Cobalt clathrochelates with

Complexes containing encapsulated metal ions (clathrochelates ) with the formula [M(dioxime)3(BR)2] are known with iron(II) 135, cobalt(ll) 136, cobalt(III) 137, and ruthenium(ll) 138 (Fig. 37) [205-220]. Generally, these macrobicyclic complexes are prepared by template synthesis from a mixture of... 

The BF4 anion in the clathrochelate [CoDma(BF)2](BF4) complex can readily be replaced by another large inorganic anion (e.g. PFe ) via an exchange reaction occurring in aqueous-acetonitrile solution in the presence of a great excess of the substituting anion salt [39]. The reduction of the [CoDma(BF)2](BF4) clathrochelate with Nal solution in acetone yielded a macrobicyclic cobalt(II) CoDma(BF)2 complex. The synthesis of the latter via a template condensation on the Co2+ ion was not yet successful. 

The interaction of the free ligand with cobalt(II) perchlorate in the presence of AgC104 as a precipitant in the nitromethane-methanol mixture made it possible to isolate the [Co(diME l,3pnsar-S6)](C104)3 clathrochelate. The reduction of this clathrochelate with sodium dithionate led to the formation of a cobalt (II) complex that readily produced a free sarcophagine [147],... 

The reduction of imBT ligand with NaBH4 in methanol led to the formation of a saturated octaazamacrocyclic amBT ligand that forms binuclear complexes with zinc(II) and copper(II) [199] and mononuclear clathrochelates with manganese, iron, cobalt, nickel, and zinc (II) [203] by treatment of the free ligand with the corresponding metal ion salts. 

Magnetochemical measurements for the solid phosphorus-containing zinc, iron, nickel, and cobalt tris-diiminates showed that the first two are diamagnetic and low-spin complexes. The cobalt and nickel(II) complexes proved to be high-spin clathrochelates with magnetic moments of 4.91BM (S=3/2) and 3.11BM (S=l), respectively [92, 93]. 

Most studies deal with cobalt clathrochelates. In several cases, nonmacrocyclic tris-diamine complexes have also been investigated to elucidate the specificity of interactions brought about by the formation of cage structures. 

A great number of papers deal with the stereospecificity of the interaction of optically active [CoNe] + complex cations with optically active anions and the stereospecificity depending on the structures of these cations and anions. A variety of tris-diamine cobalt(HI) complexes with different structures, clathrochelates with diverse capping groups, and the semiclathrochelate [Co(sen)]3+ cation have been investigated. Many investigators have employed d- and Z-tart -[Sb2(d-,Z-tart)2]2, and [As2(d-,Z-tart)2] dianions as optically active reagents [307, 310-312]. 

UV-vis and H, and ° Co NMR spectra of the cobalt(III) sarcophaginates were discussed in Section 3.1. With the exception of the apical N-methylated cobalt(III) complexes, the maxima of the d-d absorption bands in their UV-vis spectra were remarkable invariant (21 186 130 and 29 240 200 cm- ), and no correlations with redox Co3+/2+ potentials were observed. Maxima for [Co(diMe3AMHsar)]5+ and [Co(diMe2AMHsar)] cations are markedly different and approximate those observed for clathrochelate with an... 

The fell values for most macrobicyclic tris-dioximates and Ne-nSn-sarcophaginates (n = 2, 3) increase with decreasing E values. The cobalt Se-sarcophaginates and boron-capped tris-benzyldioximates drop out of linear correlation for both low-spin cobalt(II) and cobalt(III) complexes. The lack of this correlation in the first case may be attributed to the absence of structural changes in passing from the cobalt(III) complex to the cobalt(II) complex. In the second case, an increased fen value may be attributed to the special rigidity of hexaphenyl-substituted cobalt clathrochelates. 

Substituents in the macrobicyclic cobalt complexes affect their photochemical properties. These effects are more pronounced for solutions of the complexes exhibiting high redox potentials and low electron-transfer rates (Tables 42 and 52). Clathrochelates with lower redox potentials and higher electron-transfer rates are less photochemically active. As mentioned above, the [Co(diNOsar-H)]2+ cation displays the highest photochemical activity among the other complexes studied spectral changes are observed on its irradiation... 

The redox reactions of cobalt sarcophaginates with hemerythrin and cytochrome C have aroused particular interest for biochemists [316, 320, 404-406]. The kinetics of the redox reactions and relaxation dynamics of the clathrochelate cobalt tris-dioximates have been discussed in Refs. 407-409. 

The best performance was achieved with platinum for hydrogen evolution and iridium for oxygen evolution. The catalyst loading was between 0.5 and 3 mg cm . Cobalt clathrochelates were also tested for oxygen evolution, but their performance is much lower [51]. Typical voltages at 80-90 °C and 0.1 MPa are given in Table 8.7. 

Another type of clathrochelate, namely [M(L1000)]"+, is obtained on reaction of tris(butan-2,3-dione)dihydrazonato-nickel(II), -iron(II) or -cobalt(Il) with formaldehyde in acetonitrile (Eq. 4.33) [127, 128]. 

A, A-[(en)2Co(III)-iLtNH2, M02-Co(III)(en)2] " with [Mo(V)204(l , S-pdta)] . They conclude that both steps contribute to the stereoselective course of the reaction. It is noteworthy also that A-[Co(III)(en)3f associates preferentially with A-[Co(III)(edta)] but that A-[Co(III)(en)3] is formed preferentially in the oxidation of [Co(II)(en)3] by A-[Co(III)(edta)] . Again, stereoselective contributions from precursor complexation and electron transfer steps are established. Sargeson and co-workers " note that stereoselectivities as high as 10% are suggested in reactions of cobalt clathrochelates. These are in accordance with other values. 

The second type of reaction of a monocarbonyl compound to yield a macrocyclic product is represented by the condensation of [Ni(en)2]2+ or [Cu(en)2]2+ with formaldehyde in the presence of a suitable nucleophile (Scheme 4).15-16 This reaction is related to the condensations of [Co(en)3]3+ with formaldehyde plus nucleophiles to form clathrochelate compounds (Chapter 21.3), and also to the formation of the Coin[14]aneN4(02) complex (8) by reaction of a bis(ethanediamine)cobalt(III) complex with formaldehyde.17... 

In the synthesis of the boron-capped cobalt(II) tris-dioximates, ferrocenylboronic acid was also used as a capping agent [43], Reaction of this Lewis acid with anhydrous C0CI2 and dioximes in oxygen-free methanol gave clathrochelate CoNx3(BFc)2 and CoDm3(BFc)2 complexes ... 

For tin(IV) bromide, the halogenide ion detachment apparently takes place much more readily compared with that of SnF4. However, the bulky bromine atom causes steric hindrances due to its interaction with the substituents at the a-dioxime fragments. In particular, attempts to obtain clathrochelate tribromotin-capped cobalt(III) a-benzyldioximate and a-furyldioximate were not successful, whereas the corresponding trichlorotin-capped complexes were obtained [45]. 

During the synthesis of the methyne-capped cobalt(II) sarcophaginate via reduction of the chlorosarcophaginate complex with zinc dust in water (Scheme 45), an alkylzinc clathrochelate stable even in 6 molar hydrochloric acid was isolated [120],... 

The amidine-functionalized cobalt(III) sarcophaginates with apical carboxylic acid and the complex resulting from its decarboxylation, as well as the [Co(MEazasar)]3+ azasarcophaginate (formed by capping with ammonia resulting from the hydrolysis of the ethyl cyanoacetate nitrile groups), are minor clathrochelate products of this reaction [134]. 

The condensation of butanedione-2,3-dihydrazone with formaldehyde on a metal ion (Fe-, Co-" and Ni +) matrix (Scheme 74), performed by Goedken and Peng, led to the formation of clathrochelate [M(thz)](BFi)2 complexes. Direct reaction between the three components proved to be efficient only with iron(II) ion [183]. Therefore, nickel, cobalt, and iron(II) tris-dihydrazonates were preliminarily synthesized. It was noted that even when the reaction was carried out under nitrogen and cobalt(II) tris-dihydrazonate was used as the starting material, only cobalt(III) clathrochelate could be isolated from the reaction mixture. Its reduction with anhydrous hydrazine yielded cobalt(II) clathrochelate [95, 183]. 

When a-oximehydrazones were used as the chelating agents, researches succeeded in the synthesis of mono- and bis-clathrochelate iron and cobalt(II) oximehydrazonates [185-187], At the first stage, mono- and bis-semiclathrochelate iron and cobalt(II) complexes were isolated by a cross-linking with phenylboronic or ferrocenylboronic acids, and with benzene-1,4-diboronic or l,l -ferrocenyldiboronic acids. 

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