Synthesis of the β-dipyrrinyl triphyrin(2.1.1) ligand and its coordination complexes

Abstract

Functionalized β-formylphenyl triphyrin(2.1.1) was prepared by coupling β-bromo triphyrin(2.1.1) with 4-formylphenyl boronic acid under Pd(0) coupling conditions. β-Formylphenyl triphyrin(2.1.1) was treated with excess pyrrole under acid catalyzed conditions in CH₂Cl₂ to obtain dipyrramethanyl triphyrin(2.1.1), which was subjected to oxidation by treating it with DDQ to obtain the desired ligand, β-dipyrrinyl triphyrin(2.1.1). The dipyrrinyl unit of triphyrin(2.1.1) can act as a bidentate ligand to form interesting coordination complexes. Thus, the dipyrrinyl triphyrin(2.1.1) ligand was treated with BF₃·(OEt)₂ as well as metal salts such as [Ru(p-cymene)Cl₂]₂, Pd(acac)₂ and Zn(CH₃COO)₂ to obtain BODIPY-triphyrin(2.1.1), Pd(II)dipyrrin-triphyrin(2.1.1), Ru(II)-dipyrrin-triphyrin(2.1.1) and bis(Zn dipyrrin)-triphyrin(2.1.1) conjugates in good yields. The ligand and all four conjugates were freely soluble in common organic solvents and thoroughly characterized and studied by HR-MS, 1D & 2D NMR spectroscopy, absorption, cyclic voltammetry and DFT/TD-DFT studies. The optimized structures indicated that the triphyrin(2.1.1) and BODIPY/metal dipyrrin units in the conjugates were oriented w.r.t each other with an angle in the range of 25.18°–77.55°. The spectral studies indicated that the two moieties in the conjugates interact weakly and retain their individual characteristics, whereas electrochemical studies revealed their electron deficient nature. The TD-DFT studies were in agreement with the experimental observations.