Reversible Grafting in Surface Organometallic Chemistry with a Late Transition-Metal Amidinate Precursor

Abstract

Supported catalysts are central to industrial catalytic processes. While traditional synthesis methods often yield poorly defined materials, thus complicating structural elucidation, Surface Organometallic Chemistry (SOMC) offers a solution, producing well-defined structures. Recent advances in SOMC precursor development have shown that amidinate-based precursors are a privileged class of precursors to generate supported metallic nanoparticles. In that context, this study investigates the grafting mechanism of a prototypical amidinate precursor, Ir(COD)(DIA) (1-Ir), onto SiO2. Unique to amidinate complexes, grafting is shown to occur without ligand release, creating a reversible covalent bond. Using tris(tert-butoxy)silanol as a molecular analogue for a silanol group on SiO2, the structure of the grafted species is elucidated by single X-Ray diffraction, and comparison of IR spectroscopy, and X-Ray absorption spectroscopy (XAS) data. The reversibility of the reaction with O-H groups is demonstrated using variable-temperature NMR spectroscopy, IR spectroscopy, and is supported by DFT calculations. Notably, we show that a partial degrafting is also possible at elevated temperatures under vacuum.