Mechanism\nand Selectivity of Bi(V)-Aryl Oxyfunctionalization\nin Trifluoroacetic Acid Solvents

The oxidative functionalization of aromatic sp<sup>2</sup> C–H\nbonds to C–O bonds is a difficult transformation. For main-group\nmetals, the oxyfunctionalization step of a metal-aryl bond is generally\nslow and potentially problematic if carried out in a relatively strong\nacid solvent where protonation could prevent oxyfunctionalization.\nIn this work, we experimentally and computationally analyzed the oxyfunctionalization\nreaction of (Ph)<sub>3</sub>Bi<sup>V</sup>(TFA)<sub>2</sub> (TFA =\ntrifluoroacetate) in a trifluoroacetic acid (TFAH) solvent. Experiments\nshowed a single oxyfunctionalization product phenyl TFA (PhTFA) and\ntwo equivalents of benzene. Explicit/continuum solvent density functional\ntheory calculations revealed that a direct intramolecular reductive\nfunctionalization pathway is lower in energy than radical or ionic\npathways, and surprisingly from (Ph)<sub>3</sub>Bi<sup>V</sup>(TFA)<sub>2</sub>, the reductive functionalization pathway is potentially competitive\nwith protonation. In contrast, for (Ph)<sub>2</sub>Bi<sup>V</sup>(TFA)<sub>3</sub> oxyfunctionalization is significantly lower in energy than\nprotonation. For Bi<sup>III</sup>-phenyl intermediates, redox neutral\nprotonation is significantly lower in energy than a second functionalization.\nWe also examined the oxyfunctionalization versus protonation of Bi<sup>V</sup>-phenyl complexes with a coordinated biphenyl ligand and a\ncoordinated biphenyl sulfone ligand, which both resulted in oxyfunctionalization.\nFor the biphenyl ligand complex, a protonation-first mechanism is\nproposed, while for the biphenyl sulfone ligand, an oxyfunctionalization\nfirst mechanism is consistent with both calculations and experiments.