Metathesis

Abstract

The double bond isomerization of olefins is an atomic-efficient, industrially highly relevant chemical reaction. One of its emerging applications is the tandem isomerization metathesis (ethenolysis) reaction (ISOMET or IE) used for transforming plastic waste to propylene. As the double bond isomerization step is the bottleneck of the ISOMET reactions, a series of ruthenium(II) hydride complexes were investigated in the view of their C=C isomerization activity in neat conditions on terminal alkene substrates which are the major components of polyethylene (PE) pyrolysis oil. Our work revealed that the commonly applied RuHCl(CO)(PPh3)3 (1) complex can be activated with copper(I) chloride, by scavenging one phosphine ligand yielding an isolable, coordinatively unsaturated, highly soluble and reactive species, RuHCl(CO)(PPh3)2 (2). The structure of the complex is similar to the more bulky and less effective RuHCl(CO)(PCy3)2(3). The bis(triphenylphosphine) complex 2 showed remarkably high olefin isomerization activity even at room temperature with a catalyst loading as low as 0.1 mol%. The functional group tolerances – especially catalyst deactivation caused by dienes – are also discussed briefly; having relevance in tandem catalytic reactions like ISOMET of diene-containing PE pyrolysis oil.