At lower CO partial pressures, eg, 0.25 MPa (36.25 psi) and 110°C, the rate of isomerization of the -butyryl cobalt intermediate is competitive with butyryl reductive elimination to aldehyde. The product n/iso ratio of 1.6 1 obtained under these conditions reflects the equihbrium isomer ratio of the precursor butyryl cobalt tetracarbonyls (11). 

Prior to 1975, reaction of mixed butenes with syn gas required high temperatures (160—180°C) and high pressures 20—40 MPa (3000—6000 psi), in the presence of a cobalt catalyst system, to produce / -valeraldehyde and 2-methylbutyraldehyde. Even after commercialization of the low pressure 0x0 process in 1975, a practical process was not available for amyl alcohols because of low hydroformylation rates of internal bonds of isomeric butenes (91,94). More recent developments in catalysts have made low pressure 0x0 process technology commercially viable for production of low cost / -valeraldehyde, 2-methylbutyraldehyde, and isovaleraldehyde, and the corresponding alcohols in pure form. The producers are Union Carbide Chemicals and Plastic Company Inc., BASF, Hoechst AG, and BP Chemicals. 

C-19 dicarboxyhc acid can be made from oleic acid or derivatives and carbon monoxide by hydroformylation, hydrocarboxylation, or carbonylation. In hydroformylation, ie, the Oxo reaction or Roelen reaction, the catalyst is usually cobalt carbonyl or a rhodium complex (see Oxo process). When using a cobalt catalyst a mixture of isomeric C-19 compounds results due to isomerization of the double bond prior to carbon monoxide addition (80). 

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. 

In contrast, chromium (ITT) and cobalt(III) form 2 1 dye metal complexes that have nonplanar stmctures. Geometrical isomerism exists. The (9,(9 -dihydroxyazo dyes (22) form the Drew-Pfitzner or y rtype (23) (A = C = O) whereas o-hydroxy—o -carboxyazo dyes (24) form the Pfeiffer-Schetty or fac type (25), where A = CO 2 and C = O. 

Metal oxides, sulfides, and hydrides form a transition between acid/base and metal catalysts. They catalyze hydrogenation/dehydro-genation as well as many of the reactions catalyzed by acids, such as cracking and isomerization. Their oxidation activity is related to the possibility of two valence states which allow oxygen to be released and reabsorbed alternately. Common examples are oxides of cobalt, iron, zinc, and chromium and hydrides of precious metals that can release hydrogen readily. Sulfide catalysts are more resistant than metals to the formation of coke deposits and to poisoning by sulfur compounds their main application is in hydrodesulfurization. 

Quite recently, Ciampolini and coworkers have reported the synthesis of two isomeric mked oxygen-phosphorus macrocycles and the crystal structures of their cobalt complexes. Synthesis of macrocycle 27 was accomplished by condensation of 1,2-bis-(phenylphosphino)ethane dianion with 2,2 -dichlorodiethyl ether in THE. The two isomers of 27 were isolated in 1.5% and 2% yield. The synthesis is formulated in Eq. (6.17), below. 

Cesium fluonde in dimethylformamide catalyzes the isomerization offluori-nated cyclobutenes, perfluorobipyntmdines, and their oligomers to products with expanded rings [30, 31, 32] The product distribution in cobalt tnfluonde fluorina-tion depends strongly on the temperature of the reaction [33] Fluorinated 1-dimethylamino-5,6,7,8-tetrafluoro-l,4-dihydro-l,4-ethenonaphthalene rearranges in protic media to a biphenyl derivative [34] (equation 8)... 

Catalytic reduction of thiophenes over cobalt catalysts leads to thiolane derivatives, or hydrocarbons. " Noncatalytic reductions of thiophenes by sodium or lithium in liquid ammonia leads, via the isomeric dihydrothiophenes, to complete destructions of the ring system, ultimately giving butenethiols and olefins. " Exhaustive chlorination of thiophene in the presence of iodine yields 2,2,3,4,5,5,-hexachloro-3-thiolene, Pyrolysis of thiophene at 850°C gives a... 

The isomerization of an allylic amine to an enamine by means of a formal 1,3-hydrogen shift constitutes a relatively small structural change. However, this transformation could be extremely valuable if it could be rendered stereoselective. In important early studies, Otsuka and Tani showed that a chiral cobalt catalyst, prepared in situ from a Co(ii) salt, a chiral phosphine, and diisobutylaluminum hydride (Dibal-H), can bring about the conversion of certain pro-chiral olefins to chiral, isomeric olefins by double bond migra-... 

Cobalt, aquapentaammine-, 1, 3 Cobalt, aquapentacyano-anation, 1, 310 isomerization, 1,186 Cobalt, aquatetracyanosulfito-anation, 1, 310... 

Cobalt, cis-chloroamminebis(l, 2-ethanediamine)-optical isomerism, 1,12 Cobalt, chlorobis(l,2-ethanediamine)-solvation, 1,503... 

Cobalt, diamminedichloro(l, 2-ethanediamine)-hydrate thiocyanate isomerization, 1,469 reactions, 1,27... 

Cobalt, dichlorobis(AvY -dimethyl-1,2-ethanediamine)-chloride hydrate isomerization, 1, 468 Cobalt, dich orobis(l,2-ethanediamine)-base hydrolysis, 1, 304 chloride anation, 1, 469 halogen exchange, 1, 468 chloride hydrate isomerization, 1, 468 isomers, 1,191 nitrate... 

Cobalt, dichloro(l, 10-diamino-4,7-dithiadecane)-configuration, 1,199 Cobalt, dichloro(triethylenetetramine)-chirality, 1,194 isomerization, 1, 467 isomers, 1,201... 

Cobalt, pentaamminecyano-isomerization, 1,186 Cobalt, pentaamminehydroxy-thiocyanate isomerization, 1,185 Cobalt, pentaammineisonicotinamido-electron transfer, 1,373 with hexaaquachromium, 1,369 reduction... 

Cobalt, tetraammineaquahydroxy-reactions, 1, 27 Cobalt, tetraamminedichloro-isomerization, 1,182, 201,467 Cobalt, tetraamminedihydroxy-cobalt(III) salt structure, 1,184... 

Cobalt, trichlorotris(l,2-ethylenediamine)-conformation, 1, 197 Cobalt, (triethylcnetetramine)-isomerism, 1, 200,201 Cobalt, trinitrato-structure, 1,67 Cobalt, tris(acetylacetone)-structure, 1, 62,65,67 Cobalt, tris(bipyridyl)-structure, 1,64... 

Cobalt, tris(tetraaminine-p-dihydroxocobalt)-optical isomerism, 1,13... 

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