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

A Pt(II) aqua complex 5MSN 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 PtII(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 5MSN, 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 5MSN 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 5MSN 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 5MSN was also demonstrated.