Copolymers of vinyl chloride with the vinyl esters and acrylates of low molecular weight polyesters of hydroxyacids

Vinyl esters and acrylates of polyesters derived from C₁₀?C₁₈ hydroxyacids have been synthesized and copolymerized with vinyl chloride with the hope of achieving an internally plasticized poly(vinyl chloride). Copolymers containing 10–30% polyester are film-forming materials, and the films cast from THF solutions are generally flexible. A number of these vinyl chloride copolymers with polyesters at approximately 15 and 25% level have been tested for various properties. The internal plasticization is not extensive.     

Photocycloaddition of Some Difluoro(aminoenonato)boron Complexes with Arylalkenes

The photocycloaddition of some difluoro[(methylamino‐κN)alkenonato‐κO]boron complexes 1 with arylalkenes 2 is discussed. The resulting [2+2] photoaddition gave the cyclobutane and azetidine derivatives (Schemes 1, 3, and 5). Rearrangements of the cyclobutane gave 1,5‐diketones derivatives (Schemes 2, 4, and 5). The yields of the photoadducts were governed by the reduction and oxidation potentials. Furthermore, the configurations of the products established high regio‐ and stereoselectivity, suggesting the presence of a singlet exciplex. The reactivity and the stereochemistry were rationalized by means of FMO (frontier molecular orbital) calculations.     

A new organocatalyst for 1,3-dipolar cycloadditions of nitrones to α,β-unsaturated aldehydes

The triflate salt resulting from the treatment of diphenyl-S-prolinol with trimethylsilyl triflate, catalyzes the addition of nitrones to α,β-unsaturated aldehydes to provide isoxazolidines in high yields and excellent diastereo- and enantioselectivities.     

Synthesis and Electroluminescence of Metal 4‐Styryl‐8‐hydroxyquinolates

Aluminum and zinc complexes of 4‐substituted 8‐hydroxyquinoline were used effectively as emissive materials in light‐emitting diodes (LED). The substituents chosen in this study were p‐methoxy‐2‐styryl, p‐diethylamino‐2‐styryl, and naphthalene‐2‐vinyl groups. Their emission spectra were red‐shifted with respect to that of aluminum tris(hydroxylquinolate) (Alq₃) as a result of extending their π‐conjugation. All complexes formed amorphous glasses, which exhibited high thermal and electrical stability. Typical LED devices were fabricated by mixing the dyes with polyvinylcarbazole and spin‐coated to form thin films, which were sandwiched between ITO (indium tin oxide) and a metal electrode. These devices displayed yellow‐orange emissions with quantum efficiency ca. 0.4%.     

The tightness contribution to the Brønsted alpha for hydride transfer between NAD+ analogues

It has been shown that the rate of symmetrical hydride transfer reaction varies with the hydride affinity of the (identical) donor and acceptor. In that case, Marcus theory of atom and group transfer predicts that the Br?nsted alpha depends on the location of the substituent, whether it is in the donor or the acceptor, and the tightness of the critical configuration, as well as the resemblance of the critical configuration to reactants or products. This prediction has now been confirmed for hydride transfer reactions between heterocyclic, nitrogen-containing cations, which can be regarded as analogues of the enzyme cofactor, nicotinamide adenine dinucleotide (NAD+). A series of reactions with substituents in the donor gives Br?nsted alpha of 0.67 +/- 0.03 and a tightness parameter, tau, of 0.64 +/- 0.06. With substituents in the acceptor alpha = 0.32 +/- 0.03 and tau = 0.68 +/- 0.08. The reactions are all spontaneous, with equilibrium constants between 0.4 and 3 x 10(4), and the two sets span about the same range of equilibrium constants. The two tau values are essentially identical with an average value of 0.66 +/- 0.05. These results can be semiquantitatively mimicked by rate constants calculated for a linear, triatomic model of the reaction. Variational transition state theory and a physically motivated but empirically calibrated potential function were used. The computed rate constants generate an alpha value of 0.56 if the hydride affinity of the acceptor is varied and an alpha of 0.44 if the hydride affinity of the donor is varied. The calculated kinetic isotope effects are similar to the measured values. A previous error in the Born charging term of the potential function has been corrected. Marcus theory can be successfully fitted to both the experimental and computed rate constants, and appears to be the most compact way to express and compare them. The success of the linear triatomic model in qualitatively reproducing these results encourages the continued use of this easily conceptualized model to think about group, ion, and atom transfer reactions.     

Dimeric dioxomolybdenum(VI) and oxomolybdenum(V) complexes with citrate at very low pH and neutral conditions

A novel dimeric dioxomolybdenum(VI) citrate complex, K[(MoO2)2-(OH)(H2cit)2].4H2O (1), with weak coordination of beta-carboxylic acid groups and the first structural example of an oxomolybdenum(V) citrate complex, (NH4)6[Mo2O4(cit)2].3H2O (2) (H4cit = citric acid), are isolated in a very acidic solution (pH 0.5-1.0) and neutral conditions (pH 7.0-8.0), respectively. Complex 1 displays strong double hydrogen bonds through beta-carboxyl and beta-carboxylic acid groups [2.621(9) A]. Transformations of the dimeric molybdenum(VI) citrate show that protonation of a carboxyl group will weaken the coordination of molybdenum(VI) citrate. There are obvious dissociations of molybdenum(VI/V) citrate complexes based on 13C NMR observations in solution.