Influence of peripheral halogenation on axial phenoxylation kinetics of boron subphthalocyanines

We investigate the effect of peripheral fluorination and chlorination on the rate of axial phenoxylation of boron subphthalocyanines (BsubPcs), with Br and Cl as axial ligands, specifically Br-BsubPc, Br-F₁₂BsubPc, Br-Cl₁₂BsubPc, Cl-BsubPc, and Cl-F₁₂BsubPc. For this study, we use various solvents at their reflux temperature to acquire conversion of axial phenoxylation and obtain kinetic data. We found the experimentally observed reactivity of the BsubPcs used in this study followed Br-BsubPc > Cl-BsubPc > Br-F₁₂BsubPc ≈ Br-Cl₁₂SubPc >> Cl-F₁₂BsubPc. This shows that peripheral fluorination or chlorination inhibits the rate of axial phenoxylation and confirms the axial B–Br bonds to be more reactive than B–Cl bonds. Density functional theory (DFT) calculations confirm the observed kinetic data and suggest that phenoxylation proceeds primarily via the Torres mechanism.