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Article Dans Une Revue Journal of the American Chemical Society Année : 2022

Multiple Surface Site Three-Dimensional Structure Determination of a Supported Molecular Catalyst

Résumé

The structural characterization of supported molecular catalysts is challenging due to the low concentration of surface sites and the presence of several organic/organometallic surface groups resulting from the often complex surface chemistry associated with support functionalization. Here, we provide a complete atomic-scale description of all surface sites in a silica-supported iridium-N-heterocyclic carbene (Ir-NHC) catalytic material, at all stages of its synthesis. By combining a suitable isotope labelling strategy with the implementation of multi-nuclear dipolar recoupling DNP enhanced NMR experiments, the 3D structure of the Ir-NHC sites, as well as that of the synthesis intermediates were determined. As a significant fraction of parent surface fragments does not react during the multi-step synthesis, site-selective experiments were implemented to specifically probe proximities between the organometallic groups and the solid support. The NMR-derived structure of the iridium sites points to a well-defined conformation. By interpreting extended x-ray absorption fine structure (EXAFS) spectroscopy and chemical analysis data augmented by computational studies, the presence of two coordination geometries is demonstrated: Ir-NHC fragments coordinated by a 1,5-cyclooctadiene and one Cl ligand, as well as, more surprisingly, a fragment coordinated by two NHC and two Cl ligands. This study demonstrates a unique methodology to disclose individual surface structures in complex, multi-site environments, a long-standing challenge in the field of heterogeneous/supported catalysts, while revealing new, unexpected structural features of metallo-NHC supported substrates. It also highlights the potentially large diversity of surface sites present in functional materials prepared by surface chemistry, an essential knowledge to design materials with improved performances.

Domaines

Matériaux Catalyse
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Dates et versions

hal-03805170 , version 1 (07-10-2022)

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Ribal Jabbour, Marc Renom-Carrasco, Ka Wing Chan, Laura Völker, Pierrick Berruyer, et al.. Multiple Surface Site Three-Dimensional Structure Determination of a Supported Molecular Catalyst. Journal of the American Chemical Society, 2022, 144 (23), pp.10270-10281. ⟨10.1021/jacs.2c01013⟩. ⟨hal-03805170⟩
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