Supported Ru olefin metathesis catalysts via a thiolate tether.

Thiolate-coordinated ruthenium alkylidene complexes can give high Z-selectivity and stereoretentivity in olefin metathesis. To investigate their applicability as heterogeneous catalysts, we have successfully developed a methodology to easily immobilize prototype ruthenium alkylidenes onto hybrid mesostructured silica via a thiolate tether. In contrast, the preparation of the corresponding molecular complexes appeared very challenging in solution. These prototype supported complexes contain small thiolates but still, they are slightly more Z-selective than their molecular analogues. These results open the door to more active and selective heterogeneous catalysts by supporting more advanced thiolate Ru-complexes.

Pt nanoparticles immobilized in mesostructured silica: a non-leaching catalyst for 1-octene hydrosilylation.

A catalyst containing small (ca. 2.5 nm) and crystalline Pt nanoparticles embedded into the walls of a mesostructured silica framework was found to be highly active in alkene hydrosilylation reaching TONs of ca. 105. More importantly, no Pt leaching was detected. This result is remarkable because Pt leaching is a recurrent problem in alkene hydrosilylation, which often prevents heterogeneous catalysts from being used industrially. This result is in contrast to the significant Pt leaching observed for other Pt/SiO2 catalysts.

Iridium(I)/N-Heterocyclic Carbene Hybrid Materials: Surface Stabilization of Low-Valent Iridium Species for High Catalytic Hydrogenation Performance.

An Ir(I) (NHC)-based hybrid material was prepared using a methodology which allowed the precise positioning and isolation of the Ir centers along the pore channels of a silica framework. The full characterization of the material by solid-state NMR spectroscopy showed that the supported Ir sites were stabilized by the silica surface, as low-coordinated single-site complexes. The material is extremely efficient for the hydrogenation of functional alkenes. The catalytic performance (TOF and TON) is one to two orders of magnitude higher than those of their molecular Ir analogues, and could be related to the prevention of the bimolecular deactivation of Ir complexes observed under homogeneous conditions.

Platinum nanoparticles in suspension are as efficient as Karstedt's complex for alkene hydrosilylation.

Colloidal suspensions of monodisperse platinum nanoparticles of 2 nm diameter have been used to catalyze the hydrosilylation of 1-octene with a polymethylhydrosiloxane. The nanoparticles were found to be as efficient as Karstedt's complex, showing that colloid formation from homogeneous species during hydrosilylation reactions is not necessarily a deactivation pathway. These results also reactivated the debate on whether Karstedt's complex was truly homogeneous or colloidal during catalysis.