Laksmikanta Adak

Metal nanoparticles as efficient catalysts for organic reactions

Pd(0) nanoparticles have been demonstrated to be very efficient catalysts for C–C bond-forming reactions. These include coupling of vicinal-diiodoalkenes and acrylic esters and nitriles leading to the stereoselective synthesis of 2-alkene-4-yn-esters and nitriles, allylation of active methylene compounds by allyl acetate, and Hiyama cross-coupling of aryliodides with arylsilanes. Cu(0) nanoparticles catalyze aryl-sulfur bond formation, accomplishing the synthesis of functionalized aryl sulfides and aryl- and vinyl dithiocarbamates. Cu nanoparticles have also been used for the chemoselective reduction of aromatic nitro compounds.

Oxidative ortho-C-N Fusion of Aniline by OSO4. Isolation, Characterization of Oxo-Amido Osmium(VI) Complexes, and their Catalytic Activities for Oxidative C-C Bond Cleavage of Unsaturated Hydrocarbons

In an unusual reaction of osmium(VIII) oxide with p-substituted aromatic amines (X-C(6)H(4)-NH(2), where X = Me, H, Cl) in heptane afforded the brown osmium(VI)-oxo complexes [OsO(L)(2)] (1a-c, L = N-aryl-1,2-arylenediamide) in moderate yields. The ligand L is formed in situ via oxidative ortho-C-N fusion of arylamines. The reaction occurs in an inert atmosphere, and a part of Os(VIII) is used up for the oxidation of aromatic amine. Single crystal X-ray structure of a representative complex 1a is solved. The structural analysis has authenticated the ortho-C-N fusion of ArNH(2) resulting in formation of the diamide ligand, L. The complex as a whole is penta-coordinated, and the coordination sphere has a distorted square pyramidal geometry (tau = 0.26). A similar reaction of osmium(VIII) oxide with the preformed N-phenyl-1,2-phenelene diamine produced the complex 1a in nearly quantitative yield. The substituted phenazine, 5-phenyl-3-phenylimino-3,5-dihydro-phenazine-2-ylamine, is obtained as a byproduct of the latter reaction. The complexes, 1a-c, can be reduced in a reversible one-electron step, as probed by cyclic voltammetry. The one electron reduced paramagnetic Os(V) intermediate is, however, Electron Paramagnetic Resonance (EPR) silent. Solution spectra of the osmium complexes show several multiple transitions in the UV-vis region. Density functional theory calculations were employed to confirm the structural features and to support the spectroscopic assignments. The complex 1a catalyzes oxidation of a wide variety of unsaturated hydrocarbons like alkenes, alkynes, and aldehydes to the corresponding carboxylic acids in the presence of tert-butylhydroperoxide (TBHP) efficiently at room temperature.

Halogenation of carbonyl compounds by an ionic liquid, [AcMIm]X, and ceric ammonium nitrate (CAN)

An ionic liquid, acetylmethylimidazolium halide ([AcMIm]X), in combination with ceric ammonium nitrate promotes halogenations of a wide variety of ketones and 1,3-keto esters at the α-position. The ionic liquid acts here as reagent as well as reaction medium, and thus the reaction does not require any organic solvent or conventional halogenating agent. The reaction is completely arrested when the radical quencher TEMPO is used. A plausible radical mechanism is also suggested.

Amphiphilic allylation of activated alkenes by allyl acetates and allylstannanes catalyzed by palladium nanoparticles: an easy access to stereodefined substituted cyclohexene derivatives

An efficient vicinal double allylation of activated alkenes by allyl acetates and allylstannanes catalyzed by palladium nanoparticles, generated in situ from palladium(II) chloride, has been demonstrated. Several activated alkenes produce functionalized 1,7-octadiene derivatives in one pot. The additions of substituted allyl acetates are highly regioselective. The Grubbs cyclization of octadiene derivatives gives an easy access to stereodefined substituted cyclohexene derivatives.

Potential of metal nanoparticles in organic reactions

Palladium(0) nanoparticle has been used as efficient catalyst for (a) the stereoselective synthesis of (E)- and (Z)-2-alkene-4-ynoates and —nitriles by a simple reaction of vic-diiodo-(E)-alkenes with acrylic esters and nitriles and (b) for the allylation of active methylene compounds by allylacetate and its derivatives. Copper(0) nanoparticle catalyzes aryl-sulfur bond formation very efficiently. All these reactions are ligand-free.