A Static and Dynamic Density Functional Theory Study of Methanol Carbonylation

1
A Static and Dynamic Density Functional Theory
Study of Methanol Carbonylation

• Minserk Cheong,a Rochus Schmid,b and Tom Zieglerc
• a Department of Chemistry, Kyung Hee University,
  Seoul 130-701, Korea
• b Technische Universitat Munchen,
  Anorganisch-Chemisches Institut, D-85747
  Garching, Germany
• c Department of Chemistry, University of Calgary,
  Alberta, Canada T2N 1N4

2
Abstract

• Quantum mechanical calculations based on density
  functional theory (DFT) were carried out in order
  to investigate the reaction mechanism for the
  carbonylation of methanol to acetic acid by
  M(CO)2I2- (M Rh, Ir). The study included the
  initial oxidative addition of CH3I to M(CO)2I2-
  (1) M(CO)2I2- CH3I ? M(CO)2I3(CH3)-, as
  well as the migratory insertion of CO into the
  M-CH3 bond (2) M(CO)2I3(CH3)- ?
  M(CO)I3(COCH3)-. Considerations were also given
  to migratory insertion processes where the
  I--ligand trans to methyl was replaced by another
  ligand L (where L MeOH, MeC(O)OH, CO, P(OMe)3
  or SnI3-) or an empty coordination site. The
  calculated free energies of activation and heat
  of reactions are in good agreement with the
  experimental data. A full analysis is provided of
  how ligands trans to the migrating methyl group
  influence the barrier of migratory insertion.

3
Catalytic Cycle for Acetic Acid Synthesis
OC
I
M
1
OC
I
MeI
MeCOI
2
4
O
I
OC
C
I
M
OC
M
OC
I
HI
I
OC
I
I
MeOH
3
O
CO
C
I
OC
M


M Rh
, Ir
I
I
4
Thermodynamics of oxidative addition reactions
D
D
D
D
D
M
e
ta
l
H
S
G
E
G
298
(
g
)
298
(
g
)
298
(
g
)
so
l
v
298
(
s
olv)
R
h
29.5
-13.6
33.6
-22.0
13.6
I
r
22.4
-15.1
26.9
-22.5
4.4
D
D
D
D
D
M
e
ta
l
H
S
G
E
G
298
(
g
)
298
(
g
)
298
(
g
)
so
l
v
298
(
so
l
v
)
R
h
-38.9
-28.4
-30.4
18.6
-11.8
I
r
-41.4
-27.7
-33.1
14.0
-19.1
kcal/mol
5


D
G

R
C

-
1
.
0
R
C

3
T
r
a
n
s
i
t
i
o
n

S
t
a
t
e

R
e
g
i
o
n
R
C r(M-C)-r(I-C)
O
6
Comparison of static(ADF) calculations and
dynamic(PAW) calculation
Metal DH DS DG
Rh PAW ADF 19.2 13.8 -21.1 -43.9 25.5 26.9
Expt 12.0 -39.4 23.7
Ir PAW 12.1 -23.4 19.1
ADF 6.0 -44.6 19.3
Expt 12.9 -26.8 20.9
kcal/mol
7
DH




15 kcal/mol


T
r
a
n
s
i
t
i
o
n

e
x
p
t
M
i
g
r
a
t
o
r
y

I
n
s
e
r
t
i
o
n

D


S


-14 cal/molK

S
t
a
t
e
e
x
p
t
-


DG


19 kcal/mol

o
f


M
e
R
h
(
C
O
)
I

expt

2
3
R
e
a
c
t
a
n
t

D
H


18 kcal/mol


D
S


1.1 cal/molK



D
G


17 kcal/mol


D
H


- 5.6 kcal/mol


2.3 cal/molK
P
r
o
d
u
c
t
D
S






DH

-8.8


kcal/mol
e
x
p
t

S


13

D
-
cal/molK
e
x
p
t
DG

kcal/mol


-5.0


expt

0

k
cal/mol



- 6.2 kcal/mol

DG
8
?Hexpt 37 kcal/mol ?Sexpt 22
cal/molK ?Gexpt 31 kcal/mol
T
r
a
n
s
i
t
i
o
n

S
t
a
t
e
M
i
g
r
a
t
o
r
y

I
n
s
e
r
t
i
o
n

i
n

-

M
e
I
r
C
O
I

2
3
2.90

D
H


28 kcal/mol

R
e
a
c
t
a
n
t

D
S


2.0 cal/molK



D
G


28 kcal/mol

P
r
o
d
u
c
t
D
H


4.0 kcal/mol

D
S


3.6 cal/molK


0 kcal/mol
D
G


2.9 kcal/mol

9
o
f

s
t
a
t
i
c

2
1
(
A
D
F
)

c
a
l
c
u
l
a
t
i
o
n
s

.
4
8
.
2
a
n
d


d
y
n
a
m
i
c

0
(
P
A
W
)

c
a
l
c
u
l
a
t
i
o
n
s

3
5
.
3
C
0
O
6
.
2

k
J
/
m
o
l
H

126

P
A
W












6
0

J
/
m
o
l
K
S
P
A
W

G




1
1
1

k
J
/
m
o
l
P
A
W
F
r
e
e

E
n
e
r
g
y

R
e
a
c
t
i
o
n

P
r
o
f
i
l
e
l
o
m
1
/
0
J
0
0
0
.
k
0

G
D
R
C r(C-C)
10
R
e
d
u
c
t
i
o
n

o
f

m
i
g
r
a
t
i
o
n

b
a
r
r
i
e
r

b
y

s
u
b
s
t
i
t
u
t
i
n
g

i
o
d
i
n
e

t
r
a
n
s

t
o

m
e
t
h
y
l

L



C
O


M
e
O
H


A
c
O
H


P
(
O
M
e
)3


None.



A
c
t



S
n
I2.
-
L

C
O
L


I
D

H




21

1 kcal/mol

e
x
pt
D

S





-
9

2 cal/molK


e
x
pt
D

G




24

1 kcal/mol

e
x
pt
11
Activation parameters for the CO insertion
Ir(CO)2I2(CH3)Ln- ? Ir(CO)I2(COCH3)Ln-
L ?H ?S ?G
--- 21 -5.2 23
I- 28 2.0 28
CH3OH 33 -5.7 35
CH3C(O)OH 34 -4.7 36
CO 17 -3.9 18
P(OMe)3 14 1.9 13
SnI3- 22 -3.9 23
kcal/mol
12
Isomers of M(CO)2I2(CH3)Ln- and their relative
energies
L M fac,cis mer,cis mer,trans
I Rh 0.0a 1.3 0.4
Ir 0.0 4.1 4.1
CO Rh 0.0a -2.2 -2.5
Ir 0.0 -1.8 0.4
a Energies(kcal/mol) relative to fac,cis isomer
13
Activation parameters for the different isomers
of Ir(CO)3I2(CH3)
kcal/mol
Isomer ?H ?S ?G
fac,cis 17.3 -3.90 18.5
mer,cis 28.8 -1.19 29.2
24.1ª -4.34 25.4
mer,trans 16.8 -0.46 16.9
expt. 21.3 -8.6 23.8
ª Methyl group migrating to the CO which is trans
to another CO
14
Conclusion

• Static and dynamic calculation results for the
  oxidative addition and the migratory insertion
  step in the carbonylation of methanol catalyzed
  by M(CO)2I2- (MRh, Ir) are in good agreement
  with the experimental values.
• The rate-determining step for the Rh catalyst is
  the oxidative addition of CH3I, whereas for Ir it
  is the migratory insertion step.
• Enthalpic and entropic contributions to ?G can
  vary considerably depending on reaction
  conditions without changing ?G considerably.
• Detailed study on the methyl migration of
  Ir(CO)2I2(CH3)Ln- (L is trans to I-) shows that
  free energies of activation is in the order of
  P(OMe)3 lt CO lt SnI3-, none lt I- lt CH3OH,
  CH3C(O)OH.
• In predicting the reaction rate, the relative
  stabilities of various isomers should be
  considered.