Syntheses of aryl- and arylethynyl-substituted N-confused porphyrins

Palladium-catalyzed cross-coupling reactions under Suzuki, Sonogashira, and Stille conditions afford 3-aryl (9–12) and 3-arylethynyl N-confused porphyrin (NCP) silver(III) complexes (13–15) from the 3-bromo NCP complex (4) in ca. 70% yields along with the transmetalated products, 3-substituted NCP palladium(II) complexes (11-Pd to 15-Pd), in 10–30% yields. Substitution at 3-position was confirmed by the single crystal X-ray structures of 9, 13-Ag, and 13-Pd. The arylethynyl groups or five-membered heterocyclic aromatic rings at 3-position largely affected the optical properties of N-confused porphyrin, in which the longest absorption maxima of the Q-bands are shifted bathochromically by 30–120 nm. The electronic effect of substituent differs largely between palladium and silver complexes reflecting the different π-electron delocalization pathway of NCP cores. 3-Aryl- and 3-arylethynyl NCP silver(III) complexes were easily demetalated to afford the corresponding free base porphyrins by the treatment of sodium borohydride.