Macrobicyclic oximehydrazonates

Complexes with type I.II ligands are usually referred to as boron (tin, germanium, silicon, antimony)-capped macrobicyclic dioximates (oximehydrazonates, azineoximates). Their abbreviated... 

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. 

Binuclear clathrochelate iron(II) oximehydrazonates may be synthesized by the main methods used for the synthesis of macrobicycles of this type proposed for clathrochelate tris-dioximates by a direct template reaction on a metal ion the cross-linking of initial nonmacrocyclic complexes a cross-linking group exchange reaction and a ligand modification reaction. The template condensation of a mononuclear complex to a binuclear one followed by the encapsulation of another metal ion and capping reaction may be also used for the preparation of these compounds. The main methods for the synthesis of these complexes are shown in Scheme 88 [193]. 

Macrobicyclic binuclear iron(II) oximehydrazonates were synthesized by encapsulation of initial nonmacrocyclic tris-complexes with boron- and tin-containing Lewis acids and by direct template reactions on the Fe + ion (Scheme 89). 

The binuclear germanium-capped clathrochelate [Fe2DA03(Ge(CF3)3)2] oximehydrazonate was obtained by a template condensation of the tetradentate H2DAO ligand with IGe(CF3)3 in an aqueous solution in the presence of CaCOs (Reaction 52). The resulting intramolecular macrobicyclic compound precipitated from the reaction mixture, and the equilibrium shift due to the formation of the solid allowed one to isolate this complex in a relatively high yield [73]. 

Different configurations of boron- and tin-capped complexes are accounted for by essential differences in their structures the geometry of the former approaches a TP, whereas that of the latter is close to a TAP. The distortion angle q> values for macrobicyclic iron(II) oximehydrazonates were predicted from QS values in their Fe Mdssbauer spectra [188], The predicted

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The CTB in the UV-vis spectra of nonmacrocyclic iron(II) oximehydrazonates and their semi- and clathrochelate derivatives (vmax 19 600-20 600 cm-i) occupies an intermediate position between those of macrobicyclic iron(II) tris-dimethylglyoximates and those of clathrochelate complexes with dihydrazone ihz ligand. A CTB maxima in the spectra of clathrochelate complexes are substantially red shifted compared with that in the spectra of the initial semi-clathrochelates [185-187]. 

Considerable discrepancies in the geometry of macrobicyclic boron- and tin-capped oximehydrazonates were observed in their UV-vis spectra the intense Md->Ln CTBs in the spectra of the boron-capped clathrochelates are UV-shifted compared with the spectra of the tin-capped ones. The shape of the spectra is also somewhat changed an asymmetric singlet band is characteristic of the boron-capped compounds, whereas the spectra of the tin-capped ones in the visible region consist of two overlapping bands of nearly the same intensity. Similar differences have also been detected for clathrochelate iron(II) tris-dioximates (see Section 3.3) [188]. 

The UV-vis spectra of the macrobicyclic cobalt(II) oximehydra-zonates contain two CTBs in the visible region (at 18 000-19 000 and at 24 000-25 000 cm-i). In the spectra of cobalt(III) complexes, a shoulder at 18 000t20 000 cm-i and a peak at 24 000-30 000 cm-i were observed. All the absorption bands for the tris-dioximate complexes occur at slightly higher energy than the corresponding lines in spectra of the oximehydrazonate compounds [186]. 

Cyclic voltammetric data (mV) for macrobicyclic boron-, tin-, antimony- and germanium-capped iron(II) oximehydrazonates and a-dioximates [73, 74, 188],... 

Cyclic voltammetric data (mV, vs SCE in AN) for macrobicyclic iron and cobalt oximehydrazonates [186, 187, 189]. 

The redox properties of macrobicyclic iron(II) mono- and binuclear oximehydrazonates and a-dioximates formed by capping with antimony(V) and germanium(IV) triorganyles were studied by cyclic voltammetry [73, 74]. The electrochemical behaviour of these compounds is similar to that of analogous boron- and tin-capped clathrochelates. Oxidation of all mononuclear complexes involves a one-electron process, assigned to the oxidation of encapsulated iron(II) ion to iron(III) ion. This process is electrochemically... 

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