Showing papers by "Giovanni Tauzher published in 2001"

A molecular box derived from cobaloxime units held together by 4-pyridinylboronic acid residues.

Abstract: 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 possib...

A new organocobalt complex containing a CO-N-C three membered ring.

Abstract: Treatment of R = −CH2X (X = halogen) derivatives of the type [RCoIII(LNH-py)(HLNH-py)]+, where HLNH-py = 2-(2-pyridyl-ethyl)amino-3-butanone oxime and LNH-py its conjugated base with diluted NaOH, afforded a new complex containing a three-membered ring by a pathway involving the intramolecular nucleophilic addition of an equatorial nitrogen donor to the axial carbon. The X-ray analysis reveals a highly distorted structure. The C−Co−N angle is acute (42.8°) with the distortion of the coordination sphere concentrated in the Co−C axial and Co−N bonds, which move away from the pseudo-octahedral positions in the CH2X parent complex to form the C−N bond of the metallocycle. Kinetic studies of the formation of this novel complex starting from [(XCH2CoIII(LNH-py)(HLNH-py)]+ (X = Cl,Br,I) showed that the metallocycle formation rates increase in the order Cl < Br < I. Kinetic data are consistent with a mechanism involving an intermediate species resulting from the deprotonation of an amine equatorial nitrogen in a ...

New Alkyl−Cobalt(III) Complexes with Tridentate Amino−Oxime Ligands: Synthesis, Structure, and Reactivity

Abstract: The oxidative addition of alkyl halides to the CoI species generated by the reduction of [CoIII(LNHpy)(HLNHpy)](ClO4)2 (1), where HLNHpy is the tridentate 2-(2-pyridylethyl)amino-3-butanone oxime ligand and LNHpy is its conjugate base, led to the formation of a new class of organocobalt complexes of general formula [RCoIII(LNHpy)(HLNHpy)](ClO4) [R = Me (2a), Et (2b), CH2CF3 (2c), nBu (2d), and CH2Cl (2e)]. All the complexes were characterised by 1H and 13C NMR spectroscopy. The X-ray structures of 2a, 2b and 2c provide evidence for a pseudo-octahedral configuration, where HLNHpy and LNHpy act as bi- and tridentate ligands, respectively. The axial geometry in 2a is closer to that found in methylcobalamin than that reported for other models, suggesting steric and electronic cis influences of the equatorial ligands close to those of the corrin nucleus. The solution properties and the reactivity show strong analogies with those of the previously known Vitamin B12 models.