Transcript Slide 1

Hydroformylation
Aldehydes
R
+ CO + H2
side reactions
R
H
linear (normal)
R
alkene isomerization
O
H
O
Rh or Co
+
*
R
branched (iso)
R
alkene hydrogenation
* Largest homogeneous catalytic process
* > 15 billion pounds of aldehydes (alcohols) per year
• Commercial catalysts are complexes of Co or Rh
• Selectivity to linear (normal) aldehyde important
Otto Roelen (1897-1993)
HCo(CO)4 Catalyst System – Unmodified Co
H
O C
O
Co
C O
C
H
O
O C Co
C
O
C
O
C C
H
Co C O
H
R
Co
O
- CO
+ alkene
R
CO
C
Monometallic
O
C O
C
C
O
O C
Co
C
C
O
Bimetallic
C
proposed bimetallic
pathway - NOT important
in normal catalysis
O
O
R
+ CO
O C
O
3 atm CO = 1.6:1 L:B ratio
90 atm CO = 4.4:1 L:B ratio
anti-Markovnikov
hydride addition
to C=C bond to give
linear alkyl
+ CO
R
O
O
O
Rate
Determining
Step
+ H2
- CO
C O
C
CO
C
Co
H
Co
C
O
H
O C
C
O
O
O
O
C
R
Co
C
C
C
O
O
O
increasing the CO pressure keeps the back reactions from occuring this limits alkene isomerization and the corresponding opportunity for
making branched alkyl
d (aldehyde)
 k[alkene][Co][H 2][CO] -1
dt
H
Co
CO
alkene isomerization
CO
R
C
O
R
H
OC
Co
CO
Co
CO
C
O
Co
CO
CO
CO
R
R
linear alkyl
(leads to linear aldehyde)
+CO
O
OC
OC
CO
R
Co
C
O
CO
CO
branched acyl (leads to branched aldehyde)
4%
0%
72%
0.5%
0.6%
15%
1%
2%
6%
0.2%
18%
12%
5%
25%
% formyl group addition to indicated carbon
38%
HCo(CO)4(PR3) Catalyst System – Phosphine Modified
Lynn Slaugh and Richard Mullineaux; Shell Chemical Co.
Table 1. Hydroformylation of 1-hexene using Co2(CO)8/2P as catalyst precursor.
160°C, 70 atm, 1.2:1 H2/CO
PR3
pKa
Tolman n
(cm-1)
P(i-Pr)3
9.4
2059.2
160
2.8
85.0
--
PEt3
8.7
2061.7
132
2.7
89.6
0.9
PPr3
8.6
2060.9
132
3.1
89.5
1.0
PBu3
8.4
2060.3
136
3.3
89.6
1.1
PEt2Ph
6.3
2063.7
136
5.5
84.6
2.2
PEtPh2
4.9
2066.7
140
8.8
71.7
4.3
PPh3
2.7
2068.9
145
14.1
62.4
11.7
Cone
Angle °
kr x 103
(min-1)
%
Aldehyde to
Linear Prod
alcohol
HRh(CO)(PR3)2 Catalyst System
H
OC
Rh
C
O
PPh3
PPh3
- CO
+ CO
OC
Rh
Ph3P
+ alkene
PPh3
R
H
Rh
H
PPh3
PPh3
C
O
O
R
H
H
H
Rh
Ph3P
C
O
OC
PPh3
O
R
Rh
PPh3
Ph3P
R
+ CO
R
O
OC
+ H2
Rh
PPh3
PPh3
C
O
R
- CO
+ CO
OC
Rh
PPh3
Ph3P
O
OC
R
Rh
C
O
PPh3
PPh3
Need for Excess Phosphine Ligand
PPh3
Ph3P
Rh
+CO
-PPh3
PPh3
OC
H
+PPh3
PPh3
Rh
Inactive
+CO
-PPh3
CO
OC
H
PPh3
-CO
+CO
-PPh3
+PPh3
-CO
Rh
OC
H
+PPh3
PPh3
-CO
Ph
Ph
Ph
Ph
Rh
P
+ H2
P
Rh
Rh
- benzene
Rh
H
CO
highly active,
not selective
active, but not
very selective
Selective Catalyst
CO
Rh
P
Ph
Ph
PPh2
PPh2
PPh2
PPh2
PPh2
PPh2
Bisbi
Bisbi*
O
O P
O
Naphos
O
P O
O
O
PPh2
UC-44
PPh2
Xantphos
Catalyst (1 mM)
Init TOF (min-1)
Aldehyde L:B
% iso
Rh/PPh3 (1:400)
13(1)
9:1
< 0.5
Rh/Bisbi (1:5)
25(2)
70:1
< 0.5
Rh/Naphos (1:5)
27(1)
120:1
1.5
Rh/Xantphos (1:5)
13(2)
80:1
5.0
[rac-Rh2H2(m-CO)2(et,ph-P4)]2+ Catalyst System
[rac-Rh2H2(m-CO)2(et,ph-P4)]2+ Catalyst Fragmentation
HCo(CO)4
H+ + [Co(CO)4]-
strong acid in H2O, MeOH
similar to HCl !!