Synthesis of polymers bearing pendant norbornadiene moieties by addition reaction of poly(glycidyl methacrylate-co-methyl methacrylate)s with 2,5-norbornadiene-2-carboxylic acids

Polymers bearing photoresponsive norbornadiene (NBD) moieties were synthesized by the addition reaction of poly(glycidyl methacrylate-co-methyl methacrylate)s containing pendant epoxide groups with 3-phenyl-2,5-norbornadiene-2-carboxylic acid (PNBC), 3-[(phenyl)carbamoyl]-2,5-norbornadiene-2-carboxylic acid 3-[(4-acetylphenyl) carbamoyl]-2,5-norbornadiene-2-carboxylic acid (APCND), and 3-[(4-methoxyphenyl)carbamoyl]-2,5-norbornadiene-2-carboxylic acid using tetrabutylammonium bromide as a catalyst in DMF. The polymers bearing pendant PNBC or APCND moieties have higher photochemical reactivity in the film state than the polymers bearing pendant PCND or MPCND moieties. Although the pendant quadricyclane (QC) group produced by the photoirradiation of the PNBC moiety in these polymers has excellent storage stability in the film state, without catalyst at room temperature, the QC group in the polymer film with the catalyst reverts gradually to the NBD moiety at room temperature. © 1993 John Wiley & Sons, Inc.     

Microenvironmental polarity control of electron-transfer photochirogenesis. Enantiodifferentiating polar addition of 1,1-diphenyl-1-alkenes photosensitized by saccharide naphthalenecarboxylates

Enantiodifferentiating polar photoaddition of alcohol to 1,1-diphenylpropene and 1,1-diphenyl-1-butene sensitized by saccharide naphthalene(di)carboxylates was performed in nonpolar to polar solvents containing methanol, ethanol, or 2-propanol as the nucleophile to give the corresponding anti-Markovnikov alcohol adduct, that is, 1,1-diphenyl-2-alkoxy-propane and -butane in low-to-good chemical yields, depending on the sensitizer, chiral auxiliary, alcohol, solvent, and temperature employed. The excited state and intermediate involved, the reaction and enantiodifferentiation mechanism operating, and the factors controlling chemical and optical yields were elucidated from the photochemical and stereochemical outcomes under various conditions and also from the sensitizer and exciplex fluorescence quenching experiments and the molecular orbital calculations. A new strategy was developed to overcome the normally accepted tradeoff between the chemical and optical yields. This is made possible by employing protected saccharides as chiral auxiliaries and running the photoreactions not in a nonpolar but in a low-polarity solvent such as diethyl ether, which jointly enhance the "microenvironmental" polarity around the sensitizer to facilitate electron transfer, keeping the intimate interactions between the chiral sensitizer and substrate within the exciplex intermediate. By optimizing these factors, we obtained the photoadduct in enantiomeric excesses of up to 58%, which is the highest ever reported for a photosensitized bimolecular enantiodifferentiating reaction.     

Determination of chemical structures by 1H- and 13C-NMR for thermally degraded linear high density polyethylene

Chemical structures were determined for polymer residues obtained by thermal degradation of a linear high-density polyethylene. Terminal methyl, double bonds (terminal vinyl, trans-vinylene, and vinylidene), and long chain branching were identified by using ¹H- and ¹³C-NMR spectra data. The number of these functional groups per 1000 C was quantified with a relative error of about 10%.     

Palladium/Me(3)SiOTf-catalyzed bis-silylation of alpha,beta-unsaturated carbonyl compounds without involving oxidative addition of disilane

In the presence of a catalytic amount of Me(3)SiOTf and palladium(0), the addition of disilane to alpha,beta-unsaturated carbonyl compounds proceeds under very mild conditions via eta(3)-siloxyallylpalladium generated by the reaction of enone, enal, or aromatic aldehyde with palladium and Me(3)SiOTf.     

Polarographic study of the Co(II)-catalyzed reduction of nitrite

In the potential region corresponding to the reduction of Co(OH)⁺ to the metal, a catalytic polarographic current is observed in an ammoniacal buffer solution containing nitrite ion. In neutral unbuffered media, the catalytic current appears even on the limiting plateau of aquacobalt(II) reduction wave. The catalytic current is due to the reoxidation of an electrodeposited metallic cobalt to Co(II) by nitrite ion. The condition necessary for the catalytic reaction to proceed is the increase in pH at the electrode surface. It is shown that the hydroxide ion is produced as a result of the catalytic reaction.     

The first synthesis of phosphonoacrolein. Application to Diels-Alder reaction as heterodiene

The first synthesis of phosphonoacrolein 3 was made in quantitative yield by acidic treatment of beta-ethoxy-alpha-(methoxymethyl)vinylphosphonate 2, derived from a beta-ethoxy-alpha-phosphonovinyl anion and MOMCl. The phosphonoacrolein 3 easily underwent a hetero-Diels-Alder reaction with electron-rich alkenes 4a-f or alkynes 9a-c under mild conditions, and phosphono-substituted pyrans 5a-d, 6e,f or pyranopyrans 11a-c were obtained in good to excellent yields. The reaction of 3 with cyclopentadiene and cyclohexadiene led to mixtures of [2 + 4] and [4 + 2] cycloadducts 7a, 8a and 7b, 8b in modest yields. The cycloaddition reaction between 3 and pyranopyran 13 or dibromocarbene and 13 resulted in [4 + 2] or [2 + 1] cycloadducts 14 or 15 in good yields.     

Simultaneous capillary electrophoretic determination of Sb(III) and Bi(III) based on the complex-formation with a W(VI)-P(V) reagent

A capillary electrophoretic method was developed for the simultaneous determination of Sb(III) and Bi(III). A 1.0 mM W(VI)-0.10 mM P(V) complexing reagent readily reacted with a mixture of trace amounts of Sb(III) and Bi(III) to form the corresponding ternary Keggin-type complexes; [P(Sb^IIIW₁₁)O₄₀]⁶⁻ and [P(Bi^IIIW₁₁)O₄₀]⁶⁻ in 0.01 M malonate buffer (pH 2.4). Since the peaks due to the migrations of the ternary complex anions were well separated in the electropherogram, the pre-column complex-formation reaction was applied to the simultaneous CE determination of Sb(III) and Bi(III) with direct UV detection at 255 nm. The calibration curves were linear in the range of 2×10⁻⁷-5×10⁻⁵ M; a detection limit of 1×10⁻⁷ M was achieved for Sb(III) or Bi(III) (the signal-to-noise ratio=3).     

An approach to the synthesis of polyoxometalate encapsulating different kinds of oxoanions as heteroions: bisphosphitopyrophosphatotriacontamolybdate [(HPO3)2(P2O7)Mo30O90]8-

A yellow [(HPO(3))(2)(P(2)O(7))Mo(30)O(90)](8-) anion was prepared as a tetrapropylammonium (Pr(4)N(+)) salt from a 50 mM Mo(VI)-2 mM P(2)O(7)(4-)-4 mM HPO(3)(2-)-0.95 M HCl-60% (v/v) CH(3)CN system at ambient temperature. The (Pr(4)N)(8)[(HPO(3))(2)(P(2)O(7))Mo(30)O(90)] salt crystallized in the orthorhombic space group P(nma) (No. 62), with a = 30.827(2) A, b = 22.8060(15) A, c = 30.928(2) A, V = 21743(3) A(3), and Z = 4. The structure contained a (P(2)O(7))Mo(12)O(42) fragment derived from the removal of each corner-shared Mo(3)O(13) unit in a polar position from a [(P(2)O(7))Mo(18)O(54)](4-) structure, and each side of the (P(2)O(7))Mo(12)O(42) fragment was capped by a B-type (HPO(3))Mo(9)O(24) unit. The [(HPO(3))(2)(P(2)O(7))Mo(30)O(90)](8-) anion was characterized by voltammetry and IR, UV-vis, and (31)P NMR spectroscopy. Unlike the Keggin and Dawson anions and the parent [(P(2)O(7))Mo(18)O(54)](4-) anion, the [(HPO(3))(2)(P(2)O(7))Mo(30)O(90)](8-) anion exhibited two-electron redox waves in CH(3)CN with and without acid.     

Nature and energies of electrons and holes in a conjugated polymer, polyfluorene

Electrons and holes were injected selectively into poly-2,7-(9,9-dihexylfluorene) (pF) dissolved in a tetrahydrofuran (THF) and a 1,2-dichloroethane (DCE) solution, respectively, using pulse radiolysis. Transient absorption spectra of monoions of both signs revealed two bands attributable to formation of polarons, one in the visible region (pF+* at 580 nm, pF-* at 600 nm) and another in the near-IR region. Additional confirmation for the identification of pF+* and pF-* comes from bimolecular charge-transfer reactions, such as bithiophene-* + pF --> pF-* or pF+* + TTA --> +TTA+* (TTA = tri-p-tolylamine), in which known radical ions transfer charge to pF or from pF. Difference absorption spectra of pF chemically reduced by sodium in THF provided a ratio of absorbance of anions formed to bleaching of the neutral band at 380 nm. In conjunction with pulse-radiolysis results, the data show that each polaron occupies 4.5 +/- 0.5 fluorene units, most probably contiguous units. Extensive reduction of pF by sodium also revealed resistance to formation of bipolarons: excess electrons reside as separate polarons when two or more electrons were injected. Redox equilibria with pyrene and terthiophene by pulse radiolysis established reversible one-electron redox potentials of E0(pF+/0) = +0.66 V and E0(pF0/-) = -2.65 V vs Fc+/0. Together with the excited-state energy, these results predict a singlet exciton binding energy of 0.2 eV for pF in the presence of 0.1 M tetrabutylammonium tetrafluoroborate. This binding energy would increase substantially without an electrolyte.