Base-Promoted Aryl Carbon–Iodine and Carbon–Bromine Bond Cleavage with Rhodium Porphyrin Complexes: Scope and Mechanism

Base-promoted aryl carbon–iodine and carbon–bromine bond (Ar–X, X = I, Br) cleavage by rhodium porphyrin complexes was achieved to give the rhodium­(III) porphyrin aryls Rh­(ttp)Ar (ttp = tetra-<i>p</i>-tolylporphyrinato dianion). Mechanistic studies showed that Rh^II₂(ttp)₂ is the intermediate for Ar–X (X = I, Br) cleavage. The Ar–X cleavage process goes through a rhodium­(II) porphyrin radical mediated ipso-substitution mechanism

Competitive Aryl–Fluorine and Aryl–Halogen (Halogen = Cl, Br) Bond Cleavage with Iridium Porphyrin Complexes

Base-promoted competitive Ar–F and Ar–X (X = Cl, Br) bond cleavage with iridium porphyrin complexes was investigated. Mechanistic studies suggested that Ir­(ttp)⁻ (ttp = 5,10,15,20-tetra-<i>p</i>-tolylporphyrinato dianion) cleaves the Ar–F bond via nucleophilic aromatic substitution and Ir₂(ttp)₂ cleaves the Ar–X (X = Cl, Br) bond via metalloradical <i>ipso</i> substitution. Therefore, a stronger base, polar solvent, lower temperature, and iridium anion precursor favor Ar–F bond cleavage, while a weaker base, nonpolar solvent, higher temperature, and Ir₂(ttp)₂ precursor favor Ar–X (X = Cl, Br) bond cleavage

Consecutive Aromatic Carbon–Fluorine Bond and Carbon–Hydrogen Bond Activations by Iridium Porphyrins

Consecutive aromatic C–F bond and C–H bond activations of aryl fluorides were achieved by iridium porphyrins to initially give aryl and finally fluoroaryl iridium porphyrins. The C–F bond activation product is generated first, which is the precursor for the C–H bond activation. Both experimental and theoretical results support that the C–F bond is cleaved by iridium porphyrin anion through nucleophilic aromatic substitution, and the C–H bond cleavage is through homolytic aromatic substitution by iridium porphyrin radical followed by hydrogen atom abstraction. Moreover, the <i>meta</i>-fluorophenyl iridium porphyrin is the most thermodynamic stable regioisomers