Keywords
Chapter 4 Results and discussion
4.1 Synthesis of the Gr2Ph-Ind precatalyst
4.1.1 Metathesis
The synthesised GrPh2-Ind precatalyst was tested for metathesis activity with 1- octene. No metathesis products were observed with the precatalyst at various temperatures.
The metathesis results that follow were obtained with the commercial ruthenium indenylidene precatalyst. The investigation of metathesis is focussed on the characterisation of the metathesis activity with 1-octene and the in-depth investigation on the formation of the various products.
There are many factors that could influence the metathesis reactions, but the two factors that could have the biggest effect on the reactions are concentration of catalyst (catalyst load) and temperature. Consequently only concentration and temperature will be investigated.
Influence of catalyst concentration on metathesis
Table 4.1 shows the effect of catalyst load on the formation of primary (PMP), secondary (SMP) and isomerisation (IP) products. From the results it is clear that the concentration of the catalyst does not have a very big effect on the amount of products formed. The formed products are all in the same ranges for each temperature, but the turnover number (TON) does in fact increase as the catalyst load decreases. However, the selectivity decreases as catalyst concentration decreases with respect to the lower temperature of 25 °C.
Table 4.1: Summary of metathesis reactions of 1-octene with ruthenium-indenylidene at different catalyst concentrations at 25 °C and 60 °C at the reaction time of 1260 min
A catalyst load of 1:9000 (Figure 4.13) gives the highest percentage of PMPs and the selectivity is also the highest. Thus a catalyst load of 9000 is optimum for the formation of PMP and for this reason a catalyst load of 1:9000 was used for all further reactions conducted in this study.
Figure 4.13: The relationship of mole percentage of the products that formed and catalyst load at 60 °C
Influence of reaction temperature on metathesis reaction
As can be seen in Figure 4.14 the rate at which the 1-octene decreases is influenced by temperature. At 25 °C the decrease is almost linear and the rate is slow, but as the temperature is increased (35 °C, 45 °C, 60 °C and 80 °C) the decrease in 1-octene is no longer linear and the rates are dramatically increased.
Figure 4.14: Decrease of the n% of 1-octene over time at different temperatures with a catalyst load of 1:9000
0 10 20 30 40 50 60 70 80 90 100
7000 9000 11000 13000
Mole percentage (n %)
Catalyst load (Ru:1-Octene)
PMP SMP IP
0 20 40 60 80 100
0 200 400 600 800 1000 1200
n % octene
Time (min)
25°C 35°C 45°C 60°C 80°C
Figure 4.15, which shows the formation of the primary products for the ruthenium- indenylidene precatalyst at different temperatures, again indicates that the increase of the primary product is almost linear and that a slow activation is present at 25 °C. For the higher temperature reactions the activation is noticeably faster and equilibrium is eventually reached, where for the 25 °C and 35 °C reactions equilibrium is not reached by the time the metathesis reactions are terminated after 1200 min.
The decrease in primary products at 80 °C is a result of 7-tetradecene being a substrate for secondary metathesis products.
Figure 4.15 : Increase of the n% of PMPs over time at different temperatures with a catalyst load of 1:9000
Figure 4.16 and Figure 4.17 show the formation of SMPs and IPs. From these graphs the trend for the different temperatures is clear, however for 25 °C and 35 °C very little SMPs are observed. The optimum conditions for 1-octene metathesis with ruthenium- indenylidene could be just below or above 35 °C; therefore, metathesis reactions were also done at 45 °C. From the results of the 45 °C experiments we see that the percentage of PMPs formed are higher than for 35 °C and that SMP and IP percentages are also slightly higher (Figure 4.18).
0 20 40 60 80 100
0 200 400 600 800 1000 1200
n % PMP
Time (min)
25°C 35°C 45°C 60°C 80°C
Figure 4.16 : Increase of the n% of SMPs over time at different temperatures with a catalyst load of 1:9000
Figure 4.17 : Increase of the n% of IPs over time at different temperatures with a catalyst load of 1:9000
0 20 40 60 80 100
0 200 400 600 800 1000 1200
n % SMP
Time (min)
25°C 35°C 45°C 60°C 80°C
0 5 10 15 20 25
0 200 400 600 800 1000 1200
n % SMP
Time (min)
25°C 35°C 45°C 60°C 80°C
Figure 4.18 : Summary of results from metathesis experiments with ruthenium-indinylidene at different temperatures with a catalyst load of 1:9000
Figure 4.18, which is a summary of all the results of the metathesis experiments, shows the relationship between the formed products and the amount of 1-octene unreacted. Looking at 25 °C there are no secondary products that formed, but still more than 70 % of the 1- octene that did not react after 21 hours. For 35 °C the amount of 1-octene unreacted and the amount of primary products formed are both about 50 %.
At both 45 °C and 60 °C, mainly primary product had formed and a relatively small amount of 1-octene was left. It is clear that at 45 °C the amount of primary products is the most, and both the secondary products that have formed and the unreacted 1-octene are under 20 %. For 80°C primary products and secondary products are almost equal with some isomerisation products that have not converted to SMPs.
Table 4.2 shows the product distributions for the metathesis reactions when a quarter of the reaction time (300 min) had passed and at the end of the reaction (1260 min). The results show the same trend as discussed above. There is a definite difference in the amount of products formed at 25 °C to 45 °C, but at 60 °C and 80 °C it is seen that there is very little change in the amount of products and selectivity, meaning that if the reaction time should be short, and at 60 °C is the optimum temperature for the reaction. For longer reaction times and adequate conversion of substrate to product, 45 °C will be the optimum
0 10 20 30 40 50 60 70 80
25 35 45 60 80
Reaction mixture composition (n %)
Temperature °C
1-Octene PMP SMP IP
Table 4.2: Calculated results for 1-octene metathesis reations with ruthenium-indenylidene at a time of 300 and 1260 min
300 min °C % 1-octene % PMP % SMP % IP TON TOF(h-1) % Selectivity (PMP)
1:9000
25 94 6 0 0 570 114 100
35 81 19 0 0 1679 336 98
45 55 39 5 1 3519 704 86
60 14 55 28 3 4926 985 64
80 7 53 33 6 4801 960 58
1260 min °C % 1-octene % PMP % SMP % IP TON TOF(h-1) % Selectivity (PMP)
1:9000
25 73 27 0 0 2473 118 100
35 43 47 9 1 4198 200 82
45 20 60 19 1 5404 257 75
60 11 59 28 3 5290 252 66
80 4 50 39 7 4464 213 52
Although higher temperatures increase the rate of the reaction, it also increases the amount of secondary and isomerisation products which means that the catalyst loses selectivity towards forming primarily primary products. It is apparent that a reaction temperature of 45°C is the optimum, because at 1260 min the primary products are the most and the turnover number is also the highest.