Synthesis and properties of β-arylated triphyrins[2.1.1] by successive introduction of one to six aryl groups at the β-pyrrole carbons

Abstract

The β-arylated meso-tetra(p-tolyl) triphyrins[2.1.1] containing two, three, and four p-fluorophenyl groups were synthesized by reacting appropriate β-bromo triphyrin[2.1.1] with p-fluorophenyl boronic acid in toluene/THF/H₂O (1:1:1) at 80 ^οC for 8 h–12 h and their properties were compared with our previously reported β-arylated triphyrins[2.1.1] containing one and six p-fluorophenyl groups. The increase of the number of p-fluorophenyl groups at the β-pyrrole carbons induces steric hindrance at the periphery of triphyrin[2.1.1] that results in the alteration of electronic properties due to distortion in the macrocycle which is reflected in their structure, spectral and redox properties. The X-ray structure analysis revealed that β-di(p-fluorophenyl) meso-tetra(p-tolyl) triphyrin[2.1.1] was almost planar like meso-tetra(phenyl) triphyrin[2.1.1] whereas the β-hexa(p-fluorophenyl) meso-tetra(p-tolyl) triphyrin[2.1.1] was significantly distorted. The absorption spectra of β-arylated triphyrins[2.1.1] showed bathochromically shifted Soret and Q-bands with reduction in absorption coefficients and increase in the bandwidth compared to the β-unsubstituted meso-tetra(p-tolyl) triphyrin[2.1.1] and the maximum effects were noted for β-hexa(p-fluorophenyl) meso-tetra(p-tolyl) triphyrin[2.1.1]. The β-arylated meso-tetra(p-tolyl) triphyrins[2.1.1] are stable under electrochemical conditions and DFT/TD-DFT studies are in agreement with the experimental observations.