Cobalt complexes tridentate

Formazan, l-(2-hydroxy-5-suIfophenyl)-3-phenyl-5-(2-carboxyphenyl)-zinc detection, 6, 83 Formazans cobalt complexes dyes, 6, 81 metal complexes bidentate, 6, 78 color photography, 6,111 dyes, 6, 77 tetradentate, 6, 81 tridentate, 6, 79... 

The cobalt complexes reported in Fig. 17.20 can be easily produced by mixing 1 equivalent of [ ( 20) ]2 + with 3 equivalents of a bidentate ligand or 2 equivalents of a tridentate ligand under magnetic stirring in refluxing methanol for 2 h. Addition of ethyl ether results in the precipitation and isolation the product that is then usually used without any further purification. 

Cobalt complexes of tridentate metallizable azo compounds do not occupy such an important position in the dyestuffs field as chromium complexes. Without doubt the principal reason for this is the fact that 1 1 cobalt complexes cannot be prepared by methods analogous to those employed in the preparation of 1 1 chromium complexes (Section 58.2.3.1 (i)). It is, therefore, impossible to prepare unsymmetrical 2 1 cobalt(III) complex dyestuffs by methods comparable to those used in the preparation of unsymmetrical 2 1 chromium complexes. So-called unsymmetrical 2 1 cobalt complexes have been prepared48 by the interaction of cobalt(II) salts and equimolecular mixtures of two different metallizable azo dyestuffs but these are, in fact, statistical mixtures of the three possible 2 1 complexes (40a-c). 

The stability of 1 1 cobalt complex dyestuffs of this type varies considerably according to the nature of the metallizable system in the azo compound. For example, neutral aqueous solutions of 1 1 cobalt complexes of o-hydroxyarylazopyrazolones are stable almost indefinitely at 60 °C. Under similar conditions, 1 1 cobalt complexes of o.o -dihydroxydiarylazo compounds slowly decompose with loss of ammonia to give the symmetrical 2 1 cobalt(III) complex of the azo compound. The corresponding complexes of u-carboxy-o -hydroxydiarylazo compounds decompose rather more rapidly at 60 °C, and those of o-carboxyarylazopyrazolones are unstable in aqueous solution at room temperature in the absence of excess ammonia. None is sufficiently stable to be of value as a dyestuff in its own right but the isolation of complexes of this type opened the way to the production51 of pure, unsymmetrical 2 1 cobalt(III) complex dyestuffs for the first time (e.g. 42). 1 1 Cobalt complex dyestuffs have also been prepared by the interaction of tridentate metallizable azo compounds and cobalt(II) salts in the presence of inorganic nitrites. These too are reported52 to react with an equimolar quantity of a different tridentate metallizable azo compound to yield a pure unsymmetrical 2 1 cobalt(III) complex. 

It must be concluded, therefore, that the ligands do not become completely detached from the metal ion in isomerization reactions. Comparable results have been observed in the isomerization95 of potassium diaquodioxalatochromium(III) and the racemization96 of optically active potassium tris(oxalato)chromium(III) when no exchange with free ligand in solution occurs. Thus, although it is not practicable to take advantage of the desirable properties of individual isomers of 2 1 chromium and cobalt complexes of tridentate azo compounds because of the facility with which such compounds isomerize in solution, the technically important unsymmetrical 2 1 complexes are capable of practical application because they show little or no tendency to disproportionate in solution. 

A nickel-based catalyst system, which produces, in the absence of comonomers, highly short-chain branched polyethene was developed by Brookhart et al. [23]. Independently, the groups of Brookhart [24, 25, 26] and Gibson [27, 28, 29, 30] developed efficient iron- and cobalt-based catalyst systems. Nickel or palladium is typically sandwiched between two a-di-imine ligands, while iron and cobalt are tridentate complexed with imino and pyridyl ligands. 

Sulfonated Cobalt Complexes. Unlike triaqua 1 1 chromium complexes, the corresponding cobalt complexes can not be prepared in acidic solution. The 1 1 cobalt complexes are only stable in the presence of a surplus of nitrogen donor groups. Sandoz has developed sufficiently stabilized 1 1 cobalt complexes by using nitrite ions as N ligands [29], The coordinatively bound nitrite ions can easily be displaced by another tridentate azo dye [30],... 

Pyridine ligands 186 are monodentate, forming complexes of the kind presented by 189. Pyridine is coordinated in the same way in copper acetate 194 [314] and iron rhodanide complexes [315], adducts of cobalt complex with fe(salicylidene)ethyle-nediamine 195 [316] and nickel chelate, formed by tridentate N,S-donor azomethine ligand 196 [317] ... 

Fundamentally, optical isomers of the spiroheterocyclic cobalt complex must exist. Since these compounds could not be separated, we tried to synthesize the dicyano derivative under CO substitution by reaction with KCN in liquid NH3 in the hope that a separation into the optical antipodes might be possible. At 120°C, however, the reaction gave, besides K2[Co(NO)(CO)(CN)2], a complex in which the C(CH2PPh2)4 ligand is tridentate (139) ... 

Vaidyanathan VG, Nair BU. Photooxidation of DNA by a cobalt(II) tridentate complex. / Inorg Biochem 2003 94 121-6. 

The tris(mercaptophenylimidazolyl)borate iron and cobalt complexes [(Tmph)2M] (M = Fe, Co) have been synthesized by reaction of (Tmph)Tl with MI2.156 Structural characterization by X-ray diffraction demonstrates that the potentially tridentate Tmph binds through only two sulfur donors in these sandwich complexes and that the tetrahedral metal centers supplement the bonding by interactions with two BH groups. Comparison of the structures of [(Tmph)2M] with those of related tris(pyrazolyl)borate counterparts indicates that the Tm favors lower primary coordination number in divalent metal complexes. 

The asymmetric conjugate addition of diethylzinc with chalcone was also catalyzed by nickel and cobalt complex (Eq. (12.31)) [71]. A catalytic process was achieved by using a combination of 17 mol% of an aminoalcohol 34 and nickel acetylacetonate in the reaction of diethylzinc and chalcone to provide the product in 90% ee [72, 73]. Proline-derived chiral diamine 35 was also effective, giving 82% ee [74]. Camphor-derived tridentate aminoalcohol 36 also catalyzes the conjugate addition reaction of diethylzinc in the presence of nickel acetylacetonate to afford the product in 83% ee [75]. Similarly, the ligand 37-cobalt acetylacetonate complex catalyzes the reaction to afford the product in 83% ee [76]. 

Not only palladium, but many more non-metallocene late (and early) transition metal catalysts for the coordination polymerization of ethene and 1-olefins were reported [11]. Among the most significant findings in this area are the disclosures of novel highly active and versatile catalysts based on (i) bidentate diimine [N,N] nickel and palladium complexes [12], (ii) tridentate 2,6-bis(imino)pyridyl [N,N,N] iron and cobalt complexes [13], and (iii) bidentate salicyl imine [N,O] nickel complexes [14]. 

The analogous three-membered ring has been obtained with the cobalt complex containing the tridentate ligand 2-((2-pyridylmethyl)amino)-3-butanone oxime. It has been notified that intramolecular process forming the metallacycle 114 is quite rapid, whereas the carbon bonded to cobalt is inert toward intermolecular nucleophilic attack (Equation (18)). " ... 

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. 

Iron(II) complex of tris(N -tert-butylurea-ylato)-N-ethylene]aminato activates dioxygen at room temperature to afford an iron(III) complex containing a single terminal oxo ligand. X-ray structures show that the three urea molecules act as a tridentate N,N,N-hgand [52]. The tripodal ligand was also used to synthesise complexes of cobalt, iron or zinc with terminal hydroxo ligands (Scheme 8) [53]. 

In contrast with the Schiff base salen, salicylaldehyde oxime (79) (salox) complexes of Co have received comparatively little attention, but a series of bis-bidentate divalent complexes of the form iraiis-Co(sa 1 ox)2( D M SO)2 have been reported.343 The heterocyclic bidentate oxime violurate (lH,3H-pyrimidine-2,4,5,6-tetrone 5-oximate, Hvi) (80) and its /V-methyl (mvi) and /V,/V -dimethyl (dmvi) derivatives form high-spin divalent [Co(vi)]+ and Co(vi)2 complexes, whereas [Co(vi)3] is low spin.344 The mixed-ligand Co(dmvi)2(phen) complex is also low spin. The crystal structure of m-Co(pxo)2Br2 (pxo = 2-acetylpyridine-l-oxide oxime) is isostructural with the Ni11 relative.345 The dichloro complex also adopts a cis configuration. The tridentate dioximes 2,6-diformyl-4-methylphenol dioxime and 2,6-diacetyl-4-methylphenol dioxime (Hdampo) form binuclear complexes of the type (81a) and (81b) respectively.346 Cobalt oxide nanoparticles were prepared by... 

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