A Static and Dynamic Density Functional Theory Study of Methanol Carbonylation Minserk Cheong, a...
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![Page 1: A Static and Dynamic Density Functional Theory Study of Methanol Carbonylation Minserk Cheong, a Rochus Schmid, b and Tom Ziegler c a Department of Chemistry,](https://reader030.fdocuments.us/reader030/viewer/2022032704/56649d4a5503460f94a2765d/html5/thumbnails/1.jpg)
A Static and Dynamic Density Functional Theory Study of
Methanol Carbonylation
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, Koreab Technische Universitat Munchen, Anorganisch-Chemisches Institut, D-85747
Garching, Germanyc Department of Chemistry, University of Calgary, Alberta, Canada T2N 1N4
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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.
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M
OC I
OC I
M
I I
OC IC
CH3O
M
OC I
OC I
I
CH3
M
OC I
OC I
HI
H2OC
MeI
CH3O
MeCOI
MeOHI MeCO 2H
CO
1
2
3
4
Catalytic Cycle for Acetic Acid Synthesis
M= Rh +, Ir +
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Thermodynamics of oxidative addition reactions
Meta l H298(g) S298(g) G298(g) Esolv G298(solv)
Rh 29.5 -13.6 33.6 -22.0 13.6Ir 22.4 -15.1 26.9 -22.5 4.4
kcal/mol
Meta l H298(g) S298(g) G298(g) Esolv G298(solv)
Rh -38.9 -28.4 -30.4 18.6 -11.8Ir -41.4 -27.7 -33.1 14.0 -19.1
CH3I + M(CO)2I2−→ CH3 ( )M CO 2I 2 + I
-
CH3M(CO)2I2 + I- → CH3 ( )M CO 2 I3−
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I
R hO
CI
C
O
I
C
r(R
h -H)
r(C
- I)
r (Rh-C)RC=3
G
O R C = r(M-C)-r(I-C)
Transition S tate Region
O
C
OCRh
C
I
I
I
r(C
-I)
r(R
h-C
)
RC=-1.0
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Comparison of static(ADF) calculations and dynamic(PAW) calculation
Comparison of static(ADF) calculations and dynamic(PAW) calculation
Metal ‡ S‡ G‡
RhPAW
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 20.9kcal/mol
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I
O
I
C
Rh
C
I
C
O2 .7 7
2.39
1.91
OO
I
CC
Rh
C
I I
O
I
C
Rh
O
C
C
O
I
C
0 kcal/mol
‡ 18 kcal/mol
S‡ 1.1 cal/mol•K
G‡ 17 kcal/mol - 5.6 kcal/mol
S 2.3 cal/mol•K
G = - 6.2 kcal/mol
Migratory Insertion of [MeRh(CO)2I3]-
Transition State
Reactant
Product
‡expt
= 15 kcal/mol S‡
expt = -14 cal/mol•K
G ‡expt
= 19 kcal/mol
expt = -8.8 kcal/mol
S expt = - 13 cal/mol•K
G expt = -5.0 kcal/mol
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I
O
C
I
C
Ir
C
I
O
2 .77
2.50 1. 88
O
I
C
I
I r
C
C
I
O
O
C
IIr
O
C
C
O
C
I
H‡
= 28 kcal/mol
S‡
= 2.0 cal/mol•K
G‡
= 28 kcal/mol
Transition State
kcal/mol
Reactant
Product
H= 4.0 kcal/mol S = 3.6 cal/mol•K G = 2.9 kcal/mol
Migratory Insertion in [MeIrCO2I3]-
2.90
Hexpt‡ = 37 kcal/mol
Sexpt‡ = 22 cal/mol•K
Gexpt‡ = 31 kcal/mol
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Comparison of static (ADF) calculations and dynamic (PAW) calculations
H ‡expt = 155 ± 4 kJ/mol
S ‡ expt = 91 ± 8 J/mol•K G ‡ expt = 128± 4 kJ/m ol
I
O
C
I
C
Ir
C
I
O
2.60
2.42
1.80
H ‡ = 118 kJ/molS ‡ = 8 J/mol•K G ‡ A DF = 116 kJ/m ol
A DF
A DF
H ‡ = 126 kJ/molS ‡ = 60 J/mol• KG ‡ PAW = 111 kJ/m ol
PAW
PAW
-20
0
20
40
60
80
100
120
1.4 1.6 1.8 2 2.2 2.4 2.6 2.8 3
0.0
00
01
RC = r(C-C)
G k
J/m
ol
Free Energy Reaction Profile
3.53
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H‡expt = 37 ± 1 kcal/mol
S‡ expt = 22 ± 2 cal/mol•K G‡ expt = 31 ± 1 kcal/mol
Reduction of migration barrier by substituting iodine trans to methyl
O
C
I
O
C
Ir
C
II
+L or Act
-I-
O
CO
C
Ir
C
II
LL = CO; MeOH; AcOH; P(OMe)3 ; None. Act = SnI2.
H‡expt = 21 ± 1 kcal/mol
S‡ expt = -9 ± 2 cal/mol•K G‡ expt = 24 ± 1 kcal/mol
L= I- L=CO
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Activation parameters for the CO insertionActivation parameters for the CO insertion
kcal/mol
[Ir(CO)2I2(CH3)L]n- [Ir(CO)I2(COCH3)L]n-
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
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Isomers of [M(CO)2I2(CH3)L]n- and their relative energies
Isomers of [M(CO)2I2(CH3)L]n- 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
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Activation parameters for the different isomers of [Ir(CO)3I2(CH3)]
Activation parameters for the different isomers of [Ir(CO)3I2(CH3)]
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
kcal/mol
ª Methyl group migrating to the CO which is trans to another CO
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ConclusionConclusion• Static and dynamic calculation results for the oxidative addition and
the migratory insertion step in the carbonylation of methanol catalyzed by [M(CO)2I2]- (M=Rh, 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)L]n- (L is trans to I-) shows that free energies of activation is in the order of P(OMe)3 < CO < SnI3
-, none < I- < CH3OH, CH3C(O)OH. • In predicting the reaction rate, the relative stabilities of various
isomers should be considered.