Copper(II)-Mediated Aromatic ortho-Hydroxylation: A Hybrid DFT and Ab Initio Exploration

Mechanistic pathways for the aromatic hydroxylation by [CuII(L1)(TMAO)(O)]− (L1=hippuric acid, TMAO=trimethylamine N‐oxide), derived from the ON bond homolysis of its [CuII(L1)(TMAO)2] precursor, were explored by using hybrid density functional theory (B3LYP) and highly correlated ab initio methods (QCISD and CCSD). Published experimental studies suggest that the catalytic reaction is triggered by a terminal copper–oxo species, and a detailed study of electronic structures, bonding, and energetics of the corresponding electromers is presented. Two pathways, a stepwise and a concerted reaction, were considered for the hydroxylation process. The results reveal a clear preference for the concerted pathway, in which the terminal oxygen atom directly attacks the carbon atom of the benzene ring, leading to the ortho‐selectively hydroxylated product. Solvent effects were probed by using the PCM and CPCM solvation models, and the PCM model was found to perform better in the present case. Excellent agreement between the experimental and computational results was found, in particular also for changes in reactivity with derivatives of L1. Reaction mechanisms: The results of density functional theory (B3LYP) and ab initio (QCISD and CCSD) calculations were used to understand the mechanism of aromatic hydroxylation (see scheme) by a transient terminal copper–oxo complex. Two pathways, a stepwise and a concerted reaction, were considered for the hydroxylation process. The results reveal a clear preference for the concerted pathway, leading to the ortho‐selectively hydroxylated product.