151 research outputs found
From Mannose to Small Amphiphilic Polyol: Perfect Linearity Leads To Spontaneous Aggregation
No full textTerminally unsaturated and diastereochemically pure polyol derived from d-mannose shows spontaneous aggregation behavior in water solution. In order to study and clarify this unforeseen phenomenon, a conformational study based on NMR spectroscopy combined with ab initio structure analysis using the COSMO-solvation model was pursued. The results, together with X-ray diffraction studies, suggest a low energy linear conformation for this particular substrate both in solid states and in solution. For such small-sized acyclic carbohydrate derivatives, the linear conformation appears to be a key prerequisite for the unusual molecular self-assembly reported herein.peerReviewe
1-{2-[4-(4-Nitrophenyl)piperazin-1-yl]ethyl}-4-aza-1-azoniabicyclo[2.2.2]octane iodide
No full textThe title compound, C18H28N5O2+·I−, was observed as a main product in an intended 1:1 reaction between 4-iodonitrobenzene and 1,4-diazabicyclo[2.2.2]octane (DABCO). In the reaction, DABCO undergoes a ring opening to yield a quaternary salt of DABCO and 1-ethyl-4-(4-nitrophenyl)piperazine with an iodide anion. The crystal structure determination was carried out as no crystal structure had been previously reported in the investigations describing the corresponding reaction with 4-chloronitrobenze. Indeed, the crystal structure of the title compound confirms the molecular composition proposed earlier for the analogous chloride salt. The cation conformation is similar to the previously reported dinitro analogue 1-{2-[4-(2,4-dinitrophenyl)piperazin-1-yl]ethyl}-4-aza-1-azoniabicyclo[2.2.2]octane chloride [Clegg et al. (2004). Acta Cryst. E60, o291–o293]. The crystal packing is dominated by cation...I− interactions in addition to weak intermolecular C—H...O2N and C—H...N interactions between the cations
Dioxomolybdenum(VI) and -Tungsten(VI) Amino Bisphenolates as Epoxidation Catalysts
No full textLow-cost metallate salts Na2MO4·2H2O (M = molybdenum, tungsten) react with a tridentate amine bisphenol bis(2-hydroxy-3-tert-butyl-5-methylbenzyl)methylamine (H2ONOtBu) under ambient conditions in acidic methanol solutions. The reactions lead to the formation of isostructural dioxo complexes [MO2(ONOtBu)(MeOH)]·MeOH in convenient yields. Spectral data as well as X-ray analyses reveal these complexes to be isostructural. Both compounds were tested as catalysts for epoxidation of olefins using cis-cyclooctene, cyclohexene, norbornene and styrene as substrates and tert-butyl hydroperoxide and hydrogen peroxide as oxidants. The molybdenum complex catalyses selectively the oxidation of cis-cyclooctene and norbornene to corresponding epoxides, whereas oxidation of cyclohexene and styrene lead low yields as the epoxidations were associated with the formation of other oxidation products. Corresponding tungsten complex shows lower activity for epoxidation of norbornene and practically no activity for other olefins. Both complexes can also catalyse the conversion of benzoin to benzil using dimethyl sulphoxide as an oxidant, while the molybdenum complex shows higher activity.peerReviewe
Oxidovanadium(V) amine bisphenolates as epoxidation, sulfoxidation and catechol oxidation catalysts
No full textAir-stable oxidovanadium(V) complexes with tetradentate amine bisphenolate ligands were made by the reaction of VOSO4·xH2O and ligand precursors in MeOH solutions. Isolated compounds were studied as catechol oxidase models as well as catalysts for epoxidation and sulfoxidation reactions. All compounds can catalyse such oxidation reactions without notable structure-activity correlations. The 51V NMR studies indicate that the complexes turn to the number of different species during the catalytic experiments.peerReviewe
The Syntheses and Vibrational Spectra of 16O- and 18O-Enriched cis-MO2 (M=Mo, W) Complexes
No full textIn this contribution, we report convenient synthetic approaches for obtaining 16O/18O‐enriched dioxidometalVI complexes, MO2(L) (W, Mo), with a linear, tetradentate amine phenolate ligand N,N′‐dimethyl‐N,N′‐bis(2‐hydroxy‐3,5‐dimethylbenzyl)ethylenediamine (H2L) and describe their characterization by IR and Raman spectroscopy complemented by DFT computational analysis. The isotopologues of WO2(L) were made of tungstenVI trisglycolate W(eg)3 (eg=1,2‐ethanediolate dianion) and ligand H2L in the presence of either H2[16O] or H2[18O], whereas Mo16O2(L) was made using Na2MoO4⋅2H2O which was converted to Mo18O2(L) by oxido substitution using H2[18O]. The complementary IR and Raman analyses show the ν(MO2)s and ν(MO2)a at 934 and 899 cm–1 for W16O2(L) and at 914 and 898 cm–1 for Mo16O2(L), respectively. In the vibrational spectra of the 18O substituted derivatives, the ν(MO2)s were shifted to lower energy by 43 cm–1 for W18O2(L) and by 41 cm–1 for Mo18O2(L) whereas asymmetric MO2 stretches in the IR were partially overlapped by an organic ligand related stretch. However, Raman spectroscopy, accompanied by DFT calculations, allowed the deciphering the ν(MO2)a shifts of 47 cm–1 for W18O2(L) and 31 cm–1 for Mo18O2(L).peerReviewe
Poly[[myy-N,N'-bis(2-hydroxyethyl)-N,N,N',N'-tetramethylpropane-1,3-diaminium-kappa2O:O']tetra-myy-bromido-dibromidodimanganese(II)]
No full textThe asymmetric unit of the title three-dimensional coordination
polymer, [Mn2Br6(C11H28N2O2)]n, consists of one MnII
cation, half of a dicationic N,N0
-bis(2-hydroxyethyl)-
N,N,N0
,N0
-tetramethylpropane-1,3-diaminium ligand (L)
(the other half being generated by a twofold rotation axis),
and three bromide ions. The MnII cation is coordinated by a
single L ligand via the hydroxy O atom and by five bromide
ions, resulting in a distorted octahedral MnBr5O coordination
geometry. Four of the bromide ions are bridging to two
adjacent MnII atoms, thereby forming polymeric chains along
the a and b axes. The L units act as links between
neighbouring Mn—(-Br)2—Mn chains, also forming a
polymeric continuum along the c axis, which completes the
formation of a three-dimensional network. Classical O—
HBr hydrogen bonds are present. The distance between
adjacent MnII atoms is 4.022 (1) A˚ .peerReviewe
Do Extremely Bent Allenes Exist?
No full textBent allenes: Theoretical calculations show that extremely bent allenes, cyclic or acyclic, adopt a ground state that only bears a formal relationship to classical allenes. Consequently, five-membered ring allenes favor a carbene-like electronic structure and formally contain a trivalent carbon(II) center.peerReviewe
Bioinspired Mo, W and V complexes bearing a highly hydroxyl- functionalized Schiff base ligand
No full textA series of bioinspired dioxidomolybdenum(vi), dioxidotungsten(vi) and oxidovanadium(v) complexes [MoO2(H2LSaltris], [WO2(H2LSaltris] and [VO(HLSaltris)](2) were prepared by the reaction of a hydroxyl-rich Schiff base proligand N-(1,3-dihydroxy-2-(hydroxymethyl)propan 2 yl) 3,5 di-tert butylsalicylaldimine (H4LSaltrisc) with metal precursors in methanol solutions. Molybdenum and tungsten complexes crystallize as mononuclear molecules, whereas the vanadium complex forms dinuclear units. From the complexes, [VO(HLSaltris)](2) shows activity in the oxidation of 4-tert-butylcatechol and 3,5-di-tert-butylcatechol, mimicking the action of the dicopper enzyme catechol oxidase
Bioinspired Mo, W and V complexes bearing a highly hydroxyl-functionalized Schiff base ligand
No full textA series of bioinspired dioxidomolybdenum(vi), dioxidotungsten(vi) and oxidovanadium(v) complexes [MoO2(H2LSaltris)], [WO2(H2LSaltris)] and [VO(HLSaltris)]2 were prepared by the reaction of a hydroxyl-rich Schiff base proligand N-(1,3-dihydroxy-2-(hydroxymethyl)propan-2-yl)-3,5-di-tert-butylsalicylaldimine (H4LSaltris) with metal precursors in methanol solutions. Molybdenum and tungsten complexes crystallize as mononuclear molecules, whereas the vanadium complex forms dinuclear units. From the complexes, [VO(HLSaltris)]2 shows activity in the oxidation of 4-tert-butylcatechol and 3,5-di-tert-butylcatechol, mimicking the action of the dicopper enzyme catechol oxidase.peerReviewe
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