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Equilibration Reactions (equilibration + reaction)
Selected AbstractsThe Synthesis and Characterisation of Bis(phosphane)-Linked (6 - p -Cymene)ruthenium(II),Borane CompoundsEUROPEAN JOURNAL OF INORGANIC CHEMISTRY, Issue 23 2005Adrian B. Chaplin Abstract The reaction of [(,6 - p -cymene)RuCl2]2 with some bis(phosphane) ligands (dppm, dppe, dppv, dppa, dpp14b, dppf) has been investigated. In general mixtures of products were obtained, although the pendant phosphane complexes [(,6 - p -cymene)RuCl2(,1 -dppv)] and [(,6 - p -cymene)RuCl2(,1 -dppa)] were isolated and characterized in the solid state by X-ray diffraction. The later complex was obtained in lower yield and undergoes an equilibration reaction resulting in the formation of a dimeric species, where the dppa bridges two ruthenium centres, and uncoordinated phosphane; the bridging species was also structurally characterised in the solid state. In contrast, the reaction of [(,6 - p -cymene)RuCl2(PPh3)] with dppa in the presence of [NH4]PF6 results in the formation of [(,6 - p -cymene)RuCl(PPh3)(,1 -dppa)]PF6, which is stable in solution. A series of linked ruthenium,borane complexes, viz. [(,6 - p -cymene)RuCl2(,1 -phosphane-BH3)] (phosphane = dppm, dppe, dppv, dppa, dpp14b, dppf) and [(,6 - p -cymene)RuCl(PPh3)(,1 -dppa-BH3)]PF6 have been prepared from isolated pendant phosphane complexes, those generated in situ, or from a preformed phosphane,borane adduct. The solid-state structures of [(,6 - p -cymene)RuCl2(,1 -dppm-BH3)], [(,6 - p -cymene)RuCl2(,1 -dppe-BH3)] and [(,6 - p -cymene)RuCl2(,1 -dppv-BH3)] have been determined by X-ray diffraction analysis. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2005) [source] Hyperbranched cyclic and multicyclic polymers by "a2+b4" polycondensationsJOURNAL OF POLYMER SCIENCE (IN TWO SECTIONS), Issue 8 2009Hans R. Kricheldorf Abstract At first, theoretical aspects of "a2+b4" polycondensations (meaning polycondensations of difunctional and tetrafunctional monomers) are discussed and compared with what is known about "a2+b3" polycondensations. The following review of experimental results is subdivided into three sections. First, syntheses of hyperbranched polyethers and polyesters by polycondensations based on equimolar feed ratios will be reported. Second, kinetically controlled (i.e., irreversible) syntheses of multicyclic polymers using equifunctional feed ratios (i.e., a2/b4 ratios of 2:1) will be described. In the third section, syntheses of multicyclic polymers via thermodynamically controlled (reversible) "a2+b4" polycondensations will be discussed. Characteristic for these polycondensations are again equifunctional feed ratios and metal alkoxides as "a2" or "b4" monomers, which catalyze rapid equilibration reactions. Finally, potential applications of the new polymers will shortly be mentioned. © 2009 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 47: 1971,1987, 2009 [source] Biodegradable polymers with variable architectures via ring-expansion polymerizationJOURNAL OF POLYMER SCIENCE (IN TWO SECTIONS), Issue 19 2004Hans R. Kricheldorf Abstract Kinetically controlled ring-expansion polymerizations (REPs) are defined syntheses generating cyclic oligomers and polymers without linear intermediates and without equilibration reactions. This review reports syntheses of cyclic metal alkoxides and their use as initiators for REPs of lactones, cyclic diesters, and cyclocarbonates. In addition to homopolyesters, telechelic oligoesters or polyesters, random copolyesters, and A,B,A triblock copolymers can be prepared by these REPs. The in situ combination of REPs with condensation (mostly acylation) reactions allows a broad variation of end groups. The in situ combination of REPs with polycondensation enables various chain-extension reactions, including the syntheses of multiblock copolymers. With spirocyclic initiators, four-armed stars with functional end groups may be prepared. The in situ combination of REPs with condensation reactions of trifunctional or multifunctional reagents makes a broad variety of networks accessible. The average segment lengths may be controlled via the monomer/initiator ratios of the REP. All materials produced via the aforementioned REP processes are biodegradable and nontoxic, and this allows for biomedical and pharmaceutical applications. © 2004 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 42: 4723,4742, 2004 [source] The role of ring-ring equilibria in thermodynamically controlled polycondensationsMACROMOLECULAR SYMPOSIA, Issue 1 2003Hans R. Kricheldorf Abstract Thermodynamically controlled polycondensations (TCPs) involve rapid equilibration reactions, such as transesterification, transamidation, etc. An important component of these equilibration reactions is the reversible formation of cyclic oligomers and polymers by "back-biting". Therefore, TCPs were described in the previous literature in terms of ring-chain equilibria. The present study presents a complementary theory saying that ring-chain equilibria automatically include ring-ring equilibria which gain in importance with higher conversions because the molar ratio of rings versus linear chains rapidly increases. At 100% conversion, all reaction products will be cycles and the ring-ring equilibria limit the chain growth. Several polycondensations cited from the literature are discussed in the light of the new theory. [source] | ||||||||||