# Synthesis, Spectroscopic Properties, and Metalation of 3-Alkoxybenziporphyrins

## TL;DR

This paper describes the synthesis and study of 3-alkoxybenziporphyrins, focusing on their spectroscopic properties and reactions with metals.

## Contribution

The novel contribution is the synthesis and characterization of 3-alkoxybenziporphyrins and their metal complexes, revealing unique spectroscopic behaviors.

## Key findings

- 3-alkoxybenziporphyrins were successfully synthesized in good yields through a three-step process.
- Nickel(II) and palladium(II) complexes of these porphyrinoids showed enhanced diatropic properties.
- Spectroscopic titration revealed stepwise protonation and formation of monocationic and dicationic species.

## Abstract

A series of 5-alkoxy-1,3-benzenedicarbaldehydes and related dimers were prepared in three steps from dimethyl 5-hydroxyisophthalate. Acid catalyzed condensation of the dialdehydes with a tripyrrane dicarboxylic acid, followed by oxidation with 2,3-dichloro-5,6-dicyano-1,4-benzoquinone, afforded good yields of 3-alkoxybenziporphyrins, although dimeric tetraaldehydes failed to give isolatable porphyrinoid products. Proton NMR spectroscopy gave no indication of an aromatic ring current, but addition of trifluoroacetic acid resulted in the formation of dications that exhibited weakly diatropic characteristics. Spectroscopic titration with TFA demonstrated that stepwise protonation took place, generating monocationic and dicationic species. 3-Alkoxybenziporphyrins reacted with nickel(II) or palladium(II) acetate to give the related nickel(II) or palladium(II) complexes. These stable organometallic derivatives showed increased diatropic properties that were most pronounced for the palladium(II) complexes. These unique porphyrinoids provide further insights into the properties of benziporphyrins.