Cobalt complexes nitrogen

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. 

The second structural type found for organometallic cobalt porphyrins contains an organic fragment bridged between the cobalt and one pyrrolic nitrogen. Cobalt complexes of N-alkyl- or N-arylporphyrins arc well established (but will not be specifically addressed here). The bridged complexes are derivatives of these where the N-alkyl group also forms a cr-bond to cobalt. They are also related to the axially... 

The third class of metal catalysts includes nickel and cobalt complexes of Schiff bases and nitrogen macrocyclic ligands, which can form on electroreduction cobalt(I) and nickel(I) reactive intermediates for the activation of organic halides. 

Love and coworkers have reported a series of dinuclear cobalt complexes derived from a rigid binucleating macrocycle H4L 18 as shown in Fig. 26 (150). The synthesis of the dicobalt complex [Co2(L18)] (36) was achieved by an anaerobic transamination reaction between H4L18 and [Co(thf) N(SiMe3)2 2] in THF. The unsaturated species 36 forms a bis(pyridine) adduct, 36 py2 (py — pyridine), which has a cleft-like structure reminiscent of pacman diporphyrin complexes (151,152). Both cobalt ions are square pyramidal, with Col and Co2 displaced out of the N4-basal planes by 0.17 and 0.18 A, respectively. The apical sites are occupied by pyridine nitrogen atoms that are exo and endo to the cleft. Interestingly the endo pyridine is canted and reflects the... 

Pauson-Khand cyclopentenone synthesisThe cycloaddition of an alkene with an alkyne complexed with Co2(CO) usually furnishes a mixture of two cy-clopentenones when the alkene is unsymmetrical. The regioselectivity can be improved markedly if the alkene bears a heteroatom that can coordinate with the cobalt complex. Both sulfur and nitrogen ligands can improve the yield and regio-control of this reaction. 

The relative instrumental sensitivity factors for cobalt and nitrogen were determined by measuring core level (Co 2p and N Is) XPS spectra for a series of pure cobalt amine complexes of established stoichiometry. To evaluate the core level photopeak intensities, peak areas, including shake-up satellite intensity were used. The precision for the measurements of the nitrogen to cobalt atomic ratio is 10% while the accuracy is approximately 15%. Additional details of the XPS measurements are contained in the literature (24,25). 

The sorption processes for cobalt complexes can be complicated by hydrolysis reactions of the complex in solution, surface induced ligand loss processes, sorption of hydrolysis products of either amine, protonated amine, or mixed amine/aquo cobalt complexes, and oxidation/reduction processes associated with cobalt. The principal objective of the XPS studies was to evaluate, the chemical state of cobalt and amine ligands, the surface concentration of the respective elements, and the ligand to cobalt ratio as indicated by the surface nitrogen to cobalt atomic ratio. 

Cobalt forms many complexes in both the divalent and trivalent states. While the d Co2+ ion exhibits a coordination number of four or six in the trivalent state, the d Co3 ion mostly exhibits coordination number six. Also, trivalent cobalt forms more stable complexes than Co2+ ion, and there are many more of them. The most common donor atom in cobalt complexes is nitrogen. 

Cyclic silylphosphanes, see Silylphosphanes, phosphorus-rich, cyclic Cyclic sulfur-nitrogen compounds, see Sulfur-nitrogen compounds, cyclic Cyclic trithiolate ligand, 38 8-9 Cyclic voltammetry A. chroococcum Fd 1, 38 130-131 fullerene adducts, 44 19 nickel(ll) macrocyclic complexes, 44 112 Rieske proteins, 47 138, 139 Cyclidenes, as cobalt complex ligands, 44 282-284... 

The final product is ferrocyanide and cobaltic EDTA, but this goes through an intermediate which can be isolated, and which is an adduct of these twro. Dr. Wilkins tried this system out in his rapid flow rate system and found a rate of association which was about right for substitution rates on a cobaltous ion. So this seemed to be a case where perhaps the nitrogen end of a cyanide was able to coordinate into a cobaltous complex, with either concomitant cr subsequent charge transfer. Yet no transfer of ligand occurs in the overall reaction. 

Figure 6.3 Illustration of the three-coordinate complex [Co N(SiMe3)2 3]. Cobalt and nitrogen atoms are shown as black spheres, silicon atoms are grey and carbon atoms are given in white shadow. The Co-N bond length is 1.87A...

Involvement of two nucleophilic nitrogen atoms is thus typical for the amino heterocycles. The mutual disposition of the pyridine and amine nitrogen atoms allows the formation of chelate structures for the cobalt complexes of purine, 221 and 222. Structures with the N, iV -five-membered metal cycles were proven for the tri- and tetranuclear complexes of silver ) with 8-aminoquinoline (223) (92IC4370), and polymeric copper- and rhodium-acetate clusters (224). Another coordination mode can be found in the complexes of 4-amino-3,5-bis(pyridin-2-yl)-l,2,4-triazole, (225 or... 

The porphyrin-cobalt complex gives rise to the cation radical with charge spin localization at the nitrogen atom of the porphyrin ring. The cation radical thus formed acquires enhanced reactivity and can add tolane (Kochi 1986), Scheme 1-52. The main point... 

The conditions under which cobalt hydrocarbonyl was reacted with olefin were also found to affect the distribution of products and the extent of isomerization of excess olefin (62, 73, 147). At low temperatures (0° C) under carbon monoxide (1 atm) very little isomerization of excess 1-pentene occurred and the main product was the terminal aldehyde. Under nitrogen or under carbon monoxide at 25° C, extensive olefin isomerization occurred and the branched aldehyde was mainly produced. The olefin isomerization is most satisfactorily accounted for by an equilibrium between alkylcobalt and olefin-hydride cobalt complexes [Eqs. (9) and (10)]. The carbon monoxide inhibition is most easily explained if the isomerization proceeds via the tricarbonyls rather than tetracarbonyls. This also explains why ethylcobalt tetracarbonyl is not in equilibrium with hydrocarbonyl and ethylene under conditions where the isomerization is rapid (62, 73). 

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],... 

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