Biphenyl-Bridged Dicobaloximes: Synthesis, NMR, CV, and X-Ray Study
摘要:
4,4'-Disubstituted biphenyl-bridged dicobaloximes, Py(L)(2)Co-CH2-Ar-CH2-Co(L)(2)Py [L = dmgH, dpgH], have been synthesized and characterized. The cobalt-bound CH2 is diastereotopic and the dmgH (Me) shows nonequivalence in the H-1 NMR. This may occur due to atropisomerism and/or restricted rotation of the C-Ph/Co-C bond. Two X-ray structures of the biphenyl-bridged dicobaloximes, reported for the first time, show no direct or indirect interaction between the two cobaloxime units [Co(dioxime)(2)Py]. The NMR spectra and X-ray structural details complement each other. Three redox processes, Collf/coll, Co-II/Co-I, and Co-IV/Co-III, are observed in the CV study. Two cobalt centers are oxidized at different potentials as two discrete units even though these are symmetrically located with respect to each other with no interaction between them.
Synthesis, Characterization, and Variable-Temperature <sup>1</sup>H NMR Behavior of Organo-Bridged Dicobaloximes
作者:B. D. Gupta、V. Vijaikanth、Veena Singh
DOI:10.1021/om034273p
日期:2004.4.1
Organo-bridged dicobaloximes with four different dioximes Py(L)(2)CoCH2-R-CH2Co(L)(2)Py (L = dmgH, dpgH, chgH, and gH) have been synthesized and characterized by H-1 and C-13 NMR and FAB mass spectroscopy. The cis influencing order observed in dicobaloximes is similar to the previously observed order in monocobaloximes. The cyclic voltammetric results show that an irreversible single-step two-electron reduction of Co-III to Co-I takes place. The Co-C bond in 4a cleaves during crystallization and results in the formation of o-vinylbenzyl cobaloxime. The variable-temperature H-1 NMR study suggests that the Co-C bond rotation is restricted and its magnitude depends on both the nature of the bridging ligand and the dioxime.