A highly active anilinoperinaphthenone-based neutral nickel(II) catalyst for ethylene polymerization

Article abstract of DOI:10.1021/om020648f

A general synthetic route for the preparation of 2-anilinoperinaphthenones is reported. 2-(2,6-Dimethylanilino)perinaphthenone (4a) and 2-(2,6-diisopropylanilino)perinaphthenone (4b) are used as ligands for the corresponding neutral nickel(II) complexes [[(2,6-Me₂C₆H₃)NC₁₃H₇O]Ni (Ph)(PPh₃)] (5a) and [[(2,6-ⁱPr₂C₆H₃)NC₁₃H ₇O]Ni(Ph)(PPh₃)] (5b). The key features of these nickel complexes are a hindered N-aryl ring, a five-membered-ring nickel chelate, and an anionic N-donor moiety. Complexes 5a,b are active, but short-lived, ethylene polymerization catalysts with turnover numbers in excess of 60 000 mol ethylene/mol catalyst. Polymer branching is controlled by variation of temperature and pressure. A correlation between ethylene pressure and polymer molecular weight suggests that chain transfer occurs by a β-hydride elimination pathway. Finally, decomposition of 5b to free ligand is observed under the polymerization conditions employed.

Full text of DOI:10.1021/om020648f

250
Organometallics 2003, 22, 250-256
A High ly Active An ilin op er in a p h th en on e-Ba sed Neu tr a l
Nick el(II) Ca ta lyst for Eth ylen e P olym er iza tion
J ason C. J enkins and Maurice Brookhart*
Department of Chemistry, University of North Carolina at Chapel Hill,
Chapel Hill, North Carolina 27599
Received August 12, 2002
A general synthetic route for the preparation of 2-anilinoperinaphthenones is reported.
2-(2,6-Dimethylanilino)perinaphthenone (4a ) and 2-(2,6-diisopropylanilino)perinaphthenone
(4b) are used as ligands for the corresponding neutral nickel(II) complexes [[(2,6-Me2C6H3)-
NC13H7O]Ni(Ph)(PPh3)] (5a ) and [[(2,6-iPr2C6H3)NC13H7O]Ni(Ph)(PPh3)] (5b). The key
features of these nickel complexes are a hindered N-aryl ring, a five-membered-ring nickel
chelate, and an anionic N-donor moiety. Complexes 5a ,b are active, but short-lived, ethylene
polymerization catalysts with turnover numbers in excess of 60 000 mol ethylene/mol catalyst.
Polymer branching is controlled by variation of temperature and pressure. A correlation
between ethylene pressure and polymer molecular weight suggests that chain transfer occurs
by a â-hydride elimination pathway. Finally, decomposition of 5b to free ligand is observed
under the polymerization conditions employed.
In tr od u ction
different properties compared to their early metal
counterparts.2-8,11-14 The microstructue of polyethyl-
enes produced with the R-diimine nickel catalysts may
be varied from essentially linear to highly branched
simply by changing the polymerization temperature and
ethylene pressure.2,3,5,6,8 The palladium version of the
R-diimine catalysts produces highly branched polyeth-
Interest in late transition metal complexes as olefin
polymerization catalysts has been on the rise in the past
several years,1-23 stimulated in part by the discovery
of R-diimine-based cationic nickel and palladium cata-
lysts, 1.2-8,11-14 These catalysts were found to have quite
2,3,12,13
ylene regardless of polymerization conditions.
(1) Britovsek, G. J . P.; Gibson, V. C.; Wass, D. F. Angew. Chem.,
Int. Ed. 1999, 38, 428.
(2) Ittel, S. D.; J ohnson, L. K.; Brookhart, M. Chem. Rev. 2000, 100,
1169.
(3) J ohnson, L. K.; Killian, C. M.; Brookhart, M. J . Am. Chem. Soc.
1995, 117, 6414.
(4) J ohnson, L. K.; Mecking, S.; Brookhart, M. J . Am. Chem. Soc.
1996, 118, 267.
(5) Brookhart, M. S.; J ohnson, L. K.; Killian, L. K.; Arthur, S. D.;
Feldman, J .; McCord, E. F.; McLain, S. J .; Kreutzer, K. A.; Nennet, A.
M. A.; Coughlin, E. B.; Ittel, S. D.; Parthasarathy, A.; Tempel, D. J .
DuPont Diimine patent.
(6) Killian, C. M.; Tempel, D. J .; J ohnson, L. K.; Brookhart, M. J .
Am. Chem. Soc. 1996, 118, 11664.
These catalysts are also known to “chain straighten”
poly-R-olefins, producing polymers with fewer branches
than expected.2,5,6 An attractive feature of late metal
olefin polymerization catalysts is an increased func-
tional group tolerance both for comonomers and polym-
erization solvents.14,15 For example, emulsion polymer-
izations with late metal catalysts have been successfully
carried out in water,14,15,18,24 and both the nickel and
palladium R-diimine catalysts have been reported to
successfully copolymerize ethylene with alkyl acry-
lates.4,7,25 The nickel catalysts require temperatures
above 120 °C, whereas the palladium analogues are
active under milder conditions.
(7) Mecking, S.; J ohnson, L. K.; Wang, L.; Brookhart, M. J . Am.
Chem. Soc. 1998, 120, 888.
(8) Gates, D. P.; Svejda, S. A.; Onate, E.; Killian, C. M.; J ohnson,
L. K.; White, P. S.; Brookhart, M. Macromolecules 2000, 33, 2320.
(9) Small, B. L.; Brookhart, M. J . Am. Chem. Soc. 1998, 1210, 7143.
(10) Small, B. L.; Brookhart, M. J . Am. Chem. Soc. 1998, 120, 4049.
(11) Leatherman, M. D.; Brookhart, M. Macromolecules 2001, 34,
2748.
(12) Cotts, P. M.; Guan, Z.; McCord, E.; McLain, S. Macromolecules
2000, 33, 6945.
(13) Guan, Z.; Cotts, P. M.; McCord, E. F.; McLain, S. J . Science
1999, 283, 2059.
(14) Mecking, S.; Held, A.; Bauers, F. M. Angew. Chem., Int. Ed.
2002, 41, 545.
(15) Bauers, F. M.; Mecking, S. Macromolecules 2001, 34, 1165.
(16) Peuckert, M.; Keim, W. Organometallics 1983, 2, 594.
(17) Hirose, K.; Keim, W. J . Mol. Catal. 1992, 73, 271.
(18) Soula, R.; Broyer, J . P.; Llauro, M. F.; Tomov, A.; Spitz, R.;
Claverie, J .; Drujon, X.; Malinge, J .; Saudemont, T. Macromolecules
2001, 34, 2438.
(19) Britovsek, G. J .; et al. Chem. Commun. 1998, 849.
(20) Britovsek, G. J .; et al. J . Am. Chem. Soc. 1999, 121, 8728.
(21) Komon, Z. A. J .; Bu, X.; Bazan, G. C. J . Am. Chem. Soc. 2000,
122, 12379.
(22) Lee, Y. L.; Bazan, G. C.; Vela, J .; Komon, Z. J . A.; Bu, X. J .
Am. Chem. Soc. 2001, 123, 5352.
(23) Ostoya Starzewski, K. A.; Witte, J . Angew. Chem., Int. Ed. Engl.
1985, 24, 599.
Typically, the cationic nickel systems are more elec-
trophilic and thus more sensitive to protic solvents and
comonomer functional groups relative to the cationic
palladium analogues. Therefore there has been sub-
(24) Soula, R.; Saillard, B.; Spitz, R.; Claverie, J .; Llaurro, M. F.;
Monnet, C. Macromolecules 2002, 35, 1513.
(25) J ohnson, L.; Bennett, A.; Dobbs, K.; Hauptman, E.; Ionkin, A.;
Ittel, S.; McCord, E.; McLain, S.; Radzewich, C.; Yin, Z.; Wang, L.;
Wang, Y.; Brookhart, M. Polym. Mater. Sci. Eng. 2002, 86, 319.
10.1021/om020648f CCC: $25.00 © 2003 American Chemical Society
Publication on Web 12/13/2002

Neutral Nickel(II) Catalyst
Organometallics, Vol. 22, No. 2, 2003 251
Sch em e 1
stantial interest in developing neutral nickel analogues
to overcome these limitations. The most industrially
relevant neutral nickel catalysts are the SHOP-type
catalysts developed for the conversion of ethylene to
linear R-olefins.16-18 Modified SHOP catalysts convert
ethylene to high molecular weight polymers, but only
under special conditions.16,17,23 Recently, neutral nickel
catalysts that incorporate at least one bulky N-aryl ring
were reported. Salicylaldimine catalysts, 2, were de-
scribed by DuPont26 and by Grubbs.27,28 The most active
systems contain either electron-withdrawing nitro sub-
stituents in the aromatic ring or bulky substituents at
C-3, with a 9-anthracenyl group being most effective.
In the latter case, activities of 1.3 × 105 mol ethylene-
(mol Ni‚h)-1 and lifetimes in excess of 6 h were observed
at 45-50 °C.
six-membered nickel chelate while the anilinotropone
catalyst contains a five-membered nickel chelate. It is
not clear if chelate size is responsible for the difference
in activities, but Keim showed with SHOP-type systems
that an increase in activity is observed with contraction
of chelate size.30
This work examines other neutral nickel catalyst
analogues containing five-membered chelates with po-
tentially different electronic properties. We report the
synthesis and polymerization activity of 5a ,b prepared
from the anilinoperinaphthenone ligands 4a ,b. A unique
feature of the deprotonated anilinoperinaphthenone
ligand compared to the salicylaldimine and anilino-
tropone ligands is that the negative charge cannot be
delocalized by resonance onto oxygen, and thus charge
density at oxygen should be substantially less in 5 than
in 2 or 3 (Scheme 1).
Resu lts a n d Discu ssion
Liga n d Syn t h esis. The anilinoperinaphthenone
ligands, 4a and 4b, were prepared by the palladium-
catalyzed coupling of 2-bromoperinaphthenone with 2,6-
dimethyl and 2,6-diisopropylaniline, respectively, using
the methodology developed by Buchwald and Hart-
wig.31-34 Racemic 2,2′-bis(diphenylphosphino)-1,1′-bi-
naphthyl (BINAP), 1,1′-bis(diphenylphosphino)ferrocene
(DPPF), 2-di-tert-butylphosphino-1,1′-biphenyl, and 2-di-
cyclohexylphosphino-1,1′-biphenyl were screened as pos-
sible ligands for the palladium-catalyzed coupling.
2-Dicyclohexylphosphino-1,1′-biphenyl was determined
to give the best yield and the fewest side products. Both
coupling reactions were carried out with 1 equiv of
bromoperinaphthenone, 1.2 equiv of aniline, 1.4 equiv
of sodium tert-butoxide, and a 10 mol % catalyst loading
We reported catalysts of type 3 based on anili-
notropone ligands.29 High activities were observed for
the unsubstituted catalyst (6 × 104 mol ethylene mol
Ni-1 h-1), and compared with the unsubstituted sali-
cylaldimine catalyst 2a (3400 mol ethylene mol Ni-1
h-1), the anilinotropone catalyst appears to be more
reactive. Clearly a major difference between these two
systems is that the salicylaldimine catalysts possess a
(26) J ohnson, L. K.; Bennett, A. M. A.; Ittel, S. D.; Wang, L.;
Parthasarathy, A.; Hauptman, E.; Simpson, R. D.; Feldman, J .;
Coughlinm E. B. DuPont Patent.
(27) Wang, C.; Friedrich, S.; Younkin, T. R.; Li, R. T.; Grubbs, R.
H.; Bansleben, D. A.; Day, M. W. Organometallics 1998, 17, 3149.
(28) Younkin, T. R.; Connor, E. F.; Henderson, J . I.; Friedrich, S.
K.; Grubbs, R. H.; Bansleben, D. A. Science 2000, 287, 460.
(29) Hicks, F. A.; Brookhart, M. Organometallics 2001, 20, 3217.
(30) Keim, W.; Schulz, R. P. J . Mol. Catal. A 1994, 92, 21.
(31) Wolfe, J . P.; Wagaw, S.; Marcoux, J .-F.; Buchwald, S. L. Acc.
Chem. Res. 1998, 31, 805.
(32) Yang, B. H.; Buchwald, S. L. J . Organomet. Chem. 1999, 576,
125.
(33) Hartwig, J . F. Angew. Chem., Int. Ed. 1998, 37, 2046.
(34) Hartwig, J . F. Acc. Chem. Res. 1998, 31, 852.

252 Organometallics, Vol. 22, No. 2, 2003
J enkins and Brookhart
Sch em e 2
Sch em e 3
formed from 4a ,b upon deprotonation with sodium
hydride proved to be extremely difficult. The sodium
salts produced from reaction of NaH with salicylaldi-
mine and anilinotropone, precursors of 2 and 3, were
reported to be relatively stable compounds under an
inert atmosphere.27,29 Deprotonation of 4a ,b with NaH
was indicated by a distinct color change from bright red
to bright green. However, upon attempted isolation
using techniques successful for 2 and 3, protonation of
the salt was apparent from the color change back to the
original bright red color characteristic of 4a ,b. The
sodium salts could be isolated using rigorously dried
glassware and cannulae, but partial protonation oc-
curred over the course of several days’ storage in the
solid state under argon. Therefore, attempts to use the
isolated sodium salts for catalyst preparation were
abandoned in favor of an in situ technique (see below).
The extreme sensitivity of the ligand salt to adventitious
water is likely due to the higher basicity of the anion
as a result of the lack of resonance stabilization of
negative charge by the carbonyl moiety (Scheme 1).
Catalysts 5a ,b were readily synthesized by in situ
deprotonation of the anilinoperinaphthenone ligand
with excess sodium hydride in THF followed by addition
of (PPh3)2Ni(Ph)(Cl) as a solid (Scheme 3). The excess
sodium hydride in the reaction mixture does not react
with either the nickel precursor or the final product and
can be filtered away prior to product isolation. Catalysts
5a ,b were obtained as purple crystals in yields of 65%
and 70%, respectively, upon recrystallization and were
F igu r e 1. ORTEP view of 4b . Selected interatomic
distances (Å) and angles (deg): C(14)-N(15) ) 1.367(2),
C(2)-O(1) ) 1.234(2), C(14)-N(15)-C(16)-C(17) ) 104.01-
(21).
of Pd2dba3 and 2-dicyclohexylphosphino-1,1′-biphenyl at
80 °C in toluene for 18 h (Scheme 2). The required
catalyst loading was significantly higher than typically
reported for most couplings of this type, but was
necessary to produce anilinoperinaphthenones in yields
of 60-70%.31-34 Use of 5% catalyst loading led to yields
in the 40-50% range. Similar problems were not
observed with 2-triflatotropone.35
The 1H NMR spectrum of 4b is typical of both ligands
and is described here. Characteristic resonances include
a broad singlet at 6.60 ppm assigned to the N-H proton
and a sharp singlet at 6.12 ppm assigned to H3. A
doublet at 1.20 ppm, which integrates to 12 protons, is
assigned to four equivalent methyl groups of the two
isopropyl substituents and indicates that rotation about
the N-aryl bond is fast on the NMR time scale.
An X-ray quality crystal of 2-(2,6-diisopropylanilino)-
perinaphthenone (4b) was prepared by slow diffusion
of hexamethylsiloxane into a concentrated solution of
4b in toluene at room temperature. As expected, the
sterically bulky isopropyl groups hold the N-aryl ring
nearly perpendicular to the plane of the perinaph-
thenone ring. The torsion angle for the C-N (C14-
N15-C16-C17) bond was determined to be 104.01(21)°.
The C-N bond length of 1.367(2) Å is shorter than the
1.435(2) Å C-N bond of 2-(2,6-diisopropyl)anilino-
tropone, while the C-O bond lengths are similar at
1.234(2) and 1.252(2) Å, respectively.29
1
fully characterized by H, 13C, and 31P NMR spectros-
copy and elemental analysis.
For catalyst 5b, coordination of the anilinoperinaph-
thenone ligand to the nickel center causes rotation about
the N-aryl bond to become slow on the NMR time scale
and thus renders the individual methyl groups of an
1
isopropyl unit inequivalent in the H NMR spectrum.
Two doublets, each of which integrate to six protons,
are observed at 1.14 and 1.04 ppm, while in 4b one 12H
doublet is observed (see above). As expected, the broad
singlet seen for 4b at 6.60 ppm, attributed to the N-H
Ca ta lyst Syn th esis. We expected precatalysts (5a ,b)
to be available from reaction of the sodium salts of 4a ,b
with (PPh3)2Ni(Ph)Cl.27,29 Isolation of the sodium salts
1
proton, is absent. Other minor changes in the H NMR
(35) Hicks, F. A.; Brookhart, M. Org. Lett. 2000, 2, 219.
spectrum of 5b relative to 4b are observed and noted

Neutral Nickel(II) Catalyst
Organometallics, Vol. 22, No. 2, 2003 253
Ta ble 1. Eth ylen e P olym er iza tion s Ca ta lyzed by 5a ,bc
loading
(µmol)
time
(min)
temp
(°C)
pressure
(psig)
yield PE
(g)
branches/
1000 Cb
entry
catalyst
TONa
Mn
MWD
1
2
3
4
5
6
7
8
5a
5a
5b
5b
5b
5b
5b
5b
5b
5b
5b
5b
10.0
10.0
10.6
10.6
10.6
10.6
12.0
10.6
10.6
10.6
10.6
5.3
30
30
30
30
30
30
30
30
30
10
60
60
30
30
80
80
40
60
80
100
80
80
80
80
80
80
80
80
200
400
200
200
200
200
50
100
400
200
200
200
200
200
8000
3900
5600
2.24
1.08
1.66
2.17
14.00
3.18
4.44
6.02
7.28
7.02
18.54
9.40
5.31
1.01
25k
23k
171k
142k
99k
31k
37k
54k
142k
62k
3.5
3.2
1.5
2.1
1.9
2.4
2.2
2.5
2.2
2.7
1.6
1.9
1.8
2.4
51
43
17
34
43
66
72
70
27
46
44
34
36
43
7300
47 200
10 700
13 200
19 200
24 500
23 700
62 500
63 300
17 900
3400
9
10
11
12
13
14
90k
112k
80k
5b + 5PPh3
5b + 50PPh3
10.6
10.6
19k
a
b
In units of mol ethylene/mol cat. Branching numbers were determined by 1H NMR spectroscopy. c All polymerizations run in 200
mL of toluene with a maximum exotherm of 2 °C.
Sch em e 4
in the Experimental Section. Repeated attempts to grow
an X-ray quality crystal of 5b were unsuccessful;
however, on the basis of closely related structures of 2
and 3, it is very likely that the bulky triphenylphosphine
ligand is trans to the better donating and more bulky
N-aryl ligand.27,29
Eth ylen e P olym er iza tion . The anilinoperinaph-
thenone nickel complexes 5a ,b are active ethylene
polymerization catalysts. When toluene solutions of
number average molecular weight of the polymer in-
creased from 37 000 to 142 000 and the branching
decreased from 72 to 27 branches per 1000 carbon atoms
(Table 1, entries 5, 7-9). With the exception of the low-
temperature 40 °C run (entry 3) all of the Mw/Mn values
are ca. 2.0, which implies that the Mn values are at the
chain transfer limited maximum.
Catalyst lifetime was also investigated. Polymeriza-
tions at 80 °C and 200 psig were run for 10, 30, and 60
min (Table 1, entries 5, 10, 11). From 10 to 30 min the
turnover number doubled from 23 700 to 47 200, while
from 30 to 60 min the turnover number increased from
47 200 to 62 500, a 32% increase. These data indicate
that the catalyst half-life is ca. 20-30 min. The lifetimes
of these catalysts are slightly longer that the lifetimes
reported for catalyst 3.29 Entries 11 and 12 indicate that
cutting the catalyst loading in half has little effect on
the overall polymerization activity. This result implies
that mass transport issues do not compromise catalyst
turnover number at the current catalyst loadings even
though the polymerization solution becomes viscous as
polyethylene is produced.
Polymerizations with 5b were also run in the presence
of 5 and 50 equiv of triphenylphosphine. Unlike catalyst
3, a significant decrease in activity (∼65% reduction) is
observed with just 5 equiv of added PPh3 (entry 13),
while 50 equiv of added PPh3 severely inhibits ethylene
polymerization (entry 14, ∼93% reduction). Polymeri-
zation with 5b is not, however, shut down completely,
as is reported for catalysts 2a ,b.27,28 Anilinotropone
catalyst 3 is not inhibited by 5 equiv of added triphen-
ylphosphine, but 50 equiv causes the activity to drop to
one-quarter of the original value.36
complexes 5a ,b are exposed to ethylene under a variety
of conditions, polyethylenes of various molecular weights
and branching densities are produced. Results are
summarized in Table 1. Several trends are evident.
First, 5b is significantly more reactive than 5a with
turnover numbers of 47 000 and 8000, respectively,
under identical reaction conditions (200 psig ethylene,
80 °C, entries 1 and 5). The added steric bulk of the
isopropyl-substituted aryl ring greatly enhances catalyst
activity. In view of the high reactivity of 5b, the effects
of changes in ethylene pressure, reaction temperature,
and reaction time as well as polymerization in the
presence of PPh3 were investigated using this catalyst.
The reactivity of 5b was at a maximum at 80 °C and
200 psig ethylene. Catalyst turnover numbers ranged
from 5600 at 40 °C and 200 psig ethylene (entry 3) to
63 300 at 80 °C and 200 psig ethylene (entry 12).
Catalyst turnover number increased from 50 to 200 psig
ethylene, but doubling the ethylene pressure to 400 psig
resulted in a decrease in turnover number to 24 500
(entry 9). As temperature was increased from 40 °C to
100 °C, with pressure held constant at 200 psig ethyl-
ene, the number average molecular weight of the
polymer decreased from 171 000 to 31 000 and the
branching number increased from 17 to 66 branches per
1000 carbon atoms (Table 1, entries 3-6). A 13C NMR
spectrum of the polymer of entry 5, run using a protocol
reported by Cotts,12 indicated that methyl and ethyl
branches are present in an approximate ratio of 6.7:1.
Propyl branches were observed, but the signal was too
weak to integrate accurately. Analysis of the more
highly branched polymer of entry 7 revealed methyl,
ethyl, and propyl branches in an approximate ratio of
14:2:1. The methyl resonance corresponding to C4 and
longer branches integrated to approximately the same
intensity as the methyl resonance for the propyl branch.
As pressure was increased incrementally from 50 to 400
psig, with temperature held constant at 80 °C, the
Catalysts 3 and 5b have very similar activities under
identical reaction conditions (TON ) 62 100 and 62 500,
respectively). The branching numbers of the polymers
(36) Manuscript in preparation.

254 Organometallics, Vol. 22, No. 2, 2003
J enkins and Brookhart
Sch em e 5
produced with 3 follow the same temperature and
pressure trends as 5b; however, the absolute number
of branches is approximately 20 branches per 1000
carbons more for 3.29 These numbers compare favorably
to 2a and 2b, which under similar conditions have
turnover numbers of 3400 and 40 700, respectively.
Catalyst 2b, however, has a very long lifetime.27,28
The variable-temperature and -pressure experiments
suggest the branching mechanism depicted in Scheme
4, which mirrors the mechanism suggested for branch-
ing in the diimine catalyst system, 1.3 A branch in the
polymer is introduced first by â-hydride elimination of
a growing polymer chain followed by olefin rotation and
reinsertion with opposite regiochemistry. This process
may occur more than once prior to ethylene insertion
and may therefore lead to methyl as well as higher
branches. As ethylene pressure is increased, monomer
coordination and insertion become more favorable, and
therefore the unimolecular branching pathway is less
favored. Similarly, as temperature is increased, the
unimolecular branching pathway is favored over the
bimolecular ethylene coordination and insertion reac-
tion, and more branching is observed.
The fact that the molecular weight significantly
increases with ethylene pressure (e.g., Mn ) 37k, 50 psi,
80 °C; 54k, 100 psi, 80 °C; entries 7 and 8) suggests that
chain transfer to monomer is not the major chain
transfer mechanism. The alkyl olefin intermediate in
the polymerization may partition as shown in eq 3.
Pathway (a) represents insertion and propagation, while
pathway (b) represents chain transfer to monomer.37,38
If chain transfer to monomer is the sole chain transfer
mechanism, then the ratio of kct/kp should be indepen-
dent of ethylene concentration, and thus the chain
transfer limited molecular weight should be indepen-
dent of ethylene concentration. The observed depen-
dence of Mn on ethylene pressure implies a chain
transfer process that is not significantly dependent on
ethylene concentration. This is best rationalized by a
conventional â-hydride elimination mechanism shown
in eq 4. Given the qualitative Mn values and the
substantial error in these determinations, some chain
transfer may occur via the chain transfer to monomer
pathway.
Ca ta lyst Deca y. The fate of the catalyst upon
deactivation was investigated. Upon completion of a
standard polymerization using 5b, polymer was col-
lected by precipitation in methanol. The filtrate was
1
concentrated and analyzed by H NMR spectroscopy to
determine the contents of the residue. The sole species
detected was the free ligand, 4b. This observation
contrasts with the behavior of 2a , 3, and SHOP-type
catalysts, where Ni(II) bis-ligand complexes are ob-
served as the decay products.27-29 Equations 5 and 6
(Scheme 6) illustrate the contrasting behaviors of 3 and
5b.
Bis-ligand complex formation with catalysts 3 and 5b
was investigated by 1H NMR spectroscopy. For each
experiment, an NMR tube was charged with the nickel
complex and its corresponding ligand in equimolar
ratios (10.6 mM in C6D6 in each case). In each case
formation of the bis-ligand complex was observed via
1H NMR spectroscopy at 80 °C (Scheme 7). The forma-
tion of the bis-ligand complex of anilinotropone, 6, was
significantly faster (t1/2 < 1 h) than the formation of the
bis-ligand complex based on anilinoperinaphthenone
(t1/2 ) 26 h). The weaker acidity of the anilinoperinaph-
thenone N-H proton may help to explain the slow rate
of bis-ligand complex formation. Steric effects may also
play a role in the overall rate of bis-ligand complex
formation.
Formation of the bis-ligand complex of 2-anilino-
tropone as the decomposition product of the bulk po-
lymerization is best explained by reductive elimination
from a nickel-hydride intermediate to form free ligand
followed by attack of the free ligand on a Ni(II) species
present in the catalytic cycle. The slow formation of the
bis-ligand complex from 2-anilinoperinaphthenone and
5b suggests that attack of free ligand on a propagating
nickel species is too slow to be competitive with ligand
reductive elimination. Therefore only 2-anilinoperi-
naphthenone is observed as the decomposition product
of 5b after polymerization.
Con clu sion s. Active neutral nickel(II) ethylene po-
lymerization catalysts based on anilinoperinaphthenone
ligands are reported. These catalysts have an activity
that is similar to the previously reported anilinotropone-
based neutral nickel(II) ethylene polymerization cata-
lysts. The similarity in overall activity suggests that the
lack of delocalization of electron density onto the oxygen
atom has little effect on catalyst performance. The
(37) Deng, L.; Margl, P.; Ziegler, T. J . Am. Chem. Soc. 1997, 119,
1094.
(38) Deng, L.; Woo, T. K.; Cavallo, L.; Margl, P. M.; Ziegler, T. J .
Am. Chem. Soc. 1997, 119, 6177.

Neutral Nickel(II) Catalyst
Organometallics, Vol. 22, No. 2, 2003 255
Sch em e 6
2] × 1000 ) branches per 1000 carbons. CH3, CH2, and CH
refer to the integration obtained for the methyl, methylene,
and methine resonances, respectively. 13C NMR spectra of
polyethylenes were recorded in a 0.05 M Cr(acac)3 solution in
bromobenzene-d5 with 15 wt % polymer. Peaks were assigned
as described by Cotts.12 High-temperature gel permeation
chromatography (GPC) was performed by DuPont (Wilming-
ton, DE) in 1,2,4-trichlorobenzene at 135 °C using a Waters
HPLC 150C equipped with Shodex columns. A calibration
curve was established with polystyrene standards, and uni-
versal calibration was applied using Mark-Houwink constants
for polyethylene (κ), 4.34 × 10-4; (R) 0.724. Elemental analyses
were performed by Atlantic Microlabs Inc. of Norcross, GA.
Gen er a l P r oced u r e for th e Con ver sion of 2-Br om o-
per in aph th en on es to 2-An ilin oper in aph th en on es. A flame-
dried Schlenk tube was charged with 2-bromoperinaphthenone
(200 mg, 0.77 mmol), NaOtBu (105 mg, 1.08 mmol), Pd2dba3
(36 mg, 0.04 mmol), and 2-dicyclohexylphosphine-1,1′-biphenyl
(26 mg, 0.08 mmol) under argon. Toluene (3 mL) and 2,6-
dimethylaniline (115 µL, 0.93 mmol, 4a ) or 2,6-diisopropyl-
aniline (175 µL, 0.93 mmol, 4b) were added, and the reaction
mixture was heated to 80 °C and stirred for 18 h. The reaction
mixture was cooled to room temperature, diluted with CH2-
Cl2, and filtered through Celite. The filtrate was concentrated
and purified by flash chromatography on silica gel using 15%
ethyl acetate in hexanes as the eluent.
Sch em e 7
polymer branching mechanism is likely similar to the
one reported for the diimine system 1, with branching
controlled by the relative rates of Ni migration along
the chain and ethylene insertion. A significant correla-
tion between ethylene pressure and polymer molecular
weight suggests that chain transfer occurs primarily via
a â-hydride elimination pathway with little contribution
from chain transfer to monomer. The catalyst decom-
poses to free ligand, suggesting that reductive elimina-
tion of free ligand is a key step in catalyst deactivation.
A more detailed mechanistic study of the catalytic
propagation cycle and the deactivation pathway is
underway.
Exp er im en ta l Section
Gen er a l Con sid er a tion s. Argon was purified by passage
through columns of BASF R3-11 catalyst (Chemalog) and 4 Å
molecular sieves. Toluene and pentane were deoxygenated and
dried over a column of activated alumina. THF was distilled
under a nitrogen atmosphere from sodium benzophenone ketyl
prior to use. Polymer grade ethylene was used as received from
Matheson. 2-Bromoperinaphthenone,39 (PPh3)2Ni(Ph)(Cl),40
and complexes 2a ,b27 and 329 were prepared according to
literature procedures. Triphenylphosphine was purchased from
Aldrich and used without further purification.
2-(2,6-Dim eth yla n ilin o)p er in a p h th en on e. Yield: 150
mg, 65%. H NMR (400 MHz, CDCl3): δ 8.8 (d, 1H, J ) 7.4);
1
8.2 (d, 1H, J ) 7.9 Hz); 7.8 (m, 2H); 7.5 (t, 1H, J ) 7.2 Hz); 7.4
(m, 1H); 7.2 (bs, 3H); 6.6 (bs, 1H); 6.1 (s, 1H); 2.3 (s, 6H). 13C
NMR (100 MHz, CDCl3): δ 180.8, 140.0, 137.2, 136.7, 136.3,
132.3, 131.0, 130.2, 129.0, 128.6, 128.3, 127.8, 127.6, 127.0,
126.9, 124.2, 107.8, 18.7. Anal. Calcd for C21H17NO: C, 84.25;
H, 5.72; N, 4.68. Found: C, 83.41; H, 6.02; N, 4.30.
2-(2,6-Diisop r op yla n ilin o)p er in a p h th en on e. Yield: 160
mg, 58%. 1H NMR (400 MHz, CDCl3): δ 8.8 (d, 1H, J ) 8 Hz);
8.2 (d, 1H, J ) 8 Hz); 7.8 (m, 2H), 7.5 (t, 1H, J ) 4 Hz); 7.4
(m, 2H); 7.3 (m, 2H); 6.6 (bs, 1H); 6.1 (s, 1H); 3.2 (hept, 2H,
J ) 6.8 Hz); 1.2 (d, 12 H, J ) 6.8 Hz). 13C NMR (100 MHz,
CDCl3): δ 180.6, 147.8, 142.0, 136.3, 134.3, 132.4, 131.1, 130.2,
128.5, 128.1, 128.0, 127.7, 127.6, 127.0, 124.2, 207.8, 28.8, 25.5,
23.8. Anal. Calcd for C25H25NO: C, 84.47; H, 7.09; N, 3.94.
Found: C, 83.97; H, 7.21; N, 3.73.
Gen er a l P r oced u r e for th e Con ver sion of (N,O)Ni(P h )-
(P P h 3). A flame-dried Schlenk tube was charged with the
appropriate anilinoperinaphthenone (150 mg, 0.50 mmol 4a ;
200 mg, 0.56 mmol 4b), and sodium hydride (40 mg, 1.7 mmol
for 4a ; 75 mg, 3.1 mmol for 4b) under argon. THF (25 mL)
was added, and the reaction mixture was stirred for 18 h. A
color change from dark red to bright green was observed on
Nuclear magnetic resonance (NMR) spectra were recorded
on a Bruker Avance 400 NMR spectrometer. Splitting patterns
are designated as follows: s, singlet; bs, broad singlet; d,
doublet; dd, doublet of doublets; t, triplet; sept, septet; m,
1
multiplet. All H NMR spectra are reported in δ units, parts
per million (ppm) downfield from tetramethylsilane. All 13C
NMR spectra are reported in ppm relative to TMS using CDCl3
as an internal standard. 31P NMR are reported in ppm relative
to an external 85% H3PO4 standard. 1H NMR spectra of
polyethylenes were recorded in C6D5Br at 120 °C. The formula
used to calculate branching was (CH3/3)/[(CH + CH2 + CH3)/
(39) Fieser, L. F.; Newton, L. W. J . Chem. Soc. 1942, 64, 917.
(40) Hiodai, M.; Kashiwaga, T.; Ikeuchi, T.; Uchida, Y. J . Organomet.
Chem. 1971, 30, 279.

256 Organometallics, Vol. 22, No. 2, 2003
J enkins and Brookhart
both cases. Solid (PPh3)2Ni(Ph)(Cl) (348 mg, 0.50 mmol for 4a ,
391 mg, 0.56 mmol for 4b) was added under positive argon
flow, and the reaction mixture was stirred for 1 h. The reaction
mixture was filtered through Celite, and the solvent was
removed in vacuo. The residue was recrystallized from toluene/
pentane and isolated by cannula filtration.
with ethylene (3 × 100 psig) with stirring. In a glovebox a
sidearm flask was charged with the catalyst. The flask was
removed from the glovebox and placed on a vacuum line under
Ar. The catalyst was dissolved in toluene (15 mL) and cannula
transferred into the vented autoclave with the stirring motor
off. The autoclave was sealed and pressurized to the desired
level, and the stirring motor was reengaged. Temperature
control was maintained by internal cooling coils with exo-
therms less than 2 °C in every case. After the prescribed
reaction time, the stirring motor was stopped, the reactor was
vented, and the polymer was isolated via precipitation from
methanol and dried in a vacuum oven. This procedure was
employed with modifications in time, temperature, and eth-
ylene pressure. Results are summarized in Table 1.
Com p lex 5a . Yield: 225 mg, 65%. 1H NMR (400 MHz, CD2-
Cl2): δ 8.2 (d, 1H, J ) 7.4 Hz); 7.8 (d, 1H, J ) 7.4 Hz); 7.6-
7.5 (m, 8H); 7.4 (m, 3H); 7.3 (m, 8H); 6.8 (d, 2H, J ) 6.9 Hz);
6.7 (d, 2H, J ) 7.4 Hz); 6.6 (m, 1H); 6.3 (t, 1H, J ) 7.0 Hz); 6.2
(t, 2H, J ) 7.5 Hz); 5.7 (s, 1H); 2.3 (s, 6H). 13C NMR (100 MHz,
CD2Cl2): δ 190.0, 189.9, 153.5, 149.2, 148.2, 137.9, 136.9, 136.8,
134.9, 134.6, 134.5, 13.2, 130.1, 128.4, 128.3, 128.2, 127.9,
127.4, 126.6, 125.7, 125.0, 124.9, 123.2, 121.2, 105.4, 18.7. 31
NMR (162 MHz, CD2Cl2): δ 29.7 (s). Anal. Calcd for C45H36
P
-
NMR Sca le Bis-liga n d Com p lex F or m a tion Rea ction s.
A J -Young tube was charged with 7.4 µmol of both the
appropriate nickel complex and corresponding ligand. Benzene-
d6 (700 µL) was added, and bis-ligand formation was observed
NiNPO: C, 77.61; H, 5.21; N, 2.01. Found: C, 77.60; H, 5.17;
N, 1.98.
Com p lex 5b. Yield: 290 mg, 70%. 1H NMR (400 MHz, CD2-
Cl2): δ 8.2 (d, 1H, J ) 8 Hz); 7.8 (d, 1H, J ) 8 Hz); 7.5 (m,
7H); 7.4 (m, 3H); 7.3-7.2 (m, 9H); 6.9 (m, 3H); 6.8 (d, 2H, J )
7 Hz); 6.3 (t, 1H, J ) 6.8 Hz); 6.2 (t, 2H, J ) 6.4 Hz); 5.7 (s,
1H); 3.9 (hept, 2H, J ) 6.8 Hz); 1.1 (d, 6H, J ) 6.8 Hz); 1.0 (d,
6H, J ) 7.2 Hz). 13C NMR (100 MHz, CD2Cl2): δ 189.6, 155.6,
148.2, 147.7, 145.9, 145.5, 137.8, 134.5, 131.9, 131.8, 131.7,
131.4, 130.2, 128.4, 128.5, 128.3, 127.8, 126.6, 125.8, 125.2,
125.2, 124.1, 122.8, 121.2, 108.7, 28.5, 26.2, 23.9. 31P NMR (162
MHz, CD2Cl2): δ 29.3 (s). Anal. Calcd for C49H44NiNPO: C,
78.20; H, 5.89; N, 1.86. Found: C, 77.77; H, 6.25; N, 1.85.
Gen er a l P r oced u r e for High -P r essu r e Eth ylen e P o-
lym er iza tion . A 1000 mL Parr autoclave was heated under
vacuum to 125 °C and then was cooled to the desired reaction
temperature and backfilled with ethylene (3 × 100 psig). The
autoclave was charged with toluene (185 mL) and degassed
1
by H NMR spectroscopy at 80 °C. Anilinotropone: t1/2 < 1 h.
Anilinoperinaphthenone: t1/2 ) 26 h.
An ilin op er in a p h th en on e Bis-liga n d Com p lex. 1H NMR
(400 MHz, C6D6): δ 7.8 (d, 1H, J ) 8 Hz), 7.7 (m, 1H), 7.5 (d,
2H, J ) 8 Hz), 7.0 (t, 1H, J ) 8 Hz), 6.0 (d, 1H, J ) 8 Hz), 5.6
(d, 1H, J ) 7 Hz), 5.0 (sept, 2H, J ) 7 Hz), 2.0 (d, 6H, J ) 7
Hz), 1.55 (d, 6H, J ) 7 Hz).
Ack n ow led gm en t. We thank the National Science
Foundation (CHE0107810) and DuPont for support of
this work. J .C.J . thanks the University of North Caro-
lina for a Venable Fellowship.
OM020648F