Metathesis Activity and Stability of New Generation Ruthenium Polymerization Catalysts

A kinetic study of three ruthenium carbene catalysts, (H2IPr)(PCy3)(Cl)2RuCHPh, 3 (investigated extensively by Mol), (H2IMes)(Cl)2RuCH(o-iPrOC6H4), 4 (Hoveyda's catalyst), and (H2IPr)(Cl)2RuCH(o-iPrOC6H4), 5 (a new catalyst structure), was conducted under ADMET polymerization conditions. The kinetic behavior of these catalysts was compared to the classical first- and second-generation Grubbs' complexes at 30, 45, and 60 °C. Complex 3 exhibits the highest initial ADMET rate (80 DP s-1) of any phosphine complex to date and efficiently promotes metathesis even at temperatures as low as 0 °C. Complex 4 alone does not polymerize 1,9-decadiene in the bulk; however, addition of a polar solvent induces polymerization. Combining elements of catalysts 3 and 4 yielded the new complex 5. This complex results in higher polycondensation rates than previous Hoveyda-type structures and exhibits an increased stability over its parent phosphine complex. The new catalyst polymerizes 1,9-decadiene in the bulk to high polymer (Mn = 40 000 g/mol) using low catalyst loadings (0.1 mol %). The isomerization chemistry induced by complexes 3 and 5 was investigated using a model compound, 1-octene.