Industrial viability of homogeneous olefin metathesis: Beneficiation of linear alpha olefins with the diphenyl-substituted pyridinyl alcoholato ruthenium carbene precatalyst

Abstract

The catalytic performance of the diphenyl-substituted pyridinyl alcoholato ruthenium carbene precatalyst of the Grubbs 2-type was optimized for 1-octene metathesis by varying operating parameters, such as reaction temperature (30–100°C) and catalyst load (Ru/1-octene molar ratio between 1:5000 and 1:14000). Secondly, the catalyst was tested with other linear alpha olefins (LAOs). Quantities such as product distribution, selectivity, catalyst lifetime, TON and activity were used in comparing and evaluating the efficiency of the precatalyst.It was found that the precatalyst showed both metathesis and isomerization activity for the reaction with 1-octene that was strongly temperature dependent. The precatalyst also showed significant secondary metathesis activity at the optimal reaction temperature of 80°C. In this study, it was postulated and demonstrated with molecular modelling, that the metathesis reaction with the chelating bidentate precatalyst could accurately be described by a hemilabile dissociative mechanism. The reaction kinetics of the model reaction could be described by a set of three interdependent elementary reaction rate equations.In order to determine if the precatalyst is of broader value in LAO metathesis reactions it was also tested with different alpha olefins (1-hexene, 1-heptene, 1-nonene and 1-decene). The results of the LAO metathesis reactions showed that the precatalyst increased the lifetime to 35 days and thermal stability when compared to Grubbs 1 (1h lifetime) and Grubbs 2 (3h lifetime). The TON, selectivity and activity is comparable to those of the Grubbs 2 precatalyst, whilst an improvement on the Grubbs 1 results was obtained.