Preface
Chapter 4: Results and discussions 4.1 Introduction
4.3 Calculation of dissociating ligand size
4.3.1 Calculation of dissociating ligand size with the modified techniques
4.3.1.1 Dissociating ligand size calculations performed with the outer pocket technique
The dissociating ligand sizes for the G, B and A complexes were calculated with the outer pocket technique. The change in the dissociating ligand was plotted against the increasing P(4)-Ru bond length, respectively.
In Figure 4.7, the outer pocket increased in size for the preparation of dissociation and decreased in size after the dissociation occurred. In addition, the smaller G1 and G5 complexes had smaller changes in outer pocket sizes than the G2, G3 and G4 complexes. The reasoning is that the van der Waals radii according to Bondi[3] are smaller for the fluorine and hydrogen (small hard substituents) containing complexes, while the larger chlorine, bromine and iodine containing complexes are sterically more strained. The groups with the larger substituents led to an increased influence between the surrounding groups and Ph on carbene carbon.
Figure 4.7: Change in the outer pocket size of the dissociating ligand for the G complexes It was also observed that the dissociating ligand size in the case of the G1 and G5 complexes does not increase much before decreasing. Furthermore, the trends are similar in the G2 and G3 complexes, while the trend is different in the G4 complex. The iodine in the G4 containing complex has a small covalent radius, while the van der Waals radius is too large, which leads to a flaw in accessing the steric strain data when using the van der Waals radius according to Bondi.[2]
Figure 4.8 shows an increase in the dissociating ligand size as dissociation from the ruthenium in the B complexes occur. Thereafter, the change in the dissociating ligand size decreased since there is no steric strain between the ligand and the complex. A fair amount of changes in the dissociating ligand sizes were observed in the B complexes. The largest change was observed in the (a) B2 (steps 17-18), (b) B4 (steps 9-10) and (c, d) B5 (steps 10- 12 and steps 20-21) complexes. Due to the small covalent radius and too large van der Waals radius according to Bondi[3]of iodine, the steric strain data of B4 complex is flawed.[2]
-15 -10 -5 0 5 10
2 2.5 3 3.5 4 4.5 5
Change in outer pocket (ᵒ)
P(4)-Ru (Ǻ)
G1 G2 G3 G4 G5
Figure 4.8: Change in the outer pocket size of the dissociating ligand for the B complexes The molecular structures for the B2 complex at steps 17-18 are shown in Figure 4.9, while the B5 complex at steps 10-12 are shown in Figure 4.10. The molecular structure for the B5 complex at steps 20-21 is shown in Figure 4.11. In Figure 4.9, the dissociating ligand (1) and the Ph ring (2) shifted in the B2 complex. The dissociating ligand (1) decreased in size and moved away from the large (2) Ph ring, while the (2) Ph ring shifted towards the unoccupied space left by the dissociating ligand. Consequently, the shifting groups (1, 2) in the B2 complex resulted in the changes in angles observed in Figure 4.8.
Figure 4.9: Overlay of steps 17-18 of the molecular structures for the B2 complex, where step 17 is red and step 18 is blue
-12 -10 -8 -6 -4 -2 0 2 4 6
2 2.5 3 3.5 4 4.5 5
Change in outer pocket (ᵒ)
P(4)-Ru (Ǻ)
B1 B2 B3 B4 B5
a b
c d
1
2
The molecular structure of the B5 complex, between 10 and 12 (c) is shown in Figure 4.10.
The dissociating ligand (1) and the Ph ring (2) is shifted in the B5 complex. The dissociating ligand (1) decreased in size and moved away from the large Ph ring (2), while the Ph ring (2) changed orientation and rotated on the C-C axis. Consequently, the shifting groups (1, 2) in the B5 complex resulted in the changes in angles observed in Figure 4.8.
Figure 4.10: Overlay of steps 10-12 of the molecular structures for the B5 complex, where step 10 is red while step 12 is blue
The molecular structures for the B5 complex between steps 20 and 21 (d in Figure 4.8) are shown in Figure 4.11. Although the ligand showed an overall decrease in size going from the first to the last step, according to Figure 4.8, the size of the dissociating ligand increased between steps 21 and 22. The decrease in the dissociating ligand size is 0.67 °. This small change in the angles would not be observed in the superimposed molecular structures.
Therefore, it is more descriptive to calculate the change in the dissociating ligand sizes. On the other hand, the Ph ring (2) rotated around the axis and shifted towards the unoccupied space that was occupied previously by the dissociating ligand. Therefore, the shift of the Ph ring toward the unoccupied area was responsible for the change in angles observed in Figure 4.8.
1
2
Figure 4.11: Overlay of step 21 and 22 of the molecular structures for the B5 complex, where step 21 is red and step 22 is blue
The changes in the dissociating ligand size in the A complexes were plotted against the increasing P(4)-Ru bond length, as shown in Figure 4.12. The size of the dissociating ligand first increased before decreasing after dissociation, as was observed for the G and the B complexes. In addition, the trends for the G, B and A complexes are similar. However, the absolute changes in the dissociating ligand size observed in the A complexes are less than that observed in both the G and B complexes, since they do not have the Ph ring.
The largest change was observed in the (a) A4 (steps 6-7) and (b) A4 (steps 13-14) complex.
However, due to the small covalent radius and too large van der Waals radius according to Bondi of iodine the steric strain data of A4 complex is flawed.[2] However, for completeness iodine data was included.
1
2
Figure 4.12: Change in the outer pocket size of the dissociating ligand for the A complexes
4.3.1.2 Dissociating ligand size calculations performed with the inner pocket