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1.
J Am Chem Soc ; 135(46): 17610-6, 2013 Nov 20.
Artigo em Inglês | MEDLINE | ID: mdl-24131214

RESUMO

We have developed methods for installing aryl substituents directly on the phosphino groups of the 1,3-diphosphacyclobutane-2,4-diyl system. The aryl substituents tuned the electronic and structural characteristics of the biradical unit both in solution and in the solid state. 1-tert-butyl-2,4-bis(2,4,6-tri-tert-butylphenyl)-1,3-diphosphacyclobuten-4-yl anion, prepared from phosphaalkyne (Mes*C≡P; Mes* = 2,4,6-tBu3C6H2) and t-butyllithium, was allowed to react with an electron-deficient N-heterocyclic reagent. The corresponding N-heteroaryl-substituted P-heterocyclic biradicals were produced via SNAr reactions. Biradicals bearing perfluorinated pyridyl substituents exhibited photoabsorption properties comparable to those of previously reported derivatives because the highest occupied and lowest unoccupied molecular orbit levels were reduced by a similar amount. In contrast, the triazine substituent reduced the band gap of the biradical unit, and the large red shift in the visible absorption and high oxidation potential were further tuned via subsequent SNAr and Negishi coupling reactions. The amino-substituted triazine structure provided a strongly electron-donating biradical chromophore, which produced unique p-type semiconducting behavior even though there was no obvious π-overlap in the crystalline state. The single-electron transfer reaction involving Mes*C≡P, phenyllithium, and iodine afforded 1,3-diphenyl-2,4-bis(2,4,6-tri-tert-butylphenyl)-1,3-diphosphacyclobutane-2,4-diyl via the intermediate P-heterocyclic monoradical. The tetraaryl-substituted symmetric biradical product was used to determine the electron density distribution from the X-ray diffraction data. The data show highly localized radicalic electrons around the skeletal carbon atoms, moderately polarized skeletal P-C bonds in the four-membered ring, and no covalent transannular interaction.


Assuntos
Compostos Heterocíclicos/química , Compostos Organofosforados/química , Ar , Elétrons , Radicais Livres/síntese química , Radicais Livres/química , Compostos Heterocíclicos/síntese química , Modelos Moleculares , Estrutura Molecular , Teoria Quântica
2.
Chem Asian J ; 8(9): 1976-80, 2013 Sep.
Artigo em Inglês | MEDLINE | ID: mdl-23749413

RESUMO

Mind your "P"s: Silylated P-heterocyclic biradicals activated tetrahydrofuran to give the corresponding 4-siloxybutyl-substituted 1,3-diphosphacyclobutane-2,4-diyls via ring-opening of the solvent molecule. Reductive P-C bond cleavage was found as an alternative approach to 1,3-diphosphacyclobuten-4-yl anion. Redox properties of the new P-heterocyclic biradicals were discussed in terms of hitherto unknown substituent effects.

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