Reductive defluorination of (trifluoromethyl)cobamides

Brown, Kenneth L.; Zou, Xiang; Richardson, Michael W; Henry, William P.

doi:10.1021/ic00025a029

Cited by 13 publications

(8 citation statements)

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“…Nonetheless, the P value of titanium(III) citrate seems too high to accomplish such reduction. For example, the F for methylcobalamin (CH3-Cbl) is -1.57 V vs SCE (or -1.33 V vs SHE) in neutral solution (59) and that for the fluorinated analogue, CF3-Cbl, is approximately -1.26 V vs SCE (59,60) or -1.04 V vs SHE. Since chlorine is less electronegative than fluorine, the F of CCh-Cbl would be expected to be more negative than that of CF3-Cbl and therefore unlikely to be reduced by titanium(III) citrate (note: higher P is possible if the organic substituent can provide a resonance structure, as in the case of (methoxycarbonyl) methylcobalamin; however, such an effect is lacking in trihalomethylcobalamins).…”

Section: Discussionmentioning

confidence: 99%

Metallocoenzyme-Mediated Reductive Transformation of Carbon Tetrachloride in Titanium(III) Citrate Aqueous Solution

Chiu¹,

Reinhard²

1995

Environ. Sci. Technol.

117

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Section: Discussionmentioning

confidence: 99%

Metallocoenzyme-Mediated Reductive Transformation of Carbon Tetrachloride in Titanium(III) Citrate Aqueous Solution

Chiu¹,

Reinhard²

1995

Environ. Sci. Technol.

117

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“…29 The mechanism was suggested to involve reductive defluorination, followed by a second reduction to a carbene and fmlly protonation. Numerous studies have described stable metal-rbon u-bond formation in Fe and Co complexes with porphyrins and other ligands.…”

Section: R D H D a L L Y L R A D L F H A A P R Y L -* I R O N P~mentioning

confidence: 99%

“…CF3-Coin(cobamides) also have been reported to undergo reductive defluorination in aqueous solution, but the product in this case was identified as CF2H-Coin(cobamide). 29 The mechanism was suggested to involve reductive defluorination, followed by a second reduction to a carbene and finally protonation. Possibly, the difference between this mechanism and that found with CF3-FemP is due to the pH difference; the latter has been studied in alkaline solution, where hydrolysis of the difluorocarbene group into CO is more feasible than protonation.…”

Section: H+mentioning

confidence: 99%

Reactions of alkyl and fluoroalkyl radicals with nickel, iron, and manganese porphyrins

Guldi¹,

Kumar²,

Neta³

et al. 1992

J. Phys. Chem.

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The reactions of alkyl (CH,, C~HS, n-CJI9, CHZCOZ-, CH(C02-)2, CHzCN) and fluoroalkyl (CF,, CF2CI) radicals with nickel, iron, and manganese porphyrins (P) have been studied by radiolytic techniques in various solvents. All the radicals (R) react with Fe"P to form R-Fe"' P with a stable F t C bond. These products are oxidized by O2 to FelIIP. Althou h yield stable products. Reactions of alkyl radicals with NiIP result in unstable R-NinP products (tl 2 several seconds) that eventually yield NiIIP. Reactions of alkyl radicals with Ni"P are reversible, and the short-lived R-kiII'P products (tIl2milliseconds) disappear through radical reactions, with recovery of NinP. Alkyl radicals react rapidly with M@P, probably via addition to the metal, but the adduct gives MnlIIP immediately. 'CF3 radicals also react with MnlIIP by addition to C==C bonds.Ni'P and NilIP also react rapidly with the radicals to form Ni-C bonds, only the reactions of fluoroalkyl radicals with Ni f P

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“…Thus, questions of whether the presumptions about the steric consequences of α and β face structure are correct have become paramount. It is known that the RCbi + products are in a steady state under synthetic conditions due to reductive dealkylation; 8b,d, however, the ratio of diastereomers is not affected by differential rates of decomposition, as the rates of reductive destruction of pairs of α and β diastereomers by various reductants are the same …”

Section: Introductionmentioning

confidence: 99%

Organic Free Radical-Promoted Isomerization of α- and β-Alkylcobinamides¹

1996

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Anaerobic reaction of alpha- or beta-alkylcobinamides (alpha- or beta-RCbi(+)'s) with the corresponding alkyl free radical, R(*) (where R = CH(3), CH(3)CH(2), or CH(3)CH(2)OCH(2)CH(2)), generated by the Fenton reaction using Fe(2+) and an alkyl hydroperoxide, RC(CH(3))(2)OOH, causes isomerization and leads to mixtures of alpha- and beta-RCbi(+)'s. The reaction does not occur, however, under aerobic conditions or under anaerobic conditions in the presence of an excess of the free radical scavenger H-Tempo. In addition, alpha-CH(3)CH(2)Cbi(+) reacts with 50 molar equiv of tert-butyl hydroperoxide and Fe(2+) to give a mixture of alkylcobinamides that contains 6% alpha-CH(3)Cbi(+) and 94% beta-CH(3)Cbi(+), showing that multiple transalkylations occur. A Co(II)-induced isomerization and the S(H)2 mechanism are ruled out on the basis of the known reactivity of RCbi(+) and product analysis. A mechanism is proposed which involves a direct oxidative free radical displacement by an R(*) to the metal of RCbi(+) via a dialkylcobalt(IV) corrinoid species. Since the reaction leads to equilibration of the two diastereomers under mild conditions, it can be used to study the equilibria between diastereomeric RCbi(+)'s. Thus, the equilibrium for the diastereomeric ethyl-13-epicobinamides, in which the e propionamide side chain of the corrin ring has been epimerized from the alpha to the beta face of the corrinoid, lies significantly more toward the alpha diastereomer than that for the normal ethylcobinamides. This represents the most direct experimental evidence obtained to date that the corrin ring side chains control the relative steric accessibility of the two faces of the cobalt corrinoids.

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Reductive defluorination of (trifluoromethyl)cobamides

Cited by 13 publications

References 0 publications

Metallocoenzyme-Mediated Reductive Transformation of Carbon Tetrachloride in Titanium(III) Citrate Aqueous Solution

Metallocoenzyme-Mediated Reductive Transformation of Carbon Tetrachloride in Titanium(III) Citrate Aqueous Solution

Reactions of alkyl and fluoroalkyl radicals with nickel, iron, and manganese porphyrins

Organic Free Radical-Promoted Isomerization of α- and β-Alkylcobinamides¹

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Reductive defluorination of (trifluoromethyl)cobamides

Cited by 13 publications

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Metallocoenzyme-Mediated Reductive Transformation of Carbon Tetrachloride in Titanium(III) Citrate Aqueous Solution

Metallocoenzyme-Mediated Reductive Transformation of Carbon Tetrachloride in Titanium(III) Citrate Aqueous Solution

Reactions of alkyl and fluoroalkyl radicals with nickel, iron, and manganese porphyrins

Organic Free Radical-Promoted Isomerization of α- and β-Alkylcobinamides1

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Organic Free Radical-Promoted Isomerization of α- and β-Alkylcobinamides¹