Cerium-promoted formation of metal-free phthalocyanines

Treatment of phthalonitriles with 6 mol% of CeCl3 or Ce(acac)3 (acac=acetylacetonate) in refluxing 1-pentanol affords the corresponding metal-free phthalocyanines in moderate yields. This non-alkaline pathway is complementary to the base-promoted cyclization methods which are commonly employed in the synthesis of phthalocyanines. Addition of 1,8-diazabicyclo[5.4.0]undec-7-ene (DBU) greatly shortens the reaction time and increases the yield of these reactions.