Equilibria of the axial ligation of benzyl(aquo)cobaloximes by imidazole, 1-methyl imidazole, histidine, histamine, glycine, ethyl glycine ester, thiourea and urea have been spectrophotometrically measured in aqueous solutions of ionic strength 1⋅0 M (KCl) at 25°C as a function of pH. The equilibrium constants are in the order CN-> 1-methyl imidazole > imidazole > histidine > histamine > glycine > ethyl glycine ester > thiourea > urea. The order of stability of benzyl(ligand)cobaloxime is explained based on the basicity of the ligand, Co(III) → L dπ-pπ back bonding and soft-soft and soft-hard interaction. Imidazole, substituted imidazoles, histidine and histamine form more stable complexes than glycine, ethyl glycine ester in contrast to the basicity of the ligands. Benzyl(ligand)cobaloximes were isolated and characterized by elemental analysis, IR and 1 H NMR spectra.
Isoxazole derivatives R 0240Intramolecular 1,3-Dipolar Cycloaddition of Cyclo-1,3-diene-tethered Nitrile Oxides. -Nitrile oxides are generated in situ from the corresponding cyclohexadienyl, cycloheptadienyl, or cycloheptatrienyl aldoximes by sequential treatment with either BuLi/NCS or Et3N/NCS. They undergo intramolecular cycloaddition reaction to give tricycle-fused isoxazolines in a diastereoselective fashion. -(YEH*, M.-C. P.; JOU, C.-F.; YEH, W.-T.; CHIU, D.-Y.; REDDY, N. R. K.; Tetrahedron 61 (2005) 2, 493-500; Dep. Chem., Natl. Taiwan Norm. Univ., Taipei 117, Taiwan; Eng.) -Klein 22-124
Kinetics and equilibria of axial ligation of bromomethyl(aquo) cobaloxime by a series of straight chain primary amines (methylamine, ethylamine, propylamine, butylamine, pentylamine, hexylamine), cycloamines (cyclopentylamine, cyclohexylamine, cycloheptylamine) and secondary amines (N,N-dimethylamine, N,N-diethylamine) have been measured as functions of pH by spectrophotometric technique in aqueous solution, ionic strength 1 M (KCl) at 25°C. The rate of substitution of H 2 O varies with the pKa of incoming ligand, thus establishing nucleophilic participation of the ligand in the transition state. Binding and kinetic data are interpreted based on the basicity and steric influence of the entering ligand. To compare the rate constants of the entering ligands, pH independent second-order rate constants (k on) are calculated.
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