Ruthenium carbenes as catalysts for alkene metathesis
Two families of ruthenium-based olefin metathesis catalysts and their use in organic and polymer synthesis are presented. Ruthenium-allenylidene complexes [Ru=C=C=CR2(Cl)(PR3)(arene)]+ X- are efficient pre-catalysts for the Ring Closure of dienes and enynes but they are also able to polymerise strained and unstrained cyclic olefins under mild conditions. These complexes have also shown interesting recycling capacity in ionic liquid solvents. The in-situ generated catalysts readily prepared from easily available reagents: a ruthenium complex, an imidazolium salt and a base promote alkene and enyne metathesis. A two-component system for the polymerization of norbornene and cyclooctene is also presented.