Ethylene polymerization in supercritical carbon dioxide with binuclear nickel(ii) catalysts

Article abstract of DOI:10.1039/b912883b

A series of new, highly fluorinated neutral (κ²-N,O) chelated Ni(ii) binuclear complexes based on salicylaldimines bridged in p-position of the N-aryl group were prepared. The complexes are single-component catalyst precursors for ethylene poly

Full text of DOI:10.1039/b912883b

View Online / Journal Homepage / Table of Contents for this issue
This paper is published as part of a Dalton Transactions themed issue on:
Metal-catalysed Polymerisation
Guest Editors: Barbara Milani and Carmen Claver
University of Trieste, Italy and Universitat Rovira i Virgili, Tarragona, Spain
Published in issue 41, 2009 of Dalton Transactions
Image reproduced with permission of Eugene Chen
Articles published in this issue include:
PERSPECTIVES:
New application for metallocene catalysts in olefin polymerization
Walter Kaminsky, Andreas Funck and Heinrich Hähnsen,
Dalton Trans., 2009, DOI: 10.1039/B910542P
Metal-catalysed olefin polymerisation into the new millennium: a perspective outlook
Vincenzo Busico, Dalton Trans., 2009, DOI: 10.1039/B911862B
HOT PAPERS:
Activation of a bis(phenoxy-amine) precatalyst for olefin polymerisation: first evidence for an outer
sphere ion pair with the methylborate counterion
Gianluca Ciancaleoni, Natascia Fraldi, Peter H. M. Budzelaar, Vincenzo Busico and Alceo
Macchioni, Dalton Trans., 2009, DOI: 10.1039/B908805A
Palladium(II)-catalyzed copolymerization of styrenes with carbon monoxide: mechanism of chain
propagation and chain transfer
Francis C. Rix, Michael J. Rachita, Mark I. Wagner, Maurice Brookhart, Barbara Milani and James
C. Barborak, Dalton Trans., 2009, DOI: 10.1039/B911392D
Visit the Dalton Transactions website for more cutting-edge organometallic and catalysis research
www.rsc.org/dalton

PAPER
www.rsc.org/dalton | Dalton Transactions
Ethylene polymerization in supercritical carbon dioxide with binuclear
nickel(II) catalysts
Damien Guironnet, Tobias Friedberger and Stefan Mecking*
Received 30th June 2009, Accepted 1st September 2009
First published as an Advance Article on the web 21st September 2009
DOI: 10.1039/b912883b
2
A series of new, highly fluorinated neutral (k -N,O) chelated Ni(II) binuclear complexes based on
salicylaldimines bridged in p-position of the N-aryl group were prepared. The complexes are
single-component catalyst precursors for ethylene polymerization in supercritical carbon dioxide and
toluene. Solubility of the catalyst precursors in supercritical carbon dioxide is effected by a large
number of up to 18 trifluoromethyl groups per molecule. Semicrystalline polyethylene with a low degree
of branching is formed (ca. 10 branches/1000 carbon atoms). Polymer microstructures are independent
of the nature of the bridging moiety, while stability of the catalysts appears to differ.
emulsion systems this can be crucial for the control of nanoparticle
Introduction
size and structure.7d,e Concerning reactions in CO2, tailoring of the
Polymerization of olefins catalyzed by complexes of d8 metals
catalyst precursors to provide solubility in the reaction medium is
(late transition metals) has been investigated intensively recently.1
required.
In comparison to their early transition metal counterparts,
We now report binuclear salicylaldiminato Ni(II) methyl com-
they are much more tolerant towards functional groups in the
plexes soluble in dense CO2 and their polymerization properties.
substrates2a,b or reaction media.2c Thus, ethylene and 1-olefins can
be copolymerized with electron-deficient polar vinyl monomers,
such as e.g. acrylates3 or even acrylonitrile,4 and multiple insertion
of acrylates affords low molecular weight polyacrylate via an
insertion mechanism.5,6 Polymerization of ethylene and 1-olefins
can be carried out in oxygenated reaction media such as water7 or
dense carbon dioxide.8
Results and discussion
Synthesis of ligands and complexes
Most commonly, solubility of organic compounds and of catalysts,
in particular, in dense CO2 is brought about by longer perfluo-
roalkyl groups, as exemplified by the commercially available tris[3-
(perfluorooctyl)phenyl]phosphine. Introduction of such perfluoro
alkyl moieties is associated with considerable synthetic effort and
specific work up procedures. A convenient alternative can be
the introduction of a sufficiently large number of trifluoromethyl
groups. It is worth noting that such electron withdrawing groups
will also modify the electrophilicity of the metal center and conse-
quently catalytic properties (vide infra). The binuclear complexes
reported here are based on 3 differently bridged salicyladimine
ligands, 3a (benzidine bridge), 3b (methylene bridge) and 3c
(hexafluoroisopropylidene bridge).
Dianilines 1a (benzidine scaffold) and 1b (methylene bridge)
were prepared according to known procedures.18f 1c (hexaflu-
oroisopropylidene bridge) was obtained analogously by selec-
tive ortho-bromination of 4,4¢-diamino diphenyl 1,1,1,3,3,3-
hexafluoropropane, and subsequent Suzuki coupling with 3,5-
bis(trifluoromethyl)phenyl boronic acid in good yield (overall
yield: 63%). Condensation of the dianilines 1a–c with 3,5-
bis[3,5-bis(trifluoromethyl)phenyl] salicylaldehyde in toluene un-
der Dean–Starck conditions afforded the novel salicylaldimines
2a–c (Scheme 1). The crude products obtained upon solvent
evaporation were washed with methanol. The identity and purity
Dense carbon dioxide, that is liquid or supercritical CO2
(scCO2), possesses unique properties, such as the possibility of
variation of its density and solvent properties over a wide range.9
In polymerization processes and polymer processing, dense carbon
dioxide can be useful as a solvent or suspension medium.9b,10 It can
be removed conveniently by variation of the pressure, resulting
in a dry polymer powder. While free-radical polymerization in
dense CO2 has been studied most intensely,11 various examples
of coordination polymerization have been reported.12-14 Ethylene
polymerization has been studied in scCO2 with cationic palladium
2
diimine complexes8a–c as well as with neutral (k -N,O) nickel
complexes.8d,e
Current developments of late transition metal catalyzed olefin
polymerization have resulted in a renewed15 interest in neutral
Ni(II) complexes.16 This class of catalysts appears to be particularly
suited for polar (protic) reaction media.7,17 Substantial effort is
devoted to the finding of catalysts with increased polymerization
productivity. One approach studied are binuclear complexes,
which often polymerize with higher activities than their mononu-
clear analogues.18 The origin of this increased reactivity is ill-
understood, cooperative effects have been suggested to operate
in certain cases.18h Another aim of catalyst development is an
appropriate solubility in the specific reaction media. In aqueous
1
of the dianilines and di(salicylaldimines) were established by H,
13C NMR spectroscopy, mass spectrometry and elemental analysis
(see Experimental).
Reaction of the respective di(salicylaldimines) with 3 equiv-
alents of [(pyridine)2Ni(CH3)2] in cold diethylether suspension
Chair of Chemical Materials Science, Dept. of Chemistry, University
of Konstanz, 78464, Konstanz, Germany. E-mail: stefan.mecking@uni-
konstanz.de; Fax: +49 7531 885152; Tel: +49 7531 885151
This journal is
The Royal Society of Chemistry 2009
Dalton Trans., 2009, 8929–8934 | 8929
©

previously for other Ni(II)-Me salicylaldiminato complexes.16g,18f,19
Most characteristic are the high field nickel methyl resonances
1
around -1.0 ppm in the H NMR and -8 ppm in the 13C NMR
spectra. This unique resonance confirms that both metal centers
are magnetically identical in the binuclear structure, as expected.
Catalytic ethylene polymerization with binuclear (j2-N,O)
salicylaldiminato Ni(II) methyl pyridine complexes
Polymerization studies were performed in toluene as a reaction
medium (Table 1). In this case monitoring of the polymerization
via mass-flow meters, not possible with the set-up for polymeriza-
tion in supercritical fluids, gives insights on catalyst stability. The
mononuclear analogue 48d was studied as a catalyst precursor for
comparison (entries 1-7 and 1-8).
Scheme 1 Preparation of binuclear salicylaldimine ligands.
was found to be a viable route for the preparation of complexes
3a–c (Scheme 2). The relatively poor solubility of the ligand in
diethylether slows down the reaction. Consumption of the starting
material could be followed by a colour change (from yellow to dark
red), and by the evolution of methane. Decomposed excess Ni(II)
starting material was removed by filtration.
The novel catalyst precursors are active for ethylene poly-
merization at 50 ◦C under 40 bar ethylene pressure in toluene.
Independently of the bridge, activities observed were on the same
order as for the mononuclear analogue (3 ¥ 104 TO h-1 average in
a 30 min experiment). At a polymerization temperature of 70 ◦C,
higher polymerization rates were observed (Table 1). This is likely
associated with an enhanced dissociation of the pyridine donor.
At this temperature, the nature of the bridge does have a clear
effect on catalyst stability. Complexes 3a,b as well as 4 decomposed
rapidly. By contrast, 3c consumed ethylene steadily over the 30 min
duration of the experiment.
The polymers obtained are semicrystalline (c ~ 50%) with
a melt peak temperature in the range from 105 to 122 ◦C. A
relatively low number of methyl branches was detected by 13C
NMR spectroscopy (15 per 1000 carbon atoms) along with very
few ethyl branches (2 per 1000 carbon atoms). Note that these
branches result from ‘chain walking’,20 commonly observed with
late transition metal catalysts. In detail, the lowest branching
and highest polymer molecular weight was observed for 3c,
which can be related to the electron-withdrawing character of
the hexafluoropropylidine bridge. An increased electrophilicity is
2
Scheme 2 Preparation of (k -N,O) salicylaldiminato nickel-methyl pyri-
dine complexes.
All complexes are diamagnetic in solution as evidenced by sharp
resonances in the 1H and 13C NMR spectra. This suggests a square
planar coordination geometry of the nickel center, as reported
Table 1 Polymerization in toluenea
T/◦C
TOFc 103/h-1
Mn 103/g mol-1
Mw/Mn
Tme/◦C
c (%)
N
Me/1000Cf
NEt/1000Cf
d
d
e
Run
Complex
1-1
1-2
1-3
1-4b
1-5
1-6
1-7b
1-8b
3a
3a
3b
3b
3c
3c
4
50
70
50
70
50
70
50
70
18
64
20
25
29
91
32
70
23.0
3.8
25.1
2.6
38.9
12.7
14.3
8.3
2.4
3.1
2.8
3.9g
2.6
2.1
2.4
2.2
115
104
119
110
122
115
110
105
50
45
51
47
54
54
48
46
14
19
11
15
9
14
17
19
< 1
2
< 1
2
< 1
< 1
2
4
2
a Reaction conditions: 100 mL of toluene, p(ethylene) = 40 bar, t = 30 min, n(Ni) = 10 mmol. b n(Ni) = 5 mmol. c TOF in mol (C2H4) mol (Ni)-1 h-1.
d Determined by GPC. e Determined by DSC from second heat. f Determined by 13C NMR. g Bimodal distribution.
8930 | Dalton Trans., 2009, 8929–8934
This journal is
The Royal Society of Chemistry 2009
©

a
Table 2 Polymerization in scCO2
T/◦C
TOFe 103/h-1
Mn 103/g mol-1
Mw/Mn
Tmg/◦C
c (%)
N
Me/1000Ch
NEt/1000Ch
f
f
g
Run
Cat.
2-1b
2-2b
2-3
2-4b
2-5b
2-6
2-7
2-8
2-9
3a
3b
3b
3bc
3c
3c
3cc
4d
50
50
70
70
50
70
70
50
70
2.7
4.3
10.4
15.1
3.4
8.9
14.3
5.7
15.3
29.2
1.8
12.0
26.1
2.3
2.7
33.3
2.9
2.3
2.5
3.8
2.1
2.3
4.6
3.4
2.1
3.4
121
119
98
48
47
36
36
54
43
43
49
40
14
n.d.
17
17
9
14
14
5
< 1
n.d.
2
2
< 1
1
2
< 1
2
99
124
105
105
123
97
4d
10.9
19
a Reaction conditions: n(Ni) = 10 mmol, t = 30 min, m(CO2) = 45.5 g, m(C2H4) = 6 g. b m(C2H4) = 2 g. c n(Ni) = 5 mmol. d n(Ni) = 2.5 mmol. e TOF in
103 mol (C2H4) mol (Ni)-1 h-1. f Determined by GPC. g Determined by DSC from second heating. h Determined by 13C NMR.
known to reduce the tendency for b-H elimination, a key step of
both branch formation and chain transfer.16m
Experimental
Materials and general considerations
Polymerizations in scCO2 were performed in a high pressure
reactor equipped with sapphire windows, which enable a visual
monitoring of the reaction. Catalyst precursors were found to
dissolve at a moderate pressure in the supercritical fluid (50 ◦C, 35
MPa), to form a bright yellow-orange solution. After addition of
ethylene, an immediate onset of turbidity was observed due to the
precipitation of the polyethylene formed. Upon careful venting
of the reactor after the desired polymerization time, the polymer
was obtained directly as a dry powder. The binuclear complexes
polymerized ethylene in scCO2 with up to 104 TO h-1 at 70 ◦C
(Table 2). As previously observed for catalytic polymerization
of ethylene in dense carbon dioxide with other salicylaldimine
complexes,8d productivities are significantly decreased by com-
parison to polymerization in organic hydrocarbon solvent. A
possible explanation for these lower activities is an enclosure of
the intact catalyst in the precipitated polymer, which will also be
less swollen with solvent by comparison to toluene as a reaction
medium. Polymers prepared at 50 ◦C possess similar molecular
weights, degrees of branching, and melting properties as observed
in toluene. However, the reduction of polymer molecular weight
with increased reaction temperature is more pronounced in scCO2
than the organic solvent. It can be speculated that a coordinating
nature of CO2 contributes to chain transfer via an associative
mechanism.16h
Unless noted otherwise, all manipulations of metal complexes
were carried out under an inert atmosphere using standard
glovebox or Schlenk techniques. All glassware was flame-
dried under vacuum before use. Toluene and benzene were
distilled from sodium, diethylether from sodium/benzophenone
ketyl under argon. Ethylene (99.95%) and carbon dioxide
(99.9995%) supplied by Praxair and Air Liquide, respectively,
were used as received. All other solvents were commercial
grade. 4,4¢-diamino diphenyl 1,1,1,3,3,3-hexafluoropropane was
purchased from Aldrich. [(pyridine)2Ni(CH3)2] was synthesized
by a modified literature procedure21 and stored at -30 ◦C
in a glovebox. 3,5-bis[3,5-bis(trifluoromethyl)phenyl] salicyl-
aldehyde,22
3,3¢,5,5¢-tetrakis(3,5-bis(trifluoromethyl)-phenyl)-
4,4¢-diaminodiphenylmethane,18d
3,3¢,5,5¢-tetrakis-[3,5-
bis(trifluoromethyl)phenyl]benzidine,18d and complex 422 were
prepared according to reported procedures.
NMR spectra were recorded on a Varian Unity INOVA 400 or
1
on a Bruker Avance DRX 600 spectrometer. H and 13C NMR
chemical shifts were referenced to the solvent signal. NMR as-
signments were confirmed by 1H, 1H gCOSY, 1H, 13C gHSQC and
1H, 13C gHMBC experiments. Elemental analyses were performed
up to 950 ◦C on an Elementar Vario EL. High-temperature
NMR measurements of polyethylenes were performed in 1,1,2,2-
tetrachloroethane-d2 at 130 ◦C. Size exclusion chromatography
(GPC) was carried out in 1,2,4-trichlorobenzene at 160 ◦C at a
flow rate of 1 mL min-1 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 determined vs. polyethylene standards. Differential
scanning calorimetry (DSC) was performed on a Netzsch Phoenix
204 F1 at a heating rate of 10 K min-1. DSC data reported are from
second heating cycles. Polymer crystallinity was calculated based
on a melt enthalpy of 293 J g-1 for 100% crystalline polyethylene.
Summary and conclusion
Three novel highly fluorinated binuclear Ni(II) methyl pyridine
complexes of di(salicyladimines) bridged in the p-position of
the N-aryl moiety were prepared and characterized. These com-
pounds were found to be single-component catalyst precursors for
the polymerization of ethylene in supercritical carbon dioxide as a
reaction medium. A polymerization temperature of 70 ◦C resulted
in higher polymerization activities than at 50 ◦C, likely due to
enhanced pyridine dissociation, however at the expense of polymer
molecular weights, which was particularly pronounced in scCO2
by comparison to an organic reaction medium. Semicrystalline
polyethylene with a rather moderate degree of branching and
moderate molecular weight is formed invariable of the catalyst
structure. However, the bridging moiety does influence catalyst
stability over time, as observed for polymerization in toluene.
3,3¢,5,5,¢-Tetrabromo 4,4¢-diamino diphenyl
1,1,1,3,3,3-hexafluoropropane
To a suspension of tetra-n-butylammonium tribromide (17.31 g,
36 mmol) and calcium carbonate (3.59 g, 36 mmol) in 70 mL
of methanol was added a solution of 4,4¢-diamino diphenyl
1,1,1,3,3,3-hexafluoropropane (3.00 g, 9 mmol) in 30 mL of
This journal is
The Royal Society of Chemistry 2009
Dalton Trans., 2009, 8929–8934 | 8931
©

methanol, and the mixture was stirred at room temperature. The
colour changed from an initial orange to light green. After 12 h, the
solvent was removed in vacuo, and the residue was extracted with
hot toluene on a frit. The extract was concentrated to dryness and
washed twice each with water and methanol. The resulting crude
product was recrystallized from toluene as brown large needles. 1H
NMR (400 MHz, CDCl3): dH (ppm); 7.36 (s, 2 H, 3H), 4.76 (s, 2
H, NH2). 13C NMR (101 MHz, CDCl3) dC (ppm); 143.10, 133.32
acid were dissolved in 100 mL of toluene. The mixture was
degassed by several cycles of evacuating and back filling with inert
atmosphere. The mixture was stirred at 80 ◦C, and the pressure
was reduced until the solvent boiled. The mixture was kept at
80 ◦C for 12 h. The reaction mixture was concentrated, and to the
brown viscous residue was added 20 mL of methanol to afford the
precipitation of the desire product as a yellowish powder.
1
(C3), 123.97 (q, JCF = 287 Hz), 123.24, 108.13, 62.60 (septet,
=
[{(2,6-(3,5-(CF3)2C6H3)2-4-yl-C6H2)-N C(H)-(3,5-(3,5-
2JCF = 26.8, C5). Anal. calcd for C15H8Br4F6N2 (M = 649.24 g
(CF3)2C6H3)2-2-(OH)-C6H2)}2] (2a)
mol-1): C 27.72, H 1.24, N 4.32. Found: C 28.74, H 1.44, N 4.17.
Yield: 56%. 1H NMR (400 MHz, CDCl3): dH (ppm): 12.85 (2 H,
s), 8.21 (2 H, s), 8.07 (4 H, s), 8.03 (8 H, s), 7.94 (2 H, s), 7.92 (4 H,
s), 7.90 (8 H, s), 7.87 (2 H, s), 7.70 (2 H, s), 7.28 (2 H, s). MALDI-
TOF-MS: m/z 2090.2 ([M + H]+) Anal. calcd for C90H36F48N2O2
(M = 2089.2 g mol-1): C 51.74, H 1.74, F 43.65, N 1.34. Found: C
50.58, H 2.34, F 43.68, N 1.74.
3,3¢,5,5¢-Tetrakis(3,5-bis(trifluoromethyl)phenyl) 4,4¢-diamino
diphenyl 1,1,1,3,3,3-hexafluoropropane
=
[CH2{(2,6-(3,5-(CF3)2C6H3)2-4-yl-C6H2)-N C(H)-(3,5-(3,5-
To a mixture of 3,3¢,5,5,¢-tetrabromo 4,4¢-diamino diphenyl
1,1,1,3,3,3-hexafluoropropane (0.86 mmol, 0.56 g), 5 equiv. of
3,5-bis(trifluoromethyl)phenyl boronic acid (4.28 mmol, 1.10 g),
2.5 mol% [Pd(dba)2] (0.02 mmol, 12 mg), and 5 mol% triphenyl
phosphine (0.04 mmol, 11 mg) were added 20 mL of toluene,
5 mL of ethanol and 10 mL of a 2 M Na2CO3 aqueous solution
in a Schlenk flask under protective atmosphere. The suspension
was heated with vigorous stirring to 90 ◦C for 24 h. The resulting
biphasic mixture was stirred for 30 min under air (resulting in
formation of palladium black) and poured into a separatory
funnel, water and diethyl ether were added until all salts and
organic material dissolved. The aqueous phase was extracted with
additional 2 ¥ 25 mL of diethyl ether. The organic phases were
combined, and filtrated through a plug of silica to remove Pd
black. The solvents were removed under vacuum. The product
was dissolved in hot hexane and recrystallised slowly out of this
(CF3)2C6H3)2-2-(OH)-C6H2)}2] (2b)
1H NMR (400 MHz, CDCl3): dH (ppm): 12.72 (br. s, 2 H) 8.13 (s,
2 H), 7.98 (s, 4 H), 7.87 (s, 10 H), 7.81 (s, 10 H), 7.59 (d, JHH
4
=
4
2.3, 2 H), 7.45 (s, 4 H), 7.12 (d, JHH = 2.3, 2 H), 4.32 (s, 2 H).
13C NMR (101 MHz, CDCl3) dC (ppm): 169.54, 158.70, 143.88,
2
141.44, 140.60, 139.43, 138.37, 133.63, 132.93, 132.84 (q, JCF
=
2
2
33), 132.43 (q, JCF = 33), 131.87, 131.47 (q, JCF = 33), 131.45,
1
130.40, 130.12, 130.09, 129.68, 128.69, 126.90, 123.56 (q, JCF
=
273), 123.40 (q, 1JCF = 273), 123.22 (q, 1JCF = 273), 121.85, 121.58,
118.85, 40.85. MALDI-TOF-MS: m/z 2104.2 ([M + H]+) Anal.
calcd for C91H38F48N2O2 (M = 2103.2 g mol-1): C 51.97, H 1.82, F
43.36, N 1.33. Found: C 50.97, H 1.82, F 43.40, N 1.32.
=
[C(CF3)2{(2,6-(3,5-(CF3)2C6H3)2-4-yl-C6H2)-N C(H)-(3,5-(3,5-
(CF3)2C6H3)2-2-(OH)-C6H2)}2] (2c)
1
solution. Yield: 87%. H NMR (400 MHz, CDCl3): dH (ppm);
1
Yield: 75%. H NMR (600 MHz, CD2Cl2) dH (ppm): 12.52 (s,
7.84 (s, 4 H, 11-H), 7.81 (s, 8 H, 8-H), 7.18 (s, 4 H, 3-H), 3.77
(s, 4 H, NH2). 13C NMR (101 MHz, CDCl3) dC (ppm): 141.66 (s,
2 H), 8.16 (s, 2 H), 8.05 (s, 4 H), 7.89 (s, 16 H), 7.87 (br. s, 2 H,
OH), 7.71 (s, 4 H), 7.70 (d, 4JHH = 2.1, 2 H), 7.24 (d, 4JHH = 2.1,
2 H). 13C NMR (151 MHz, CD2Cl2) dC (ppm): 170.46, 159.01,
146.87, 141.76, 140.25, 138.89, 134.37, 133.28, 133.25, 132.73 (q,
2
C7), 140.56 (s, C1), 132.75 (s, C3), 133.06 (q, JCF = 33.7, C9),
1
129.76 (s, C8), 125.30 (s, C4), 123.40 (s, C2), 124.44 (q, JCF
=
287.5, C10) (q, 1JCF = 273.3, C6), 122.38 (septet, 3JCF = 3.5, C11),
63.82 (septet, 2JCF = 26.0, C5). Anal. calcd for C47H20F30N2 (M =
1182.63 g mol-1): C 47.73, H 1.70, N 2.37. Found: C 48.31, H 2.31,
N 2.32.
2JCF = 33), 132.68 (q, JCF = 33), 132.27, 132.04 (q, JCF = 33),
2
2
1
131.98, 130.74, 130.61, 130.14, 128.85, 127.37, 124.04 (q, JCF
=
273), 123.91 (q, 1JCF = 273), 123.62 (q, 1JCF = 273), 122.59, 122.16,
121.74, 119.16. MALDI-TOF-MS: m/z 2240.2 ([M + H]+). Anal.
calcd for C93H36F54N2O2 (M = 2239.2 g mol-1): C 49.88, H 1.62, F
45.82, N 1.25. Found: C 49.85, H 2.26, F 45.84, N 1.20
General procedure for the synthesis of (j2-N,O)-salicylaldiminato
nickel methyl pyridine complexes
5 mL of cold diethylether were added to a mixture of 3 equiv. of
[(pyridine)2NiMe2] and the respective difunctional salicylaldimine
in a 25 mL Schlenk tube under stirring. A slow evolution of
methane was observed within 15 to 30 min. The deep red mixture
was stirred for another 120 min at 25 ◦C. The solvent was removed
in vacuo. The residue was dissolved in a small amount of benzene
and filtered through a syringe filter. The volatiles were removed
by sublimation at -10 ◦C (crushed ice/sodium chloride) under
General procedure for condensation of anilines with
3,5-(bis(trifluoromethyl)phenyl) salicylaldehyde.
In a flask equipped with a Dean–Stark condenser, the aniline, the
aldehyde (1.1 equiv.) and a catalytic amount of p-toluenesulfonic
8932 | Dalton Trans., 2009, 8929–8934
This journal is
The Royal Society of Chemistry 2009
©

high vacuum (10-3 mbar) to yield quantitatively pure pyridine
complexes.
syringe in the glovebox. In a slight argon stream, solvent from
the reaction was pulled into the syringe several times, dissolving
and transferring to the reactor the catalyst precursor. The reactor
was closed and a constant ethylene pressure was applied. After the
desired reaction time, the reactor was rapidly vented and cooled
to room temperature. The reaction mixture was stirred with an
excess volume of methanol. The polymer was isolated by filtration,
washed several times with methanol, and dried in vacuo at 50 ◦C
=
[{[(2,6-(3,5-(CF3)2C6H3)2-4-yl-C6H2)-N C(H)-(3,5-(3,5-
(CF3)2C6H3)2-2-O-C6H2)-j2-N,O]Ni(CH3)(pyridine)}2] (3a)
Yield: 93%. 1H NMR (400 MHz, CD2Cl2) dH (ppm): 8.22 (s, 8 H),
7.90 (br. s, 4 H), 7.82 (s, 4 H), 7.72 (s, 6 H), 7.60 (s, 2 H), 7.57,
(s, 4 H), 7.07 (s, 2 H), 6.95 (s, 4 H), 6.90 (s, 2 H), 6.72, (s, 2 H),
6.58 (br. s, 2 H), 6.15 (br. s, 4 H), -0.89 (s, 6 H). Anal. calcd for
C102H50F48N4Ni2O2 (M = 2392.82 g mol-1): C 51.20, H 2.12, N
2.34. Found: C 51.89, H 2.29, N 2.17.
Polymerizations in supercritical carbon dioxide (scCO2)
The polymerizations in scCO2 were carried out in a high-pressure
view cell (NWA GmbH, Lo¨rrach, Germany). The stainless steel
cell has a variable internal volume between 30 and 60 cm3 tuneable
by means of a piston operated by a hydraulic system. The piston
material is a transparent sapphire which, together with a sapphire
view window on the opposite side of the cell, allows for visually
observing the contents of the cell. The cell contents can be agitated
by means of a magnetically coupled stainless steel mechanical
propeller stirrer. Heating is provided by means of two stainless steel
cartridge heaters lodged in cavities of the metallic body of the cell.
The temperature inside the cell is measured by a thermocouple,
and the pressure is monitored with a Bourdon type manometer.
The gases were introduced via high pressure pumps (up to 60
MPa for carbon dioxide and up to 40 MPa for ethylene) which
employ the corresponding cold condensed liquids as a reservoir.
The rate of the ethylene addition was controlled by a two way
HPLC valve, with an internal loop volume of 1 mL. The quantities
of gases introduced were estimated by the change in piston position
and the pressure. Prior to a polymerization experiment, the reactor
was heated under a low pressure of carbon dioxide (6 MPa) to the
desired reaction temperature for 30 to 60 min, and then flushed
3 times with carbon dioxide. The catalyst precursor was added as
a compressed pellet via a modified syringe to the empty reactor.
The reactor was closed and filled with carbon dioxide to the
desired pressure (10 MPa). Under continuous stirring the pressure
was increased (to 30 MPa) by decreasing the cell volume via the
piston, and the ethylene was added at constant pressure. After the
addition of the desired amount of monomer, polymerizations was
carried out at a pressure of 65 MPa, adjusted by moving the piston
forward. The reaction was stopped by increasing the volume of the
cell and the reactor was carefully vented.
=
[CH2{[(2,6-(3,5-(CF3)2C6H3)2-4-yl-C6H2)-N C(H)-(3,5-(3,5-
(CF3)2C6H3)2-2-O-C6H2)-j2-N,O]Ni(CH3)(pyridine)}2] (3b)
Yield: 89%. 1H NMR (400 MHz, CD2Cl2) dH (ppm): 8.32 (s, 8 H),
8.08 (m, 4 H), 8.03 (s, 4 H), 7.87 (s, 4 H), 7.75 (s, 4 H), 7.69 (s,
4 H), 7.61 (s, 2 H), 7.57 (s, 2 H), 7.51 (m, 2 H), 7.44 (s, 4 H), 7.14
(s, 2 H), 6.92 (m, 4 H), 4.30 (s, 2 H), -1.07 (s, 6 H). 13C NMR
(101 MHz, CD2Cl2) dC (ppm): 168.83, 165.04, 150.97, 149.19,
142.77, 141.70, 141.40, 139.91, 137.49, 134.12, 133.68, 133.41,
1
1
132.24 (q, JCF = 273), 132.38 (q, JCF = 273), 131.97, 131.14,
1
131.13, 130.90 (q, JCF = 273), 129.58, 126.42, 126.40, 124.21,
2
2
124.14, 124.11 (q, JCF = 33), 124.09 (q, JCF = 33), 124.06 (q,
2JCF = 33), 122.05, 122.01, 121.01, 120.57, 120.25, 40.88, -7.37.
Anal. calcd for C103H52F48N4Ni2O2 (M = 2406.85 g mol-1): C 51.40,
H 2.18, N 2.18. Found: C 51.86, H 2.26, N 2.12.
=
[C(CF3)2{[(2,6-(3,5-(CF3)2C6H3)2-4-yl-C6H2)-N C(H)-(3,5-(3,5-
(CF3)2C6H3)2-2-O-C6H2)-j2-N,O]Ni(CH3)(pyridine)}2] (3c)
Yield: 77%. 1H NMR (400 MHz, CD2Cl2) dH (ppm): 8.26 (s, 8 H),
3
8.08 (dt, JHH = 5.1, 4 H, meta-pyr), 8.06 (s, 4 H), 7.89 (s, 4 H),
7.78 (s, 4 H), 7.68 (s, 4 H), 7.65 (s, 4 H), 7.62 (s, 2 H), 7.60 (d,
4JHH = 2.5, 2 H), 7.54 (t, JHH = 7.7, 2 H), 7.18 (d, JHH = 2.5,
2 H), 6.94 (t, 3JHH = 7.7, 4 H, ortho-pyr), -1.12 (s, 6 H).13C NMR
(101 MHz, CD2Cl2) dC (ppm): 168.54, 165.26, 151.63, 150.96,
142.66, 141.24, 140.68, 137.66, 134.59, 134.10, 133.39, 132.97,
132.55 (q, 2JCF = 33), 132.47 (q, 2JCF = 33), 132.39, 132.25, 131.04,
131.02, 130.96 (q,2JCF = 33), 129.60, 129.58, 126.47, 126.44,
3
4
1
1
124.59, 124.25, 124.11 (q, JCF = 273), 124.04 (q, JCF = 273),
123.91 (q, 1JCF = 273), 122.70, 120.77, 120.69, 120.41, -7.68. Anal.
calcd for C105H50F54N4Ni2O2 (M = 2540.18 g mol-1): C 49.59, H
1.98, F 40.35, N 2.20. Found: C 49.74, H 2.02, F 40.32, N 2.11.
Acknowledgements
Financial support by the BMBF (project 03 ¥ 5505) is gratefully
acknowledged. S. M. is indebted to the Fonds der Chemischen
Industrie.
Polymerizations in organic solvent
The polymerizations in organic solvent were carried out in a
250 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. A valve controlled by a pressure trans-
ducer allowed for applying and keeping up a constant ethylene
pressure. The required flow of ethylene, corresponding to ethylene
consumed by polymerization, 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, back-filled with argon, and charged
with solvent. The catalyst precursor was weighed into a dry
References
1 (a) S. D. Ittel, L. K. Johnson and M. Brookhart, Chem. Rev., 2000,
100, 1169–1203; (b) V. C. Gibson and S. K. Spitzmesser, Chem. Rev.,
2003, 103, 283–316; (c) S. Mecking, Angew. Chem., Int. Ed., 2001, 40,
534–540; (d) S. Mecking, Coord. Chem. Rev., 2000, 203, 325–351; (e) Z.
Guan, Chem.–Eur. J., 2002, 8, 3086–3092; (f) J. Durand and B. Milani,
Coord. Chem. Rev., 2006, 250, 542–560; (g) G. J. Domski, J. M. Rose,
G. M. Coates, A. D. Bolig and M. Brookhart, Prog. Polym. Sci., 2007,
32, 30–92.
2 (a) L. S. Boffa and B. M. Novak, Chem. Rev., 2000, 100, 1479–1493;
(b) A. Berkefeld and S. Mecking, Angew. Chem., Int. Ed., 2008, 47,
This journal is
The Royal Society of Chemistry 2009
Dalton Trans., 2009, 8929–8934 | 8933
©

2538–2542; (c) S. Mecking, A. Held and F. M. Bauers, Angew. Chem.,
Int. Ed., 2002, 41, 544–561.
13 Polycarbonate synthesis from CO2 and epoxide: (a) D. J. Darensbourg,
N. W. Stafford and T. Katsurao, J. Mol. Catal. A: Chem., 1995, 104,
L1–L4; (b) C. A. Costello, E. Berluche, S. J. Han, D. A. Sysyn, M. S.
Super and E. J. Beckman, PMSE preprints, 1996, 74, 430; (c) M. Duper,
E. Berluche, C. Costello and E. Beckman, Macromolecules, 1997, 30,
368–372.
3 (a) L. K. Johnson, S. Mecking and M. Brookhart, J. Am. Chem. Soc.,
1996, 118, 267–268; (b) S. Mecking, L. K. Johnson, L. Wang and M.
Brookhart, J. Am. Chem. Soc., 1998, 120, 888–899; (c) L. Johnson, L.
Wang, S. McLain, A. Bennett, K. Dobbs, E. Hauptman, A. Ionkin,
S. Ittel, K. Kunitsky, W. Marshall, E. McCord, C. Radzewich, A.
Rinehart, K. J. Sweetman, Y. Wang, Z. Yin and M. Brookhart, ACS
Symp. Ser., 2003, 857, 131–142; (d) E. Drent, R. van Dijk, R. van
Ginkel, B. van Oort and R. I. Pugh, Chem. Commun., 2002, 744–745;
(e) K. M. Skupov, P. R. Marella, M. Simard, G. P. A. Yap, N. Allen, D.
Conner, B. L. Goodall and J. P. Claverie, Macromol. Rapid Commun.,
2007, 28, 2033–2038.
14 Phenyl acetylene polymerization: H. Hori, C. Six and W. Leitner,
Macromolecules, 1999, 32, 3178–3182.
15 Early work: (a) W. Keim, F. H. Kowaldt, R. Goddard and C Kru¨ger,
Angew. Chem., Int. Ed. Engl., 1978, 17, 466–467; (b) K. A. Ostoja-
Starzewski and J. Witte, Angew. Chem., Int. Ed. Engl., 1987, 26, 63–64;
(c) U. Klabunde and S. D. Ittel, J. Mol. Catal., 1987, 41, 123–134.
16 (a) C. Wang, S. Friedrich, T. R. Younkin, R. T. Li, R. H. Grubbs,
D. A. Bansleben and M. W. Day, Organometallics, 1998, 17, 3149–
3151; (b) L. K. Johnson, A. M. A. Bennett, S. D. Ittel, L. Wang,
A. Parthasarathy, E. Hauptman, R. D. Simpson, J. Feldman, E. B.
Coughlin, (DuPont) WO98/30609, 1998; (c) T. R. Younkin, E. F.
Connor, J. I. Henderson, S. K. Friedrich, R. H. Grubbs and D. A.
Bansleben, Science, 2000, 287, 460–462; (d) F. A. Hicks and M.
Brookhart, Organometallics, 2001, 20, 3217–3219; (e) R. Soula, J. P.
Broyer, M. F. Llauro, A. Tomov, R. Spitz, J. Claverie, X. Drujon, J.
Malinge and T. Saudemont, Macromolecules, 2001, 34, 2438–2442;
(f) V. C. Gibson, A. Tomov, A. J. P. White and D. J. Williams, Chem.
Commun., 2001, 719–720; (g) M. Zuideveld, P. Wehrmann, C. Ro¨hr
and S. Mecking, Angew. Chem., Int. Ed., 2004, 43, 869–873; (h) J. C.
Jenkins and M. Brookhart, J. Am. Chem. Soc., 2004, 126, 5827–
5842; (i) L. Zhang, M. Brookhart and P. S. White, Organometallics,
2006, 25, 1868–1874; (j) P. Kuhn, D. Se´meril, C. Jeunesse, D. Matt,
M. Neuburger and A. Mota, Chem.–Eur. J., 2006, 12, 5210–5219;
(k) I. Go¨ttker-Schnetmann, P. Wehrmann, C. Ro¨hr and S. Mecking,
Organometallics, 2007, 26, 2348–2362; (l) S.-M. Yu, A. Berkefeld, I.
Go¨ttker-Schnetmann, G. Mu¨ller and S. Mecking, Macromolecules,
2007, 40, 421–428; (m) A. Bastero, I. Go¨ttker-Schnetmann, C. Ro¨hr
and S. Mecking, Adv. Synth. Catal., 2007, 349, 2307–2316; (n) J. Pietsch,
P. Braunstein and Y. Chauvin, New J. Chem., 1998, 22, 467–472; (o) F.
Speiser, P. Braunstein and L. Saussine, Acc. Chem. Res., 2005, 38,
784–793; (p) D. Guironnet, T. Ru¨nzi, I. Go¨ttker-Schnetmann and S.
Mecking, Chem. Commun., 2008, 4965–4967; (q) Y. Schneider, J. D.
Azoulay, R. C. Coffin and G. C. Bazan, J. Am. Chem. Soc., 2008, 130,
10464–10465.
4 T. Kochi, S. Noda, K. Yoshimura and K. Nozaki, J. Am. Chem. Soc.,
2007, 129, 8948–8949.
5 D. Guironnet, P. Roesle, T. Ru¨nzi, I. Go¨ttker-Schnetmann and S.
Mecking, J. Am. Chem. Soc., 2009, 131, 422–423.
6 Also cf(a) W. Weng, Z. Shen and R. F. Jordan, J. Am. Chem. Soc., 2007,
129, 15450–15451; (b) C. Chen, S. Luo and R. F. Jordan, J. Am. Chem.
Soc., 2008, 130, 12892–12894; (c) K. M. Skupov, L. Piche and J. P.
Claverie, Macromolecules, 2008, 41, 2309–2310; (d) S. Liu, S. Borkar,
D. Newsham, H. Yennawar and A. Sen, Organometallics, 2007, 26,
210–216.
7 (a) A. Held, F. M. Bauers and S. Mecking, Chem. Commun., 2000, 301–
302; (b) A. Tomov, J.-P. Broyer and R. Spitz, Macromol. Symp., 2000,
150, 53–58; (c) R. Soula, C. Novat, A. Tomov, R. Spitz, J. Claverie,
X. Drujon, J. Malinge and T. Saudemont, Macromolecules, 2001, 34,
2022–2026; (d) I. Go¨ttker-Schnetmann, B. Korthals and S. Mecking,
J. Am. Chem. Soc., 2006, 128, 7708–7709; (e) S.-M. Yu and S. Mecking,
Macromolecules, 2009, 42, 3669–3673.
8 (a) L. K. Johnson, C. M. Killian, S. D. Arthur, J. Feldman, E. F.
McCord, S. J. McLain, K. A. Kreutzer, M. A. Bennett, E. B. Coughlin,
S. D. Ittel, A. Parthasarathy, D. J. Tempel, M. S. Brookhart (DuPont,
Univ. North Carolina) WO 96/23010, 1996; (b) T. J. De Vries, R.
Duchateau, M. A. G. Vorstman and J. T. F. Keurentjes, Chem.
Commun., 2000, 263–264; (c) T. J. De Vries, M. F. Kemmere and J. T. F.
Keurentjes, Macromolecules, 2004, 37, 4241–4246; (d) A. Bastero,
G. Francio`, W. Leitner and S. Mecking, Chem.–Eur. J., 2006, 12,
6110–6116; (e) D. Guironnet, I. Go¨ttker-Schnetmann and S. Mecking,
Macromolecules, 2009, DOI: 10.1021/ma901397q.
9 (a) Chemical Synthesis Using Supercritical Fluids ed. P. G. Jessop and
W. Leitner, Wiley-VCH, Weinheim, 1999; (b) Supercritical Carbon
Dioxide in Polymer Reaction Engineering ed. M. F. Kemmere and
T. Meyer, Wiley-VCH, Weinheim, 2005.
10 (a) J. L. Kendall, D. A. Canelas, J. L. Young and J. M. DeSimone,
Chem. Rev., 1999, 99, 543–563; (b) S. L. Wells and J. DeSimone, Angew.
Chem., Int. Ed., 2001, 40, 518–527.
11 (a) J. M. DeSimone, E. E. Maury, Y. Z. Menceloglu, J. B. McClain,
T. J. Romack and J. R. Combes, Science, 1994, 265, 356–359; (b) S.
Beuermann, M. Buback, C. Schmaltz and F. D. Kuchta, Macromol.
Chem. Phys., 1998, 199, 1209–1216; (c) A. I. Cooper, W. P. Hems and
A. B. Holmes, Macromol. Rapid Commun., 1998, 19, 353–357; (d) U.
Beginn, R. Najjar, J. Ellmann, R. Vinokur, R. Martin and M. Moeller,
J. Polym. Sci., Part A: Polym. Chem., 2006, 44, 1299–1316; (e) A. M.
Gregory, K. J. Thurecht and S. M. Howdle, Macromolecules, 2008, 41,
1215–1222.
12 Ring opening metathesis polymerization: (a) A. Fu¨rstner, L. Acker-
mann, K. Beck, H. Hori, D. Koch, K. Langemann, M. Liebl, C. Six and
W. Leitner, J. Am. Chem. Soc., 2001, 123, 9000–9006; (b) A. Fu¨rstner,
D. Koch, K. Langemann, W. Leitner and C. Six, Angew. Chem., Int.
Ed. Engl., 1997, 36, 2466–2469; (c) C. D. Mistele, H. H. Thorp and
J. M. DeSimone, J. Macromol. Sci., Part A: Pure Appl. Chem., 1996,
33, 953–960.
17 (a) A. Berkefeld and S. Mecking, J. Am. Chem. Soc., 2009, 131, 1565–
1574; (b) A. Berkefeld, M. Drexler, H. Mo¨ller and S. Mecking, J. Am.
Chem. Soc., 2009, 131, 12613–12622.
18 (a) K. Kurtev and A. Tomov, J. Mol. Catal., 1994, 88, 141–150; (b) D.
Zhang and G.-X Jin, Organometallics, 2003, 22, 2851–2854; (c) D.
Zhang and G.-X Jin, Inorg. Chem. Commun., 2006, 9, 1322–1325; (d) T.
Hu, L.-M. Tang, X.-F. Li, Y.-S. Li and N.-H. Hu, Organometallics,
2005, 24, 2628–2632; (e) S. S, D. J. Joe, S. J. Na, Y.-W. Park, C. H.
Choi and B. Y. Lee, Macromolecules, 2005, 38, 10027–10033; (f) P.
Wehrmann and S. Mecking, Organometallics, 2008, 27, 1399–1408;
(g) B. A. Rodriguez, M. Delferro and T. J. Marks, Organometallics,
2008, 27, 2166–2168; (h) B. A. Rodriguez, M. Delferro and T. J. Marks,
J. Am. Chem. Soc., 2009, 131, 5902–5919.
19 E. F. Connor, T. R. Younkin, J. I. Henderson, A. W. Waltman and R. H.
Grubbs, Chem. Commun., 2003, 2272–2273.
20 (a) L. K. Johnson, M. C. Killian and M. Brookhart, J. Am. Chem. Soc.,
1995, 117, 6414–6415; (b) Z. Guan, P. M. Cotts, E. F. McCord and S. J.
McLain, Science, 1999, 283, 2059–2062; (c) Also cf.: V. M. Moehring
and G. Fink, Angew. Chem., Int. Ed. Engl., 1985, 24, 1001–1003.
21 J. Ca`mpora, M.d.M. Conejo, K. Mereiter, P. Palma, C. Pe´rez, M. L.
Reyes and C. Ruiz, J. Organomet. Chem., 2003, 683, 220–239.
22 P. Wehrmann, M. Zuideveld, R. Thomann and S. Mecking, Macro-
molecules, 2006, 39, 5995–6002.
8934 | Dalton Trans., 2009, 8929–8934
This journal is
The Royal Society of Chemistry 2009
©