Chemistry Reference
In-Depth Information
The discrepancy between the two catalysts was elucidated by Truhlar et al. [
170
] with aid of a
computational density functional method named Mo6-L. They found that the benzylidine ligand in
both catalysts rotates and serves as a toggle switch to trigger the metathesis reaction. The rotation
precedes dissociation in the Grubbs 1 catalyst but occurs in synchronization with the dissociation in
the Grubbs 2 catalyst [
170
].
L
Cl
L
L
H
R"
Cl
Cl
H
H
-PR
3
rotation
Ru
Ru
Ru
R'
Cl
rotation
R'
Cl
R'
PR
3
Cl
R"
When the olefin substrate coordinates to ruthenium in the Grubbs 1, the catalyst must overcome
electronic effects stemming from the rotation, a barrier that is lower in Grubbs 2.
Following are examples of polymerization reactions that were carried out with Grubbs
catalysts [
170
]:
O
O
n
O
N
CH
3
n
O
N
O
O
CH
3
n
OCH
3
OCH
3
OCH
3
OCH
3
Another example, using a different ruthenium catalyst
is polymerization of cyclohexenyl
norbornene to form high molecular weight products [
171
]:
RuCl
3
.xH
2
O
Alcohol, Heat, C
6
H
5
Cl
The versatility of these catalysts was further illustrated, when ring-opening metathesis
polymerizations of norbornene were carried out in liquid carbon dioxide at high pressure, using Ru
(H
2
O)
6
-(Tos)
2
. The product was reported to be
-ditactic polynorbornene [
172
]. It should be noted,
however, that stereoselective polymerizations of norbornene are not confined to these catalysts only.
cis
