Copper Catalyzed C-H Activation.

Activation of C-H bonds and their application in cross coupling chemistry has received a wider interest in recent years. The conventional strategy in cross coupling reaction involves the pre-functionalization step of coupling reactants such as organic halides, pseudo-halides and organometallic reagents. The C-H activation facilitates a simple and straight forward approach devoid of pre-functionalization step. This approach also addresses the environmental and economical issues involved in several chemical reactions. In this account, we have reported C-H bond activation of small organic molecules, for example, formamide C-H bond can be activated and coupled with ß-dicarbonyl or 2-carbonyl substituted phenols under oxidative conditions to yield carbamates using inexpensive copper catalysts. Phenyl carbamates were successfully synthesized in moderate to good yields by cross dehydrogenative coupling (CDC) of phenols with formamides using copper catalysts in presence of a ligand. We have also prepared unsymmetrical urea derivatives by oxidative cross coupling of formamides with amines using copper catalysts. Synthesis of N,N-dimethyl substituted amides, 5-substituted-γ-lactams and α-acyloxy ethers was carried out from carboxylic acids using recyclable CuO nanoparticles. Copper nanoparticles afforded N-aryl-γ-amino-γ-lactams by oxidative coupling of aromatic amines with 2-pyrrolidinone. Reusable transition metal HT-derived oxide catalyst was used for the synthesis of N,N-dimethyl substituted amides by the oxidative cross-coupling of carboxylic acids and substituted benzaldehydes. Overview of our work in this area is summarized.

Metal free oxidative coupling of aryl formamides with alcohols for the synthesis of carbamates.

A direct transformation of N-aryl formamides to the corresponding carbamates via the formation of isocyanate intermediates is achieved in good yields using hypervalent iodine as an oxidant.

Copper catalyzed oxidative coupling of amines with formamides: a new approach for the synthesis of unsymmetrical urea derivatives.

Direct access to unsymmetrical urea derivatives via copper catalysed C-H/N-H coupling of formamides with amines has been developed at room temperature. This protocol is also applied to the synthesis of chiral urea derivatives.

Simple metal-free organic D-pi-A dyes with alkoxy- or fluorine substitutions: application in dye sensitized solar cells.

Two new metal-free organic sensitizers with simplest structural variations have been synthesized for application in nanocrystalline TiO2 sensitized solar cells. The donor-pi-bridge-acceptor (D-pi-A) structure dyes, Y2 and Y3 each designed with three parts, an electron donor unit (substituted phenyl), a linker unit (thiophene), and an anchor unit (cyanoacrylic acid) showed maximal monochromatic incident photon to current conversion efficiencies (IPCE) in a device reaching upto 67% and 82% respectively. The organic sensitizers with 3,4,5-trimethoxy phenyl (Y3) as donor moieties obtained better solar light to electrical energy conversion efficiencies of 3.30% where as the organic sensitizer with 2,4-difluoro phenyl as donor (Y2) showed comparatively lower efficiency of 1.02%. The efficiency obtained with the reference sensitizer N719 under similar fabrication and evaluation conditions was 5.84%.

Separation of platinum and rhodium from chloride solutions containing aluminum, magnesium and iron using solvent extraction and precipitation methods.

The solvent extraction and precipitation methods have been used to develop a process to separate platinum and rhodium from a synthetic chloride solutions containing other associated metals such as (mg/L): Pt-364, Rh-62, Al-13880, Mg-6980, Fe-1308 at <1M HCl acidity. At pH 3.4, the quantitative precipitation of Al and Fe was achieved using 10 wt% Na(3)PO(4)·12H(2)O, with ~4% loss of Pt and Rh due to adsorption phenomenon. The selective separation of platinum was carried out with 0.01 M Aliquat 336 (a quaternary ammonium salt) at an aqueous to organic ratio (A/O) of 3.3 in two stages. Stripping of Pt from loaded organic (LO) at O/A ratio 6 with 0.5 M thiourea (tu) and HCl indicated that ~99.9% stripping efficiency. In stripping studies, needle like crystals of Pt were found and identified as tetrakis (thiourea) platinum (II) chloride ([Pt(tu)(4)]Cl(2)). The selective precipitation of rhodium was performed with (NH(4))(2)S from platinum free raffinate with a recovery of >99%.

Functionalization of mesoporous carbon with superbasic MgO nanoparticles for the efficient synthesis of sulfinamides.

Highly basic MgO nanoparticles with different sizes have been successfully immobilized over mesoporous carbon with different pore diameters by a simple wet-impregnation method. The prepared catalysts have been characterized by various sophisticated techniques, such as XRD, nitrogen adsorption, electron energy loss spectroscopy, high-resolution TEM, X-ray photoelectron spectroscopy, and the temperature-programmed desorption of CO(2). XRD results reveal that the mesostructure of the support is retained even after the huge loading of MgO nanoparticles inside the mesochannels of the support. It is also demonstrated that the particle size and dispersion of the MgO nanoparticles on the support can be finely controlled by the simple adjustment of the textural parameters of the supports. Among the support materials studied, mesoporous carbon with the largest pore diameter and large pore volume offered highly crystalline small-size cubic-phase MgO nanoparticles with a high dispersion. The basicity of the MgO-supported mesoporous carbons can also be controlled by simply changing the loading of the MgO and the pore diameter of the support. These materials have been employed as heterogeneous catalysts for the first time in the selective synthesis of sulfinamides. Among the catalysts investigated, the support with the large pore diameter and high loading of MgO showed the highest activity with an excellent yield of sulfinamides. The catalyst also showed much higher activity than the pristine MgO nanoparticles. The effects of the reaction parameters, including the solvents and reaction temperature, and textural parameters of the supports in the activity of the catalyst have also been demonstrated. Most importantly, the catalyst was found to be highly stable, showing excellent activity even after the third cycle of reaction.

CuI nanoparticles for C-N and C-O cross coupling of heterocyclic amines and phenols with chlorobenzenes.

Employing CuI nanoparticles as an efficient catalyst for the cross-coupling reactions of various N/O nucleophilic reagents with aryl chlorides could be successfully carried out under mild conditions in the absence of both the ligands and strong bases. A variety of products including N-arylimidazoles and aryl ethers were synthesized in good to excellent yields.

Asymmetric hydrosilylation of ketones catalyzed by magnetically recoverable and reusable copper ferrite nanoparticles.

Herein we present magnetically recoverable and reusable copper ferrite nanoparticles for asymmetric hydrosilylation of several ketones. Up to 99% enantiometric excess was obtained at room temperature using polymethylhydrosiloxane as the stoichiometric reducing agent. The copper ferrite nanoparticles were magnetically separated, and the efficiency of the catalyst remains almost unaltered up to three cycles.

Trifunctional N,N,O-terdentate amido/pyridyl carboxylate ligated Pd(II) complexes for Heck and Suzuki reactions.

Trifunctional N,N,O-terdentate amido/pyridyl carboxylate Pd(II) complexes were highly active and stable phosphine-free catalysts for Heck and room-temperature Suzuki reactions with high turnover numbers up to ca. 10(4).

An efficient copper-aluminum hydrotalcite catalyst for asymmetric hydrosilylation of ketones at room temperature.

A catalyst system consisting of a copper-aluminum hydrotalcite-chiral diphosphine ligand effects asymmetric hydrosilylation of several ketones, using polymethylhydrosiloxane (PMHS) as the stoichiometric reducing agent at room temperature, with moderate-to-excellent enantioselectivities. The catalyst is recovered by simple centrifugation, and the efficiency of the catalyst remains almost unaltered even after several cycles.

Rhodium fluorapatite catalyst for the synthesis of trisubstituted olefins via cross coupling of Baylis-Hillman adducts and arylboronic acids.

Treatment of fluorapatite (prepared by incorporating basic species F(-) in apatite in situ by coprecipitation) with an aqueous solution of RhCl(3) resulted in rhodium-exchanged fluorapatite catalyst (RhFAP), which successfully promoted cross coupling of Baylis-Hillman adducts with arylboronic acids to yield trisubstituted olefins. A variety of arylboronic acids and Baylis-Hillman adducts were converted to the corresponding trisubstituted olefins, demonstrating the versatility of the reaction. The reaction is highly stereoselective. RhFAP was recovered quantitatively by simple filtration and reused with almost consistent activity.

Nanoengineering of surface modified silica particles to form core-shell and hollow nanospheres of iron oxide.

The method of synthesizing nanoshell of alpha-Fe2O3 on silica core nanoparticle and hollow alpha-Fe2O3 nanoparticles is described. The silica particles of approximately 160 nm diameter were surface modified using 3-aminopropyltrimethoxysilane (APS) for easy adsorption of iron on it. These particles were treated with FeCl3 and further heat treated up to 1000 degrees C to get alpha-Fe2O3 shell of thickness approximately 20 nm. The hollow iron oxide particles were prepared using sacrificial core removal using dilute HF solution. The particles were characterized for their structure, morphology, bonding and surface chemistry using Transmission Electron Microscopy (TEM), X-ray Diffraction (XRD), Fourier Transform Infra Red Spectroscopy (FTIR), and X-ray Photoelectron Spectroscopy (XPS).

An efficient base-free N-arylation of imidazoles and amines with arylboronic acids using copper-exchanged fluorapatite.

N-Arylation of imidazoles and amines with arylboronic acids was accomplished with copper-exchanged fluorapatite (CuFAP) in methanol at room temperature. The products N-arylimidazoles and N-arylamines were isolated in good to excellent yields. A variety of arylboronic acids were converted to the corresponding N-arylimidazoles and N-arylamines, demonstrating the versatility of the reaction.

Enantioselective nitroaldol (Henry) reaction using copper(II) complexes of (-)-sparteine.

The dichloro[(-)-sparteine-N,N']copper(II) complex provides Henry adducts with high enantioselectivities (73-97% ee) in Henry reaction between nitromethane and various aldehydes.