Clathrochelate iron(II) tris-nioximates with non-equivalent capping groups and their precursors: synthetic strategies, X-ray structure, and reactivityстатья
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Аннотация:ABSTRACT
Template cross-linking of nioxime using equimolar amounts of boric
and 4-vinylphenylboronic acids on an iron(II) ion as a matrix gave a
mixture of mono- and divinyl-terminated clathrochelate products,
which were chromatographically isolated in moderate yields and
characterized by X-ray diffraction. The target complex FeNx3(BOCH3)
(4-BC6H4CH=CH2) with non-equivalent capping groups was also
obtained in a low yield using a transmetallation (re-boronation) of
its dimethoxyboron-capped clathrochelate precursor. Re-boronation
of the monomethoxyboron-capped cage complex with benzene-1,4-
diboronic acid as a bifunctional Lewis-acidic agent afforded mainly
the clathrochelate product of its 1:1 re-boronation having a terminal
B(OH)2 group. The iron(II) clathrochelate with labile triethylantimony
capping groups underwent a transmetallation on the surface of silica
gel giving an immobilized Sb, Si-capped macrobicyclic intermediate.
Its desorption with 4-vinylphenylboronic acid unexpectedly gave
the monovinyl-terminated iron(II) semiclathrochelate as the major
product, isolated in a high yield; it was X-ray structurally characterized.
The geometry of FeN6-coordination polyhedra of the above semiand
clathrochelates is intermediate between a trigonal prism and a
trigonal antiprism; that of the monocapped iron(II) semiclathrochelate
is more TAP-distorted and its pseudoencapsulated iron(II) ion is
shifted from the center of this polyhedron by 0.02 Å in the direction
of the capping boron atom.