Ligand-Assisted Carbonyl Bond Activation in Single Diastereomeric Complexes on Platinum

• Published in: ACS catalysis 2022-10, Vol.12 (19), p.12186-12194
• Main Authors: Zeng, Yang, Lemay, Jean-Christian, Dong, Yi, Garcia, James, Groves, Michael. N, McBreen, Peter H.
• Format: Article
• Language: English
• ISSN: 2155-5435; 2155-5435
• DOI: 10.1021/acscatal.2c03253

It is a significant challenge to relate ligand-assisted bond activation on metal surfaces to specific adsorption and intermolecular binding structures. To address this objective, we studied carbonyl bond activation in single chirality transfer complexes formed by methyl 3,3,3-trifluoropyruvate (i.e., MTFP) and (R)-1-(1-naphthyl)­ethylamine (i.e., (R)-NEA) on a Pt(111) surface. The experiments combined reflectance absorbance infrared spectroscopy (RAIRS), scanning tunneling microscopy (STM), and density functional theory (DFT) methods. While STM measurements, in combination with DFT calculations, permit the study of single surface complexes, RAIRS is an ensemble technique that yields a composite spectrum resulting from an often heterogeneous distribution of molecular structures on the sampled surface. We show that the intrinsic thermal behavior of the MTFP/(R)-NEA/Pt­(111) system facilitates meaningful comparison between single complex measurements by STM and ensemble measurements by RAIRS in that the vibrational signal can be attributed to a small number of complexation configurations, one of which has a high relative abundance. We take advantage of mode mixing in a ν­(CF3) + ν­(CO)keto vibration to detect a spectroscopic signature for complexation-induced carbonyl bond activation. A red-shift of the band correlates with DFT-predicted lengthening of the bridge-bonded carbonyl group. While the intensity of the shifted band is in the majority due to the most abundant complexation configuration, minority states produce line broadening. In addition to providing insight on rate-enhancement in enantioselective reactions on catalysts bearing chiral auxiliaries, the study contributes to the development of ligand control of reactivity and selectivity in heterogeneous catalysis.