A Molecular Box Derived from Cobaloxime Units Held Together by 4-Pyridinylboronic Acid Residues

The reaction of CH3Co(DH)2H2O with 4-pyridinyl boronic acid in methanol or water affords the dinuclear
complexes [MeCo(DH)(DB(OR)(4-Py))]2, with R = Me (2) or H (3), respectively, through reaction of boron
with the oxime oxygens of the alkylcobaloxime and coordination of the pyridinyl N to cobalt. The reaction is
strongly pH dependent, and the formation of the complexes requires a neutral medium. The complexes have been
fully characterized by 1H and 13C NMR spectroscopy, ESI-MS spectrometry, and elemental analysis. The X-ray
structure shows that in 2, the pyridinyl groups are facing each other and nearly perpendicular both to the plane
of the Co B Co1 B1 atoms and to the mean equatorial plane, so that the complex may be considered a molecular
box. A dimeric arrangement has already been found in the related [MeCo(DH)(DB(OMe)(3-Py))]2 (1) complex,
which forms a distorted molecular rectangle [Dreos, R.; Nardin, G.; Randaccio, L.; Tauzher, G.; Vuano, S. Inorg.
Chem. 1997, 36, 2463]. The dimerization is possible in both cases, as the conformational freedom of the B bridge
compensates for the different position (3- or 4-) of the pyridinyl N donor.