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Substitution Mechanism (substitution + mechanism)
Selected AbstractsBis(fluoromesityl) Palladium Complexes, Archetypes of Steric Crowding and Axial Protection by ortho Effect , Evidence for Dissociative Substitution Processes , Observation of 19F,19F Through-Space CouplingsEUROPEAN JOURNAL OF INORGANIC CHEMISTRY, Issue 11 2004Camino Bartolomé Abstract Bisarylated complexes trans -[Pd(Fmes)2(SR2)2] [Fmes = 2,4,6-tris(trifluoromethyl)phenyl (fluoromesityl); SR2 = SMe2, tht; tht = tetrahydrothiophene] are precursors for various bisarylated fluoromesityl palladium(II) complexes by ligand-substitution reactions. Boiling under reflux in acetonitrile gives the mixed complexes trans -[Pd(Fmes)2(NCMe)(SR2)], whereas boiling under reflux in toluene leads to trans -[PdCl2L2] (L = PMe3, tBuNC, pTol-NC, 4-MePy), in the presence of neutral monodentate ligands, or to (NnBu4)[trans -Pd(Fmes)2I(SR2)] when treated with (NnBu4)I. trans -[Pd(Fmes)2(SMe2)2] reacts with bidentate ligands, also boiling under reflux in toluene, to give [Pd(Fmes)2(L,L)] [L,L = Me2bipy, 2,2, - biquinolyl, ,2N,N, -OCPy2, dppm (Ph2PCH2PPh2), dppe (Ph2PCH2CH2PPh2), pte (PhSCH2CH2SPh), ,2S,N -SPPh2Py, ,2O,N -OPPhPy2], or the bimetallic complex [Pd(Fmes)2(,-1,N:1,2,O:2,N -Py2MeCO)Pd(Fmes)(SMe2)] (characterized by X-ray diffractometry) when treated with (OH)(CH3)CPy2. The crowding associated with two Fmes groups produces several interesting features: (1) trans complexes are preferred over cis complexes, against the expected electronic preferences; (2) the low-temperature NMR spectra of several complexes, or the X-ray diffraction structure of [Pd(Fmes)2(2,2, - biquinolyl)], reveal significant structural distortions associated with steric crowding; (3) the need for boiling under reflux in the synthesis suggests a dissociative substitution mechanism, which is unknown so far for Pd; (4) some of the complexes show 19F,19F through-space couplings. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2004) [source] Theoretical Studies on ortho -Oxidation of Phenols with Dioxygen Mediated by Dicopper Complex: Hints for a Catalyst with the Phenolase Activity of TyrosinaseADVANCED SYNTHESIS & CATALYSIS (PREVIOUSLY: JOURNAL FUER PRAKTISCHE CHEMIE), Issue 4-5 2007Hiroshi Naka Abstract Theoretical studies on the chemo- and regioselective ortho -oxidation reaction of phenols mediated by a biomimetic (,,,2:,2peroxo)dicopper(II) complex were performed using unrestricted hybrid density functional theory (UB3LYP) calculations, with the aim of providing a guide for the development of new bio-inspired catalysts with the phenolase activity of tyrosinase. Energetic, structural, and electronic analyses suggested the involvement of a side-on (,,,2:,2)-Cu2O2 complex as an active intermediate, and a single electron transfer (SET)-induced electrophilic aromatic substitution mechanism is proposed for the rate-determining CO bond forming process; this is consistent with experimental observations. Moreover, the inherent roles of, and requirement for, two copper ions in this reaction have been elucidated. [source] Synthesis and characterization of sulfonated-fluorinated, hydrophilic-hydrophobic multiblock copolymers for proton exchange membranesJOURNAL OF POLYMER SCIENCE (IN TWO SECTIONS), Issue 4 2009Xiang Yu Abstract Hydrophilic/hydrophobic block copolymers as proton exchange membranes (PEMs) has become an emerging area of research in recent years. These copolymers were obtained through moderate temperature (, 100 °C) coupling reactions, which minimize the ether-ether interchanges between hydrophobic and hydrophilic telechelic oligomers via a nucleophilic aromatic substitution mechanism. The hydrophilic blocks were based on the nucleophilic step polymerization of 3,3,-disulfonated, 4,4,-dichlorodiphenyl sulfone with an excess 4,4,-biphenol to afford phenoxide endgroups. The hydrophobic (fluorinated) blocks were largely based on decafluoro biphenyl (excess) and various bisphenols. The copolymers were obtained in high molecular weights and were solvent cast into tough membranes, which had nanophase separated hydrophilic and hydrophobic regions. The performance and structure-property relationships of these materials were studied and compared to random copolymer systems. NMR results supported that the multiblock sequence had been achieved. They displayed superior proton conductivity, due to the ionic proton conducting channels formed through the self-assembly of the sulfonated blocks. The nano-phase separated morphologies of the copolymer membranes were studied and confirmed by atomic force microscopy. Through control of a variety of parameters, including ion exchange capacity and sequence lengths, performances as high, or even higher than those of the state-of-the-art PEM, Nafion, were achieved. © 2009 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 47: 1038,1051, 2009 [source] Search-based many-to-one component substitutionJOURNAL OF SOFTWARE MAINTENANCE AND EVOLUTION: RESEARCH AND PRACTICE, Issue 5 2008Nicolas Desnos Abstract In this paper, we present a search-based automatic many-to-one component substitution mechanism. When a component is removed from an assembly to overcome component obsolescence, failure or unavailability, most existing systems perform component-to-component (one-to-one) substitution. Thus, they only handle situations where a specific candidate component is available. As this is not the most frequent case, it would be more flexible to allow a single component to be replaced by a whole component assembly (many-to-one component substitution). We propose such an automatic substitution mechanism, which does not require the possible changes to be anticipated and which preserves the quality of the assembly. This mechanism requires components to be enhanced with ports, which provide synthetic information on components' assembling capabilities. Such port-enhanced components then constitute input data for a search-based mechanism that looks for possible assemblies using various heuristics to tame complexity. Copyright © 2008 John Wiley & Sons, Ltd. [source] | ||||||||||