Modeling of Ru and Fe based olefin metathesis
Michael T. Feldmann
Richard P. Muller
William A. Goddard, III
Materials and Process Simulation Center, Caltech
Olefin metathesis is an important reaction for many chemical processes including polymerization. It has
been shown that the Grubbs ruthenium-based catalyst is very efficient at olefin metathesis with high functional group
tolerance. It has been so successful that we would quickly deplete the world of its supply of ruthenium if we were to use it
for all its applications. Looking at related elements that have a higher natural abundance leads to iron. Iron should have
similar electronic behavior which could lead to a successful iron based olefin metathesis catalyst.
The mechanism of the ruthenium-based Grubbs catalyst of the formula L2X2Ru=CHR has been
examined. Experimentally it has been shown that L=PCy3,PiPr3, X=Cl, and R=CHPh2 produce an effective catalyst. When
X=Cl and R=H in our theoretical study, L was varied from a simple phosphine to a carbene and an sp 2 nitrogen donating
ligand. Understanding gained from this mechanism has allowed for possible performance enhancement of the rutheniumbased catalyst. In addition, the iron-based analog is showing promise as the ligand effects are being understood and tuned
to the needs of the iron-based reaction pathway.
Acknowledgements: NSF-Che
• What is olefin metathesis?
R1
R1
+
R2
2
R2
R1
R2
• What is the reactive intermediate?
R2
M
R1
R2
R2
M
M
R3
R1
R3
R1
R3
• Why should anyone care about olefin metathesis?
Ring closing metathesis (RCM)
R
R
M
M
R
M
M
M
Ring opening metathesis polymerization (ROMP)[1]
n
Acyclic diene metathesis (ADMET)
n
M
• What do we know about the Grubbs catalyst?
Ring-closing kinetics:[2]
Addition of CuCl or CuCl2 speed up reaction
(Cu acts as a phosphine scavenger)
Structure of starting catalyst:[2][3][4]
Cy 3P
Cl
Ph3P
Cl
Ru
Cl
Ru
Ph
Cl
Ph3P
Cy 3P
Ph
Activity for various ligands:[2]
X=> Cl>Br>>I
L=> PCy3>PiPr3>PCy2Ph>PiPr2Ph>>PPh3
X tends to be small and electronegative
L tends to have large cone angle and be electron donating
Ph
Ph
Scheme 1: L-dissociation
C
PH3
Cl
Ru
Cl
+
PH3
Ru
Cl
-PH3
Cl
PH3
CH 2
Cl
Cl
Ru
PH3
A
CH 2
Cl
+PH3
CH 2
-
H3P
+
Ru
Cl
D
B
Cl
-
Ru
Cl
PH3
C
CH 2
Scheme 2: olefin-association
[2][5]

PH3
Cl

PH3
Cl
+
Ru
-PH3
PH3
Cl
Cl
CH 2
+PH3
Ru
Cl
Cl
-
PH3
Ru
+
Cl
PH3
-
CH 2
Cl
Cl
PH3

-
Ru
+
PH3
Cl
H2C
Ru
PH3

PH3
Cl

Cl
H2C
+
PH3
PH3
Ru
PH3
CH 2

Cl
Cl
Ru
H2C

Cl
-
Ru

Cl
Scheme 2b: olefin-association

C
PH3
Cl
+
PH3
Cl
Ru
Ru
CH 2
+
PH3
PH3
Ru
Cl
PH3

-
Cl
PH3
Cl
CH 2
+
-PH3
Cl
H2C
Ru
Cl
Ru

PH3
Cl
Cl
PH3
PH3
+PH3
Ru

PH3
Cl
Cl
Ru
`

CH 2
Cl
Cl
PH3
CH 2
Ru
Cl
+
Cl
Cl
-
H3P
CH 2 +
Cl
B
Cl
-
Ru
Cl
PH3
Cl
PH3
C
CH 2
Ru
D
Reaction pathway (Ru: X=Cl, L=PH3)
16.4
PH3
Cl
Cl
PH3
Ru

Cl
Cl
Ru
CH 2
`
7.1
Cl
PH3
Ru
PH3
Cl
Cl
Cl
Ru
Cl
Cl
CH2
B
Cl
B
Cl
0.0
H 3P
Cl

Ru
PH3
Ru
PH3
PH3
CH 2
Ru
D
-3.6
Cl
PH3
CH 2
Ru
-5.7
-6.9
PH3
PH3
A()
Ru
Cl
Cl
Cl
Ru
CH 2
Cl
Cl
-12.3 kcal/mol
PH3
C
C
CH 2
Cl
CH 2
PH3
A()
Reaction pathway (b) (Ru: X=Cl, L=PH3)
PH3
28.6 Cl
Ru

H2C
PH3
Cl
Cl
Cl
Ru

16.4
PH3
Cl
Cl
Ru
CH 2
`
7.1
Cl
PH3
PH3
Cl
PH3
Ru
Cl
Cl
CH 2
PH3
Cl
Cl
CH2
Cl
B
Ru
PH3
Cl
Ru
Cl
Ru
H 3P
0.0
Cl

PH3
B
Ru
D
PH3
-3.6
PH3
-5.7
A()
Ru
Cl
Ru
Cl
-6.9
Cl
CH 2
Ru
Cl
Cl
-12.3 kcal/mol
CH 2
C
PH3
C
CH 2
Cl
CH 2
PH3
A()
N
Ru catalyst: X=Cl L=
H
N
Cl
HN
Ru
Cl
CH 2
N
N
Cl
Ru
Cl
CH 2
N
H
B
B
0.0
Cl
H
N
N
N
H
Cl
Ru
PH3
D
Ru
Cl
N
Cl
CH 2
N
Cl
Ru
Cl
CH 2
N
H
H3P
A
A
-19.6
H
N
H
N
-21.1
N
N
Cl
Ru
Cl
Cl
Ru
CH 2
Cl
N
N
-28.9 kcal/mol
N
H
A
N
H
A
CH 2
[6]
Ru catalyst: X=Cl L=
HN
NH
lC
HN
uR
2 HC
HN
lC
lC
HN
2 HC
HN
uR
HN
B
lC
lC
3HP
0.0
lC
A
2 HC
B
lC
lC
uR
2 HC
NH
HN
lC
C
C
CH 2
Cl
HN
uR
Cl
Ru
uR
2 HC
HN
PH3
HN
lC
HN
NH
A
-9.1
-8.6
-9.7
lC
H
N
uR
D
lC
HN
HN
HN
HN
lC
HN
lC
uR
2 HC
uR
2 HC
lC
HN
lC
HN
HN
A
-37.0 kcal/mol
HN
A
• Why is using Ru not ideal?
Ruthenium is scarce. If we were to use the Ru-based Grubbs catalyst
for all the applications it is suited for we would soon deplete the
world’s supply of ruthenium.
• Why not just use Fe?
Iron-based Grubbs catalysts don’t work.
Iron tends to be high spin.
Fe catalyst: X=Cl L=PH3
PH3
Fe
Cl
Fe
Cl
Cl
CH 2
Cl
CH 2
PH3
B
0.0B
(-1.3)
PH3
Fe
Cl
Cl
PH3
(-5.3)
Fe
CH 2
Cl
PH3
A
PH3
A
-9.5 kcal/mol
-13.9
Cl
H 3P
Cl
Fe
D
(triplet surface)
(-28.9)
Cl
CH 2
N
Fe catalyst: X=Cl L=
HN
0.0
(-2.8)
H
N
Cl
Fe
Cl
CH 2
N
N
Cl
Fe
N
H
Cl
B
H
N
CH 2
B
H
N
-12.1
Cl
(-14.9)
N
Cl
Fe
Cl
CH 2
N
N
H
Cl
N
Fe
Cl
Fe
D
Cl
N
-20.2 kcal/mol
N
N
H
N
H
A
A
(triplet surface)
(-27.6)
CH 2
Fe catalyst: X=Cl L=
HN
NH
Cl
NH
Fe
NH
CH 2
Cl
Cl
NH
Fe
Cl
CH 2
NH
B
B
(0.8)
0.0
-1.0
Cl
Fe
NH
NH
CH 2
Cl
NH
Cl
Fe
NH
CH 2
Cl
C
C
-13.9
NH
NH
NH
NH
Cl
Fe
(triplet surface)
Cl
CH 2
Fe
Cl
(-22.8)
NH
Cl
H
N
NH
(-30.0)
-32.0 kcal/mol
NH
Fe
NH
A
Cl
CH 2
Cl
D
NH
A
Conclusions
•
•
•
•
Scheme 1 is the supported mechanism
Mixed “L”-ligand systems look promising
High spin state of iron may be a major issue
Strong electron donors remedy some of the high
spin state issues for the iron-based catalyst
Acknowledgements:
National Science Foundation
References:
1.) J.A. Tallarico, P.J. Bonitatebus,Jr., M.L. Snapper, J. Am. Chem. Soc., 1997, 119, 7157-7158.
2.) E.L. Dias, S.T. Nguyen, R.H. Grubbs, J. Am. Chem. Soc., 1997, 119, 3887-3897.
3.) Z. Wu, S.T. Nguyen, R. Grubbs, J.W. Ziller, J. Am. Chem. Soc., 1995, 117, 5503-5511.
4.) P. Schwab, R. Grubbs, J.W. Ziller, J. Am. Chem. Soc., 1996, 118, 100-110.
5.) O.M. Aagaard, R.J. Meier, F. Buda, J. Am. Chem. Soc., 1998, 120, 7174-7182.
6.) T. Weskamp, W.C. Schattenmann, M. Spiegler, W.A. Herrmann, Angew. Chem. Int. Ed. 1998, 37, 2490-2493.