Vitamin B12 Model Complexes Research Articles

Electrocatalytic reactivity of imine/oxime-type cobalt complex for direct perfluoroalkylation of indole and aniline derivatives.

Imine/Oxime-type cobalt complexes, regarded as simple vitamin B12 model complexes, were utilized as catalysts for direct C-H perfluoroalkylations of indole and aniline derivatives with nonafluorobutyl iodide (n-C4F9I) as the readily available perfluoroalkyl source. The synthetic approach described herein was performed under mild reaction conditions driven by controlled-potential electrolysis at -0.8 V vs. Ag/AgCl in organic solvents. The mechanistic investigations suggest that a nonafluorobutyl radical is mediated by homolytic cleavage of the cobalt(iii)-carbon bond in the catalytic cycle. This is the first report concerning a fluoroalkylation reaction of (hetero)aromatics catalyzed by the simple vitamin B12 model complex. The convenient electrocatalytic method employing a simple cobalt complex provides a facile synthesis method toward novel fluoroalkylated compounds, demonstrating potential applications in the fields of pharmaceutical chemistry and materials science.

Paired Electrolysis for Amide Formation Catalyzed By Vitamin B12 Model Complex Under Aerobic Condition

Electroorganic synthesis is currently expanding into various interdisciplinary fields because of its versatile application to molecular transformations as well as sustainable and economical advantage. Electroorganic synthesis is especially recognized as green process in synthetic organic chemistry since redox process of substrate is progressed by electric current without chemical reagent and waste after the reaction. Among the various methods in electroorganic synthesis, paired electrolysis is excellent method that electrochemical power is used both on the working electrode and the counter electrode to form synthetic useful compounds.1-4 Here we report the paired electrolysis mediated by vitamin B12 derivative,5 cobalt complex, under aerobic condition to form various amide compounds from trichloromethylated organic compounds and tertiary amines. Reference A. Paddon, M. Atobe, T. Fuchigami, P. He, P. Watts, S. J. Haswell, G. J. Pritchard, S. D. Bull, F. Marken, J. Applied Electrochem., 2006, 36, 617.J. Llorente, B. H. Nguyen, C. P. Kubiak, K. D. Moeller, J. Am. Chem. Soc., 2016, 138, 15110.Senboku, K. Nagakura, T. Fukuhara, S. Hara, Tetrahedron, 2015, 71, 3850.Kim, R. Uchiyama, Y. Kitano, M. Tada, K. Chiba, J. Electroanal. Chem., 2001, 507, 152.H. Shimakoshi, Y. Hisaeda, Current Opinion in Electrochemistry, 2018, in press. Figure 1

Reprint of: Impact of the corrin framework of vitamin B12 on the electrochemical carbon-skeleton rearrangement in comparison to an imine/oxime planar ligand; tuning selectivity in 1,2-migration of a functional group by controlling electrolysis potential

Among the coenzyme B12-dependent enzymes, methylmalonyl-CoA mutase (MMCM) catalyzes the carbon-skeleton rearrangement reaction between R-methylmalonyl-CoA and succinyl-CoA. Diethyl 2-bromomethyl-2-phenylmalonate, an alkyl bromide substrate having two different migrating groups (phenyl and carboxylic ester groups) on the β-carbon, was applied to the electrolysis mediated by a hydrophobic vitamin B12 model complex, heptamethyl cobyrinate perchlorate in this study. The electrolysis of the substrate at −1.0V vs. Ag-AgCl by light irradiation afforded the simple reduced product (diethyl 2-methyl-2-phenylmalonate) and the phenyl migrated product (diethyl 2-benzyl-2-phenylmalonate), as well as the electrolysis of the substrate at −1.5V vs. Ag-AgCl in the dark. The electrolysis of the substrate at −2.0V vs. Ag-AgCl afforded the carboxylic ester migrated product (diethyl phenylsuccinate) as the major product. The selectivity for the migrating group was successfully tuned by controlling the electrolysis potential. We clarified that the cathodic chemistry of the Co(III) alkylated heptamethyl cobyrinate is critical for the selectivity of the migrating group through mechanistic investigations and comparisons to the simple vitamin B12 model complex, an imine/oxime-type cobalt complex.

Impact of the corrin framework of vitamin B12 on the electrochemical carbon-skeleton rearrangement in comparison to an imine/oxime planar ligand; tuning selectivity in 1,2-migration of a functional group by controlling electrolysis potential

Among the coenzyme B12-dependent enzymes, methylmalonyl-CoA mutase (MMCM) catalyzes the carbon-skeleton rearrangement reaction between R-methylmalonyl-CoA and succinyl-CoA. Diethyl 2-bromomethyl-2-phenylmalonate, an alkyl bromide substrate having two different migrating groups (phenyl and carboxylic ester groups) on the β-carbon, was applied to the electrolysis mediated by a hydrophobic vitamin B12 model complex, heptamethyl cobyrinate perchlorate in this study. The electrolysis of the substrate at −1.0V vs. Ag-AgCl by light irradiation afforded the simple reduced product (diethyl 2-methyl-2-phenylmalonate) and the phenyl migrated product (diethyl 2-benzyl-2-phenylmalonate), as well as the electrolysis of the substrate at −1.5V vs. Ag-AgCl in the dark. The electrolysis of the substrate at −2.0V vs. Ag-AgCl afforded the carboxylic ester migrated product (diethyl phenylsuccinate) as the major product. The selectivity for the migrating group was successfully tuned by controlling the electrolysis potential. We clarified that the cathodic chemistry of the Co(III) alkylated heptamethyl cobyrinate is critical for the selectivity of the migrating group through mechanistic investigations and comparisons to the simple vitamin B12 model complex, an imine/oxime-type cobalt complex.

Electrochemical Reduction of Alkenes Mediated By Vitamin B12 Model Complex

Naturally-occurring B12(cobalamin)-dependent enzymes catalyze various molecular transformations that are of particular interest from the viewpoint of biological chemistry as well as synthetic organic chemistry and catalytic chemistry. The CoI species of B12 derivative is widely known as a supernucleophile that forms an alkylated complex by reaction with an alkyl halide.1 The alkylated complex is a useful reagent for forming radical species as the cobalt-carbon bond is readily cleaved homolytically by photolysis. Recently, application of CoI complex for proton reduction was extensively studied and electrochemical hydrogen evolutions by cobalt complex have been reported.2 In these studies, Co-H complex is thought to be an intermediate for hydrogen evolution. These results prompted us to investigate application of cobalamin derivative for new bio-isnpired reaction.3 The electrochemically generated CoI species of B12 derivative may reacts with proton (CF3COOH, CH3COOH etc..) to form Co-H complex, and can utilize for alkene reduction (Figure 1). Scope of substrate, detailed reaction mechanism, comparison to catalysis of other cobalt complex will be reported. References (1) a) M. Giedyk, H. Shimakoshi, K. Goliszewska, D. Gryko, Y. Hisaeda, Dalton Trans., 2016, in press (Inside cover); b) H. Shimakoshi, Z. Luo, T. Inaba, Y. Hisaeda, Dalton Trans., 2016, in press (Back cover). (2) a) V. Artero, M. Chavarot-Kerlidou, and M. Fontecave, Angew. Chem. Int. Ed., 50, 7238 (2011), b) W. T. Eckenhoff, R. Eisenberg, Dalton Trans, 41, 13004 (2011). (3) H. Shimakoshi and Y. Hisaeda, ChemPlusChem, 79, 1250 (2014) (Back cover). Figure 1

Synthesis, characterization, Co–S bond reactivity of a vitamin B12 model complex having pentafluorophenylthiolate as an axial ligand

Heptamethyl (aquo)(pentafluorophenylthiolate)cobyrinate perchlorate, [(H2O)(C6F5S)Cob(III)7C1ester]ClO4, was synthesized as a B12 model complex having a thiolate ligand in the axial position. The axial ligand change in heptamethyl (diaquo)cobyrinate diperchlorate, [(H2O)2Cob(III)7C1ester](ClO4)2, from H2O to C6F5S(-) afforded the B12-thiolate complex. The B12-thiolate model complex was characterized by UV-vis, NMR and ESI-mass spectroscopies. The coordination of C6F5S(-) to the cobalt center affected the spectroscopic properties of the corrin ring through the electronic interaction between the axial ligand (C6F5S(-)) and the equatorial ligand (corrin). The photolysis of the B12-thiolate model complex led to the homolytic cleavage of the Co(iii)-S bond to form the Co(II) complex and the phenyl thiyl radical. The thermolysis of the B12-thiolate model complex also led to the homolytic cleavage of the Co(III)-S bond. Furthermore, the reactivity of the Co(III)-S bond of the B12-thiolate model complex was applied to the catalytic oxidation of C6F5SH to C6F5S-SC6F5.

Carbon-Skeleton Rearrangement Reaction Mediated by Simple Vitamin B12 Model Complex with Electrochemical Duet Process

not Available.

Methyl-transfer reaction to alkylthiol catalyzed by a simple vitamin B12 model complex using zinc powder

The catalytic methyl-transfer reaction from methyl tosylate to 1-octanethiol was carried out in the presence of a simple vitamin B12 model complex, [Co(III){(C2C3)(DO)(DOH)pn}Br2], with zinc powder as the reducing reagent at 50°C. Such a catalytic reaction proceeded via the formation and dissociation of a cobalt–carbon bond in the simple vitamin B12 model complex under non-enzymatic conditions. The mechanism for the methyl-transfer reaction was investigated by electronic and mass spectroscopies. The Co(I) species, which is generated from the reduction of the catalyst by the zinc powder, and its methylated CH3–Co complex were found to be indispensable intermediates.

Vitamin B12 model complex catalyzed methyl transfer reaction to alkylthiol under electrochemical conditions with sacrificial electrode

Catalytic methyl transfer reactions from methyl tosylate to 1-octanethiol catalyzed by heptamethyl cobyrinate perchlorate, [Cob(II)7C(1)ester]ClO(4), were investigated under electrochemical conditions. As a model study for the cobalamin-dependent methyl transfer reaction from methyltetrahydrofolate to homocysteine, controlled-potential electrolyses were carried out at -1.0 V vs. Ag/AgCl using a zinc plate as the sacrificial anode at 50 degrees C in the dark. A turnover behaviour for the methyl transfer reaction was observed for the first time under non-enzymatic reaction conditions. Co(I) species, which is generated from the continuous electrolysis of [Cob(II)7C(1)ester]ClO(4), and its methylated CH(3)-Co complex were found to be important intermediates. The mechanism for such a methyl transfer reaction was investigated by product analysis, electronic spectroscopy and ESR spin-trapping experiments. A simple vitamin B(12) model complex was also utilized as the catalyst for the methyl transfer reaction.

Electron-Transfer Oxidation of Coenzyme B12Model Compounds and Facile Cleavage of the Cobalt(IV)−Carbon Bond via Charge-Transfer Complexes with Bases. A Negative Temperature Dependence of the Rates

The electron-transfer oxidation and subsequent cobalt-carbon bond cleavage of vitamin B12 model complexes were investigated using cobaloximes, (DH)2Co(III)(R)(L), where DH- = the anion of dimethylglyoxime, R = Me, Et, Ph, PhCH2, and PhCH(CH3), and L = a substituted pyridine, as coenzyme B12 model complexes and [Fe(bpy)3](PF6)3 or [Ru(bpy)3](PF6)3 (bpy = 2,2'-bipyridine) as a one-electron oxidant. The rapid one-electron oxidation of (DH)2Co(III)(Me)(py) (py = pyridine) with the oxidant gives the corresponding Co(IV) complexes, [(DH)2Co(IV)(Me)(py)]+, which were well identified by the ESR spectra. The reorganization energy (lambda) for the electron-transfer oxidation of (DH)2Co(Me)(py) was determined from the ESR line broadening of [(DH)2Co(Me)(py)]+ caused by the electron exchange with (DH)2Co(Me)(py). The lambda value is applied to evaluate the rate constants of photoinduced electron transfer from (DH)2Co(Me)(py) to photosensitizers in light of the Marcus theory of electron transfer. The Co(IV)-C bond cleavage of [(DH)2Co(Me)(py)]+ is accelerated significantly by the reaction with a base. The overall activation energy for the second-order rate constants of Co(IV)-C bond cleavage of [(DH)2Co(IV)(Me)(py)]+ in the presence of a base is decreased by charge-transfer complex formation with a base, which leads to a negative activation energy for the Co(IV)-C cleavage when either 2-methoxypyridine or 2,6-dimethoxypyridine is used as the base.

ChemInform Abstract: Electroorganic Reactions Mediated by Vitamin B12 Model Complexes

AbstractChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 100 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a “Full Text” option. The original article is trackable via the “References” option.

Photokatalytische Bildung von Wasserstoff aus Thiolen in Gegenwart von Vitamin B12-Modellverbindungen mit Azid als photochemischem Opferliganden

Photocatalytic Hydrogen Formation from Thioles in the Presence of Vitamin-B12 Model Complexes with Azide as Photochemical Sacrificial Ligand The photolysis of [N3Co(chelat)B] complexes (1–3) (chelat = dimethylglyoxime, dmg; N,N′-o-phynylenebis(salicylidenimine), salphen; N,N′-ethylene-bis(salicylidenimine), salen; B = pyridine) leads by homolytic cleavage of the Co–N3 bond to both coordinatively unsaturated cobalt(II) chelates [Co(chelat)B] and N3 ligand radicals that undergo fast decay to dinitrogen. The photolysis of the cobalt (III) complexes 1–3 in the presence of thiophenole and other thioles proceeds catalytically and yields the corresponding disulphides and dihydrogen. The mechanism of this photocatalytic generation of dihydrogen is due to the catalytic activity of the coordinatively unsaturated cobalt(II) species formed photochemically. A photocatalytic cycle is proposed describing the generation of hydrogen. Possible photochemical and thermal steps of that cycle are discussed.

Photochemische Untersuchungen von Vitamin B12-Modellverbindungen mit Azid bzw. Thiolat als Axialliganden - Precursorverbindungen f�r koordinativ unges�ttigte Cobalt(II)-Komplexe

Photochemistry of Azido and Thiolato Vitamin-B12 Model Complexes as Precursor Compounds for Coordinatively Unsaturated Cobalt(II) Complexes The photolysis of [LCo(chelat)B] complexes (1–3) (L = azide, N; thiolate, RS−; chelat = dimethylglyoxime, dmg; N,N′-o-phenylene-bis(salicylidenimine), salphen; N,N′-ethylene-bis(salicylidenimine), salen; B = pyridine, imidazole, triphenylphosphine) leads upon the homolytic cleavage of the CoL bond to both coordinatively unsaturated reactive cobalt(II) chelates [Co(chelat)B] and ligand radicals L•. The efficiency of these photochemical redox reactions is described in relation to the structure of the cobalt(III) chelates, the wavelength of irradiation, the light-intensity as well as the solvents and substrates used during the photochemical experiments. Further, sensitization experiments using [Ru(bipy)3]Cl2 as sensitizer are described and the redox potentials of the investigated complexes are discussed.

ChemInform Abstract: Transition‐Metal NMR Spectroscopy. Part 14. Electronic and Steric Influence of Axial and Equatorial Ligands in Vitamin B12 Model Complexes (I)‐(IV) Derived from Cobaloxime: Electrochemical and 59Co‐NMR Studies.

ChemInform Abstract: Transition‐Metal NMR Spectroscopy. Part 14. Electronic and Steric Influence of Axial and Equatorial Ligands in Vitamin B12 Model Complexes (I)‐(IV) Derived from Cobaloxime: Electrochemical and 59Co‐NMR Studies.

Redox Behavior of Simple Vitamin B12 Model Complexes and Electrochemical Catalysis of Carbon-Skeleton Rearrangements

Abstract Various cobalt complexes of 4,10-dipropyl-5,9-diazatrideca-4,9-diene-3,10-dione dioxime, (C2C3)(DOH)2pn, were prepared, and redox behavior of them was investigated by means of cyclic voltammetry; Co(II)/Co(I) redox potentials in the range of −0.69 through −0.7 V vs. Ag/AgCl. The monomethylated complex, which has a cobalt–carbon bond at one axial site of the nuclear cobalt, was disproportionated to the dimethylated complex, involving two cobalt–carbon bonds at both axial sites, and the CoI species by one-electron reduction. The dimethylated complex was inactive for electrochemical reduction, but transformed into the monomethylated complex via cleavage of a cobalt–carbon bond upon electrochemical oxidation. The electrolyses of 1-bromo-2,2-bis(ethoxycarbonyl)propane, 1-bromo-2-cyano-2-ethoxycarbonylpropane, and 2-acetyl-1-bromo-2-ethoxycarbonylpropane in the presence of [CoIII{(C2C3)(DO)(DOH)pn}Br2] in N,N-dimethylformamide did not proceed in a divided cell at −2.0 V vs. Ag/AgCl, since the corresponding dialkylated complexes, inactive for electrochemical reduction, were formed in the course of reaction. When imidazole was added to solutions for the electrolysis, the reaction proceeded efficiently by the trans effect arising from the coordinated axial base and the corresponding carbon-skeleton rearrangement products were obtained. On the other hand, the carbon-skeleton rearrangement proceeded in an undivided cell even in the absence of imidazole; the dialkylated complex was decomposed to give the monoalkylated complex and the reduction and rearrangement products by electrochemical oxidation on the anode.

Carbon-Skeleton Rearrangement of an Alkyl Ligand Coordinated to Simple Vitamin B12 Model Complexes in Synthetic Bilayer Membrane

Abstract The carbon-skeleton rearrangement of an alkyl ligand coordinated to the nuclear cobalt of simple vitamin B12 model complexes formed with diimine–dioxime-type ligands took place efficiently in a synthetic bilayer membrane under irradiation with visible light.

Cyanide-Coordination Effect on Photochemical Carbon-Skeleton Rearrangements of Alkyl Ligands Coordinated to Vitamin B12 Model Complexes

Abstract The cyanide ion induced the heterolytic cleavage of the cobalt–carbon bond involved in vitamin B12 model complexes by its coordination to the central cobalt atom and enhanced the carbon-skeleton rearrangements via formation of anionic intermediates under anaerobic irradiation with the visible light.

Redox Behavior of Simple Vitamin B12 Model Complexes with Cobalt–Carbon Bonds and Catalytic Carbon-Skeleton Rearrangements

Abstract The cobalt complex of 2,10-diethyl-3,9-dipropyl-1,4,8,11-tetraazaundeca-1,3,8,10-tetraene-1,11-diol catalyzed electrolyses of alkyl halides with electron-withdrawing groups at the β-position to afford rearrangement products via oxidation of the corresponding dialkylated complexes as intermediates.

Characterization of a Simple Vitamin B12 Model Complex and Its Catalysis in Electrochemical Carbon-Skeleton Rearrangement

Abstract The electrochemical carbon-skeleton rearrangement reaction of 2,2-bis(ethoxycarbonyl)-1-bromopropane was catalyzed by the cobalt complex of 2,10-diethyl-3,9-dipropyl-1,4,8,11-tetraazaundeca-1,3,8,10-tetraene-1,10-diol, which was characterized by ESR spectroscopy and cyclic voltammetry.

Interactions of a vitamin B12 model complex with amino-acids and oligopeptides. A visible and nuclear magnetic resonance spectroscopic study

Substitution of the water molecule of [MeCo(tn)H2O] ClO4 by some amino-acids and simple oligopeptides has been studied by 1H n.m.r. and visible absorption spectroscopy. Amino-acids bind to cobalt through –NH2, imidazole, nitrogen and –S–; formation constants are higher for the sulphur ligands while no Co–CH3 bond breaking is observed. Amino-acid protons nearest to cobalt undergo anomalous high fields shifts; for the trans methyl and the equatorial ligand proton shifts, the ring current effect of the entering ligand is the major factor. The existence of µ-amino-acido-complexes and of preferred orientation in solution of some ligands in the sixth co-ordination position is proposed.