Inversion at carbon in the cleavage of cobalt-carbon bonds by mercuric ion

Fritz, Helmut; Espenson, James H.; Williams, Dennis A.; Molander, Gary A.

doi:10.1021/ja00815a012

Cited by 44 publications

(11 citation statements)

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“…Heterolytic dissociation follows the catalytic process of R-Co III as MeCbl and leads to a “supernucleophilic” Co I with a lone electron pair (Scheme , Track A) . Another type of heterolysis appears in the case of electrophilic attack, such as with a mercury salt (represented as MX 2 ) that can trap the alkyl group (R – ) and produce an X-Co III complex (Scheme , Track B). , Reactions involving heterolysis of R-Co III have been summarized by Marzilli and co-workers . The last pathway, for example with AdoCbl, involves homolytic cleavage of the C–Co bond, producing a stable paramagnetic Co II complex and a reactive carbon-centered radical, such as 5′-deoxyadenosyl radical (R • in Scheme , Track C).…”

Section: Vitamin B12-type Organocobalt(iii)mentioning

confidence: 99%

Organocobalt Complexes as Sources of Carbon-Centered Radicals for Organic and Polymer Chemistries

2019

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Organocobalt(III) complexes (R-Co III ), defined as cobalt complexes featuring a carbon−cobalt bond, are largely used to produce carbon-centered radicals by homolytic cleavage of their C−Co bond under mild conditions. They are key compounds in cutting-edge developments in the fields of organic chemistry, biochemistry, medical research, radical reactions, and organometallic chemistry. This is the first Review of the use of R-Co III in both organic and polymer chemistries. Although pioneering works in organic synthesis have largely contributed to the implementation of R-Co III in polymer design, the two fields have evolved independently, with many breakthroughs on both sides. The main motivation of this Review is to confront both fields to stimulate cross-fertilization. It notably describes the most important synthetic pathways for R-Co III , the influence of the ligand structure and the environment of the complex on the C−Co bond strength, the modes of formation of the radicals, and the most relevant R-Co III -promoted radical reactions, with a focus on the main reaction mechanisms. CONTENTS 6.4. Polymerizations 6938 7. Conclusions 6945 Author Information 6946 Corresponding Author 6946 ORCID 6946 Notes 6946 Biographies 6946 Acknowledgments 6946 References 6946

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Section: Vitamin B12-type Organocobalt(iii)mentioning

confidence: 99%

Organocobalt Complexes as Sources of Carbon-Centered Radicals for Organic and Polymer Chemistries

2019

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“…1 /, [CH3Cd(z-C3H70)]4 + CH4 (7) stable tetramer is then slowly decomposed by z'-C3H7OH to liberate the remaining methyl group as methane (eq 8). This…”

Section: Resultsmentioning

confidence: 99%

Formation of transient dimethylzinc, dimethylcadmium, and dimethyllead species via methylation of zinc(2+), cadmium(2+), and lead(2+) by a trans-dimethylcobalt complex

Witman¹,

Weber²

1977

Inorg. Chem.

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The methylation reactions in ¡'-C3H7OH of Zn2+, Cd2+, and Pb2+ by an excess of the PYm-dimethylcobalt complex, (CH3)2Co(BDMl,3pn), are discussed. (BDMl,3pn is a mononegative, tetradentate dioxime diimine ligand formed by the condensation of 2 mol of 2,3-butanedione and 1 mol of 1,3-propanediamine.) With a 2:1 complexmetal ratio a very rapid reaction forms CH3Co(BDM 1,3pn)+ and CH3M+ (M2+ = Zn2+, Cd2+, and Pb2+). Then in a slower reaction CH3M+ reacts with a second mole of (CH3)2Co(BDM 1,3pn) to form unstable (CH3)2M species. These compounds rapidly react yielding CH4 and a variety of nonvolatile products such as [CH3Cd(i-C3H70)]4. The progress of the reactions was followed by the absorbance decrease of (CH3)2Co(BDMl,3pn) and a GC analysis of CH4.

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“…The mechanism of oxidative addition of alkyl halides to reduced cobalt species has long been debated, with claims of S N 2 nucleophilic displacements by cobalt(I) "supernucleophiles" (including observations of inversion) by Schrauzer 37 and others [38][39][40][41][42][43] and claims of other mechanisms (including observations of retention). [44][45][46][47][48][49] A recent, clever electrochemical study by Zhou et al 50 showed that cobalt(I) reagents, including cob-(I)alamin and cobalt(I) heptamethylcobyrinate, can react with alkyl halides by two-electron as well as one-electron mechanisms depending on the steric demands of the organic group and the nature of the leaving group.…”

Section: T H I S C O N T E N T Imentioning

confidence: 99%

Diastereomeric Control in the Formation of Carbon−Cobalt Bonds in Organocobalt Corrinoids: Reactions of Cobalt(II) Corrinoids with Organic Hydroperoxides¹

et al. 1997

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1,1-Dimethylpropyl hydroperoxide reacts with cobalt(II) cobinamide via a Fenton-like reaction to produce a mixture of the diastereomeric alpha- and beta-ethylcobinamides (CH(3)CH(2)Cbi(+)'s, in which the organic ligand is in the "lower" or "upper" axial ligand position, respectively), the composition of which depends on the ratio of starting materials. When the hydroperoxide reagent is in excess, <2% of the CH(3)CH(2)Cbi(+) product is the alpha diastereomer, a product distribution which agrees with previous observations of the equilibrium mixture. This distribution apparently arises because the previously demonstrated CH(3)CH(2)(*)-promoted isomerization of CH(3)CH(2)Cbi(+) diastereomers leads to equilibration. However, when cob(II)inamide is in excess over hydroperoxide, the CH(3)CH(2)Cbi(+) product contains 87% alpha diastereomer and 13% beta diastereomer. Evidently, under these conditions, trapping of the CH(3)CH(2)(*) radical is sufficiently rapid to prevent the radical-induced isomerization of diastereomers and a kinetically controlled product distribution results. This condition has been used to study the relative energetics of kinetically controlled alpha and beta alkylation of cob(II)inamide by CH(3)CH(2)(*). For cob(II)inamide itself, the alpha diastereomer is enthalpically stabilized relative to the beta diastereomer in the transition state for carbon-cobalt bond formation, but an even larger entropic stabilization of the beta diastereomer causes the latter to be the predominant product. The entropic preference for the beta diastereomer is shown to be the result of the differential side chain configurations at the alpha and beta faces of the cobalt corrinoids by experiments with side-chain-altered analogs. When the downwardly projecting f side chain is enlarged by esterification of the N-methylated nucleotide 1-alpha-D-ribofuranosyl-3,5,6-trimethylbenzimidazole 3'-phosphate, the proportion of the alpha diastereomer in the alkylated product drops to 74% and the effect is due solely to an increased entropic preference for the beta diastereomer. Similarly, when the normally downwardly projecting e propionamide side chain is epimerized to the upward (beta) face of the corrin, the proportion of the alpha diastereomer in the product is increased to 95% and the effect is entirely entropic again. Taken together with previous work, the results lead to a general picture of the energetics of alkyl radical + cobalt(II) corrinoid combination reactions and their microscopic reverse, the homolytic dissociation of carbon-cobalt bonds, a rare instance in which the subtleties of such diastereomeric control can be understood at a very fundamental level.

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Inversion at carbon in the cleavage of cobalt-carbon bonds by mercuric ion

Cited by 44 publications

References 1 publication

Organocobalt Complexes as Sources of Carbon-Centered Radicals for Organic and Polymer Chemistries

Organocobalt Complexes as Sources of Carbon-Centered Radicals for Organic and Polymer Chemistries

Formation of transient dimethylzinc, dimethylcadmium, and dimethyllead species via methylation of zinc(2+), cadmium(2+), and lead(2+) by a trans-dimethylcobalt complex

Diastereomeric Control in the Formation of Carbon−Cobalt Bonds in Organocobalt Corrinoids: Reactions of Cobalt(II) Corrinoids with Organic Hydroperoxides¹

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Inversion at carbon in the cleavage of cobalt-carbon bonds by mercuric ion

Cited by 44 publications

References 1 publication

Organocobalt Complexes as Sources of Carbon-Centered Radicals for Organic and Polymer Chemistries

Organocobalt Complexes as Sources of Carbon-Centered Radicals for Organic and Polymer Chemistries

Formation of transient dimethylzinc, dimethylcadmium, and dimethyllead species via methylation of zinc(2+), cadmium(2+), and lead(2+) by a trans-dimethylcobalt complex

Diastereomeric Control in the Formation of Carbon−Cobalt Bonds in Organocobalt Corrinoids: Reactions of Cobalt(II) Corrinoids with Organic Hydroperoxides1

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Diastereomeric Control in the Formation of Carbon−Cobalt Bonds in Organocobalt Corrinoids: Reactions of Cobalt(II) Corrinoids with Organic Hydroperoxides¹