Homogeneous and heterogeneous electrocatalytic reduction of halo-organic compounds by (NiIILi)2+ (Li= tetraaza-macrocyclic ligand) in aqueous solutions (original) (raw)
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Dalton transactions (Cambridge, England : 2003), 2016
A growing number of halogenated organic compounds have been identified as hazardous pollutants. Although numerous advanced oxidative processes have been developed to degrade organohalide compounds, reductive and nucleophilic molecular approaches to dehalogenate organic compounds have rarely been reported. In this manuscript, we employ nickel(ii)-ate complexes bearing the o-phenylenebis(N-methyloxamide) (Me2opba) tetraanionic ligand as nucleophilic reagents that can react with alkyl halides (methyl up to the bulky isobutyl) by O-alkylation to give their respective imidate products. Four new nickel(ii) complexes have been characterized by X-ray crystallography, and the salient structural parameters and FT-IR vibrational bands (∼1655 cm(-1)) concur with their assignment as the imidate tautomeric form. To the best of our knowledge, this is the first report on the nucleophilic reactivity of Ni(II)(Me2opba) with halogenated organic compounds. The parent nickel(ii) Me2opba complex exhibits...
Polyhedron, 1997
411 rights reserved. Prmtcd in Great Bntaln 0277 5387 'Y7 51 7.w t O.llO The preparation, chemistry and crystal structure of the nickel(I1) complex of N-hydroxyethylazacyclam [3-(2'.hydroxyethyl)-1,3,5,8,12=penta=azacyclotetradecane nickel(H) perchlorate]. Abstract-The reaction of formaldehyde and ethanolamine with the nickel(l1) complex of 1,9-diamino-3,7diazanonane (2,3,2-tet) gives the nickel(H) complex of the macrocycle 3-hydroxyethyl-1,3,5,8. I2-penta-azacyclotetradecane (L) which can be readily isolated as the perchlorate salt. The crystal structure of [NiL](ClO,), has been determined. The nickel atom is in an essentially planar environment with N,. Ns, N, and N,? acting as donors with Ni-N bond distances in the range I .93&l ,938 8, The ligand has a trans III configuration of the W-NH centres with chair six-membered and gauche five-membered chelate rings. The hydroxyethyl group on N, is axial. The two perchlorate anions lie in the axial sites but the Ni-O(4) and the Ni-O(7) distances of 2.X36(3) and 3.028(3) 8, indicate that there is no bonding interaction between these centres. In aqueous solution the complex is predominantly square planar. Addition of HCI leads to axial addition of chloride while addition of thiocyanate gives the trcms-[NiL(NCS),] complex. The ligand readily folds to give &-complexes. Thus addition of ethylenediamine to [NiLI'+ gives cis-[NiL(en in solution.
Nickel(I)(salen)-electrocatalyzed reduction of benzyl chlorides in the presence of carbon dioxide
Journal of Electroanalytical Chemistry, 2001
The electrochemical carboxylation of a series of substituted benzyl and benzylic-type chlorides Y-C 6 H 4 CH(Z)Cl (Z= H; Y=H, 4-CF 3 , 4-OCH 3 , 3-OCH 3 ; and Y=H; Z= Ph, CH 3 ), catalyzed by nickel(I)(salen), was investigated in acetonitrile by cyclic voltammetry and controlled-potential electrolysis. For all of the chlorides investigated, remarkable catalytic currents were measured under atmospheric CO 2 pressure. For most chlorides, controlled-potential electrolysis yields the corresponding carboxylic acid as the main product, the other significant product being the substituted toluene. The results indicate that the extent of carboxylation is strongly influenced by the structure of the halide. Electron-withdrawing groups, either on the phenyl ring or on the benzylic carbon, favor the formation of the carboxylate. In the first step of the electrocatalytic process, the halide reacts with electrogenerated [Ni I (salen)] − to form the benzyl radical. Further reduction of the radical to the corresponding carbanion is followed by electrocarboxylation in competition with protonation by residual water. The yield of the carboxylic acid is determined by the ease of reduction of the benzylic radical, which in turn reflects the nucleophilicity and basicity of the ensuing carbanion.
Catalytic Reduction of Unsaturated Halides by Ni(II) Complexes
Portugaliae Electrochimica Acta, 1999
Radical cyclisation is rapidly becoming an important method for the formation of cyclic systems. Hence, some electrochemical results obtained in the study of electroreductive intramolecular cyclisation of different types of unsaturated halides using nickel(II) complexes as mediators, are presented.
Reductive Cyclisations using Environmentally Friendly Electrochemical Methodologies
ECS Transactions, 2007
The electrochemical reductive cyclization of unsaturated organic halides was examined in the presence of Ni(II) complexes associated to macrocyclic ligands. Ni(0) or Ni(I) intermediate species were obtained according to the nature of the ligand. The reactions could be carried out in protic solvents such as ethanol, buthanol or ethanol-water mixtures and still be catalytic and highly efficient.
Active nickel-based reduction of organic compounds
Russian Chemical Bulletin, 2000
The reducing system NiCl 2 •2H 2 O-Li-arene cat (cat is catalyst) was proposed for use to reduce a wide range of organic compounds, including alkenes, alkynes, carbonyl compounds, imines, halogenated derivatives, sulfonates, aromatic compounds, hydrazines, azo and azoxy compounds, N oxides, and nitrones. The degree of reduction can be controlled for some substrates. Deuterium can be incorporated in the reaction products using nickel chloride deuteriohydrate. Nitrones, N alkoxyamides, and acyl azides are also reduced with the Li-arene cat system containing no nickel salt.
International Journal of Electrochemical Science, 2018
The following bidentate Schiff base: 2-[(4-Methoxybenzyl)iminomethyl]-phenol (HL), was employed as an asymmetric ligand in the synthesis of two mononuclear nickel(II) and cobalt(III) complexes (Ni(II)-2L and Co(III)-3L). This ligand has been synthesized via condensation of salicylaldehyde and 4-methoxybenzylamine in methanolic solution, while the both complexes result from complexation of metal(II) chloride hydrate salts with HL. These coordination compounds were structurally characterized by elemental analysis, FT-IR, UV-Vis, 1 H NMR and 13 C NMR spectral studies. Moreover, the electrochemical properties of both complexes were studied by cyclic voltammetry in DMF solution containing 0.1 M tetra-n-butylammonium tetrafluoroborate (Et 4 NBF 4). This study reveals that each complex showed successively two redox couples: M(III)/M(II) and M(II)/M(I). Finally, the electrocatalytic activity of these complexes has been examined and it has been found that the both complexes worked as effective homogeneous electrocatalysts for the electroreduction of bromocyclopentane and iodobenzene using glassy carbon as working electrode.
Inorganic Chemistry, 2015
Basic methanolysis of a sterically hindered aminobis(Sarylthiocarbamate) affords a novel aminobis(thiophenolate) pincer-type ligand NS 2 2− ; the in situ generated dianion reacts cleanly with Ni 2+ and Zn 2+ resulting in dimeric complexes with bridging thiophenolate ligands, as determined spectroscopically and by X-ray crystallography. The C 2 -symmetric [Ni(NS 2 )] 2 dimer (1) has a square planar coordination geometry around the Ni 2+ ions, while the [Zn(NS 2 )] 2 analogue is characterized by a distorted tetrahedral geometry around each independent Zn 2+ ion. Addition of the neutral monodentate donor L = 2,6-xylylisocyanide to [Ni(NS 2 )] 2 affords the monomeric complex [LNi(NS 2 )] (3), which is characterized in the solid state by a square planar geometry with the isocyanide donor trans to the tertiary amine of NS 2 . The pincer NS 2 ligand provides redox plasticity to 1, manifested in the accessibility of the putative Ni + Ni + and Ni 3+ Ni 3+ dimeric complexes, based on comparative cyclic voltammetry studies with 2 and 3. The redox properties of 1 endow it with hydrogenase-type activity, as evidenced in the electrocatalytic reduction of protons in a mixed aqueous/organic phase, as well as the oxidation of hydrides from NaBH(OAc) 3 . Both 1 and 3 are resilient under protic and oxidative conditions, as evidenced in reactivity tests monitored by UV−vis spectroscopy.
Journal of Molecular Structure, 2018
The electrocatalytic activity of N, N 0-bis(2-hydroxy-1-naphthaldehyde)-1,3-phenylenediimine, NMPD, and its Ni(II) complex in reduction of CO 2 was studied in an N, N 0 edimethylformamide, DMF, solvent by cyclic voltammetry and chronoamperometry methods. According to the cyclic voltammetry studies, the potential of CO 2 reduction was À1.40 V and À1.18 V versus Ag/AgCl/KCl (sat'd) in the presence of the NMPD ligand and its Ni(II) complex respectively. In this way, the overpotential of CO 2 reduction was reduced for about 700 mV and 920 mV in the presence of NMPD and its Ni(II) complex respectively. However, in the presence of NMPD, a higher increase was observed in the catalytic current of CO 2 reduction with respect to the Ni(II) complex. By chronoamperometry, the homogeneous catalytic rate constant, k, for the electron transfer between the NMPD ligand and CO 2 as well as the Ni(II) complex and CO 2 was found to be 24.90 ± 0.98 M À1 s À1 and 0.71 ± 0.05 M À1 s À1 respectively. The diffusion coefficients, D, of the NMPD ligand and the Ni(II) complex in the DMF solvent were also determined as 9.8 Â 10 À6 cm 2 s À1 and 8.9 Â 10 À6 cm 2 s À1 respectively. Considering the results and also the molecular structure of the ligand, the electrocatalytic behavior of these compounds toward CO 2 reduction are discussed in detail.
Electrochimica Acta, 2000
Two series of binuclear macrocyclic nickel(II) complexes with varying lengths of the chain linking the two macrocyclic rings were characterised by cyclic voltammetry under argon and CO 2 . The first series consisted of binuclear complexes [Ni 2 L 2-6 ] 4 + containing pentaaza macrocycles with (CH 2 ) n bridges (n= 2, 3, 4, 6) or a p-xylyl linkage (L 6 ). In general, the two nickel sites in the binuclear complexes behave independently with the currents corresponding to the simultaneous transfer of two electrons. The redox potentials are remarkably constant along this series, but the peak separations increase, reflecting slower electron transfer due to more effective adsorption on the electrode. Electrochemical data for the electrocatalytic reduction of CO 2 in MeCN/10% H 2 O revealed catalytic waves for CO 2 reduction with E p c close to −1.7 V and catalytic currents (i p c ) which are about half those of the mononuclear complex, proposed to be due to steric constraints allowing strong interaction of only one nickel centre of the binuclear one on the surface. The catalytic currents increased slightly as the linking chain length increased as the stereochemical constrains were relaxed somewhat. There was also a splitting in the catalytic peaks of the bismacrocyclic complexes which could reflect two types of adsorbed catalyst sites. In the more sterically crowded series of complex, [Ni 2 L 7 ] 4 + along with the series of linked heptaaza macrocyclic complexes [Ni 2 L 9-11 ] 4 + much more positive redox potentials were observed due to both alkylation of the coordinated nitrogen atoms, which decreases the ligand field, and the introduction of steric barriers to axial coordination. These steric barriers prevented strong electrode interaction and led to a lower catalytic activity. Indeed, the complex [Ni 2 L 7 ] 4 + did not even show any interaction with CO 2 in dry acetonitrile. The complexes showed well separated peaks due to solution and surface catalytic activity, and the surface catalytic currents were now comparable to mononuclear complexes at the same effective concentration. We proposed that the less effective absorption on the electrode arising from ligand steric interactions places far fewer stereochemical constraints on the adsorption of both nickel centres to the same extent as the binuclear complex, and hence the catalytic currents for binuclear complex and mononuclear complex are comparable.