Cobalt, isomerism isomers

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). 

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. 

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. 

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... 

The formation of isomeric aldehydes is caused by cobalt organic intermediates, which are formed by the reaction of the olefin with the cobalt carbonyl catalyst. These cobalt organic compounds isomerize rapidly into a mixture of isomer position cobalt organic compounds. The primary cobalt organic compound, carrying a terminal fixed metal atom, is thermodynamically more stable than the isomeric internal secondary cobalt organic compounds. Due to the less steric hindrance of the terminal isomers their further reaction in the catalytic cycle is favored. Therefore in the hydroformylation of an olefin the unbranched aldehyde is the main reaction product, independent of the position of the double bond in the olefinic educt ( contrathermodynamic olefin isomerization) [49]. 

No cases of cis/trans isomerism have yet been reported among organo-cobalt(III) complexes, even among compounds not covered by this review. Complexes such as [R2Co(bipy)2] all have the cis configuration steric hindrance would be greatly increased by the coplanarity of the two bipyridyl ligands in the trans isomer 123). 

By studying the NMR spectra of the products, Jensen and co-workers were able to establish that the alkylation of (the presumed) [Co (DMG)2py] in methanol by cyclohexene oxide and by various substituted cyclohexyl bromides and tosylates occurred primarily with inversion of configuration at carbon i.e., by an 8 2 mechanism. A small amount of a second isomer, which must have been formed by another minor pathway, was observed in one case (95). Both the alkylation of [Co (DMG)2py] by asymmetric epoxides 129, 142) and the reduction of epoxides to alcohols by cobalt cyanide complexes 105, 103) show preferential formation of one isomer. In addition, the ratio of ketone to alcohol obtained in the reaction of epoxides with [Co(CN)5H] increases with pH and this has been ascribed to differing reactions with the hydride (reduction to alcohol) and Co(I) (isomerization to ketone) 103) (see also Section VII,C). 

Thiocarbamate (tc, RHNCSO-) is a monodentate ambidentate ligand, and both oxygen- and sulfur-bonded forms are known for the simple pentaamminecobalt(III) complexes. These undergo redox reactions with chromium(II) ion in water via attack at the remote O or S atom of the S- and O-bound isomers respectively, with a structural trans effect suggested to direct the facile electron transfer in the former.1045 A cobalt-promoted synthesis utilizing the residual nucleophilicity of the coordinated hydroxide in [Co(NH3)5(OH)]2+ in reaction with MeNCS in (MeO)3PO solvent leads to the O-bonded monothiocarbamate, which isomerizes by an intramolecular mechanism to the S-bound isomer in water.1046... 

Molecules which contain a chiral cobalt as well as an asymmetric nitrogen exist in four possible optical isomeric forms. These are represented for Co(sar)(hbg) +, hbg = NH2C( = NH)NHC(=NH)NH2 in Fig. 7.12. All four optically-active isomers have been isolated and characterized by cd, nmr and vis/uv absorption spectroscopy. The kinetics of... 

Raffinate-II typically consists of40 % 1-butene, 40 % 2-butene and 20 % butane isomers. [RhH(CO)(TPPTS)3] does not catalyze the hydroformylation of internal olefins, neither their isomerization to terminal alkenes. It follows, that in addition to the 20 % butane in the feed, the 2-butene content will not react either. Following separation of the aqueous catalyts phase and the organic phase of aldehydes, the latter is freed from dissolved 2-butene and butane with a counter flow of synthesis gas. The crude aldehyde mixture is fractionated to yield n-valeraldehyde (95 %) and isovaleraldehyde (5 %) which are then oxidized to valeric add. Esters of n-valeric acid are used as lubricants. Unreacted butenes (mostly 2-butene) are hydroformylated and hydrogenated in a high pressure cobalt-catalyzed process to a mixture of isomeric amyl alcohols, while the remaining unreactive components (mostly butane) are used for power generation. Production of valeraldehydes was 12.000 t in 1995 [8] and was expected to increase later. 

All these methods have found applications in theoretical considerations of numerous problems more or less directly related to solvent extraction. The MM calculated structures and strain energies of cobalt(III) amino acid complexes have been related to the experimental distribution of isomers, their thermodynamic stability, and some kinetic data connected with transition state energies [15]. The influence of steric strain upon chelate stability, the preference of metal ions for ligands forming five- and six-membered chelate rings, the conformational isomerism of macrocyclic ligands, and the size-match selectivity were analyzed [16] as well as the relation between ligand structures, coordination stereochemistry, and the thermodynamic properties of TM complexes [17]. 

Cobalt carbonyl hydride, [Co(CO)4H], when treated with butadiene gives a mixture of two isomeric compounds [Co(C4H7)(CO)3] (6,128,165). The same mixture of isomers is formed when Na[Co(CO)4] is treated with crotyl bromide, i.e., a l-bromobut-2-enc/3-bromobut-l-enc mixture (109). These two compounds, [Co(C4H7)(CO)3], have been shown by their nmr spectra to be the two geometrical isomers (XLIII) and (XLIV) of 7r-cro ty 11 ri car bo n y 1 co halt (165). 

Such a configuration should on replacement of one ammonia molecule by acidic or other monovalent radicle yield only one compound, and this is proved to be the case. On the other hand, if two acidic, or other groups replace two ammonia groups in the complex, isomerism should be possible, yielding two isomers of the formula [M(NII3)4R2 R. In the case of dinitro-tctrammino-cobaltic nitrate, [Co(NIi2)4(N02)2 N03, two isomeric forms are known to exist, one brown in colour, the other yellow. The two substances may be represented by the following formula —... 

Further, the frans-series of salts has never been found to give isomers, as they are symmetrica], and therefore such isomerism should not exist. 1-bromo-C-ammino-diethylcnediamino-cobaltic bromide therefore exists in only one form, and the configuration is given by... 

Isomerism due to Asymmetric Cobalt Atoms.—Werner established his formulas for the cobalt-ammines by proving the fact suggested by his theory that certain of the cobalt atoms in the ammines were centres of asymmetry, and therefore optical activity should be possible. Having established this for some of the simple cobalt-ammines, he then showed that in many of the polynuclear compounds optical activity exists. Thus he prepared optically active isomers of tetraethylenedianaino-... 

The unsymmetrical nature of / -mercaptoethylamine should lead to geometric isomerism among its metal complexes, cis and trans isomers might be expected with the square planar nickel (II) and palladium (II) derivatives and facial and peripheral isomers with cobalt (III). However, during the course of the preparation of various samples in which the procedure and experimental conditions were varied, no evidence of such isomerism was apparent (6, 15). This is particularly evident in the case of the cobalt (III) complex, CoL3. Samples prepared by the addition of cobalt (II) chloride 6-hydrate to strongly basic aqueous solution of the ligand and by displacement of ammonia and (ethylenedinitrilo)-... 

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