Modification of alkyne-functionalized asymmetric phthalocyanines by CuI-catalyzed azide-alkyne cycloaddition

Abstract

The use of asymmetric phthalocyanines (Pcs) as platforms for the preparation of several asymmetric hexatriazolyl-monohydroxyphthalocyanines via copper(I)-catalyzed azide-alkyne cycloaddition (CuAAC) reaction was investigated. Asymmetric Pcs 5a and 5b were prepared through statistical macrocyclization of phthalonitriles (Pns) 1a and 2 to give PMB-protected 4a and 4b, which afforded asymmetric Pcs 5a and 5b after acidic cleavage. The ‘ROMP-Capture-Release’ method as a synthetic approach to prepare asymmetric Pc 5b was also evaluated. TIPS-protection of the terminal alkynes was necessary to prevent cross-coupling during the ring-opening metathesis polymerization (ROMP) step. Zinc Pc 5b was successfully used as a scaffold for functional modification under CuAAC conditions using several azides bearing hydrophobic, photo-crosslinkable, or electroactive moieties. Monitoring the CuAAC reaction by both UV/Vis and FTIR spectroscopies provided insight into the role of azide equivalent, reaction time, and catalyst on reaction progress.