Copper oxide surfaces modified by alkylphosphonic acids with terminal pyridyl-based ligands as a platform for supported catalysis

Abstract

Self-assembled monolayer (SAM) films of phosphonates have been successfully formed via reaction of 11-hydroxyundecylphosphonic acid or 4,4′-di(methylenephosphonic acid)-2,2′-bipyridine with the oxide layer of copper via the Tethering by Aggregation and Growth (TBAG) deposition method. The hydroxyl-terminated SAM was further modified with isonicotinic acid or 4,4′-dicarboxy-2,2′-bipyridine through a Steglich esterification reaction. These three surfaces derivatized with pyridyl-based ligands are potential platforms for supported catalysis. As a proof of concept, [Ru(CO)3Cl2]2 was bound to the surfaces through the pyridyl-based ligands to yield tethered analogs of the known carbon dioxide reduction catalyst, [Ru(bpy)(CO)2Cl2]. Surface modification reactions were confirmed through specular reflectance infrared (IR) spectroscopy and X-ray photoelectron spectroscopy (XPS). Characteristic core binding energies were observed in the XPS analyses for phosphorus (P 2p), nitrogen (N 1s), and ruthenium (Ru 3p and Ru 3d), verifying the presence of the various surface functionalizations. IR and XPS data indicate that the phosphonate binding to the copper surface is tridentate in nature.