Oxidation-reduction reactions of complexes with macrocyclic ligands. Energetics and dynamics of methyl exchange

Endicott, John F.; Balakrishnan, K. P.; Wong, Chung-Lai

doi:10.1021/ja00537a017

Cited by 29 publications

(21 citation statements)

References 0 publications

Supporting

Mentioning

Contrasting

Order By: Relevance

“…I '). In analogy to studies by Endicott et al [9] on 'methylbridged electron-transfer reactions' and by Johnson et al [lo], a CH, transfer not involving free CH, radicals probably also operates here'). Such a mechanism could presumably also account for the equilibration of Coa-and Cop-methylated nucleotide-free cobyrinicacid derivatives in CO-containing aqueous solution, as observed by Friedrich et al [12].…”

Section: + 3 5 4 +supporting

confidence: 58%

Thermal Methyl‐Group Transfer between Methylcobalt(III) Corrinates and Cobalt(II) Corrinates. Equilibration Experiments with Heptamethyl Cobyrinates and Cobalamins

Kräutler

Hughes

Caderas

1986

Helvetica Chimica Acta

View full text Add to dashboard Cite

Separate neutral aqueous solutions of either a) methylcob(II1)alamin (2) and (heptamethyl cob(I1)yrinate) perchlorate (3) or of b) cob(I1)alamin ( = vitamin B12r; 4) and [Cob-methyl(heptamethy1 cob(l1I)yrinate)) perchlorate (5) equilibrated thermally at r.1. according to 2 + 3 * 4 + 5. The corresponding equilibrium constant & was determined (Ke = 0.63 f 0.15). This equilibration experiment indicates that the coordination of the nucleotide function in methylcob(1I)alamin (2) hardly affects the thermodynamics of the Co-C bond homolysis in aqueous solution when compared to nucleotide-free methylcorrinoids such as 5.

show abstract

Section: + 3 5 4 +supporting

confidence: 58%

Thermal Methyl‐Group Transfer between Methylcobalt(III) Corrinates and Cobalt(II) Corrinates. Equilibration Experiments with Heptamethyl Cobyrinates and Cobalamins

Kräutler

Hughes

Caderas

1986

Helvetica Chimica Acta

View full text Add to dashboard Cite

show abstract

“…Equilibrium constants for exchange of methyl groups between cobalt complexes containing different equatorial ligands are generally small but are not statistical (i.e., K ) 1). [44][45][46] …”

Section: Discussionmentioning

confidence: 99%

Cis-Influence of Hydroporphyrin Macrocycles on Axial Ligation Equilibria and Alkyl Exchange Reactions of Alkylcobalt(III) Porphyrin Complexes

Stolzenberg¹,

Summers²

2000

Inorg. Chem.

View full text Add to dashboard Cite

Stability constants are reported for the coordination of pyridine and substituted pyridines to the alkylcobalt(III) complexes of octaethylporphyrin (OEP), t-octaethylchlorin (OEC), and ttt-octaethylisobacteriochlorin (OEiBC) in toluene solution. The stability constants correlate with the base strength of the nitrogenous ligand. A cis-influence of the macrocycle saturation level on the stability constants is observed. Stability constants for coordination of a given pyridine ligand to an alkylcobalt(III) complex are roughly 10 times smaller than the stability constants for the corresponding cobalt(II) complex. Analysis of a thermodynamic cycle demonstrates that this leads to decreased stability of the complex with respect to Co-C bond homolysis upon ligand coordination, a "base-on" effect. Alkyl exchange occurs between cobalt complexes of different tetrapyrroles. Equilibrium data establish that the exchange is nonstatistical and that the Co-C bond is stabilized by increasing the saturation of the tetrapyrrole macrocycle.

show abstract

“…Although most investigated L/Mt x+1 -R bond homolyses are indeed consistent with an S H 1 mechanism, an S H 2 process (Scheme 7) has been documented for the methyl radical transfer in various L/Co III -CH 3 -L /Co II systems (L = or = L) with ∆H ‡ as low as 7.5 kcal•mol −1 and very negative ∆S ‡ (ca. −20 cal•mol −1 •K −1 ) [59]. The alkyl and benzyl radical transfer from [(dmgH) 2 Co III -R] to another organic radical R • , to yield RR and [(dmgH) 2 Co II ], also adopts an S H 2 mechanism [60], as are other metalcarbon bond homolyses [61].…”

Section: Bond Cleavage Barriermentioning

confidence: 99%

A journey into metal–carbon bond homolysis

Poli¹

2021

Comptes Rendus. Chimie

View full text Add to dashboard Cite

This article surveys the current knowledge in metal alkyl complexes with homolytically weak metal-carbon bonds, therefore prone to thermally produce alkyl radicals. It outlines the role of a metal complex as a moderator to control the radical reactivity ("persistent radical effect"). It describes the methods that have been used so far (as well as others that are potentially available) to investigate the metal-carbon bond cleavage thermodynamic and kinetic parameters, including their caveats and limitations. A number of systems scrutinized in the author's own laboratory and in those of collaborators are presented and discussed. These investigations have combined metal complexes and alkyl radicals, with guidance and understanding provided by DFT calculations, to achieve higher performance in the controlled radical polymerization of challenging monomers (vinyl acetate, vinylidene fluoride) and in olefin radical cross-coupling, and have brought to light mechanistic questions of more general relevance.

show abstract

Oxidation-reduction reactions of complexes with macrocyclic ligands. Energetics and dynamics of methyl exchange

Cited by 29 publications

References 0 publications

Thermal Methyl‐Group Transfer between Methylcobalt(III) Corrinates and Cobalt(II) Corrinates. Equilibration Experiments with Heptamethyl Cobyrinates and Cobalamins

Thermal Methyl‐Group Transfer between Methylcobalt(III) Corrinates and Cobalt(II) Corrinates. Equilibration Experiments with Heptamethyl Cobyrinates and Cobalamins

Cis-Influence of Hydroporphyrin Macrocycles on Axial Ligation Equilibria and Alkyl Exchange Reactions of Alkylcobalt(III) Porphyrin Complexes

A journey into metal–carbon bond homolysis

Contact Info

Product

Resources

About