Abstract:
In this study different ruthenium carbene complexes, Grubbs 1 and 2 were investigated
for the reactions of 1-, 2-, 3-octene and 1-tetradecene. All reactions were conducted in
glass mini reactors equipped with Mininert® valves under a dry nitrogen atmosphere. A
heating block was used to heat the reactors. Gas chromatography was used to
determine the product composition of reaction mixtures.
The influence of reaction temperature, solvents and catalyst concentration on the
reactions of 1-octene were investigated. The optimum reaction conditions for activity
and selectivity with Grubbs 1 and 2 were determined. Increased temperature for Grubbs
2 results in decrease in activity in the homometathesis reaction of 1-octene while the
product yield increased as a result of isomerisation. Grubbs 2 catalyst displayed a
higher metathesis product yield (65%) at lower temperatures (25°C) with 1-octene and
lower metathesis products (less than 10%) at higher temperatures (100°C). Grubbs 1
displayed higher metathesis products (55-64%) at both lower (25°C) and higher
temperatures (100°C). Secondary metathesis products due to isomerisation were less
than 20% with Grubbs 2 the more active isomerization catalyst.
Grubbs 1 and 2 were active for the metathesis of both 2- and 3-octene. With 2-octene
high yields of secondary metathesis products were observed. The optimum reaction
conditions for the metathesis of 1-octene were used for the reaction of 2-, 3-octene and
1-tetradecene. A higher metathesis yield (70%) was obtained with 2-octene. Secondary
metathesis products (Cg - C13) and oligomers (C16 and longer) were obtained in the
presence of Grubbs 2. Grubbs 1 and 2 also catalysed the metathesis of 1-tetradecene.
The reaction is very slow in the presence of Grubbs 1 and little metathesis products are
observed (less than 20%). In the presence of Grubbs 2 40% primary and less than 10%
secondary metathesis products were observed. The reaction mixture of 1- and 2-octene
in the presence of Grubbs 1 and 2 produced metathesis products less than 20%. Cross
metathesis was observed from the mixture, C9 and C13 were produced.
Both Grubbs 1and 2 showed a high activity and selectivity towards the metathesis
reaction of 1-octene. These catalysts showed that they are still active at high alkene/Ru
molar ratios and in different solvents that were used. Relatively high turnover numbers
(TON) were obtained for both Grubbs 1 and 2. NMR studies confirmed the existence of
the original benzylidene complex and the formation of the active heptylidene and
methylidene complexes.
