Macrocyclic clathrochelates

CLATHROCHELATED METAL PERCHLORATES, HYDRAZINEMETAL NITRATES METAL PERCHLORATES organic ligands, POLYAZACAGED METAL PERCHLORATES SOLVATED OXOSALT INCIDENTS, URANYL MACROCYCLIC PERCHLORATE LIGANDS... 

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... 

Coordinated ligand reactions of this type have been used to synthesize a variety of macrocyclic complexes of the clathrochelate type,382 and somewhat similar reactions have been used quite generally in the macrocycle field.383... 

Ca-nonsymmetric iron(II) clathrochelates have been obtained by the cycloaddition of a-dioximes to initial square-planar macrocyclic iron (II) bis-dioximates by the Reaction 13 ... 

The cycloaddition reaction proceeds under more rigid conditions and takes more time than a direct template condensation on the iron(II) ion. This can be explained by the fact that the overall mechanism of clathrochelate synthesis involves an intermediate tris-complex formation step. It is evident that macrocyclic square-planar iron(II) bis-dioximates are relatively kinetically stable, and the... 

In the absence of F ion acceptors, a clathrochelate is not formed and the reaction completed at a stage of cis-addition of the protonated dioxime to a square-planar macrocycle. With certain dioximes (H2NX and H2Dm), in the absence of the base the reaction yields a mixture of symmetric clathrochelates. In other cases, only a mixture of decomposition products has been formed [64]. 

The methods for the preparation of the clathrochelate complexes discussed in this section are, in most cases, similar to those for the macrocyclic compounds described in detail in Refs. 7, 11, 14, 15 and 17. In contrast to clathrochelates of other types, they are prepared largely via interaction between a preformed clathrochelate ligand and the appropriate metal salt. In other cases, the synthesis of these clathrochelates occurs via either template encapsulation or rearrangement from square-planar complexes (Scheme 74). 

The calculated ligand field parameters are close to the values obtained for low-spin macrocyclic polyamines and clathrochelate boron-capped cobalt(III) tris-dioximates (see above). The ligand field strength in trichlorotin-capped cobalt(III) tris-dioximates is substantially higher than that in nonmacrocyclic and tribromotin-capped complexes and slightly exceeds that in their boron-capped analogs [44],... 

The sTjTe Mdssbauer parameters for the tin-, germanium-, and antimony-capped clathrochelate compounds (Tables 22-24) are typical low-spin iron(II) complexes. The increase in the ligand field strength (a "macrocyclic" effect), causes the increase in s-electron density on the iron nucleus, is less pronounced for these compounds than for their boron-capped analogs experimental ISs are only slightly lower than those calculated from a PIS concept. 

The use of kinetic and thermodynamic approaches along with physicochemical and X-ray diffraction data, as well as their comparison with earlier results for complexes with synthetic macrocyclic ligands, have allowed one to make sufficiently well-grounded conclusions about the mechanisms of synthesis and decomposition of clathrochelates. 

Kinetically inert low-spin cobalt (III) clathrochelates are reversibly reduced by accepting one electron to yield kinetically labile cobalt(II) complexes. In the case of the usual amines (for instance, ammonia), the reduction is, as a rule, accompanied by irreversible decay of the amine cobalt complex. This reaction is slower for chelating amines macrocyclic and especially macrobicyclic amines produce complexes with cobalt(II) ion that are stable over a long time. This fact facilitates the study of the reduction of cobalt(III) complexes to cobalt(II) ones. In most cases, the reactions of macrobicyclic ligands do not interfere with this process. 

The luminescence properties of macrobicyclic mixed bipyridine-bipyrazine and macrocyclic polybipyrazine europium(III) complexes were reported in Ref. 380. A noticeable enhancement in the lifetime and fluorescence quantum yield for the macrobicyclic [Eu(bpy.bpy.bpz)]3+ cation was observed in comparison with other europium(III) clathrochelates and attributed to the introduction of the bpz fragment. Among the four studied europium(III) complexes, only the macrobicyclic one is stable in dilute aqueous solution [380]. 

Although clathrochelates are most closely related to thio- and aza-macrocyclic d-metal complexes, they display several specific features of their own. The number of publications is also essentially different. Numerous papers and several monographs dealing with classical macrocyclic complexes have been published [7-17], whereas the quantity of papers concerning the chemistry and physical chemistry of clathrochelates does not exceed three hundred. 

Bridged or reinforced azamacrocycles, which have pairs of nitrogen atoms of an aza-macrocycle linked, usually by an a,cu-alkandiyl bridge, 154 are prepared by reaction of a cyclic amine with a bifunctional nucleophile, such as an a,cu-dibromoalkane or an a,cu-ditosyl-alkane-diol. Bis(acyl esters), amides, and halides react with amines to form bicyclic amides which can be reduced to the bicyclic amines.155 The bridge can have internal functions, such as C=C or o-C6H4 (or include hetero atoms, thus forming clathrochelates).156... 

The template synthesis represents an elegant method that uses metal ions to direct reactions of ligands and provides a useful route to macrocyclic structures. Several books159-161 describe the template processes that involve reactions on matrices used to synthesize polyazamacrocyles, crown ethers, cryptands, rotaxanes, knots,159 clathrochelates,160 phthalocyanines,161 etc. which are applied, e.g., as molecular switches, in ion exchange, electron transfer or catalysis. An example of clathrochelate synthesis is given in Chapter 1.33... 

An original pathway for producing reversible iron(II) clathrochelated structures has been discovered [131]. In particular, the clathrochelate systems [Fe(L 245)] +, [Fe(L 1010)] +, [Fe(L 244)] " and [Fe(L lOll)] were produced by treating complexes of superstructural macrocyclic ligands [Fe(L245)] +, [Fe(L1010)] +, [Fe(L244)] + and [Fe(LlOll)] with base in methanol in an inert atmosphere (Scheme 4-14). 

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