Chlorobis(dimethylglyoximato)(pyridine)cobalt(III)

Abstract

[23295-32-1] C13H19ClCoN5O4 (MW 403.75) InChI = 1S/C5H5N.2C4H7N2O2.ClH.Co/c1-2-4-6-5-3-1;2*1-3(5-7)4(2)6-8;;/h1-5H;2*7H,1-2H3;1H;/q;;;;+1/p-1/b;2*5-3+;; InChIKey = AZACUGZFZPADCG-YAFREIOTSA-M (starting material for alkyl(pyridine)cobaloxime(III) complexes,1 precursor for cobaloximes(II) and cobaloximes(I),2 which have found widespread applications as catalysts for carbon–carbon,3 carbon–oxygen,4 carbon–nitrogen,5 and carbon–hydrogen6 bond formations) Alternate Name: chloro(pyridine)cobaloxime(III), trans-[bis(2,3-butanedione dioximato)chloro(pyridine)cobalt(III)], chloropyridine cobaloxime, ClCo(dmgH)2py, Cl[CoIII]py. Physical Data: mp 235 °C; polarographic half-wave potentials (acetonitrile solution, vs. Ag/AgNO3 electrode): −0.65, −1.45, −2.42, −2.91 V. 1H, 13C, and 15N-NMR chemical shifts,18, 19 UV/Vis absorptions,18 IR frequencies (KBr),20 solid-state geometry (X-ray diffraction),21 and EXAFS data22 were determined. Solubility: sol CH2Cl2; limited sol ethyl acetate, hot ethanol; sparingly sol most other organic solvents and water. Chloro(pyridine)cobaloxime(III) can be replaced without any change in reactivity by its 4-tert-butylpyridine7 derivative which has good solubility in toluene, carbon tetrachloride, alcohols and ethyl acetate. Handling, Storage, and Precautions: forms brown, air stable crystals. The axial pyridine ligand can be removed by dilute acid extraction from ethyl acetate solutions of chloro(pyridine)cobaloxime(III). Due to their low solubility in common organic solvents, chloro(pyridine)cobaloxime(III) and -cobaloxime(II) (often the cobalt remainder in cobaloxime mediated transformations) are easily removed by adsorptive filtration of the reaction mixture on a short silica gel column. Acidic aqueous ethanol solutions of chloro(pyridine)cobaloxime(III) are photodecomposed when irradiated at wavelengths below 500 nm, yielding cobalt(II) salts, dimethylglyoxime, and pyridinium salts. For some applications the use of either iodo- or bromocobaloxime(III)7 is advantageous, as activation of the halogen–carbon bond is essential for chlorocobaloxime(III) to be employed in organic synthesis. However, reduction potentials, bond strengths, and photostabilities increase on moving from the iodo to the chloro ligand,8 so iodo(pyridine)cobaloxime(III) must be stored in tinted bottles.9 Inhalation of chlorocobaloxime(III) dust and contact with eyes should be avoided; wearing of protecting gloves for handling this compound is recommended. This compound should be handled in a fume hood.