Andrew Yeung
CHEM636
Scope
 Overview
 Polyketones and their synthesis
 Timeline of development
 Catalyst selection
 Palladium vs. nickel
 Ligands
 Mechanism
 Initiation & termination
 Propagation
Properties
O
 Low Tg of 15 °C, high Tm of 257 °C (PK-E)
 Polar ketone groups give strong inter-chain forces,
backbone allows flexibility
 Resistant to organic solvents, impermeable to gases
 Easily recycled
 Prone to UV degradation (C=O)
Drent, E.; Mul, W. P.; Smaardijk, A. A., Polyketones. In Encyclopedia of Polymer Science and Technology, John Wiley & Sons, Inc.: 2002.
n
Applications
O
 Hoses for automotive,
food and medical
applications
 Flame retardant materials
 Metal-replacement
plastics
Drent, E.; Mul, W. P.; Smaardijk, A. A., Polyketones. In Encyclopedia of Polymer Science and Technology, John Wiley & Sons, Inc.: 2002.
G. Morrison, Materials and Assembly, Mechanical Engineering, May 1999,
http://www.memagazine.org/backissues/membersonly/may99/departments/tech_focus/techfocus1.html.
Nelco Products, Inc.; Victrex USA, Inc.
n
Feedstock
R
+
O
O
O
CO
n
n
n
R = H, CH3, C6H5, etc.
 α-Olefins (ethylene, propylene,
 Carbon monoxide
styrene, etc.)
 Functionalized α-olefins
(CH2OH, CH2CN, COOH)
 Internal olefins are less
reactive (norbornene,
norbornadiene)
 Terpolymerization can modify
properties (typ. 6 % propylene
for Carilon)
Drent, E.; Mul, W. P.; Smaardijk, A. A., Polyketones. In Encyclopedia of Polymer Science and Technology, John Wiley & Sons, Inc.: 2002.
Timeline of development
Ph
Ph
P
2+
2X
Pd
P
Ph
Ph
Cl
R3 P
Pd Cl
R3 P
1967 – First Pd(II)
catalyst reported
by Gough at ICI
1940s – CO/C2H4 copolymerization first
observed by Walter Reppe
C2H4
+
K2Ni(CN)4
CO
H2O
1996 – Shell
commercialized
polyketones
(“Carilon”)
1983 – Discovery
of high-yielding
Pd catalysts at
Shell
O
+
O
+HO
O
n
Drent, E.; Mul, W. P.; Smaardijk, A. A., Polyketones. In Encyclopedia of Polymer Science and Technology, John Wiley & Sons, Inc.: 2002.
G. Morrison, Materials and Assembly, Mechanical Engineering, May 1999,
http://www.memagazine.org/backissues/membersonly/may99/departments/tech_focus/techfocus1.html.
Interesting observations
 Non-chelating phosphine complexes give side products,
e.g. methyl propionate
 Perfect co-polymerization (no polyethylene or
polycarbonyl defects)
O
O
O
+
CO
[Pd]
O
O
O
O
O
O
O
O
O
O
O
O
Bianchini, C.; Meli, A. Coord. Chem. Rev. 2002, 225 (1-2), 35-66.
Drent, E.; Budzelaar, P. H. M. Chem. Rev. 1996, 96, 663.
O
O
O
O
Palladium or nickel?
O
Ph Ph
P
+
Pd
P
Ph Ph
O CH3
CO CH3OH
O
O
OH
Ph Ph
P
+
Pd H
P
Ph Ph
Ph Ph
P
Pd
P
Ph Ph
OH
 Palladium catalysts are most
CO
well-studied, used industrially
 Deactivation via hydride
 Benzoquinone helpful as a
sacrificial oxidant
Shultz, C. S.; DeSimone, J. M.; Brookhart, M. Organometallics 2000, 20, 16.
Bianchini, C.; Meli, A. Coord. Chem. Rev. 2002, 225, 35.
Ph Ph
P
Pd
P
Ph Ph
Ph Ph
P
2+
Pd
P
Ph Ph
O
O
Ph Ph
P
Pd
P
Ph Ph
Palladium or nickel?
 Nickel catalysts are attractive
 less expensive, already used for SHOP process
(ethylene oligomerization)
 However
Ph
 Despite lower barriers to migratory insertion,
catalyst fails because the catalytic resting state is
too stable
 Different mechanism – five-coordinate resting state
 CO must be introduced late – it poisons Ni(II)
Shultz, C. S.; DeSimone, J. M.; Brookhart, M. Organometallics 2000, 20, 16.
O
Ph
Ph
P
P
+
Pd
CO
P
Ph
Ph
O
Ph
P
Ni
+
O
CO
P
Ph
Ph
Monodentate vs. bidentate ligands
 Monodentate phosphines
undergo cis/trans
isomerization
 When phosphines are
mutually trans, solvolysis is
a competing reaction
 Bidentate phosphines do not
suffer from this problem
Drent, E.; Budzelaar, P. H. M. Chem. Rev. 1996, 96, 663.
P
P
cis/trans
O
Pd
O
P
Pd
[ ]
P
[ ]
CH3OH
P
O
O
+
H
Pd
P
[ ]
Length of alkylidene bridge
 dppp ligand experimentally
O
n
Ligand
n
Productivity
(g polymer/g Pd · h)
Ph2P(CH2)PPh2
2
1
Ph2P(CH2)2PPh2 100
1000
Ph2P(CH2)3PPh2 180
6000
Ph2P(CH2)4PPh2 45
2300
Ph2P(CH2)5PPh2 6
1800
Ph2P(CH2)6PPh2 2
5
Bianchini, C.; Meli, A. Coord. Chem. Rev. 2002, 225 (1-2), 35-66.
determined to be best
 No clear explanation for this
effect
 Chelate ring size of 6 is best
 Ring size affects catalyst
stability, barriers to migratory
insertion, kinetic stability of
intermediates, etc.
Initiation and termination
 End group analysis (13C NMR) shows 50 % ester, 50 %
ketone: keto ester, diketone and diester (GC, MS)
 Two independent initiation and two termination routes:
 Initiation & termination by methanolysis
 Hydride initiation
Drent, E.; Van Broekhoven, J. A. M.; Doyle, M. J. J. Organomet. Chem. 1991, 417, 235.
Bianchini, C.; Meli, A. Coord. Chem. Rev. 2002, 225 (1-2), 35-66.
Drent, E.; Budzelaar, P. H. M. Chem. Rev. 1996, 96, 663.
End group analysis
Drent, E.; Van Broekhoven, J. A. M.; Doyle, M. J. J. Organomet. Chem. 1991, 417, 235.
Initiation & termination by
methanolysis
[Pd]
OCH 3
O
CO
[Pd]
C2H4
[Pd]
O
OCH 3
O
O CH3
CH3OH
[Pd]
[Pd]
H
+
O
H3C
P
[Pd]
O
CH3OH
[Pd]
P
OCH 3
+
O
P
O
P
 Methoxy complex is first formed by methanolysis of palladium pre-
catalyst
 Initiation by methanolysis gives an ester “head”, but can give both
ester and ketone “tails”
Drent, E.; Budzelaar, P. H. M. Chem. Rev. 1996, 96, 663.
Hydride initiation
C2H4
[Pd]
H
[Pd]
CO
O
[Pd]
 Gives ketone “head”
 β-hydrogen elimination from a palladium methoxide
 Water gas shift reaction
 Wacker-type oxidation of ethylene
 Hydrogen activation
 Alcoholysis (from termination)
Drent, E.; Budzelaar, P. H. M. Chem. Rev. 1996, 96, 663.
Hydride initiation
C2H4
[Pd]
H
 β-hydrogen elimination
 Water gas shift reaction
 Wacker-type oxidation
of ethylene
 Hydrogen activation
 Alcoholysis
CO
[Pd]
[Pd]
[Pd]
[Pd]
[Pd]
+
+
CO
O
CH3
+
H2O
[Pd]
H
+
CH 2O
[Pd]
H
+
CO 2
C 2 H4
+ CH 3OH
[Pd]
H
+
[Pd]
+
H2
[Pd]
H
+
+
CH 3OH
[Pd]
[Pd]
H
+
+
+
H
CH3
O
+
H
O
P
Drent, E.; Budzelaar, P. H. M. Chem. Rev. 1996, 96, 663.
O
O
H3C
O
P
Propagation
O
CO
[Pd]
+ CO
- C2H4
[Pd]
resting state
P
[Pd]
CO
O
- CO
- CO
+ C2H4
+ CO
+ CO
P
O
P
+ CO
- CO
+ CO
- C2H4
- C2H4
[Pd]
- C2H4
+ C2H4
O
O
[Pd]
O
- CO
+ C2H4
+ C2H4
P
[Pd]
P
[Pd] = (phen)Pd2+
Rix, F. C.; Brookhart, M.; White, P. S. J. Am. Chem. Soc. 1996, 118, 4746.
Shultz, C. S.; Ledford, J.; DeSimone, J. M.; Brookhart, M. J. Am. Chem. Soc. 2000, 122, 6351.
O
P
Binding affinity of CO versus C2H4
K1
CH3
[Pd]
+
C2 H4
CH3
+
[Pd]
CO
CO
2
3
 K1 = (4.48 ± 3.14) × 10-6, ΔG° = (5.12 ± 0.31) kcal/mol
 K1 is small; Pd binds more strongly to CO than C2H4
 Concentration of palladium ethylene-alkyl complex is
kept very low
Rix, F. C.; Brookhart, M.; White, P. S. J. Am. Chem. Soc. 1996, 118, 4746.
Determination of K1
CH3
CH3
S
[Pd]
+
CO
KA

[Pd]
+
S
2
CO
4
CH3
CH3
[Pd]
+
S
KB
CH 3CN
[Pd]
NCCH
CH3
NCCH
3
+
3
5
4
[Pd]
S
+
CH3
KC
C2H4
+
[Pd]
5
3
Rix, F. C.; Brookhart, M.; White, P. S. J. Am. Chem. Soc. 1996, 118, 4746.
CH 3CN
Binding affinity of CO versus C2H4
K1
CH3
[Pd]
+
CH3
+
[Pd]
C2 H4
CO
2
3

K at-66 °C
ΔG° (kcal/mol)
KA
(7.66 ± 3.45) × 10-4
3.0 ± 0.2
KB
(6.81 ± 0.27) × 10-3
2.05 ± 0.02
KC
(8.58 ± 1.8) × 10-1
0.07 ± 0.09
K1
(4.48 ± 3.14) × 10-6
5.12 ± 0.31
Rix, F. C.; Brookhart, M.; White, P. S. J. Am. Chem. Soc. 1996, 118, 4746.
CO
Migratory insertion reactions of (phen)Pd(R)(L)
R
L
ΔG‡
(± 0.1
kcal/mol)
Temp.
(°C)
CH3 (CD2Cl2)
CO
15.4
-66
CH3 (acetone-d6)
CO
15.15
-65
CH2CH2COCH3
CO
15.0
-66
COCH3
C2H4
16.6
-46
COCH2CH2COCH3 C2H4
17.2
-44.4
CH3
C2H4
18.5
-25
CH2CH3
C2H4
19.4
-25
Rix, F. C.; Brookhart, M.; White, P. S. J. Am. Chem. Soc. 1996, 118, 4746.
 No acceleration from a
polar solvent (1-2)
 Reactions 4-7 insensitive
to ethylene concentration
(intramolecular)
 Alkyl migration to
ethylene ~ 3 kcal/mol
more difficult than for acyl
migration (3 & 7)
 Alkyl-ethylene migratory
insertion is disfavored
Determination of k &
‡
ΔG
Migratory insertion reactions of (phen)Pd(R)(L)
R
L
ΔG‡
(± 0.1
kcal/mol)
Temp.
(°C)
CH3 (CD2Cl2)
CO
15.4
-66
CH3 (acetone-d6)
CO
15.15
-65
CH2CH2COCH3
CO
15.0
-66
COCH3
C2H4
16.6
-46
COCH2CH2COCH3 C2H4
17.2
-44.4
CH3
C2H4
18.5
-25
CH2CH3
C2H4
19.4
-25
Rix, F. C.; Brookhart, M.; White, P. S. J. Am. Chem. Soc. 1996, 118, 4746.
Determination of k &

O
O
1.7 equiv. CO
[Pd]
[Pd]
CO
16, 11 %
14
O
O
O
[Pd]
CO
18, 70 %
+
[Pd]
O
19, 19 %
Rix, F. C.; Brookhart, M.; White, P. S. J. Am. Chem. Soc. 1996, 118, 4746.
‡
ΔG
Determination of k &
‡
ΔG
O
O
O
[Pd]
CO
18
+
[Pd]
O
19
O
O
[Pd]
CO
18
O
[Pd]
CO
16
Rix, F. C.; Brookhart, M.; White, P. S. J. Am. Chem. Soc. 1996, 118, 4746.
 Excess CO
 k = 7.7 × 10-4 s-1
 ΔG‡ = 15.0 kcal/mol
 No added CO
 k = 8.5 × 10-4 s-1
 ΔG‡ = 14.9 kcal/mol
Perfect polymer
 Double carbonylation is strongly disfavored
thermodynamically
 Multiple ethylene insertions are rare (prob. = 7.57 × 10-7),
even with low CO concentrations
 Concentration of alkyl-ethylene complex is very low
 Exchanges ethylene for CO readily
 Alkyl migration onto ethylene has a higher energy barrier
 β-coordination of ketone helps ensure CO coordinates next
 Result: perfectly alternating co-polymerization
Chen, J. T.; Sen, A. J. Am. Chem. Soc. 1984, 106, 1506.
Rix, F. C.; Brookhart, M.; White, P. S. J. Am. Chem. Soc. 1996, 118, 4746.
Drent, E.; Budzelaar, P. H. M. Chem. Rev. 1996, 96, 663.