Highly active binuclear neutral nickel(II) catalysts affording high molecular weight polyethylene

Article abstract of DOI:10.1021/om700942z

A series of new binuclear neutral κ²-N,O-chelated Ni(II) complexes [(H₂C)_n {[(2,6-R₂-4-yl-C ₆H₂)-N=C(H)-(3,5-I₂-2-O-C₆H ₂)-κ²-N,O]Ni(CH₃)(pyridine)} ₂] (R = iPr, 3,5-(CF₃)₂C₆H ₃; n = 0, 1) are reported. The complexes are single-component catalyst precursors for ethylene polymerization. Catalyst activities exceed those of mononuclear analogues studied substantially. With 3.4 × 10 ⁵ TO h^-1 high molecular weight polymer is obtained (M _w 9.2 × 10⁵ g mol^-1; M_n 2.8 × 10⁵ g mol^-1). Semicrystalline polyethylene with a low degree of branching is formed (2 to 12 branches/1000 carbon atoms; prepared at 30 to 70 °C polymerization temperature), with T_m 112 to 136 °C. Polymerization in aqueous emulsion affords polyethylene dispersions.

Full text of DOI:10.1021/om700942z

Organometallics 2008, 27, 1399–1408
1399
Highly Active Binuclear Neutral Nickel(II) Catalysts Affording High
Molecular Weight Polyethylene
Peter Wehrmann and Stefan Mecking*
Lehrstuhl für Chemische Materialwissenschaft, Fachbereich Chemie, UniVersität Konstanz,
UniVersitätsstrasse 10, D-78457 Konstanz, Germany
ReceiVed September 21, 2007
A series of new binuclear neutral κ2-N,O-chelated Ni(II) complexes [(H2C)n{[(2,6-R2-4-yl-C6H2)-
NdC(H)-(3,5-I2-2-O-C6H2)-κ2-N,O]Ni(CH3)(pyridine)}2] (R ) iPr, 3,5-(CF3)2C6H3; n ) 0, 1) are reported.
The complexes are single-component catalyst precursors for ethylene polymerization. Catalyst activities
exceed those of mononuclear analogues studied substantially. With 3.4 × 105 TO h-1, high molecular
weight polymer is obtained (Mw 9.2 × 105 g mol-1; Mn 2.8 × 105 g mol-1). Semicrystalline polyethylene
with a low degree of branching is formed (2 to 12 branches/1000 carbon atoms; prepared at 30 to 70 °C
polymerization temperature), with Tm 112 to 136 °C. Polymerization in aqueous emulsion affords
polyethylene dispersions.
by analogy to ethylene polymerization by cationic diimine
complexes, which have been studied in much detail mechanisti-
cally, bulky substituents are considered to retard chain transfer
by blocking the axial positions on the metal center. Concerning
catalyst activity, an order of magnitude difference in polymer-
ization activity corresponds to a difference in the overall
Introduction
Olefin polymerization by cationic complexes of d8 metals (late
transition metals) has been studied intensely in the past decade.1
Due to their functional group tolerance, ethylene and 1-olefins
can be copolymerized with polar monomers such as acrylates.2
Substantial branching, and unique branching patterns can be
introduced in ethylene homopolymerization.3,4 These studies
prompted renewed interest in neutral nickel(II) ethylene po-
lymerization catalysts.5,6 By comparison to their cationic Ni(II)
counterparts, they are more tolerant toward polar reagents. Thus,
polymerization can be carried out in aqueous emulsion to afford
polyolefin dispersions.7–9 There is a strong interest in the
discovery of more active neutral Ni(II) polymerization catalysts
that polymerize ethylene to high molecular weight polymer. As
a guideline for accessing high molecular weight (Mn) polymer,
(5) (a) Wang, C.; Friedrich, S.; Younkin, T. R.; Li, R. T.; Grubbs, R. H.;
Bansleben, D. A.; Day, M. W. Organometallics 1998, 17, 3149–3151. (b)
Johnson, L. K.; Bennett, A. M. A.; Ittel, S. D.; Wang, L.; Parthasarathy,
A.; Hauptman, E.; Simpson, R. D.; Feldman, J.; Coughlin, E. B. (DuPont)
WO98/30609, 1998. (c) Younkin, T. R.; Connor, E. F.; Henderson, J. I.;
Friedrich, S. K.; Grubbs, R. H.; Bansleben, D. A. Science 2000, 287, 460–
462. (d) Hicks, F. A.; Brookhart, M. Organometallics 2001, 20, 3217–
3219. (e) Soula, R.; Broyer, J. P.; Llauro, M. F.; Tomov, A.; Spitz, R.;
Claverie, J.; Drujon, X.; Malinge, J.; Saudemont, T. Macromolecules 2001,
34, 2438–42. (f) Gibson, V. C.; Tomov, A.; White, A. J. P.; Williams, D. J.
Chem. Commun. 2001, 719–20. (g) Zuideveld, M.; Wehrmann, P.; Röhr,
C.; Mecking, S. Angew. Chem., Int. Ed. 2004, 43, 869–873. (h) Jenkins,
J. C.; Brookhart, M. J. Am. Chem. Soc. 2004, 126, 5827–5842. (j) Zhang,
L.; Brookhart, M.; White, P. S. Organometallics 2006, 25, 1868–1874. (k)
Kuhn, P.; Sémeril, D.; Jeunesse, C.; Matt, D.; Neuburger, M.; Mota, A.
Chem.-Eur. J. 2006, 12, 5210–5219. (l) Göttker-Schnetmann, I.; Wehr-
mann, P.; Röhr, C.; Mecking, S. Organometallics 2007, 26, 2348–2362.
(m) Yu, S.-M.; Berkefeld, A.; Göttker-Schnetmann, I.; Müller, G.; Mecking,
S. Macromolecules 2007, 40, 421–428. (n) Bastero, A.; Göttker-Schnetmann,
I.; Röhr, C.; Mecking, S. AdV. Synth. Catal. 2007, 349, 2307–2316.
(6) Early work: Keim, W.; Kowaldt, F. H.; Goddard, R.; Krüger, C.
Angew. Chem., Int. Ed. Engl. 1978, 17, 466–467. (b) Ostoja Starzewski,
K. A.; Witte, J. Angew. Chem., Int. Ed. Engl. 1985, 24, 599–601. (c)
Klabunde, U.; Ittel, S. D. J. Mol. Catal. 1987, 41, 123–134.
* 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. Angew. Chem Int. Ed. 2001, 40, 534–540.
(d) Mecking, S. Coord. Chem. ReV. 2000, 203, 325–351. (e) Berkefeld, A.;
Mecking, S. Angew. Chem. Int. Ed. 2008, in press.
(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. K.; McLain,
S. J.; Sweetman, K. J.; Wang Y.; Bennett, A. M. A.; Wang, L.; McCord,
E. F.; Lonkin, A.; Ittel, S. D.; Radzewich, C. E.; Schiffino, R. S. (Du Pont)
WO2003044066, 2003. (d) 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. (e) Li, W.;
Zhang, X.; Meetsma, A.; Hessen, B. J. Am. Chem. Soc. 2004, 126, 12246–
12247. (f) Chen, G.; Guan, Z. J. Am. Chem. Soc. 2004, 126, 2662–2663.
(g) Luo, S.; Jordan, R. F. J. Am. Chem. Soc. 2006, 128, 12072–12073.
Also cf.: (h) Drent, E.; van Dijk, R.; van Ginkel, R.; van Oort, B.; Pugh,
R. I. Chem. Commun. 2002, 744–745.
(7) (a) Held, A.; Bauers, F. M.; Mecking, S. Chem. Commun. 2000,
301–302. (b) Bauers, F. M.; Mecking, S. Macromolecules 2001, 34, 1165–
1171. (c) Bauers, F. M.; Mecking, S. Angew. Chem., Int. Ed. 2001, 40,
3020–3022. (d) Bauers, F. M.; Chowdhry, M. M.; Mecking, S. Macromol-
ecules 2003, 36, 6711–6715. (e) Bauers, F. M.; Thomann, R.; Mecking, S.
J. Am. Chem. Soc. 2003, 125, 8838–8840. (f) Kolb, L.; Monteil, V.;
Thomann, R.; Mecking, S. Angew. Chem., Int. Ed. 2005, 44, 429–432. (g)
Wehrmann, P.; Mecking, S. Macromolecules 2006, 39, 5963–5964. (h)
Wehrmann, P.; Zuideveld, M. A.; Thomann, R.; Mecking, S. Macromol-
ecules 2006, 39, 5995–6002. (j) Göttker-Schnetmann, I.; Korthals, B.;
Mecking, S. J. Am. Chem. Soc. 2006, 128, 7708–7709. (k) Weber, C. H. M.;
Chiche, A.; Krausch, G.; Rosenfeldt, S.; Ballauf, M.; Harnau, L.; Göttker-
Schnetmann, I.; Tong, Q.; Mecking, S. Nano Lett. 2007, 7, 2024–2029.
(8) (a) Tomov, A.; Broyer, J.-P.; Spitz, R. Macromol. Symp. 2000, 150,
53–58. (b) Soula, R.; Novat, C.; Tomov, A.; Spitz, R.; Claverie, J.; Drujon,
X.; Malinge, J.; Saudemont, T. Macromolecules 2001, 34, 2022–2026. (c)
Soula, R.;Saillard, B.;Spitz, R.;Claverie, J.;Llaurro, M. F.;
Monnet, CMacromolecules2002, 35, 1513–1523.
(3) (a) Killian, M. C.; Johnson, L. K.; Brookhart, M. J. Am. Chem. Soc.
1995, 117, 6414–6415. (b) Guan, Z.; Cotts, P. M.; McCord, E. F.; McLain,
S. J. Science 1999, 283, 2059–2062.
(4) For an earlier example of a nickel(II) complex producing branched,
low molecular weight ethylene homopolymer see: Keim, W.; Appel, R.;
Storeck, A.; Krüger, C.; Goddard, R. Angew. Chem., Int. Ed. Engl. 1981,
20, 116–117. (b) Keim, W. Ann. N.Y. Acad. Sci. 1983, 415, 191–200. Also
cf.: (c) Moehring, V. M.; Fink, G. Angew. Chem., Int. Ed. Engl. 1985, 24,
1001–3. (d) Stapleton, R. A.; Chai, J.; Nuanthanom, A.; Flisak, Z.; Nele,
M.; Ziegler, T.; Rinaldi, P. L.; Soares, J. B. P.; Collins, S. Macromolecules
2007, 40, 2993–3004.
10.1021/om700942z CCC: $40.75
2008 American Chemical Society
Publication on Web 03/05/2008

1400 Organometallics, Vol. 27, No. 7, 2008
Wehrmann and Mecking
activation energy of chain growth of 1–2 kcal. This may be
brought about by subtle changes of the catalyst structure.
salicylaldiminato moieties are bridged via the p-position of the
N-aryls.15 An anthryl substituent in the 3-position of the
phenolate moiety, the introduction of which in the salicylalde-
hyde employed for salicylaldimine synthesis requires some
synthetic effort, provides steric bulk. The nature and geometry
of the bridge (R2) has a profound effect on the catalytic
properties. In copolymerizations of ethylene with polar-
substituted norbornenes, the binuclear complexes incorporate a
significantly larger portion of the norbornene derivative. This
is suggested to be the result of a prearrangement of the polar
comonomer by interaction of its polar functional group with
the second metal center. In ethylene polymerization, no sub-
stantial difference was observed between mono- and binuclear
complexes; ethylene is converted with 7 × 104 TO-1 to 105
TO-1 (in experiments of 5 to 10 min total duration).
We report a series of conveniently accessible novel binuclear
salicylaldiminato nickel(II) methyl complexes, which polymerize
ethylene to high molecular weight polymer with high catalyst
activities at the same time, and polymerization in aqueous
systems with these complexes.
Results and Discussion
Ligands and Complexes. Anilines and Salicylaldimines.
Tetraisopropylbenzidine (7a) was prepared from 2,6-diisopro-
pylaniline by bromination to afford 4-bromo-2,6-diisopropyl-
aniline (97% yield) and palladium-catalyzed oxidative coupling
of the latter to afford 7a in 40% yield as pinkish crystals (eq
16
1).
Ethylene polymerization with binuclear phosphinoenolate
complexes 1 as catalyst precursors was studied.10 Activities of
up to 1.8 × 105 TO h-1 were observed, which is higher than
that of analogous mononuclear complexes. As with mononuclear
Ni(II) phosphinoenolate complexes, number average molecular
weights are rather low (Mn ≈ 1 × 104 g mol-1), and activation
by a phosphine scavenger is required for these polymerizations.
Complexes 2, derived from 2,5-disubstituted amino-p-benzo-
qinones, polymerize ethylene with catalyst activities around 6
× 103 TO h-1 and afford polyethylene with a molecular weight
(1)
of up to Mn ) 1.3 × 105 g mol
.
-1 11 Salicylaldiminato complexes
4,4′-Diamino-2,2′,6,6′-tetraisopropyldiphenylmethane (7b) was
commercially available.
3 and 4, with a bridging moiety derived from 2,4,6-trialkyl-m-
phenylene diamines, were reported recently.12,13 By comparison
to an analogous mononuclear complex investigated, a slightly
higher molecular weight and broader molecular weight distribu-
tion were found (Mn ) 2.3 × 104 g mol-1; Mw/Mn ) 6.1; for
3, R1 ) Me, R2 ) Ph R3 ) H). In mononuclear Ni(II)
salicylaldiminato complexes, bulky substituents in 2-position
of the phenolate moiety enhance polymerization activity and
facilitate phosphine dissociation, which is a prerequisite for
formation of the active catalyst.5c In the binuclear 5, the
phenolate moiety coordinating the other metal center, respec-
tively, serves this purpose.14 In contrast to the unsubstituted
mononuclear analogue, these binuclear complexes are active for
ethylene polymerization without any added phosphine scaven-
ger, with an activity of ca. 1.6 × 104 TO h-1. In 6, the
For the preparation of di(terphenylanilines) 8a and 8b (eq
2), the bromides tetrabromobenzidine and 4,4′-diamino-2,2′,6,6′-
tetrabromodiphenylmethane were prepared by bromination of
benzidine and 4,4′-diaminodiphenylmethane with tetra-n-butyl-
ammonium tribromide (63% and 82% yield, respectively).
Suzuki coupling with 3,5-bis(trifluoromethyl)phenylboronic acid
afforded 8a and 8b (74% and 95% yield, respectively).
2,4,6-Tris[3,5-bis(trifluoromethyl)phenyl]aniline (9) was ob-
tained analogously by Suzuki coupling of 2,4,6-tribromo aniline
with the boronic acid.
Salicylaldimines (10 to 12) were obtained from the above
anilines and 3,5-diiodosalicylaldehyde by condensation in
toluene with azeotropic removal of water. The crude products
obtained upon solvent evaporation were recrystallized from dry
methanol.
(9) (a) Reviews: Mecking, S.; Held, A.; Bauers, F. M. Angew. Chem.,
Int. Ed. Engl. 2002, 41, 544–561. (b) Mecking, S.; Claverie, J. In Late
Transition Metal Polymerization Catalysis; Rieger, B.; Baugh, L. S.; Kacker,
S., Striegler, S., Eds.; Wiley-VCH: Weinheim, 2003; pp 231–278. (c)
Claverie, J. P.; Soula, R. Prog. Polym. Sci. 2003, 28, 619–662. (d) Mecking,
S. Colloid Polym. Sci. 2007, 285, 605–619.
1
The salicylaldimines and anilines were characterized by H
and 13C{1H} NMR spectroscopy. Resonances were assigned
completely by two-dimensional NMR experiments (COSY,
ROESY, HSQC, HMBC). The compounds are pure by elemental
analysis.
(10) Kurtev, K.; Tomov, A. J. Mol. Catal. 1994, 88, 141–150.
(11) Zhang, D.; Jin, G.-X. Organometallics 2003, 22, 2851–2854.
(12) Zhang, D.; Jin, G.-X. Inorg. Chem. Commun. 2006, 9, 1322–1325.
(13) Chen, Q.; Yu, J.; Huang, J. Organometallics 2007, 26, 617–625.
(14) Hu, T.; Tang, L.-M.; Li, X.-F.; Li, Y.-S.; Hu, N.-H. Organometallics
2005, 24, 2628–2632.
(15) S, S.; Joe, D. J.; Na, S. J.; Park, Y.-W.; Choi, C. H.; Lee, B. Y.
Macromolecules 2005, 38, 10027–33.
(16) Bamfield, P.; Quan, P. M. Synthesis 1978, 7, 537–538.

Highly ActiVe Binuclear Neutral Nickel(II) Catalysts
Organometallics, Vol. 27, No. 7, 2008 1401
CH2-aryl) is sensitive to the substitution pattern, e.g., to an
incomplete condensation of the anilines to the imines. They are
a useful indicator for the purity of the compounds.
1
In the H NMR spectra of the isopropyl-substituted com-
plexes, the -CH(CH3)2 septet signal is shifted to lower field
by comparison to the free ligands (Table 1). In the complexes,
the -CH(CH3)2 methyl groups give rise to a set of two doublets.
This inequivalence indicates that rotation around the N-aryl
and the aryl-isopropyl bonds is hindered. For the 2,6-diaryl-
substituted complexes, only a single signal (quartet) is observed
for CF3 (1JFC ) 272 Hz) and CCF3 (2JFC ) 38 Hz) of the 3,5-
(F3C)2C6H3 groups in the 2,6-positions of the N-aryl rings. This
gives no indication of hindered rotation.
(2)
Polymerization Studies. The novel binuclear complexes were
studied as single-component catalyst precursors for ethylene
polymerization (Table 2). Like their mononuclear analogues,
highest average activities (in experiments of 30 to 60 min
duration) are observed at reaction temperatures of 50 to 60 °C
(Figure 1). The maximum activities observed are significantly
higher for the binuclear complexes (13a: 2.7 × 104 TO h-1
and 13b: 1.7 × 104 TO h-1 vs 15: 7.5 × 103 TO h-1 at 50 °C;
14a: 1.2 × 105 TO h-1 and 14b: 1.8 × 105 TO h-1 at 50 °C vs
16: 6.4 × 104 TO h-1 at 60 °C; 40 atm ethylene pressure in all
cases) (Figure 2).
The nature of the bridge (n ) 0 or 1) does not have a clear
effect on the polymerization activity comparing the iPr- and the
3,5-(CF3)2C6H3-substituted complexes (note that activities are
discussed in terms of mol monomer converted per mol of Ni(II)
present, not mol of binuclear complex present). The additional
electron-withdrawing 3,5-(CF3)2C6H3 moiety in the mononuclear
complex 17 results in only a small increase in catalyst activity
by comparison to 16. Catalyst stability over time was studied
for 13a (entries 17 and 18). Over 1 h polymerization time, no
decrease in catalyst activity was observed.
Polymer molecular weights are influenced by the reaction
temperature; with increasing polymerization temperature mo-
lecular weights decrease, as expected. The molecular weights
of the polymers formed at 50 °C (where polymerization activities
are high) with the binuclear complexes are significantly higher
than of the polymers formed with the mononuclear analogues.
The observation of higher molecular weights and higher
polymerization activities at the same time is an indication that
the higher activities by comparison to the mononuclear com-
plexes is rather due to an intrinsically higher rate of chain
growth, than to a more efficient activation of the catalyst
precursors (dissociation of pyridine).
Complexes. The binuclear salicylaldiminato Ni(II) meth-
ylpyridine complexes 13a and 14a,b were prepared by reaction
of the salicylaldimines with [(pyridine)2NiMe2] at –30 °C in
Et2O. One metal-bound methyl group per Ni(II) center is
expelled as methane. The crystalline, orange to red compounds
were isolated in 80% to 90% yield. As an alternative nickel
source, [(tmeda)NiMe2] was employed in the synthesis of 13b,
with added pyridine in toluene as a solvent at -30 °C. 13b
was isolated in 90% yield (for a comparison of [(pyridine)2-
NiMe2] and [(tmeda)NiMe2] as Ni(II) sources cf. ref 5l). For
comparative purposes of their catalytic properties (vide infra),
the mononuclear complex 17 and the known compounds 157b
and 165g were prepared by analogous procedures.
Polymer microstructures were analyzed by high-temperature
13C NMR spectroscopy (Figure 3). A low degree of branching
was observed. For the samples analyzed, 2 to 12 methyl
branches per 1000 carbon atoms were found (Table 2). As
expected, the degree of branching increases with the polymer-
ization temperature and depends to some extent also on the
catalyst precursor. For polymers prepared at polymerization
temperatures of 60 or 70 °C a small portion of ethyl branches
(e1/1000 C atoms) was also observed (entries 23 and 24). No
higher branches were detected. Molecular weights correlate with
branching, as ꢀ-hydride transfer is a key step for both the
formation of branches as well as chain transfer; with increased
branching, molecular weights of the polyethylenes decrease. For
samples prepared at polymerization temperatures of g60 °C this
results in decreased melting temperatures of 110 to 120 °C.18
The observation of a single signal for the Ni-Me group in
the 1H as well as 13C NMR spectra of the binuclear complexes
13 and 14 shows that only a single isomer is present. By analogy
to similar compounds, for which X-ray crystal structure analyses
were obtained, the trans arrangement of the Ni-Me group and
the coordinating O-atom was concluded.5g,l,n,17 The characteristic
signal of the imine protons (HNdC) is shifted to higher field
by comparison to the free ligand in all complexes (Table 1).
The pyridine signals are broadened in 1H as well as 13C NMR
spectra, which indicates exchange processes to occur. Within
experimental error of the signal integration, no excess free
pyridine is observed.
In the methylene-bridged complexes (13b, 14b) and the
corresponding salicylaldimines (10b, 11b) employed for their
synthesis, the shift of the signals of the methylene protons (aryl-
For the mononuclear complex 16, it has been found that
dissociation of pyridine limits polymerization activities, par-
ticularly at lower polymerization temperatures.20 By comparison
(17) Connor, E. F.; Younkin, T. R.; Henderson, J. I.; Waltman, A. W.;
Grubbs, R. H. Chem. Commun. 2003, 2272–2273.

1402 Organometallics, Vol. 27, No. 7, 2008
Wehrmann and Mecking
Table 1. Characteristic NMR Signals of Complexes 13a,b, 14a,b, and 17 and of the Corresponding Free Salicylaldimines (CD2Cl2, 25°C, 1H: 600
MHz, 13C: 151 MHz)
1H NMR/δ [ppm]
13C NMR/δ [ppm]
b
compound
Ni-CH3
-0.57
-CHCH3
-CHCH3
-HCdN-
Ar2CH2
Ni-CH3
-CF3
complex 13aa
ligand 10a
complex 13b
ligand 10b
complex 14a
ligand 11a
complex 14b
ligand 11b
complex 17
ligand 12
4.13
3.08
3.89
2.98
1.06 1.57
1.32
1.06 1.40
1.21
7.26
8.26
7.48
8.18
7.50
7.90
7.52
7.84
7.55
7.92
-6.2
-7.5
-7.7
-7.9
-7.7
-1.07
-0.91
-0.98
-0.91
3.94
4.04
123.8
123.24
123.5
123.5
4.31
4.35
123.50, 123.45
123.31, 123.51
a C6D6, 25 °C. b Intensity ratio 1:2 for 12 and 17.
Table 2. Polymerization Resultsd
polymerization conditions
results
run cat. precursor n(cat.) [µmol] (Ni) T [°C] t [min] yield [g] Tm [°C] crystallinity Mn [103 g mol-1
]
Mw/Mn TOF [103 h-1
]
branches /1000C
1
2
3
4
5
6
7
8
16
16
16
16
8
15
15
15
10
10
7
30
50
60
70
20
30
20
30
50
60
70
30
30
50
50–90a
50
50
50
70
50
30
50
60
70
60
60
60
60
15
15
60
60
30
60
38
15
60
25
30
60
60
30
60
60
60
60
60
60
7.0
20
27
24
10
3.7
3.3
4.7
17
21
3.6
22
9.4
21
31
3.8
7.7
3.8
10.2
4.8
16
22
29
23
131
121
119
116
133
126
136
131
127
122
118
131
135
128
130
124
132
129
112
132
131
123
119
117
43%
51%
56%
46%
47%
51%
53%
48%
53%
52%
51%
52%
51%
54%
54%
49%
46%
51%
47%
48%
49%
51%
52%
53%
154
23
12
10
401
69
162
147
74
13
15
280
272
83
49
24
72
95
21
95
2.0
2.7
2.3
2.1
2.9
2.4
2.1
2.1
3.2
2.5
2.1
3.3
2.0
3.0
2.8
2.8
5.3
4.9
2.1
4.6
2.0
2.9
1.9
2.1
32
48
64
55
141
52
17
24
124
49
42
341
34
184
220
8
27
26
21
17
4b
9b
n.d.
n.d.
n.d.
n.d.
2b
16-tmeda
16-tmeda
14a
14a
14a
14a
14a
14a-tmeda
14b
14b
14b
15
13a
13a
13a
13b
17
7
n.d.
9
10
15
5
4b
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
n.d.
n.d.
4b
9
10
10
10
18
10
10
17
10
14
15
15
14
2b
4b
n.d.
10b
4b
n.d.
n.d.
4b
377
28
17
40
54
71
60
2b
17
17
17
6b
12c
12c
10
a Highly exothermic; b Methyl branches exclusively; c ca. 1/1000 C ethyl branches; n.d.: not determined. d Reaction conditions: p(ethylene) ) 40 bar;
reaction medium 200 mL of toluene; TOF in 103 mol(ethylene) · mol(Ni)-1 · h-1
.
Figure 1. Polymerization activities for different complexes (average
activities; 40 atm ethylene pressure).
Figure 2. Polymer molecular weight (Mn) vs polymerization
temperature for different complexes.
to pyridine, the tertiary amine N,N,N′,N′-tetramethylethylene
diamine (tmeda) binds much weaker.21 The tmeda complex 14a-
tmeda was prepared by reacting [(tmeda)NiMe2] with salicyl-
aldimine 11a without any added pyridine and isolated by
removal of solvent. The compound was utilized without further
spectroscopic analysis. For comparison, polymerization with the

Highly ActiVe Binuclear Neutral Nickel(II) Catalysts
Organometallics, Vol. 27, No. 7, 2008 1403
Figure 3. 13C NMR spectrum of slightly branched high molecular weight polyethylene prepared (tetrachloroethane-d2; 130 °C). Assignments
according to ref 19.
Figure 4. TEM image of polyethylene particles (prepared with 14b, entry 29 in Table 3).
mononuclear 16-tmeda21 was studied. Both complexes are
highly active at polymerization temperatures of 20 to 30 °C.
At the catalyst loadings studied (Table 2), limitation of the
reaction time to 15 min was required to prevent the polymer
formed from blocking the stirrer, which resulted in exotherms
of up to 100 °C. At 30 °C, 14a-tmeda polymerized ethylene
with an average activity of 3.4 × 105 TO h-1 (entry 12). This
is more than an order of magnitude higher than the activity
observed with the pyridine analogue 14a at this temperature.
At the same time, high molecular weight polymer with Mw 9.1
× 105 g mol-1 and Mn 2.8 × 105 g mol-1 is obtained.
emulsion technique.7c,8b,22 Pyridine complexes were dissolved
in a small amount of toluene and hexadecane as a hydrophobe.
The solution was miniemulsified in an aqueous SDS solution
by means of high shear generated by ultrasonication. Exposure
to ethylene in a pressure reactor afforded polyethylene disper-
sions (Table 3). The binuclear complexes polymerized ethylene
in aqueous emulsion with up to 6 × 103 TO h-1. As observed
previously for catalytic polymerizations in aqueous emulsions
with various κ2-N,O-coordinated Ni(II) catalysts,5m,7c,g produc-
tivities are much decreased by comparison to polymerization
in organic solvents. Polymer molecular weights and melting
points are similar to those obtained in nonaqueous polymeriza-
tions under otherwise identical conditions, overall. Polymeri-
zation activity is sustained for hours (entries 28 and 29). This
is also confirmed by following the ethylene uptake with mass
flow meters (Supporting Information). A tentative explanation
for the lower activities observed in the aqueous systems vs
polymerization in toluene (Table 2) is a deactivation of the
catalyst precursor during miniemulsion preparation and in the
very early stages of the polymerization.
Polymerization in Aqueous Emulsions. To prepare a
polymer dispersion, a high degree of dispersion of the catalyst
precursor in the initial reaction mixture is required. For a
lipophilic catalyst precursor, this can be achieved by a mini-
(18) (a) Flory, P. J. Trans. Faraday Soc. 1955, 51, 848–857. (b) Sanchez,
I. C.; Eby, R. K. J. Res. Nat. Stand. 1973, 77A, 353–358. (c) Alamo, R. G.;
Mandelkern, L.; Stack, G. M.; Krönke, C.; Wegner, G. Macromolecules
1994, 27, 147–156. (d) Alamo, R. G.; Mandelkern, L. Macromolecules 1989,
22, 1273–1277. (e) Mathot, V. B. F., Ed. Calorimetry and Thermal Analysis
of Polymers; Hanser: Munich, 1994; pp 231-298.
TEM images of the dispersions show a rather broad distribu-
tion of particle size, in agreement with the DLS traces (Figure
4). A substantial portion of the particles appears to have an
(19) Randall, J. C. J. Macromol. Sci., ReV. Macromol. Chem. Phys. 1989,
C29, 201–317.
(20) Wehrmann, P. Dissertation; University of Konstanz, 2007.
(21) Bastero, A.; Kolb, L.; Wehrmann, P.; Bauers, F. M.; Göttker, I.;
Monteil, V.; Thomann, R.; Chowdhry, M. M.; Mecking, S. Polym. Mat.
Sci. Eng. 2004, 90, 740–1.
(22) Mecking, S.; Monteil, V.; Huber, J.; Kolb, L.; Wehrmann, P.
Makromol. Symp. 2006, 236, 117–123.

1404 Organometallics, Vol. 27, No. 7, 2008
Wehrmann and Mecking
Table 3. Polymerization Results in Aqueous Emulsionsd
results
polymerization conditions
n(cat.)
[µmol](Ni) [°C] [min] yield [g] Tm [°C] crystallinityc [103 g mol-1
cat.
precursor
T
t
polymer
Mn
polymer
solids content
particle
sizeb
c
run
]
Mw/Mn
TOF
2a
25
9a
26
27
16
16
15
24
10
23
26
10
23
24
23
29
33
33
50
50
50
50
60
50
50
50
25
25
50
50
60
60
30
60
60
25
60
180
60
105
60
20
3.9
17
3.8
2.9
21
4.0
8
1.6
2.4
1.2
1.5
121
119
127
122
116
128
123
123
134
135
120
120
51%
47%
53%
54%
49%
54%
53%
52%
50%
50%
51%
49%
23
24
74
23
15
83
27
32
2.7
2.0
3.2
2.4
2.2
3.0
2.5
2.9
2.7
3.1
3.4
2.1
48 000
5800
124 000
5900
4000
184 000
6200
4000
2500
1700
1300
2.0
146 nm
14a
14a
14a
1.9
1.5
125 nm
n.d.
14a 14b
28
29
30
31
32
33
14b
14b
14a-tmeda
14a-tmeda
15
2.0
4.0
0.8
1.2
0.6
0.75
136 nm
235 nm
60 nm
70 nm
48 nm
n.d.
232
212
22
13a
60
24
1600
a From Table 2 for comparison. Reaction medium: 200 mL of toluene. b Volume average from DLS. c From DSC of isolated bulk polymer; n.d.: not
determined. d Reaction conditions: p(ethylene): 40 bar; reaction medium: 200 mL of water, 1.5g of SDS, 1 mL of toluene, 1 mL of hexadecane; TOF in
mol(ethylene) · mol(Ni)-1 · h-1
.
approximately circular circumference, but irregular structures
are also observed.
Experimental Section
Materials and General Considerations. Unless noted otherwise,
all manipulations of nickel complexes were carried out under an
inert atmosphere using standard glovebox or Schlenk techniques.
Toluene and pentane were distilled from sodium and diethyl ether
from sodium/benzophenone under argon. Hexadecane was degassed
under argon. Demineralized water was distilled under nitrogen and
degassed three times after distillation. Pyridine was distilled from
CaH2. 4,4′-Diaminodiphenyl methane (>98%), 4,4′-diamino-
2,2′,6,6′-tetraisopropyldiphenylmethane (techn. > 80%, 7b), and
benzidine (>98%) supplied by Fluka, 3,5-bis(trifluoromethyl)phenyl
bromide supplied by ABCR, 2,4,6-tribromoaniline (98%) supplied
by Lancaster, 2,6-diisopropylaniline (92%) and tetra-n-butylam-
monium tribromide (>98%) supplied by Acros, and 3,5-diiodosalic-
ylaldehyde (97%) supplied by Aldrich were used as received.
[(tmeda)NiMe2] was supplied by MCAT (Konstanz, Germany).
[(pyridine)NiMe2] was obtained by modification of a literature
procedure.23 Complexes 157b and 165g were prepared according
to published procedures.
Summary and Conclusions
Four novel binuclear Ni(II) methylpyridine complexes of
di(salicylaldimines) bridged in the p-position of the N-aryl
moiety were prepared and characterized, and their polymeriza-
tion properties toward ethylene studied. The pyridine complexes
are active over the entire temperature range studied, 20 to 70
°C, as single-component catalyst precursors, without the neces-
sity of an activator. Maximum productivities were observed at
50 °C in the experiments performed; at higher temperatures
some deactivation occurs. In addition to the pyridine complexes,
a complex of the less strongly coordinating tertiary amine tmeda
was studied. A high activity was observed at a low polymeri-
zation temperature of 20 °C. As with the mononuclear com-
plexes, substitution in the 2,2′,6,6′-position of the N-aryl
moieties with 3,5-bis(trifluoromethyl)phenyl groups results in
more active catalysts than isopropyl substitution.
NMR spectra were recorded on a Varian Unity INOVA 400 or
on a Bruker AC 250 spectrometer. 1H and 13C NMR chemical shifts
were referred to the solvent signal. High-temperature NMR
measurements of polyethylenes were performed in 1,1,2,2-tetra-
chloroethane-d2 at 130 °C. The branching structure was assigned
according to refs 19 and 24. 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 crystallinities were calculated based on a melt enthalpy
of 293 J g-1 for 100% crystalline polyethylene. Gel permeation
chromatography (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
determined 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. Dynamic light scattering
was carried out on a Malvern Nano Zeta Sizer. For the determi-
nation of particle size, a few drops of a latex sample were diluted
with ca. 3 mL of water. TEM images were obtained on a Zeiss
Libra 120 instrument. Dispersions were dialyzed for TEM analysis
to remove any free surfactant and applied to a copper grid. The
acceleration voltage was 120 keV, and the samples were not
contrasted. Elemental analyses were performed up to 950 °C on
Polymerization activities of all binuclear complexes are
substantially higher than those of mononuclear analogues, that
is, compounds with either R ) H or R ) 3,5-(F3C)2C6H3 instead
of the bridging moiety. A maximum activity of 3.4 × 105 TO
h-1 was observed, with formation of high molecular weight
polymer of Mw 9.2 × 105 g mol-1 and Mn 2.8 × 105 g mol-1
.
At the same time, the catalyst precursors are conveniently
accessible. The higher polymerization activity of the binuclear
complexes by comparison to the mononuclear analogues appears
to be due rather to an intrinsically higher rate of chain growth,
than to a more efficient activation of the catalyst precursors
(dissociation of pyridine). The origin of the higher chain growth
rates, which corresponds to a difference in activation energy of
only ca. 1 kcal, remains unclear. The observation of high
polymerization activities (g105 TO h-1) and formation of high
molecular weight polymer (Mn g 105 g mol-1) at the same time
has not been reported for binuclear neutral Ni(II) polymerization
catalysts. Polymer microstructure is affected by chain walking
only to a small extent. Linear polyethylenes with, for example,
two methyl branches per 1000 carbon atoms (polymerization
temperature 30 °C) are obtained.
Polymerizations can be carried out in aqueous emulsions, to
afford dispersions of high molecular weight linear polyethylene.
Productivities are substantially lower than in polymerizations
in nonaqueous systems, however, as observed previously for
mononuclear salicylaldiminato-substituted neutral Ni(II) po-
lymerization catalysts.
(23) Cámpora, J.; Conejo, M. d. M.; Mereiter, K.; Palma, P.; Pérez, C.;
Reyes, M. L.; Ruiz, C. J. Organomet. Chem. 2003, 683, 220–239.
(24) Axelson, D. E.; Levy, G. C.; Mandelkern, L. Macromolecules 1979,
12, 41–52.

Highly ActiVe Binuclear Neutral Nickel(II) Catalysts
Organometallics, Vol. 27, No. 7, 2008 1405
an Elementar Vario EL. Mass spectrometry with ESI was carried
out on a Bruker Esquire 3000 plus instrument in positive mode.
Samples were applied as methanol solutions. EI-MS was performed
on a Finnegan MAT instrument at 20 to 400 °C and 30 to 70 eV
electron energy (note that for higher molecular weights, >ca. 700 g
mol-1, M were underestimated by ca. 1 g mol-1).
1H NMR (400 MHz, C6D6): δ/ppm 6.89 (4 H, 3-H), 3.91 (4 H,
NH2), 3.01 (2 H, 5-H). Anal. Calcd for C13H10Br4N2 (M ) 513.85
g mol-1): C 30.39, H 1.96, N 5.45. Found: C 28.71, H 1.71, N
5.48.
General Procedure for Suzuki Coupling. Aryl bromide, 3,5-
bis(trifluoromethyl)phenylboronic acid (1.1 equiv), and sodium
carbonate (2 equiv) were placed in a Schlenk tube. The tube was
evacuated and back-filled with argon. Via septum, water (5 mL),
ethanol (10 mL), and toluene (30 mL) were added. An orange
solution of bis(dibenzylidene acetone)palladium(II) (0.5 mol %)
and triphenylphosphine (1 mol %) in 5 mL of toluene was added,
and the mixture was stirred for 12 h at 90 °C. Further workup was
carried out as outlined for the individual compounds.
3,3′,5,5′-Tetrakis(3,5-bis(trifluormethyl)phenyl)-4,4′-diamino-
diphenylmethane (8b). A 1.0 g (2.0 mmol) amount of 3,3′,5,5′-
tetrabromo-4,4′-diaminodiphenylmethane was reacted as outlined
above. The biphasic mixture was filtered through a paper filter,
and the phases were separated. The aqueous phase was extracted
twice with diethyl ether. The combined organic phases were dried
over MgSO4, and the solvent was removed in vacuo. The residue
was recrystallized from pentane to afford 1.9 g (1.9 mmol; 95%
yield) of 8b as a pale yellow powder.
Synthesis of Anilines and Salicylaldimines. 4-Bromo-2,6-
diisopropylaniline. To tetra-n-butylammonium tribromide (34.3 g,
71 mmol), calcium carbonate (30 g), and 50 mL of methanol, a
solution of 2,6-diisopropylaniline (12.6 g, 71 mmol) in 30 mL of
methanol was added and the mixture was stirred overnight. During
this time, the color changed from bright yellow to slightly greenish.
The solvent was removed in vacuo, and the residue was suspended
in toluene. Washing with aqueous EDTA solution resulted in
complete dissolution of the solid. The aqueous phase was separated
and extracted twice with toluene. The combined organic phases
were dried over magnesium sulfate, and the solvent was removed
in vacuo. 17.7 g (69 mmol, 97%) of 2,6-diisopropyl-4-bromoaniline
1
was obtained as an orange-red oil. H NMR (400 MHz, CDCl3):
3
δ/ppm 7.13 (2 H, Ar-H), 3.86 (2 H, NH), 2.84 (sep, JHH ) 6.8
Hz, 2 H, CH-CH3), 1.22 (d, J ) 6.8 Hz, 12 H, CH3). 13C NMR
(101 MHz, CDCl3): δ/ppm 139.08, 133.99, 125.15, 110.37 (C-Aryl),
27.51 (CH-CH3), 21.79 (CH3)
2,2′,6,6′-Tetraisopropylbenzidine (7a).16 Sodium formiate (125
mmol, prepared from sodium hydroxide and formic acid), dode-
cyltrimethyl ammonium bromide (1.0 g), palladium on charcoal
(0.46 g; 3 wt % Pd), sodium hydroxide (1.8 g), 2,6-diisopropyl-
4-bromoaniline (7.7 g, 30 mmol), and 50 mL of water were refluxed
with vigorous stirring, with a slow stream of air through the reaction
mixture. After 10 h, another batch of sodium formiate (125 mmol)
was added, and refluxing was continued for 20 h. After cooling to
room temperature, to the biphasic mixture was added 100 mL of
diethyl ether. The aqueous phase was extracted twice with diethyl
ether. The combined organic phases were dried over magnesium
sulfate. After concentration in vacuo, a red oil was obtained, from
which the product crystallized slowly in the form of pale violet
crystals. The product was recrystallized from pentane, to afford
1.8 g (5.1 mmol; 34% yield) of 7a.
1H NMR (600 MHz, CD2Cl2): δ/ppm 8.06 (8 H, 6-H), 7.98 (4
H, 8-H), 7.13 (4 H, 3-H), 4.01 (4 H, 10-H), 3.73 (4 H, NH). 13C
NMR (151 MHz, CD2Cl2): δ/ppm 141.57 (C5), 139.11 (C1), 132.23
2
(q, JCF ) 32.9 Hz, C7), 132.09 (C4), 131.33 (C3), 129.81 (C6),
1
125.83 (C2), 123.47 (q, JCF ) 272.6 Hz, C9), 121.54 (C8), 39.83
(C10). EI-MS: m/z 1046.2 (M+). Anal. Calcd for C45H22F24N2 (M
) 1046.63 g mol-1): C 51.64, H 2.12, N 2.68. Found: C 51.44, H
2.43, N 2.67.
1H NMR (400 MHz, CD2Cl2): δ/ppm 7.31 (4 H, 3-H), 3.88 (4
H, N-H), 3.11 (sep, 2JHH ) 6.7 Hz, 4 H, 5-H), 1.45 (d, 3JHH ) 6.7
Hz, 24 H, 6-H). 13C NMR (151 MHz, CD2Cl2): δ/ppm 139.21 (C1),
132.83 (C2), 132.74 (C4), 121.36 (C3), 28.16 (C5), 22.44 (C6). EI-
MS m/z 352.6 (M+). Anal. Calcd for C24H36N2 (M ) 352.56 g
mol-1): C 81.76, H 10.29, N 7.95. Found: C 81.05, H 9.65, N
7.42.
3,3′,5,5′-Tetrabromo-4,4′-diaminodiphenylmethane. To a sus-
pension of tetra-n-butylammonium tribromide (9.6 g, 20 mmol) and
calcium carbonate (2.2 g, 22 mmol) in 50 mL of methanol was
added a solution of 4,4′-diaminodiphenylmethane (1 g, 5 mmol) in
30 mL of methanol, and the mixture was stirred at room temper-
ature. The color 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 and washed
with methanol to afford 2.1 g (4.1 mmol, 82%) of 3,3′,5,5′-
tetrabromo-4,4′-diaminodiphenylmethane as brown needles.
3,3′,5,5′-Tetrabromobenzidine. A 29 g (60 mmol) sample of
tetra-n-butylammonium tribromide and 6.6 g (66 mmol) of CaCO3
were suspended in 50 mL of methanol. A solution of 2.8 g (15
mmol) of benzidine in 30 mL of methanol was added under stirring.
The color changed from pale orange to green, with slight gas
evolution. After stirring for 12 h, the reaction mixture was
evaporated to dryness. The residue was extracted on a frit with hot
toluene. The extract was concentrated and chilled. The crystalline
precipitate formed was isolated, recrystallized from toluene, and
washed with methanol to afford 4.7 g (9.4 mmol, 63%) of
1
tetrabromobenzidine as pale brown needles. H NMR (400 MHz,
CDCl3): δ/ppm 7.50 (4 H, Ar-H), 4.57 (br, 4 H, NH). EI-MS: m/z
500.3 (M+). Anal. Calcd for C12H8Br4N2 (M ) 499.82 g mol-1):
C 28.84, H 1.61, N 5.60. Found: C 28.71, H 1.71, N 5.48.
2,2′,6,6′-Tetrakis[3,5-bis(trifluoromethyl)phenyl]benzidine (8a).
A 2.3 g (4.6 mmol) portion of 2,2′,6,6′-tetrabromobenzidine were
reacted according to the general procedure for Suzuki coupling.
The crude product precipitated as a gray solid. It was separated,
washed with methanol, dissolved in hot toluene, and filtered over

1406 Organometallics, Vol. 27, No. 7, 2008
Wehrmann and Mecking
diatomaceous earth. The product crystallized from the filtrate upon
cooling. Drying in vacuo afforded 3.5 g (3.4 mmol, 74%) of 8a as
yellow-white needles.
NMR (151 MHz, CD2Cl2): δ/ppm 165.16 (C7), 160.46 (C2), 149.44
(C4), 144.36 (C8), 140.90 (C6), 139.50 (C9), 139.36 (C11), 122.38
(C10), 120.32 (C1), 87.03 (C5), 79.83 (C3), 28.46 (C12), 23.45 (C13).
Anal. Calcd for C38H40I4N2O2 (M ) 1064.35 g mol-1): C 42.88,
H 3.79, N 2.63. Found: C 42.81, H 3.89, N 2.71.
[CH2{(2,6-iPr2)2-4-yl-C6H2)-NdC(H)-(3,5-I2-2-(OH)-
C6H2)}2] (10b). Yield: 41%. 1H NMR (600 MHz, CD2Cl2): δ/ppm
4
4
8.22 (d, JHH ) 2.0 Hz, 2 H, 4-H), 8.18 (2 H, 7-H), 7.73 (d, JHH
) 2.0 Hz, 2 H, 6-H), 7.14 (4 H, 10-H), 4.04 (2 H, 14-H), 2.98
1H NMR (600 MHz, CD2Cl2): δ/ppm 8.11 (8 H, 6-H), 8.01 (4
H, 8-H), 7.47 (4 H, 3-H), 3.83 (4 H, N-H). 13C NMR (151 MHz,
3
3
(sept, JHH ) 6.8 Hz, 4 H, 12-H), 1.21 (d, JHH ) 6.8 Hz, 24 H,
13-H). 13C NMR (151 MHz, CD2Cl2): δ/ppm 165.09 (C7), 160.59
(C2), 149.31 (C4), 143.01 (C8), 140.80 (C6), 139.10 (C9), 138.99
(C11), 123.82 (C10), 120.31 (C1), 87.05 (C5), 79.64 (C3), 41.75
(C14), 28.26 (C12), 23.44 (C13). ES-MS: m/z 1077.9 (M+). Anal.
Calcd for C39H42I4N2O2 (M ) 1078.38 g mol-1): C 43.44, H 3.93,
N 2.60. Found: C 43.47, H 4.20, N 2.53.
2
CD2Cl2): δ/ppm 141.39 (C5), 139.94 (C1), 132.30 (q, JCF ) 33.3
Hz, C7), 130.86 (C4), 129.91 (C6), 128.79 (C3), 126.14 (C2), 123.44
1
(q, JCF ) 272.5 Hz, C9), 121.76 (C8). EI-MS: m/z 1032.6 (M+).
Anal. Calcd for C44H20F24N2 (M ) 1032.63 g mol-1): C 51.98, H
1.95, N 2.71. Found: C 51.17, H 2.07, N 2.67.
2,4,6-Tris[3,5-bis(trifluoromethyl)phenyl]aniline. A 1.6 g (4.7
mmol) amount of 2,4,6-tribromoaniline was reacted according to
the above general procedure for Suzuki coupling. Workup analogous
to 8b afforded 2.3 g (3.2 mmol; 68%) of 2,4,6-tris[3,5-bis(trifluo-
romethyl)phenyl]aniline.
[{(2,6-(3,5-(CF3)2C6H3)2-4-yl-C6H2)-NdC(H)-(3,5-I2-2-(OH)-
C6H2)}2] (11a). Yield: 79%. 1H NMR (400 MHz, CD2Cl2): δ/ppm
4
12.94 (2 H, OH), 8.14 (d, JHH ) 1.5 Hz, 2 H, 4-H), 8.01 (8 H,
4
13-H), 7.95 (4 H, 15-H), 7.90 (6 H, 7-H, 10-H), 7.29 (d, JHH
)
1.5 Hz, 2 H, 6-H). 13C NMR (101 MHz, CD2Cl2): δ ppm 168.04
(C7), 159.76 (C2), 150.53 (C4), 144.51 (C8), 140.73 (C6), 140.39
(C12), 138.15 (C11), 133.17 (C9), 131.95 (q, 2JCF ) 33.7 Hz, C14),
1H NMR (600 MHz, CD2Cl2): δ/ppm 8.16 (4 H, 6-H), 8.13 (2
H, 11-H), 8.07 (2 H, 8-H), 7.91 (1 H, 13-H), 7.58 (2 H, 3-H), 4.02
(2 H, NH). 13C NMR (151 MHz, CD2Cl2): δ/ppm 142.27 (C10),
130.16 (C13), 129.94 (C10), 123.24 (q, JCF ) 272.5 Hz, C16),
1
121.78 (C15), 119.33 (C1), 86.55 (C5), 80.15 (C3). ES-MS: m/z
1742.8 (M+). Anal. Calcd for C58H24F24I4N2O2 (M ) 1744.4 g
mol-1): C 39.93, H 1.39, N 1.61. Found: C 41.79, H 1.92, N 1.58.
2
141.81 (C1), 140.95 (C5), 132.61 (q, JCF ) 33.4 Hz, C7), 132.18
2
(q, JCF ) 33.5 Hz, C12), 130.00 (C6), 129.74 (C3), 128.84 (C4),
126.58 (C11), 126.31 (C2), 123.68 (q, 1JCF ) 272.8 Hz, C14), 123.50
(q, 1JCF ) 273.0 Hz, C9), 122.14 (C8), 120.56 (C13). EI-MS m/z )
729.5 (M+). Anal. Calcd for C30H13F18N (M ) 729.4 g mol-1): C
49.40, H 1.80, N 1.92. Found: C 49.16, H 1.95, N 2.00.
General Procedure for Condensation of Anilines with 3,5-
Diiodosalicylaldehyde. In a flask equipped with a Dean–Stark
condenser, the aniline, 3,5-diiodosalicylaldehyde (1.2 equiv), and
a catalytic amount of p-toluenesulfonic acid were dissolved in 200
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 7 h, while the solvent
collected in the Dean–Stark condenser was removed periodically
(to collect a total of ca. 150 mL). The reaction mixture was
concentrated, and to the brown viscous residue was added 20 mL
of pentane, which initiated crystallization of the product. The crude
product was recrystallized from methanol, to afford the aldimine
as a yellow solid.
[CH2{(2,6-(3,5-(CF3)2C6H3)2-4-yl-C6H2)-NdC(H)-(3,5-I2-2-
(OH)-C6H2)}2] (11b). Yield: 60%. 1H NMR (600 MHz, CD2Cl2):
δ/ppm 13.01 (2 H, OH), 8.11 (2 H, 4-H), 7.93 (8 H, 13-H), 7.91 (4
H, 15-H), 7.84 (2 H, 7-H), 7.53 (4 H, 10-H), 7.24 (2 H, 6-H), 4.35
(2 H, 17-H). 13C NMR (151 MHz, CD2Cl2): δ/ppm 168.32 (C7),
160.06 (C2), 150.65 (C4),143.56 (C8), 140.90 (C6), 139.81 (C11),
132.93 (C9), 132.14 (q, 2JCF ) 34.0 Hz, C14), 130.38 (C13), 130.07
(C12), 123.54 (q, 1JCF ) 272.7 Hz, C16), 121.81 (C15), 119.66 (C1),
86.79 (C5), 80.34 (C3), 40.89 (C17). ES-MS: m/z 1756.4 (M+). Anal.
[{(2,6-iPr2-4-yl-C6H2)-NdC(H)-(3,5-I2-2-(OH)-C6H2)}2] (10a).
Yield: 75%. 1H NMR (600 MHz, CD2Cl2): δ/ppm 8.26 (2 H, 7-H),
8.25 (b, 2 H, 4-H), 7.78 (b, 2 H, 6-H), 7.47 (4 H, 10-H), 3.08 (sept,
3JHH ) 6.8 Hz, 4, 12-H), 1.32 (d, 3JHH ) 6.8 Hz, 24 H, 13-H). 13
C

Highly ActiVe Binuclear Neutral Nickel(II) Catalysts
Organometallics, Vol. 27, No. 7, 2008 1407
Calcd for C59H26F24I4N2O2 (M ) 1758.43 g mol-1): C 40.30, H
1.50, N 1.59. Found: C 39.65, H 1.67, N 1.55.
1382.02 g mol-1): C 44.32, H 4.08, N 4.05. Found: C 44.72, H
4.10, N 4.55.
General Procedure for Complex Synthesis from [(pyridine)2-
NiMe2]. [(pyridine)2NiMe2] (248 mg, 1.0 mmol) and the salicyla-
ldimine (0.51 mmol) were weighed into a Schlenk flask and
suspended in 20 mL of diethyl ether at -30 °C. The reaction
mixture changed to a dark red color and an orange precipitate
formed, while being warmed to 0 °C under stirring over the course
of 4 h. The solvent was removed in vacuo, and the orange-red
residue was washed twice with cold pentane.
[(2,4,6-(3,5-(CF3)2C6H3)3C6H2)-NdC(H)-(3,5-I2-2-(OH)-
C6H2)] (12). Yield: 42%. 1H NMR (400 MHz, CD2Cl2): δ/ppm
4
12.87 (1 H, OH), 8.1 (2 H, 18-H), 8.14 (d, JHH ) 2.0 Hz, 1 H,
4-H), 8.04 (1 H, 20-H), 8.01 (4 H, 13-H), 7.96 (2 H, 15-H), 7.90
4
(1 H, 7-H), 7.85 (2 H, 10-H), 7.29 (d, JHH ) 2.0 Hz, 1 H, 6-H).
13C NMR (151 MHz, CD2Cl2): δ/ppm 168.18 (C7), 159.78 (C2),
150.63 (C4),145.15 (C8), 141.36 (C17), 141.05 (C6), 140.17 (C12),
137.34 (C11), 133.33 (C9), 132.49 (q, 2JCF ) 33.6 Hz, C19), 132.09
(q, 2JCF ) 33.6 Hz, C14), 130.18 (C10, C13), 129.93 (C20), 127.50
[{[(2,6-iPr2-4-yl-C6H2)-NdC(H)-(3,5-I2-2-O-C6H2)-K2-
N,O]Ni(CH3)(pyridine)}2] (13a). Yield: 80%. 1H NMR (600 MHz,
C6D6): δ/ppm 8.63 (br, 4 H, 13-H), 8.12 (2 H, 4-H), 7.65 (4 H,
10-H), 7.26 (2 H, 7-H), 7.18 (2 H, 6-H), 6.68 (2 H, 15-H), 6.33 (4
1
1
(C18), 123.51 (q, JCF ) 273.2 Hz, C21), 123.31 (q, JCF ) 273.2
Hz, C16), 121.9 (C15), 119.32 (C1), 86.79 (C5), 80.34 (C3). ES-
MS: m/z 1083.9 (M+). Anal. Calcd for C37H15F18I2NO (M ) 1085.3
g mol-1): C 40.95, H 1.39, N 1.29. Found: C 41.30, H 1.74, N
1.48.
3
H, 14-H), 4.13 (sept, JHH ) 6.6 Hz, 4 H, 16-H), 1.57, 1.06 (d,
3JHH ) 6.6 Hz, 24 H, 17-H), -0.57 (6 H, 12-H). 13C NMR (151
MHz, C6D6): δ/ppm 165.67 (C7), 164.09 (C2), 152.33 (C13), 149.40
(C4), 149.06 (C8), 142.06 (C6), 141.45 (C9), 140.87 (C11), 136.18
(C14), 123.21 (C15), 122.94 (C10), 120.87 (C1), 97.48 (C5), 72.78
(C3), 28.79 (C16), 24.92, 23.20 (C17), -6.19 (C12). Anal. Calcd
for C50H56I4N4Ni2O2 (M ) 1367.99 g mol-1): C 43.90, H 3.98, N
4.10. Found: C 44.46, H 4.31, N 4.54.
Synthesis of Complexes. [CH2{[(2,6-iPr2-4-yl-C6H2)-NdC(H)-
(3,5-I2-2-O-C6H2)-K2-N,O]Ni(CH3)(pyridine)}2] (13b). A solution
of salicylaldimine 10b (0.5 mmol) in 10 mL of toluene was added
dropwise to a solution of [(tmeda)Ni(CH3)2]25 (1.0 mmol) in 15
mL of toluene at -30 °C. One milliliter of pyridine was added.
The reaction mixture was warmed to 0 °C over the course of 4 h
with stirring. After filtering over diatomaceous earth, the solvent
was removed in vacuo, and the orange residue was washed twice
with cold pentane, to afford 13b in 91% yield. 1H NMR (400 MHz,
CD2Cl2): δ/ppm 8.88 (d, 3JHH ) 5.1 Hz, 4 H, 13-H), 7.95 (d, 4JHH
) 2.2 Hz, 2 H, 4-H), 7.70 (br, 4 H, 14-H), 7.48 (2 H, 7-H), 7.30
(d, 4JHH ) 2.2 Hz, 2 H, 6-H), 7.25 (t, 3JHH ) 6.7 Hz, 2 H, 15-H),
[{[(2,6-(3,5-(CF3)2C6H3)2-4-yl-C6H2)-NdC(H)-(3,5-I2-2-O-C6H2)-
1
K2-N,O]Ni(CH3)(pyridine)}2] (14a). Yield: 90%. H NMR (400
3
MHz, CD2Cl2): δ/ppm 8.38 (d, JHH ) 5 Hz, 4 H, 13-H), 8.29 (8
4
H, 17-H), 8.02 (4 H, 19-H), 7.88 (d, JHH ) 2.1 Hz, 4 H, 4-H),
7.76 (2 H, 10-H), 7.65 (br, 2 H, 15-H), 7.50 (2H, 7-H), 7.16 (br, 4
4
H, 14-H), 7.08 (d, JHH ) 2.1 Hz, 2 H, 6-H), -0.95 (6 H, 12-H).
13C NMR (151 MHz, CD2Cl2): δ/ppm 167.09 (C7), 163.61 (C2),
151.39 (C13), 149.73 (C8, C4), 141.56 (C6), 140.78 (C16), 138.07
2
(C11),137.00 (C15), 134.14 (C9), 131.75 (q, JCF ) 33.5 Hz, C18),
1
130.57 (C17), 129.64 (C10), 123.81 (q, JCF ) 273.22 Hz, C20),
123.60 (C14), 121.82 (C19), 119.57 (C1), 96.45 (C5), 72.32 (C3),
-7.69 (C12). Anal. Calcd for C70H38F24I4N4Ni2O2 (M ) 2048.04 g
mol-1): C 41.02, H 1.87, N 2.74. Found: C 41.21, H 2.21, N 2.91.
[CH2{[(2,6-(3,5-(CF3)2C6H3)2-4-yl-C6H2)-NdC(H)-(3,5-I2-2-O-
C6H2)-K2-N,O]Ni(CH3)(pyridine)}2] (14b). Yield: 82%. 1H NMR
(600 MHz, CD2Cl2): δ/ppm 8.43 (d, JHH ) 3.0 Hz, 4 H, 13-H),
8.30 (8 H, 17-H), 8.05 (4 H, 19-H), 7.93 (2 H, 4-H), 7.72 (br, 2 H,
15-H), 7.52 (2 H, 7-H), 7.42 (4 H, 10-H), 7.22 (br, 4 H, 14-H),
7.11 (2 H, 6-H), 4.31 (2 H, 21-H), -0.98 (6 H, 12-H). 13C NMR
(151 MHz, CD2Cl2): δ/ppm 167.12 (C7), 163.55 (C2), 151.40 (C13),
149.63 (C4), 148.42 (C8), 141.54 (C6), 141.00 (C16), 139.32 (C11),
3
6.92 (4 H, 10-H), 3.94 (2 H, 18-H), 3.88 (sept, JHH ) 6.8 Hz, 4
H, 16-H), 1.40, 1.06 (d, 3JHH ) 6.8 Hz, 24 H, 17-H, 17′-H), -1.07
(6 H, 12-H). 13C NMR (151 MHz, CD2Cl2): δ/ppm 164.89 (C7),
163.16 (C2), 152.14 (C13), 148.55 (C4), 146.94 (C8), 141.78 (C9),
140.30 (C11), 138.75 (C18), 136.79 (C14), 123.77 (C10), 123.52
(C14), 120.49 (C1), 96.05 (C5), 71.74 (C3), 28.10 (C16), 24.50, 22.57
(C17,C17′), -7.54 (C12). Anal. Calcd for C51H56I4N4Ni2O2 (M )
(25) Kaschube, W.; Poerschke, K. R.; Wilke, G. J. Organomet. Chem.
1988, 355, 525–532.

1408 Organometallics, Vol. 27, No. 7, 2008
Wehrmann and Mecking
2124.26 g mol-1): C 40.71, H 2.94, N 3.96. Found: C 40.72, H
3.02, N 3.93.
Polymerizations were carried out in a 1 L stainless steel
mechanically stirred (500 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 transducer 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 and then
back-filled with argon.
For nonaqueous polymerizations, 200 mL of toluene was added
to the reactor, and it was flushed with ethylene and stirred under 5
atm of ethylene for 30 min. The catalyst precursor was weighed
into a dry syringe in the drybox. The reactor was vented, and in a
slight ethylene stream, toluene from the reactor was pulled up 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 400 mL of methanol. The polymer
was isolated by filtration, washed several times with methanol, and
dried in vacuo.
For polymerization in aqueous emulsion, 170 mL of degassed
water was introduced to the reactor and ethylene pressure was
applied in order to presaturate the solution. The catalyst precursor
was dissolved in 2 mL of toluene and 0.1 mL of hexadecane (the
latter functions as a hydrophobe). This toluene solution was added
to 20 mL of an aqueous solution of 0.75 g of SDS. The cooled
biphasic mixture was homogenized under an argon atmosphere by
means of an ultrasonic homogenizer (Bandelin HD2200 with KE76
tip, operated at 120 W, 8 min). The resulting miniemulsion was
cannula-transferred to the pressure reactor. The pressure 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. A 100 mL aliquot was precipitated by pouring into
200 mL of methanol. The polymer was washed three times with
methanol and dried in vacuo at 50 °C. The rest of the polymer
dispersion was filtered through glass wool.
137.03 (C15), 133.54 (C9), 131.66 (q, 2JCF ) 32.8 Hz, C18), 131.46
(C10), 130.50 (C17), 123.68 (C14), 123.52 (q, 1JCF ) 272.9 Hz, C20),
121.60 (C19), 119.59 (C1), 96.38 (C5), 72.18 (C3), 40.33 (C21),
-7.93 (C12). Anal. Calcd for C71H40F24I4N4Ni2O2 (M ) 2062.07 g
mol-1): C 41.35, H 1.96, N 2.72. Found: C 40.92, H 2.11, N 2.62.
[[(2,4,6-(3,5-(CF3)2C6H3)3C6H2)-NdC(H)-(3,5-I2-2-O-C6H2)-
K2-N,O]Ni(CH3)(pyridine)] (17). Yield: 89%. 1H NMR (400 MHz,
CD2Cl2): δ/ppm 8.42 (br, 2 H, 13-H), 8.34 (4 H, 17-H), 8.15 (2 H,
22-H), 8.09 (2 H, 19-H), 7.99 (d, 4JHH ) 2.1 Hz, 1 H, 24-H), 7.92
(1 H, 4-H), 7.78 (br, 1 H), 7.69 (br, 2 H, 14-H), 7.55 (s, 1 H), 7.20
(br, 2 H), 7.14 (d, 4JHH ) 2.1 Hz, 1 H), -0.91 (s, 3 H). 13C NMR
(151 MHz, CD2Cl2): δ/ppm 167.07 (C7), 163.68 (C2), 151.41 (C13),
150.37 (C8), 149.85 (C4), 141.61 (C6), 141.40 (C11), 140.57 (C16),
2
137.25 (C21), 137.10 (C14), 134.45 (C9), 132.40 (d, JCF ) 33.7
2
Hz, C23), 131.90 (q, JCF ) 33.4 Hz, C18), 130.58 (C17), 129.84
(C10), 127.54 (C22), 123.76 (C15), 123.53 (q, 1JCF ) 273.3 Hz, C20),
123.45 (q, 1JCF ) 272.0 Hz, C25), 121.99 (C19), 119.55 (C1), 96.49
(C5), 72.38 (C3), -7.70 (C12). Anal. Calcd for C43H22F18I2N2NiO
(M ) 1237.12 g mol-1): C 41.75, H 1.79, N 2.26. Found: C 42.17,
H 2.17, N 2.30.
Acknowledgment. Financial support by BASF AG is
gratefully acknowledged. We thank Ralf Thomann (Freiburg)
for TEM analyses and Lars Bolk for GPC analyses. S.M. is
indebted to the Fonds der Chemischen Industrie and to the
Hermann-Schnell Foundation.
Supporting Information Available: Mass flow traces of eth-
ylene uptake during polymerization. This material is available free
of charge via the Internet at http://pubs.acs.org.
N,N,N′,N′-Tetramethylethylenediamine (tmeda) Complexes.
These were prepared analogously to the above general procedure
for pyridine complexes, omitting the addition of pyridine. 14a-
tmeda: yield 92%. Anal. Calcd for C72H62F24I4N6Ni2O2 (M )
OM700942Z