Issue 17, 2025

Synthesis, structure, and properties of antiaromatic PV[double bond, length as m-dash]O complexes of triphyrins(2.1.1)

Abstract

A series of antiaromatic stable PV[double bond, length as m-dash]O complexes of meso-tetra(p-tolyl) triphyrin(2.1.1) and its β-substituted derivatives were synthesized in 38–48% yields by treating an appropriate aromatic free base triphyrin(2.1.1) with PCl3 in toluene/Et3N at reflux for 4–6 h. During the reaction, 14π aromatic meso-tetra(p-tolyl) triphyrin(2.1.1) is reduced to a 16π macrocycle and complexes with PV[double bond, length as m-dash]O to form antiaromatic PV[double bond, length as m-dash]O complexes of meso-tetra(p-tolyl) triphyrins(2.1.1). The X-ray structure obtained for one of the PV[double bond, length as m-dash]O triphyrin(2.1.1) complexes revealed that unlike the almost planar structure of free base meso-tetraaryl triphyrin(2.1.1), PV[double bond, length as m-dash]O triphyrin(2.1.1) was highly distorted and adopted a domed structure with P(V) placed at a distance of 0.927 Å above the mean plane defined by the four meso-carbon atoms. NMR studies indicated the paratropic ring current effect in the PV[double bond, length as m-dash]O triphyrin(2.1.1) complexes and the outer β-pyrrole protons which appear in the downfield region of 7.50–8.20 ppm in free base triphyrin(2.1.1) experienced significant upfield shifts and appeared in the region of 3.50–4.50 ppm in PV[double bond, length as m-dash]O triphyrin(2.1.1) complexes, supporting the switching of aromatic 14π free base triphyrin(2.1.1) to antiaromatic 16π PV[double bond, length as m-dash]O triphyrin(2.1.1) complexes. The PV[double bond, length as m-dash]O triphyrin(2.1.1) complexes show one intense absorption band in the 300–350 nm region and an antiaromatic characteristic broad band in the lower energy region of 450–1000 nm. The electrochemical studies revealed that the PV[double bond, length as m-dash]O triphyrin(2.1.1) complexes undergo very easy oxidations and difficult reductions compared to their corresponding free base triphyrins(2.1.1). DFT/TD-DFT calculations were carried out to support the experimental observations.

Graphical abstract: Synthesis, structure, and properties of antiaromatic PV [[double bond, length as m-dash]] O complexes of triphyrins(2.1.1)

Supplementary files

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Article information

Article type
Paper
Submitted
27 Jan 2025
Accepted
20 Mar 2025
First published
02 Apr 2025

Dalton Trans., 2025,54, 6935-6945

Synthesis, structure, and properties of antiaromatic PV[double bond, length as m-dash]O complexes of triphyrins(2.1.1)

A. Sharma and M. Ravikanth, Dalton Trans., 2025, 54, 6935 DOI: 10.1039/D5DT00221D

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