Ethylene polymerization by palladium alkyl complexes containing bis(aryl)phosphino-toluenesulfonate ligands

Article abstract of DOI:10.1021/om700869c

The reaction of L′₂PdR₂ (L′ = pyridine (py), pyridazine; L′₂ = cyclooctadiene, TMEDA) with 2-{(2OMe-Ph)₂P}-4-Me-benzenesulfonic acid ([PO-OMe]H, [1a]H) or 2- {(2-Et-Ph)₂P}-4-Me-benzenesulfonic acid ([PO-Et]H, [1b]H) yields [PO-OMe]Pd(R)(L) (L = py, R = CH₂SiMe₃ (2a), CH ₂^tBu (3a), CH₂Ph (4a); R = Me, L = pyridazine (5a), py (6a), PPh₃ (7a)) or [PO-Et]Pd(Me)(py) (6b). 2a and 6b have square-planar structures in which the alkyl group is cis to the phosphine and the [PO]Pd chelate rings are puckered. The reaction of 2a and 3a with B(C ₆F₅)₃ yields {[PO-OMe]Pd(R)}₂ (R = CH₂SiMe₃ (8a), CH₂^tBu (9a)). 8a is a sulfonate-bridged dimer in the solid state. 2a, 6a, and 6b polymerize ethylene to linear polyethylene that contains low levels of Me branches, one C=C unit per chain (mostly 1- or 2-olefins), and M_n in the range 6000 to 19 000. 6a is slightly more active but produces polymers with similar molecular weight and structure compared to 6b. 6a copolymerizes ethylene and hexene at low ethylene pressure (5 atm), but no α-olefin incorporation is observed at high pressure (30 atm). An ethylene polymerization mechanism is proposed, which involves insertion and chain transfer of [PO]Pd(R)(ethylene) species (II) and ethylene trapping and much slower chain-walking of the [PO]Pd(CH ₂CH₂R) species (III) formed by insertion of II.

Full text of DOI:10.1021/om700869c

6624
Organometallics 2007, 26, 6624–6635
Ethylene Polymerization by Palladium Alkyl Complexes Containing
Bis(aryl)phosphino-toluenesulfonate Ligands
Javier Vela, Graham R. Lief, Zhongliang Shen, and Richard F. Jordan*
Department of Chemistry, The UniVersity of Chicago, 5735 South Ellis AVenue, Chicago, Illinois 60637
ReceiVed August 30, 2007
The reaction of L′2PdR2 (L′ ) pyridine (py), pyridazine; L′2 ) cyclooctadiene, TMEDA) with 2-{(2-
OMe-Ph)2P}-4-Me-benzenesulfonic acid ([PO-OMe]H, [1a]H) or 2-{(2-Et-Ph)2P}-4-Me-benzenesulfonic
t
acid ([PO-Et]H, [1b]H) yields [PO-OMe]Pd(R)(L) (L ) py, R ) CH2SiMe3 (2a), CH2 Bu (3a), CH2Ph
(4a); R ) Me, L ) pyridazine (5a), py (6a), PPh3 (7a)) or [PO-Et]Pd(Me)(py) (6b). 2a and 6b have
square-planar structures in which the alkyl group is cis to the phosphine and the [PO]Pd chelate rings are
puckered. The reaction of 2a and 3a with B(C6F5)3 yields {[PO-OMe]Pd(R)}2 (R ) CH2SiMe3 (8a),
t
CH2 Bu (9a)). 8a is a sulfonate-bridged dimer in the solid state. 2a, 6a, and 6b polymerize ethylene to
linear polyethylene that contains low levels of Me branches, one CdC unit per chain (mostly 1- or
2-olefins), and Mn in the range 6000 to 19 000. 6a is slightly more active but produces polymers with
similar molecular weight and structure compared to 6b. 6a copolymerizes ethylene and hexene at low
ethylene pressure (5 atm), but no R-olefin incorporation is observed at high pressure (30 atm). An ethylene
polymerization mechanism is proposed, which involves insertion and chain transfer of [PO]Pd(R)(ethylene)
species (II) and ethylene trapping and much slower chain-walking of the [PO]Pd(CH2CH2R) species
(III) formed by insertion of II.
Scheme 1
Introduction
The development of catalysts that can incorporate polar vinyl
monomers in olefin insertion polymerization reactions would enable
the direct synthesis of functionalized polyolefins under mild
conditions.1 Brookhart and co-workers showed that (R-diimine)P-
dR+ catalysts copolymerize ethylene and alkyl acrylates (Scheme
1).2 However, (R-diimine)PdR+ species undergo fast chain-walking
(reversible ꢀ-H elimination/reinsertion), which results in the
formation of highly branched copolymers in which the acrylate
units are located at branch ends.3 In contrast, Pugh and co-workers
reported that catalysts generated in situ from 2-{(2-OMe-Ph)2P}-
benzenesulfonic acid and Pd(dba)2 (dba ) dibenzylidene acetone)
or Pd(OAc)2 produce linear ethylene/acrylate copolymers with in-
chain acrylate incorporation (Scheme 1).4 It was proposed that the
active species in these reactions are [PO]PdR complexes ([PO] )
generic phosphine sulfonate ligand). The formation of linear
copolymers by [PO]PdR catalysts suggests that chain-walking is
slow relative to chain growth. DFT calculations by Ziegler indeed
show that the barrier to ꢀ-H elimination is higher for [PO]PdR
species than for (R-diimine)Pd(R)+ species.5 Pugh and co-workers
also showed that in situ-generated [PO]PdR species catalyze the
nonalternating copolymerization of ethylene and CO.6
* Corresponding author. E-mail: rfjordan@uchicago.edu.
(1) (a) Boffa, L. S.; Novak, B. M. Chem. ReV. 2000, 200, 1479. (b)
Dong, J. Y.; Hu, Y. L. Coord. Chem. ReV. 2006, 250, 47. (c) Drent, E.;
Budzelaar, P. H. M. Chem. ReV. 1996, 96, 663. (d) Müller, G.; Rieger, B.
Prog. Polym. Sci. 2002, 27, 815. (e) Chung, T. C. Prog. Polym. Sci. 2002,
27, 39. (f) Ittel, S. D.; Johnson, L. K.; Brookhart, M. Chem. ReV. 2000,
100, 1169. (g) Sen, A.; Borkar, S. J. Organomet. Chem. 2007, 692, 291.
(h) Boz, E.; Nemeth, A. J.; Ghiviriga, I.; Jeon, K.; Alamo, R. G.; Wagener,
K. B. Macromolecules 2007, 40, 6545. (i) Baughman, T. W.; Chan, C. D.;
Winey, K. I.; Wagener, K. B. Macromolecules 2007, 40, 6564. (j) Functional
Polymers: Modern Synthetic Methods and NoVel Structures; Patil, A. O.,
Schulz, D. N., Novak, B. M., Eds.; ACS Symposium Series 704; American
Chemical Society: Washington, DC, 1998. (k) Padwa, A. R. Prog. Polym.
Sci. 1989, 14, 811.
(4) (a) Drent, E.; van Dijk, R.; van Ginkel, R.; van Oort, B.; Pugh, R. I.
Chem. Commun. 2002, 744. (b) Drent, E.; Pello, D. H. L. Eur. Pat. 0632084,
1995. (c) Drent, E.; Sjardijn, W.; Suykerbuyk, J. C. L. S.; Wanninger, K.
PCT Int. Appl. WO 00 106615, 2000.
(5) (a) Haras, A.; Anderson, G. D. W.; Michalak, A.; Rieger, B. R.;
Ziegler, T. Organometallics 2006, 25, 4491. (b) Haras, A.; Michalak, A.;
Rieger, B.; Ziegler, T. Organometallics 2006, 25, 946. (c) Haras, A.;
Michalak, A.; Rieger, B.; Ziegler, T. J. Am. Chem. Soc. 2005, 127, 8765.
(6) Drent, E.; van Dijk, R.; van Ginkel, R.; van Oort, B.; Pugh, R. I.
Chem. Commun. 2002, 964.
(2) (a) Leatherman, M. D.; Svejda, S. A.; Johnson, L. K.; Brookhart,
M. J. Am. Chem. Soc. 2003, 125, 3068. (b) Shultz, L. H.; Tempel, D. J.;
Brookhart, M. J. Am. Chem. Soc. 2001, 123, 11539. (c) Gottfried, A. C.;
Brookhart, M. Macromolecules 2001, 34, 1140. (d) Tempel, D. J.; Johnson,
L. K.; Huff, R. L.; White, P. S.; Brookhart, M. J. Am. Chem. Soc. 2000,
122, 6686. (e) Johnson, L. K.; Killian, C. M.; Brookhart, M. J. Am. Chem.
Soc. 1995, 117, 6414.
(3) For olefin/silyl-vinyl-ether copolymerization by (R-diimine)PdR+
see: Luo, S. J.; Jordan, R. F. J. Am. Chem. Soc. 2006, 128, 12072.
10.1021/om700869c CCC: $37.00
2007 American Chemical Society
Publication on Web 11/21/2007

Ethylene Polymerization by Palladium Alkyl Complexes
Organometallics, Vol. 26, No. 26, 2007 6625
chemical shifts (δ ) ca. 10) and large 1JPH values ([1a]H, 597
Hz; [1b]H, 556 Hz) for the PH hydrogen.
Scheme 2
[PO]Pd(R)(py) Complexes. The reaction of cis-Pd(R)2(py)2
(py ) pyridine) with [1a]H affords [PO-OMe]Pd(R)(py) (R )
t
CH2SiMe3 (2a), CH2 Bu (3a), CH2Ph (4a); eq 1). Similarly, the
reaction of {PdMe2(pyridazine)}n with [1a]H affords [PO-OMe-
]Pd(Me)(pyridazine) (5a, eq 2). Complex 2a is also formed by the
reaction of (COD)Pd(CH2SiMe3)2 (COD ) 1,5-cyclooctadiene)
with [1a]H and pyridine (eq 3). As described by Allen et al., the
reaction of (TMEDA)PdMe2 with [1a]H or [1b]H and pyridine
affords [PO-OMe]Pd(Me)(py) (6a) and [PO-Et]Pd(Me)(py) (6b,
eq 4).8a Similarly, the reaction of (TMEDA)PdMe2 with [1a]H and
PPh3 affords [PO-OMe]Pd(Me)(PPh3) (7a, eq 5). The [PO]P-
d(R)(py) complexes are soluble in CHCl3, CH2Cl2, and hot toluene
(80 °C) and are stable in the solid state but decompose slowly
(days) in CD2Cl2 solution at room temperature.
Following the work of Pugh and co-workers, several groups
have investigated the chemistry of discrete [PO]Pd(R)(L)
complexes and their performance in ethylene/acrylate and
ethylene/CO copolymerization.7–10 In addition, in situ-generated
and discrete [PO]PdR species have been found to catalyze other
interesting copolymerizations, including vinyl acetate/CO,11
ethylene/norbornene,12 ethylene/functionalized-norbornene,13 eth-
ylene/acrylonitrile,14 and ethylene/vinyl ether copolymeriza-
tion,15 to produce linear copolymers.
To help understand the copolymerization behavior of [PO]
PdR catalysts, we have investigated their ethylene polymeriza-
tion properties.16 Here we describe the synthesis and ethylene
polymerization characteristics of [PO]Pd(R)(L) complexes
containing 2-{(2-OMe-Ph)2P}-4-Me-benzene-sulfonate) (1a, [PO-
OMe]-) or 2-{(2-Et-Ph)2P}-4-Me-benzene-sulfonate) (1b, [PO-
Et]-) ligands (Scheme 2). The phosphine unit in 1a is slightly
smaller and more electron-donating than that in 1b.17,18
(1)
(2)
(3)
Results and Discussion
[PO] Ligands. The phosphine-sulfonic acids [PO-OMe]H
([1a]H) and [PO-Et]H ([1b]H) were synthesized by literature
routes.4b,8e,9 A methyl group was incorporated para to the
sulfonate to simplify NMR spectra. These compounds are
zwitterions in solution, as indicated by low-field 1H NMR
(7) Kochi, T.; Yoshimura, K.; Nozaki, K. Dalton Trans. 2006, 25.
(8) (a) Allen, N. T.; Goodall, B. L.; McIntosh, L. H., III. Eur. Pat. Appl.
1760086, 2007. (b) Allen, N. T.; Goodall, B. L.; McIntosh, L. H., III. Eur.
Pat. Appl. 1760097, 2007. (c) Kirk, T. C.; Goodall, B. L.; McIntosh, L. H.,
III. Eur. Pat. Appl. 1762572, 2007. (d) Allen, N. T.; Goodall, B. L.;
McIntosh, L. H., III. U.S. Pat. Appl. 049712, 2007. (e) McIntosh, L. H.,
III; Allen, N. T.; Kirk, T. C.; Goodall, B. L. Can. Pat. Appl. 2556356,
2007. (f) Goodall, B. L.; Allen, N. T.; Conner, D. M.; Kirk, T. C.; McIntosh,
L. H., III; Shen, H. Polym. Prepr. 2007, 48, 202.
(9) Hearly, A. K.; Nowack, R. J.; Rieger, B. Organometallics 2005,
24, 2755.
(4)
(5)
(10) Newsham, D. K.; Borkar, S.; Sen, A.; Conner, D. M.; Goodall,
B. L. Organometallics 2007, 26, 3636.
(11) Kochi, T.; Nakamura, A.; Ida, H.; Nozaki, K. J. Am. Chem. Soc.
2007, 129, 7770.
(12) Skupov, K. M.; Marella, P. M.; Hobbs, J. L.; McIntosh, L. H.;
Goodall, B. L.; Claverie, J. P. Macromolecules 2006, 39, 4279.
(13) Liu, S.; Borkar, S.; Newsham, D.; Yennawar, H.; Sen, A.
Organometallics 2007, 26, 210.
(14) Kochi, T.; Noda, S.; Yoshimura, K.; Nozaki, K. J. Am. Chem. Soc.
2007, 129, 8948.
(15) Luo, S.; Vela, J.; Lief, G. R.; Jordan, R. F. J. Am. Chem. Soc.
2007, 129, 8946.
(16) Previous studies have noted that [PO]PdR catalysts produce linear
polyethylene. See refs 8, 10, and 12–14.
Molecular Structures of [PO]Pd(R)(py) Complexes. The
molecular structures of [PO-OMe]Pd(CH2SiMe3)(py) (2a) and
[PO-Et]Pd(Me)(py) (6b) were determined by X-ray diffraction
(Figures 1 and 2). In both cases, the geometry at palladium is
square planar, the alkyl ligand is cis to the phosphine, and the
[PO]Pd chelate ring adopts a puckered conformation, with one
P-aryl group occupying a pseudoaxial position and the other a
pseudoequatorial position. In 2a, the methoxy group of the
(17) The cone angle of P(2-Et-Ph)2Ph (194°) is larger than that of P(2-
OMe-Ph)2Ph (183°). (a) Suomalainen, P.; Laitinen, R.; Jaäskeläinen, S.;
Haukka, M.; Pursiainen, J. T.; Pakkanen, T. A. J. Mol. Catal. A: Chem.
2002, 179, 93. (b) Reinius, H. K.; Suomalainen, P.; Riihim¨ aki, H.; Karvinen,
E.; Pursiainen, J.; Krause, A. O. I. J. Catal. 2001, 199, 302. (c) Suomalainen,
P.; Riihim¨ aki, H.; Jaäskeläinen, S.; Haukka, M.; Pursiainen, J. T.; Pakkanen,
T. A. Catal. Lett. 2001, 77, 125.
(18) The Tolman electronic parameters show that P(2-OMe-Ph)3 (ν1 )
2058 cm-1) is a better donor than P(2-Et-Ph)3 (ν1 ) 2066 cm-1) Tolman,
C. A. Chem. ReV. 1977, 77, 313.

6626 Organometallics, Vol. 26, No. 26, 2007
Vela et al.
2
sonance with a small JPC value (<4 Hz) and one 2-OMe-Ph
resonance.21 These results are consistent with a cis arrangement
of alkyl and phosphine ligands and fast inversion of the [PO-
OMe]Pd chelate ring. Similarly, for PPh3 adduct 7a, a small
2
3JPH (6 Hz) for the methyl group, a large JPP value (403 Hz),
and one 2-OMe-Ph 1H and 13C resonance are observed,
consistent with a cis arrangement of the methyl and phosphine
groups and fast chelate ring inversion.
1
The variable-temperature H NMR spectra of 2a (OMe and
PdCH2 regions) are shown in Figure 3. As the temperature is
lowered from 20 to -80 °C, the 2-OMe-Ph resonance splits
into two singlets. Also, as the temperature is lowered, the
-CH2SiMe3 resonance splits into two doublets (JHH ) 11),
indicating that these methylene hydrogens are diastereotopic in
the static structure, as expected in the limit of slow chelate ring
inversion. The activation parameters determined by line shape
analysis of the 2-OMe-Ph and -CH2SiMe3 signals are identical
(∆Hq ) 8.5 kcal/mol, ∆Sq ) -8 eu, ∆Gq) 10.1 kcal/mol at
-60 °C), indicating that the line shape changes result from the
same dynamic process. The NOESY spectrum (-80 °C) of 2a
contains cross-peaks between the -CH2SiMe3 hydrogens and
the ortho and meta hydrogens of one 2-OMe-Ph ring. These
results show that the solution structure of 2a is similar to the
solid-state structure and that [PO-OMe]Pd chelate ring inversion
is facile. Similar results are observed for 6a. The activation
parameters for ring inversion in 6a (∆Hq ) 7.5 kcal/mol, ∆Sq
) -14 eu, ∆Gq ) 10.5 kcal/mol at -50 °C) are similar to
those for 2a, despite the large steric difference between the Pd-
alkyl ligands in the two species.
Figure 1. Molecular structure of [PO-OMe]Pd(CH2SiMe3)(py) (2a).
Hydrogen atoms are omitted. Selected bond distances (Å) and angles
(deg): Pd(1)-C(6) 2.041(3), Pd(1)-P(1) 2.2430(8), Pd(1)-N(1)
2.130(2), Pd(1)-O(3) 2.149(2), S(1)-O(3) 1.484(2), S(1)-O(4)
1.431(2), S(1)-O(5) 1.437(2), O(3)-Pd(1)-P(1) 94.01(6),
C(6)-Pd(1)-N(1) 90.8(1), C(6)-Pd(1)-P(1) 91.23(9), N(1)-
Pd(1)-O(3) 83.97(8).
1
In contrast, the H NMR spectrum of 6b at 22 °C contains
two sets of 2-Et-Ph resonances (1:1 intensity ratio), which
coalesce to a single set of resonances at elevated temperature
due to chelate ring inversion (see Supporting Information). The
activation parameters determined by line shape analysis are ∆Hq
) 15.7 kcal/mol, ∆Sq ) 1.2 eu, and ∆Gq ) 15.3 kcal/mol at
55 °C). The higher barrier for chelate ring inversion for 6b
versus 2a and 6a probably results from the larger size and
greater attendant steric crowding of the o-Et substituent in 6b
compared to the o-OMe group in 2a and 6a.
Figure 2. Molecular structure of [PO-Et]PdMe(py) (6b). Hydrogen
atoms are omitted. Selected bond distances (Å) and angles (deg):
Pd(1)-C(1) 2.026(3), Pd(1)-P(1) 2.231(1), Pd(1)-N(1) 2.103(2),
Pd(1)-O(3) 2.177(2), S(1)-O(1) 1.484(2), S(1)-O(2) 1.448(2),
S(1)-O(3) 1.443(2), O(1)-Pd(1)-P(1) 86.48(5), C(1)-Pd(1)-N(1)
89.55(9), C(1)-Pd(1)-P(1) 95.47(8), N(1)-Pd(1)-O(1) 88.83(7).
Base-Free {[PO-OMe]Pd(R)}2 Complexes. The reaction of
2a and 3a with 1 equiv of B(C6F5)3 results in quantitative
t
formation of {[PO-OMe]Pd(R)}2 (R ) CH2SiMe3 (8a), CH2 Bu
equatorial 2-OMe-Ph ring (O(1)) sits above an axial coordination
site, but the Pd---O distance (Pd(1)-O(1), 3.52 Å)19 is too long
for a significant Pd---O interaction.20 There are no close Pd---H
contacts involving the [PO]- ligands in 2a or 6b.19b
(9a)) and B(C6F5)3(py) (Scheme 3). X-ray crystallographic
analysis shows that 8a exists as a sulfonate-bridged dimer in
the solid state (Figure 4). The central eight-membered ring
adopts a chair conformation, with O(1), S(1), O(3), O(1A),
S(1A), and O(3A) forming a plane and Pd(1) and Pd(1A) lying
above and below this plane. The geometry at palladium is square
planar, and the [PO]Pd chelate ring is puckered. The methoxy
group of the pseudoequatorial 2-OMe-Ph ring (C(12)-C(17))
points toward Pd, but as for 2a, the long Pd(1A)-O(4) distance
(3.67 Å) rules out a significant interaction. The ortho hydrogen
(H(20)) of the pseudoaxial 2-OMe-Ph ring (C(19)-C(24))
makes a short contact with Pd (H(20)-Pd(1A), 2.67 Å). Close
M---H contacts involving the ortho-hydrogens of diarylphos-
phine ligands are common in square-planar d8 metal complexes
Solution Structures and Dynamics of [PO]Pd(R)(L)
Complexes. The ambient-temperature 1H NMR spectra of [PO-
OMe]Pd(R)(L) complexes 2a-6a contain one doublet for the
Pd-CH2R′ hydrogens (3JPH ) 2–7 Hz) and one 2-OMe-Ph
resonance. The 13C NMR spectra contain one Pd-CH2R′ re-
(19) (a) ∑(Pd and O covalent radii) ) 2.04 Å; ∑(Pd and O van der
Waals radii) ) 3.15 Å); ∑(Pd and H covalent radii) ) 2.68 Å; ∑(Pd and
H van der Waals radii) ) 2.83 Å; radii taken from Webelements, see: http://
www.webelements.com/. (b) The shortest Pd---H contacts are as follows:
2a: Pd(1)-H(18), 2.9 Å; 6b: Pd(1)-H(20A), 2.8 Å.
(20) Pd-OR2 distances in neutral square-planar Pd(II) complexes are
in the range 2.11–2.20 Å. (a) Bei, X.; Uno, T.; Norris, J.; Turner, H. W.;
Weinberg, W. H.; Guram, A. S. Organometallics 1999, 18, 1840. (b) Kim,
Y.; Verkade, J. G. J. Organomet. Chem. 2003, 669, 32. Pd-OR2 distances
in neutral five-coordinate Pd(II) complexes are in the range 2.92–3.00 Å.
(c) Ma, J.-F.; Kojima, Y.; Yamamoto, Y. J. Organomet. Chem. 2000, 616,
149.
(21) Similar 3JPH values were reported for phosphinosulfonamide nickel
methyl complexes in which the alkyl group is cis to the phosphine. Rachita,
M. J.; Huff, R. L.; Bennett, J. L.; Brookhart, M. J. Polym. Sci. Part A:
Polym. Chem. 2000, 38, 4627.

Ethylene Polymerization by Palladium Alkyl Complexes
Organometallics, Vol. 26, No. 26, 2007 6627
1
Figure 3. Variable-temperature H NMR spectra (500 MHz) of [PO-OMe]Pd(CH2SiMe3)(py) (2a). The OMe (a) and PdCH2SiMe3 (b)
regions are shown. The singlet at δ ) 0 is due to SiMe4. The chemical shift scale is in units of δ.
Scheme 3
Figure 4. Molecular structure of {[PO-OMe]Pd(CH2SiMe3)}2 (8a).
Hydrogen atoms are omitted. Selected bond lengths (Å) and angles
(deg): Pd(1)-P(1A) 2.2009(9), Pd(1)-O(3A) 2.201(2), Pd(1)-C(1)
2.027(3), Pd(1)-O(1) 2.142(2), S(1)-O(3) 1.469(2), S(1)-O(2)
1.435(2), S(1)-O(1) 1.471(2), O(3A)-Pd(1)-P(1A) 81.05(6),
C(1)-Pd(1)-O(1) 93.2(1), O(3A)-Pd(1)-O(1) 89.60(8), P(1A)-
and have been characterized as weak hydrogen bonds or agostic
Pd(1)-C(1) 95.97(9).
interactions.22
1
in 4a and has a large JCH value (154 Hz) consistent with η3-
The NMR spectra of 8a generated in situ in CD2Cl2 are
coordination.23
identical to those of solutions of crystalline 8a. The 1H spectrum
of 8a contains a sharp OMe resonance (δ 3.57) and broad
singlets for the methylene (δ 0.67) and methyl hydrogens (δ
-0.31) of the -CH2SiMe3 group, and the 31P spectrum contains
a broad singlet at δ 28.1. These data do not differentiate between
monomeric and dimeric structures. Complex 9a is insufficiently
(6)
soluble for NMR analysis.
Generation of [PO-OMe]Pd(η3-CH2Ph). Abstraction of
pyridine from 4a by B(C6F5)3 produces the CD2Cl2-soluble
Ethylene Polymerization by [PO]Pd(R)(py) Catalysts.
complex [PO-OMe]Pd(η3-CH2Ph) (10a), which is presumed to
Ethylene polymerization results are summarized in Table 1.
be monomeric (eq 6). The 13C NMR PdCH2Ph resonance is
shifted downfield by 16.9 ppm from the corresponding signal
Under conditions similar to those used by Pugh and co-workers
for ethylene/MA copolymerization (toluene, 80 °C, 30 atm
ethylene, 1 h),4 [PO-OMe]PdR catalysts generated in situ from
Pd(dba)2 and 1.2 equiv of [1a]H produce polyethylene in low
(22) (a) Angulo, I. M.; Bouwman, E.; van Gorkum, R.; Lok, S. M.;
and variable yield (entry 1). Ethylene uptake monitoring
experiments show that the activity of the in situ-generated
catalyst ceases after ca. 1 h at 80 °C. The loss of activity is
Lutz, M.; Spek, A. L. J. Mol. Catal. 2003, 202, 97. (b) Dossett, S. J.; Gillon,
A.; Orpen, A. G.; Fleming, J. S.; Pringle, P. G.; Wass, D. F.; Jones, M. D.
Chem. Commun. 2001, 699. (c) Cooley, N. A.; Green, S. M.; Wass, D. F.;
Heslop, K.; Orpen, A. G.; Pringle, P. G. Organometallics 2001, 20, 4769.
(d) Yao, W.; Eisenstein, O.; Crabtree, R. H. Inorg. Chim. Acta 1997, 254,
105. (e) Brookhart, M.; Green, M. L. H.; Wong, L. L. Prog. Inorg. Chem.
1988, 36, 1.
(23) Albers, I.; Álvarez, E.; Cámpora, J.; Maya, C. M.; Palma, P.;
Sánchez, L. J.; Passaglia, E. J. Organomet. Chem. 2004, 689, 833.

6628 Organometallics, Vol. 26, No. 26, 2007
Vela et al.
Table 1. Ethylene Polymerization with [PO]-Palladium Catalystsa
b
b
[Pd]
T
P
time yield
productivity
(g/mol · h · atm)
Mn GPC Mw/Mn
Mn NMR
no.
% int.
Tm
run
catalyst
(mM) (°C) (atm) (h)
(g)
(103)
12.1
GPC
(103)
Me brc chains/Pd unsat.d (°C)
1
2
3e
4
5
6
7
8
9
[1a]H/Pd(dba)2 0.40
[1b]H/Pd(dba)2 2.0
[1b]H/Pd(dba)2 2.0
80
135
135
80
80
80
80
80
120
80
80
80
80
80
80
80
80
30
15
15
30
30
30
30
15
15
30
2
1
3
0.40
4.70
700
3100
10 600
9800
7700
13 600
7700
22 900
21 200
4200
76 100
42 500
36 400
23 200
16 600
30 800
33 000
2.3
14.2
4.10
0.20
21.8
27.2
17.9
20.8
17.4
4.80
17.6
11.5
17.7
19.3
20.1
19.3
16.1
7.20
2.2
5.8
9.0
1.4
1.2
0.8
1.1
1.6
5.1
1.0
7.0
3.4
1.8
1.8
1.2
3.2
3g
1.4
11
800
14
8.5
23
11
20
66
130
13
12
19
23
26
9.6
23
39
133.9
100.0
80.1
3
15.9
6b
6b
6a
2a
6a
6a
0.10
0.20
0.20
0.25
0.20
0.20
0.20
0.10
0.10
0.10
0.10
0.10
0.20
0.22
1
1
1
1
1
1
1.47
2.30
4.09
2.87
3.43
3.18
18.8
24.7
17.1
17.9
15.9
4.00
14.8
10.5
18.6
18.9
18.9
19.1
13.5
6.20
2.1
2.5
2.2
2.3
2.4
2.5
2.9
2.4
2.0
2.1
2.1
2.1
2.5
2.0
44
42
30
26
38
57
26
74
38
47
30
18
47
60h
136.1
134.4
133.4
138.4
131.6
124.3
133.6
125.9
130.1
131.9
133.0
134.2
130.4
110.7
10 6a
11 6a
12 6a
13 6a
14 6a
15 6a
16 6a
17f 6a
18
1
1
1
1
1
1
1
22.9
0.76
1.06
1.82
2.32
2.50
1.54
1.82
5
10
20
30
5
5
a These data are representative for [PO]Pd catalysts. Under the specified isothermal conditions, polymer yields varied 10–15%, but polymer structure
varied very little. The solvent was toluene in all cases. Total solution volume was 50 mL in all cases. b Determined by GPC using universal calibration.
c Number of methyl branches per 1000 C. Does not include Me end groups. Determined by 1H NMR assuming one Me end per chain. d (internal
unsaturation)/(total unsaturation) × 100. e CH3CN (2.2 M) also added. f Hexene (0.80 M) also added. g Also contains 16 Bu branches and 2 Me chain
ends/1000 C. h Also contains 7% vinylidene unsaturation.
accompanied by Pd0 formation. Complexes 2a, 6a, and 6b
polymerize ethylene in toluene at 80 °C over the ethylene
pressure range of 2-30 atm. These discrete catalysts exhibit
sustained catalyst activity even after 18 h at 80 °C (entry 10).
Polyethylene Structure. Complexes 2a, 6a, and 6b produce
linear polyethylene with low levels of methyl branches. Longer
branches were not observed by 13C NMR. The polyethylene
Tm values vary between 130 and 138 °C.24 The 1H NMR spectra
of the polyethylenes contain resonances for terminal
(PCHdCH2, i.e., vinyl end groups) and internal (PCHdCHP)
1
double bonds (P ) polymer chain, Figure 5). The H NMR
data do not establish the position of the internal double bonds
relative to the chain ends. However, the 13C NMR spectra of
low molecular weight polyethylenes generated at high polym-
erization temperature (entries 2, 9) and/or in the presence of
acetonitrile (entry 3) show that the internal olefins are mainly
2-olefins (90%), with only small amounts of 3-olefins (10%),
and that the E/Z ratio is ca. 3:1 (Figure 6).25–27 The polyeth-
1
Figure 5. Olefin region of the H NMR spectra of polyethylenes
obtained with [PO-OMe]PdMe(py) (6a). The chemical shift scale
is in δ units. The assignments are indicated by the structures (P )
polyethylene chain). 1H NMR conditions: 120 °C in CDCl2CDCl2
ylenes obtained with 2a, 6a, and 6b have number average
molecular weights (Mn’s) between 6000 and 19 000 and
polydispersities in the range of 2.0 to 2.9, as determined by
1
GPC. The Mn values determined by H NMR assuming that
(residual H peak at δ 5.98 and one 13C satellite at δ 5.76). (a)
Polymer from entry 11 in Table 1; ethylene pressure 2 atm; 74%
internal olefins. (b) Polymer from entry 15 in Table 1; ethylene
pressure 30 atm; 18% internal olefins.
1
there is one CdC unit per chain are similar to those obtained
by GPC.
(24) For a discussion of the relationship between branching and thermal
behavior of polyethylene see: Sworen, J. C.; Smith, J. A.; Wagener, K. B.;
Baugh, L. S.; Rucker, S. P. J. Am. Chem. Soc. 2003, 125, 2228.
(25) 1H NMR assignments for polymers are based on ref 24 and: (a)
Smith, J. A.; Brzezinska, K. R.; Valenti, D. J.; Wagener, K. B. Macromol-
ecules 2000, 33, 3781. (b) Baughman, T. W.; Sworen, J. C.; Wagener, K. B.
Macromolecules 2006, 39, 5028. (c) Cheng, H. N.; Lee, G. H. J. Polym.
Sci. B: Polym. Phys. 1987, 25, 2355.
Influence of Reaction Conditions on Polymerization
Behavior. Increasing the polymerization temperature from 80
to 120 °C results in a significant drop in Mn but does not strongly
influence the polymer yield or the number of methyl branches
(entry 8 vs 9, Table 1).
As shown by entries 11-15 in Table 1, and Figure 7, the
polymer yield increases as the ethylene pressure is raised but
begins to level off above ca. 20 atm, and Mn increases between
2 and 10 atm but is constant between 10 to 30 atm. Increasing
the ethylene pressure decreases the number of Me branches
(entries 11-15). There is some tendency for the internal-olefin/
terminal-olefin ratio to decrease as the ethylene pressure is raised
(entries 11–15); however these values are somewhat variable.
[PO]Ligand Effects. [PO-OMe]Pd(Me)(py) (6a) is slightly
more active in ethylene polymerization than [PO-Et]Pd(Me)(py)
(26) 13C NMR assignments for polymers are based on: (a) Barrera-
Galland, G.; de Souza, R. F.; Santos-Mauler, R.; Nunes, F. F. Macromol-
ecules 1999, 32, 1620. (b) Randall, J. C.; Hsieh, E. T. In NMR and
Macromolecules; ACS Symposium Series 247; Randall, J. C., Ed.; American
Chemical Society: Washington, D.C., 1984; Chapter 9. (c) Breitmaier, E.;
Voelter, W. Carbon-13 NMR Spectroscopy, 3rd ed.; VCH: New York, 1987;
pp 192–193.
(27) Control experiments show that the internal olefins are produced
during the polymerization reaction, that only a minor degree of isomerization
occurs during polymer isolation and NMR analysis, and that palladium black
does not cause isomerization of polymer double bonds under the conditions
used for polymerization, polymer isolation, or NMR analysis.

Ethylene Polymerization by Palladium Alkyl Complexes
Organometallics, Vol. 26, No. 26, 2007 6629
Scheme 4
Figure 6. Olefin region of the 13C{1H} NMR spectrum of a low
molecular weight polyethylene produced by in situ-generated [PO-
Et]PdR catalyst (entry 3 in Table 1). The chemical shift scale is in
units of δ. NMR conditions: 120 °C in CDCl2.
In contrast, at 5 atm ethylene pressure, the addition of
1-hexene (0.8 M, which corresponds to ca. twice the ethylene
concentration under these conditions)28 results in the formation
of an ethylene/1-hexene copolymer (entry 17, Table 1; 3.4 mol
% hexene incorporation). The 13C NMR spectra of the ethylene/
hexene copolymers show that methyl and butyl branches are
present but that ethyl, propyl, and pentyl branches are not.
Compared to an ethylene homopolymerization under similar
conditions (entry 16 in Table 1), the incorporation of 1-hexene
does not affect the polymer yield or the number of Me branches,
1
but causes a ca. 2-fold drop in Mn. The H NMR spectrum of
the ethylene/hexene copolymers contain resonances for the 1-
and 2-olefin chain ends observed in the ethylene homopolymers
and a vinylidene resonance (H2CdCRR′; δ 4.76, 120 °C,
CDCl2CDCl2). The vinylidene units are most likely formed by
1,2-hexene insertion followed by ꢀ-H elimination.29
Chain-Walking and Olefin Isomerization. To probe if
[PO]PdR species can chain-walk, the reaction of the base-free
dimer 9a with 6-chloro-1-hexene was investigated. As shown
in Scheme 4, insertion of 6-chloro-1-hexene followed by chain-
walking would produce a ꢀ-chloro-alkyl complex, which is
expected to undergo fast ꢀ-Cl elimination to produce [PO-
OMe]PdCl.30
The reaction of 9a with 6 equiv of 6-chloro-1-hexene in
CD2Cl2 at room temperature does yield [PO-OMe]PdCl, which
was characterized as the pyridine adduct [PO-OMe]Pd(Cl)(py)
(11a), along with a complex mixture of chlorohexenes (g4
isomers), undecenes (g6 isomers), chloroundecenes (g6 iso-
mers), and oligomers derived from multiple (1-4) insertions
t
of 6-chloro-1-hexene into [PO-OMe]PdCH2 Bu or [PO-OMe]-
PdH followed by ꢀ-H or ꢀ-Cl elimination. These products are
likely formed by insertion, chain-walking, ꢀ-H elimination, and
ꢀ-Cl elimination, as outlined in Scheme 5 (similar chemistry
could occur after 2,1 insertion). To rule out the possibility that
[PO-OMe]PdCl is formed by direct reaction of the C-Cl bond
of 6-chloro-1-hexene (e.g., by oxidative addition), 9a was treated
with a mixture of 6-chloro-1-hexene and 1-chloropentane. The
6-chloro-1-hexene was converted to similar products observed
in the absence of 1-chloropentane, while the 1-chloropentane
Figure 7. Effect of ethylene pressure on (a) polymer yield and (b)
molecular weight in ethylene polymerization by 6a. Polymerization
conditions: toluene (50 mL), 80 °C, 1 h reaction. Circles: 5 µmol
of 6a (entries 11–15 in Table 1). Triangles: 10 µmol of 6a. The
curves merely guide the eye.
(28) Lee, L.; Ou, H.; Hsu, H. Fluid Phase Equilib. 2005, 231, 221.
(29) Competitive 2,1 hexene insertion cannot be ruled out, since this
process would produce a Bu branch following further chain growth, or an
internal olefin following chain transfer, both of which are observed.
(30) (a) Foley, S. R.; Stockland, R. A., Jr.; Shen, H.; Jordan, R. F. J. Am.
Chem. Soc. 2003, 125, 4350. (b) Shen, H.; Jordan, R. F. Organometallics
2003, 22, 1878. (c) Gaynor, S. G. Macromolecules 2003, 36, 4692. (d)
Stockland, R. A., Jr.; Foley, S. R.; Jordan, R. F. J. Am. Chem. Soc. 2003,
125, 796. (e) Zhu, G.; Lu, X. Organometallics 1995, 14, 4899. (f) Kang,
M.; Sen, A.; Zakharov, L.; Rheingold, A. L. J. Am. Chem. Soc. 2002, 124,
12080.
(6b), but the two catalysts produce polymers with very similar
molecular weight and structure (entries 4 vs 15; 5 vs 6).
r-Olefin Copolymerization. The addition of 1-hexene or
1-tridecene at high ethylene pressure (30 atm) does not affect
polymer yield, Mn, or structure. Under these high-pressure
conditions, the R-olefin is not incorporated in the polymer. In
addition, analysis of the liquid phase after the polymerization
showed that no significant R-olefin isomerization occurs.

6630 Organometallics, Vol. 26, No. 26, 2007
Vela et al.
Scheme 5
polymerization behavior of base-free {[PO]PdR}2 species such
as 8a and 9a will be discussed elsewhere.
Conclusions
[PO-OMe]Pd(R)(L) and [PO-OMe]Pd(R)(L) complexes are
easily prepared by the reaction of [PO-OMe]H ([1a]H) or [PO-
Et]H ([1b]H) with L′2PdR2 precursors. [PO]Pd(R)(L) complexes
have square-planar structures in which the alkyl group is cis to
the phosphine, and the [PO]Pd chelate rings are puckered and
invert rapidly on the NMR time scale. The reaction of [PO-
t
OMe]Pd(R)(py) (R ) CH2SiMe3 (2a), CH2 Bu (3a)) with
B(C6F5)3 yields {[PO-OMe]Pd(R)}2 (R ) CH2SiMe3 (8a),
t
CH2 Bu (9a)). 8a is a sulfonate-bridged dimer in the solid state.
2a, [PO-OMe]Pd(Me)(py) (6a), and [PO-Et]Pd(Me)(py) (6b)
polymerize ethylene to linear polyethylene that contains low
levels of Me branches, one CdC unit per chain (mostly 1- or
2-olefins), and Mn in the range 6000 to 19 000. 6a is slightly
more active but produces polymers with similar molecular
weight and structure compared to 6b. 6a copolymerizes ethylene
and hexene at low ethylene pressure (5 atm), but no R-olefin
incorporation is observed at higher pressure (30 atm). A
polymerization mechanism involving insertion and chain transfer
of [PO]Pd(R)(ethylene) species (II), and ethylene trapping and
much slower chain-walking of the [PO]Pd(CH2CH2R) species
(III) formed by insertion of II, is consistent with these results.
The similarity of the ethylene polymerization behavior of 6a
and 6b and the absence of Pd---OMe interactions in the solid-
state structures of 2a and 8a suggest that Pd---OMe coordination
is not important in the chemistry discussed here.
was not consumed. These results provide strong evidence that
[PO]Pd(R) species can chain-walk and isomerize olefins.
Polymerization Mechanism. The polymerization mechanism
in Scheme 6 is consistent with the observations described above.
The active [PO]Pd(1-alkyl) species likely exist as equilibrium
mixtures of the pyridine and ethylene adducts I and II. NMR
studies show that this equilibrium lies far to the side of I at
room temperature and low ethylene pressure. The increase in
polymer yield at higher ethylene pressures results from shifting
of the equilibrium to the ethylene adduct II. II can undergo
chain transfer to monomer to generate the observed 1-olefin
chain ends. Alternatively II can undergo insertion to give a base-
free [PO]Pd(1-alkyl) species, III, which may exist transiently
as a ꢀ-agostic species (not shown).5 III can be trapped by
ethylene to regenerate II or isomerize by chain-walking to a
[PO]Pd(CMeHP) secondary alkyl species (IV). IV is trapped
by ethylene, generating a [PO]Pd(CMeHP)(ethylene) complex,
V (which would be in equilibrium with the corresponding
pyridine adduct). V can undergo chain transfer to release a
2-olefin or insertion to generate a methyl branch. The observed
increase in the number of methyl branches and the tendency
for increased internal unsaturation with decreasing ethylene
pressure are consistent with competitive ethylene trapping and
chain-walking of III. IV can chain-walk further, leading to
3-olefin or (3+)-olefin chain ends or longer branches, but
because chain-walking is slow, these products are present only
at trace levels or are not observed. Our results are also consistent
with chain transfer by associative olefin exchange of the
[PO]Pd(H)(olefin) species formed by ꢀ-H elimination of III or
IV (i.e., chain-walk intermediates). An alternative source of Me
branches is 2,1 insertion of vinyl chain ends into [PO]PdH
followed by growth. However, the lack of reactivity of added
R-olefin at high ethylene pressure and the lack of an increase
in Me branches in ethylene/1-hexene copolymerization com-
pared to ethylene homopolymerization at low ethylene pressure
imply that this process is unimportant. An alternative source of
internal olefins is Pd-catalyzed isomerization of vinyl chain ends
under the reaction conditions, as observed in Scheme 5. This
process is probably important at low ethylene pressure, but the
lack of reactivity of added R-olefin at 30 atm ethylene pressure
suggests that it is insignificant at high ethylene pressure. The
Experimental Section
General Procedures. All experiments were performed using
drybox or Schlenk techniques under a nitrogen atmosphere.
Nitrogen was purified by passage through columns containing
activated molecular sieves and Q-5 oxygen scavenger. Diethyl ether
was distilled from sodium benzophenone ketyl. CH2Cl2 and CD2Cl2
were distilled from CaH2. Pentane and toluene were purified by
passage through columns of activated alumina and BASF R3-11
oxygen scavenger. Pd(dba)2 and PdCl2 (Strem), and (COD)PdCl2
(Boulder) were used as received. [PO-OMe]H ([1a]H) and [PO-
Et]H ([1b]H) were synthesized by literature routes; details are
provided in the Supporting Information.4b,8e,9 {PdMe2(pyrida-
zine)}n,31 (TMEDA)PdMe2,32 and (COD)Pd(CH2Si(CH3)3)233 were
prepared by literature procedures or modifications thereof. Ethylene
(polymer grade) was purchased from Matheson and used as
received. 1-Hexene was dried over sodium and vacuum distilled
prior to use. Elemental analyses were performed by Midwest
Microlab, LLC.
NMR spectra of organometallic complexes were recorded at
ambient temperature unless otherwise indicated. 1H and 13C
chemical shifts are reported relative to SiMe4 and were determined
1
by reference to the residual H and 13C solvent resonances. 11B
chemical shifts are reported relative to BF3(Et2O), and 19F chemical
shifts are reported relative to CFCl3. Coupling constants are given
in Hz. JCH values were determined from gated-{1H}13C spectra.
NMR assignments for 2a were determined by NOESY, HMQC,
1
and H{31P} NMR experiments. NMR assignments for all other
complexes were made by comparison of chemical shift patterns
(31) Byers, P. K.; Canty, A. J.; Skelton, B. W.; White, A. H. J.
Organomet. Chem. 1987, 336, C55.
(32) De Graaf, W.; Boersma, J.; Smeets; Wilberth, J. J.; Spek, A. L.;
Van Koten, G. Organometallics 1989, 8, 2907.
(33) Pan, Y.; Young, G. B. J. Organomet. Chem. 1999, 577, 257.

Ethylene Polymerization by Palladium Alkyl Complexes
Organometallics, Vol. 26, No. 26, 2007 6631
Scheme 6
and JHH and JPC values to those for 2a. The numbering scheme for
NMR assignments is given in Figure 8.
CH2SiMe3), 1.4 (s, CH2SiMe3). 31P{1H} NMR (CD2Cl2): δ 24.6
(s). Anal. Calcd for C30H36NO5PPdSSi: C, 52.36; H, 5.27; N, 2.04.
Found: C, 52.10; H, 5.23; N, 2.18.
NMR spectra for polymers were obtained as follows. A mixture
of polymer (1H NMR: 30–60 mg; 13C NMR: 85–95 mg) and
CDCl2CDCl2 (0.7 g) in an NMR tube was heated to 120 °C (e15
min), affording a homogeneous solution. The tube was inserted into
a preheated NMR probe at 120 °C, and NMR spectra were obtained
after a 5 min temperature equilibration period. 1H NMR: 400 MHz,
pulse width 90°, acquisition time 3.7 s, pulse delay 42 s; 13C{1H}
NMR: 100 MHz, pulse width 60°, acquisition time 4.0 s; pulse
delay 4.0 s.
Synthesis of [PO-OMe]Pd(CH2SiMe3)(py) (2a) from (COD)
Pd(CH2SiMe3)2. A flask was charged with (COD)Pd(CH2SiMe3)2
(0.233 g, 0.60 mmol) and [PO-OMe]H (0.224 g, 0.539 mmol) and
cooled to -78 °C, and THF (25 mL) was added by vacuum-transfer.
The mixture was stirred for 45 min and then allowed to warm to
room temperature. Pyridine (0.220 mL, 2.70 mmol) was added by
syringe, and the mixture was stirred for 2.5 h. The volatiles were
removed under vacuum. The resulting solid was triturated with
pentane (25 mL) and dried under vacuum. The solid was dissolved
in CH2Cl2 (25 mL) and filtered through Celite. The filtrate was
concentrated to ca. 3 mL and stored at -35 °C, yielding several
crops of colorless crystals. Yield: 0.280 g (81%).
Pd(R)2(py)2 Complexes. Pd(R)2(py)2 complexes (R′
)
t
CH2SiMe3, CH2 Bu, CH2Ph) were prepared by the method of
Cámpora.34 cis-Pd(CH2SiMe3)2(py)2 was isolated as a yellow
crystalline solid (50%). Isolation of cis-Pd(CH2Ph)2(py)2 and cis-
t
t
Pd(CH2 Bu)2(py) was more difficult due to their thermal sensitivity,
[PO-OMe]Pd(CH2 Bu)(py) (3a). A solution of cis-Pd(CH2
and crude samples of these complexes were used in the syntheses
of [PO-OMe]Pd(CH2 Bu)(py) and [PO-OMe]Pd(CH2Ph)(py), result-
ing in lower yields in these cases.
tBu)2(py)2 (0.559 g, 1.37 mmol) and pyridine (1.0 mL, 12 mmol)
in CH2Cl2 (15 mL) was cooled to -78 °C, and a solution of [PO-
OMe]H (0.572 g, 1.37 mmol) in CH2Cl2 (10 mL) was added
dropwise. The mixture was allowed to warm to room temperature
and was stirred for 1.5 h. The resulting solution was filtered through
a medium-porosity frit, concentrated under vacuum to 5 mL, and
placed in a freezer at -20 °C. Several crops of colorless crystals
were obtained by filtration. The crystals became opaque when dried
under vacuum. Yield: 0.325 g (35%). Mp: 181 °C (dec). 1H NMR
(CD2Cl2): δ 8.88 (d, JHH ) 5, 2H, o-py), 7.94 (m, 2H, H6-ArOMe),
7.90 (t, JHH ) 8, 1H, p-py), 7.82 (dd, JHH ) 8, JPH ) 5, 1H, H3-
ArSO3), 7.56 (t, JHH ) 8, 2H, m-py), 7.50 (t, JHH ) 8, 2H, H4-
ArOMe), 7.22 (m, 2H, H2/H4-ArSO3), 7.10 (t, JHH ) 8, 2H, H5-
ArOMe), 6.96 (dd, JHH ) 8, JPH ) 4, 2H, H3-ArOMe), 3.62 (s,
6H, OMe), 2.25 (s, 3H, Me-ArSO3), 1.44 (d, JPH ) 6, 2H,
CH2CMe3), 0.38 (s, 9H, CMe3). 13C{H} NMR (CD2Cl2): δ 161.4
(s, C2-ArOMe), 151.5 (s, o-py), 146.4 (d, JPC ) 15, C2-ArSO3),
139.3 (d, JPC ) 14, C5-ArSO3), 138.9 (s, C3-ArSO3), 138.2 (d, JPC
t
Synthesis of [PO-OMe]Pd(CH2SiMe3)(py) (2a) from Pd(CH2
SiMe3)2(py)2. A solution of Pd(CH2SiMe3)2(py)2 (0.482 g, 1.10
mmol) in CH2Cl2 (20 mL) was cooled to -78 °C. A solution of
[PO-OMe]H (0.458 g, 1.10 mmol) in CH2Cl2 (15 mL) was added
dropwise while the mixture was stirred. The resulting clear brown
solution was warmed to room temperature and stirred for 1 h. The
mixture was concentrated under vacuum to 5 mL and placed in a
freezer at -20 °C. Several fractions of colorless crystals were
collected by filtration. The crystals became opaque upon drying
under vacuum. Yield: 0.511 g (68%). Mp: 186 °C (dec). 1H NMR
(CD2Cl2): δ 8.82 (d, JHH ) 5, 2H, o-py), 7.88 (m, 4H, p-py/H3-
ArSO3/H6-ArOMe), 7.52 (m, 4H, m-py/H4-ArOMe), 7.24 (d, JHH
) 8, 1H, H4-ArSO3), 7.20 (d, JPH ) 11, 1H, H6-ArSO3), 7.08 (t,
JHH ) 8, 2H, H5-ArOMe), 6.95 (dd, JHH ) 8, JPH ) 4.6, 2H, H3-
ArOMe), 3.61 (s, 6H, OMe), 2.26 (s, 3H, Me-ArSO3), 0.30 (d, JPH
) 5, 2H, CH2SiMe3), -0.58 (s, 9H, CH2SiMe3). 13C{1H} NMR
) 8, C6-ArSO3), 135.5 (s, p-py), 133.8 (s, m-py), 131.0 (d, JPC
)
(CD2Cl2): δ 161.0 (s, C2-ArOMe), 151.5 (s, o-py), 146.2 (d, JPC
)
2, C4-ArSO3), 128.2 (d, JPC ) 9, C6-ArOMe), 127.1 (d, JPC ) 50,
C1-ArSO3), 125.6 (s, C5-ArOMe), 121.0 (d, JPC ) 11, C4-ArOMe),
116.3 (d, JPC ) 52, C1-ArOMe), 111.8 (d, JPC ) 5, C3-ArOMe),
55.6 (s, OMe), 39.6 (s, CMe3), 35.1 (s, CH2CMe3), 32.4 (s, CMe3),
21.5 (s, Me-ArSO3). 31P{1H} NMR (CD2Cl2): δ 25.7 (s). Anal.
Calcd for C31H36NO5PPdS: C, 55.40; H, 5.40; N, 2.08. Found: C,
55.15; H, 5.29; N, 1.98.
14, C2-ArSO3), 139.0 (s, p-py), 138.5 (d, JPC ) 8, C3-ArSO3), 135.6
(d, JPC ) 2, C6-ArSO3), 133.8 (d, JPC ) 2, m-py), 131.1 (s, C4-
ArSO3), 127.8 (d, JPC ) 9, C6-ArOMe), 127.6 (s, C5-ArSO3), 126.9
(d, JPC ) 88, C1-ArSO3), 125.7 (d, JPC ) 2, C5-ArOMe), 120.9 (d,
JPC ) 13, C4-ArOMe), 116.8 (d, JPC ) 55, C1-ArOMe), 111.9 (d,
JPC ) 4, C3-ArOMe), 55.4 (s, OMe), 21.5 (s, Me-ArSO3), 7.0 (s,
[PO-OMe]Pd(CH2Ph)(py) (4a). A solution of cis-Pd(CH2Ph)2
(py)2 (0.864 g, 1.93 mmol) in CH2Cl2 (20 mL) was cooled to -78
°C. A solution of [PO-OMe]H (0.805 g, 1.93 mmol) in CH2Cl2
(34) Cámpora, J.; Conejo, M. D. M.; Mereiter, K.; Palma, P.; Pérez,
C.; Reyes, M. L.; Ruiz, C. J. Organomet. Chem. 2003, 683, 220.

6632 Organometallics, Vol. 26, No. 26, 2007
Vela et al.
for 1 h at room temperature. Pyridine (12.1 mL, 150 mmol) was
added, and the resulting pale yellow solution was stirred for 35
min. The mixture was concentrated to ca. 20 mL under vacuum,
and Et2O (100 mL) was added. A pale yellow precipitate formed
and was collected by filtration and purified twice by dissolution in
CH2Cl2 (20 mL) and precipitation with Et2O (100 mL). The final
product was dried under vacuum to give 6a as a white powder.
Figure 8. Numbering scheme used for NMR labeling.
1
Yield: 12.5g, 69%. H NMR (CD2Cl2): δ 8.75 (d, JHH ) 5, 2H,
(15 mL) was added dropwise. The dark solution was warmed to
room temperature and stirred for 1 h. The solvent was removed
under vacuum, and ether (20 mL) was added. The resulting
suspension was stirred for 10 min at room temperature and filtered
to afford a yellow solid. The solid was dried under vacuum, taken
up in CH2Cl2 (20 mL), filtered, concentrated under vacuum, and
cooled to -20 °C. Several crops of a bright yellow powder were
o-py), 7.94 (dd, JHH ) 6, JPH ) 5, 1H, H3-ArSO3), 7.87 (t, JHH
)
8, 1H, p-py), 7.70–7.52 (br, 4H, H4-ArOMe/H6-ArOMe), 7.50 (t,
JHH ) 7, 2H, m-py), 7.27 (d, JHH ) 8, 1H, H4-ArSO3), 7.11–6.97
(m, 5H, H6-ArSO3/H3-ArOMe/H5-ArOMe), 3.67 (s, 6H, OMe), 2.25
(s, 1H, CH3ArSO3), 0.23 (d, 3H, JPH ) 3, PdMe). 13C{1H} NMR
(CD2Cl2): δ 161.0 (s, C2-ArOMe), 150.7 (s, o-py), 146.3 (d, JPC
)
16, C2-ArSO3), 138.9 (d, JPC ) 8, C3-ArSO3), 138.6 (s, C6-ArSO3),
137.8 (br s, C4-ArOMe), 135.4 (s, p-py), 133.5 (s, m-py), 131.1 (s,
C4-ArSO3), 127.8 (d, JPC ) 8, C5-ArSO3), 127.5 (d, JPC ) 50, C1-
ArSO3), 125.4 (s, C5-ArOMe), 120.8 (d, JPC ) 12, C6-ArOMe),
116.7 (d, JPC ) 57, C1-ArOMe), 111.8 (s, C3-ArOMe), 55.6 (s,
OMe), 21.2 (s, CH3ArSO3), 0.27 (d, JPC ) 4, PdMe). 31P{1H} NMR
(CD2Cl2): δ 19.8 (s). ESI-MS (CH2Cl2/MeOH, 1:1 by volume,
positive ion scan, m/z): 616.0 (MH+).
1
obtained by filtration. Yield: 0.31 g (23%). Mp: 219 °C (dec). H
NMR (CD2Cl2): δ 8.47 (d, JHH ) 5, 2H, o-py), 7.86 (dd, JHH ) 8,
JPH ) 5, 1H, H3-ArSO3), 7.73 (m, 3H, p-py/H6-ArOMe), 7.58 (t,
JHH ) 7, 2H, m-py), 7.29 (t, JHH ) 6, 2H, H5-ArOMe), 7.27 (d,
JHH ) 8, 1H, H4-ArSO3), 7.15 (d, JPH ) 12, 1H, H6-ArSO3), 7.08
(t, JHH ) 7, 2H, H4-ArOMe), 7.01 (dd, JHH ) 8, JPH ) 4, 2H,
H3-ArOMe), 6.84 (t, JHH ) 7, 1H, p-CH2Ph), 6.73 (t, JHH ) 8, 2H,
m-CH2Ph), 6.40 (d, JHH ) 8, 2H, o-CH2Ph) 3.69 (s, 6H, ArOMe),
2.45 (d, JPH ) 5, 2H, CH2Ph), 2.25 (s, 3H, Me-ArSO3). 13C{1H}
NMR (CD2Cl2): δ 161.3 (s, C2-ArOMe), 151.0 (s, o-py), 146.4 (d,
JPC ) 15, C2-ArSO3), 138.9 (d, JPC ) 6, C3-ArSO3), 138.4 (m,
ipso-CH2Ph), 138.1 (s, C6-ArSO3), 135.6 (s, p-py), 133.9 (s, m-py),
131.2 (d, JPC ) 2, C5-ArSO3), 128.6 (s, o-CH2Ph), 128.3 (s,
m-CH2Ph), 128.0 (d, JPC ) 9, C6-ArOMe), 127.6 (s, C4-ArSO3),
125.3 (s, p-CH2Ph), 124.2 (s, C5-ArOMe), 121.2 (d, JPC ) 11, C4-
ArOMe), 116.2 (d, JPC ) 55, C1-ArOMe), 112.0 (d, JPC ) 4, C3-
ArOMe), 55.8 (s, OMe), 22.9 (s, CH2Ph), 21.5 (s, Me-ArSO3); the
C1-ArSO3 was not observed, probably due to overlap with signals
in the δ 124-128 region. 31P{1H} NMR (CD2Cl2): δ 20.7 (s). Anal.
Calcd for C33H32NO5PPdS: C, 57.27; H, 4.66; N, 2.02. Found: C,
57.41; H, 4.80; N, 2.04.
[PO-Et]Pd(Me)(py) (6b). A solution of [PO-Et]H (1.61 g, 3.90
mmol) and (TMEDA)PdMe2 (0.985 g, 3.90 mmol) in CH2Cl2 (40
mL) was cooled to -78 °C and stirred for 20 min. Pyridine (1.57
mL, 19.5 mmol) was added dropwise over 2 min. The mixture was
stirred at -78 °C for 30 min, warmed to room temperature, and
stirred for 45 min. A pale yellow solution formed. The volatiles
were removed under vacuum to afford a pale yellow solid. This
material was recrystallized from CH2Cl2/hexanes (1:1 by volume,
-30 °C, 4 days) to afford [PO-Et]Pd(Me)(py) as pale yellow
crystals, which were isolated by filtration, washed with hexanes,
and dried under vacuum. Yield: 0.980 g, 41%. 1H NMR (CD2Cl2):
δ 8.80 (m, 2H, H2-py), 8.05 (dd, JHH ) 8, JPH ) 5, 1H, H3-ArSO3),
7.88 (m, 1H, H4-py), 7.50 (m, 2H, H3-py), 7.4–7.2 all other aromatic
protons (broadened due to exchange), 6.85 (d, JPH ) 10, 1H, H6-
ArSO3), 3.22 (s, 2H, ArCH2CH3), 3.10 (s, 1H, ArCH2CH3), 2.77
(s, 1H, ArCH2CH3), 2.22 (s, 3H, CH3ArSO3), 1.58 (s, ArCH2CH3),
0.88 (s, ArCH2CH3), 0.40 (d, JPH ) 2, 3H, Pd-CH3). 13C{1H} NMR
(CD2Cl2): δ 150.7 (s, o-py), 148.5 (d, JPC ) 43, C1-ArEt), 147.2
(d, JPC ) 14, C2-ArSO3), 140.4 (d, JPC ) 8, C3-ArSO3), 138.8 (s,
C5-ArSO3), 136.3 (br, C6-ArEt), 135.2 (s, p-py), 134.1 (br s, C5-
ArEt), 132.3 (s, m-Py), 131.7 (d, JPC ) 43, C2-ArEt), 129.9 (br s,
C3-ArEt), 129.3 (d, JPC ) 9, C6-ArSO3), 126.8 (d, JPC ) 48, C1-
ArSO3), 126.4 (br s, C4-ArEt), 125.6 (s, C4-ArSO3), 29.0 (s,
ArCH2CH3), 28.0 (s, ArCH2CH3), 21.2 (s, CH3ArSO3), 15.6 (s,
ArCH2CH3), 13.9 (s, ArCH2CH3), 3.2 (s, Pd-CH3). 31P{1H} NMR
(CD2Cl2): δ 19.5 (s). ESI-MS (CH2Cl2/MeOH, 1:1 by volume,
positive ion scan, m/z): 612.0 (MH+). Anal. Calcd for
[PO-OMe]Pd(Me)(pyridazine) (5a). A suspension of [PdMe2
(pyridazine)]n (0.132 g, 0.610 mmol) in CH2Cl2 (15 mL) was cooled
to -78 °C, and a solution of [PO-OMe]H (0.254 g, 0.610 mmol)
in CH2Cl2 (15 mL) was added dropwise while the mixture was
stirred. The resulting bright yellow suspension was allowed to warm
to room temperature to afford a colorless solution. The solution
was stirred at room temperature for 1 h, concentrated to 4 mL, and
placed in a freezer at -20 °C. Several fractions of a microcrystalline
white solid were collected by filtration. Yield: 0.263 g (70%). Mp:
1
80 °C (dec). H NMR (CD2Cl2): δ 9.42 (br s, 2H, C4H4N2), 7.95
(dd, JHH ) 7.9, JPH ) 5, 1H, H3-ArSO3), 7.74 (br s, 2H, C4H4N2),
7.60 (br s, 2H, H6-ArOMe), 7.54 (t, JHH ) 8, 2H, H4-ArOMe),
7.28 (d, JHH ) 8, 1H, H4-ArSO3), 7.10 (d, JPH ) 12, 1H, H6-ArSO3),
7.03 (t, JHH ) 8, 2 H, H5-ArOMe), 6.97 (dd, JHH ) 8, JPH ) 5,
2H, H3-ArOMe), 3.66 (s, 6H, ArOMe), 2.26 (s, 3H, Me-ArSO3),
0.44 (d, JPH ) 2, 3H, Pd-Me). 13C{1H} NMR (CD2Cl2): δ 161.2
(d, JPC ) 2, C2-ArOMe), 153.5 (br s, C4H4N2), 146.4 (d, JPC ) 15,
C2-ArSO3), 139.1 (d, JPC ) 6, C6-ArSO3), 138.0 (br s, C5-ArSO3),
135.6 (d, JPC ) 2, C3-ArSO3), 133.7 (s, C5-ArOMe), 131.2 (s, C4-
ArSO3), 129.7 (br s, C4H4N2), 128.1 (d, JPC ) 9, C6-ArOMe), 127.7
(d, JPC ) 49, C1-ArSO3), 121.0 (d, JPC ) 11, C4-ArOMe), 116.9
(d, JPC ) 57, C1-ArOMe), 112.1 (d, JPC ) 5, C3-ArOMe), 55.9 (s,
ArOMe), 21.5 (s, Me-ArSO3), 3.6 (s, Pd-Me). 31P{1H} NMR
(CD2Cl2): δ 22.2 (s). Anal. Calcd for C26H27N2O5PPdS: C, 50.62;
H, 4.41; N, 4.54. Found: C, 50.31; H, 4.46; N, 4.53.35
1
C29H32NO3PPdS(0.12CH2Cl2) (CH2Cl2 content determined by H
NMR): C, 56.75; H, 5.57; N, 2.20. Found: C, 56.77; H, 5.13; N,
2.13.
[PO-OMe]Pd(Me)(PPh3) (7a). A solution of (TMEDA)PdMe2
(0.129 g, 0.511 mmol) and PPh3 (0.134 g, 0.511 mmol) in CH2Cl2
(5 mL) was cooled to -78 °C, and a solution of [PO-OMe]H (0.213
g, 0.511 mmol) in CH2Cl2 (10 mL) was added dropwise while the
mixture was stirred. The mixture was allowed to warm to room
temperature and was stirred for 2 h. The solvent was removed under
vacuum to give an off-white solid. The solid was recrystallized
from a mixture of CH2Cl2 (8 mL) and hexanes (2 mL) at -20 °C.
Yield: 0.160 g (39%). Mp: 174.3 (dec). 1H NMR (CD2Cl2): δ 7.90
(dd, JHH ) 8, JPH ) 6, 1H, H3-ArSO3), 7.68 (m, 6H, PPh3/H6-
ArOMe), 7.44 (m, 13H, PPh3/H4-ArOMe), 7.28 (dd, JHH ) 8, JPH
) 1, 1H, H4-ArSO3), 7.06 (dd, JPH ) 9, JPH ) 2, 1H, H6-ArSO3),
7.00 (t, JHH ) 8, 2H, H5-ArOMe), 6.96 (dd, JHH ) 88, JPH ) 5,
2H, H3-ArOMe), 3.67 (s, 6H, ArOMe), 2.24 (s, 3H, Me-ArSO3),
-0.12 (t, JPH ) 6, 3H, Pd-Me). 13C{1H} NMR (CD2Cl2): δ 161.3
[PO-OMe]Pd(Me)(py) (6a). A solution of (TMEDA)PdMe2
(7.37 g, 29.2 mmol) in CH2Cl2 (130 mL) was prepared, and [PO-
OMe]H (12.2 g, 29.2 mmol) was added. The mixture was stirred
(35) The reaction of 5a with B(C6F5)3 does not result in pyridazine
abstraction, but rather proceeds by methide abstraction to yield
[MeB(C6F5)3]-, which was identified by NMR and ESI-MS, and unidentified
Pd products.

Ethylene Polymerization by Palladium Alkyl Complexes
Organometallics, Vol. 26, No. 26, 2007 6633
(d, JPC ) 4, C2-ArOMe), 146.7 (d, JPC ) 16, C2-ArSO3), 139.4 (d,
JPC ) 6, C3-ArSO3), 137.8 (br s, PPh3), 135.9 (d, JPC ) 4, C6-
ArSO3), 135.2 (d, JPC ) 13, PPh3), 133.4 (s, C4-ArSO3), 131.2 (d,
JPC ) 2, C5-ArSO3), 131.0 (d, JPC ) 2, C6-ArOMe), 128.9 (d, JPC
) 10, PPh3), 128.4 (d, JPC ) 53, C1-ArSO3), 127.9 (d, JPC ) 8,
C4-ArOMe), 121.0 (d, JPC ) 11, C5-ArOMe), 116.8 (d, JPC ) 46,
C1-ArOMe), 111.7 (d, JPC ) 5, C3-ArOMe), 55.8 (s, ArOMe), 21.5
(s, Me-ArSO3), 0.04 (d, JPC ) 4, Pd-Me). 31P{1H} NMR (CD2Cl2):
δ 27.3 (d, JPP ) 403), 7.90 (d, JPP ) 403, PPh3).
190 °C. Anal. Calcd for C52H62O10P2Pd2S2: C, 52.66; H, 5.27.
Found: C, 52.49; H, 5.22.
Generation of [PO-OMe]Pd(η3-CH2Ph) (10a). An NMR tube
was charged with [PO-OMe]Pd(CH2Ph)(py) (0.030 g, 0.043 mmol)
and B(C6F5)3 (0.022 g, 0.043 mmol), and CD2Cl2 (0.6 mL) was
added by vacuum transfer at -196 °C. The tube was warmed to
room temperature and shaken to dissolve the solids. NMR spectra
were obtained after 1 h and showed that [PO-OMe]Pd(η3-CH2Ph)
and B(C6F5)3(py) had formed. 1H NMR (CD2Cl2): δ 8.40 (br s,
B(C6F5)3(py).36 Pyridine (0.280 mL, 3.50 mmol) was added by
syringe to a solution of B(C6F5)3 (0.598 g, 1.17 mmol) in CH2Cl2
(10 mL) at room temperature. The solution was stirred for 30 min.
The solvent was removed under vacuum to afford an oily white
product. This product was recrystallized from CH2Cl2/hexanes (3:8
by volume) at room temperature to afford large colorless crystals
after 2 days. The crystals were washed with hexanes and dried under
1H, Ar), 7.91 (m, 1 H, Ar), 7.55 (m, 5 H, Ar/Bn), 7.26 (d, JHH
)
8, 1H, Ar), 7.02 (m, 7 H, Ar/Bn), 6.78 (br s, 1H, Bn), 3.70 (s, 6H,
MeOPh), 2.58 (br s, 2H, CH2Bn), 2.18 (s, 3H, CH3ArSO3). 13C{1H}
NMR (CD2Cl2): δ 160.9 (d, JPC ) 5, ArOMe), 146.5 (d, JPC ) 16,
ArSO3), 141.7 (d, JPC ) 6, ArSO3), 135.8 (br s, ArSO3), 135.0 (s,
ArSO3), 133.7 (d, JPC ) 3, Bn), 133.5 (s, ArSO3), 131.6 (d, JPC
)
2, Bn), 130.4 (d, JPC ) 5, ArSO3), 128.7 (d, JPC ) 45, ArSO3),
128.6 (d, JPC ) 9, ArOMe), 121.3 (d, JPC ) 10, ArOMe), 117.4
(d, JPC ) 52, ArOMe), 117.3 (br s, Bn), 111.6 (d, JPC ) 5, ArOMe),
55.9 (s, ArOMe), 39.7 (br s, JCH ) 154, Bn), 21.4 (s, Me-ArSO3).
31P{1H} NMR (CD2Cl2): δ 6.61 (s).
1
vacuum. H NMR (CD2Cl2): δ 8.60 (d, JHH ) 6, 2 H, o-py), 8.21
(t, JHH ) 8, 1 H, p-py), 7.71 (t, JHH ) 8, 2 H, m-py). 13C{1H}
NMR (CD2Cl2): δ 148.2 (d, JCF ) 250, C2-C6F5), 147.2 (s, o-py),
143.2 (s, p-py), 140.6 (d, JCF ) 249, C4-C6F5), 137.8 (d, JCF
)
248, C3-C6F5), 126.2 (s, m-py), 118.5 (br, C1-C6F5). 19F{1H} NMR
(CD2Cl2): δ -131.8 (d, JFF ) 38), -157.5 (t, JFF ) 38), -164.0
(t, JFF ) 38). 11B{1H} NMR (CD2Cl2): δ -3.7 (br s). Anal. Calcd
for C23H5BF15N: C, 46.74; H, 0.85; N, 2.37. Found: C, 46.63; H,
1.18; N, 2.26.
[PO-OMe]PdCl(py) (11a). A mixture of [1a]H (0.512 g, 1.23
mmol), CH2Cl2 (15 mL), and pyridine (0.25 mL, 3.1 mmol) was
stirred at room temperature. A solution of (COD)PdCl2 (0.351 g,
1.23 mmol) in CH2Cl2 (15 mL) was added dropwise, and the
mixture was stirred at room temperature for 1 h. The solvent was
removed under vacuum to afford an orange solid. The solid was
dissolved in CH2Cl2 (30 mL), and the solution was washed with
H2O (2 × 10 mL), dried over MgSO4, filtered, and dried under
vacuum. The resulting solid was recrystallized from CH2Cl2/hexanes
(3:1 v/v) to afford several crops of orange crystals, which were
identified as [PO-OMe]PdCl(py) · (1/3CH2Cl2) by 1H NMR and
{[PO-OMe]Pd(CH2SiMe3)}2 (8a). A resealable NMR tube was
charged with [PO-OMe]Pd(CH2SiMe3)(py) (0.0320 g, 0.0465
mmol) and B(C6F5)3 (0.0238 g, 0.0465 mmol), and CD2Cl2 (0.5
mL) was added by vacuum transfer at -196 °C. The tube was
warmed to room temperature and agitated, producing a dark yellow
solution. The tube was maintained at 21 °C for 12 h, during which
time a mixture of yellow crystals and a dark brown supernatant
1
elemental analysis. Yield: 0.688 g (56%) Mp: 195 °C (dec). H
1
formed. H NMR analysis showed that [PO-OMe]Pd(CH2SiMe3)
NMR (CD2Cl2): δ 8.86 (m, 2H, py), 7.99 (m, 2H, H6-ArOMe),
7.88 (m, 2H, py, H3-ArSO3), 7.61 (t, JHH ) 7, 2H, py), 7.48 (t, JHH
) 6, 2H, H4-ArOMe), 7.36 (d, JHH ) 8, 1H, H4-ArSO3), 7.14 (d,
JHP ) 12, 1H, H6-ArSO3), 7.11 (t, JHH ) 6, 2H, H5-ArOMe), 6.98
(dd, JHH ) 8, JPH ) 5, 2H, H3-ArOMe), 3.71 (s, 6H, ArOMe),
2.29 (s, 3H, Me-ArSO3). 13C{1H} NMR (CD2Cl2): δ 161.0 (s, C2-
ArOMe), 150.5 (s, py), 144.1 (d, JPC ) 13, C2-ArSO3), 140.1 (d,
JPC ) 8, C3-ArSO3), 139.5 (s, py), 138.6 (d, JPC ) 11, C6-ArSO3),
135.4 (d, JPC ) 2, C4-ArSO3), 134.7 (d, JPC ) 2, py), 132.1 (d, JPC
(py) was completely consumed and that B(C6F5)3(py) and {[PO-
OMe]Pd(CH2SiMe3)}2 were present. The yellow crystals were
isolated by removal of the solvent by syringe under a stream of
nitrogen, washed with pentane (2 × 1 mL), dried under vacuum,
and identified as {[PO-OMe]Pd(CH2SiMe3)}2. Yield: 0.020 g
1
(71%). Mp: 190 °C (dec). H NMR (CD2Cl2): δ 7.9 (m, 3H, H6-
ArOMe/H3-ArSO3), 7.51 (t, JHH ) 8, 2H, H4-ArOMe), 7.27 (d,
JHH ) 8, 1H, H4-ArSO3), 7.17 (d, JPH ) 11, 1H, H6-ArSO3), 7.03
(t, JHH ) 8, 2H, H5-ArOMe), 6.92 (dd, JPH ) 5, JHH ) 8, 2H,
H3-ArOMe), 3.57 (s, 6H, ArOMe), 2.25 (s, 3H, Me-ArSO3), 0.67
(br s, 2H, CH2SiMe3), -0.31 (s, 9H, CH2SiMe3). 13C{1H} NMR
(CD2Cl2): δ 160.9 (s, C2-ArOMe), 147.3 (s, C2-ArSO3), 135.4 (s,
C3-ArSO3), 134.0 (s, C6-ArSO3), 131.3 (s, C4-Ar-SO3), 129.0 (s,
C6-ArOMe), 128.9 (s, C5-ArSO3), 127.8 (d, JPC ) 53, C1-ArSO3),
126.6 (s, C5-ArOMe), 121.2 (d, JPC ) 12, C4-ArOMe), 116.4 (d,
JPC ) 62, C1-ArOMe), 111.9 (d, JPC ) 4, C3-ArOMe), 55.6 (s,
ArOMe), 21.5 (s, Me-ArSO3), 12.0 (br s, CH2SiMe3), 1.69 (s,
CH2SiMe3). 31P{1H} NMR (CD2Cl2): δ 28.2 (br s). Anal. Calcd
for C26H33Cl2O5PPdSSi: C, 45.00; H, 4.79. Found: C, 44.85; H,
4.64.
) 2, C5-ArSO3), 127.4 (d, JPC ) 9, C6-ArOMe), 126.4 (d, JPC
57, C1-ArSO3), 125.5 (d, JPC ) 2, C5-ArOMe), 121.1 (d, JPC
13, C4-ArOMe), 114.8 (d, JPC ) 67, C1-ArOMe), 112.1 (d, JPC
)
)
)
5, C3-ArOMe), 56.1 (s, ArOMe), 21.6 (s, Me-ArSO3). 31P{1H}
NMR (CD2Cl2): δ 5.8 (s). Anal. Calcd for C26.3H25.7Cl1.7NO5PPdS:
C, 47.58; H, 3.89; N, 2.11. Found: C, 47.59; H, 3.91; N, 2.07.
Ethylene Polymerization. Ethylene polymerizations were per-
formed in a 300 mL stainless steel Parr autoclave equipped with a
water cooling loop, thermocouple, and magnetically coupled stirrer
and controlled by a Parr 4842 controller. In the glovebox, the
catalyst or catalyst precursors were weighed into a glass autoclave
liner. Anhydrous toluene (50 mL) was added. The liner was placed
in the autoclave, and the autoclave was assembled, brought out of
the box, and hooked to the controller and to an ethylene delivery
system. The reactor was heated to the desired temperature (typically
80 °C), and stirring (200 rpm) was started. The desired temperature
was usually reached after 12 min. The autoclave was maintained
at this temperature for 20 min to ensure complete dissoluton of the
catalyst. (Control experiments showed that complete dissolution
of the [PO]Pd(R)(py) complexes to make a 0.4 mM solution in
toluene occurs within ca. 12 min at 80 °C.) The reactor was
pressurized with ethylene, and the ethylene uptake was monitored
with a mass flow-meter. After the desired reaction time, the ethylene
flow was terminated and the pressure was released. The mixture
was cooled to room temperature, and the polymer was collected
by filtration, washed with boiling toluene, acetone, and hexanes
t
{[PO-OMe]Pd(CH2 Bu)}2 (9a). A solution of [PO-OMe]Pd
t
(CH2 Bu)(py) (0.643 g, 0.958 mmol) in CH2Cl2 (10 mL) was cooled
to -78 °C, and a solution of B(C6F5)3 (0.491 g, 0.958 mmol) in
CH2Cl2 (10 mL) was added slowly. The mixture was allowed to
warm to room temperature and was stirred for 1 h. The solvent
was removed under vacuum, and the resulting tan solid was rinsed
with benzene (2 × 10 mL) and hexanes (2 × 10 mL). The resulting
white solid was dried under vacuum. Yield: 0.292 g (51.4%). Mp:
(36) (a) Massey, M. A.; Park, A. J. J. Organomet. Chem. 1964, 2, 245.
(b) Duchateau, R.; Santen, R. A. V.; Yap, G. P. A. Organometallics 2000,
19, 809. (c) Sánchez-Nieves, J.; Frutos, L. M.; Royo, P.; Castaño, O.;
Herdtweck, E. Organometallics 2005, 24, 2004. (d) Focante, F.; Camurati,
I.; Resconi, L.; Guidotti, S.; Beringhelli, T.; D’Alfonso, G.; Donghi, D.;
Maggioni, D.; Mercandelli, P.; Sironi, A Inorg. Chem. 2006, 45, 1683. Note:
the NMR data reported in this reference differ from those reported here.

6634 Organometallics, Vol. 26, No. 26, 2007
Vela et al.
Table 2. X-Ray Diffraction Data for [PO-OMe]Pd(CH2SiMe3)(py) (2a), [PO-Et]Pd(Me)(py) (6b), and {[PO-OMe]Pd(CH2SiMe3)}2 (8a)
[PO-OMe]Pd(CH2SiMe3)(py) (2a)
[PO-Et]Pd(Me)(py) (6b)
{[PO-OMe]Pd(CH2SiMe3)}2 (8a)
formula
fw
C30H36NO5PPdSSi + 1.5 CH2Cl2
818.76 (including solvent)
C29H32NO3PPdS
611.99
C25H30O5PPdSSi + CH2Cl2
692.94 (including solvent)
cryst syst
space group
b (Å)
monoclinic
P21/c
18.043(3)
monoclinic
P21/c
22.544(4)
monoclinic
C2/c
23.794(5)
c (Å)
16.306(3)
14.590(5)
12.759(3)
ꢀ (deg)
104.454(3)
90.0
3496(1)
127.19(2)
90.0
2685(1)
100.44(3)
90.0
6276(2)
γ (deg)
V(Å3)
Z
4
4
8
T (K)
100
100
100
cryst color, habit
GOF on F2
R indices (I > 2σ(I))a
R indices (all data)a
clear, brick
1.023
R1 ) 0.0325, wR2 ) 0.0918
R1 ) 0.0366, wR2 ) 0.0936
clear, plate
1.155
R1 ) 0.0367, wR2 ) 0.0791
R1 ) 0.0418, wR2 ) 0.0815
clear, prism
1.082
R1 ) 0.0361, wR2 ) 0.0871
R1 ) 0.0374, wR2 ) 0.0881
a R1 ) ∑|Fo| - |Fc|/∑|Fo|; wR2 ) [∑[w(Fo - Fc ) ]/∑[w(Fo2)2]]1/2, where w ) q[σ2(Fo2) + (aP)2 + bP]-1
.
2
2 2
(10 mL each), and dried under high vacuum overnight. Unless
otherwise stated, all polymerizations proceeded under isothermal
conditions. Exotherms were avoided by using total palladium
concentrations below 0.4 mM for the in situ-generated catalysts
and below 0.2 mM for the discrete catalysts.
When less than 6 mg of catalyst was used (i.e., [Pd] < 0.1 mM),
the catalyst was introduced by means of a freshly prepared stock
solution. In this case, an aliquot of a solution of the catalyst in
CH2Cl2 (1 mg/mL) was added to the glass autoclave liner. The
liner was placed in a desiccator, and the CH2Cl2 was removed under
vacuum. Toluene was added to the liner, the reactor was assembled,
and the polymerization was carried out as described above.
Ethylene/1-Hexene Copolymerizations. The procedure de-
scribed above was used, but 1-hexene was added to the reactor via
a syringe port after the catalyst solubilization period, immediately
prior to pressurizing with ethylene.
Polymer Characterization. Gel permeation chromatography was
performed with a Polymer Laboratories PL-GPC 220 instrument
using 1,2,4-trichlorobenzene solvent (stabilized with 125 ppm BHT)
at 150 °C. A set of three PLgel 10 µm mixed-B LS columns was
used. Samples were prepared at 160 °C. Molecular weights were
determined by GPC using narrow polystyrene standards and are
corrected for linear polyethylene by universal calibration using the
Mark–Houwink parameters of Rudin: K ) 1.75 × 10-2 cm3/g and
R ) 0.67 for polystyrene and K ) 5.90 × 10-2 cm3/g and R )
0.69 for polyethylene.37,38
DSC measurements were performed on a TA Instruments DSC
2920 instrument. Samples (10 mg) were annealed by heating to
170 °C at 20 °C/min, cooled to 40 °C at 40 °C/min, and then
analyzed while being heated to 170 °C at 20 °C/min.
Analysis of the polymers by inductively coupled plasma (ICP)
atomic absorption revealed that ca. 50% of the initial palladium
content is present in the isolated polymers. The speciation of the
residual palladium is unknown, and the polymers themselves are
not active as ethylene polymerization catalysts.
Reaction of 9a with 6-Chloro-1-hexene. An NMR tube was
charged with 9a (0.0150 g, 0.0253 mmol) and hexamethylbenzene
(4.1 mg, 0.025 mmol, internal standard), and CD2Cl2 (0.5 mL) and
6-chloro-1-hexene (0.1518 mmol, 6 equiv) were added by vacuum
transfer at -196 °C. The mixture was warmed to room temperature
and shaken to afford a white suspension. The suspension gradually
became orange. After 19 h at room temperature, the volatiles were
vacuum transferred to a separate tube and analyzed by GC-MS,
which showed that a mixture of chlorohexenes (M+ ) 118, 4
isomers), undecenes (M+ ) 154, 6 isomers), and chloroundecenes
(M+ ) 188, 6 isomers) was present. The nonvolatiles were
suspended in CH2Cl2 (0.5 mL), and pyridine (0.1 mmol, 4 equiv)
was added. The mixture was warmed to room temperature, shaken
for 5 min to afford a red solution, extracted with hexanes (3 × 1
mL), and dried under vacuum to afford an orange solid. The orange
1
solid was dissolved in CD2Cl2 (0.5 mL) and analyzed by H and
31P{1H} NMR, which established that 11a was the major Pd species
present (>93%). The hexanes extract was concentrated under
vacuum to afford an oily white solid (10 mg), which was analyzed
by GC-MS, which showed that a mixture of chlorohexene oligomers
was present; MS (n ) number of 6-chloro-1-hexene units in the
oligomer): M+ ) 202 (n ) 2 + H - Cl; 11 isomers), 236 (n ) 2;
t
8 isomers), 272 (n ) 2 + CH2 Bu - Cl; 9 isomers), 306 (n ) 2 +
t
CH2 Bu - H; 8 isomers), 320 (n ) 3 +H - Cl; 9 isomers), 354 (n
t
) 3; 9 isomers), 390 (n ) 2 + CH2 Bu - Cl; 2 isomers, other
isomers are likely present but were not observed due to overlap
with peaks from trimers, which have much higher intensities), 424
t
(n ) 3 + CH2 Bu - H; 9 isomers); analogous n ) 4, 5 oligomers
were also observed.
Reaction of 9a with 6-Chloro-1-hexene in the Presence of
1-Chloropentane. An NMR tube was charged with 9a (0.0158 g,
0.0266 mmol), CD2Cl2 (0.5 mL), 6-chloro-1-hexene (0.0071 g,
0.0596 mmol), 1-chloropentane (0.0125 g, 0.117 mmol), and
tetramethylsilane (0.0028 g, 0.0263 mmol, internal standard). The
resulting suspension was shaken for 20 h at room temperature. The
volatiles were vacuum transferred to a separate tube and analyzed
by 1H NMR and GC-MS, which showed that 100% of the starting
1-chloropentane was present (relative to tetramethylsilane) along
with a mixture of chlorohexenes (4 isomers), undecenes (8 isomers),
and chloroundecenes (8 isomers). The nonvolatile fraction was
worked up, analyzed as described above, and found to contain a
mixture of 11a and chlorohexene oligomers similar to that observed
in the absence of 1-chloropentane.
X-Ray Crystallography. Crystallographic data are summarized
in Table 2, and full details are provided in the Supporting
Information. Data were collected on a Bruker Smart Apex diffrac-
tometer using Mo KR radiation (0.71073 Å). Direct methods were
used to locate many atoms from the E-map. Repeated difference
Fourier maps allowed recognition of all expected non-hydrogen
atoms. Following anisotropic refinement of all non-H atoms, ideal
H atom positions were calculated. Final refinement was anisotropic
for all non-H atoms and isotropic-riding for H atoms. ORTEP
diagrams are drawn with 50% probability ellipsoids. Specific
comments for each structure follow. 2a: Crystals of 2a were
obtained by crystallization at -20 °C. Two CH2Cl2 molecules are
present, one of which is disordered between two positions at a center
(37) Grinshpun, V.; Rudin, A. Makrom. Chem., Rapid Commun. 1985,
6, 219.
(38) Poly-ethylene-co-1-hexene copolymers have similar Mark-Hownik
parameters to those for polyethylene. See ref 37 and: (a) Spatorico, A. L.;
Coulter, B. J. Polym. Sci. Polym. Phys. 1973, 11, 1139. (b) Lin, F. C.;
Stivala, S. S.; Biesenberger, J. A. J. Appl. Polym. Sci. 1973, 17, 1073. (c)
Scholte, Th. G.; Meijerink, N. L. J.; Schofelleers, H. M.; Brands, A. M. G.
J. Appl. Polym. Sci. 1984, 29, 3763.

Ethylene Polymerization by Palladium Alkyl Complexes
Organometallics, Vol. 26, No. 26, 2007 6635
of symmetry. 6b: Crystals of 6b were obtained from CH2Cl2/
hexanes (1:1 v/v) at -30 °C. 8a: Crystals of 8a were obtained from
the reaction of 2a with B(C6F5)3 in CD2Cl2 at 21 °C. One CH2Cl2
molecule is present, which is disordered between two positions with
0.5 occupancy at each site.
Brian Goodall, Nathan Allen, and David Conner for assistance
with synthetic procedures, Francis Acholla for ICP analysis,
and Ian Steele for X-ray crystallography.
Supporting Information Available: Ligand synthesis proce-
dures, additional NMR data for complexes and polymers, and
crystallographic data for 2a, 6b, and 8a (cif files). This material is
available free of charge via the Internet at http://pubs.acs.org.
Acknowledgment. This work was supported by the National
Science Foundation-Grant Opportunities for Academic Liaison
with Industry (GOALI) program (NSF-CHE-0516950) and the
Department of Energy (DE-FG-02-00ER15036). We thank
OM700869C