Water-soluble complexes [(κ2-P,O-phosphinesulfonato)PdMe(L)] and their catalytic properties

Article abstract of DOI:10.1021/om9003225

Palladium(II) phosphinosulfonato methyl complexes [(PAO)PdMeL] (PΛO=κ²-P,O-2-(2-RC₆H₄) ₂PC₆H₄SO₃ with R = OMe (a), 2,6-(MeO)₂C₆H₃ (b)) rendered w

Full text of DOI:10.1021/om9003225

4072 Organometallics 2009, 28, 4072–4078
DOI: 10.1021/om9003225
Water-Soluble Complexes [(K2-P,O-Phosphinesulfonato)PdMe(L)] and
Their Catalytic Properties
‡
‡
,‡
Dao Zhang,†,‡ Damien Guironnet, Inigo Gottker-Schnetmann, and Stefan Mecking*
€
†Department of Chemistry, Fudan University, Handan Road 220 Shanghai, People’s Republic of China, and
‡Chair of Chemical Materials Science, Department of Chemistry, University of Konstanz,
Universita€tsstrasse 10, D-78457 Konstanz, Germany
Received April 27, 2009
Palladium(II) phosphinosulfonato methyl complexes [(P∧O)PdMeL] (P∧O=κ2-P,O-2-(2-RC6H4)2-
PC6H4SO3 with R=OMe (a), 2,6-(MeO)2C6H3 (b)) rendered water-soluble by monodentate ligands
L=tri(sodium phenylsulfonate)phosphine (TPPTS; 3a) and L=H2N(CH2CH2O)nMe (n = ca. 52, 4a,
4b) were prepared. While aqueous solutions of 3a are inactive toward ethylene, with 4a and,
particularly, 4b very small particles of ca. 20 nm size of linear polyethylene are obtained, as
anticipated. Catalyst activities and polymer molecular weights are low. This contrasts with the high
polymerization activity of the amine complexes 4a,b and polymer molecular weights obtained in
nonaqueous polymerizations in toluene. NMR spectroscopic studies reveal that the inactivity of 3a
(also observed in nonaqueous polymerizations) is due to a lack of dissociation of the sulfonated
phosphine from the Pd(II) center. The catalyst precursors 4a,b are stable in aqueous solutions, also
at elevated temperature (70 °C). Decomposition occurs upon addition of ethylene monomer in the
presence of water. These findings are supported by polymerization experiments with known lipophilic
analogues of 3 and 4.
Introduction
and 1-olefins can be copolymerized with electron-deficient
vinyl monomers such as acrylates,2 and polymerizations can
be carried out in aqueous systems to afford dispersions of
submicrometer particles.3 In comparison to traditional free-
radical routes,4 which are applied on a large scale for the
preparation of environmentally friendly coatings and paints,
catalytic polymerizations enable a control of polymer micro-
structure. A general prerequisite for obtaining submicrom-
eter particles is a high degree of dispersion of the initial
reaction mixture. For the more common lipophilic catalyst
precursors, this can be provided by mini-3 or microemul-
sions.5 An alternative approach are water-soluble catalyst
precursors.6 Due to an efficient nucleation, nanoparticles
with sizes of only ca. 10 to 30 nm ; a size range that is
challenging to access by any given polymerization type7 ;
and unique morphologies are obtained.6d,8 These particles
can, for example, contribute to a fundamental understanding
of crystallization in confinement, crystallinity can be a
Olefin polymerization by cationic complexes of d8 metals
(late transition metals) has been studied intensely in the past
decade.1 These catalysts are much more tolerant toward
polar reagents in general by comparison to their highly
oxophilic early transition metal counterparts. Thus, ethylene
*Corresponding author. E-mail: stefan.mecking@uni-konstanz.de.
(1) (a) Ittel, S. D.; Johnson, L. K.; Brookhart, M. Chem. Rev. 2000,
100, 1169–1203. (b) Gibson, V. C.; Spitzmesser, S. K. Chem. Rev. 2003, 103,
283–316. (c) Mecking, S. Coord. Chem. Rev. 2000, 203, 325–351. (d)
Mecking, S. Angew. Chem Int. Ed. 2001, 40, 534–540. (e) Guan, Z.
Chem.;Eur. J. 2002, 8, 3086–3092. (f) Domski, G. J.; Rose, J. M.; Coates,
G. W.; Bolig, A. D.; Brookhart, M. Prog. Polym. Sci. 2007, 32, 30–92. (g)
Berkefeld, A.; Mecking, S. Angew. Chem., Int. Ed. 2008, 47, 2538–2542.
(h) Blank, F.; Janiak, C. Coord. Chem. Rev. 2009, 253, 827–861.
(2) (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. (c) Johnson, L.; Wang, L.;
McLain, S.; Bennett, A.; Dobbs, K.; Hauptman, E.; Ionkin, A.; Ittel, S.;
Kunitsky, K.; Marshall, W.; McCord, E.; Radzewich, C.; Rinehart, A.;
Sweetman, K. J.; Wang, Y.; Yin, Z.; Brookhart, M. ACS Symp. Ser. 2003,
857, 131–142. (d) Popeney, C. S.; Camacho, D. H.; Guan, Z. J. Am. Chem.
Soc. 2007, 129, 10062–10063.
(5) Monteil, V.; Wehrmann, P.; Mecking, S. J. Am. Chem. Soc. 2005,
127, 14568–14569.
(6) (a) Kolb, L.; Monteil, V.; Thomann, R.; Mecking, S. Angew.
(3) (a) Bauers, F. M.; Mecking, S. Angew. Chem., Int. Ed. 2001, 40,
3020–3022. (b) Soula, R.; Novat, C.; Tomov, A.; Spitz, R.; Claverie, J.;
Drujon, X.; Malinge, J.; Saudemont, T. Macromolecules 2001, 34, 2022–
2026.
€
Chem., Int. Ed. 2005, 44, 429–432. (b) Gottker-Schnetmann, I.; Korthals, B.;
Mecking, S. J. Am. Chem. Soc. 2006, 128, 7708–7709. (c) Korthals, B.;
€
Gottker-Schnetmann, I.; Mecking, S. Organometallics 2007, 26, 1311–
(4) (a) Distler, D. Wa€ssrige Polymerdispersionen; VCH: Weinheim,
1999. (b) Lovell, P. A.; El-Aasser, M. S. Emulsion Polymerization and
Emulsion Polymers; Wiley: Chichester, U.K., 1997. (c) Urban, D.;
Takamura, K. Polymer Dispersions and their Industrial Applications;
Wiley-VCH: Weinheim, 2002. (d) Chemistry and Technology of Emulsion
Polymerisation; Van Herk, A., Ed.; Blackwell Publishing Ltd.: Oxford,
U.K., 2005. (e) Charleux, B.; Ganachaud, F. Polymerization in Aqueous
Dispersed Media. In Macromolecular Engineering; Matyjaszewski, K.,
Gnanou, Y., Leibler, L., Eds.; Wiley-VCH: Weinheim, 2007; Vol. 1, pp 605-
642.
1316. (d) Yu, S.-M.; Mecking, S. Macromolecules 2009, 42, 3669-
3673. For a slow suspension type polymerization cf.: (e) Wang, L.; Lu, R.
S.; Bau, R.; Flood, T. C. J. Am. Chem. Soc. 1993, 115, 6999–7000.
(7) (a) Candeau, F. In Polymerization in Organized Media; Paleos, C.
M., Ed.; Gordon and Breach Sci. Publ.: Philadelphia, 1992; pp 215-283. (b)
Antonietti, M.; Basten, R.; Lohmann, S. Macromol. Chem. Phys. 1995, 196,
441–466. (c) Pavel, F. M. J. Dispersion Sci. Technol. 2004, 25, 1–16.
(8) Weber, C. H. M.; Chiche, A.; Krausch, G.; Rosenfeldt, S.;
€
Ballauf, M.; Harnau, L.; Gottker-Schnetmann, I.; Tong, Q.; Mecking,
S. Nano Lett. 2007, 7, 2024–2029.
r
pubs.acs.org/Organometallics
Published on Web 06/25/2009
2009 American Chemical Society

Article
Organometallics, Vol. 28, No. 14, 2009 4073
source of anisotropy, and such particles can serve as crystal-
line mesoscopic building blocks for ultrathin films.9,10
For these studies, Ni(II) salicylaldiminato complexes
[(N∧O)NiMe(L)], which are rendered water-soluble by a
highly hydrophilic ligand L, were employed as catalyst pre-
cursors.6b,6c The resulting catalysts possess a limited lifetime
in highly disperse aqueous systems,6b and the polymeri-
zation of polar vinyl monomers such as acrylates suffers
from either low effectivity or rapid catalyst deactivation.11
An interesting class of catalysts in this context are neutral
Pd(II) complexes of chelating phosphinosulfonates.1g,12-18
Due to a much decreased propensity for β-hydride elimina-
tion19 by comparison to their cationic Pd(II) diimine coun-
terparts,20 they polymerize ethylene in a linear fashion.
Acrylates and various other vinyl comonomers,12,13,15,17
including even acrylonitrile,16a can be incorporated in linear
copolymers, and multiple insertions of acrylate observed in
acrylate homooligomerization possess the mechanistic char-
acteristics of an insertion polymerization of an electron-
deficient vinyl monomer.18 Polymerizations with these cat-
alysts in aqueous emulsions13,17 have also been reported to
afford dispersions of ethylene copolymers with acrylates13b
or norbornene.13a
analogue b, respectively, with [(tmeda)PdMe2] (tmeda = N,
N,N0,N0-tetramethylethylenediamine) afforded the tmeda-
bridged binuclear complexes 1a and 1b, respectively
(Scheme 1).13c Both compounds are slightly soluble in
CD2Cl2 and CDCl3 and highly soluble in DMSO-d6 (for
which the tmeda ligand can be exchanged18). They are stable
in the solid state but decomposed slowly in CD2Cl2 solution
at room temperature. Pyridine complexes13c,15b,18 2a,b were
prepared for comparison of their catalytic and spectroscopic
properties.
For the preparation of complexes of hydrophilic ligands L,
DMF was found to be a suitable solvent that enables reaction
of the starting materials despite their very different polarity
and consequently solubility in most solvents. Displacement
of tmeda from 1a and 1b, respectively, afforded complexes
3a, 4a, and 4b of the water-soluble phosphine TPPTS
(tri(sodiumphenylsulfonate)phosphine) and the amine
H2N(CH2CH2O)nMe (n=ca. 52). As anticipated, all three
compounds are sufficiently water-soluble (solubility >200
μmol/L) and stable in the solid state. Their identity was
1
established unambiguously by H, 13C, and 31P NMR and
elemental analysis (cf. Experimental Section). Only a single
isomer was observed regarding the arrangement of ligands at
the square-planar Pd(II) center for all three compounds.21
Key spectroscopic features (Table 1) are a single doublet
resonance for the Pd-CH3 hydrogen atoms (3JPH = 1.6 and
2.8 Hz, respectively) in 4a and 4b and accordingly a single
13C NMR resonance originating from the Pd-CH3 moiety
(2JPC 6.0 and 7.4 Hz, respectively) and a single 31P NMR
resonance at δ 19.18 (4a) and 20.51 (4b) ppm. Similarly, for
the TPPTS adduct 3a, a virtual triplet 1H resonance at δ 0.04
ppm (3JPH=6.4 Hz) for the methyl group and two 31P NMR
doublet resonances at δ 8.19 and 29.14 ppm coupling with
one another with 2JPP=402 Hz were observed. The observed
values of coupling constants 3JPH and 2JPP are in agreement
with a cis arrangement of the metal-bound methyl moiety
and the phosphine donors.
We now report the preparation and catalytic properties of
water-soluble neutral κ2-P,O-phosphinesulfonato Pd(II)
complexes.
Results and Discussion
Synthesis and Characterization of Complexes. Reaction of
the o-phosphinesulfonate a, and its more bulky substituted
(9) (a) Sommer, J.; Reiter, G. Adv. Polym. Sci. 2006, 200, 1–36. (b)
€
Reiter, G.; Castelein, G.; Sommer, J.-U.; Rottele, A.; Thurn-Albrecht, T.
Phys. Rev. Lett. 2001, 87, 226101-1 to -4. (c) Montenegro, R.; Antonietti,
M.; Mastai, Y.; Landfester, K. J. Phys. Chem. B 2003, 107, 5088–5094.
(10) (a) Tong, Q.; Krumova, M.; Mecking, S. Angew. Chem., Int. Ed.
€
2008, 47, 4509–4511. (b) Tong, Q.; Krumova, M.; Gottker-Schnetmann, I.;
Mecking, S. Langmuir 2008, 24, 2341–2347.
(11) (a) Waltman, A. W.; Younkin, T. R.; Grubbs, R. H. Organo-
Reactivity toward Ethylene. The behavior of aqueous
solutions of the novel water-soluble complexes toward ethy-
lene (40 atm) was studied. For comparison, polymerization
with these complexes in the absence of water, and nonaqu-
eous and aqueous polymerizations with their lipophilic
analogues 1a,b and 2a,b were carried out (Table 2). For
polymerizations in aqueous emulsions, the lipophilic catalyst
precursors were dispersed in the initial reaction mixture as a
mini-emulsion of a solution of the catalyst precursor in a
small amount of methylene chloride, analogous to refs 13a
and 13c. Overall, results of these comparative experiments
with the tmeda and pyridine complexes catalyst (entries 1 to
10) are in agreement with the previous notes of Claverie
et al.13 Polymerization in emulsion afforded polyethylene
dispersions, along with a substantial portion of coagulated
polymer. Formation of coagulate (amounting to half of the
amount of polymer formed) occurred particularly with the
tmeda-bridged complexes 1a,b, which are much less soluble
in methylene chloride versus their pyridine analogues. Poly-
mer yields and corresponding catalyst activities in aqueous
systems, as well as polymer molecular weights, are reduced
considerably versus nonaqueous polymerizations in toluene.
€
metallics 2004, 23, 5121–5123. (b) Berkefeld, A.; Drexler, M.; Moller,
H. M.; Mecking, S. J. Am. Chem. Soc. 2009, in press.
(12) Drent, E.; van Dijk, R.; van Ginkel, R.; van Oort, B.; Pugh, R. I.
Chem. Commun. 2002, 744–745.
(13) (a) Skupov, K. M.; Marella, P. M.; Hobbs, J. L.; McIntosh, L.
H.; Goodall, B. L.; Claverie, J. P. Macromolecules 2006, 39, 4279–4281.
(b) Claverie, J. P.; Goodall, B. L.; Skupov, K. M.; Marella, P. R.; Hobbs, J.
Polym. Prepr. 2007, 48, 191–192. (c) Skupov, K. M.; Marella, P. R. M.;
Simard, M.; Yap, G. P. A.; Allen, M.; Conner, D.; Goodall, B. L.; Claverie, J.
P. Macromol. Rapid Commun. 2007, 28, 2033–2038. (d) Skupov, K. M.;
Piche, L.; Claverie, J. P. Macromolecules 2008, 41, 2309–2310.
(14) (a) Allen, N. T.; Goodall, B. L.; McIntosh, L. H., III. U.S. Pat.
US2007049712A1. (b) Allen, N. T.; Goodall, B. L.; McIntosh, L. H., III.
Eur. Pat. EP1760086A2. (c) McIntosh, L. H., III; Allen, N. T.; Kirk, T.
C.; Goodall, B. L. Canadian Patent CA2556356A1. Goodall, B. L.;
Allen, N. T.; Conner, D. M.; Kirk, T. C.; McIntosh, L. H.III. Polym.
Prepr. 2007, 48, 202.
(15) (a) Luo, S.; Vela, J.; Lief, G. R.; Jordan, R. F. J. Am. Chem. Soc.
2007, 129, 8946–8947. (b) Vela, J.; Lief, G. R.; Shen, Z.; Jordan, R. F.
Organometallics 2007, 26, 6624–6635. (c) Weng, W.; Shen, Z.; Jordan, R. F.
J. Am. Chem. Soc. 2007, 129, 15450–15451.
(16) (a) Kochi, T.; Noda, S.; Yoshimura, K.; Nozaki, K. J. Am.
Chem. Soc. 2007, 129, 8948–8949. (b) Kochi, T.; Yoshimura, K.; Nozaki, K.
Dalton Trans. 2006, 25–27.
(17) (a) Liu, S.; Borkar, S.; Newsham, D.; Yennawar, H.; Sen, A.
Organometallics 2007, 26, 210–216. (b) Newsham, D. K.; Borkar, S.; Sen,
A.; Conner, D. M.; Goodall, B. L. Organometallics 2007, 26, 3636–3638. (c)
Borkar, S.; Newsham, D. K.; Sen, A. Organometallics 2008, 27, 3331–3334.
(18) Guironnet, D.; Roesle, P.; Runzi, T.; Gottker-Schnetmann, I.;
Mecking, S. J. Am. Chem. Soc. 2009, 131, 422–423.
(19) Haras, A.; Anderson, G. D. W.; Michalak, A.; Rieger, B.;
Ziegler, T. Organometallics 2006, 25, 4491–4497.
€
€
(21) No significant differences were observed in a 1H NMR spectrum
of complex 4a acquired in CD2Cl2 at -15 °C, which supports that indeed
the single resonance observed at room temperature originates from a
single isomer, rather than different isomers in rapid equilibrium.
(20) Johnson, L. K.; Killian, C. M.; Brookhart, M. J. Am. Chem. Soc.
1995, 117, 6414–6415.

4074 Organometallics, Vol. 28, No. 14, 2009
Zhang et al.
Scheme 1. Synthesis of Complexes
Table 1. Selected NMR Data of the Complexesa
1H NMR δ [ppm]
Pd-CH3
13C NMR δ [ppm]
solvent and
reference
complex
Pd-CH3
31P NMR δ [ppm]
1a
1b
2a
2b
3a
0.01
0.10 (s)
0.24 (s)
0.23 (d, JHP=2.1 Hz)
0.04 (vt, JHP=6.4 Hz)
1.40
1.24
CDCl3, this work
CDCl3, 13c
CD2Cl2, 18
CDCl3, 13c
CD3OD, this work
10.15(s)
21.54 (s)
16.90(s)
29.14 (d, JPP = 402 Hz),
8.19 (d, JPP = 402 Hz)
19.18 (s)
0.40 (d, JPC = 4 Hz)
1.30
0.43 (d, JPC = 4.3 Hz)
4a
4b
0.04 (d, JHP=2.8 Hz),
1.67 (br s, Pd-NH2)
-0.06 (d, JHP=1.6 Hz),
1.62 (br s, Pd-NH2)
-3.65 (d, JPC = 6.0 Hz)
-0.65 (d, JPC = 7.4 Hz)
CD2Cl2, this work
CD2Cl2, this work
20.51 (s)
a 25 °C; 1H: 400 MHz, 13C: 100.5 MHz, 31P: 161.8 MHz.
Table 2. Polymerization Results
solids
particle
size hΦ [nm]
entry n(Pd) (μmol) solvent T/°C time/min yield/g content/wt % TOF d Mne,f/g mol-1 Mw/Mn Tmg [°C]
χg
e
1
2
3
4
5
6
7
8
9
1a (100)
1a (25)
1b (56)
1b (8)
2a (110)
2a (20)
2b (56)
2b (30)
2b (30)
2b (5)
3a (100)
3a (50)
4a (43)
4a (41)
4b (20)
4b (20)
4b (20)
4b (20)
4b (40)
4b (13)
emuls.a
tolueneb
emuls.a
tolueneb
emuls.a
tolueneb
emuls.a
emuls.a
emuls.a
tolueneb
H2O c
100
80
80
80
100
80
100
100
80
260
25
60
10
300
60
120
60
60
30
60
60
60
65
60
60
1.31
8.80
0.42
9.57
1.27
9.97
1.60
0.38
0.56
6.51
trace
trace
0.040
2.55
0.020
0.070
0.048
0.011
0.087
16.50
0.63i
0.25
1.3
110
32000
473
274000
83
17 800
97
13 900 e
1 070 f
9.27
5.0
137
75%
171 k
139
163000e
420 f
140
53
71%
57%
77%
75%
n.d. j
73%
72%
18 800e,
2.48
4.50
3.05
5.12
134
124
n.d. j
130
137
1.6i
0.38
0.56
511 1 000 e/ 1 050 f
453
663
164
149
159
2 400 e
5 300 e
10
11
12
13
14
15
16
17
18
19
20
80
100
80
92 600
tolueneb
H2O c
100
0.021 i
33
2040
36
125
86
19
97
57 800
142
66%
n.d. j
tolueneb 100
H2O c
H2O c
H2O c
H2O c
H2O c
100
80
60
40
80
0.020
0.070
0.048
0.011
0.087
115
76
113
68%
53%
67%
n.d. j
20
660 f
60
60
480
45
24
1 210 f
123
135
62%
78%
23
tolueneb 100
20 400 e
2.24
a Polymerization conditions: 100 mL of H2O, 2.0 mL of CH2Cl2, 0.25 mL of hexadecane, 750 mg of SDS, 40 bar of C2H4, polymer obtained as latex.
b Polymerization conditions: 100 mL of toluene, 40 bar of C2H4. c Polymerization conditions: 100 mL of H2O, 750 mg of SDS, 40 bar of C2H4, polymer
obtained as nanoparticle dispersion. d mol[C2H4] ꢀ mol[Pd] -1 ꢀ h-1
.
e From GPC versus linear PE standards at 160 °C. f Determined by 1H NMR.
g Crystallinity, determined by DSC from the second heating cycle. h Volume average particle size determined by DLS. i Partial coagulation. j Not
determined. k Bimodal particle size distribution.
Monitoring of the catalyst activity via the uptake of ethylene
(determined by means of mass flow meters) revealed a
maximum activity after 10 to 20 min, which ceased comple-
tely after ca. 1 h.
No polymerization activity was observed for an aqueous
solution of the TPPTS complex, 3a (entry 11). To shed
light on the reactivity of 3a, solutions of the complex in
D2O (Figure 1) and also H2O/SDS were studied by NMR

Article
Organometallics, Vol. 28, No. 14, 2009 4075
Figure 1. High-field region of 1H NMR spectra (left) and 31P NMR spectra (right) of D2O solutions of 3a acquired at 25 °C (bottom)
and 75 °C (top). 1H chemical shifts are referenced to residual solvent signal (δ 4.72 ppm).
spectroscopy at ambient and elevated temperature. A single
resolved 1H triplet resonance is observed for the Pd-Me
moiety at room temperature; also a single set of 31P reso-
nances with a coupling constant typical for trans-arranged
phosphines is observed. Heating to 75 °C does not result in
any significant changes in the spectra. A slight broadening of
the Pd-Me resonance is indicative of somewhat increased
dynamics. Note that the apparent shift of the 1H resonance
with temperature results from referencing to the water
solvent signal, which varies with temperature. This observed
behavior of 3a contrasts with corresponding salicylaldimi-
Figure 2. High-field region of the 1H NMR spectra of com-
nato Ni(II) complexes [(N∧O)NiMe(TPPTS)], for which a
pounds 4a (left) and 4b (right) in DMSO-d6/D2O (v/v 2:1)
solutions at 25 and 70 °C. 1H chemical shifts are referenced to
residual undeuterated DMSO solvent signal (δ 2.54 ppm).
solvent-dependent dissociation of the phosphine was ob-
served. Displacement occurred increasingly in the order
CD3OD < DMSO-d6 < D2O.6b For 3a, no free phosphine
(δ -4.9) was observed in either solvent. Upon addition of
ethylene to D2O solutions of 3a, no evidence for chain
growth or any other reaction, e.g., decomposition of the
complex, was observed at either 25 or 75 °C. As a conclusion,
the lack of any observable catalytic activity with 3a in
aqueous solution even under 40 atm of ethylene (entry 12)
can be attributed to a hindered dissociation of the sulfonated
phosphine ligand. Note that, while this likely also contri-
butes to the lack of catalytic activity of 3a in an attempted
nonaqueous polymerization in toluene (entry 10), in this case
the low solubility of 3a in toluene even at high temperature
additionally hinders polymerization from occurring.
period of 45 min studied. Catalyst activities and molecular
weights of the polymers obtained resemble the observed
behavior of the corresponding tmeda and amine complexes,
1 and 2.
1H NMR spectra of solutions of 4a and 4b, respectively, in
solutions of DMSO-d6/D2O mixtures (v/v 2:1) at room
temperature and 70 °C revealed no evidence for decomposi-
tion or other reactions of the catalyst precursors with water
(Figure 2). Merely a very small amount of black solid,
presumably palladium black, was observed in solutions of
4b after acquisition of the NMR spectra.
By contrast, aqueous solutions of the water-soluble amine
complexes 4a and 4b displayed an, albeit low, activity for
ethylene polymerization (entries 13 and 15-19). A maximum
activity of 102 turnovers h-1 was observed with 4b at 80 °C in
a 1 h polymerization experiment (entry 16). Optically trans-
parent dispersions with a low content of ca. 20 nm particles
composed of low molecular weight material were obtained.
Comparison of experiments with different polymerization
times reveals that the catalyst is largely deactivated within 1 h
(entries 16 and 19). Accordingly, a black solid, presumably
elemental metal, was observed in the reaction mixture after
polymerization runs. The low productivity observed with
aqueous solutions of 4a and 4b is primarily due to a rapid
deactivation of the active species in the presence of water,
rather than to an insufficient activation. Thus, a very high
polymerization activity was observed with a nonaqueous
toluene solution of 4b, making the exothermic reaction
difficult to control (entry 20). Monitoring of the ethylene
consumption indicated stability of the catalyst over the
Upon addition of ethylene to the NMR tubes at room
temperature, no changes of the spectra were observed apart
from the signal of free ethylene. However, upon keeping the
NMR tube sample of 4b for ca. 5 min at 70 °C, formation of
palladium black was observed, along with the gradual dis-
appearance of the Pd-Me signal and the ingrowth of weak
signals of products of chain growth in the 1H NMR spectra.
4a reacted significantly slower than 4b, while the half-life of
4b based on disappearance of the Pd-Me signal was ca. 5 min
at 70 °C; for 4a, formation of an observable amount
of palladium black and of chain growth products required
ca. 20 min.
By comparison, in neat DMSO-d6 solutions in the absence
of water, 4a and 4b were much less reactive toward ethylene
also at 70 °C. Thus, disappearance of the Pd-Me signal of 4b
required ca. 1 h.
This decomposition in aqueous solutions contrasts with
the properties of neutral salicylaldiminato Ni(II) alkyl com-
plexes, for which detailed mechanistic studies revealed that

4076 Organometallics, Vol. 28, No. 14, 2009
Zhang et al.
Figure 3. Particle sizes and size distribution of polymer dispersions as determined by dynamic light scattering (173° backscattering).
Entry numbers refer to entries in Table 2.
Figure 4. (a) TEM image of polymer particles (Table 1, entry 9). (b) Electron diffraction on a particle.
decomposition in the presence of water (by hydrolysis) of
Ni-alkyl bonds is at most a minor deactivation pathway
even under chain growth conditions.22a An accelerated
decomposition in the presence of both ethylene and water
has been observed previously also for cationic diiimine
Pd(II) alkyl complexes.22b,23 Theoretical studies suggest the
possibility of Pd(II)-alkyl bond hydrolysis as well as Wack-
er-type reactions in this case.
micrographs are in agreement with particle sizes determined
by DLS. The larger particles obtained with lipophilic catalyst
precursor mini-emulsions are very thin platelets (Figure 4).
Apart from thicker aggregates (three more electron dense
large particles in the center of Figure 4a), these platelets
(which partially overlap in Figure 4a) appear to possess a
very uniform thickness. This indicates that these are single
lamella crystalline particles.8 The small (<10 nm) electron
dense spots observed are likely Pd(0) nanoparticles formed
by decomposition of the catalyst. Electron diffraction of a
single particle confirms its crystalline nature (Figure 4b). For
the samples obtained with water-soluble catalyst precursors,
the low polymer content relative to the surfactant and Pd(0)
content in combination with the generally low contrast of
very small polymer particles hindered a detailed analysis of
particle structure from the TEM micrographs.
Polymer Microstructure and Particle Morphology. 1H and
13C NMR spectroscopy of the polymeric materials prepared
reveals an essentially linear structure, with a very low degree
of methyl branches (ca. 1 per 1000 carbon atoms), as
expected. Terminal as well as internal olefinic end groups
are both observed, in roughly similar amounts or with a
preference for the latter. The relatively low melting points of
some samples obtained in aqueous systems are a result of low
polymer molecular weight (e.g., entries 5 and 16).
DLS traces indicate a relatively broad particle size dis-
tribution both for the dispersion of very small particles
obtained with aqueous catalyst precursor solutions and
for large polyethylene particles originating from mini-
emulsions of lipophilic catalyst precursors (Figure 3). TEM
Conclusions
The coordination of sulfonated phosphine (TPPTS) or
poly(ethylene glycol)-substituted amine to the (κ2-P,O-phos-
phinesulfonato)PdMe fragment affords stable water-soluble
complexes, which were isolated in high yield and fully
characterized by NMR spectroscopy. While the TPPTS
complex is inactive toward ethylene due to hindered phos-
phine dissociation, aqueous solutions of the amine com-
plexes polymerize ethylene to ca. 20 nm particles of low
molecular weight linear polyethylene. Catalyst productivity
is low, in contrast to polymerization with these catalyst
(22) (a) Berkefeld, A.; Mecking, S. J. Am. Chem. Soc. 2009, 131,
1565–1574. (b) Held, A.; Mecking, S. Chem.;Eur. J. 2000, 6, 4623–4629.
€
(23) (a) Hristov, I. H.; DeKock, R. L.; Anderson, G. D. W.; Gottker
genannt Schnetmann, I.; Mecking, S.; Ziegler, T. Inorg. Chem. 2005, 44,
€
7806–7818. (b) DeKock, R. L.; Hristov, I. H.; Anderson, G. D. W.; Gottker
genannt Schnetmann, I.; Mecking, S.; Ziegler, T. Organometallics 2005, 24,
2679–2687.

Article
Organometallics, Vol. 28, No. 14, 2009 4077
precursors in the absence of water, due to a rapid deactiva-
tion in the aqueous system.
CD3OD): δ 161.1 (d, JPC = 2.6 Hz), 147.3 (d, JPC = 15.4 Hz),
145.9 (d, JPC=15.4 Hz), 136.9 (br m), 136.6 (d, JPC=13.6 Hz),
135.4 (d, JPC=3.3 Hz), 133.3 (s), 131.2 (d, JPC=12.6 Hz), 130.4
(d, JPC = 2.5 Hz), 130.1 (d, JPC = 2.1 Hz), 130.0 (d, JPC = 2.5
Hz), 129.5 (d, JPC=6.3 Hz), 129.1 (s), 128.8 (d, JPC=10.4 Hz),
128.4 (s), 127.1 (d, JPC=7.4 Hz), 120.7 (d, JPC=10.7 Hz), 115.4
(d, JPC=48.9 Hz), 111.3 (d, JPC=4.3 Hz), 55.0 (s, OCH3), 0.43
(d, JPC = 4.3 Hz, Pd-CH3). 31P{1H} NMR (162 MHz, 25 °C,
CD3OD): δ 29.14 (d, JPP = 402 Hz), 8.19 (d, JPP = 402 Hz).
Anal. Calcd for C39H33Na3O14P2PdS4 (M = 1091.27 g mol-1):
C 42.92, H 3.05. Found: C 41.81, H 2.98.
Experimental Section
Materials and General Considerations. Unless noted other-
wise, all manipulations of metal complexes were carried out
under an inert atmosphere using standard glovebox or Schlenk
techniques. Toluene and diethyl ether were distilled from so-
dium/benzophenone, and methylene chloride and DMF from
CaH2 under argon. Hexadecane was degassed by sparging
with argon. Demineralized water was distilled under a nitrogen
atmosphere and degassed three times after distillation. Pyridine
was distilled from CaH2. TPPTS supplied by Fluka and
H2N(CH2CH2O)nMe (n = ca. 52) supplied by Aldrich were
used as received. [(TMEDA)PdMe2],24 the phosphinesul-
fonates a,b,12,13 and their corresponding palladium complexes
1a,2a18 and 1b,2b13c were prepared according to published
procedures.
[K2-P,O-2-{Di(2-methoxyphenyl)phosphino}benzenesulfona-
to]methyl{monoaminomonomethoxypoly(ethyleneoxide)}palladium-
(II) (4a). To a mixture of 1a (54 mg, 46 μmol) and H2N
(CH2CH2O)nMe (200 mg, 100 μmol) in a septum-capped
Schlenk tube (25 mL) was added DMF (5 mL) via syringe at
20 °C with stirring under argon. After stirring the resulting
brown-yellow mixture for 1 h, the solvent was carefully removed
under vacuum. The crude residue was washed with diethyl ether
(3 ꢀ 10 mL) and dried under vacuum to afford a yellow powder
(213 mg, 84 μmol, 91% yield).
NMR spectra were recorded on a Varian Unity INOVA 400
spectrometer. Chemical shifts were referenced to the residual 1H
and 13C solvent resonances and to external 85% H3PO4 (31P),
respectively. Elemental analyses were performed up to 950 °C on
an Elementar Vario EL. For high-temperature NMR spectros-
copy of polyethylenes, a mixture of polymer and CDCl2CDCl2
in an NMR tube was heated to 115 °C, affording a homogeneous
solution. The tube was inserted into a preheated NMR probe at
115 °C, and NMR spectra were obtained after a 5 min tempera-
ture equilibration period. Methyl branches were quantified from
13C NMR spectra according to ref 25. Number average molec-
1H NMR (400 MHz, 25 °C, CD2Cl2): δ0.04 (d, JHP=2.8Hz,3H,
Pd-CH3), 1.67 (br s, 2H, NH2), 2.80 (br s, 2H,CH2CH2NH2), 3.08
(br s, 2H, CH2CH2-NH2), 3.34 (s, 3H, CH2CH2OCH3), 3.57-3.63
(m, (CH2CH2)n and OCH3), 3.75 (m, 4H, CH2CH2OCH3), 6.93 (m,
2H, Ar-H), 7.00 (m, 2H, Ar-H), 7.26 (m, 2H, Ar-H), 7.44 (m, 1H,
Ar-H), 7.51(m, 4H, Ar-H), 8.03 (m, 1H, Ar-H). 13C{1H} NMR
(100.5 MHz, 25 °C, CD2Cl2): δ 160.7 (d, JPC = 2.5 Hz), 148.6 (d,
JPC = 15.4 Hz), 137.7 (br s), 134.8 (d, JPC = 2.1 Hz), 133.2 (d, JPC
=
1.8 Hz), 130.1(d, JPC = 2.3 Hz), 128.5 (d, JPC = 7.0 Hz), 128.0 (d,
JPC = 48.8 Hz), 127.6 (d, JPC = 8.4 Hz), 120.6 (d, JPC = 11.7 Hz),
116.4 (d, JPC = 55.5 Hz), 111.4 (d, JPC = 4.5 Hz), 72.1 (s), 71.1 (s),
70.7 (br m), 58.8 (s), 55.3 (s), 42.9 (d, JPC = 1.6 Hz, H2NCH2-),
-3.65 (d, JPC = 6.0 Hz, Pd-CH3). 31P{1H} NMR (162 MHz, 25 °C,
CD2Cl2): δ 19.18 (s). Anal. Calcd. for C126H234NO57PPdS (M =
2844.64 g mol-1): C 53.20, H 8.29, N 0.49. Found: C 52.88, H 8.89,
N 0.54.
1
ular weights (Mn) were estimated from H NMR spectra for
lower molecular weight samples. Gel permeation chromatogra-
phy (GPC) was carried out in 1,2,4-trichlorobenzene at 160 °C
on a Polymer Laboratories 220 instrument equipped with Olexis
columns with differential refractive index, viscosity, and light
scattering (15° and 90°) detectors. Data reported were deter-
mined via universal calibration (for samples with Mn < 105
g mol-1) and triple detection (Mn>105 g mol-1). Both methods
were in good agreement with one another. Differential scanning
calorimetry (DSC) was performed on a Netzsch Phoenix 204 F1
at a heating and cooling rate of 10 K min-1. DSC data reported
are from second heating cycles. Polymer crystallinities were
calculated on the basis of a melt enthalpy of 293 J g-1 for
100% crystalline polyethylene. Dynamic light scattering was
carried out on a Malvern Nano Zeta Sizer. For the determina-
tion of particle size, a few drops of a latex sample were diluted
with ca. 3 mL of water. TEM images were obtained on a Libra
120 Zeiss instrument. Samples were not contrasted.
[K2-P,O-2-{Di(2-(2,6-dimethoxyphenyl)phenyl)phosphino}-
benzenesulfonato]methyl{monoaminomonomethoxypoly(ethyle-
neoxide)}palladium(II) (4b). To a mixture of 1b (80 mg, 50 μmol)
and H2N(CH2CH2O)nMe (200 mg, 100 μmol) in a septum-
capped Schlenk tube (25 mL) was added DMF (5 mL) via
syringe at 20 °C with stirring under argon. After stirring of the
resulting brown-yellow mixture for 1 h, the solvent was carefully
removed under vacuum. The crude residue was washed with
diethyl ether (3 ꢀ 10 mL) and dried under vacuum to afford a
yellow powder (243 mg, 89 μmol, 89% yield).
1H NMR (400MHz, 25 °C, CD2Cl2): δ -0.06(d, JHP=1.6 Hz,
3H, Pd-CH3), 1.62 (br s, 2H, NH2), 1.92(br s, 2H, CH2CH2NH2),
2.82 (br s, 2H, CH2CH2NH2), 3.34 (s, 3H, CH2CH2OCH3), 3.40
(s, 6H, OCH3), 3.56 - 3.65 (m, (CH2CH2)n), 3.69 (s, 6H, OCH3),
6.28 (d, JHP = 8.4 Hz, 2H), 6.41 (d, J = 8.4 Hz, 2H), 6.99 (t,
JHP=8.0 Hz, 1H), 6.99-7.15 (m, 5H), 7.30 (t, JHP=8.0 Hz, 2H),
7.42 (t, JHP=8.0 Hz, 2H), 7.55 (t, JHP=8.0 Hz, 1H), 7.61-7.71
(m, 3H). 13C{1H} NMR (100.5 MHz, 25 °C, CD2Cl2): δ 157.6 (s),
148.7 (d, JPC=36.9 Hz), 141.1 (d, JPC=1.7 Hz), 140.0 (s), 136.2
(d, JPC = 8.3 Hz), 135.1 (s), 133.8 (d, JPC = 8.8 Hz), 129.9 (d,
JPC = 2.2 Hz), 129.7 (s), 128.7 (s), 127.9-127.8 (m), 127.5, 126.1
(d, JPC=9.1 Hz), 119.0 (d, JPC = 2.1 Hz), 103.2 (s), 72.1 (s), 71.7
(s), 70.7 (br m), 58.8 (s), 55.2 (s), 54.9 (s), 42.4 (s), -0.65 (d,
JPC = 7.4 Hz, Pd-CH3). 31P{1H} NMR (162 MHz, 25 °C,
CD2Cl2): δ 20.51 (s). Anal. Calcd for C140H246NO59PPdS
(M = 3056.88 g mol-1): C 55.01, H 8.11, N 0.46. Found: C
54.75, H 7.79, N 0.55.
Synthesis of Metal Complexes. [K2-P,O-2-{Di(2-methoxy-
phenyl)phosphino}benzenesulfonato]methyl{sodium tri(m-sulfo-
natophenyl)phosphine}palladium(II) (3a). To a mixture of 1a
(93 mg, 80 μmol) and TPPTS (90 mg, 160 μmol) in a septum-
capped Schlenk tube (25 mL) was added DMF (5 mL) via
syringe at 20 °C with stirring under argon. After stirring
the resulting brown-yellow mixture for 1 h, the solvent was
carefully removed under vacuum. The crude residue was washed
with CH2Cl2 (3 ꢀ 10 mL) and diethyl ether (3ꢀ5 mL) and dried
under vacuum to yield a white powder (166 mg, 152 μmol, 95%
yield).
1H NMR (400 MHz, 25 °C, CD3OD): δ 0.04 (vt, JPH = 6.4
Hz, 3H, Pd-CH3), 3.70 (s, 6H, OCH3), 7.04 (m, 4H, Ar-H), 7.31
(m, 1H, Ar-H), 7.41 (m, 3H, Ar-H), 7.50-7.59 (m, 6H, Ar-H),
7.83-7.87 (m, 3H, Ar-H), 7.97 (vt, J=8.0 Hz, 4H, Ar-H), 8.16
(vt, J=6.4 Hz, 3H, Ar-H). 13C{1H} NMR (100.5 MHz, 25 °C,
Variable-Temperature NMR Experiments. J. Young NMR
tubes were charged with solid complexes in a glovebox. Gen-
erally, 6 mg of 3a or 10 mg of 4a and 4b was dissolved in 500 μL
of solvent. The tube was sealed, taken out of the box, and
inserted into a preheated NMR probe at the desired tempera-
ture. NMR spectra were obtained after a 5 min temperature
(24) de Graaf, W.; Boersma, J.; Smeets, W. J. J.; Spek, A. L.; van
Koten, G. Organometallics 1989, 8, 2907–2917.
(25) (a) Randall, J. C. J. Macromol. Sci., Rev. Macromol. Chem. Phys.
1989, C29, 201–317. (b) Axelson, D. E.; Levy, G. C.; Mandelkern, L.
Macromolecules 1979, 12, 41–52.

4078 Organometallics, Vol. 28, No. 14, 2009
Zhang et al.
equilibration period. For NMR experiments with ethylene, the
J. Young NMR tube was charged with the solid complex
and solvent in the glovebox and closed. The tube was removed
from the box and connected with a three-way stopcock to
the Schlenk line and to the ethylene gas supply. The tube
was cooled to -78 °C in a dry ice/2-propanol bath and charged
with ca. 1 atm of ethylene by several pump-fill cycles. The
NMR tubes was sealed, warmed to room temperature, and
shaken briefly prior to recording NMR spectra. For NMR
experiments at elevated temperature, the tube was inserted into
a preheated NMR probe at the desired temperature and NMR
spectra were obtained after a 5 min temperature equilibration
period.
Ethylene Polymerizations. Ethylene polymerizations were
performed in a 100 mL stainless steel mechanically stirred (750
rpm) pressure reactor equipped with a heating/cooling jacket
supplied by a thermostat controlled by a thermocouple dipping
into the polymerization mixture. This setup enabled control of
polymerization temperature with an exotherm of <5 °C. A
valve controlled by a pressure transducer allowed for applying
and keeping up a constant ethylene pressure. The required flow
of ethylene, corresponding to ethylene consumed by polymeri-
zation, was monitored by a mass flow meter and recorded
digitally. Prior to a polymerization experiment, the reactor
was heated under vacuum to the desired reaction temperature
for 30-60 min and then backfilled with argon. After the desired
reaction time the reactor was rapidly vented and cooled to room
temperature.
tion, washed several times with methanol, and dried overnight
under vacuum at 50 °C.
For polymerization in aqueous emulsion, 80 mL of degassed
water was introduced to the reactor and heated to the desired
temperature with stirring, and ethylene pressure was applied in
order to presaturate the solution. The catalyst precursor, pre-
viously weighed into a Schlenk tube in the drybox, was dissolved
in 2 mL of dichloromethane and 0.25 mL of hexadecane (the
latter functions as a hydrophobe). This solution was added to 20
mL of an aqueous solution of 0.75 g of SDS. The biphasic
mixture was homogenized under an argon atmosphere by means
of an ultrasonic homogenizer (Bandelin HD2200 with KE76 tip,
operated at 120 W, 2 min). The resulting mini-emulsion was
cannula-transferred to the pressure reactor. The reactor was
flushed with ethylene, a constant ethylene pressure was then
applied, and the reaction mixture was brought rapidly to the
desired temperature. After the specified reaction time, the
reactor was vented and cooled. The emulsion was filtered
through glass wool. For determination of yields and for further
polymer analysis, a specified portion of the latex was precipi-
tated by pouring into excess methanol. The polymer was washed
three times with methanol, H2O, and acetone and dried over-
night under vacuum at 50 °C.
For polymerization in aqueous solution, 100 mL of an
aqueous solution of the catalyst precursor and 0.75 g of SDS
were introduced to the reactor, and the pressure reactor was
flushed with ethylene and further subjected to an identical
procedure to that described in the previous paragraph for
polymerization in emulsion.
For nonaqueous polymerizations, 90 mL of dry toluene was
added to the reactor, heated to the desired temperature with
stirring, and flushed and pressurized with ethylene three times.
The catalyst precursor, previously weighed into a Schlenk tube
in the glovebox, was dissolved in 10 mL of toluene and injected
into the reactor with a syringe. The reactor was closed, and a
constant ethylene pressure was applied. After the desired reac-
tion time, the reactor was cooled to room temperature and
vented. The reaction mixture was stirred with an excess volume
of methanol. The precipitated polymer was isolated by filtra-
Acknowledgment. We thank Marina Krumova for
TEM and Lars Bolk for high-temperature GPC and
DSC analysis of polyethylene. Financial support for
D.Z. by the Fudan University/University of Konstanz
scholar exchange program and Shanghai Leading Aca-
demic Discipline Project (B108) is gratefully acknowl-
edged.