Selective Formation of a Coordinatively Unsaturated Metal Complex at a Surface: A SiO₂‐Immobilized, Three‐Coordinate Ruthenium Catalyst for Alkene Epoxidation

Unsaturated but air-stable: A three-coordinate Ru complex, 2, highly active for alkene epoxidation and recyclable in air, was prepared on SiO2 by exploiting the exothermic reaction between O2 and isobutyraldehyde (IBA) to eliminate a p-cymene ligand from a coordinatively saturated precursor 1 (Ru red, Cl dark blue, N green, S yellow, O blue, C gray, H white). In contrast, direct activation with O2 alone was calculated to be endothermic.