Reactions Of Cobaloximes Research Articles

The reaction of cobaloximes with hydrogen: products and thermodynamics.

A cobalt hydride has been proposed as an intermediate in many reactions of the Co(dmgBF2)2L2 system, but its observation has proven difficult. We have observed the UV-vis spectra of Co(dmgBF2)2L2 (1) in CH3CN under hydrogen pressures of up to 70 atm. A Co(I) compound (6a) with an exchangeable proton is eventually formed. We have determined the bond dissociation free energy and pK(a) of the new O-H bond in 6a to be 50.5 kcal/mol and 13.4, respectively, in CH3CN, matching previous reports.

Reactions of Cobaloximes with Alkenyl Triflates and Halides as a New Method for the Preparation of Cobalt−sp2Carbon Bonds

Cobaloxime complex [(pyridine)2(dimethylglyoxime)2Co(II)] (generated in situ) reacts with a number of alkenyl triflates and halides in the presence of zinc, providing a new, simple route to alkenyl...

Reactions of cobaloximes with vinyl allenes as a route to 1-cobaloxime substituted 1,3-dienyl complexes

The preparation of two vinyl allenes are described along with their hydrometallation reactions to produce 1-cobaloxime substituted 1,3-dienyl complexes. Thermal and Lewis acid catalyzed Diels–Alder reactions of these dienyl complexes are then discussed.

オルガノコバロキシムの反応と合成への応用

Alkyl- and alkenylcobaloximes are conveniently prepared by the reaction of cobaloxime (I) with alkyl halides, vinyl halides, and acetylenes. The organocobaloximes thus obtained are convenient and versatile radical source for organic syntheses. The cobaloxime group is conveniently transformed into other functions by a variety of radicophiles. The organo radical from organocobaloxime attacks intramolecular or intermolecular olefin in the same manner as a general organo radical. Contrary to the conventional tin hydride method, an organocobaloxime gives not a reduction product but an olefinic product. The olefinic function thus formed is useful for further chemical transformation. The coexisting cobaloxime (II) radical modifies reactivity of the olefinic and arenic part of the organo radical containing sulfur function. The cobaloxime moiety activates an intramolecular diene and arene system to cause cycloaddition and aromatic substitution respectively.

Alkyl transfer from quaternary ammonium salts to cobalt (I): Model for the cobalamin-dependent methionine synthase reaction

The reaction of cobaloxime(I) with diverse quaternary ammonium salts leads, in general, to a group transfer from nitrogen to cobalt. The behaviour of the salts in these transalkylations is consistent with an S N2 mechanism, involving Co(I) as a nucleophile. In a model study of the cobalamin-dependent methionine synthase reaction, 5- 13CH 3-methyl labelled 5,5,6,7-tetramethyl-5,6.7,8-tetrahydropteridinium salt( 23) -a model of the natural coenzyme 5-CH 3H 4-folate ( 1)- was allowed to react with cobaloxime(I) and cobalamin(I). In each case the formation of the methyl transfer product, namely, methylcobaloxime and mothylcobalamin, respectively, was shown by 13C-NMR spectroscopy.

Reaction of cobaloxime(II) with hydroxide ions

Reaction of cobaloxime(II) with hydroxide ions

Homolytic displacements at carbon centres. Part 1. Reaction of allyl- and allenyl-cobaloximes with polyhalogenomethanes

Allyl- and allenyl-cobaloximes react with bromotrichloromethane to give 4,4,4-trichlorobutene and 4,4,4-trichlorobutynes, respectively, and bromocobaloxime(III). The reactions of the allylcobaloximes, carried out at room temperature, are nearly quantitative, but those of the allenylcobaloximes, performed at higher temperatures, are dependent upon the nature of the allenyl group and of the other axial ligand; the yield of trichlorobutyne is appreciably higher with imidazole than with pyridine as the axial ligand, and decreases with increasing substitution on the allenyl ligand. The reactions are believed to involve novel chain processes in which the chain-carrying trichloromethyl radical, formed by the reaction of cobaloxime(II) with the bromotrichloromethane, attacks regiospecifically at the γ-carbon of the allyl or allenyl ligand to displace the other chain propagating species, cobaloxime(II), and give the observed organic product. Since cobaloxime(II) neither dimerises nor disproportionates under these conditions, two important chain terminating steps are eliminated. The main side reaction with allenylcobaloximes involves the formation of the corresponding acetylenic hydrocarbon, the additional hydrogen atom being derived from the dimethylglyoximato hydroxy group, probably as a consequence of attack of the trichloromethyl radical on the metal. The application of the reaction to other polyhalogenomethanes and related radical precursors is also demonstrated.

Electron-transfer reactions of cobaloximes. Part II. The transition from outer- to inner-sphere mechanisms with vanadium(II): a non-linear free-energy relation

The reduction of a series of cationic cobaloximes of the form [Co(Hdmg)2L2]+ by V2+(aq) has been investigated [Hdmg = dimethylglyoximato(1–); L = EtNH2, PhNH2, py, or 3,5-Me2py]. Rate constants and activation parameters at 25 °C are reported. A plot of ΔG‡ for these reactions against E½ for the polarographic reduction is used to illustrate the progression from inner- to outer-sphere mechanism as the base strength of the axial ligands if lowered.

Electron-transfer reactions of cobaloximes: kinetics and mechanisms of the vanadium(II) reduction of diammine-, amminebromo-, and amminechloro-bis(dimethylglyoximato)cobalt(III)

The kinetics of the title reactions have been studied and their activation parameters and rate laws at 25 °C determined. It is concluded from these that the monohalogeno-complexes react by an outer-sphere mechanism while the reaction of the diammine complex is a substitution-controlled inner-sphere process. It is suggested that the reaction of Cr2+(aq) with the latter complex proceeds also by an inner-sphere mechanism.