Department of Chemistry

A metallaborane of novel structure, [(Cp*Mo) 2B 3H 3Se 2{Fe(CO) 2} 2{Fe(CO) 3} 2] (2; Cp* = η 5-C 5Me 5), with tetracapped pentagonal bipyramidal geometry, isolated from the reaction of [(Cp*Mo) 2B 4H 4Se 2], 1 with [Fe 2(CO) 9]; the title compound exhibit an 11-vertex closo-cage geometry, having eight skeletal electron pairs (sep) and 98 valence electrons, appropriate for its geometric structure. © The Royal Society of Chemistry 2012.

The title compound (C13H30N2O 7S) has been determined from three-dimensional X-ray diffraction data. The crystals are monoclinic, a = 22.654(8) Å, b = 8.652(4) Å, c = 23.925(9) Å, β= 123.880(9)°, V= 3893(3) Å3, Z = 8, Dcalc =1.192 g/cm3, space group C2/c. The structure was solved by direct methods and refined by full-matrix least squares method (R = 0.051). The ammonium cation is displaced by 1.08 Å from the mean plane of the ligand causing hydrogen bonding with the macrocyclic O atoms in a perching arrangement. The thiocyanate anion forms an extended hydrogen bonded chain with the cation via the occluded water molecule. © 2004 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

The “borrowing hydrogen” (BH) approach for the N-alkylation of phenylenediamines using alcohols as coupling partners is highly challenging due to the selectivity issue of the generated products. Furthermore, the development of base-metal systems that can potentially substitute precious metals with competitive activity is a major challenge in BH catalysis. We present herein an efficient protocol for the N,N′-di-alkylation of aromatic diamines using an in situ-generated Ni-NHC complex from NiCl2 and the ligand L1, which gave access to a wide range of N,N′-di-alkylated orthophenylene diamines (rather than the generally observed benzimidazole derivatives), meta- and para-phenylene diamines along with 2,6-diamino pyridine derivatives in good to excellent yields. Moreover, the catalyst system was also successful in the derivatization of a clinically important drug molecule, Dapsone. Notably, the present protocol could be applied effectively to synthesize unsymmetrically substituted N,N′-di-alkylated diamines via sequential alkylation and is the first report in the base-metal system to the best of our knowledge. Diverse control experiments including the deuterium incorporation studies suggest that the present protocol proceeds via a BH sequence.

We report on the synthesis and the characterization of a novel cobalt trimesate metal-organic framework, designated as KCL-102. Powder X-ray diffraction pattern of KCL-102 is dominated by a reflection at 10.2◦ (d-spacing = 8.7 Å), while diffuse reflectance UV-Vis spectroscopy indicates that the divalent cobalt centers are in two different coordination geometries: tetrahedral and octahedral. Further, the material shows low stability in humid air, and it transforms into the well-known phase of hydrous cobalt trimesate, Co3 (BTC)2·12H2O. We associated this transition with the conversion of the tetrahedral cobalt to octahedral cobalt.

Human intestinal bile salts are well-known for their solubilization and emulsification action in cosmetics, medicines, and chemicals. Here, an effort has been made to understand the solubilization mechanism of bioactive diet capsaicin (Cap) and indole-3-carbinol (I3C) in sodium taurocholate (NaTC) bile salt aggregates using both intrinsic and extrinsic fluorescent probes. Fluorescence study concludes that the NaTC micelle solubilizes both Cap and I3C. An increase in nonpolarity of the NaTC micellar environment is responsible for the solubilization of both Cap and I3C which is further confirmed by using an extrinsic probe Nile red (NR). Both Cap and I3C bind to the NaTC micelle as confirmed from the binding constant value. The location of both the bioactive molecules in the NaTC micelle has been confirmed from fluorescence quenching study using potassium iodide as a quencher. The effect of both I3C and Cap on the size of the NaTC micelle has been analyzed using dynamic light scattering.

The performance of semiconductor devices can be fine-tuned through chemical transformation of their nanostructured components. Such transformations are often carried out in controlled conditions. Herein, the use of electrospray deposition of metal ions from solutions in air is reported, to bring about chemical transformations across mm2-sized areas of nanostructures. This is illustrated with monolayer assemblies of ultrathin tellurium nanowires (NWs). The process does not require any reducing agent and can transform the NWs chemically, in the solid state itself, under ambient conditions. By using suitable masks, the beam of ions can be patterned to localize such transformations with nanometer precision to obtain aligned multiphasic NWs, containing atomically precise phase boundaries. By controlling the time of exposure of the spray, the scope of the process is further expanded to produce tellurium-metal telluride core–shell NWs. The method described here represents a crucial step for ambient processing of nanostructured components, useful for applications such as semiconductor device fabrication.

A series of orange-red emitting phosphor compositions Sr1.9-x Bax Eu0.05 Li0.05 MoO6 (x=0-1.9) have been synthesized and characterized by powder X-ray diffraction (XRD) and photoluminescence. XRD results reveal a phase transition from orthorhombic to pseudocubic structure for x0.2. All the compositions show broad charge-transfer band absorption in the near-ultraviolet (UV) region. Orange-red emission is observed for compositions with lower x values (x0.6), whereas orange emission is observed for compositions with higher x values. Select compositions in this system of compounds could find potential applications as orange-red phosphors for white light generation using near-UV/blue GaN -based light emitting diodes. © 2006 The Electrochemical Society.

Building upon the chemistry of Rh–N,S-heterocyclic carbene complex, [(Cp*Rh)(L2)(1-benzothiazol-2-ylidene)], 2 (Cp*=η5-C5Me5; L=C7H4NS2) with various monoboranes-Lewis adducts, we explored the chemistry of 2 with BH3⋅thf at elevated temperature. As a result, mild thermolysis of 2 with BH3⋅thf led to the formation of bis(sigma)borate [(η4-C5Me5H)Rh(η2-H3BL)], 3 and a bis-zwitterionic species [Cp*RhS(BH2L2)], 4 with the concomitant release of BH3⋅bt (bt=benzothiazole). The RhS3C2N2B2 atoms in 4 generates two six membered rings fused by a common Rh−S bond, which may be considered as a bicycle [4.4.0] cage at the rhodium center. In an effort to generate the iridium analogue of 3, reaction of [Cp*IrCl2]2 with Na[H3B(mbt)] (mbt=2-mercaptobenzothiazole) was carried out that produced bis(sigma)borate complex [(η4-C5Me5H)Ir(η2-H3BL)], 1. The solid state X-ray structures of 1 and 3 showed that the Cp*H ligand coordinated to the metal center in a η4-fashion. In compound 3, the methyl group is oriented towards rhodium center, whereas it is away from Ir center in 1. In addition, the DFT computations were performed to shed light on the bonding and electronic structures of these compounds.

The first catalytic enantioselective nitroso aldol reaction of distal dialdehydes is reported. The reaction is catalyzed by simple l-proline at room temperature and subsequent reduction delivered biologically potent and synthetically versatile N-O bond containing five- and six-membered heterocycles, 1,2-oxazinanes, and isoxazolidines in high yields and excellent enantioselectivities (up to >99% ee). The method was further exploited to prepare chiral 3-hydroxypiperidines and -pyrrolidines that are otherwise difficult to access.

A remarkable upfield shift of the pyα protons of complexed 2,2′-bipyridine in [cis-Pd(bpy)(NO3)2] is observed which is considered to originate from the anisotropic influence of suitably positioned coordinated nitrate anions around the Pd(II) centre of the molecule. A typical complexation-induced downfield shift is observed for the NH2 protons in [cis-Pd(en)(NO3)2] where 'en' stands for ethylenediamine. © 2006 Elsevier Ltd. All rights reserved.