The Synthesis and Properties of Free-Base [14]Triphyrin(2.1.1) Compounds and the Formation of Subporphyrinoid Metal Complexes

• Published in: Chemistry : a European journal 2011-04, Vol.17 (16), p.4396-4407
• Main Authors: Xue, Zhao Li, Mack, John, Lu, Hua, Zhang, Lei, You, Xiao Zeng, Kuzuhara, Daiki, Stillman, Martin, Yamada, Hiroko, Yamauchi, Seigo, Kobayashi, Nagao, Shen, Zhen
• Format: Article
• Language: English
• Subjects: Availability; Chemical reactions; Chemistry; electrochemistry; Formations; Heteroaromatic compounds; magnetic circular dichroism; Mathematical analysis; Organic chemistry; porphyrinoids; structure elucidation; Synthesis; triphyrins; X-rays
• ISSN: 0947-6539; 1521-3765
• DOI: 10.1002/chem.201003100

The synthesis of [14]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 [14]triphyrins(2.1.1) in yields of up to 35 % based on the reaction of diethylpyrrole (1 a) and fused pyrroles of bicyclo[2.2.2]octadiene (BCOD) (2 a–e) and dihydroethanonaphthalene (4 a) with various aryl aldehydes. The concentration of BF3⋅OEt2 catalyst plays the key role in determining the yield of the [14]triphyrin(2.1.1) macrocycle relative to the conventional tetrapyrrole porphyrin product. Retro‐Diels–Alder reactions of 2 a–e and 4 a result in the formation of [14]tribenzotriphyrin (2.1.1) (3 a–e) and [14]trinaphthotriphyrin(2.1.1) (5 a). 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)] (6 a) and [RuII(CO)2Cl(triphyrin)] (7 a) complexes based on a modified retro‐Diels–Alder reaction. X‐ray structures are reported for 4 a and 6 a. A general synthetic approach for the synthesis of free‐base [14]triphyrin(2.1.1) compounds and metal [14]tribenzotriphyrin(2.1.1) complexes (see graphic) is described based on a modified Lindsey‐method reaction. The mechanism of [14]triphyrins (2.1.1) formation is described in detail and the effects of exocyclic ring annulation with benzo and naphtho rings are examined based on optical spectroscopy, theoretical calculations, and electrochemical measurements.