Base-Promoted Selective Aryl Carbon−Bromine Bond Cleavage by Iridium(III) Porphyrin for Iridium(III) Porphyrin Aryl Synthesis: A Metalloradical Ipso Addition−Elimination Mechanism

K2CO3 was found to promote selective aryl carbon−bromine bond (Ar−Br) cleavage by a high-valent iridium(III) porphyrin carbonyl chloride (IrIII(ttp)(CO)Cl, ttp = 5,10,15,20-tetra-p-tolylporphyrinato dianion) in benzene solvent at elevated temperature to give iridium(III) porphyrin aryls (IrIII(ttp)Ar) in high yields. Ir(ttp)(CO)Cl is reduced in alkaline media to give an [Ir(ttp)]2 intermediate. [Ir(ttp)]2 then cleaves the Ar−Br bond via a radical-type addition−elimination reaction (radical ipso -substitution) to yield Ir(ttp)Ar and a bromine radical.