Abstract:
Olefin isomerization of allylic ethers and alcohols is catalyzed by RuII(H2O)6(tos)2 (tos = p-toluenesulfonate) (1) under mild conditions in aqueous solution to yield the corresponding carbonyl compounds. Non-allylic olefins are also isomerized, although homoallylic alcohols exhibit stability toward isomerization. An exclusive 1,3-hydrogen shift is observed in the isomerization of allyl-1,1-d2 alcohol to propionaldehyde-1,3-d2 and allyl-1,1-d2 methyl ether to 1-propenyl-1,3-d2 methyl ether by 1 in aqueous solution. The presence of crossover products from the isomerizations of mixtures of (a) allyl-3-13C alcohol and allyl-1,1-d2 alcohol and (b) allyl-1,1-d2 methyl ether and allyl ethyl ether demonstrates that the isomerization of both alcohols and ethers occurs via intermolecular hydrogen shifts. A modified metal hydride addition-elimination mechanism involving exclusive Markovnikov addition to the double bond directed by the oxygen functionality of the substrate has been proposed. © 1994 American Chemical Society.
Abstract:
Thermally labile dendrimers based on the reversible furan-maleimide Diels-Alder reaction are described. First through fourth generation benzyl aryl ether based dendrons 3a-d that contained furan moieties at their focal point were allowed to react with bismaleimide central linker 4 to provide the corresponding dendrimers 5-8. Thermal degradation and reassembly of these dendrimers were studied under a variety of conditions and monitored by GPC and NMR. © 2007 American Chemical Society.
Abstract:
The ring-opening metathesis polymerization (ROMP) of exo-N-methyl-7-oxabicyclo[2.2.1]-hept-5-ene-2,3-dicarboximide (1) was accomplished in aqueous solution under mild conditions using the simple ruthenium(II) coordination complex RuII(H2O)6(tos)2 (tos = p-toluenesulfonate) (2). The polymerization yield was nearly quantitative. The resultant high molecular weight polymer (poly-1) exhibited a glass transition temperature (Tg) of 225°C and was thermally stable up to 402°C. The thermal and radiative stabilities of poly-1 were further investigated. Poly-1 was hydrogenated to yield its saturated analogue, which had a lower Tg (170°C) but a higher temperature of decomposition (430°C). Complex 2 was deactivated by coordination of free maleimides formed during the polymerization of carboximide-functionalized monomers capable of undergoing retro Diels-Alder chemistry. The scope of this polymerization was therefore limited to carboximide-functionalized monomers that are stable toward retro Diels-Alder reactions at the polymerization temperature. Both ruthenium (II)-1 and ruthenium(II)-N-methylmaleimide olefin complexes were identified. © 1992 American Chemical Society.
Abstract:
Eight poly(aryl) ether dendritic wedges attached to the periphery of a phthalocyanine significantly decreases self-association of these chromophores in solution and the condensed state.
Abstract:
We studied Langmuir and Langmuir-Blodgett monolayers from amphiphiles with traditional (carboxylic) and bulky functionalized (epoxy) terminal groups at the air-water and air-solid interfaces. We demonstrated that the molecules with a central azobenzene fragment and carboxylic (AA-1 molecule) and bulky epoxy (AE-1 molecule) polar groups formed orthorhombic unit cells with larger than expected area per alkyl tail. The higher order of symmetry indicated by the appearance of higher Qxy peaks revealed that the alkyl tails formed a herringbone structure with limited long range ordering. In the condensed monolayer, the azobenzene group of the AA-1 molecules was oriented vertically in contrast to the AE-1 molecule that was significantly tilted. In addition, the presence of the bulky epoxy focal groups caused a less dense lateral packing of the azobenzene groups. We suggest that the bulky focal group causes intramonolayer packing which can enhance the ability of the chemically grafted azobenzene groups for photoisomerization. © 2005 Elsevier B.V. All rights reserved.
