Debkumar Bandyopadhyay

Facile regiospecific aromatic hydroxylation in palladium azopyridines and structural characterization of phenolato product

Abstract The reaction of Na2PdCl4 with 2-(arylazo)pyridines (A) in ethanol affords yellow complexes of composition [PdACl2] in which the PdCl2 fragment has acis configuration [ν(Pd Cl): 350, 365 cm−1]. Upon treating [PdACl2] with dilute sodium hydroxide in air the pendent aryl group is selectively hydroxylated at theortho position, affording the phenolato complex [PdBCl] in high yields [B− is deprotonated 2-(2′-hydroxyarylazo)pyridine]. A possible reaction pathway is proposed by analogy with the hydroxylation of certain organic compounds by OH−/O2. The crystal and molecular structure of one [PdBCl] complex is reported. In the highly planar complex, the Pd N(azo) length is significantly shorter than the Pd N(pyridine) length. A single Pd Cl stretch at 365 cm−1 characterizes [PdBCl] which, unliked [PdACl2], has a structured intense absorption in the visible region near 670 nm.

Mechanism of Palladium−Carbon Bond Oxidation: Dramatic Solvent Effect

Pentafluoroiodosylbenzene (C6F5IO) selectively oxidizes Pd−C bonds of a series of cyclopalladated 2-(alkylthio)azobenzene complexes. The kinetics of oxygen atom insertion into the Pd−C bond of one representative compound has been studied in detail to understand the mechanism of this reaction. At 20 °C Pd−C bond oxidation takes place smoothly in acetonitrile at a rate of 0.08 M-1 s-1, whereas this reaction does not proceed in solvents such as dichloromethane and chloroform. The ΔH⧧ and ΔS⧧ values for this reaction are 55.5 ± 3.5 kJ/mol and −75.7 ± 11.5 eu, respectively. Among other oxidants, hydroperoxy radical (for example, t-BuOO•) is found to be extremely efficient, whereas the highly electrophilic oxoiron(IV) porphyrin cation radical (oxene) is incapable of oxidizing the Pd−C bond. Oxene, however, selectively oxidizes the thioether functionality. These observations suggest that nucleophilic attack of the oxidant molecule on palladium(II) could be the most crucial step prior to Pd−C bond oxidation. A la...

Cytochrome P-450 model compound catalyzed selective hydroxylation of C–H bonds: Dramatic solvent effect

Selective hydroxylation of cyclohexane and cyclohexene by t-BuOOH in presence of F2oTPPFe(III)Cl as the catalyst has been achieved at room temparature in high yields.

Oxygen insertion into the metal–carbon bond of cyclopalladated 2-(alkylsulphinyl)azobenzenes by peracids. High yield regiospecific aromatic hydroxylation

The title reaction occurs by an associative mechanism involving heterolytic O–O cleavage; the sequence azobenzene →(1)→(2)→ azophenol leading to overall regiospecific aromatic hydroxylation has been realised.

Iron(III) porphyrin-catalysed oxidation reactions by m-chloroperbenzoic acid: Nature of reactive intermediates

The reaction of m-chloroperbenzoic (m-CPBA) acid with meso-tetrakis (pentafluorophenyl) porphynatoiron(III) chloride (F20TPPFe(III)Cl ) has been studied in dichloromethane and acetonitrile medium at 25 ± 1°C. The reactive intermediates formed in this reaction have been quantitatively trapped by 2,4,6-tri t-butylphenol (TTBP) in both the solvents. It has been observed that the kinetic plots of the formation of TTBP• radical in dichloromethane are all multiexponential, supporting the formation of more than one reactive intermediate in this solvent. In acetonitrile solvent the formation of TTBP• radical was however observed to be distinctly single exponential. Different kinds of reactive intermediates are proposed in these two solvents.

Stabilisation of copper(I) by an azoimine ligand: redox properties and reactions of bis(phenylazoacetaldoximato)bis(phenylacetaldoxime)dicopper(I)

The high preference of phenylazoacetaldoxime, MeC(NOH)NNPh (HL), for copper(I) is rationalised in terms of electronic and steric factors. The complex [Cu2(HL)2(L)2](1) undergoes a one-electron oxidation at ∼0.8 V vs. saturated calomel electrode to an unstable CuIICuI species. Tertiary phosphines displace HL from (1) affording [CuL(PR3)2][R = Ph (2a) or C6H4Me-p(2b)]. (2a) reacts with HCl to form [{Cu(PPh3)Cl}4] and with HClO4 to give the complex [Cu(HL)(PPh3)2(ClO4)]. All complexes having the chelated CuL or Cu(HL) fragment are shown to have a characteristic low-energy metal-to-ligand charge-transfer transition (700–900 nm).

Chlorido{5-chloro-2-[2-(methyl-sulfanyl)phenyl-diazen-yl]phenyl}-platinum(II).

The title compound, [Pt(C13H10ClN2S)Cl], contains a Pt atom tetracoordinated by a benzene C, a diazene N, a Cl and an S atom in an approximately square-planar geometry. The molecules dimerize through a nonbonded S⋯S interaction [S⋯S = 3.523 (18) Å]. There are no hydrogen bonds and the crystal packing is stabilized by four intermolecular π–π interactions; the centroid–centroid distances are 3.804 (3), 3.638 (3), 3.804 (3) and 3.638 (3) Å, and the corresponding perpendicular distances are 3.369, 3.448, 3.406 and 3.466 Å.

Reactive intermediates in iron(III) porphyrin-catalyzed oxidation reactions

In iron(III) porphyrin-catalyzed oxidation of organic substrates by various monooxo transfer agents, oxoiron(IV) porphyrin cation radical(oxene) has been thought to be the most probable reactive intermediate. Our work, as reported here, indicates that oxo transfer to suitable substrates is possible by a distinctly different route. In case of MCPBA, the oxo transfer is very strongly solvent dependent. For example, in pure toluene solvent, intermediacy of oxene is not at all important, whereas in dichloromethane-methanol mixed solvent, the role of oxene is very significant. We also note that solvent molecules are susceptible to self oxidation by various oxidizing systems.