Suman Sahoo

A Highly Active Bifunctional Iridium Complex with an Alcohol/Alkoxide-Tethered N-Heterocyclic Carbene for Alkylation of Amines with Alcohols

A series of new iridium(III) complexes containing bidentate N-heterocyclic carbenes (NHC) functionalized with an alcohol or ether group (NHC-OR, R = H, Me) were prepared. The complexes catalyzed the alkylation of anilines with alcohols as latent electrophiles. In particular, biscationic Ir(III) complexes of the type [Cp*(NHC-OH)Ir(MeCN)](2+)2[BF(4)(-)] afforded higher-order amine products with very high efficiency; up to >99% yield using a 1:1 ratio of reactants and 1-2.5 mol % of Ir, in short reaction times (2-16 h) and under base-free conditions. Quantitative yields were also obtained at 50 °C, although longer reaction times (48-60 h) were needed. A large variety of aromatic amines have been alkylated with primary and secondary alcohols. The reactivity of structurally related iridium(III) complexes was also compared to obtain insights into the mechanism and into the structure of possible catalytic intermediates. The Ir(III) complexes were stable towards oxygen and moisture, and were characterized by NMR, HRMS, single-crystal X-ray diffraction, and elemental analyses.

Single Site Supported Cationic Rhodium(I) Complexes for the Selective Redox Isomerization of Allylic Alcohols

The isomerization of allylic alcohols to carbonyl compounds by a heterogeneous rhodium complex is reported. Different silica material supports and catalyst/ligand systems were evaluated. The most efficient catalyst in terms of catalytic activity and stability was found to be a cationic rhodium(I) complex with sulfonated phosphine ligands anchored on a mesoporous aluminosilica AlSBA‐15. The heterogeneous complex catalyzed the isomerization of a variety of allylic alcohols in excellent yields with very low catalyst loadings (0.5 mol %). The catalyst could be recycled without significant loss of activity or selectivity. The optimized catalyst was characterized by N2 sorption, powder X‐ray diffraction, transmission electron microscopy, as well as solution and solid‐state nuclear magnetic resonance, and Fourier Transform infrared spectroscopies.

Immobilized Molybdovanadophosphoric Acid for Selective Oxidations

In this review, we have summarized our work on the immobilization of molybdovanadophosphoric acids onto mesoporous silica and mesoporous carbon by different approaches such as amine functionalization and ionic liquid functionalization. All catalyst materials were well characterized by various ex-situ and in situ techniques for their structural integrity and physico-chemical properties. These materials were tested in different selective oxidation processes to develop environmentally benign protocols for the synthesis of fine chemicals and tried to study their mechanisms.

Supported Heteropoly Acids and Multicomponent Polyoxometalates as Eco-Friendly Solid Catalysts for Bulk and Fine Chemicals Synthesis

Supported heteropoly acids are an important class of eco-friendly solid catalysts which offer strong acidity or redox properties. Part 1 of this chapter gives the detailed description of Keggin heteropoly acids such as silicotungstic acid (STA) and phosphotungstic acid (PTA) supported on zirconia as thermally stable, reusable solid catalysts which can be used for variety of organic transformations such as alkylation, acylation, and allylation. The catalysts are characterized by various techniques such as X-ray diffraction, N2 sorption measurements, DTG–DTA, UV–Vis spectroscopy, FTIR pyridine adsorption, NH3-TPD, FT-Raman, and 31P MAS NMR. These supported HPA catalysts found to be highly active and selective with a long catalytic lifetime in the discussed reactions. Part 2 of this chapter describes the preparation of inorganic–organic hybrid materials by immobilization of molybdo-vanadophosphoric acids onto mesoporous silicas such as MCM-41, MCM-48, and SBA-15. The study has been further extended to mesoporous carbon and ethane-bridged SBA-15. All catalyst materials were characterized by elemental analysis, FTIR, N2 physisorption measurements, XRD, UV/Vis, XPS, CP-MAS-NMR, SEM, and TEM for their structural integrity and physicochemical properties. These materials were applied for various selective and controlled oxidation processes to develop environmentally benign protocols for synthesis of fine chemicals and tried to study their mechanisms. Further, a simple cation exchanged form of H5[PMo10V2O40]·32.5H2O supported on ionic liquid-modified SBA-15 (V2ILSBA) and its application in catalyzed aerobic oxidation of primary and secondary alcohols to corresponding aldehydes and ketones with no trace of over oxidation has been discussed.