We report a variety of manganese-based catalysts containing both chelating diphosphine (bis(diphenylphosphino)methane (dppm: 1, 2, and 7) or 1,2-bis(diphenylphosphino)ethane (dppe: 3)), and ...mixed-donor phosphinoamine (2-(diphenylphosphino)ethylamine (dppea: 4–6)) ligands for the upgrading of ethanol and methanol to the advanced biofuel isobutanol. These catalysts show moderate selectivity up to 74% along with turnover numbers greater than 100 over 90 h, with catalyst 2 supported by dppm demonstrating superior performance. The positive effect of substituting the ligand backbone was also displayed with a catalyst supported by C-phenyl-substituted dppm (8) having markedly improved performance compared to the parent dppm catalysts. Catalysts supported by the phosphinoamine ligand dppea are also active for the upgrading of ethanol to n-butanol. These results show that so-called PNP-pincer ligands are not a prerequisite for the use of manganese catalysts in Guerbet chemistry and that simple chelates can be used effectively.
The platinum(0)-diphosphine complex Pt(CO)(L1) (3, where L1 = 1,2-C6H4(CH2PtBu2)2) and its diphosphinite analogue Pt(CO)(L2) (11, where L2 = 1,2-C6H4(OPtBu2)2) act as Lewis bases in conjunction ...with the main group Lewis acid B(C6F5)3 to form frustrated or cooperative Lewis pairs. These systems activate dihydrogen, ethene/carbon monoxide, and phenylacetylene, leading to products that depend on the exact ligand used. These subtle changes to ligand structure influence reactivity, most notably in hydrogen activation where a variety of dinuclear species of the type (diphos)Pt(μ-H)3Pt(diphos)+ or (diphos)Pt(μ-H)(μ-CO)Pt(diphos)+ are observed. Activation of ethene with the Lewis pair leads to a previously reported coupling product and the mechanism is probed. The basicity of Pt(CO)(L) is demonstrated by deprotonation of phenylacetylene. Preliminary studies with an analogous palladium complex Pd(CO)(L1) 33 suggests related chemistry may be exploited for this metal. These results provide further examples of cooperative Lewis pair behavior in which one of the components is based on a transition metal complex.
Hydrogen bonding with fluoride is a key interaction encountered when analyzing the mode of action of 5′-fluoro-5′-deoxyadenosine synthase, the only known enzyme capable of catalyzing the formation of ...a C–F bond from F–. Further understanding of the effect of hydrogen bonding on the structure and reactivity of complexed fluoride is therefore important for catalysis and numerous other applications, such as anion supramolecular chemistry. Herein we disclose a detailed study examining the structure of 18 novel urea–fluoride complexes in the solid state, by X-ray and neutron diffraction, and in solution phase and explore the reactivity of these complexes as a fluoride source in SN2 chemistry. Experimental data show that the structure, coordination strength, and reactivity of the urea–fluoride complexes are tunable by modifying substituents on the urea receptor. Hammett analysis of aryl groups on the urea indicates that fluoride binding is dependent on σp and σm parameters with stronger binding being observed for electron-deficient urea ligands. For the first time, defined urea–fluoride complexes are used as fluoride-binding reagents for the nucleophilic substitution of a model alkyl bromide. The reaction is slower in comparison with known alcohol–fluoride complexes, but SN2 is largely favored over E2, at a ratio surpassing all hydrogen-bonded complexes documented in the literature for the model alkyl bromide employed. Increased second-order rate constants at higher dilution support the hypothesis that the reactive species is a 1:1 urea–fluoride complex of type UF− (U = urea) resulting from partial dissociation of the parent compound U2F−. The dissociation processes can be quantified through a combination of UV and NMR assays, including DOSY and HOESY analyses that illuminate the complexation state and H-bonding in solution.
We report intermolecular transition metal frustrated Lewis pairs (FLPs) based on zirconocene aryloxide and phosphine moieties that exhibit a broad range of small molecule activation chemistry that ...has previously been the preserve of only intramolecular pairs. Reactions with D2, CO2, THF, and PhCCH are reported. By contrast with previous intramolecular examples, these systems allow facile access to a variety of steric and electronic characteristics at the Lewis acidic and Lewis basic components, with the three-step syntheses of 10 new intermolecular transition metal FLPs being reported. Systematic variation to the phosphine Lewis base is used to unravel steric considerations, with the surprising conclusion that phosphines with relatively small Tolman steric parameters not only give highly reactive FLPs but are often seen to have the highest selectivity for the desired product. DOSY NMR spectroscopic studies on these systems reveal for the first time the nature of the Lewis acid/Lewis base interactions in transition metal FLPs of this type.
A library of novel dispiro compounds containing oxindole-pyrrolo-carbazole hybrid frame works has been synthesized in a fully regio- and stereoselective fashion by the three-component 1,3-dipolar ...cycloaddition of azomethineylides generated in situ from the condensation of isatins and benzylamine with 2-arylidene/heteroarylidene-2,3,4,9-tetrahydro-1H-carbazole-1-one. The structures of the compounds were established by FT-IR, 1H NMR, 13C NMR, X-ray diffraction and elemental analysis. The synthesized dispiro heterocycles have been screened for in vitro cytotoxic activity by MTT assay and displayed enviable growth inhibition on both the cancer cell lines i.e. breast cancer cell line MCF-7 and lung cancer cell line A-549. Morphological changes and apoptosis induction have been studied by inverted light microscopic, fluorescent microscopic techniques and by flow cytometry analyses. The preliminary structure activity relationships were also carried out. Data indicated that among dispiro-carbazole compounds,6-chloro-4'-(thiophen-2-yl)-5′-phenyl-3,4-dihydrodispirocarbazole-2,3′-pyrrolo-2′,3″-indole-9(H)-1,2″-dione 7e could be exploited as a significant therapeutic drug against breast cancer as well as lung cancer cell proliferation.
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•The dispiro hybrid compounds were synthesized in a fully regio- and stereoselective fashion.•Compounds showed selective growth inhibition on both MCF-7 cell line and A-549 cell line.•Tested cells were visualized using fluorescent microscopic technique.•The preliminary structure activity relationships were also established.•Chloro substituted dispirooxindole-pyrrolo-carbazole exploited as a significant therapeutic drug.
A variety of conceptions of qualitative research exist. This leads to a situation in which there are competing claims as to what counts as good-quality work. These competing claims revolve around the ...issue of criteria and how they are used to pass judgment on qualitative research. Those involved in sport and exercise sciences need to reflect on this issue with a view to generating further dialogue and a greater understanding of difference within the research community.
Two ideal types of researcher, one a criteriologist the other a relativist, are constructed to illustrate how each might judge qualitative studies of different kinds.
A comparison of the ways in which the criteriologist and the relativist draw on different assumptions to judge qualitative studies illustrates the constraining nature of the former and the expansive possibilities of the latter.
Criteria should be viewed as lists of characterizing traits that are open to reinterpretation as times, conditions, and purposes change. Researchers need to adopt the role of connoisseur in order to pass judgment on different kinds of study in a fair and ethical manner.
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•New Cu(II) complexes characterized.•DNA/Protein binding studies carried out.•Cytotoxicity studies against human cancer cell lines done.
A Cu(II) complex was obtained from the ...reaction of 4-(diethylamino)-3-quinolin-3-ylimino-methyl-2-phenol with CuCl2(PPh3)2. The ligand coordinated to the metal ion in a monobasic bidentate fashion. The molecular structure of the complex has been confirmed by single crystal X-ray diffraction. Both the ligand and complex were characterized by various spectroscopic techniques. Using the UV-visible and fluorescence spectroscopic studies, the binding interactions of the compounds with CT-DNA and bovine serum albumin protein were evaluated. The results indicated that the compounds are efficient DNA/protein binders. The cytotoxicity of the ligand and complex against A549 (lung cancer) and MCF7 (breast cancer) cell lines was also investigated in vitro conditions using the MTT assay method which showed significant anticancer activity.
Claisen-Schmidt condensation of 2,3,4,9-tetrahydro-1H-carbazol-1-one with 3-bromo-4-methoxy benzaldehyde afforded the 2-(3'-bromo-4'-methoxybenzylidene)-2,3,4,9-tetrahydro-1H-carbazol-1-one 3. ...Compound 3 was allowed to react with different organic reactants, hydroxylamine hydrochloride, malononitrile and guanidine nitrate through condensation cum cycloaddition reactions to afford a series of the respective novel hetero annulated carbazoles such as isoxazolo-, pyrido- and pyrimido carbazoles. The structures of the compounds were established by FT-IR, 1H NMR, 13C NMR, X-ray diffraction and elemental analysis. The compounds have been screened for in vitro anti-tumor activity by MTT assay and displayed enviable selective growth inhibition on MCF-7 cell line compared to A-549 cell line. Apoptotic morphological changes in MCF-7 and A-549 cells were visualized using fluorescent microscopic technique. The preliminary structure activity relationships were also carried out. Data pointed out that among pyrimido carbazole compounds, 2-amino-4-(3'-bromo-4'-methoxyphenyl)-8-chloro-11H-pyrimido 4,5-acarbazole could be exploited as an excellent therapeutic drug against cancer cell proliferation.
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•Compounds showed selective growth inhibition on MCF-7 compared to A-549 cell line.•Tested cells were visualized using fluorescent microscopic technique.•The preliminary structure activity relationships were also carried out.•Chloro substituted pyrimidocarbazole exploited as an excellent therapeutic drug.
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