Solution phase and polymer bound ruthenium carbene complexes for olefin metathesis

Several ruthenium carbene complexes have been shown to catalyse olefin metathesis. In this work the ligand environment of Grubbs first generation catalyst was modified in a systematic manner with ligands related Grubbs Schiff base ligand in order to determine the effect of various ligand structural features on carbene stability and catalytic activity. Linker ligands were then synthesized based on promising solution phase ligands. These linker ligands were attached to Merrifield resin and treated with Grubbs first generation catalyst in order to generate polymer bound ruthenium carbene complexes. These polymer bound complexes were then evaluated for catalytic activity and stability. The polymer bound complexes were found to be significantly more thermally stable than the corresponding solution phase complexes.;In the course of this work it was discovered that the carbene moiety of Grubbs first generation catalyst equilibrates with alkenes in the reaction mixture. The equilibrium constants for carbene exchange were determined for several alkenes having a wide range of steric demand. Relative Gibbs free energies of formation were calculated for the resulting carbene complexes. The free energies increased with increasing steric demand of the carbene and spanned 5.6 kcal/mol. This thermodynamic data complements the extensive kinetic data obtained by Grubbs.