Cobalt complexes interactions

Yong et al. developed a cobalt-catalyzed [2+2+2] cyclotrimerization of terminal alkynes in good yields in aqueous media (80/20 mixture of water and ethanol) at room temperature. A cyclopentadienyl cobalt complex bearing a pendant phosphine ligand was used as a catalyst (Eq. 4.59). The cyclotrimerization of internal alkynes resulted in lower yields and required an elevated temperature, most likely due to steric interactions. For example, cyclotrimerization of 2,5-dimethyl-3-hexyne gave hexaisopropylbenzene in 51% yield and the reaction of diphenylethyne resulted in a 47% yield of hexaphenylbenzene.112... 

Fig. 13 A two-dimensional infinite network is formed via pairs of (+)N-H -N(+) interactions in the [PF6] salt of the cobalt complex Co(terpy)22+ (top), while a quarter of the potential HB interactions are not formed leading to a broken network in the case of the [BF4] salt (bottom) [46]... 

Up to now, the solubility decrease of cobalt complexes with these modiflers has not been explained satisfyingly. It is assumed that the changes in the solvatization characteristics observed are caused by different interactions of the solute with the mixture of organic components and CO2 the modifier-solute (olefin/aldehyde-complex) interaction probably is stronger than the solute-scC02 interaction. Future theoretical treatment may also improve the... 

Cobalt vapor interacts with norbornene to produce Co(C7H10)3, a 15-electron complex, apparently isostructural with Ni(C7H10)3. The cobalt complex is soluble in hydrocarbon solvents to afford deep blue solutions decomposing rapidly and autocatalytically at -15° (5a, 134). It has not yet been possible to isolate this complex in a pure state but some of the reactions have been examined by trapping experiments ... 

It is suggested that this occurs by interaction of the isopropyl side chain with the cobalt complexes in solution, leading to C—C bond cleavage and subsequent hydrogenation (97). 

There has been some work on interactions between LSRs and transition metal complexes, both NMR shifts and relaxation rates being studied. Presumably the mode of interaction is by means of bridges formed by the donor atoms of one complex which bond in a labile manner to the metal ion of the second complex. Interactions examined include those between [Eu(fod-d[Pg.1104]

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. 

Finally of note is the l,5-cyclooctanediylbis(pyrazolyl)borate complex BBN(pz)2 2Ni (7, BBN = borabicyclononane), which, as previously observed of its cobalt analogue,8 9 exhibits significant agostic bonding between nickel and the bridgehead protons located above and below the N4 plane. While this situation was confirmed crystallographically for the cobalt system, interactions in 7 were implied solely on the basis... 

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