Adsorption of Phenylboronic Acid Derivatives on Rutile TiO 2 (110)

Abstract

Using high-resolution synchrotron-radiation photoelectron spectroscopy and near-edge X-ray-absorption fine structure, we have investigated the adsorption of three phenylboronic acid derivatives on rutile TiO2(110) at 300–700 K: 4-acetylphenylboronic acid, 1,4-phenylenediboronic acid, and 2,4,6-triphenylboroxine. Both 4-acetylphenylboronic acid and 1,4-phenylenediboronic acid adsorb in a singly deprotonated monodentate configuration at 300 K, which converts to a fully deprotonated bidentate species at 550 K. 2,4,6-Triphenylboroxine undergoes a ring-opening reaction upon adsorption on the surface and forms the fully deprotonated bidentate species already at 300 K. In the case of 1,4-phenylenediboronic acid, the upward-pointing boronic-acid groups polymerize into boronic anhydride chains upon heating starting at 350 K. For 2,4,6-triphenylboroxine, we find a slow boron–carbon bond cleavage over a wide temperature range, resulting in a slow disappearance of the phenyl rings from the surface. For 4-acetylphenylboronic acid, we observe a loss of the carbonyl group at 500–550 K. In addition, we observe the formation of trigonal boron oxide (B2O3) for all three molecules at temperatures above 600 K.