An efficient two-step synthesis of metal-free phthalocyanines using a Zn(II) template

Abstract

The templating effects of strongly coordinating ions like Co(II), Cu(II), and Zn(II) can dramatically improve the yields of phthalocyanine synthesis. The main problem with this approach is the lack of reported conditions for the subsequent removal of such ions to generate metal-free phthalocyanines. During our synthesis of guanidine-containing phthalocyanines we discovered a new demetallation reaction that, to the best of our knowledge, provides the first examples of Zn(II) removal without destroying the phthalocyanine itself. This demetallation reaction appears to be general as it works for electron rich, electron poor, and unsubstituted phthalocyanines. Zn(II)-templated cyclotetramerization, followed by Zn(II) removal provides a high-yielding route (80 – 90 %) to diverse, metal-free phthalocyanines. In contrast, the reported yields with existing methods are typically 10 – 60 %. Given the general importance of metal-free phthalocyanines in photovoltaic devices, chemical sensors, and data storage devices, we are confident this new route to metal-free phthalocyanines will be of general interest.