1-Phenyl-3-{4-[4-(4-undecyl­oxybenzoyl­oxy)phenyl­oxycarbon­yl]phen­yl}triazene 1-oxide

The X-ray crystallographic study of the title compound, C37H41N3O6, at 150 K establishes the N-oxide form of the triazene 1-oxide unit. There is one intra­molecular N—H⋯O hydrogen-bonding inter­action and the crystal packing is stabilized by one N—H⋯O, three C—H⋯O and three C—H⋯π inter­molecular inter­actions. The dihedral angles between pairs of adjacent benzene rings are 14.9 (3), 56.3 (1) and 56.0 (1)

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\u27-hydroxyarenes (H 2L) have been activated by [Rh(PPh 3) 3Cl] in a toluene medium. Here the cyclometallation is accompanied by metal centered oxidation [Rh(i)?Rh(iii)]. All the resulting cyclometallates [Rh(PPh 3) 2(L)Cl] (2-5) have been isolated in a pure form. The characterization of the cyclometallates [Rh(PPh 3) 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\u27-hydroxyarenes via terdentate C(naphthyl), N(diazene), O(phenolato/ naphtholato) donor centers & one chloride ion in a plane along with two axial trans PPh 3 molecules. Intermolecular association in the solid state is observed due to C-H...p and p...p 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

Diferric Oxo-Bridged Complexes of a Polydentate Aminopyridyl Ligand: Synthesis, Structure and Catalytic Reactivity

The catalytic reactivity of a group of diferric oxo-bridged complexes (1-3) of a tetradentate ligand (bpmen = N,N\u27-dimethyl-N,N\u27-bis(2-pyridylmethyl)-1,2-diaminoethane) toward alkane hydroxylation has been evaluated. Among the three complexes, the µ-oxo diiron(III) complex [Fe(bpmen)(µ-O)FeCl3] (1) has been synthesized for the first time. The complex 1 has been characterized by spectroscopic analysis and X-ray crystallography. At room temperature, the µ-oxo diiron(III) complexes 1-3 have been found to be useful catalysts in hydroxylation of alkanes with m-chloroperbenzoic acid as oxidant. [Fe(bpmen)(µ-O)FeCl3] (1) has been found to be the most active catalyst. Moreover, the catalytic ability of the complexes in the oxidation of alcohols to ketones with hydrogen peroxide at room temperature has also been investigated

Regioselective and Regiospecific C(naphthyl)-H Bond Activation: Isolation, Characterization, Crystal Structure and TDDFT Study of Isomeric Cyclopalladates

The C2(naphthyl)-H, C3(naphthyl)-H and C8(naphthyl)-H bonds of the naphthyl group present in a group of naphthylazo-2\u27-hydroxyarenes (H2L) have been activated at room temperature by palladium(II) and stable cyclopalladates of the type [PdL(B)] have been isolated in presence of neutral Lewis bases (B). The activation of C2(naphthyl)-H and C8(naphthyl)-H bonds of 1-(2\u27-hydroxynaphthylazo) naphthalene (H2L1) lead to the formation of isomeric cyclopalladates 2a & 2b respectively. The single crystal X-ray structures of both the isomers show the naphthylazonaphtholate is coordinated to palladium(II) as a dianionic terdentate C,N,O-donor and Lewis base B occupies the fourth position in the coordination sphere. The ortho-palladate (2a) contains both five-membered carbopalladacycle and azonaphtholato chelate ring whereas a five-membered carbopalladacycle and a six-membered azonaphtholato chelate ring are present in peri-palladate (2b). On the other hand, only C3(naphthyl)-H bond of 2-(2\u27-hydroxyarylazo) naphthalene (H2L2 & H2L3) has been found to be regiospecifically activated by palladium(II). The role of auxiliary donors on the regioselective and regiospecific C(naphthyl)-H bond activation and the rationale behind the formation of isomeric cyclopalladates have been discussed. All of the cyclopalladates absorb strongly in the ultraviolet and visible region. The Time-dependent density functional theory (TDDFT) calculations reveal that the high energy absorptions are predominantly due to intraligand p-p* and the low energy absorptions originate from intraligand p-p* with a small admixture of metal-to-ligand charge-transfer transitions

Regiospecific C(naphthyl)-H Bond Activation by Platinum(II)-Isolation, Characterization, Reactivity and TD-DFT Study of the Cycloplatinate Complexes

The regiospecific activation of C(naphthyl)-H bonds in a group of naphthylazo-2\u27-hydroxyarene ligands (H2L) has been achieved by platinum(II) compounds under different reaction conditions, and stable cycloplatinates [PtIIL(D)] have been isolated in presence of neutral Lewis bases (D). Structures of the cycloplatinate complexes of platinum(II) have been established by single-crystal X-ray crystallography. the platinum(II) centres are surrounded by a C,N,O-terdentate ligand frame (L) and Lewis base (D) in a distorted square planar fashion. These cycloplatinate species have been found to react with halogens and methyl iodide undergoing metal-centered two electron oxidation affording platinum(IV) cycloplatinates with distorted octahedral geometry. in the reactions with halogens and methyl iodide, trans oxidative addition has been found for [Pt(L)D] (D = 4-picoline), whereas cis addition has been observed for [Pt(L)D] where D is a more sterically demanding triphenylphosphane. Structures of two representative platinum(IV) cycloplatinate species have been determined by single-crystal X-ray crystallography. a time dependent (TD)-DFT study of representative cycloplatinate compounds has been performed. Optical absorption spectra of the cycloplatinate compounds in dichloromethane have been simulated using the TD-DFT method, and the experimental spectra are in very good agreement

Electrochemical Generation of High-Valent Oxo-Manganese Complexes Featuring an Anionic N5 Ligand and Their Role in O―O Bond Formation

Generation of high-valent oxomanganese complexes through controlled removal of protons and electrons from low-valent congeners is a crucial step toward the synthesis of functional analogues of the native oxygen evolving complex (OEC). In-depth studies of the water oxidation activity of such biomimetic compounds help to understand the mechanism of O―O bond formation presumably occurring at the last step of the photosynthetic cycle. Scarce reports of reactive high-valent oxomanganese complexes underscores the impetus for the present work, wherein we report the electrochemical generation of the non-heme oxomanganese(IV) species, [(dpaq)MnIV(O)]+ (2), through a proton-coupled electron transfer (PCET) process from the hydroxomanganese complex [(dpaq)MnIII(OH)]ClO4 (1). Controlled potential spectroelectrochemical studies of 1 in wet acetonitrile at 1.45 V vs. NHE revealed quantitative formation of 2 within 10 min. The high-valent oxomanganese(IV) transient exhibited remarkable stability and could be reverted to the starting complex (1) by switching the potential to 0.25 V vs. NHE. The formation of 2 via PCET oxidation of 1 demonstrates an alternate pathway for the generation of the oxomanganese(IV) transient (2) without the requirement of redox-inactive metal ions or acid additives as proposed earlier. Theoretical studies predict that one-electron oxidation of [(dpaq)MnIV(O)]+ (2) forms a manganese(V)-oxo (3) species, which can be oxidized further by one-electron to a formally manganese(VI)-oxo transient (4). Theoretical analyses suggest that the first oxidation event (2 to 3) takes place at the metal-based d-orbital whereas, in the second oxidation process (3 to 4), the electron eliminates from an orbital composed of equitable contribution from metal and ligand, leaving a single electron in the quinoline-dominated orbital in the doublet ground spin state of the manganese(VI)-oxo species (4). This mixed metal- ligand (quinoline)-based oxidation is proposed to generate a formally Mn(VI) species (4), a non-heme analogue of the species ‘compound I’, formed in the catalytic cycle of cytochrome P-450. We propose that the highly electrophilic species 4 catches water during cyclic voltammetry experiments and results in O―O bond formation leading to electrocatalytic oxidation of water to hydrogen peroxide

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...&pi interactions were also detected in 1i. The intermolecular hydrogen bonding and intermolecular C-H...p interactions arrange the phenyl triazene-1-oxide fragments of the molecules in layers within the molecular assembly

Novel Synthetic Route to Liquid Crystalline 4,4\u27-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\u27-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\u27-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\u27-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

Structure of Liquid Crystalline 1-Phenyl-3-{4-[4-(4-Octyloxybenzoyloxy) Phenyloxycarbonyl]phenyl}triazene-1-Oxide At Low Temperature

The molecular structure of 1-phenyl-3-{4-[4-(4-octyloxybenzoyloxy)- phenyloxycarbonyl]phenyl}triazene-1-oxide, a member of newly developed liquid crystalline homologous series, has been investigated by crystal X-ray crystallography at low temperature (100K). The title compound crystallizes in the triclinic crystal class in the space group P[image omitted] with cell parameters a=5.766(5), b=12.151(10), c=21.751(17), =79.089(13), =88.646(14), =84.278(14), V=1489(2)3 for Z=2. It establishes the N-oxide form of the triazene-1-oxide moiety. The overall molecule is not planar, the dihedral angles between pairs of adjacent benzene rings are 14.00 (10), 52.36 (07), and 50.57 (07). Intramolecular N-HO hydrogen-bonding is present within the triazene-1-oxide moiety of the title compound. The compound forms inversion dimer via an intermolecular N-HO and an intermolecular C-HO links. The dimers are then linked into chains in a parallel fashion by C-HO hydrogen bonds. The crystal packing is further stabilized by C-H interactions