- Beyond PEG2000: Synthesis and functionalisation of monodisperse pegylated homostars and clickable bivalent polyethyleneglycols
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A new strategy to access highly monodisperse, heterobifunctional linear polyethylenglycols (PEGs) has been designed. This was built around unidirectional, iterative chain extension of a 3-arm PEG homostar. A mono-(4,4′-dimethoxytriphenylmethyl) octagol building block, DmtrO-EG 8-OH, was constructed from tetragol. After six rounds of chain extension, the monodisperse homostar reached the unprecedented length of 56 monomers per arm (PEG2500). The unique architecture of the synthetic platform greatly assisted in facilitating and monitoring reaction completion, overcoming kinetic limitations, chromatographic purification of intermediates, and analytical assays. After chain terminal derivatisation, mild hydrogenolytic cleavage of the homostar hub provided heterobifunctional linear EG56 chains with a hydroxyl at one end, and either a toluene sulfonate, or a tert-butyl carboxylate ester at the other. A range of heterobifunctional, monodisperse PEGs was then prepared having useful cross-linking functionalities (-OH, -COOH, -NH2, -N3) at both ends. A rapid preparation of polydisperse PEG homostars, free of multiply cross-linked chains, is also described. The above approach should be extendable to other high value oligomers and polymers.
- Szekely, Gyoergy,Schaepertoens, Marc,Gaffney, Piers R.J.,Livingston, Andrew G.
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supporting information
p. 10038 - 10051
(2014/08/18)
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- METHOD FOR THE SYNTHESIS OF INITIATORS FOR TELECHELIC POLYISOBUTYLENES
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A new methodology for the synthesis of a novel difunctional- and a known trifunctional initiator, i.e., 1,3-di(2-methoxy-2-propyl)-5-isopropyl benzene and 1,3,5-tri(2-methoxy-2-propyl) benzene, respectively, for the preparation of di- and tri-telechelic polyisobutylenes. The synthesis proceeds in three steps: 1) catalytic peroxidation of 1,3,5-triisopropylbenzene, 2) reduction of the peroxides to the corresponding alcohols, and 3) methylation of the alcohols. By controlling the conversion of the key peroxidation step the relative ratio of di- and tri-fiinctional intermediates can be controlled. By the use of the 1,3-di(2-methoxy-2-propyl)-5-isopropyl-benzene, well-defined di-methoxy telechelic polyisobutylenes can be synthesized. Although the overall combined yield of the two initiators was only 14-20%, because of the low cost of the starting material, reagents used, and simple manipulations these compounds represent the most cost effective initiators to-date for the preparation of telechelic polyisobutylenes.
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Page/Page column 15-16
(2012/07/27)
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- The effect of the oxidation state of molybdenum complexes on the catalytic transformation of terminal alkynes: Cyclotrimerization vs. polymerization
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Reactions of monosubstituted alkynes (PhC≡CH, tBuC≡ CH, nBuC≡CH, HOCH2C≡CH, HO(CH 3)2CC≡CH) in the presence of molybdenum(0) and molybdenum(II) carbonyl complexes (Mo(CO)6/hv, [Mo(CO) 4(pip)2] (pip = piperidine), [Mo(CO)4(pip) 2]/SnCl4, [Rpip]2[{(μ-Cl)Mo(μ-Cl) (SnCl3)(CO)3}2] (R = C3H 5, H)) lead to the formation of cyclotrimerization and polymerization products, which were characterized by chromatography (GC-MS, GPC) and by 1H and 13C NMR spectroscopy. The effect of the oxidation state of the molybdenum catalyst on the transformation of the terminal alkynes was observed: cyclotrimerization vs. polymerization. Only molybdenum(II) complexes lead to the formation of polyenic polymers. Moreover, reaction of prop-2-yn-1-ol initiated by [Mo(CO)4(pip)2] in dichloromethane leads to the formation of oligomers containing the vinylidene unit. Mechanistic NMR studies show that η2-alkyne complex formation is the principal feature of all transformations of alkynes catalyzed by molybdenum complexes.
- Czelu?niak, Izabela,Kociecka, Paulina,Szymańska-Buzar, Teresa
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- Nickel-catalyzed addition of benzenethiol to alkynes: Formation of carbon-sulfur and carbon-carbon bonds
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Nickel-catalyzed addition of benzenethiol to alkynes leads to alkenyl and dienyl sulfides; the direction of the process can be controlled by varying the PhSH/alkyne ratio. An advanced procedure, which ensures higher yields of 2-phenylsulfanylalkenes, includes gradual addition of alkyne to the other reactants. The structures of conjugated dienyl sulfides formed in the reaction were determined by 2D NMR spectroscopy.
- Ananikov,Zalesskiy,Orlov,Beletskaya
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p. 2109 - 2113
(2007/10/03)
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- COTRIMERIZATION REACTIONS OF ACETYLENIC ALCOHOLS IN THE PRESENCE OF BISPHOSPHINE NICKEL COMPLEXES. X-RAY MOLECULAR STRUCTURE OF 1,3,5-TRIS(1-HYDROXY-1-METYLETHYL)BENZENE (1,3,5-TIMEB) AND OF THE ADDUCT OF 1,3,5-TIMEB WITH 2,5-DIMETHYLHEX-3-YN-2,5-DIOL
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The catalytic cyclotrimerization reactions of 2-methylbut-3-yn-2-ol (Mb), 3-methylpent-4-yn-3-ol (Mp),1-ethynylcyclohexane-1-ol (Ec) and 2,5-dimethylhex-3-yn-2,5-diol (DMED) have been studied in the presence of and .The cyclic cotrimers of Mb-Mp, Mb-Ec and the adduct of 1,3,5-tris(1-hydroxy-1-methylethyl)benzene (TIMEB) with DMED have been characterized.The molecular structures of the adduct TIMEB-DMED and of TIMEB have been determined by X-ray crystallography; TIMEB-DMED: monoclinic, a=16.999(3), b=8.907(1), c=32.142(4) Angstroem, z=8, space group C2/c.Each TIMEB molecule is linked to adjacent TIMEB and DMED molecules to originate on one side centrosymmetric tetramers and on the other side tetramers having 21 symmetry.TIMEB: monoclinic, a=28.001(4), b=5.989(1), c=17.127(3) Angstroem, z=8, space group P21/c.A network of H...O hydrogen bonds links together the molecules of TIMEB.
- Furlani, Anita,Hornemann, Karl Heinz,Russo, Maria Vittoria,Villa, Angiola Chiesi,Guastini, Carlo
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p. 429 - 436
(2007/10/02)
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- LIGANDEIGENSCHAFTS- UND -KONZENTRATIONSSTEUERUNGEN IM SYSTEM 3-METHYLBUT-1-IN-3-OL/Ni(COD)2/P-LIGANDEN
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The phosphorus/nickel ratio for 18 P ligands was varied over several orders of magnitude and the effect upon the oligomerisation of 3-methylbut-1-yn-3-ol with Ni(COD)2 as catalyst was examined.Some conclusions could be drawn concerning association phenomena.The resulting changes in product composition were correlated with steric and electronic characteristics of the ligands.Steric control dominated and contributed ca. 70percent of the observed effects.
- Hartmann, W.,Preuss, K. D.,Singer, H.
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p. 235 - 246
(2007/10/02)
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- A SYSTEMATIC STUDI OF THE CATALYTIC ACTIVITY OF BIS(PHOSPHINE)NICKEL(II) COMPLEXES IN THE CYCLOTRIMERIZATION REACTION OF ACETYLENES. III. CATALYTIC ACTIVITY OF ACETYLIDES
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The catalytic activities of CR)L2> complexes (L = Bu3P, Ph3P; R = Ph or C(CH3)2OH) and of analogous complexes in the cyclotrimerization reactions of phenylacetylene (PA) and 2-methyl-3-butyn-2-ol (MB) have been compared.In agreement with previous proposal, the monoacetylide complexes are reaction intermediates: in fact, the induction periods are reduced and the distributions of reaction products are very similar.The complexes CR)2L2> are also active catalysts and the catalytic activity is influenced by the ligand L.Reactions carried out in NH(C2H5)2 as solvent are also reported.
- Bicev, Peter,Furlani, Anita,Russo, Maria Vittoria
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