Synthesis and Metalation of Dimethoxybenziporphyrins, Thiabenziporphyrins, and Dibenziporphyrins

Dimethoxybenzitripyrranes
were prepared in excellent yields by
reacting benzene dicarbinols with BF3·Et2O and excess pyrrole in refluxing 1,2-dichloro­ethane. Reaction
with a pyrrole dialdehyde in the presence of TFA, followed by oxidation
with DDQ, afforded good yields of meso-diphenyl­dimethoxy­benzi­porphyrins.
These dimethoxy­porphyrinoids exhibited weakly diatropic properties
that were enhanced upon protonation. The dimethoxy­benzi­tripyrranes
also reacted with a thiophene dicarbinol to give dimethoxy­thiabenzi­porphyrins,
and the nonplanar nature of this system was demonstrated by X-ray
crystallography. The dimethoxy­benzi­porphyrins reacted
with palladium­(II) acetate to give the related organometallic derivatives,
but the thiabenzi­porphyrins underwent a demethylation to afford
palladium­(II) thiaoxybenzi­porphyrins. Related palladium­(II)
complexes were also prepared from previously reported thiacarba­porphyrinoids.
The X-ray structure for one of the complexes showed that the six-membered
ring is very distorted and the thiophene ring is strongly tilted out
of the plane of the macrocycle. The dimethoxy­benzi­tripyrranes
also reacted with dimethoxy­benzene dicarbinols to give the first
examples of dibenzi­porphyrins, thereby further demonstrating
the versatility of this synthetic methodology.