5-Phenyl- and 5,10-diphenyltetrabenzoporphyrins: Novel synthetic approach, physicochemical study with an emphasis on NMR spectroscopy, and identification of benzylated derivatives

Abstract

Novel synthetic approach to low-symmetry meso-phenylsubstituted tetrabenzoporphyrins (TPBs) by Zn(OAc)2 templated assembly of phthalonitrile in the presence of benzyltriphenylphosphonium chloride has been proposed affording two main products: 5-phenyl-21H,23H-TBP (1) and 5,10-diphenyl-21H,23H-TBP (2) with higher yield for compound 1. Procedure for isolation of 1 and 2 in individual high purity state has been developed supplemented with selection of an appropriate NMR solvent system (CDCl3 with 1% additive of CF3COOH) that allowed full signal assignment in 1Н and 13С spectra to be made utilizing homonuclear 1H–1H (COSY, NOESY, TOCSY) and heteronuclear 1H–13C (HSQC) correlation techniques. Isolation and physicochemical study of a mixture of monobenzylated co-products 1a−g were carried out as well involving 1D and 2D NMR spectroscopies, which for the first time allowed not only to find out their structure, but also to determine the ratio of the positional isomers formed.