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Kinetics and Mechanism of the Activation of Molecular Hydrogen by Bis(dimethylglyoximato)cobalt(II) Derivatives

DOI: 10.1039/DT9800000276

Source and publish data:

Journal of the Chemical Society, Dalton Transactions p. 276 - 283 (1980)

Update date:2022-08-04

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Authors:

Simandi, Laszlo I.Simandi, Laszlo I.

Budo-Zahonyi, EvaBudo-Zahonyi, Eva

Szeverenyi, ZoltanSzeverenyi, Zoltan

Nemeth, SandorNemeth, Sandor

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Article abstract of DOI:10.1039/DT9800000276

The reaction of H2 with bis(dimethylglyoximato)cobalt(II), , and its 1:1 pyridine (py) adduct yields 3-aminobutan-2-one oxime via hydrogenation of the co-ordinated Hdmg(1-).Excess of Hdmg(1-) is hydrogenated catalytically.The initial rate of H2 uptake is first order with respect to H2 pressure and second order with respect to overall cobalt concentration.Axial co-ordination of py, NEt2H, and PPh3 enhances the rate, the five-co-ordinate adducts being more reactive than the parent cobaloxime(II).The spectrophotometric stability constants for the 1:1 and 1:2 py adducts are 186 and 0.75 dm3mol-1, respectively, at 20 deg C.The rate-determining step of H2 uptake is a bimolecular reaction of two hydridocobaloxime(III) species.In the absence of py, the overall rate coefficient is 3.1 and 9.4 dm6mol-2s-1 in MeOH and 50percent v/v methanol-water, respectively, at 20 deg C.For the reactions involving the 1:1 adduct with py, the corresponding values are 34.7 and 323 dm6mol-2s-1, respectively.Hydrogenation of the intermediate, containing one CH-NHOH moiety, is interpreted in terms of N-O bond cleavage by cobaloxime(II) followed by reduction of the resulting cobaloxime(III) by hydridocobaloxime(III).

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