Clathrochelates apical

An apical functionalization of clathrochelates enables one to obtain complexes with improved chemical, physicochemical, biomimetic, and bioactive properties and characteristics that are primary governed by functionalized groups [65]. The possibility of an apical modification of macrobicyclic a-dioximates and oximehydrazonates is indicated by the relative availability of functionalized boron-containing Lewis acids as efficient capping agents. 

The introduction of lipophilic substituents is of interest for producing surface-active compounds (surfactants) and liquid-crystal systems. The complexes with allyl substituents at the apical boron atoms are precursors for the synthesis of linear and netlike polymeric clathrochelates. 

It is undoubtedly of interest that the substituents in the clathrochelate framework and in apical groups affect the structure and properties of macrobicyclic complexes. In particular, it was noted that N-methylation of the complexes must stabilize the lowest oxidation states of the encapsulated metal ion. In this case, one should take into account the steric effects of substituents whose introduction influences the dissociation kinetics of the sarcophaginates [112]. 

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]. 

In all cases, except for 9-acetylanthracene, both Cs-symmetric amine clathrochelates with apical aromatic substituents and Ca-nonsymmetric imine sarcophaginates with substituents in the methylene units have been formed (Scheme 59). The reaction of 9-acetylanthracene under the same conditions led only to the aroyl-type sarcophaginate, since in this case a bulky substituent inhibits the condensation of a keto group with an amino group to give imine. 

The apical functionalized oximehydrazonate clathrochelates were also obtained stepwise from initial semiclathrochelate precursors followed by H -catalyzed condensation with an excess of formaldehyde or TOF (Scheme 79) [67]. 

Apically functionalized clathrochelate iron(II) oximehydrazonate with an appended pyridyl and its complex with [Co(H2Nx)(HNx)]Br2 cobaloxime were prepared by Scheme 82 [189],... 

With pentaazamacrobicyclic clathrochelates, not only the nitrogen atoms of the side units but also capping apical nitrogen atoms take part in the coordination. Synthesis of such complexes was performed by interaction of the presynthesized macrobicyclic ligand (Scheme 94) with copper, zinc, cobalt, and nickel(II) perchlorates in boiling methanol [204]. 

Analysis of kinetic and structural data permitted Sargeson and coworkers to establish a mechanism of Cu ion extrusion from a sarcophaginate cavity [4, 5]. A spontaneous Cu-N bond rupture via a dissociative mechanism takes place at the first stage. It accounts for the fact that the rate of transition of a clathrochelate complex to a square-planar one is independent of the concentration of ion. Then noncoordinated amino group protonates and a second amino group of the same ethylenediamine moiety coordinates in the apical position... 

It has been pointed out [52] that there is a correlation between the Hammet S (Tpara constants of the apical substituents and the redox potentials of the corresponding iron clathrochelates. Meanwhile, such a correlation is observed only inside the two groups of complexes with (a) OH, OCH3, F, Cl, and Br and (b) CH3, CsHs, and i-C4H9 substituents. No reasons are given for the existence of two groups of complexes. In spite of the fact that the cyclic voltammetry evidence indicates that the Fe +/ + couple is quasi-reversible, the electrolytic oxidation has failed to isolate stable iron(III) complexes [52]. 

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... 

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