ACS Catalysis
Research Article
a
Table 4. Copolymerization of Ethylene and MA with Clay- and Silica-Supported Complexes 1-L
b
M (NMR) (g mol−1)b
entry
substrate and pretreatment
complex
1-pyr
1-pyr
time (min)
yield (g)
χ(MA)
n
3
4
4
4
4
4
4
4
-1
-2
-3
-4
-5
-6
-7
−
30
30
0.93
0.49
0.56
0.71
0.24
0.76
2.20
3.4
3.2
2.2
4.3
2.5
2.5
2.3
4.9 × 10
3
clay
clay
clay
2.1 × 10
−
+
3
[1-Cl NR ]
30
1.8 × 10
4
−
+
c
3
[1-Cl NR ]
30
4.7 × 10
4
d
3
silica, iw
1-pyr
1-pyr
1-pyr
15
3.7 × 10
d
3
silica, iw
60
2.6 × 10
d
3
silica, iw
240
2.7 × 10
a
Polymerization conditions: 10 μmol of 1-L on 120 mg of clay (montmorillonite, treated with a 6 M H SO /1 M Li SO mixture) or 200 mg of
2
4
2
4
b
1
silica, 0.2 M MA, total volume (MA and toluene) of 100 mL, polymerization temperature of 90 °C. Determined by H NMR spectroscopy at 130
c
d
°C in C D Cl . Addition of 1 equiv of AgBF . Incipient wetness.
2 2 4 4
diimine catalysts) on silica, the active species are cationic and
bound by electrostatic interactions with their aluminum alkyl
counterion, which have reacted to form covalent bonds to the
this shows that the nature of the active single-site species is
advantageously retained upon supporting.
8
,9
support.
ASSOCIATED CONTENT
■
SEM images of the catalyst-charged silica support before and
after polymerization show that no fragmentation of the support
occurs under polymerization conditions (Figure 5 and Figures
S9−S16 of the Supporting Information). The spherical,
microporous silica particles (10−100 μm in diameter) are
unaltered and embedded in the polymer matrix after
precipitation of polyethylene during workup.
Time-dependent polymerization experiments also show that
silica-supported complex 1-pyr remains active over some hours
but is still slowly deactivated over a prolonged polymerization
time (entries 3-14−3-17).
*
S
Supporting Information
Supplemental data and figures, CIF files, general experimental
procedures, synthesis, additional NMR spectra, and crystal
AUTHOR INFORMATION
■
5152. Telephone: +49 7531 88-5151.
Montmorillonite clay- and silica-supported complexes 1-L
further allow a copolymerization of ethylene and methyl
acrylate without any cocatalysts such as MAO (Table 4).
Whereas both substrates do not influence the degree of MA
incorporation significantly (2.5−4 mol % MA), productivity
and molecular weights are both slightly reduced in the presence
of silica or clay. Silica-supported complex 1-pyr is less active
than the free complex (entry 4-1 vs entry 4-6) but retains its
activity over some hours and is only deactivated slowly (entries
Notes
The authors declare no competing financial interest.
ACKNOWLEDGMENTS
■
Financial support by the DFG (Me1388/10-1) is gratefully
acknowledged. We thank Anke Friemel and Ulrich Haunz for
support with NMR measurements and Dr. Marina Krumova for
SEM.
4
-5−4-7).
REFERENCES
■
(
1
1) Johnson, L. K.; Mecking, S.; Brookhart, M. J. Am. Chem. Soc.
CONCLUSION
■
996, 118, 267−268.
Both, adsorption on inorganic substrates and tethering to
polystyrene for neutral phosphine sulfonato Pd(II) complexes
afford active (co)polymerization catalysts without any addi-
tional scavenger or cocatalysts. Covalent binding to function-
alized polystyrene has a stronger influence on activity, which
decreases by ∼1 order of magnitude. This is likely due to a
limited diffusion of the monomer substrate and the polymer
product in the macropores of these microbeads (∼0.1 mm in
size).
(2) Mecking, S.; Johnson, L. K.; Wang, L.; Brookhart, M. J. Am.
Chem. Soc. 1998, 120, 888−899.
(3) Drent, E.; van Dijk, R.; van Ginkel, R.; van Oort, B.; Pugh, R. I.
Chem. Commun. 2002, 744−745.
(
̈
4) Guironnet, D.; Caporaso, L.; Neuwald, B.; Gottker-Schnetmann,
I.; Cavallo, L.; Mecking, S. J. Am. Chem. Soc. 2010, 132, 4418−4426.
5) Nakamura, A.; Ito, S.; Nozaki, K. Chem. Rev. 2009, 109, 5215−
244.
6) Nakamura, A.; Anselment, T. M. J.; Claverie, J.; Goodall, B.;
(
5
(
Jordan, R. F.; Mecking, S.; Rieger, B.; Sen, A.; van Leeuwen, P. W. N.
M.; Nozaki, K. Acc. Chem. Res. 2013, 46, 1438−1449.
(7) Ittel, S. D.; Johnson, L. K.; Brookhart, M. Chem. Rev. 2000, 100,
1169−1203.
Clay and microporous silica as supports have a less
pronounced impact on the catalyst activity. 1-pyr on silica is
quite stable under copolymerization conditions. While the
possible occurrence of a leaching of small portions of the
catalyst is difficult to rule out, results clearly show that catalysis
occurs predominantly by supported species. To the best of our
knowledge, this is the first demonstration of ethylene−acrylate
insertion copolymerization by supported solid catalysts.
For all supported catalysts, polymer microstructures are not
dramatically different from those of polymers obtained with
soluble catalysts. Highly linear polymers are obtained in all
cases. Differences in acrylate comonomer incorporation can be
ascribed to steric congestion imparted by the support. Overall,
(8) Severn, J. R.; Chadwick, J. C.; Duchateau, R.; Friedrichs, N.
Chem. Rev. 2005, 105, 4073−4147.
(
(
2
9) Hlatky, G. G. Chem. Rev. 2000, 100, 1347−1376.
10) Ma, Z.; Sun, W.-H.; Zhu, N.; Li, Z.; Shao, C.; Hu, Y. Polym. Int.
002, 51, 349−352.
11) Bahuleyan, B. K.; Oh, J. M.; Chandran, D.; Ha, J. Y.; Hur, A. Y.;
Park, D.-W.; Ha, C. S.; Suh, H.; Kim, I. Top. Catal. 2010, 53, 500−509.
12) Kurokawa, H.; Hayasaka, M.; Yamamoto, K.; Sakuragi, T.;
Ohshima, M.; Miura, H. Catal. Commun. 2014, 47, 13−17.
(13) Schrekker, H. S.; Kotov, V.; Preishuber-Pflugl, P.; White, P.;
Brookhart, M. Macromolecules 2006, 39, 6341−6354.
(
(
2
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dx.doi.org/10.1021/cs5005954 | ACS Catal. 2014, 4, 2672−2679