Cobalt -complex

The molecular structure of the fra j-diferrocenyl-cobalt isomer is illustrated in Fig. 7-29 [115]. 

The cyclobutadiene ring is distorted square planar, in that one carbon is out of the plane formed by the remaining three carbon atoms by 0.035 A. The cyclopenta-dienyl rings of the two ferrocenyl groups are eclipsed. 

In the case of the tetraferrocenyl compound, the first one-electron oxidation is well shaped, whereas the successive oxidation waves of the three remaining ferrocenyl groups merge in a single broad peak. 

There are no significant differences among the redox potentials of the complexes. It has only to be noted that the appearance of discrete oxidation steps for the ferrocenyl groups indicates that the cyclobutadiene ring allows electronic interaction between its substituents. 

Complex Ferrocenyl-centered oxidation Cobalt(i) oxidation 

The redox behaviour of cobalt complexes is fairly similar to that of iron 

As usual, we begin our examination with tetracoordinate complexes. 

In spite of the structural analogies with [FenCl4]2-, which undergoes reversible oxidation to [FemCl4]-, the Co(II) complex is oxidized at notably higher potential values and the corresponding monoanion [ComCl4]- is not stable (El-/- = + 0.98 V vs. SCE A-Ep = 260 mV and W pa = 0.7, at 0.2 Vs-1).124 

We now pass to the planar tetracoordinate Co(II) complexes with the many times cited Schiff bases salen and saloph. 

As deduced from their magnetic moments [Con(salen)] /zeff=2.38 Mb [Con(saloph)] Meff 2.74 mb], 27 they are low spin complexes. Even if the spin-orbit contribution makes such value slightly greater than expected, it indicates an electronic configuration with a single unpaired electron (d7-dyz2dxz2dz22dxy ). 

Controlled electron-transfer chain catalysed nucleophilic substitution reactions of di- and trinuclear metal carbonyls allows sequential and regioselective coordination of polydentate ligands. This type of reaction has been illustrated by the syntheses of (tCFg)3C3]Co3(C0)g L (n = 1-3 L = 

or Ph 9H-telluroxanthene, 10-ethyl-3,7-dimethyIphenotellurazine or phenothiazine) and the 5-coordinate complexes [RhCl(CO)2b2] (L = 2-diphenylphosphinothio-phene) and [Rh(CO) (PPh ) 21 21 1 2 monobasic bidentate chelate anions e.g. acac, oxinate, salicylaldehydato, or dibenzoyl- 

3 Cyclopentadlenyl Complexes.- The chelate complexes [CpCo(bid)I]I (bid = dppp, dppb, or dpae) result from the reactions of [CpCo(C0)l2l with the Group V donor ligands.The reactions of [(n -R)Rh(C0)2] (R = CgH, CgMe, or C H N02) and [(n-C H PPhj)Rh(CO)2] with PPh proceed by an associative 

Phosphine ligands displace one or two carbonyl groups from 

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In the presence of suitable nickel or cobalt complexes, propargyl alcohol trimerizes to a mixture of l,3,5-ben2enetrimethanol [4464-18-0] and 1,2,4-trimethanol [25147-76-6] hen-zene (28). 

Upon treatment with suitable cobalt complexes, methylbutynol cyclizes to a 1,2,4-substituted benzene. Nickel complexes give the 1,3,5-isomer (196), sometimes accompanied by linear polymer (25) or a mixture of tetrasubstituted cyclooctatetraenes (26). 

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,... 

V-methyl aniline formed in the initial step to give the leuco base of methyl violet. Treatment with aqueous acid produces the dye. Because Michler s hydrol may also react with dimethyl aniline instead of the /V-methyl aniline to give crystal violet, commercial-grade methyl violet is usually a mixture. A cobalt complex has converted 4,T-dimethylaminodipheny1methane and dimethyl aniline in the presence of atmospheric oxygen to crystal violet in one step (50). 

Of these dyes, Acid Yellow 151 (37) still has the greatest market among the yellows. As reported by USITC, production had increased to 1989 tons in 1985 from 706 tons in 1975. It is produced by coupling diazotized 2-amino-l-phenol-4-sulfonamide to acetoacetanilide followed by metallizing with cobalt to obtain a 1 2 cobalt complex. Acid Orange 24 (38), which is sulfanilic acid coupled to resorcinol to which diazotized mixed xyUdines have been coupled, is an unsymmetrical primary diasazo dye with a bihinctional coupling component. 

Another class of metal complex dyes is derived from the formazan stmcture. These dyes are appHed to wool and nylon from a neutral or weakly acidic dyebath analogous to the 2 1 premetallized OjO -dihydroxyazo complexes. The bluish-gray dye Cl Acid Black 180 [11103-91-6] (61) (Cl 13710) is a 2 1 cobalt complex of the formazan type. 

Cl 12196), a 2 1 cobalt complex, illustrates this second type. 

Porphyrin, octaethyl-, cobalt complex cyclic voltammetry, 4, 399 <73JA5140)... 

Concentration limits of the diphosphate-ion, admissible to determination of magnesium and cobalt, manganese and cobalt, zinc and cobalt by spectrophotometric method with application of the l-(2-pyridylazo)-resorcinol (PAR) are presented. Exceeding maintenance of the diphosphate-ion higher admissible supposes a preliminary its separation on the anionite in the H+-form. The optimum conditions of cobalt determination and amount of the PAR, necessary for its full fastening are established on foundation of dependence of optical density of the cobalt complex with PAR from concentration Co + and pH (buffer solutions citrate-ammoniac and acetate-ammoniac). 

The Auger depth profile obtained from a plasma polymerized acetylene film that was reacted with the same model rubber compound referred to earlier for 65 min is shown in Fig. 39 [45]. The sulfur profile is especially interesting, demonstrating a peak very near the surface, another peak just below the surface, and a third peak near the interface between the primer film and the substrate. Interestingly, the peak at the surface seems to be related to a peak in the zinc concentration while the peak just below the surface seems to be related to a peak in the cobalt concentration. These observations probably indicate the formation of zinc and cobalt complexes that are responsible for the insertion of polysulfidic pendant groups into the model rubber compound and the plasma polymer. Since zinc is located on the surface while cobalt is somewhat below the surface, it is likely that the cobalt complexes were formed first and zinc complexes were mostly formed in the later stages of the reaction, after the cobalt had been consumed. 

Physical techniques can be used to investigate first order reactions because the absolute concentrations of the reactants or products are not required. Dixon et. al [3] studied the base hydrolysis of cobalt complex, [Co(NH3)5L]3+, where L = (CH3)2SO, (NH2)2C = O, (CH3)03P = O in glycine buffers. 

Other, closely related, nicotinic acid derivatives and the unsubstituted system itself have also been studied and undergo similar reactions. Moreover, the approach may be extended to 2,2 -bipyridyls. Newkome and his collaborators have used the 2,2 -bipyridyl unit 19) as an electrophile in which ortho-hr ommes served as leaving groups. They have also used halomethyl systems and formed the macrocycles from these systems . A compound derived from the latter starting material 20) is reported to form a cobalt complex, in which both nitrogens and only one of the oxygen atoms participate in the binding . The two precursor units are shown below as 79 and 20, respectively. 

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. 

Figure 26.2 O2 bridges in dinuclear cobalt complexes (a) peroxo (02 ) bridge, and (b) superoxo (02 ) bridge.

According to X-ray data, 2,5-diamino-l,3,4-triazole retains its diamino form in the heterovalent cobalt complex 375 (91IC4858) and in the polymeric complex with manganese thiocyanate (93ICA53). 

Cobalt complex 83 was obtained by the reaction of [CpCo(SMe2)3l2(BF4)2 with pentamethylpyrrole [88AG(E)579]. Full cobalt sandwich of 2,5-di-terr-butyl-pyrrole is also known [91JCS(CC)1368]. Meanwhile, attempts to synthesize other pyrrolyl complexes of cobalt, (Ti -2,5-dimethylpyrrole)cobalttricarbonyl and the 3,4-dimethyl analog, have been unsuccessful [87JOM(330)231]. 

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. 

In its complex compounds, of which there are many thousands, Co almost invariably has a +3 oxidation number. Apparently, Co+s ion accompanied by six coordinating groups is particularly stable. Cobalt complexes are important in biochemistry. Some enzyme reactions go through a cobalt-complexing mechanism. Although only small traces are needed, cobalt is essential to the diet. 

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