| Abstract
| - Liquid or supercritical carbon dioxide (scCO2) is a versatile reaction medium for ring-openingmetathesis polymerization (ROMP) and ring-closing olefin metathesis (RCM) reactions using well-definedmetal catalysts. The molybdenum alkylidene complex 1 and ruthenium carbenes 2 and 3 bearing PCy3 orN-heterocyclic carbene ligands, respectively, can be used and are found to exhibit efficiency similar to that inchlorinated organic solvents. While compound 1 is readily soluble in scCO2, complexes 2 and 3 behave likeheterogeneous catalysts in this reaction medium. Importantly, however, the unique properties of scCO2 providesignificant advantages beyond simple solvent replacement. This pertains to highly convenient workup proceduresboth for polymeric and low molecular weight products, to catalyst immobilization, to reaction tuning by densitycontrol (RCM versus acyclic diene metathesis polymerization), and to applications of scCO2 as a protectivemedium for basic amine functions. The latter phenomenon is explained by the reversible formation of thecorresponding carbamic acid as evidenced by 1H NMR data obtained in compressed CO2. Together with itsenvironmentally and toxicologically benign character, these unique physicochemical features sum up to a veryattractive solvent profile of carbon dioxide for sustainable synthesis and production.
|
