Dehalogenation of chloroalkanes by nickel(i) porphyrin derivatives, a computational study

Abstract

The nickel(i) octaethylisobacteriochlorin anion ([OEiBCh-Ni]) is commonly used as a synthetic model of cofactor F from Methyl-Coenzyme M Reductase. In this regard, experimental studies show that [OEiBCh-Ni] can catalyze dehalogenation of aliphatic halides in DMF solution by a highly efficient S2 reaction. To better understand this process, we constructed theoretical models of the dehalogenation of chloromethane by a simple nickel(i) isobacteriochlorin anion and compared its reactivity with that of similar Ni complexes with other porphyrin-derived ligands: porphyrin, chlorin, bactreriochlorin, hexahydroporphyrin and octahydroporphyrin. Our calculations predict that all of the porphyrin derivative's model reactions proceed through low-spin complexes. Relative to the energy of the separate reactants the theoretical activation energies (free-energy barriers with solvation corrections) for the dehalogenation of chloromethane are similar for all of the porphyrin derivatives and range for the different functionals from 10-15 kcal mol for B3LYP to 5-10 kcal mol for M06-L and to 13-18 kcal mol for ωB97X-D. The relative free energies of the products of the dehalogenation step, L-Ni-Me adducts, have a range from -5 to -40 kcal mol for all functionals; generally becoming more negative with increasing saturation of the porphyrin ligand. Moreover, no significant differences in the theoretical chlorine kinetic isotope effect were discernable with change of porphyrin ligand.

A Nickel(II)‐Containing Vitamin B12 Derivative with a Cofactor‐F430‐type π‐System

“…In contrast to the total synthesis of these macrocycles, an alternative semisynthetic approach to nickel‐containing corrinoid derivatives starting from B 12 is still lacking. New efforts in this pioneering area are of fundamental interest for a better understanding of the similarities and differences in the properties and reactivities of Ni‐ and Co‐containing cofactors . Applications in medicinal chemistry and environmental sensing can also be envisaged …”

“…[2,5,7] Structural evidence for F430 was first obtained by comparing its characteristic absorption with l max % 430 nm to those of synthetic Ni II -containing hydrocorrin and hydrocorphin deriv-atives. [11][12][13][14] Applications in medicinal chemistry and environmental sensing can also be envisaged. [11][12][13][14] Applications in medicinal chemistry and environmental sensing can also be envisaged.…”

“…[8] In contrast to the total synthesis of these macrocycles, [8][9][10] an alternative semisynthetic approach to nickelcontaining corrinoid derivatives starting from B 12 is still lacking.New efforts in this pioneering area are of fundamental interest for ab etter understanding of the similarities and differences in the properties and reactivities of Ni-and Cocontaining cofactors. [11][12][13][14] Applications in medicinal chemistry and environmental sensing can also be envisaged. [15][16][17][18] In this study,w es et out to synthesize and investigate modified B 12 derivatives with ac entral Ni II ion and ac orrin chromophore with 12 instead of 14 p electrons ( Figure 1, middle), reminiscent of the core structure of cofactor F430 (Figure 1, right).…”

Ein NiII‐haltiges Vitamin‐B12‐Derivat mit einem Kofaktor‐F430‐artigen π‐System

“…[8] Eine im Gegensatz zu der Totalsynthese dieser Makrozyklen stehende,a lternative Partialsynthese von nickelhaltigen Corrinderivaten, direkt ausgehend von B 12 , wurde bislang noch nicht vorgestellt. [11][12][13][14] Anwendungen im Gebiet der medizinischen Chemie sowie als Chemosensoren in Te chnik und Umwelt sind ebenfalls voraussehbar. [11][12][13][14] Anwendungen im Gebiet der medizinischen Chemie sowie als Chemosensoren in Te chnik und Umwelt sind ebenfalls voraussehbar.…”

“…[8][9][10] Neue Bemühungen in diesem Pioniergebiet sind von grundlegendem Interesse für ein besseres Verständnis von Gemeinsamkeiten und Unterschieden in den Eigenschaften Ni-und Co-haltiger Kofaktoren. [11][12][13][14] Anwendungen im Gebiet der medizinischen Chemie sowie als Chemosensoren in Te chnik und Umwelt sind ebenfalls voraussehbar. [15][16][17][18] Ziel dieser Untersuchung war es,m odifizierte B 12 -Derivate mit einem zentralen Nickelion und einem Corrinchromophor mit 12 anstelle von 14 p-Elektronen (Abbildung 1, mittig), ähnlich der Kernstruktur von F430 (Abbildung 1, rechts), zu synthetisieren und näher zu untersuchen.…”