The Experts below are selected from a list of 318 Experts worldwide ranked by ideXlab platform
Ken D Shimizu - One of the best experts on this subject based on the ideXlab platform.
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molecular playdough conformationally programmable molecular receptors based on Restricted Rotation
Organic and Biomolecular Chemistry, 2009Co-Authors: Roger D Rasberry, Ken D ShimizuAbstract:A new method for rapidly tailoring molecular properties is presented in which the three-dimensional shape of a malleable framework is controlled by heating with a template molecule.
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solvent programmable polymers based on Restricted Rotation
Journal of the American Chemical Society, 2009Co-Authors: Yagang Zhang, Judith M Lavin, Ken D ShimizuAbstract:Solvent programmable polymers (SPPs) were developed that can modulate their recognition properties by heating in different solvents. These highly cross-linked polymer gels were able to respond to differences in solvent polarity at elevated temperatures via Rotation about a Caryl−Nimide bond of a carboxylic acid monomer. When heated in polar solvents such as water, the number of solvent accessible carboxylic acids in the polymers increases. When heated in nonpolar solvents such as toluene, the number of solvent accessible carboxylic acids decreases. On cooling to rt, these changes are preserved and maintained even when the polymer is removed from the solvent imprinting environment. The solvent memory is due to the reestablishement of Restricted Rotation around that Caryl−Nimide bond, which locks the carboxylic acid recognition groups into either a solvent accessible or inaccessible orientation. The solvent programmability was also shown to be reversible. The fidelity of the SPP switching process did not de...
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shape persistent and shape adaptable macrocycles based on Restricted Rotation studies building toward macromolecular playdough
Synthesis, 2002Co-Authors: Yong S Chong, Ken D ShimizuAbstract:A rigid 48-membered macrocycle 1 was synthesized and studied that comprises two atropisomeric N,N'-diarylnaphthalene-diimide building blocks that adopt stable syn and anti conformations due to Restricted Rotation about two C a r y l -N i m i d e bonds. The resulting macrocycle maintains three distinct conformations: anti/ anti, syn/anti and syn/syn conformers that are stable and separable at room temperatures, and each with distinct shapes and sizes as measured by GPC. At elevated temperatures, macrocycle 1 was conformationally flexible and showed interconversion of the respective isomers. Conformational preferences established at higher temperatures were preserved on cooling to room temperature as the Restricted Rotation was reestablished and the macrocycle becomes conformationally rigid.
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molecules with shape memory based on Restricted Rotation
Organic Letters, 2001Co-Authors: Dongsook Choi, Yong S Chong, Daniel C Whitehead, Ken D ShimizuAbstract:Diimide 1 and octaimide 2 both adopt two stable conformations at room temperature as a result of Restricted Rotation about two Caryl−Nimide single bonds, a compact “folded” and an open “unfolded” structure. Predictable ratios of folded and unfolded rotamers can be achieved by heating in solvents of appropriate polarity as measured by the Reichardt's parameter (ET30). On cooling to room temperature, the resulting conformational changes are “locked in” as Restricted Rotation is reestablished.
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an axially chiral phosphine ligand based on Restricted Rotation in n arylimides
Tetrahedron Letters, 2001Co-Authors: Yizhao Chen, Mark D Smith, Ken D ShimizuAbstract:Abstract Described is the preparation, resolution, and absolute configuration of a new axially chiral monodentate phosphine ligand. The chirality of the ligand is derived from Restricted Rotation about a central N imide C aryl bond, resulting in enantiomeric atropisomers that are stable and separable up to >120°C. Finally, the ability of the new axially chiral phosphine ligand is demonstrated in a Pd-catalyzed allylic alkylation reaction.
Angelo Sironi - One of the best experts on this subject based on the ideXlab platform.
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highly emitting concomitant polymorphic crystals of a dinuclear rhenium complex
Journal of the American Chemical Society, 2010Co-Authors: Elsa Quartapelle Procopio, Matteo Mauro, Monica Panigati, Daniela Donghi, Giuseppe Dalfonso, Pierluigi Mercandelli, Angelo Sironi, Luisa De ColaAbstract:The dinuclear complex [Re2(μ-Cl)2(CO)6(μ-4,5-(Me3Si)2pyridazine)] gives in the solid state two polymorphs (yellow, 1Y, and orange, 1O), which can be either concomitantly or separately obtained on varying the crystallization rate. Both crystal phases exhibit intense photoluminescence from the lowest lying triplet metal-to-ligand charge transfer state, much stronger than in solution (quantum yields 0.56 and 0.52, for 1O and 1Y respectively, vs 0.06 in toluene), likely due to the Restricted Rotation of the Me3Si groups in the solid state. A clean, irreversible 1O → 1Y single-crystal-to-single-crystal phase transition occurs at 443 K, as revealed by variable temperature X-ray diffraction analysis. In spite of the absence of any strong intermolecular interactions in both forms, 1O and 1Y show very different absorption and emission maxima (λabs 370 and 393 nm, λem 534 and 570 nm, for 1Y and 1O, respectively). This behavior highlights the importance of the local organization of molecular dipoles in perturbing th...
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bis pentafluorophenyl borinic acid a cyclic trimer in the solid state and a monomer with hindered Rotation around the b oh bond in solution
Organometallics, 2003Co-Authors: Tiziana Beringhelli, Daniela Donghi, Giuseppe Dalfonso, Pierluigi Mercandelli, Daniela Maggioni, Angelo SironiAbstract:The title molecule in the solid state exists as a cyclic trimer, with B−O(H)−B bridges and a cyclohexane-like structure (C2 twist-boat conformation); dissolution in toluene-d8 affords the B(C6F5)2OH monomer, in which the low-temperature 19F NMR data reveal Restricted Rotation of the OH substituent around the Ar2B−OH bond (Ea = 39 kJ mol-1), as a result of the partial double-bond character of this interaction.
Shinji Toyota - One of the best experts on this subject based on the ideXlab platform.
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Rotational isomerism involving an acetylenic carbon vii Restricted Rotation about acetylenic axis in a diphenylethyne derivative with sterically crowded m terphenyl moieties
Bulletin of the Chemical Society of Japan, 2005Co-Authors: Shinji Toyota, Yukihiro Yoshida, Takashi Yanagihara, Michio GoichiAbstract:Bis(2,4,4″,6-tetramethyl-1,1′:3′,1″-terphenyl-2′-yl)ethyne was prepared by the Hart reaction and the Stille coupling as a sterically crowded diphenylethyne derivative. The barrier to Rotation about...
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Rotational isomerism involving an acetylenic carbon part 5 Restricted Rotation about acetylenic axis in sterically crowded bis 1 phenyl 9 anthryl ethynes
Tetrahedron Letters, 2003Co-Authors: Shinji Toyota, Toshiaki MakinoAbstract:Abstract The title sterically crowded di-9-anthrylethyne derivative with 3,5-iPr2-phenyl groups at 1-position showed a barrier to Rotation about the acetylenic axis of 18.0 kcal mol−1 based on a dynamic NMR study, which is an extremely high value for acyclic diarylethynes. The mechanism of the dynamic stereochemistry and the substituent effect on the Rotational barrier are discussed.
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Rotational isomerism involving an acetylenic carbon iv synthesis and structure of bis 1 1 3 1 terphenyl 2 yl ethynes molecular design of sterically congested alkynes toward Restricted Rotation about acetylenic axis
Organic and Biomolecular Chemistry, 2003Co-Authors: Shinji Toyota, Taku Iida, Chinatsu Kunizane, Naoki Tanifuji, Yukihiro YoshidaAbstract:The title diphenylethyne derivative with 4-methylphenyl (tolyl) groups at all the ortho positions was synthesized by the Stille or Sonogashira coupling from the corresponding iodide. The X-ray structure revealed that the two terminal phenyl groups at the sp carbons are twisted by 63° out of the coplanar conformation to avoid steric interactions between the tolyl groups. The relative stabilities of possible conformers were analyzed by the PM3 calculations. The axially chiral derivative with two methoxymethyl groups showed no evidence of Restricted Rotation about the acetylenic axis by VT NMR measurements, its barrier being less than 35 kJ mol−1. The spectroscopic features and reactivities of this sterically congested alkyne are also described.
Daniela Donghi - One of the best experts on this subject based on the ideXlab platform.
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highly emitting concomitant polymorphic crystals of a dinuclear rhenium complex
Journal of the American Chemical Society, 2010Co-Authors: Elsa Quartapelle Procopio, Matteo Mauro, Monica Panigati, Daniela Donghi, Giuseppe Dalfonso, Pierluigi Mercandelli, Angelo Sironi, Luisa De ColaAbstract:The dinuclear complex [Re2(μ-Cl)2(CO)6(μ-4,5-(Me3Si)2pyridazine)] gives in the solid state two polymorphs (yellow, 1Y, and orange, 1O), which can be either concomitantly or separately obtained on varying the crystallization rate. Both crystal phases exhibit intense photoluminescence from the lowest lying triplet metal-to-ligand charge transfer state, much stronger than in solution (quantum yields 0.56 and 0.52, for 1O and 1Y respectively, vs 0.06 in toluene), likely due to the Restricted Rotation of the Me3Si groups in the solid state. A clean, irreversible 1O → 1Y single-crystal-to-single-crystal phase transition occurs at 443 K, as revealed by variable temperature X-ray diffraction analysis. In spite of the absence of any strong intermolecular interactions in both forms, 1O and 1Y show very different absorption and emission maxima (λabs 370 and 393 nm, λem 534 and 570 nm, for 1Y and 1O, respectively). This behavior highlights the importance of the local organization of molecular dipoles in perturbing th...
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bis pentafluorophenyl borinic acid a cyclic trimer in the solid state and a monomer with hindered Rotation around the b oh bond in solution
Organometallics, 2003Co-Authors: Tiziana Beringhelli, Daniela Donghi, Giuseppe Dalfonso, Pierluigi Mercandelli, Daniela Maggioni, Angelo SironiAbstract:The title molecule in the solid state exists as a cyclic trimer, with B−O(H)−B bridges and a cyclohexane-like structure (C2 twist-boat conformation); dissolution in toluene-d8 affords the B(C6F5)2OH monomer, in which the low-temperature 19F NMR data reveal Restricted Rotation of the OH substituent around the Ar2B−OH bond (Ea = 39 kJ mol-1), as a result of the partial double-bond character of this interaction.
Giuseppe Dalfonso - One of the best experts on this subject based on the ideXlab platform.
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highly emitting concomitant polymorphic crystals of a dinuclear rhenium complex
Journal of the American Chemical Society, 2010Co-Authors: Elsa Quartapelle Procopio, Matteo Mauro, Monica Panigati, Daniela Donghi, Giuseppe Dalfonso, Pierluigi Mercandelli, Angelo Sironi, Luisa De ColaAbstract:The dinuclear complex [Re2(μ-Cl)2(CO)6(μ-4,5-(Me3Si)2pyridazine)] gives in the solid state two polymorphs (yellow, 1Y, and orange, 1O), which can be either concomitantly or separately obtained on varying the crystallization rate. Both crystal phases exhibit intense photoluminescence from the lowest lying triplet metal-to-ligand charge transfer state, much stronger than in solution (quantum yields 0.56 and 0.52, for 1O and 1Y respectively, vs 0.06 in toluene), likely due to the Restricted Rotation of the Me3Si groups in the solid state. A clean, irreversible 1O → 1Y single-crystal-to-single-crystal phase transition occurs at 443 K, as revealed by variable temperature X-ray diffraction analysis. In spite of the absence of any strong intermolecular interactions in both forms, 1O and 1Y show very different absorption and emission maxima (λabs 370 and 393 nm, λem 534 and 570 nm, for 1Y and 1O, respectively). This behavior highlights the importance of the local organization of molecular dipoles in perturbing th...
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bis pentafluorophenyl borinic acid a cyclic trimer in the solid state and a monomer with hindered Rotation around the b oh bond in solution
Organometallics, 2003Co-Authors: Tiziana Beringhelli, Daniela Donghi, Giuseppe Dalfonso, Pierluigi Mercandelli, Daniela Maggioni, Angelo SironiAbstract:The title molecule in the solid state exists as a cyclic trimer, with B−O(H)−B bridges and a cyclohexane-like structure (C2 twist-boat conformation); dissolution in toluene-d8 affords the B(C6F5)2OH monomer, in which the low-temperature 19F NMR data reveal Restricted Rotation of the OH substituent around the Ar2B−OH bond (Ea = 39 kJ mol-1), as a result of the partial double-bond character of this interaction.