Showing papers on "Pyridine published in 2008"
TL;DR: A review of the catalytic activity of metal complexes of binaphthyl compounds and their combinations with salen Schiff base is presented in this paper, where the pyridyl bis (imide) and pyridine bis(imine) complexes of cobalt(II), iron(II) ions have been used as catalysts in the polymerization of ethylene and propylene.
1,237 citations
TL;DR: Partly ordered mesoporous alumina with hydrous aluminum nitrate as the precursor exhibits reactant size selectivity in hydrogenation of acetone, D-glucose, and D-(+)-cellobiose as a test reaction, indicating the potential applications in shape-selective catalysis.
Abstract: The facile synthesis of highly ordered mesoporous aluminas with high thermal stability and tunable pore sizes is systematically investigated. The general synthesis strategy is based on a sol-gel process associated with nonionic block copolymer as templates in ethanol solvent. Small-angle XRD, TEM, and nitrogen adsorption and desorption results show that these mesoporous aluminas possess a highly ordered 2D hexagonal mesostructure, which is resistant to high temperature up to 1000 degrees C. Ordered mesoporous structures with tunable pore sizes are obtained with various precursors, different acids as pH adjustors, and different block copolymers as templates. These mesoporous aluminas have large surface areas (ca. 400 m2/g), pore volumes (ca. 0.70 cm3/g), and narrow pore-size distributions. The influence of the complexation ability of anions and hydro-carboxylic acid, acid volatility, and other important synthesis conditions are discussed in detail. Utilizing this simple strategy, we also obtained partly ordered mesoporous alumina with hydrous aluminum nitrate as the precursor. FTIR pyridine adsorption measurements indicate that a large amount of Lewis acid sites exist in these mesoporous aluminas. These materials are expected to be good candidates in catalysis due to the uniform pore structures, large surface areas, tunable pore sizes, and large amounts of surface Lewis acid sites. Loaded with ruthenium, the representative mesoporous alumina exhibits reactant size selectivity in hydrogenation of acetone, D-glucose, and D-(+)-cellobiose as a test reaction, indicating the potential applications in shape-selective catalysis.
615 citations
TL;DR: Two catalytic protocols of the oxidative C-C bond formation have been developed on the basis of the C-H bond activation of pyridine N-oxides and their corresponding ortho-alkenylated N-oxide derivatives are obtained in good to excellent yields.
Abstract: Two catalytic protocols of the oxidative C−C bond formation have been developed on the basis of the C−H bond activation of pyridine N-oxides. Pd-catalyzed alkenylation of the N-oxides proceeds with excellent regio-, stereo-, and chemoselectivity, and the corresponding ortho-alkenylated N-oxide derivatives are obtained in good to excellent yields. Direct cross-coupling reaction of pyridine N-oxides with unactivated arene was also developed in the presence of Pd catalyst and Ag oxidant, which affords ortho-arylated pyridine N-oxide products with high site-selectivity.
605 citations
TL;DR: A general method for copper-catalyzed arylation of sp (2) C-H bonds with p K a's below 35 has been developed and two arylcopper-phenanthroline complex intermediates were independently synthesized.
Abstract: A general method for copper-catalyzed arylation of sp2 C−H bonds with pKaʼs below 35 has been developed. The method employs aryl halide as the coupling partner, lithium alkoxide or K3PO4 base, and DMF, DMPU, or mixed DMF/xylenes solvent. A variety of electron-rich and electron-poor heterocycles such as azoles, caffeine, thiophenes, benzofuran, pyridine oxides, pyridazine, and pyrimidine can be arylated. Furthermore, electron-poor arenes possessing at least two electron-withdrawing groups on a benzene ring can also be arylated. Two arylcopper−phenanthroline complex intermediates were independently synthesized.
520 citations
TL;DR: In this paper, the authors evaluate the hierarchy of supramolecular heterosynthons that involve two of the most relevant functional groups in the context of active pharmaceutical ingredients, carboxylic acids and alcohols, in competitive environments.
Abstract: A Cambridge Structural Database (CSD) analysis was conducted in order to evaluate the hierarchy of supramolecular heterosynthons that involve two of the most relevant functional groups in the context of active pharmaceutical ingredients, carboxylic acids and alcohols, in competitive environments. The study revealed that 34% of the 5690 molecular carboxylic acid entries and 26% of the 25 035 molecular alcohol entries form supramolecular homosynthons, whereas the remaining entries form supramolecular heterosynthons with other functional groups, in particular Narom, CONH2, C−O−C, C═O, and chloride anions. Further refinement of this raw data revealed the following: 98% occurrence of the COOH···Narom supramolecular heterosynthon in the 126 crystal structures that contain acid and pyridine moieties in the absence of other hydrogen bond donors or acceptors; and 78% occurrence of the OH···Narom supramolecular heterosynthon in 228 crystal structures that contain hydroxyl and pyridine moieties (excluding intramolec...
402 citations
TL;DR: The C-2 selective alkenylation of pyridine derivatives is achieved with a catalyst consisting of nickel and Lewis acid, demonstrating a broad substrate scope and proceeds with high chemo-, regio-, and stereoselectivities under mild conditions compared with previous examples of direct C−H functionalization of p Pyridines.
Abstract: The C-2 selective alkenylation of pyridine derivatives is achieved with a catalyst consisting of nickel and Lewis acid. Use of diorganozinc compounds as the Lewis acid catalyst gives C-2 monoalkenylation products, whereas AlMe3 changes the reaction course to afford C-2 dienylated products, which are derived from double insertion of alkynes into the C(2)−H bond. The reaction demonstrates a broad substrate scope and proceeds with high chemo-, regio-, and stereoselectivities under mild conditions compared with previous examples of direct C−H functionalization of pyridines.
366 citations
359 citations
TL;DR: In this paper, a rhodium-catalyzed chelation-assisted C-H activation of alpha, β-unsaturated ketoximes and the reaction with alkynes to afford highly substituted pyridine derivatives is described.
279 citations
TL;DR: The synthesis, spectroscopy, and X-ray diffraction analysis of a discrete iron nitride complex stabilized by the sterically encumbering Nanchored tris(carbene) ligand are presented, enabling the first room-temperature spectroscopic characterization of a terminal Fe nitride species.
Abstract: Coordination compounds of iron in high oxidation states have been invoked as reactive intermediates in biocatalyses. Iron(IV) ferryl species are examples of such highly reactive species that have long been known to be at the catalytic centers of oxygenases. Supported by X-ray diffraction studies on nitrogenase, the iron nitride moiety has recently been suggested to be present at the site of biological nitrogen reduction. As a result, well-characterized high-valent iron complexes have been sought as biomimetic models for transformations mediated by iron-containing enzymes. To gain understanding of iron nitride reactivity and the possible role of such species in biocatalysis, insight into the molecular structure of complexes stabilizing the [FeN] synthon is highly desirable. Whereas significant progress has been made in the synthesis and spectroscopic elucidation of Fe=NR and Fe N species, X-ray crystallographic characterization of a complex with a terminal Fe N functionality has not been accomplished. The first mononuclear Fe=O entity crystallographically characterized was stabilized in an octahedral environment provided by a macrocyclic tetra-N-methylated cyclam ligand. Similar cyclam derivatives also allow the stabilization and detailed spectroscopic characterization of octahedral Fe and Fe nitride complexes in unusually high oxidation states. 10] Recently, Peters and Betley developed a stunningly redox-rich iron system employing the tripodal tris(phosphino)borate ligand system (PhBP3 ), which stabilizes tetrahedral L3Fe=Nx species in oxidation states ranging from + I to + IV. Remarkably, this ligand system enabled the first room-temperature spectroscopic characterization of a terminal Fe nitride species. Concentration-dependent coupling to the Fe-N2-Fe I dinuclear product, however, prevents crystallization of this nitride species. We herein present the synthesis, spectroscopy, and most significantly, the X-ray diffraction analysis of a discrete iron nitride complex stabilized by the sterically encumbering Nanchored tris(carbene) ligand, tris[2-(3-aryl-imidazol-2-ylidene)ethyl]amine (TIMEN, R= xylyl (xyl), mesityl (mes)). Structurally and electronically related to the tetrahedral phosphinoborate ligand system by Peters and Betley, this tripodal N-heterocyclic carbene (NHC) system coordinates a high-spin Fe center in a trigonal-planar fashion, thus forming four-coordinate complexes with the metal ion in trigonalpyramidal environments. Under inert atmosphere, treatment of TIMEN with one equivalent of anhydrous ferrous chloride in pyridine at room temperature yields the four-coordinate Fe complexes [(TIMEN)Fe(Cl)]Cl (1, 1) as analytically pure, white powders in 80% yield (Scheme 1).
203 citations
199 citations
TL;DR: Bis(imino)pyridine iron dinitrogen and dialkyl complexes are well-defined precatalysts for the chemo- and regioselective reduction of aldehydes and ketones, representing one of the most active iron-catalyzed carbonyl reductions reported to date.
TL;DR: The reaction of pyridine-2,6-dicarboxylic acid (H2PDA) and oxalic acid with Ln2O3/Ce(NO3)3 under hydrothermal conditions generated a series of new one-, two-, and three-dimensional (1D, 2D,...
Abstract: The reaction of pyridine-2,6-dicarboxylic acid (H2PDA) and oxalic acid (H2ox) with Ln2O3/Ce(NO3)3 under hydrothermal conditions generated a series of new one-, two-, and three-dimensional (1D, 2D, ...
TL;DR: This new methodology was successfully applied to the short synthesis of norchelerythrine and found that either acidic or basic reaction conditions, depending on the reactivity of the substrate, could be applied to smoothly convert the azide starting materials into the desired isoquinoline products in moderate to good yields.
Abstract: The reaction of 2-alkynyl-1-methylene azide aromatics 1 with iodine and/or other iodium donors, such as the Barluenga reagent (Py2IBF4/HBF4) and NIS, gave highly substituted cyclization products, namely, the 1,3-disubstituted 4-iodoisoquinolines 2, in good to high yields. Not only simple 2-alkynyl benzyl azides 1a-j and their substituted analogues 1k-u and 6 but also heteroaromatic analogues, including pyridine 8, pyrroles 10a-c, furane 10d, and thiophenes 10e-g, gave the corresponding isoquinoline derivatives in excellent to allowable yields. Electron-donating and electron-accepting substituents on the aromatic ring were equally tolerated, and either acidic or basic (or even neutral) reaction conditions, depending on the reactivity of the substrate, could be applied to smoothly convert the azide starting materials into the desired isoquinoline products in moderate to good yields. Limits were found only in connection with the substituent at the alkyne terminus, where electron-neutral or electron-donating substituents are clearly favored. The iodine-mediated electrophilic cyclization of 1 most probably proceeds through the iodonium ion intermediate 4 followed by nucleophilic cyclization of the azide and subsequent elimination of N2. This new methodology was successfully applied to the short synthesis of norchelerythrine.
TL;DR: The functional group tolerance and substrate scope for bis(imino)pyridine iron catalyzed olefin hydrogenation have been examined in this paper, where the observed turnover frequencies increase with steric protection of the nitrogen donor.
TL;DR: The first class of luminescent biotinylation reagents derived from rhenium(I) polypyridine complexes displayed intense and long-lived orange-yellow to greenish-yellow emission upon irradiation in aqueous buffer under ambient conditions.
Abstract: We report here the design of the first class of luminescent biotinylation reagents derived from rhenium(I) polypyridine complexes. These complexes [Re(N−N)(CO)3(py-biotin-NCS)](PF6) (py-biotin-NCS = 3-isothiocyanato-5-(N-((2-biotinamido)ethyl)aminocarbonyl)pyridine; N−N = 1,10-phenanthroline (phen) (1a), 3,4,7,8-tetramethyl-1,10-phenanthroline (Me4-phen) (2a), 4,7-diphenyl-1,10-phenanthroline (Ph2-phen) (3a)), containing a biotin unit and an isothiocyanate moiety, have been synthesized from the precursor amine complexes [Re(N−N)(CO)3(py-biotin-NH2)](PF6) (py-biotin-NH2 = 3-amino-5-(N-((2-biotinamido)ethyl)aminocarbonyl)pyridine; N−N = phen (1c), Me4-phen (2c), Ph2-phen (3c)). To investigate the amine-specific reactivity of the isothiocyanate complexes 1a−3a, they have been reacted with a model substrate ethylamine, resulting in the formation of the thiourea complexes [Re(N−N)(CO)3(py-biotin-TU-Et)](PF6) (py-biotin-TU-Et = 3-ethylthioureidyl-5-(N-((2-biotinamido)ethyl)aminocarbonyl)pyridine; N−N = phen (1b...
TL;DR: An unrestricted density functional theory indicates that the dd state, in which both the Ir-N (pyrazolyl) bond lengths increase considerably, exists almost at the same energy as that for the phosphorescent state.
Abstract: Novel neutral mixed-ligand Ir(N∧C∧N)(N∧C)X complexes (N∧C∧N = 1,3-bis(3-methylpyrazolyl)benzene (bpzb), 1,5-dimethyl-2,4-bis(3-methylpyrazolyl)benzene (dmbpzb), and 1,5-difluoro-2,4-bis(3-methylpyrazolyl)benzene (dfbpzb); N∧C = 2-phenyl pyridine (ppy); and X = Cl or CN) have been synthesized and characterized. An X-ray single-crystal structure of the complex Ir(dmbpzb)(ppy)Cl shows that the nitrogen atom in the ppy ligand occupied the trans position to the carbon atom in the tridentate N∧C∧N ligand of dmbpzb with the Ir−C bond length of 1.94(1) A, whereas the coordinating carbon atom occupied the trans position of chlorine. Electrochemical data show that the complexes exhibit an oxidation Ir(III/IV) process in the potential range of +0.5∼0.9 V and two irreversible reductions at approximately −2.6 and −3.0 V against Fc0/Fc+, respectively. All of the Ir(III) complexes do not emit phosphorescence at room temperature, although strong phosphorescence is exhibited at 77 K with the 0−0 transition centered at aro...
TL;DR: In this paper, three new Re(CO)3Cl complexes (ReL1−ReL3) containing the N,N-bidentate ligands 1-(2-pyridyl)-3-phenylimidazo[1,5-a]pyridine (L1), 1-( 2-polytetrameric)-3-(4-tert-butylphenyl)imidazo [1, 5-a]-polyteneric (PTHI), and 1-(1.5)-dimethylaminophen
TL;DR: A model for the surface ligand composition could be developed for nanoparticles prepared using technical grade TOPO or other high-boiling solvents with added acidic phosphorus compounds.
Abstract: The surface ligand composition of CdSe nanoparticles prepared using technical grade tri-n-octylphosphine oxide (TOPO) was investigated using a nucleophilic ligand displacement methodology and 31P {1H} NMR spectroscopy. 4-(N,N-Dimethylamino)pyridine (DMAP) and benzyltrimethylammonium propionate were added to tetrahydrofuran solutions of CdSe nanoparticles prepared in technical grade TOPO. DMAP was shown to be a sufficiently strong nucleophile to displace the more weakly coordinating ligands, TOPO, TOPSe, di-n-octylphosphinate, and n-octylphosphonate (OPA). Benzyltrimethylammonium propionate was shown to be a stronger nucleophile than DMAP in that it could displace all the aforementioned surface-bound ligands as well as a previously unidentified surface-bound phosphorus species. Independent synthesis and 31P {1H} NMR spectral matching confirmed that the new species was P,P′-(di-n-octyl) dihydrogen pyrophosphonic acid (PPA). The PPA was shown to form during the nanoparticle synthesis via the dehydrative cond...
TL;DR: In this article, two new zeolites SSZ-33 and SSZ35 were investigated with respect to their acidic properties using different probe molecules to characterize the accessibility and acid strength of Lewis and Bronsted acid sites.
Abstract: Two novel zeolites SSZ-33 and SSZ-35 were investigated with respect to their acidic properties using different probe molecules to characterize the accessibility and acid strength of Lewis and Bronsted acid sites. Ammonia, pyridine, pivalonitrile, and acetonitrile-d 3 were used as probe molecules, and the results were correlated with 27 Al and 'H magic angle spinning (MAS) NMR. Both SSZ-33 and SSZ-35 zeolites were found to possess bridging Si-OH-Al groups of virtually uniform and high acid strength. For both SSZ-33 and SSZ-35, there is the typical presence of highly disturbed OH groups (IR band around 3500 cm -1 ), which amounts to almost half of the overall Bronsted acidity. It was found that almost all bridging Si-OH-Al groups in SSZ-33 are located in the 12-MR rings. Both acetonitrile-d 3 and pyridine sorptions suggest the presence of two types of Lewis sites in SSZ-35, differing in acid strength and electron-acceptor properties, whereas in the SSZ-33 zeolite only one type is present. The relative strength of these sites is higher than that of the Bronsted type for SSZ-35 and is of comparable strength for SSZ-33. 1 H and 27 Al MAS NMR measurements during thermal treatment allowed the assignment of NMR peaks to different surface OH species and the establishment of their relation to IR bands. NMR spectroscopy enabled the quantitative analysis of both free and hydrogen-bonded OH groups separately, showing that for both zeolites the amount of disturbed sites is higher than the number of free OH groups.
TL;DR: The results indicate that enhancement of the emission properties in pyridine is due to faster radiative rate related to formation of asymmetrical nine-coordinated structure, Sm(hfa)3(phen)(py) (py = p Pyridine).
Abstract: The effect of solvent molecule on the emission properties of Sm(hfa)3(phen)2 (hfa = hexafluoroacetylacetonato, phen = phenanthoroline) was investigated using acetone, acetonitrile, and pyridine. 5G(5/2) --> 5H(9/2) transition intensities in pyridine were found to be larger than those in corresponding acetone and acetonitrile. The radiative rate constant in pyridine (4.8 x 10(2) s(-1)) was 2 times larger than those in acetonitrile (2.6 x 10(2) s(-1)) and acetone (2.3 x 10(2) s(-1)), although the nonradiative transition via vibrational relaxation (k(nr) = 1.7 x 10(4) s(-1)) in pyridine was the same as those in acetone and acetonitrile (k(nr) = 1.8 x 10(4) s(-1)), resulting in the enhanced emission quantum yield of Sm(III) complex in pyridine (2.7%). The coordination structures of Sm(hfa)3(phen)2 in acetonitrile, acetone, and pyridine were estimated by X-ray single-crystal analyses. These results indicate that enhancement of the emission properties in pyridine is due to faster radiative rate related to formation of asymmetrical nine-coordinated structure, Sm(hfa)3(phen)(py) (py = pyridine).
TL;DR: Zr-TUD-1 is a Lewis acidic, stable and recyclable catalyst for the Meerwein-Ponndorf-Verley (MPV) reaction and for the Prins reaction.
Abstract: A three-dimensional, mesoporous, silicate containing zirconium, Zr-TUD-1, was synthesized by a direct hydrothermal treatment method with triethanolamine as a complexing and templating reagent to ensure that zirconium was incorporated as isolated atoms. The mesoporosity of Zr-TUD-1 was confirmed by X-ray diffraction (XRD), N(2) sorption and high-resolution transmission electron micrograph (HR-TEM) studies. The nature and strength of the Lewis acid sites present in Zr-TUD-1 were evaluated by FTIR studies of pyridine adsorption and temperature-programmed desorption of ammonia. FTIR, X-ray photoelectron spectroscopic (XPS) and UV/Vis spectroscopic studies showed that, at Si/Zr ratios of 25 and higher, all the zirconium was tetrahedrally incorporated into the mesoporous framework, while at low Si/Zr ratios, a small part of the zirconium was present as ZrO(2) nanoparticles. Zr-TUD-1 is a Lewis acidic, stable and recyclable catalyst for the Meerwein-Ponndorf-Verley (MPV) reaction and for the Prins reaction.
TL;DR: In this article, a variety of functionalized (hetero)aryl bromides, bearing either electron-withdrawing or electron-releasing substituents, can be employed for direct arylations of pyridine, oxazoline, pyrazole, or ketimine derivatives as pronucleophiles.
TL;DR: Two new trans- and cis-[(NHC)(2)PdX(2)] (X=Cl, Br) complexes of N/O-functionalized N-heterocyclic carbenes employed in a highly convenient amine-free Sonogashira cross-coupling reaction in air in a polar mixed aqueous medium are reported.
Abstract: Two new trans- and cis-[(NHC)(2)PdX(2)] (X=Cl, Br) complexes of N/O-functionalized N-heterocyclic carbenes employed in a highly convenient amine-free Sonogashira cross-coupling reaction in air in a polar mixed aqueous medium are reported. Specifically, the trans-[{1-benzyl-3-(3,3-dimethyl-2-oxobutyl)imidazol-2-ylidene}(2)PdBr(2)] (3) and cis-[{1-benzyl-3-(N-tert-butylacetamido)imidazol-2-ylidene}(2)PdCl(2)] (4) complexes effectively catalyzed the Sonogashira cross-coupling reaction of aryl iodides with substituted acetylenes in air in a mixed solvent (DMF/H(2)O, 3:1 v/v) under amine-free conditions. Interestingly, these trans- and cis-[(NHC)(2)PdX(2)] (X=Cl, Br) complexes, with two N-heterocyclic carbene ligands, exhibited superior activity compared with the now popular PEPPSI (pyridine enhanced precatalyst preparation, stabilization and initiation)-themed analogues, trans-[(NHC)Pd(pyridine)X(2)] (X=Cl, Br), 3 a and 4 a, with one N-heterocyclic carbene ligand and a "throw away" pyridine ligand in a trans disposition to each other. The higher activities of 3 and 4 compared with PEPPSI analogues 3 a and 4 a are attributed to more-electron-rich metal centers, as revealed by DFT studies, in the former complexes and is in concurrence with a more electron-rich metal center being effective in facilitating the oxidative addition of aryl halide, often a rate-determining step in palladium-mediated cross-coupling reactions. Complexes 3 and 4 were prepared from the corresponding silver analogues by transmetalation with [(cod)PdCl(2)], whereas the corresponding PEPPSI analogues 3 a and 4 a were obtained directly from the imidazolium halide salts by reaction with PdCl(2) in pyridine in the presence of K(2)CO(3) as base.
TL;DR: The key to the high activity of the Pd-phosphine catalyst is the rational design of the reaction parameters, the presence of water in the reaction mixture, good solubility of reactants and catalyst in n-butanol/water (3:1), and the electron-rich and sterically demanding nature of the phosphine ligand.
Abstract: A dicyclohexyl(2-sulfo-9-(3-(4-sulfophenyl)propyl)-9H-fluoren-9-yl)phosphonium salt was synthesized in 64% overall yield in three steps from simple commercially available starting materials. The highly water-soluble catalyst obtained from the corresponding phosphine and [Na(2)PdCl(4)] enabled the Suzuki coupling of a broad variety of N- and S-heterocyclic substrates. Chloropyridines (-quinolines) and aryl chlorides were coupled with aryl-, pyridine- or indoleboronic acids in quantitative yields in water/n-butanol solvent mixtures in the presence of 0.005-0.05 mol % of Pd catalyst at 100 degrees C, chloropurines were quantitatively Suzuki coupled in the presence of 0.5 mol % of catalyst, and S-heterocyclic aryl chlorides and aryl- or 3-pyridylboronic acids required 0.01-0.05 mol % Pd catalyst for full conversion. The key to the high activity of the Pd-phosphine catalyst is the rational design of the reaction parameters (i.e., the presence of water in the reaction mixture, good solubility of reactants and catalyst in n-butanol/water (3:1), and the electron-rich and sterically demanding nature of the phosphine ligand).
TL;DR: A catalytic asymmetric Henry reaction has been developed with use of a sulfonyldiamine-CuCl complex as a catalyst and a series of new binaphthyl-containing sulfonyndiamine ligands were readily synthesized in two steps starting from commercially available chiral 1,2-diamines.
Abstract: A catalytic asymmetric Henry reaction has been developed with use of a sulfonyldiamine−CuCl complex as a catalyst. A series of new binaphthyl-containing sulfonyldiamine ligands (2a−h) were readily synthesized in two steps starting from commercially available chiral 1,2-diamines. The (R,R)-diamine-(R)-binaphthyl ligand (2d)−CuCl complex smoothly catalyzed the enantioselective Henry reaction with the assistance of pyridine to give the corresponding adduct with high enantiomeric excess (up to 93%). Moreover, the 2d−CuCl−pyridine system promotes the diastereoselective Henry reaction in syn-selective manner to give the adduct in up to 99% yield with 92:8 syn/anti selectivity. The enantiomeric excess of the syn-adduct was 84% ee.
TL;DR: In this paper, the pyridine adsorption/DRIFTS technique was used to remove weak, medium strong, and strong Lewis acid sites and recover the surface of the original alumina.
Abstract: γ-Alumina surfaces pretreated at different temperatures (25 to 450 °C) and their rehydration after pyridine adsorption were studied using the conventional pyridine adsorption/DRIFTS technique. The results show that hydration at ambient temperature cannot convert all of the surface-coordinatived unsaturated Al sites to six-coordination, and weak and medium strong Lewis acid sites can still be observed for the fully hydrated γ-alumina. Dehydration at above 200 °C starts to generate strong Lewis acid sites. The number of weak, medium strong, and strong Lewis acid sites changes with dehydration temperature and all types of Lewis acid sites have adjacent OH groups. A good correlation between the number of Lewis acid sites and the intensity of perturbed OH groups is observed. Rehydration of the pyridine-adsorbed 450 °C pre-dehydrated alumina leads to removal of the pyridine adsorbed on the strong and medium strong Lewis acid sites and recovery of the surface of the original alumina. Water cannot replace the pyr...
TL;DR: In this article, a new family of neutral heteroleptic Ir(F2ppy)2L (F 2ppy = 2-(2,4-difluorophenyl)pyridine) complexes bearing different triazole derivatives (L = 2,2,3-triazol-5-yl) pyridine as the third ligand were used for the first time as ancillary ligands in iridium(III) complexes, and the results indicate that such molecules are good candidates as blue and green-emitting dopants in LED devices
Abstract: We report on the study of a new family of neutral heteroleptic Ir(F2ppy)2L (F2ppy = 2-(2,4-difluorophenyl)pyridine) complexes bearing different triazole derivatives (L = 2-(1,2,3-triazol-5-yl)pyridine) as the third ligand. Two of these ligands were used for the first time as ancillary ligands in iridium(III) complexes. A full photophysical and electrochemical study of these complexes is reported here, together with theoretical investigations at the density functional theory (DFT) level. The complexes were also obtained as single crystals and their structures were determined by X-ray crystallography. The newly reported complexes exhibit blue emission with high quantum yields in solution. Photophysical results are also compared to those reported for their 1,2,4-triazole isomer analogues. The emitting state is a mixture between the triplet metal-to-ligand charge transfer (3MLCT) and triplet inter-ligand charge transfer (3ILCT) states, and it is more localized on the F2ppy ligand as supported by DFT calculations. In addition, this paper reports some preliminary tests of polymer light-emitting diodes (PLEDs) doped with these iridium complexes. The results indicate that such molecules are good candidates as blue- and green-emitting dopants in LED devices.
TL;DR: It is observed that AlMe2Cl plays a specific role in generating the active species for the pyridine-based complexes, presumably to form a bimetallic species which suppresses the beta-hydride elimination process, hence resulting in reduced chain transfer and more linear structure.
Abstract: An α-diimine ligand (1) containing an axial donating pyridine group is developed for late metal polymerization catalysis. Despite having no substitution on the bottom face of the ligand, the nickel and palladium complexes of 1 are highly active for ethylene polymerization, producing linear high molecular weight polymers. For example, 1−NiBr2 (3) forms PE with a Mn of up to 109 224 g/mol with 1.4 branches/1000 C’s. Similarly, 1−PdMeCl (5) forms PE with a Mn of up to 880 379 g/mol with 5.1 branches/1000 C’s. In sharp contrast, catalysts containing the control ligand (2) consisting of a noncoordinating phenyl group gave only low molecular weight branched oligomers. It is observed that AlMe2Cl plays a specific role in generating the active species for the pyridine-based complexes. Presumably, the pyridine group may interact with AlMe2Cl to form a bimetallic species which suppresses the β-hydride elimination process, hence resulting in reduced chain transfer and more linear structure.
TL;DR: In this paper, two novel zeolites SSZ-33 and SSZ35 were investigated with respect to their acidic properties using different probe molecules to characterize the accessibility and acid strength of Lewis and Bronsted acid sites.
Abstract: Two novel zeolites SSZ-33 and SSZ-35 were investigated with respect to their acidic properties using different probe molecules to characterize the accessibility and acid strength of Lewis and Bronsted acid sites. Ammonia, pyridine, pivalonitrile, and acetonitrile-d3 were used as probe molecules, and the results were correlated with 27Al and 1H magic angle spinning (MAS) NMR. Both SSZ-33 and SSZ-35 zeolites were found to possess bridging Si−OH−Al groups of virtually uniform and high acid strength. For both SSZ-33 and SSZ-35, there is the typical presence of highly disturbed OH groups (IR band around 3500 cm-1), which amounts to almost half of the overall Bronsted acidity. It was found that almost all bridging Si−OH−Al groups in SSZ-33 are located in the 12-MR rings. Both acetonitrile-d3 and pyridine sorptions suggest the presence of two types of Lewis sites in SSZ-35, differing in acid strength and electron-acceptor properties, whereas in the SSZ-33 zeolite only one type is present. The relative strength o...
TL;DR: In this paper, the rhodium(I) complexes (PNP)Rh(X) were shown to be active catalysts for H−D exchange between arenes and water.