Pinaki Bandyopadhyay

Aromatic hydroxylation: the direct oxidation of C–Pd into C–OPd

The C–Pd bond in cyclopalladated azobenzenes [(1) and (3)] is converted into the C–OPd function [(2) and (5)] in good yield by stoicheiometric reactions with m-chloroperbenzoic acid; in effect azobenzene is successively oxidised to 2-hydroxyazobenzene and 2,2′-hydroxyazobenzene.

Fluorescence signaling systems for sensing Hg(II) ion derived from A2B-corroles

Selective detection of Hg(II) ions in solution by a series of novel free base bis-(nitrophenyl) corroles (1-4) with general formula A(2)B (where A = nitrophenyl, and B = N,N-dimethylaminophenyl, thienyl, naphthyl and tridecyloxyphenyl group) is described. Among the free base corroles, 4, with a tridecyloxy long chain moiety, has been found to exhibit the highest Hg(II) sensing ability. The detection is based on the fluorescence quenching of the corroles, arising from the combined effect of static (coordination) and dynamic (exciplex formation) factors.

OXYGEN INSERTION INTO PALLADIUM-ARENE BONDS BY IODOSYLBENZENE

Abstract The regiospecific hydroxylation of the naphthyl ring at the C(2) position of unsymmetrical 1-(phenylazo)naphthalene 1 was achieved via oxygen atom insertion into the palladium-naphthyl bond of 2 with iodosylbenzene, followed by demetallation. The insertion of oxygen atom into the PdC(phenyl) bond of the cyclopalladated azobenzenes 5 was also achieved with iodosylbenzene.

Binuclear oxomolybdenum(V) complexes with mercaptocarboxylic acids: synthesis, characterization and electrochemistry

Abstract A number of stable bis(μ-oxo) and μ-oxo-μ-sulfido binuclear oxomolybdenum(V) complexes of the type R2[Mo2O4L2]·5H2O (1) and R2[Mo2O3SL2]·5H2O (2) with different mercaptocarboxylic acids (H2L) have been synthesized (where H2L = 2-mercaptobenzoic acid, 2-mercaptoproprionic and 3-mercaptopropionic acid, and R = Ph4P+). The complexes have been characterized by elemental analysis, conductivity measurement and spectral (IR, UV-VIS and 1H-NMR) data. The electrochemical behaviour of the complexes in DMF have also been examined by cyclic voltammetry at a glassy carbon electrode.

Cyclopalladated arylsulfides and sulfoxides: Synthesis, characterization and reactivity toward m-chloroperbenzoic acid

Abstract A number of stable di-μ-halogeno-bridged cyclopalladated complexes [Pd 2 L 2 Cl 2 ] have been synthesized (where L = arylsulfides and their corresponding sulfoxides). The cyclopalladated compounds have been characterized on the basis of elemental analysis and spectroscopic (IR, UV-vis, and 1 H and 13 C NMR) data. Regioselective aromatic metaloxylation (PdAr → PdOAr) or di-μ-halogeno-bridged cyclopalladated complexes occur with m -chloroperbenzoic acid at room temperature without any oxidation of sulfur atoms.

C(naphthyl)-H bond activation by rhodium: isolation, characterization and TD-DFT study of the cyclometallates{

The C1(naphthyl)–H, C2(naphthyl)–H, C3(naphthyl)–H and C8(naphthyl)–H bonds of the naphthyl group present in a group of naphthylazo–2′–hydroxyarenes (H2L) have been activated by [Rh(PPh3)3Cl] in a toluene medium. Here the cyclometallation is accompanied by metal centered oxidation [Rh(I)→Rh(III)]. All the resulting cyclometallates [Rh(PPh3)2(L)Cl] (2–5) have been isolated in a pure form. The characterization of the cyclometallates [Rh(PPh3)2(L)Cl] have been done on the basis of spectral (IR, UV–vis, and FAB mass) data. The structures of the representative cyclometallates 2a, 3a, 4a, 4b and 5b have been determined by X-ray diffraction. In all the cyclometallates, rhodium(III) is coordinated to naphthylazo–2′–hydroxyarenes via terdentate C(naphthyl), N(diazene), O(phenolato/ naphtholato) donor centers & one chloride ion in a plane along with two axial transPPh3 molecules. Intermolecular association in the solid state is observed due to C–H⋯π and π⋯π interactions. Compounds show an oxidative response within 0.93 to 1.11 V (vs.SCE) and a reductive response at ∼ −1.0 V (vs.SCE). Both the responses are based on the coordinated diazene function and are irreversible in nature, indicating limited stability of the oxidized and reduced species. The electronic structures of selected cyclometallates have been calculated using a TD-DFT model and the simulated spectra are consistent with the observed spectra of those cyclometallates.

A non-heme cationic Fe(III)-complex intercalated in montmorillonite K-10: synthesis, characterization and catalytic alkane hydroxylation with H2O2 at room temperature

A non-heme iron complex cis-[FeIII(cyclam)Cl2]Cl (cyclam = 1,4,8,11-tetraazacyclotetradecane) has been intercalated into smectite montmorillonite K-10. The intercalated solid has been characterized using EDXRF, AAS, TGA, PXRD, IR and UV-visible analyses. The heterogeneous iron(III)–cyclam has been found to be capable of hydroxylating C–H bonds as strong as those in cyclohexane (BDE = 99.7 kcal mol−1) using benign H2O2 at room temperature. The reactivity of the heterogeneous catalytic system is found to significantly improve in comparison with that of cis-[FeIII(cyclam)Cl2]Cl/H2O2 under homogeneous conditions. The catalytic reactions are marked by a very high selectivity for alcohols which is comparable with the best known non-heme catalysts with H2O2. The results critically reflect the role of the clay matrix surrounding the cationic metal complex in tuning the catalytic activity and selectivity of alkane hydroxylation.

Synthesis and Liquid Crystalline Properties of Novel Triazene-1-oxide Derivatives

A new group of compounds, C6H5-N(O)=N-NH-C6H4-C(O)-O-C6H4-CH=N-C6H4-OR, ( 1 ), [R = n-alkyl group; 1a (R = C7H15 ) to 1h (R = C14H29)], has been designed and synthesized to develop triazene-1-oxide based liquid crystals. All the compounds have been characterized on the basis of their spectral data. Their thermal behavior has been examined and found to exhibit thermotropic liquid crystalline behavior over a wide range of temperature. All members of this family uniformly show nematic phase behavior on melting up to the clearing point during heating as well as on phase entering up to the solidification during cooling. An odd–even effect on transition temperatures has been observed during heating as well as cooling.

Novel synthetic route to liquid crystalline 4,4′‐bis(n‐alkoxy)azoxybenzenes: spectral characterisation, mesogenic behaviour and crystal structure of two new members

A simple synthetic method has been developed for the preparation of long‐chain 4,4′‐bis(n‐alkoxy)azoxybenzenes by reductive coupling of 4‐n‐alkoxynitrobenzenes using zinc powder and ammonium chloride in aqueous ethanol medium at ambient temperature. The new method was employed to synthesise known members (n = 1–12) of the 4,4′‐bis(n‐alkoxy)azoxybenzene (C n H2n+1OPhN(O) = NPhOC n H2n+1) series and also two hitherto unknown members (n = 13–14) of the series. The new compounds were characterised using spectral (IR, UV–visible, 1H NMR and FAB‐MS) data. The mesogenic behaviour of both compounds was studied by polarising optical microscopy, differential scanning calorimetry and small‐angle X‐ray diffraction techniques. The crystal structure of 4,4′‐bis(n‐tetradecyloxy)azoxybenzene was determined using single‐crystal X‐ray diffraction data. The packing of the molecules in the crystalline state is found to be a precursor to the smectic C phase structure.

Liquid crystalline aryltriazene‐1‐oxides with two ester units: synthesis, characterisation, structure and thermal properties

A new series of mesogenic triazene‐1‐oxides, C6H5–N(O) = N–NH–C6H4–C(O)–O–C6H4–O–(O)C–C6H4–OR (1, R = n‐alkyl group from CH3 to C14H29), was designed and synthesised. All members of this new series were characterised on the basis of spectral and analytical data. The thermotropic liquid crystalline behaviour of the compounds was observed over a wide temperature range using optical microscopy. The mesophase structure was confirmed by a small‐angle X‐ray diffraction study of a representative member (1k). The molecular structure of compound 1i was determined using the single crystal X‐ray diffraction method as a representative case. Dimer formation in the solid state occurs due to intermolecular N–H…O and C–H…O interactions. Intermolecular C–H…π interactions were also detected in 1i. The intermolecular hydrogen bonding and intermolecular C–H…π interactions arrange the phenyl triazene‐1‐oxide fragments of the molecules in layers within the molecular assembly.