Synthesis, structure, spectroscopic properties, and electrochemistry of (1,8,15,22-tetrasubstituted phthalocyaninato)lead complexes

Three (1,8,15,22-tetrasubstituted phthalocyaninato)lead complexes Pb[Pc(α-OR)₄] [H₂Pc(α-OC₅H ₁₁)₄ = 1,8,15,22-tetrakis(3-pentyloxy)phthalocyanine; H₂Pc(α-OC₇H₁₅)₄ = 1,8,15,22-tetrakis(2,4-dimethyl-3-pentyloxy)phthalocyanine; H ₂Pc(α-OC₁₀H₇)₄ = 1,8,15,22-tetrakis(2-naphthyloxy)phthalocyanine] (1-3) have been prepared as racemic mixtures by treating the corresponding metal-free phthalocyanines H ₂Pc(α-OR)₄ (4-6) with Pb(OAc)₂· 3H₂O in refluxing n-pentanol. The molecular structure of Pb[Pc(α-OC₅H₁₁)₄] (1) in the solid state has been determined by single-crystal X-ray diffraction analysis. This compound, having a nonplanar structure, crystallizes in the monoclinic system with a P2₁/c space group. Each unit cell contains two pairs of enantiomeric molecules, which are linked by weak coordination of the Pb atom of one molecule with an aza nitrogen atom and its neighboring oxygen atom from the alkoxy substituent of another molecule, forming a pseudo-double-decker supramolecular structure in the crystals with a short ring-to-ring separation, 2.726 Å, and thus a strong ring-ring π-π interaction. The decreased molecular symmetry for these complexes has also been revealed by the NMR spectra of 1 and 2. The methyl protons of the 3-pentyloxy and 2,4-dimethyl-3-pentyloxy side chains of 1 and 2, respectively, are chemically inequivalent. In addition to the elemental analysis and various spectroscopic characterizations, these compounds have also been electrochemically studied. Two one-electron oxidations and up to five one-electron reductions have been revealed by cyclic voltammetry (CV) and differential pulse voltammetry (DPV) methods.