Synthesis of functional polyolefins using cationic bisphosphine monoxide-palladium complexes

Article abstract of DOI:10.1021/ja303507t

The copolymerization of ethylene with polar vinyl monomers, such as vinyl acetate, acrylonitrile, vinyl ethers, and allyl monomers, was accomplished using cationic palladium complexes ligated by a bisphosphine monoxide (BPMO). The copolymers formed by these catalysts have highly linear microstructures and a random distribution of polar functional groups throughout the polymer chain. Our data demonstrate that cationic palladium complexes can exhibit good activity for polymerizations of polar monomers, in contrast to cationic α-diimine palladium complexes (Brookhart-type) that are not applicable to industrially relevant polar monomers beyond acrylates. Additionally, the studies reported here point out that phosphine-sulfonate ligated palladium complexes are no longer the singular family of catalysts that can promote the reaction of ethylene with many polar vinyl monomers to form linear functional polyolefins.

Full text of DOI:10.1021/ja303507t

Communication
pubs.acs.org/JACS
Synthesis of Functional Polyolefins Using Cationic Bisphosphine
Monoxide−Palladium Complexes
Brad P. Carrow and Kyoko Nozaki*
Department of Chemistry and Biotechnology, Graduate School of Engineering, The University of Tokyo, 7-3-1 Hongo, Bunkyo-ku,
Tokyo 113-8656, Japan
S
* Supporting Information
catalyze coordination−insertion polymerization of olefins with
ABSTRACT: The copolymerization of ethylene with
polar vinyl monomers, such as vinyl acetate, acrylonitrile,
vinyl ethers, and allyl monomers, was accomplished using
cationic palladium complexes ligated by a bisphosphine
monoxide (BPMO). The copolymers formed by these
catalysts have highly linear microstructures and a random
distribution of polar functional groups throughout the
polymer chain. Our data demonstrate that cationic
palladium complexes can exhibit good activity for
polymerizations of polar monomers, in contrast to cationic
α-diimine palladium complexes (Brookhart-type) that are
not applicable to industrially relevant polar monomers
beyond acrylates. Additionally, the studies reported here
point out that phosphine-sulfonate ligated palladium
complexes are no longer the singular family of catalysts
that can promote the reaction of ethylene with many polar
vinyl monomers to form linear functional polyolefins.
polar vinyl monomers have to date been those ligated by α-
diimines,4 or by phosphine-sulfonates.5 While Pd and Ni
complexes ligated by α-diimines catalyze the formation of
highly branched polymers,4b linear polymer microstructures are
obtained with phosphine-sulfonate-ligated Pd and Ni catalysts.6
Of these two important classes of catalysts, those ligated by
phosphine-sulfonates exhibit much higher activity for copoly-
merizations with challenging polar vinyl monomers such as
vinyl acetate,7 acrylonitrile,8 vinyl halides,9 and vinyl ethers10
compared to catalysts ligated by α-diimines.
An important structural feature of catalysts containing
phosphine-sulfonates is the presence of one strong and one
weak σ-donor ligand. We hypothesized that palladium
complexes containing a bidentate ligand featuring a non-
symmetric strong/weak σ-donor framework other than the
combination of a phosphine and sulfonate anion could also
promote the formation of highly linear, random copolymers by
coordination−insertion polymerization, even though such
activity across a range of polar vinyl monomers has to date
been restricted exclusively within the phosphine-sulfonate
family of catalysts.11 In this study we describe the synthesis
of a series of cationic palladium complexes ligated by
bisphosphine monoxides (BPMOs) and the successful
application of these complexes as catalysts for the polymer-
ization of ethylene and a number of challenging polar vinyl
monomers.12 Our data highlight a new class of transition metal
catalyst that effects the formation of highly linear, random
copolymers from ethylene and polar vinyl monomers by
coordination−insertion polymerization.
The synthesis of BPMO complexes used in this study are
summarized in Scheme 2. An admixture of free BPMO and
(cod)PdMeCl (cod = 1,5-cyclooctadiene) formed an inter-
mediate (BPMO)PdMeCl complex, which upon treatment with
silver(I) salt and 2,6-lutidine afforded complexes 2−5 in good
isolated yields (49−72%) as air- and moisture-stable solids. We
found that homopolymerization of ethylene (3 MPa) occurred
in the presence of 2−5 (6.0 μmol) in toluene (15 mL) at 80 °C
(Table 1). Polymerization activity increased when the
substituents on the phosphine were isopropyl rather than
phenyl groups. Additionally, the molecular weight of the
obtained polyethylene was higher when the substituents on the
phosphine oxide moiety of the BPMO ligand were tert-butyl
rather than phenyl groups. Among complexes 2−5, the highest
espite their ubiquity, polyolefins such as polyethylene and
D
polypropylene are not appropriate for all applications.
Polyolefins are inherently nonpolar, which engenders certain
material properties such as limited adhesion, dye retention,
printability, and compatibility that can restrict their efficacy.
Incorporation of polar functional groups into polyolefins even
in small amounts, however, can significantly enhance such
properties in the resulting 'functional polyolefins'.1 Thus, the
development of methods for the controlled synthesis of
functional polyolefins from industrially relevant monomers
holds the potential to expand the range of applications available
to this indispensible class of materials.
Transition-metal-catalyzed coordination−insertion polymer-
ization of olefins and polar vinyl monomers has recently
emerged as a powerful method for the synthesis of functional
polyolefins with defined polymer architectures, molecular
weight distributions, and comonomer incorporation (Scheme
1).2,3 The most successful late transition metal complexes that
Scheme 1
Received: April 12, 2012
Published: May 16, 2012
© 2012 American Chemical Society
8802
dx.doi.org/10.1021/ja303507t | J. Am. Chem. Soc. 2012, 134, 8802−8805

Journal of the American Chemical Society
Communication
activity (entry 4) was observed when the BPMO substituents
were isopropyl groups on the phosphine and tert-butyl groups
on the phosphine oxide. The polyethylene formed by these
cationic BPMO complexes was confirmed by quantitative 13C
NMR spectroscopic analysis to be highly linear. For example,
only ca. 3 methyl branches per 1000 carbon atoms were
observed in the polyethylene formed by catalyst 5 (entry 7),
and no higher alkyl branching was detected.
Scheme 2
We also prepared stable, coordinatively saturated BPMO−
palladacycle precatalysts that obfuscate the additional ancillary
ligand (e.g., pyridines) often employed for the synthesis of
stable, single-site polymerization precatalysts. The removal of
superfluous ancillary ligands proved beneficial for copolymer-
izations using BPMO−Pd catalysts (vide infra).13,14 Thus, two
new air- and moisture-stable BPMO complexes 7 and 8 were
isolated in 73% and 96% yield, respectively, by addition of
BPMO to the μ-chloride palladium dimer 615 and subsequent
Table 1. Homopolymerization of Ethylene in the Presence of
Cationic BPMO−Palladium Complexes
a
abstraction of chloride by a Ag(I) salt (Scheme 2, bottom).16
7
catalyst
(μmol)
time
(h)
yield
(g)
activity
Mw/
Mn
exhibited lower activity (entries 5 and 8) than 5 because of low
solubility in toluene. This limitation could be overcome by
changing the counteranion from SbF6 to the weakly
coordinating tetrakis[3,5-bis(trifluoromethyl)phenyl]borate
b
entry
(kg mol−1 h−1
)
Mn (103)
1
2
3
4
2 (6.0)
3 (6.0)
4 (6.0)
5 (6.0)
7 (6.0)
8 (6.0)
5 (0.75)
7 (0.75)
8 (0.75)
3
3
1
1
1
1
1
1
1
1.14
0.66
0.79
2.01
1.05
2.10
1.41
0.94
2.11
63
36
0.8 (1.8)
16 (38)
0.9 (1.9)
39 (91)
12 (27)
39 (92)
15 (34)
25 (58)
29 (69)
1.8
2.5
1.8
2.3
3.6
2.6
2.6
1.9
2.1
(BArF ) anion (entries 6 and 9). Using 8, an o-acetanilido
130
4
palladium BPMO complex having BArF as the counteranion,
340
4
c
5
180
linear polyethylene was formed with an activity of 2800 kg
mol−1 h−1, which represents one of the more active Pd catalysts
for ethylene polymerization reported to date.17
6
350
d
7
1900
1300
2800
d
8
d
The BPMO−Pd complexes 5 and 8 were also successfully
applied to the copolymerization of ethylene and polar vinyl
monomers (Table 2). Coordination−insertion polymerizations
involving vinyl acetate (1a) are rare;7a,18 yet the reaction of
ethylene and vinyl acetate proceeded in the presence of either
cationic BPMO complex 5 or 8 (entries 1 and 2). Quantitative
13C NMR spectroscopic analysis of the resulting polymers was
consistent with vinyl acetate incorporation into the main chain
as well as at the initiating and terminating chain ends, based on
comparison to previously reported spectroscopic data for
9
a
Conditions: toluene (15 mL), ethylene (3 MPa), and palladium
catalyst (6.0−0.75 μmol) were stirred in a 50 mL stainless steel
b
autoclave at 80 °C. Number-average molecular weight was measured
by size-exclusion chromatography using polystyrene as an internal
standard and corrected by universal calibration. Molecular weights
c
before universal calibration are shown in parentheses. A mixture of 1
d
mL of CH2Cl2 and 14 mL of toluene was used. 100 °C.
Table 2. Copolymerization of Ethylene and Polar Vinyl Monomers in the Presence of Cationic BPMO−Palladium
ab
,
Complexes
d
d
catalyst
(μmol)
monomer
(mL)
solvent
(mL)
temp
(°C)
time
(h)
yield
(g)
activity
Mw/ incorp.
Me br.
c
entry
monomer
(kg mol−1 h−1
)
Mn (103)
Mn
(%)
(/103 C)
1
2
3
5 (20)
8 (10)
5 (10)
1a (FG = OAc)
12
12
3
3
80
80
80
15
16
12
0.21
0.18
0.18
0.72
1.1
1.5 (3.4)
1.3 (3.0)
7.5 (17)
2.5
2.5
2.7
1.3
1.4
1.0
1.5
1.7
1.0
1a
3
1b (FG =
CH2OAc)
12
1.4
4
5
6
8 (10)
5 (20)
5 (20)
1b
3
12
5
80
80
80
12
89
20
0.94
0.09
0.12
7.6
15 (35)
2.7 (6.0)
5.8 (13)
2.2
4.2
1.9
1.2
0.7
−
1.0
e
1c (FG = Cl)
2.4
3
0.05
0.31
0
1d (FG =
CH2Cl)
12
1.1
7
8 (10)
5 (10)
8 (6)
1d
3
12
80
20
86
72
21
20
18
0.18
0.50
0.30
0.28
0.23
0
0.93
0.58
0.69
0.66
1.2
8.6 (20)
1.4 (3.5)
1.6 (3.5)
9.3 (21)
8.0 (19)
−
2.9
2.4
2.7
1.9
2.4
−
0.7
2.1
2.5
2.0
4.1
−
0.6
1.8
0.1
1.4
0.5
−
8
1e (FG = CN)
2.5
2.5
5
2.5
2.5
10
100
100
80
9
1e
10
11
12
5 (20)
8 (10)
5 (10)
1f (FG = OBu)
1f
5
10
80
1g (FG =
CO2Me)
2.5
2.5
80
−
13
8 (6)
1g
2.5
2.5
80
12
0
−
−
−
−
−
a
Conditions: catalyst (6−20 μmol), toluene, ethylene (3 MPa), and comonomer were stirred in a 50 mL stainless steel autoclave at the indicated
b
temperature. See Supporting Information for ratios of main chain versus chain end incorporation and turnover numbers for each monomer.
c
Number-average molecular weight was measured by size-exclusion chromatography using polystyrene as an internal standard and corrected by
d
universal calibration. Molecular weights before universal calibration are shown in parentheses. Determined by quantitative 13C NMR analysis.
e
1
Determined by H NMR analysis (CDCl2CDCl2, 120 °C).
8803
dx.doi.org/10.1021/ja303507t | J. Am. Chem. Soc. 2012, 134, 8802−8805

Journal of the American Chemical Society
Communication
ethylene/vinyl acetate copolymers.7a The activity of 8
compared to 5 was higher, and this activity is higher than the
best case reported using catalysts ligated by phosphine-
sulfonates, while incorporation ratios of vinyl acetate were
similar.
Copolymerization of the related monomer allyl acetate (1b)
with ethylene was also successful using either BPMO complex 5
or 8 as the catalyst (entries 3 and 4). Similar to the relative
activity observed for ethylene/vinyl acetate copolymerization, 8
proved to be more active than 5 for ethylene/allyl acetate
copolymerization. The polymer molecular weight (Mn)
obtained from the reaction using 8 as the catalyst (entry 4)
was higher by a factor of ca. 2 compared to that obtained using
a phosphine-sulfonate-ligated catalyst under otherwise identical
reaction conditions.19
complexes for polymerization of ethylene and acrylonitrile, but
the microstructure of polymers formed by BPMO-ligated
catalysts is also different from those formed by phosphine-
sulfonate-ligated catalysts.
The copolymerization of ethylene and vinyl ethers has thus
far been difficult with cationic α-diimine Pd catalysts unless the
O-substituent of the vinyl ether is a bulky silyl group.10a,b
Concomitant hompolymerization of the vinyl ether in the
presence of electrophilic, cationic α-diimine Pd catalysts is
particularly problematic. In contrast, we found that cationic
BPMO complex 5 or 8 did in fact promote the copolymeriza-
tion of ethylene and butyl vinyl ether (1f) with incorporation
ratios of 2.0−4.1% (entries 10 and 11). Analysis of the polymer
microstructure by 13C NMR spectroscopy indicates that in-
chain incorporation of butyl vinyl ether occurred along with
incorporation at the initiating chain end. This result represents
only the second example of the copolymerization of simple
alkyl vinyl ethers and ethylene by a coordination−insertion
pathway.10c
Finally, the reaction of ethylene and methyl acrylate (1g) was
examined using cationic BPMO complexes as catalysts. In the
presence of either complex 5 or 8, no polymer product was
isolated after 12−18 h (entries 12 and 13). Although many late
transition metal complexes catalyze the copolymerization of
ethylene and methyl acrylate,2 very few can also catalyze the
copolymerization of ethylene and other polar monomers such
as vinyl acetate, acrylonitrile, and vinyl ethers. In the case of
cationic BPMO−Pd complexes such as 5 or 8, the reactivity
profile is exactly reversed. While the origin of the inability of 5
or 8 to catalyze the copolymerization of ethylene and methyl
acrylate is currently unclear, these data again highlight some of
the unique characteristics of cationic BPMO polymerization
catalysts as compared to α-diimine and phosphine-sulfonate
based systems.
In summary, we have identified a new family of Pd complexes
ligated by bisphosphine monoxides (BPMOs) that act as
catalysts for the polymerization of ethylene and polar vinyl
monomers. The polar monomers that are applicable to these
conditions include some of the historically most challenging
polar vinyl monomers for polymerization by a coordination−
insertion mechanism. These catalysts lead to copolymers that
are highly linear and have a random distribution of the polar
monomer throughout the polymer chain. The studies described
in this report also provide several perspectives for future
development of catalysts for the copolymerization of ethylene
and polar vinyl monomers. First, cationic Pd complexes can in
fact function as catalysts for coordination−insertion polymer-
ization of ethylene and industrially relevant polar vinyl
monomers other than acrylates, even though many prior
studies of cationic α-diimine Pd complexes suggest otherwise.
Our data also demonstrate that combinations of a strong and
weak σ-donor motif in a bidentate ligand other than the
combination of a tertiary phosphine and a sulfonate anion can
lead to Pd catalysts that form highly linear, random copolymers
by a coordination−insertion mechanism. Future studies will
focus on exploring in detail how the BPMO ligand influences
the catalyst activity and resulting polymer properties, as well as
the identification of new families of bidentate ligands with a
weak/strong σ-donor motif that lead to transition metal
catalysts for coordination−insertion polymerization with polar
vinyl monomers.
We next explored reactions of halogenated monomers, which
are some of the most challenging substrates for coordination−
insertion polymerizations due to catalyst poisoning by rapid β-
halogen elimination following migratory insertion. Coordina-
tion−insertion polymerization of ethylene and vinyl chloride
(1c), an important halogenated monomer in industry, has not
yet been achieved.9a While we did isolate a polymer product
from the reaction of ethylene and vinyl chloride in the presence
of 5 (entry 5), the absence of a resonance corresponding to a
1
chloro methine moiety (−CHCl−) in the H NMR spectrum
of the product indicates negligible incorporation of 1c. The low
activity and low polymer molecular weight are consistent with
previous reports of rapid chain termination and simultaneous
catalyst deactivation by β-halogen elimination following
insertion of 1c.9b,c,20 In contrast, copolymerization of allyl
chloride (1d) and ethylene in the presence of 5 or 8 was
successful (entries 6 and 7). Incorporation of halogenated 1d
into the main chain was confirmed by 13C NMR spectroscopy.
The incorporation ratios were similar to that reported for
phosphine-sulfonate-based catalysts, but polymer molecular
weight (Mn) was again improved by a factor of ca. 2 under
otherwise identical reaction conditions.19
The polymerization of ethylene and acrylonitrile (1e) was
accomplished using our cationic BPMO−Pd catalysts (entries 8
and 9). Recent experimental and theoretical studies suggest
catalyst inhibition during coordination−insertion polymer-
ization of ethylene and acrylonitrile can be attributed to strong
σ-coordination (N-bound) over π-coordination of the polar
monomer to the metal center, which is an insurmountable
obstacle to subsequent migratory insertion for cationic (and
electrophilic) α-diimine catalysts that cannot readily participate
in π-backbonding.8c,21 Such logic was used to distinguish why
ethylene/acrylonitrile copolymerizations promoted by neutral
phosphine-sulfonate-ligated Pd complexes were successful,
whereas cationic α-diimine Pd complexes are inactive for this
transformation.8d Nevertheless, the reaction of ethylene and
acrylonitrile in the presence of the cationic complex 5 or 8
indeed provided a polymer product. Analysis of the resulting
polymer microstructure by 13C NMR spectroscopy confirmed
that acrylonitrile had been incorporated into the polymer main
chain, as well as at the initiating and terminating chain ends
with incorporation ratios of 2.0−2.5%. While the terminal chain
ends in ethylene/acrylonitrile copolymers formed by phos-
phine-sulfonate-based catalysts were exclusively alkenyl nitrile
moieties,8a we observed a combination of olefinic chain ends in
addition to alkenyl nitrile chain ends for copolymers formed by
5 or 8. Thus, not only are the activities of cationic BPMO−Pd
complexes markedly different from cationic α-diimine Pd
8804
dx.doi.org/10.1021/ja303507t | J. Am. Chem. Soc. 2012, 134, 8802−8805

Journal of the American Chemical Society
Communication
(10) (a) Luo, S.; Jordan, R. F. J. Am. Chem. Soc. 2006, 128, 12072−
12073. (b) Chen, C.; Luo, S.; Jordan, R. F. J. Am. Chem. Soc. 2010,
132, 5273−5284. (c) Luo, S.; Vela, J.; Lief, G. R.; Jordan, R. F. J. Am.
Chem. Soc. 2007, 129, 8946−8947.
(11) Grubbs-type salicylaldimine palladium or nickel complexes,
although active for copolymerization of ethylene with functionalized
norbenenes by an insertion mechanism, are not compatible with other
polar monomers such as (meth)acrylates, vinyl acetate, vinyl chloride,
ASSOCIATED CONTENT
* Supporting Information
Experimental procedures, characterization of palladium com-
pounds and polymers, and crystallographic data for 7 and [o-
(iPr2P)C6H4(P(O)tBu2)]Pd(Me)(Cl) (9). This material is
available free of charge via the Internet at http://pubs.acs.org.
■
S
or vinyl ethers. (a) Berkefeld, A.; Drexler, M.; Moller, H. M.; Mecking,
̈
AUTHOR INFORMATION
Corresponding Author
nozaki@chembio.t.u-tokyo.ac.jp
■
S. J. Am. Chem. Soc. 2009, 131, 12613−12622. (b) Connor, E. F.;
Younkin, T. R.; Henderson, J. I.; Hwang, S.; Grubbs, R. H.; Roberts,
W. P.; Litzau, J. J. J. Polym. Sci., Part A: Polym. Chem. 2002, 40, 2842−
2854. (c) Waltman, A. W.; Younkin, T. R.; Grubbs, R. H.
Organometallics 2004, 23, 5121−5123. (d) Groux, L. F.; Weiss, T.;
Reddy, D. N.; Chase, P. A.; Piers, W. E.; Ziegler, T.; Parvez, M.; Benet-
Buchholz, J. J. Am. Chem. Soc. 2005, 127, 1854−1869.
Notes
The authors declare no competing financial interest.
ACKNOWLEDGMENTS
■
(12) Oligomerization of ethylene (ref 12c) and alternating
copolymerization of ethylene and CO have been reported using
palladium or nickel BPMO complexes. (a) Mecking, S.; Keim, W.
Organometallics 1996, 15, 2650−2656. (b) Keim, W.; Maas, H.;
Mecking, S. Z. Naturforsh. B 1995, 430−438. (c) Brassat, I.; Keim, W.;
The authors are grateful to Yoshitaka Aramaki and Dr. Shingo
Ito (U Tokyo) for X-ray analysis. This work was supported by
Funding Program for Next Generation World-Leading
Researchers, Green Innovation and the Global COE Program
“Chemistry Innovation through Cooperation of Science and
Engineering” from MEXT, Japan.
Killat, S.; Mothrath, M.; Mastrorilli, P.; Nobile, C. F.; Suranna, G. P. J.
̈
Mol. Catal. A: Chem. 2000, 157, 41−58. (d) Cole-Hamilton, D. J.;
Robertson, R. A. M. Catal. Met. Complexes 2003, 27, 37−86.
(13) (a) Friedberger, T.; Wucher, P.; Mecking, S. J. Am. Chem. Soc.
REFERENCES
■
̈
2011, 134, 1010−1018. (b) Neuwald, B.; Olscher, F.; Gottker-
̈
(1) (a) Chung, T. C. Functionalization of Polyolefins; Academic Press:
London, 2002; (b) Dong, J.-Y.; Hu, Y. Coord. Chem. Rev. 2006, 250,
47−65. (c) Padwa, A. R. Prog. Polym. Sci. 1989, 14, 811−833.
(d) Yanjarappa, M. J.; Sivaram, S. Prog. Polym. Sci. 2002, 27, 1347−
1398. (e) Nomura, K.; Kitiyanan, B. Curr. Org. Synth. 2008, 5, 217−
226.
(2) For thorough reviews of functional polyolefin synthesis by
coordination−insertion polymerization, see: (a) Boffa, L. S.; Novak,
B. M. Chem. Rev. 2000, 100, 1479−1494. (b) Nakamura, A.; Ito, S.;
Nozaki, K. Chem. Rev. 2009, 109, 5215−5244. (c) Ittel, S. D.; Johnson,
L. K.; Brookhart, M. Chem. Rev. 2000, 100, 1169−1204. (d) Goodall,
B. L. Top. Organomet. Chem. 2009, 26, 159−178.
(3) Free radical polymerizations of olefins and polar monomers have
been commercialized, but such processes often suffer from poor
selectivity, molecular weight distribution, and control over the polymer
microstructure; see: Encyclopedia of Polymer Science and Engineering,
2nd ed.; Mark, H. F., Bikales, N., Overberger, C. G., Menges, G.,
Kroschwitz, J. I., Eds.; Wiley-Interscience: New York, 1985; Vol. 1.
(4) (a) Johnson, L. K.; Mecking, S.; Brookhart, M. J. Am. Chem. Soc.
1996, 118, 267−268. (b) Mecking, S.; Johnson, L. K.; Wang, L.;
Brookhart, M. J. Am. Chem. Soc. 1998, 120, 888−899.
(5) (a) Murray, R. E. U.S. Patent 4,689,437, August 25, 1987.
(b) Drent, E.; van Dijk, R.; van Ginkel, R.; van Oort, B.; Pugh, R. I.
Chem. Commun. 2002, 744−745. (c) Drent, E.; van Dijk, R.; van
Ginkel, R.; van Oort, B.; Pugh, R. I. Chem. Commun. 2002, 964−965.
(6) (a) Haras, A.; Anderson, G. D. W.; Michalak, A.; Rieger, B.;
Ziegler, T. Organometallics 2006, 25, 4491−4497. (b) Noda, S.;
Nakamura, A.; Kochi, T.; Chung, L. W.; Morokuma, K.; Nozaki, K. J.
Am. Chem. Soc. 2009, 131, 14088−14100.
Schnetmann, I.; Mecking, S. Organometallics 2012, 31, 3128−3137.
(14) We also investigated the copolymerization of ethylene and CO
using our BPMO catalysts; the activity of 2 or 5 compared to 7 or 8
was significantly lower for this process. See Supporting Information for
tabular data.
(15) Peh, G.-R.; Kantchev, E. A. B.; Er, J.-C.; Ying, J. Y. Chem.Eur.
J. 2010, 16, 4010−4017.
(16) The structures of 7 and 8 were confirmed by multinuclear NMR
spectroscopic and single crystal X-ray analyses. See Supporting
Information for details.
(17) For a report of an extremely active Pd catalyst for ethylene
polymerization, see: Skupov, K. M.; Marella, P. R.; Simard, M.; Yap, G.
P. A.; Allen, N.; Conner, D.; Goodall, B. L.; Claverie, J. P. Macromol.
Rapid Commun. 2007, 28, 2033−2038.
(18) Kochi, T.; Nakamura, A.; Ida, H.; Nozaki, K. J. Am. Chem. Soc.
2007, 129, 7770−7771.
(19) Ito, S.; Kanazawa, M.; Munakata, K.; Kuroda, J.-i.; Okumura, Y.;
Nozaki, K. J. Am. Chem. Soc. 2011, 133, 1232−1235.
(20) Boone, H. W.; Athey, P. S.; Mullins, M. J.; Philipp, D.; Muller,
R.; Goddard, W. A. J. Am. Chem. Soc. 2002, 124, 8790−8791.
(21) Stojcevic, G.; Prokopchuk, E. M.; Baird, M. C. J. Organomet.
Chem. 2005, 690, 4349−4355.
(7) (a) Ito, S.; Munakata, K.; Nakamura, A.; Nozaki, K. J. Am. Chem.
Soc. 2009, 131, 14606−14607. (b) Williams, B. S.; Leatherman, M. D.;
White, P. S.; Brookhart, M. J. Am. Chem. Soc. 2005, 127, 5132−5146.
(8) (a) Kochi, T.; Noda, S.; Yoshimura, K.; Nozaki, K. J. Am. Chem.
Soc. 2007, 129, 8948−8949. (b) Stojcevic, G.; Prokopchuk, E. M.;
Baird, M. C. J. Organomet. Chem. 2005, 690, 4349−4355. (c) Wu, F.;
Foley, S. R.; Burns, C. T.; Jordan, R. F. J. Am. Chem. Soc. 2005, 127,
1841−1853. (d) Nozaki, K.; Kusumoto, S.; Noda, S.; Kochi, T.;
Chung, L. W.; Morokuma, K. J. Am. Chem. Soc. 2010, 132, 16030−
16042.
(9) (a) Weng, W.; Shen, Z.; Jordan, R. F. J. Am. Chem. Soc. 2007,
129, 15450−15451. (b) Kang, M.; Sen, A.; Zakharov, L.; Rheingold, A.
L. J. Am. Chem. Soc. 2002, 124, 12080−12081. (c) Foley, S. R.;
Stockland, R. A.; Shen, H.; Jordan, R. F. J. Am. Chem. Soc. 2003, 125,
4350−4361.
8805
dx.doi.org/10.1021/ja303507t | J. Am. Chem. Soc. 2012, 134, 8802−8805