New capping agents for oximehydrazonate clathrochelates: sterically controlled synthesis, structural characterization and intramolecular reactions

The H+-ion-catalyzed interaction of boron- and tin-containing semiclathroch elates with an excess of triethyl orthoformate resulted in the formation of the single clathrochelate product for each of these precursors. H-1 and C- 13 NMR spectra indicate that the boron- and tin-containing clathrochelate p roducts are different isomers with cis and trans orientation of ethoxy grou ps and semiclathrochelate fragment. The boron complexes underwent intramole cular condensation under vigorous conditions to produce a tripod capping fr agment. The molecular structures of diacetylmonooxime hydrazonate [FeDXO3(B C6H5)(HCOC2H5)(3)](BF4) and cyclohexanedione-1,2-monooxime hydrazonate [FeC XO3(BC6H5)(HCOC2H5)(3)](BF4). 1/2C(6)H(6) complexes were determined by X-ra y crystallography. The iron(II) ion has a distorted trigonal prismatic coor dination (twist angles phi = 18.2 degrees and 10.8 degrees, respectively) w ith Fe-N distances (similar to 1.91 Angstrom) typical for clathrochelate tr is-dioximates. All ethoxy groups and the semiclathrochelate fragment are lo cated on the same side of the 1,3,5-triazacyclohexane ring. Thus, the boron -containing compounds have the cis configuration. The tin-containing comple xes are expected to have a trans configuration. Different configurations of boron- and tin-containing complexes are accounted for by essential differe nces in their structures obtained from Mossbauer Fe-57 spectra: the geometr y of the former approaches a trigonal prism (phi similar to 10-20 degrees), whereas that of the latter is close to trigonal antiprism ((phi similar to 50 degrees). The semiclathrochelates undergo similar reactions with the ot her active trifunctional agents (e.g. trichloroacetaldehyde). Cyclic voltam ograms of synthesized compounds have shown the influence the degree of cycl ization on redox potentials of the central iron ion. (C) 1999 Elsevier Scie nce S.A. All rights reserved.