Ethylene polymerization and ethylene/methyl 10-undecenoate copolymerization using nickel(II) and palladium(II) complexes derived from a bulky P,O chelating ligand

Article abstract of DOI:10.1021/om0201516

The article presented ethylene polymerization and ethylene/methyl 10-undecenoate copolymerization using nickel(II) and palladium(II) complexes. The complexes were derived from a bulky P,O chelating ligand. The catalysts employed for the polymerization studies were cationic nickel allyl complex and the palladium methyl complexes. It was concluded that the Ni(II) and Pd(II) complexes were active for the polymerization of ethylene but the Ni(II) allyl complex demonstrated very slow rates of initiation.

Full text of DOI:10.1021/om0201516

2836
Organometallics 2002, 21, 2836-2838
Eth ylen e P olym er iza tion a n d Eth ylen e/Meth yl
10-Un d ecen oa te Cop olym er iza tion Usin g Nick el(II) a n d
P a lla d iu m (II) Com p lexes Der ived fr om a Bu lk y P ,O
Ch ela tin g Liga n d
Weijun Liu, J on M. Malinoski, and Maurice Brookhart*
Department of Chemistry, University of North Carolina at Chapel Hill,
Chapel Hill, North Carolina 27599-3290
Received February 21, 2002
Sch em e 1
Summary: Cationic Ni(II) and Pd(II) complexes based
on the bulky P,O ligand phenacyldi-tert-butylphosphine
have been shown to be active for the polymerization of
ethylene and copolymerization of ethylene and methyl
10-undecenoate, a functionalized monomer.
The discovery in 1995 that Ni(II) and Pd(II) diimine
complexes of the general type [(ArNdC(R)C(R)dNAr)-
M(CH3)(OEt2)]+BAr′4- (Ar ) 2,6-(Me)2C6H3, 2,6-(i-Pr)2-
C6H3; Ar′ ) 3,5-(CF3)2C6H3) are highly active catalysts
for polymerization of ethylene and R-olefins has led to
renewed interest in late-metal catalysts for olefin
polymerizations.1-6 An attractive aspect of late-metal
catalysts is their reduced oxophilicity and potential
functional group compatibility. The key structural
feature of these d8 metal catalysts is incorporation of
bulky substituents on the ligand which serve to retard
chain transfer and lead to high-molecular-weight poly-
mers. In addition to the aryl-substituted diimine ligands,
other bulky chelating ligands employed on Ni(II) and
Pd(II) centers for ethylene polymerization include N,O,
P,P, and P,O systems.7-9 We report here use of the
readily prepared10 P,O chelate phenacyldi-tert-butyl-
(1) Reviews on late-transition-metal-catalyzed olefin polymeriza-
tion: (a) Ittel, S. D.; J ohnson, L. K.; Brookhart, M. Chem. Rev. 2000,
100, 1169. (b) Britovsek, G. J . P.; Gibson, V. C.; Wass, D. F. Angew.
Chem., Int. Ed. 1999, 38, 429.
(2) J ohnson, L. K.; Killian, C. M.; Brookhart, M. J . Am. Chem. Soc.
1995, 117, 6414.
(3) J ohnson, L. K.; Mecking, S.; Brookhart, M. J . Am. Chem. Soc.
1996, 118, 267.
(4) Mecking, S.; J ohnson, L. K.; Wang, L.; Brookhart, M. J . Am.
Chem. Soc. 1998, 120, 888.
(5) Tempel, D. J .; J ohnson, L. K.; Huff, R. L.; White, P. S.; Brookhart,
M. J . Am. Chem. Soc. 2000, 122, 6686.
(6) Gates, D. P.; Svejda, S. A.; On˜ate, E.; Killian, C. M.; J ohnson,
L. K.; White, P. S.; Brookhart, M. Macromolecules 2000, 33, 2320.
(7) Recent examples of neutral nickel catalysts employing N,O
chelate ligands for olefin polymerization: (a) J ohnson, L. K.; Bennett,
A. M. A.; Ittel, S. D.; Wang, L.; Parthasarathy, S.; Hauptman, E.;
Simpson, R. D.; Feldman, J .; Coughlin, E. B. WO 9830609, 1997. (b)
Wang, C.; Friedrich, S.; Younkin, T. R.; Li, R. T.; Grubbs, R. H.;
Bansleben, D. A.; Day, M. W. Organometallics 1998, 17, 3149. (c)
Younkin, T. R.; Connor, E. F.; Henderson, J . I.; Friedrich, S. K.; Grubbs,
R. H.; Bansleben, D. A. Science 2000, 287, 460. (d) Hicks, F. A.;
Brookhart, M. Organometallics 2001, 20, 3217.
(8) P,P ligands in ethylene polymerization: (a) Cooley, N. A.; Green,
S. M.; Wass, D. F.; Heslop, K.; Orpen, A. G.; Pringle, P. G. Organo-
metallics 2001, 20, 4769. (b) Wass, D. F. WO 01/10876 (to BP
Chemicals). (c) Dossett, S. J .; Gillon, A.; Orpen, A. G.; Fleming, J . S.;
Pringle, P. G.; Wass, D. F.; J ones, M. D. Chem. Commun. 2001, 699.
(9) Recent examples of cationic P,O Ni-allyl catalysts: (a) Mecking,
S.; Keim, W. Organometallics 1996, 15, 2650. (b) Komon, Z. J . A.; Bu,
X.; Bazan, G. C. J . Am. Chem. Soc. 2000, 122, 1830. (c) Komon, Z. J .
A.; Bu, X.; Bazan, G. C. J . Am. Chem. Soc. 2000, 122, 12379.
(10) Moulton, C. J .; Shaw, B. L. J . Chem. Soc., Dalton Trans. 2 1980,
299.
phosphine (1) as a supporting ligand on Ni(II) and
Pd(II) centers for ethylene polymerization and copolym-
erization of ethylene and methyl 10-undecenoate, a
functionalized monomer.
The catalysts employed for polymerization studies are
the cationic nickel allyl complex 3 and the palladium
methyl complexes 5 and 6. Synthetic routes to these
compounds are depicted in Scheme 1. Treatment of
[(C3H5)NiCl]2 with 1 yields the neutral π-allyl complex
10.1021/om0201516 CCC: $22.00 © 2002 American Chemical Society
Publication on Web 06/13/2002

Communications
Organometallics, Vol. 21, No. 14, 2002 2837
Ta ble 1. Eth ylen e P olym er iza tion Da ta a
amt of cat.
(106 mol)
ethylene pressure
(atm)
temp
(°C)
reacn time
(h)
yield
(g)
TOF
b
entry
cat.
(10-3 h-1
)
Mw
PDI
1
2
3
3
3
3
3
3
5
5
6
6
5
5
6
6
8.2
4.1
4.1
4.1
16.4
10
10
10
10
3.88
3.88
3.88
3.88
1.0
6.8
13.6
27.2
27.2
1.0
1.0
1.0
1.0
13.6
13.6
13.6
13.6
60
3
1
1
1
2.5
3
3
3
3
3
3
3
3
0.131
14.8
27.6
77.9
23.9
0.204
0.612
0.009
0.352
0.135
6.582
0.052
6.526
0.570
128
239
677
20.8
0.242
0.727
0.011
0.418
0.413
20.2
5500
6100
10000
14000
1900
300e
300
350
330
380
280
2.1
2.5
2.7
2.5
5.0
26 (42)c
26 (46)c
26 (88)c
50
4
5d
6
25
60
25
60
25
80
25
80
7
8
9
10
11
12
13
0.159
20.0
400
340
a
b
All polymerizations run in toluene, except entry 5. Determined by GPC. c Highest temperature recorded during polymerization (result
of reaction exotherm). Polymerization run in 95 mL of CH2Cl2 + 5 mL of EtOAc. e Mn value determined by 1H NMR spectroscopic analysis
of the oligomer.
d
Ta ble 2. P olym er iza tion Da ta Dem on str a tin g Slow
2, in which the ligand carbonyl group remains uncom-
plexed. Abstraction of chloride from 2 with NaBAr′4
In itia tion a
temp
(°C)
time
(min)
yield
(g)
TOF
yields the cationic bidentate complex 3. The palladium
complex 4 is generated by displacement of COD (1,5-
cyclooctadiene) from (COD)PdMeCl with 1 followed by
chloride abstraction with NaBAr′4 in the presence of
either Et2O or CH3CN to yield 5 or 6.
b
entry
(10-4 h-1
)
Mw
PDI
1
2
3
4
5
30
30
30
30
30
15
20
25
30
40
0.5
2.5
4.4
15.3
33.4
8.6
33.5
47.4
136
15 400
14 900
13 700
9 800
2.4
2.3
2.1
2.4
2.3
224
8 400
Results of ethylene polymerization studies using 3,
5, and 6 are summarized in Table 1. Exposure of 3 to 1
atm of ethylene results in rather low yields of PE (entry
1). However, polymerizations run at 6.8-27.2 atm
exhibit very high activities that are comparable to
highly active early-metal catalysts.11-15 At catalyst
loadings of 2 × 10-5 M, the reaction exotherm cannot
be completely controlled by the internal cooling manifold
inside the autoclave reactor (entries 2-4). Increasing
the ethylene pressure results in an increase in the
reaction exotherm, polymerization activity, and polymer
molecular weight. In all cases the polymer produced by
3 is a white powdery solid with Tm values between 127
a
Conditions: 0.8 µmol of 3; 200 mL of toluene; 27.2 atm of
b
ethylene. Determined by GPC.
pressures the product is an amorphous solid (Tm ) 22
°C, 16 branches/1000 carbons).
An NMR investigation of the reaction of 3 with
ethylene has been carried out. Exposure of 3 to 10 equiv
of ethylene in CD2Cl2 at 25 °C results in consumption
of ethylene and formation of polyethylene with a
-(CH2)n- resonance appearing at 1.28 ppm but no
decrease in the intensity of the Ni-allyl resonances.
These observations suggest that only a small fraction
of 3 is initiated, followed by very rapid propagation and
chain growth. Slow initiation of 3 was verified by
polymerization experiments summarized in Table 2.
Using a very low catalyst loading (0.8 µmol in 200 mL
of toluene) and 400 psig of ethylene, the reaction
exotherm could be better controlled. As seen by examin-
ing entries 1-5, TOF’s (calculated from polymer yields)
dramatically increase with time. Only 0.5 g of PE forms
after 15 min, yet after 40 min 33.4 g of PE is produced,
corresponding to a TOF of 2.24 × 106 h-1. Recognizing
that little polymer is formed in the first 20 min and that
at 40 min all catalyst may still not be activated, the
intrinsic TOF of this catalyst under these conditions
must exceed 3 × 106 h-1 (8.4 × 104 kg of PE (mol of
Ni)-1 h-1).16,17
1
and 131 °C. H NMR analysis indicates linear polymer
chains with 6-8 methyl branches per 1000 carbons.
Catalyst 3 remains active toward ethylene polymeriza-
tion in the presence of 5% ethyl acetate (entry 5),
although the polymer molecular weight is reduced and
a broadened molecular weight distribution is observed.
Pd catalysts 5 and 6 show modest activity at 25 and
60 °C under 1 atm of ethylene pressure. The more labile
ether complex is typically more reactive than the
acetonitrile adduct, particularly at low temperatures.
Much higher activities are exhibited by 5 and 6 at 13.6
atm and increase with increasing temperatures. At high
temperature and pressure the activities of 5 and 6 are
approximately equal. The Pd catalysts generate low-
molecular-weight PE oligomers with Mn ≈ 350 as
1
determined by H NMR analysis. The physical proper-
Exposure of 5 to 5 equiv of ethylene in CD2Cl2 at -78
°C generates the methyl ethylene complex 7, which was
ties of the PE generated by 5 and 6 change considerably
with ethylene pressure. At 1 atm of ethylene pressure,
the oligomeric product is a viscous oil (Tm ) 5 °C, 42
branches per 1000 carbons), while at higher ethylene
(16) In comparison, certain Ni(II) R-diimine catalysts exhibit eth-
ylene polymerization activities of up to 1.0 × 105 kg of PE (mol of Ni)-1
6
h-1
.
(17) Shell higher olefin process (SHOP) systems based on the neutral
nickel P,O catalysts of the type [Ph2PC(R)dC(R)O]Ni(Ph)L generate
low-molecular-weight oligomers to high-molecular-weight PE (Mn up
to 106 g mol-1) with activities of up to 1.4 × 103 kg of PE (mol of Ni)-1
h-1 depending on reaction conditions: (a) Keim, W.; Kowalt, F. H.;
Goddard, R.; Kru¨ger, C. Angew. Chem., Int. Ed. Engl. 1978, 17, 466.
(b) Klabunde, U.; Ittel, S. D. J . Mol. Catal. 1987, 41, 123. (c)
Starzewski, K. A. O.; Witte, J . Angew. Chem., Int. Ed. Engl. 1987, 26,
63.
(11) Waymouth, R. M.; Coates, G. W. Science 1995, 267, 217.
(12) Brintzinger, H. H.; Fischer, D.; Mulhaupt, R.; Rieger, B.;
Waymouth, R. M. Angew. Chem., Int. Ed. Engl. 1995, 34, 1143.
(13) Kaminsky, W.; Arndt, M. In Applied Homogeneous Catalysis
with Organometallic Compounds; Kaminsky, W., Arndt, M., Eds.;
VCH: New York, 1996; Vol. I, pp 220-236.
(14) McKnight, A. L.; Waymouth, R. M. Chem. Rev. 1998, 98, 2587.
(15) Coates, G. W. Chem. Rev. 2000, 100, 1223.

2838 Organometallics, Vol. 21, No. 14, 2002
Ta ble 3. Cop olym er iza tion of Eth ylen e/Meth yl 10-Un d ecen oa tea
Communications
comon concn
(M)
pressure
(psig)
temp
(°C)
yield
(g)
TON
(C2H4)
comon incorp
(mol %)
b
entry
Mw
PDI
1
2
3
4
5
0.90
0.45
0.22
0.22
0.22
100
100
100
100
200
60
60
60
80
60
0.31
2.1
3.2
3.1
3.9
900
8 000
12 800
12 000
15 700
4.8
1.6
1.0
1.2
0.63
3400
4000
4500
3300
4300
1.7
1.8
1.8
1.8
1.8
a
b
All polymerizations run in toluene. Determined by GPC.
Sch em e 2
to ethylene in the presence of methyl 10-undecenoate
results in the formation of random copolymers (Table
3). In comparison to ethylene homopolymerization ex-
periments (Table 1), productivities of the copolymeriza-
tions are greatly reduced and yield lower molecular
weight material. Increasing the concentration of methyl
10-undecenoate in the reaction solution results in an
increase in comonomer incorporation but a decrease in
copolymer yield. An increase in ethylene pressure
results in decreased comonomer incorporation, while an
increase in reaction temperature has little effect on
activity and methyl 10-undecenoate incorporation.
In summary, the Ni(II) and Pd(II) complexes de-
scribed are active for the polymerization of ethylene but
the Ni(II) allyl complex demonstrates very slow rates
of initiation. The Ni complex exhibits very high activity
at high ethylene pressures, generating linear PE of
modest molecular weights. Pd catalysts 5 and 6 are an
order of magnitude less active than 3, forming low-
moleculr-weight PE oligomers in which the degree of
branching decreases with increasing ethylene pressure.
Complex 3 has been shown to copolymerize ethylene and
methyl 10-undecenoate with polar comonomer incorpo-
ration of up to ca. 5%. The reason for the high insertion
barrier in the Pd system relative to R-diimine catalysts
is unclear and is a focus of our current investigations.
characterized by NMR spectroscopy (Scheme 2). Warm-
ing to 0 °C results in migratory insertion and chain
growth. The first-order rate constant for migratory
insertion of the methyl ethylene complex at 0 °C was
measured by monitoring decrease of the methyl reso-
nance and found to be k1 ) 4.3 × 10-5 s-1, with ∆Gq )
21.4 kcal/mol. The average rate of subsequent insertions
was estimated from both the decrease in the bound
ethylene signal and the increase of the oligomer
-(CH2)n- signal and found to be ksubs ) 2.1 × 10-5 s-1
,
with ∆Gq ) 21.8 kcal/mol. These barriers are consider-
ably larger than those for insertion in previously studied
Pd(II) R-diimine complexes.2,5 For example, the rate of
insertion for ethylene into the Pd-Me bond for a typical
R-diimine Pd(II) complex at -30 °C has been found to
be kobs ) 1.9 × 10-3 s-1, with ∆Gq ) 17.2 kcal/mol.
Since polymerization of ethylene in the presence of
ethyl acetate occurs with good activity, the use of 3 for
copolymerization of ethylene and the polar comonomer
methyl 10-undecenoate was examined. Exposure of 3
Ack n ow led gm en t . We thank DuPont and the
National Science Foundation (Grant No. CHE-0107810)
for financial support of this work.
Su p p or tin g In for m a tion Ava ila ble: Text giving experi-
mental details for the synthesis and characterization of
complexes 2-7 and general polymerization procedures. This
material is available free of charge via the Internet at
http://pubs.acs.org.
OM0201516