Oximes clathrochelates

Two interesting monoborylated clathrochelates 139 and 140 are known (Fig. 38), in which three oxime functions are joined together by a BR group, while the other half of the ligand is capped by a carbon or a phosphorus atom, respectively. 

In mixed oximesarcophaginate [Co(tamox)]Cl(C104)2-H20 and [Co(tamox-H)]Cl2-3H20 semiclathrochelates whose symmetry resembles a TAP ( 52°), the Co-N(oxime) and Co-N(amine) distances are substantially different (co 1.90-1.91 and ca 1.97-1.98A, respectively). The observed N-0 distance (co 1.90A) in these compounds is appreciably greater than that of clathrochelate cobalt(III) tris-dioximates (ca 1.83A). This may account for unsuccessful attempts to prepare the corresponding clathrochelate complexes via cross-linking with boric and phenylboronic acids [182]. 

The IR spectra of all these complexes also consist of two characteristic very intense and narrow bands of the C-F bond stretching vibrations at 1150-1185 cm-f Apart from the vc=n of oxime groups at 1560-1590 cm-i, characteristic of clathrochelate a-dioxima-tes, for germanium-capped oximehydrazonate clathrochelates, the vc=N of hydrazonate fragments have been observed at 1620 cm-i [73]. 

The hydrophosphoryl ligands have coordination properties similar to those of oximes and form the stable complexes represented in Scheme 144. This Scheme shows the pathway of synthesis of the phosphorus-containing analogs of clathrochelate tris-dioximates. 

Although cobalt] II) forms square planar complexes with oximes, and as consequence cannot be used as a three-dimensional template, the cobalt] II) encapsulated species [Co (L879)] has been prepared by reduction of [Co ]L879)]BF4 with Nal in acetonitrile-acetone mixture. Macrobicyclic clathrochelate structures for both complexes have been proved by X-ray diffraction [69]. 

The Lewis acid/oxime [66] and the formaldehyde/hydrazone [127, 128] capping processes permit the assembly of clathrochelate iron(II) or cobalt(II) complexes [M(L1001)]+ to [M(L1006)]+ based on miscellaneous oxime-hydrazone ligand systems (Eq, 4,34) [129, 130],... 

Nucleophilic displacement at centres other than carbon (for example, boron, silicon etc.) is an effective tool for producing new chelate rings via heteroatom-heteroatom bond formation. This procedure has been widely used for coupling oxime groups in the synthesis of clathrochelates and related monomacrocyclic oxime-based species. 

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