The synthesis of triphyrin(2.1.1) compounds is described. In contrast with conventional subporphyrins, which consistently contain a central boron atom, free-base heteroaromatic compounds can be formed. A modified Lindsey method was used to prepare a range of different triphyrins(2.1.1) in yields of up to 35% based on the reaction of diethylpyrrole (1a) and fused pyrroles of bicyclo[2.2.2]octadiene (BCOD) (2a-e) and dihydroethanonaphthalene (4a) with various aryl aldehydes. The concentration of BF3OEt2 catalyst plays the key role in determining the yield of the triphyrin(2.1.1) macrocycle relative to the conventional tetrapyrrole porphyrin product. Retro-Diels-Alder reactions of 2a-e and 4a result in the formation of tribenzotriphyrin (2.1.1) (3a-e) and trinaphthotriphyrin(2.1.1) (5a). The effects of exocyclic ring annulation on the electronic structure are examined in detail based on optical spectroscopy, theoretical calculations, and electrochemical measurements. The availability of free-base compounds enables the formation of [ReI(CO)3(triphyrin)] (6a) and [Ru II(CO)2Cl(triphyrin)] (7a) complexes based on a modified retro-Diels-Alder reaction. X-ray structures are reported for 4a and 6a.
ASJC Scopus subject areas
- Organic Chemistry