posted on 2021-06-11, 15:05authored byFrédéric A. Perras, Alexander L. Paterson, Zoha H. Syed, A. Jeremy Kropf, David M. Kaphan, Massimiliano Delferro, Marek Pruski
Although single-site, supported organometallic
catalysts were designed
with homogeneity in mind, little is strictly known about their atomic-level
structure and uniformity. This is in large part due to the inability
of conventional characterization tools to provide structural information
with adequate resolution and range for this purpose. Here, we show
that dynamic nuclear polarization (DNP)-enhanced solid-state nuclear
magnetic resonance (NMR) enables the measurement of distances between
the surface and individual carbons, making it possible to orient complexes
and molecules on surfaces. We use this approach to determine the orientation
and configuration of naturally 13C-abundant acetate and
supported organoiridium(III) pincer complex, both supported on γ-Al2O3. By combining solid-state NMR and extended X-ray
absorption fine structure spectroscopy (EXAFS) experiments with periodic
density functional theory (DFT) calculations, we are able to determine
the three-dimensional arrangement of ligands around the metal center
and thereby identify the structure of the supported complex at a resolution
reminiscent of that associated with single-crystal diffractometry.