Base-Promoted Selective Aryl C-Br and C-I Bond Cleavage by Iridium(III) Porphyrin: Reduction of IrIII-OH to IrII for Metalloradical Ipso Substitution of Aryl-Halogen Bonds

Base-promoted selective aryl carbon-bromine and carbon-iodine bond (Ar-X, X = Br, I) cleavage by iridium(III) porphyrin carbonyl chloride (Ir-III(ttp)(CO)Cl) was achieved in the presence of base (K2CO3, NaOH) to give iridium(III) porphyrin aryls (Ir-III(ttp)Ar). Mechanistic studies revealed that the base undergoes ligand substitution with Ir(ttp)(CO)Cl to yield an iridium hydroxo species (Ir-III(ttp)OH). The hydroxo ligand most likely reduces the Ir(III) center to give iridium(II) porphyrin dimer ([Ir-II(ttp)](2)) and H2O2. In a competitive pathway, [Ir-II(ttp)](2) disproportionates in the presence of base and residual water to give an iridium(III) hydride (Ir-III(ttp)H) and Ir(ttp)OH. In a productive process, [Ir(ttp)](2) undergoes Ir-III(ttp) metalloradical-mediated ipso substitution of Ar-X via an addition-elimination pathway to form Ir(ttp)Ar and Ir(ttp)X. Ir(ttp)X is recycled by reacting with base to regenerate [Ir(ttp)](2) for subsequent Ar-X cleavage.