Premium
One‐Electron‐Reduced and ‐Oxidized Stages of Donor‐Substituted 1,1,4,4‐Tetracyanobuta‐1,3‐dienes of Different Molecular Architectures
Author(s) -
Kivala Milan,
Stanoeva Tsvetanka,
Michinobu Tsuyoshi,
Frank Brian,
Gescheidt Georg,
Diederich François
Publication year - 2008
Publication title -
chemistry – a european journal
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.687
H-Index - 242
eISSN - 1521-3765
pISSN - 0947-6539
DOI - 10.1002/chem.200800716
Subject(s) - electron paramagnetic resonance , chemistry , delocalized electron , tetracyanoethylene , hyperfine structure , electron donor , molecular orbital , crystallography , photochemistry , density functional theory , computational chemistry , molecule , nuclear magnetic resonance , organic chemistry , atomic physics , physics , catalysis
A series of monomeric and oligomeric donor‐substituted 1,1,4,4‐tetracyanobuta‐1,3‐dienes (TCBDs) with various topologies have been synthesized by means of thermal [2+2] cycloaddition between tetracyanoethylene (TCNE) and donor‐substituted alkynes, followed by retro‐electrocyclization. One‐electron‐reduced and ‐oxidized stages of the donor‐substituted TCBDs were generated by chemical methods. The obtained radical anions and radical cations were studied by using electron paramagnetic resonance/electron nuclear double resonance (EPR/ENDOR) spectroscopy, supported by density functional theory (DFT) calculations. The extent of π‐electron delocalization in the paramagnetic species was investigated in terms of the EPR parameters. Despite favorable molecular orbital (MO) coefficients, the EPR results suggest that in radical anions the spin and charge are confined to the electron‐withdrawing TCBD moieties on the hyperfine EPR timescale. The observed spin localization is presumably caused by an interplay between the nonplanarity of the studied π systems, limited π‐electron conjugation, and very likely counterion effects. In radical cations, an analogous spin and charge localization confined to the electron‐donating N , N ‐dialkylaniline moieties was found. In this case, an efficient electron delocalization is disabled by small MO coefficients at the joints between the donor and acceptor portions of the studied TCBDs.