Hw. Boone et al., N,N'-DIPHENYL-1,4(5)-DIMETHOXYANTHRAQUINONE DIIMINES - BUTTERFLY INVERSION OF ANTHRAQUINONE DIIMINES, Journal of organic chemistry, 60(16), 1995, pp. 5279-5283
Model compounds for polyaromatic quinone imines were synthesized and c
haracterized by variable-temperature H-1 NMR spectroscopy and X-ray si
ngle crystal structure determination. N,N'-Diphenyl-1,4(5)-dimethoxyan
thraquinone 9,10-diimines were synthesized by condensing 2 equiv of an
iline with 1,5-dimethoxyanthraquinone (15DMAQ) and 1,4-dimethoxyanthra
quinone (14DMAQ), respectively, in the presence of titanium tetrachlor
ide and 1,4-diazabicyclo[2.2.2]octane (DABCO). The X-ray single crysta
l structure determination of the diimine of 15DMAQ is reported. The co
ndensation of aniline with anthraquinones results in a buckling of the
anthraquinone ring system, giving it a ''butterfly'' conformation whi
le the diimine of 15DMAQ has an anti configuration with the N-phenyl r
ings lying above the methoxy substituents. The diimine of 14DMAQ has a
syn configuration, again with these N-phenyl rings lying above the me
thoxy substituents. The symmetrical structural butterfly conformations
of the diimines allowed for the observation of a dynamic butterfly in
version by variable-temperature H-1 NMR spectroscopy. The energy barri
ers for the butterfly inversion of N-phenyl 15DMAQ and 14DMAQ diimines
are 9.5 kcal/mol. The implications of the crystal structure and molec
ular dynamics for the polymeric structures are discussed.