Mesoporous Silica Nanoparticle Rigid Anchor Attached Pt Complex for Catalytic H/D Exchange of Aromatic Substrates

A Pt(II) aqua complex 5 supported by mesoporous silica nanoparticle (MSN)-immobilized sulfonated CNN pincer ligand featuring a rigid SiO₃ tether was prepared. This hybrid material was tested as a catalyst in H/D exchange reactions of C(sp²)-H bonds of selected aromatic substrates and D₂O-2,2,2-trifluoroethanol-d₁ (TFE-d₁) mixtures or CD₃CO₂D acting as a source of exchangeable deuterium. The catalyst immobilization served as a means to not only enable the catalyst's recyclability but also minimize the coordination of sulfonate groups and the metal centers originating from different catalyst's moieties that would preserve reactive Pt^II(OH₂) fragments needed for catalytic C-H bond activation. In the same vein, the use of a rigid tether was expected to help suppress potentially strong intraparticle coordination of MSN's silanol groups and Pt(II) that could inhibit the catalytic H/D exchange. The particle size distribution, porosity, surface area, elemental composition of 5, and the pincer ligand loading were characterized using scanning electron microscopy (SEM), transmission electron microscopy (TEM), energy-dispersive X-ray (EDX) analysis, N₂ sorption, and alkaline digestion with subsequent ¹H NMR and ESI-MS analyses of the resulting solutions. It was found that 5 is a more active catalyst of the H/D exchange reactions of benzene, thiophene, anisole, and/or toluene than analogous molecular Pt(II) aqua complexes 1 and 5, which exhibited 2-10 times lower TON after 24 h of reaction under otherwise identical conditions. The greater activity and chemical robustness of 5 allowed us to effectively use the catalyst in the H/D exchange reactions with acetic acid-d₄, which is a more readily available source of exchangeable deuterium than TFE-d₁ at 120 °C. The recyclability of 5 was also demonstrated.