Tetraiodophthalocyanines: Simple and convenient synthetic protocol and structural modification via Sonogashira cross-coupling reaction

Planar and sandwich-type iodo-substituted phthalocyanines – precursors for cross-coupling reactions were synthesized starting from 4-iodophthalonitrile via a novel user-friendly synthetic strategy. For this purpose, 4-iodophthalonitrile was prepared following the multi-step protocol, including nonclassical version of diazotization/iodination reaction in the presence of p-toluenesulfonic acid. Tetraiodophthalocyaninato Zinc(II) was obtained using a solvent-free microwave-assisted synthesis. For the first time, the polyphosphoric acid was applied to the demetallation of halogen-substituted phthalocyanine complex. Under these conditions, demetallation of Zinc(II) complex occurred in a good yield without the oxidation of peripheral iodogroups. The Sonogashira cross-coupling reaction between the 2(3),9(10),16(17),23(24)-tetraiodophthalocyanine and model (trimethylsilyl)acetylene resulted in a target compound in a high yield (94%). The versatility of iodo-substituted phthalocyanine precursors was demonstrated on the examples of the synthesis of novel tetra-(3-hydroxyprop-1-yn-1-yl)- phthalocyaninato Zinc (II) (52% yield), bis [tetra(2-trimethyhilyethynyl)phthalocyaninato] Lutetium (III) (45% yield). Target compounds were identified by nuclear magnetic resonance, infrared spectroscopy, and mass spectrometry. UV–Vis properties of target compounds were investigated and compared with literature data. The key compounds were characterized by elemental analysis.