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Diimine Ligand (diimine + ligand)
Selected AbstractsInvestigation of the stereodynamics of tris-(, -diimine),transition metal complexes by enantioselective dynamic MEKCELECTROPHORESIS, Issue 2 2009Sabrina Bremer Abstract Enantiomerization of octahedral tris(, -diimine),transition metal complexes was investigated by enantioselective dynamic MEKC. Varying both the transition metal ion (Fe2+, Fe3+, and Ni2+) and the bidentate diimine ligand (1,10-phenanthroline and 2,2,-bipyridyl), the enantiomer separations were performed either in a 100,mM sodium tetraborate buffer (pH 9.3) or in a 100,mM sodium tetraborate/sodium dihydrogenphosphate buffer (pH 8.0) both containing sodium cholate as chiral surfactant. The unified equation of dynamic chromatography was employed to determine apparent reaction rate constants from the electropherograms showing distinct plateau formation. Apparent activation parameters ,H, and ,S, were calculated from temperature-dependent measurements between 10.0 and 35.0°C in 2.5,K steps. It was found that the nature of the central metal ion and the ligand strongly influence the enantiomerization barrier. Surprisingly, complexes containing the 2,2,-bipyridyl ligand show highly negative activation entropies between ,103 and ,116,J (K,mol),1 while the activation entropy of tris(1,10-phenanthroline) complexes is positive indicating a different mechanism of interconversion. Furthermore, it was found that the Ni2+ complexes are stereostable under the conditions investigated here making them a lucent target as enantioselective catalysts. [source] Single-Electron-Transfer Reactions of ,-Diimine dpp-BIAN and Its Magnesium Complex (dpp-BIAN)2,Mg2+(THF)3EUROPEAN JOURNAL OF INORGANIC CHEMISTRY, Issue 4 2006Igor L. Fedushkin Abstract The reactions of (dpp-BIAN)Mg(THF)3 (1) {dpp-BIAN = 1,2-bis[(2,6-diisopropylphenyl)imino]acenaphthene} with ethyl halides EtX (X = Cl, Br, I) in hexane proceed by single-electron transfer (SET) from the metal complex to the organic halide. Complexes [(dpp-BIAN)(Et)]MgX(THF)n [X = Cl, n = 0 (2); X = Br, n = 2 (3); X = I, n = 1 (4)] are the products of ethyl transfer to an imine carbon atom of a coordinated diimine ligand. The compound [(dpp-BIAN)(Et)]MgBr (3a) was obtained from the reaction of free dpp-BIAN with ethylmagnesiumbromide in hexane. In this case SET from the Grignard reagent to the neutral diimine takes place. Compounds 2,4 and 3a were isolated as crystals and characterized by 1H NMR spectroscopy. The molecular structure of 3 was determined by single-crystal X-ray analysis. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2006) [source] Unsymmetrical ,-diimine nickel (II) complex with rigid bicyclic ring ligand: Synthesis, characterization, and ethylene polymerization in the presence of AlEt2ClJOURNAL OF APPLIED POLYMER SCIENCE, Issue 1 2008Ting Li Abstract Unsymmetrical ,-diimine ligand 1 was successfully synthesized via condensation of trimethylaluminum (TMA) metalated 2-methyl-6-isopropyl-aniline with rigid bicyclic aliphatic diketone camphorquinone. Syn- and anti-stereoisomers were detected by 13C NMR in the condensation product. The corresponding ,-diimine nickel (II) complex 1 was prepared from the exchange reaction of (DME)NiBr2 with the ligand 1, and displayed high activity for ethylene polymerization in the presence of diethylaluminum chloride (AlEt2Cl). The resultant polymers were confirmed by gel permeation chromatography and 13C NMR characterization to be broad molecular weight distribution polyethylene with various branches, and high degree of branching, even at low polymerization temperature ,10°C. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci, 2008 [source] Molecular structure determination of Ni(II) diimine complex and DMA analysis of Ni(II) diimine-based polyethenes ,JOURNAL OF POLYMER SCIENCE (IN TWO SECTIONS), Issue 9 2001J. O. Liimatta Abstract Dynamic mechanical thermoanalysis showed that polyethene, prepared under suitable polymerization conditions with the Brookhart-type catalyst dibromo- N,N,-1,2-acenaphthylenediylidenebis[2,6-bis(1-methylethyl)benzeneamine]Ni(II)/methylaluminoxane (MAO), behaved like an elastomer, even though no comonomer was added. A structural characterization showed that the polymers contained methyl to hexyl branches and some longer branches. The effect of the polymerization conditions on branching was investigated through variations in the pressure and temperature of the polymerization. Depending on the degree and type of branching, polyethene was either quite amorphous or highly crystalline with a high melting temperature. The solid-state structure of the catalyst dibromo- N,N,-1,2-acenaphthylenediylidenebis[2,6-bis(1-methylethyl)benzeneamine]Ni(II) consisted of two centrosymmetrically related monomeric moieties, where Ni atoms were bridged by two bromide ligands. The Ni atom was five-coordinated, with a square pyramidal coordination polyhedron. The sixth coordination site of the octahedral geometry was effectively blocked by the isopropyl groups of the 2,6-C6H3(i -Pr) substituents of the diimine ligand. In solution in the presence of MAO, the longer bridging NiBr bonds broke, and the complex dissociated to a monomeric species. © 2001 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 39: 1426,1434, 2001 [source] Conversion of carbon dioxide to cyclic carbonates using diimine Ru(II) complexes as catalystsAPPLIED ORGANOMETALLIC CHEMISTRY, Issue 2 2009Mahmut Ulusoy Abstract Cationic diimine Ru(II) complexes were synthesized and tested as catalysts for the formation of cyclic organic carbonates from CO2 and liquid epoxides (propylene oxide, epichlorohydrine, 1,2-epoxybutane and styrene oxide) which served as both reactant and solvent. The reaction rates not only depended on the type of ligand, but also on reaction conditions such as temperature, pressure, base, the epoxide substrates and the use of an additional solvent. Reaction rates in terms of turnover frequencies up to 4050 molproduct molcat.,1 h,1 at 99% selectivity were achieved by optimizing the diimine ligand as well as the reaction temperature and CO2 pressure. Consistent with CV measurements, the electron donating group on the p -position of the aryl ring accelerated the reaction rate. Copyright © 2008 John Wiley & Sons, Ltd. [source] Magneto,Structural Correlations in Discrete MnII -WV Cyano-Bridged Assemblies with Polyimine LigandsEUROPEAN JOURNAL OF INORGANIC CHEMISTRY, Issue 26 2010Robert Podgajny Abstract We present the magneto,structural correlations for two novel discrete cyano-bridged assemblies based on cationic complexes of manganese(II) with diimine ligands and octacyanotungstate(V) ions. The crystal structure of [MnII(terpy)(dmf)(H2O)2][MnII(terpy)(H2O)(dmf)(,-NC)WV(CN)7]2·6H2O (1) (terpy = 2,2,;6,,2,-terpyridine, dmf = dimethylformamide) contains dinuclear {MnIIWV}, cyano-bridged anions, while the crystal structure of [MnII(phen)3]2[MnII(phen)2(,-NC)2WV(CN)6]2(ClO4)2·9H2O (2) (phen = 1,10-phenanthroline) is built of tetranuclear {MnII2WV2}2, square anions. Intramolecular Mn,W magnetic interactions through the cyano bridges are represented by magnetic coupling constants J = ,39 cm,1 for the {MnIIWV}, unit in 1 and J1 = ,25.7 and J2 = ,16.7 cm,1 for the {MnII2WV2}2, unit in 2. J and J1 represent relatively strong W,CN,Mn interactions and are ascribed to the bridges in b positions of TPRS-8 (trigonal prism square-face bicapped) of [W(CN)8]3, polyhedra, favoring the strongest electronic interactions between the d,d orbital of W and the ,* orbitals of CN,, whereas J2 is related to the m vertex of [W(CN)8]3,. The magnetic properties of 1 and 2 are compared with reference compounds and discussed in the context of the type of coordination polyhedra of [W(CN)8]3, as well as the metric parameters of cyano-bridged W,CN,Mn linkages. We found the type of coordination polyhedra and bridging mode of [W(CN)8]3, to be the most important factors influencing the magnitude of the Mn,W magnetic interaction. [source] 16-Electron (Arene)ruthenium Complexes with Superbasic Bis(imidazolin-2-imine) Ligands and Their Use in Catalytic Transfer HydrogenationEUROPEAN JOURNAL OF INORGANIC CHEMISTRY, Issue 29-30 2009Thomas Glöge Abstract The ligands N,N, -bis(1,3,4,5-tetramethylimidazolin-2-ylidene)-1,2-ethanediamine (BLMe) and N,N, -bis(1,3-diisopropyl-4,5-dimethylimidazolin-2-ylidene)-1,2-ethanediamine(BLiPr) react with [(,5 -C5Me5)RuCl]4 to afford cationic 16-electron half-sandwich complexes [(,5 -C5Me5)Ru(BLR)]+ (R = Me, 3; R = iPr, 4), which resist coordination of the chloride counterion because of the strong electron-donating ability of the diimine ligands. Upon reaction with [(,6 -C6H6)RuCl2]2 or [(,6 -C10H14)RuCl2]2, these ligands stabilize dicationic 16-electron benzene and cymene complexes of the type [(,6 -C6H6)Ru(BLR)]2+ (R = Me, 5; R = iPr, 6) and [(,6 -C10H14)Ru(BLR)]2+ (R = Me, 7; R = iPr, 8). The X-ray crystal structure of [5]Cl2 reveals the absence of any direct Ru,Cl interaction, whereas a long Ru,Cl bond, supported by two CH···Cl hydrogen bonds, is observed for [(6)Cl]Cl in the solid state. Treatment of the dichlorides of 6 and 8 with NaBF4 affords [6](BF4)2 and [8](BF4)2, which are composed of individual dications and tetrafluoroborate ions with no direct Ru,F interaction. All complexes catalyze the transfer hydrogenation of acetophenone in boiling 2-propanol. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2009) [source] Great Framework Variation of Polymers in the Manganese(II) Maleate/,,,,-Diimine System: Syntheses, Structures, and Magneto-Structural CorrelationEUROPEAN JOURNAL OF INORGANIC CHEMISTRY, Issue 15 2003Chengbing Ma Abstract Three novel manganese(II) coordination polymers, [Mn (maleate)(phen)]n (1; phen = 1,10-phenanthroline), [Mn(maleate)(phen)]n·nH2O (2), and [Mn(maleate)(bpy)]n (3; bpy = 2,2,-bipyridine), have been synthesized by treatment of Mn2+ with maleic acid with participation of chelate diimine ligands, and have been identified by single-crystal X-ray diffraction to have either one-dimensional (1D) zigzag chain structures (1 and 2) or a two-dimensional (2D) sinuous layer structure (3). Each maleate dianion coordinates to three Mn centers, in different bridging modes (syn - anti in 1 and 2, syn - syn and anti - anti in 3). These compounds represent an interesting example of structural topology variation from 1D to 2D mediated by chemically similar auxiliary chelate ligands. Variable-temperature magnetic susceptibility measurements show weak anti-ferromagnetic exchange interactions between the adjacent MnII ions, with J = ,0.06 cm,1 (2) and J = ,1.3 cm,1, zJ, = ,0.27 cm,1 (3). The differences in the magnitudes of these coupling interactions agree well with the nature of the carboxylate-bridging coordination of maleate. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2003) [source] The Effect of Counterion/Ligand Interplay on the Activity and Stereoselectivity of Palladium(II),Diimine Catalysts for CO/p -Methylstyrene CopolymerizationCHEMISTRY - A EUROPEAN JOURNAL, Issue 5 2007Barbara Binotti Dr. Abstract The catalytic activity and stereoselectivity of complexes [Pd(,1,,2 -C8H12OMe)(ArNC(R,)C(R,)NAr)]X in the copolymerization of CO and p -methylstyrene have been correlated with their interionic structure in solution and in the solid state, as determined by 19F,1H-HOESY NMR spectroscopy and X-ray diffraction studies, respectively. The highest productivity is obtained with unhindered diimine ligands bearing electron-donating substituents and with the least coordinating counterion. Copolymers with a microstructure ranging from atactic to predominantly isotactic are obtained. The degree of isotacticity increases as the steric hindrance in the apical positions and the coordinating ability of the counterion increase. The counterion is located close to the diimine in both solution and the solid state but it moves toward the palladium as the steric hindrance in the apical positions decreases. When the latter is small the counterion competes with the substrate for apical coordination, and consequently it affects the productivity. In the case of ortho -dimethyl-substituted ligands the counterion is confined in the back, above the NC(R,)C(R,)N moiety, and does not affect the productivity. However, it contributes to increasing the stereoregularity of the copolymer by making the aryl moieties more rigid. With R,=Me and Ar=o -Me2C6H3 an ll of 81,% and 72,% was obtained with X,=CF3SO3, or BArF,, respectively. The isotacticity of the copolymers produced by ortho -monosubstituted catalysts depends greatly on the counterion and ranges from 30,% to 59,% with X,=BArF, and X,=CF3SO3,, respectively, with Ar=o -EtC6H4 and R,=Me. Based on the interionic structural results, this effect can be explained by a greater reduction of the copolymerization rate of Cs -symmetric isomers with respect to their C2 -symmetric counterparts. [source] | |||||||||||||