Unlocking PEG-400: A Sustainable Reaction Medium for Phthalocyanine Synthesis and Pd-Catalyzed C–C Bond Formation

<jats:p>The replacement of conventional high-boiling polar organic solvents with sustainable and recyclable alternatives is a central challenge in green chemistry, especially for transformations that require harsh conditions and prolonged heating. In this work, we demonstrate that poly(ethylene glycol)-400 (PEG-400) can efficiently replace traditional and harmful solvents such as N,N-dimethylaminoethanol (DMAE) and N,N-dimethylformamide (DMF) in the synthesis of phthalocyanines. PEG-400 enables high-temperature cyclotetramerization reactions under operationally simple and comparatively safer conditions, providing isolated yields of 50-83% across a range of metalated and metal-free derivatives and substitution patterns, while maintaining solvent loss and waste generation at relatively low levels. Remarkably, PEG-400 is also compatible with in-pot palladium-catalyzed C-C coupling reactions. This enables sequential cyclotetramerization followed by Sonogashira or Suzuki coupling without isolation of the macrocyclic intermediate, affording functionalized products in up to 75% yield and providing access to more complex derivatives in a more practical way. Green metrics analyses, such as E-factor and PMI, further support the improved material-efficiency profile of the method when compared to representative literature procedures. Overall, these results demonstrate that PEG-400 combines thermal robustness with compatibility toward Pd-catalyzed cross-coupling reactions, establishing it as a versatile and sustainable medium for resource-efficient multi-step organic synthesis and the preparation of highly functionalized phthalocyanine derivatives. The strategy provides a basis for potential extension to preparative-scale processes.</jats:p>