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Bulky Ligands (bulky + ligand)
Selected AbstractsSix-Membered N-Heterocyclic Carbenes with a 1,1,-Ferrocenediyl Backbone: Bulky Ligands with Strong Electron-Donor Capacity and Unusual Non-Innocent CharacterEUROPEAN JOURNAL OF INORGANIC CHEMISTRY, Issue 31 2009Ulrich Siemeling Abstract The stable, crystalline N-heterocyclic diaminocarbene fc[N(CH2tBu)-C-N(CH2tBu)] (2d, fc = 1,1,-ferrocenediyl) was prepared by deprotonation of its formamidinium precursor fc[N(CH2tBu)-CH-N(CH2tBu)][BF4] (1d) and used for the preparation of the 16 valence electron complexes [Mo(2d)(CO)4], [RhCl(2d)(cod)] (cod = 1,5-cyclooctadiene) and [RhCl(2d)(CO)2]. 1d, 2d and [RhCl(2d)(cod)] were structurally characterised by single-crystal X-ray diffraction studies. The electrochemical properties of 2d, its 2-adamantyl analogue 2c, its complex [RhCl(2d)(CO)2] and of the precursors 1d and 1,1,-bis(neopentylamino)ferrocene were investigated by electrochemistry. The carbenes are easily oxidised to the corresponding radical cation, whose persistent nature is unprecedented in the chemistry of N-heterocyclic carbenes. The spin density is located at the Fe atom and the carbene C atom according to the results of EPR spectroscopic studies and DFT calculations.(© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2009) [source] Stereoselective polymerization of rac -lactide with a bulky aluminum/Schiff base complexJOURNAL OF POLYMER SCIENCE (IN TWO SECTIONS), Issue 23 2004Zhaohui Tang Abstract An aluminum/Schiff base complex {[2,2-dimethyl-1,3-propylenebis(3,5-di- tert -butylsalicylideneiminato)](isopropanolato)aluminum(III) (2)} based on a bulky ligand and aluminum isopropoxide was prepared and employed for the stereoselective ring-opening polymerization (ROP) of rac -lactide (rac -LA). The initiator was characterized with nuclear magnetic resonance (NMR), crystal structure measurements, and elemental analysis. It contained a five-coordinate aluminum atom that was trigonal bipyramidal in the solid state according to the crystal structure measurements. The two conformational stereoisomers of 2 exchanged quickly on the NMR scale. Compound 2 polymerized rac -LA into a crystalline polymer that was characterized with 1H NMR, wide-angle X-ray diffraction, electrospray ionization mass spectrometry, and gel permeation chromatography. The kinetics of the polymerization were first-order in both the monomer and initiator, and there was a linear relationship between the rac -LA conversion and the number-average molecular weight of poly(rac -LA) with a narrow molecular distribution (1.04,1.08). These features showed that the polymerization was well controlled. The high melting temperature (196,201 °C) and isotacticity of poly(rac -LA) indicated that complex 2 was a highly stereoselective initiator for the ROP of rac -LA. The stereoselectivity was as high as 90%, and the stereoblocks of poly(rac -LA) by complex 2 contained an average of 20 units (average block length = 20) of enantiomerically pure lactic acid. The activation energy (23.6 kJ mol,1) was obtained according to an Arrhenius equation. © 2004 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 42: 5974,5982, 2004 [source] cis -Dichloridobis{dimethyl[3-(9-phosphabicyclo[3.3.1]non-9-yl)propyl]amine-,P}platinum(II)ACTA CRYSTALLOGRAPHICA SECTION C, Issue 4 2009Peter N. Bungu The title compound, [PtCl2(C13H26NP)2], is a rare example of a sterically bulky ligand adopting a cis geometry in a square-planar complex. It crystallizes on a twofold rotation axis which bisects the Pt centre and the P,Pt,P, and Cl,Pt,Cl, angles. The ligand exhibits a random packing disorder in the N,N -dimethylpropylamine substituent, with the two orientations refining to occupancies of 0.404,(15) and 0.596,(15). Weak intermolecular interactions between a Cl and a H atom of the ligand of a neighbouring molecule result in extended chains along the a axis. The effective cone angle for the dimethyl[3-(9-phosphabicyclo[3.3.1]non-9-yl)propyl]amine (Phoban[3.3.1]-C3NMe2) ligand was determined as being in the range 160,181°, depending on the choice of atoms used in the calculations. [source] Synthesis, Crystal Structure, and Catalytic Properties of Novel Dioxidomolybdenum(VI) Complexes with Tridentate Schiff Base Ligands in the Biomimetic and Highly Selective Oxygenation of Alkenes and SulfidesEUROPEAN JOURNAL OF INORGANIC CHEMISTRY, Issue 5 2010Abdolreza Rezaeifard Abstract Four novel dioxidomolybdenum(VI) complexes [MoO2(Lx)(CH3OH)] have been synthesized, using 2[(E)-(2-hydroxy-2-phenylethylimino)methyl]phenol derivatives as tridentate ONO donor Schiff base ligands (H2Lx) and MoO2(acac)2. A monoclinic space group was determined by X-ray crystallography from single-crystal data of a sample of these new complexes. The epoxidation of alkenes by using tert -butyl hydroperoxide and oxidation of sulfides to sulfoxides by urea hydrogen peroxide were efficiently enhanced with excellent selectivity under the catalytic influence these new MoVI complexes. The high efficiency and relative stability of the catalysts have been observed by turnover numbers and UV/Vis investigations. The electron-poor and bulky ligands promoted the effectiveness of the catalysts. [source] Ionic Iridium(III) Complexes with Bulky Side Groups for Use in Light Emitting Cells: Reduction of Concentration QuenchingADVANCED FUNCTIONAL MATERIALS, Issue 13 2009Carsten Rothe Abstract Here, the photophysics and performance of single-layer light emitting cells (LECs) based on a series of ionic cyclometalated Ir(III) complexes of formulae and where ppy, bpy, and phen are 2-phenylpyridine, substituted bipyridine and substituted phenanthroline ligands, respectively, are reported. Substitution at the N,N ligand has little effect on the emitting metal-ligand to ligand charge-transfer (MLLCT) states and functionalization at this site of the complex leads to only modest changes in emission color. For the more bulky complexes the increase in intermolecular separation leads to reduced exciton migration, which in turn, by suppressing concentration quenching, significantly increases the lifetime of the excited state. On the other hand, the larger intermolecular separation induced by bulky ligands reduces the charge carrier mobility of the materials, which means that higher bias fields are needed to drive the diodes. A brightness of ca. 1000,cd,m,2 at 3,V is obtained for complex 5, which demonstrates a beneficial effect of bulky substituents. [source] Exploring pathways to reduce the distribution of active sites in the Ziegler,Natta polymerization of propyleneJOURNAL OF POLYMER SCIENCE (IN TWO SECTIONS), Issue 17 2007David Ribour Abstract Chemical treatments of classical supported Ziegler,Natta precatalysts were conducted by using additional bulky ligands to attempt to narrow and homogenize the active sites distribution in propylene polymerization. Additions of monodentate ligands such as bis(trimethylsilyl)amide, cyclopentadienyl derivates or triphenylsilanol were seen to slow down the polymerization without modifying the distribute properties of polypropylenes. In the case of multidentate ligands (porphines or biquinolines), in addition to the poisoning of active sites, an extraction of titanium from the catalyst surface is observed. A decrease of both melting point and isotacticity (II%) of polymers using these compounds suggest that the most isospecific titanium sites are first extracted from the MgCl2 -surface. The narrowing of the molecular weight distribution confirms that the highly isospecific sites are the most active sites, producing the higher molecular weight polymers. Moreover, this study shows that the distributed properties of polymers are due to the chemical diversity of the active sites with various steric and electronic environments at the catalyst surface and not to mass transfer limitations. © 2007 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 45: 3941,3948, 2007 [source] [Pt(topy)(Htopy)(ONO2)] complex (Htopy = 2- p -tolylpyridine) and its analogs: 195Pt NMR spectra and fabrication of light-emitting devicesAPPLIED ORGANOMETALLIC CHEMISTRY, Issue 4 2009Hiroto Fukuda Abstract We report fast, high-yield syntheses of a series of [Pt(C,N)(HC,N)X] complexes, where HC,N is 2-phenylpyridine (Hppy) or 2- p -tolylpyridine (Htopy) and X, is Cl,, Br,, I,, ONO2,, NO2, or SCN,. The structure of [Pt(topy)(Htopy)(ONO2)] was analyzed by single-crystal X-ray diffraction. Substitution of Cl, with Br, or I, in our complexes shifted the 195Pt NMR peaks upfield in the order Cl, < Br, < I,, but the magnitudes of their shifts were one-tenth those observed for non-cyclometalated platinum(II) complexes. As the two nitrato complexes showed strong emissions in acetonitrile solution,three to six times those of other complexes,they were used to fabricate OLEDs. Although their emissions were not particularly strong, devices fabricated with platinum(II) complexes containing bulky ligands emitted green light with a short lifetime (,). Copyright © 2009 John Wiley & Sons, Ltd. [source] Rhodium-Catalyzed Allylation of Aldehydes with Homoallylic Alcohols by Retroallylation and Isomerization to Saturated Ketones with Conventional or Microwave HeatingCHEMISTRY - AN ASIAN JOURNAL, Issue 1 2008Yuto Sumida Abstract The treatment of an aldehyde with a tertiary homoallylic alcohol at 100,250,°C in the presence of cesium carbonate and a rhodium catalyst leads to allyl transfer from the homoallylic alcohol to the aldehyde. The process includes Rh-mediated retroallylation to form an allyl rhodium species as the key intermediate. The homoallylic alcohol formed initially through allyl transfer is converted under the reaction conditions into the corresponding saturated ketone when bulky ligands are used. Microwave heating at 250,°C accelerates the reaction significantly. [source] | |||||||||||||