Investigation of indenylidene-derivatives of Grubbs type precatalyst for 1-octene metathesis

Abstract

The ideal metathesis precatalyst is a catalyst with high metathesis activity, high selectivity, enhanced thermal stability, great handling characteristics (high tolerance towards moisture and air) and tolerance to a wide range of functional groups. Ru based precatalysts satisfy most of these requirements. Further improvement of Ru based precatalysts could possibly be obtained by changing the ligands. It has been shown that changing the carbene ligand from a phenylidene to an indenylidene improved the activity, thermal stability and ultimately lifetime of the precatalyst. Another way of changing the ligands is to substitute one of the chlorine ligands and the PCy3 ligand with a hemilabile ligand. In a previous study a Grubbs 2-type precatalyst was developed, which contained a hemilabile pyridinyl alcoholate ligand with two phenyl substituents. This catalyst, referred to as the PUK-Grubbs 2 (Gr2Ph) precatalyst, showed an increase in stability, activity, selectivity and lifetime in comparison with Grubbs 2. In this study the optimization of a ruthenium-indenylidene precatalyst was done and an in depth investigation into the formation of the metathesis products were conducted. The optimum reaction conditions were obtained, the mechanisms for formation of the observed metathesis products identified as well as possible carbene species that can exist during the reactions. Variations of the ruthenium-indenylidene precatalyst were investigated via molecular modelling. This includes the addition of groups to the indenylidene carbene species as well as Gr2Ph variations of the ruthenium-indenylidene precatalyst and its derivatives. The change in the energy needed for the activation of the precatalyst was observed.