Publication Date:
2012-04-15
Description:
Air-tolerant 2,4-bis(2,4,6-tri- t -butylphenyl)-1,3-diphosphacyclobutane-2,4-diyl singlet biradicals can be prepared by utilizing the unique reactivity of a kinetically stabilized P≡C triple bond compound. In this procedure, we studied the spectroscopic properties of a fundamental unsymmetrical P-heterocyclic biradical containing both PEt and PMe moieties, and the effects of the PCH 2 OMe group in relation to the stability of the P-heterocyclic biradical skeleton. The experimentally observed nuclear magnetic resonance and photo-absorption parameters of 1-ethyl-3-methyl-2,4-bis(2,4,6-tri- t -butylphenyl)-1,3-diphosphacyclobutane-2,4-diyl were discussed based on our previous findings and density functional theory calculations, suggesting particular structural characteristics of the P-heterocyclic biradical skeleton and aromatic substituent effects on the sp 2 -C atoms in the 4-membered ring. Introduction of the methoxymethyl group in the P 2 C 2 biradical moiety gave more stabilized 1,3-diphosphacyclobutane-2,4-diyl derivatives. In comparison with considerably unstable biradicals bearing propargyl substituents, relatively higher lowest unoccupied molecular orbital energies suggest reluctant oxidation of the P-heterocyclic skeleton. Copyright © 2011 John Wiley & Sons, Ltd. UV-Vis photo-absorption properties for air-tolerant 1,3-diphosphacyclobutane-2,4-diyls as singlet biradicals indicate that employed sterically bulky aromatic substituents such as Mes* on the sp 2 -C atoms substantially conjugate with the cyclic skeleton to protect the biradical moiety effectively. The PR groups control the biradical stability by altering the electronic structures of the particular 4-membered heterocyclic system.
Print ISSN:
0894-3230
Electronic ISSN:
1099-1395
Topics:
Chemistry and Pharmacology
,
Physics
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