Copper(II) ethylene polymerization catalysts: Do they really exist?

Article abstract of DOI:10.1021/om800625f

The reactions of two types of copper(II) ethylene polymerization catalysts, [(sal)CuCl]₂ (sal = 2-{C(H)=N(2,6-ⁱPr₂-C ₆H₃)}-4,6-^tBu₂-phenoxide) and (α-diimine)CuCl₂ (α-diimine = [2,6-ⁱPr ₂-C₆H₃)-N=C(Me)]₂), with methylaluminoxane (MAO) and trimethylaluminum (TMA) have been investigated. In both examples, facile and irreversible ligand (L) transfer from copper to TMA present in MAO was observed, resulting in formation of the corresponding (sal)AlMe₂ and (imino-amido)AlMe₂ complexes. The (imino-amido)AlMe₂ complex is formed by α-diimine ligand transfer to aluminum followed by alkylation of one imino moiety in the ligand backbone. Both aluminum complexes were active catalysts for ethylene polymerization with activities similar to their Cu(II) precursors. Simple addition of a neutral salicylaldimine or α-diimine ligand to MAO in the absence of any copper species resulted in the formation of the corresponding LAlMe₂ complexes, which are again active for ethylene polymerization. These results indicate that ethylene polymerization does not occur by a migratory insertion mechanism at the copper center, but is the result of ligand transfer to aluminum, and it is the resulting LAlMe₂/LAlMe ⁺ complexes that are likely the active species.

Full text of DOI:10.1021/om800625f

Organometallics 2008, 27, 5333–5338
5333
Copper(II) Ethylene Polymerization Catalysts: Do They Really
Exist?
Jeremy A. Olson,† Ramon Boyd,† J. Wilson Quail,‡ and Stephen R. Foley*,†
Department of Chemistry, UniVersity of Saskatchewan, and Saskatchewan Structural Sciences Centre,
110 Science Place, S7N 5C9, Saskatoon, Saskatchewan, Canada
ReceiVed July 3, 2008
The reactions of two types of copper(II) ethylene polymerization catalysts, [(sal)CuCl]2 (sal )
2-{C(H)dN(2,6-iPr2-C6H3)}-4,6-tBu2-phenoxide) and (R-diimine)CuCl2 (R-diimine ) [(2,6-iPr2-C6H3)-
NdC(Me)]2), with methylaluminoxane (MAO) and trimethylaluminum (TMA) have been investigated.
In both examples, facile and irreversible ligand (L) transfer from copper to TMA present in MAO was
observed, resulting in formation of the corresponding (sal)AlMe2 and (imino-amido)AlMe2 complexes.
The (imino-amido)AlMe2 complex is formed by R-diimine ligand transfer to aluminum followed by
alkylation of one imino moiety in the ligand backbone. Both aluminum complexes were active catalysts
for ethylene polymerization with activities similar to their Cu(II) precursors. Simple addition of a neutral
salicylaldimine or R-diimine ligand to MAO in the absence of any copper species resulted in the formation
of the corresponding LAlMe2 complexes, which are again active for ethylene polymerization. These
results indicate that ethylene polymerization does not occur by a migratory insertion mechanism at the
copper center, but is the result of ligand transfer to aluminum, and it is the resulting LAlMe2/LAlMe+
complexes that are likely the active species.
reports of copper complexes being active for the polymerization
of ethylene to high molecular weight polyethylene were reported
by the groups of Stibrany and Gibson employing either
(bisbenzimidazole)CuCl2 systems5 (1) or (R-diimine)CuCl2 (2).6
Since then, several other reports have emerged of LCuCl2 or
L2Cu complexes employing salicylaldiminato7 (3), pyrazolylpy-
rimidine8 (4), and chiral pyrazolylquinoline9 (5) ligands that
were also active for ethylene polymerization (Figure 1). Apart
from complex 3, all the reported copper precatalysts maintain
a very similar coordination environment about the metal center.
In all cases, methylaluminoxane (MAO) was used as a cocatalyst
with moderate to very low activities and high polymer molecular
weights reported (Table 1). No mechanism for polymerization
was deduced, although a coordination/insertion mechanism was
postulated in some cases.5
We initially intended to investigate the generality of homo-
geneous Cu(II) systems for ethylene polymerization and the
factors that influence both catalyst activity and polymer mo-
lecular weight. However, given that no Cu(II) alkyl species has
ever been isolated due to rapid reduction at the metal center,10
it appeared unlikely that ethylene polymerization could occur
by a migratory insertion mechanism at the Cu(II) center. While
Introduction
Early transition metal complexes have long dominated the
field of homogeneous ethylene polymerization and have been
the subject of numerous reviews.1 Research into late transition
metal systems began in earnest when Brookhart discovered that
R-diimine-ligated nickel and palladium systems produced high
molecular weight polyethylene with an activity comparable to
early transition metal systems.2 Since this discovery, there has
been tremendous research into a variety of late transition metal
systems, and this has been the subject of several recent reviews.3
One general trend that has emerged is to explore the reactivity
of transition metals not previously known to polymerize ethylene
via a migratory insertion mechanism. Late transition metal
species have been especially targeted for the development of
catalysts for the copolymerization of ethylene with polar
monomers due to their greater functional group tolerance.4
Direct copolymerization of ethylene with polar monomers
remains one of the most sought after goals in the design of new
olefin polymerization catalysts. Copper has become an attractive
candidate for the homo- and copolymerization of ethylene with
functionalized monomers. It was only recently that the first
* Corresponding author. E-mail: stephen.foley@usask.ca.
† Department of Chemistry, University of Saskatchewan.
‡ Saskatchewan Structural Sciences Centre.
(1) (a) Zhang, J.; Wang, X.; Jin, G.-X. Coord. Chem. ReV. 2006, 250,
95. (b) Alt, H. G.; Koeppl, A. Chem. ReV. 2000, 100, 1205. (c) Scheirs, J.,
Kaminsky, W., Eds. Metallocene-Based Polyolefins, Preparation, Properties,
and Technology; Wiley: West Sussex, 2000. (d) Britovsek, G. J. P.; Gibson,
V. C.; Wass, D. F. Angew. Chem., Int. Ed. 1999, 38, 428.
(2) Johnson, L. K.; Killian, C. M.; Brookhart, M. J. Am. Chem. Soc.
1995, 117, 6414.
(3) (a) Kuhn, P.; Semeril, D.; Matt, D.; Chetcuti, M. J.; Lutz, P. Dalton
Trans. 2007, 5, 515. (b) Sun, W.-H.; Zhang, D.; Zhang, S.; Jie, S.; Hou, J.
Kinet. Catal. 2006, 47, 278. (c) Gibson, V. C.; Spitzmesser, S. K. Chem.
ReV. 2003, 103, 283. (d) Ittel, S. D.; Johnson, L. K.; Brookhart, M. Chem.
ReV. 2000, 100, 1169.
(4) (a) Sen, A.; Borkar, S. J. Organomet. Chem. 2007, 692, 3291. (b)
Boffa, L. S.; Novak, B. M. Chem. ReV. 2000, 100, 1479.
(5) (a) Stibrany, R.; Schultz, D.; Kacker, S.; Patil, A. (Exxon Research
and Engineering) WO 99/30822, 1999. (b) Stibrany, R. T.; Schulz, D. N.;
Kacker, S.; Patil, A. O.; Baugh, L. S.; Rucker, S. P.; Zushma, S.; Berluche,
E.; Sissano, J. A. Macromolecules 2003, 36, 8584.
(6) Gibson, V. C.; Tomov, A.; Wass, D. F.; White, A. J. P.; Williams,
D. J. J. Chem. Soc., Dalton Trans. 2002, 2261.
(7) Gallette, A. M. R.; Carlini, C.; Giaiacopi, S.; Martinelli, M.; Sbrana,
G. J. Polym. Sci., Part A: Polym. Chem. 2007, 45, 1134.
(8) Bushuev, M. B.; Krivopalov, V. P.; Semikolenova, N. V.; Peresyp-
kina, E. V.; Virovets, A. V.; Sheludyakova, L. A.; Lavrenova, L. G.;
Zakharov, V. A.; Larionov, S. V. Russ. J. Coord. Chem. 2006, 32, 208.
(9) Larionov, S. V.; Savel’eva, Z. A.; Semikolenova, N. V.; Klevtsova,
R. F.; Glinskaya, L. A.; Boguslavskii, E. G.; Ikorskii, V. N.; Zakharov,
V. A.; Popov, S. A.; Tkachev, A. V. Russ. J. Coord. Chem. 2007, 33, 436.
(10) (a) Cohen, H.; Meyerstein, D. Inorg. Chem. 1986, 25, 1505. (b)
Ferraudi, G. Inorg. Chem. 1978, 17, 2506.
10.1021/om800625f CCC: $40.75
2008 American Chemical Society
Publication on Web 09/19/2008

5334 Organometallics, Vol. 27, No. 20, 2008
Olson et al.
Scheme 1
poorly understood.14 Facile ligand transfer from nickel to
aluminum has been previously reported by Collins et al.
employing electron-rich Ni(II) iminophosphonamide complexes
in the presence of TMA.15 Herein we detail ligand transfer
studies between copper and aluminum and ethylene polymer-
ization activities of the resulting complexes.
Figure 1. Reported Cu(II) ethylene polymerization precatalysts.
Table 1. Results of Ethylene Polymerization Studiesa
Results and Discussion
activity
yield (g PE/
MAO
P
T
To investigate the reactivity of copper(II) complexes with
aluminum alkyl species, we first synthesized a (sal)Cu(II)
complex (sal ) salicylaldiminato). The particular interest in
bulky sal ligands stems from neutral nickel ethylene polymer-
ization catalysts, (sal)Ni(Ph)PPh3, developed by Grubbs.16
Reaction of the sodium salt of bulky salicylaldimine 6 with
CuCl2 resulted in formation of [(sal)CuCl]2 (7) as a paramagnetic
(µeff ) 2.23 µB) dark green solid in 74% yield (Scheme 1). In
the IR spectra of 7, the azomethine band (νCN ) 1612 cm-1) is
shifted to lower wavenumber compared to that of the free ligand
(νCN ) 1622 cm-1), consistent with coordination through the
azomethine nitrogen. Elemental analysis is consistent with the
proposed structure for 7, and a crystal structure determination
clearly showed that 7 is a dinuclear chloride-bridged dimer in
the solid state, consistent with previously proposed structures
for a [(sal)CuCl]2-type complex (Figure 2).17,18 Somewhat
surprisingly, given the near ubiquitous employment of sal
ligands across the periodic table, dinuclear four-coordinate
chloride-bridged [(sal)CuCl]2 complexes are rare species with
no previous characterization by crystallography. The crystal
structure of 7 shows that the geometry about each metal center
is a distorted square-planar environment, as indicated by
N-Cu-O/Cl-Cu-Cl dihedral angles of 18° and 22° for Cu1
and Cu2, respectively. The Cu1 · · · Cu2 distance is 3.330 Å.
Upon activation with MAO, copper complex 7 was active
for ethylene polymerization, albeit with low activity (Table 1).
Addition of the neutral salH ligand 6 to MAO in the absence
of any copper complex resulted in the formation of species that
entry precat. (equiv) (atm) (°C) (g) mmol)
Mw
Mw/Mn
1
2
3
4
5
6
6
7
8
9
10
11
2a
200
200
200
200
200
200
200
3 mL
>200
500
500
200
500
500
4.7 70 0.028
4.7 70 0.034
4.7 70 0.046
4.7 70 0.031
4.7 70 0.007
4.7 70 0.030
4.7 70 0.010
1.4 7.2 × 105
1.7 1.0 × 105
2.3 1.1 × 106
1.6 6.7 × 105
0.35 1.4 × 106
1.5 4.1 × 105
0.5 4.2 × 105
0
3.6
1.5
3.3
2.0
5.5
1.1
1.1
7
8b
95
4.7 70
50 80
0
1
“high”
1056 2a
5.0 70 trace
4.5 20 0.4
>5 × 106
116 2b
23
5.5
350
650
>5 × 106
127
137
149
3
4
5
80
10
10
80 0.11
35 0.7
35 1.3
a Reaction conditions: Fischer-Porter glass reactor, toluene (20 mL),
precatalyst (20 µmol), reaction time: 24 h. Average of 2 experiments.
Molecular weights determined by GPC at 140 °C. b Control experiment
performed in the absence of any complex or ligand (3 mL ) 200 equiv
for entries 1-7). For entries 9-14, results taken from the literature.5-9
many Cu(I) alkyl species exist, they are usually unstable at
ambient temperatures unless supported by bulky electron-rich
phosphine or N-heterocyclic carbene ligands.11
We now propose that ethylene polymerization does not occur
by a migratory insertion mechanism at the copper center, but
in fact ligand transfer occurs from copper to trimethylaluminum
(TMA) present in MAO, and it is the resulting aluminum alkyl
complexes (LAlMe2/LAlMe+) that are likely the active species
for ethylene polymerization. Commercial MAO solutions con-
tain large amounts of trimethylaluminum (30-35%),12 and
aluminum complexes are well known to polymerize ethylene,13
although the polymerization mechanism in these systems is
(14) Theoretical studies suggest that ꢀ-H transfer dominates over chain
propagation in cationic aluminum alkyl species, indicating that more
complex structures for the active species may be involved: (a) Talarico,
G.; Budzelaar, P. H. M. Organometallics 2000, 19, 5691. (b) Talarico, G.;
Busico, V.; Budzelaar, P. H. M. Organometallics 2001, 20, 4721.
(15) (a) Stapleton, R. A.; Chai, J.; Taylor, N. J.; Collins, S. Organo-
metallics 2006, 25, 2514. (b) 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.
(11) (a) Mankad, N. P.; Gray, T. G.; Laitar, D. S.; Sadighi, J. P.
Organometallics 2004, 23, 1191. (b) Pasynkiewicz, S.; Pikul, S.; Poplawska,
J. J. Organomet. Chem. 1985, 293, 125.
(12) (a) Pe´deutour, J.-N.; Radhakrishnan, K.; Cramail, H.; Deffieux, A.
J. Mol. Catal. A: Chem. 2002, 185, 119. (b) Chen, E. Y.; Marks, T. Chem.
ReV. 2000, 100, 1391.
(16) Younkin, T. R.; Conner, E. F.; Henderson, J. I.; Friedrich, S. K.;
Grubbs, R. H.; Bansleben, D. A. Science 2000, 287, 460.
(17) Donnia, A. M.; El-Boraey, H. A. Transition Met. Chem. 1993, 18,
315.
(13) (a) Shaver, M. P.; Allan, L. E.; Gibson, V. C. Organometallics
2007, 26, 2252. (b) Pappalardo, D.; Mazzeo, M.; Montefusco, P.; Tedesco,
C.; Pellecchia, C. Eur. J. Inorg. Chem. 2004, 1292. (c) Pappalardo, D.;
Tedesco, C.; Pellecchia, C. Eur. J. Inorg. Chem. 2002, 621. (d) Cameron,
P. A.; Gibson, V. C.; Redshaw, C.; Segal, J. A.; Solan, G. A.; White, A. J. P.;
Williams, D. J. J. Chem. Soc., Dalton Trans. 2001, 1472. (e) Korolev, A. V.;
Ihara, E.; Guzei, I. A.; Young, V. G.; Jordan, R. F. J. Am. Chem. Soc.
2001, 123, 8291. (f) Bruce, M.; Gibson, V. C.; Redshaw, C.; Solan, G. A.;
White, A. J. P.; Williams, D. J. Chem. Commun. 1998, 2523. (g) Coles,
M. P.; Jordan, R. F. J. Am. Chem. Soc. 1997, 119, 8125.
(18) X-ray structure determination of 7: C54H76Cl2Cu2N2O2, Mw 983.15,
dark green, crystal size (0.20 × 0.10 × 0.10 mm3), triclinic, space group
j
P1, a ) 12.7591(6) Å, b ) 14.5248(9) Å, c ) 17.2981(11) Å, R )
111.594(2)°, ꢀ ) 100.070(3)°, γ ) 104.797(3)°, V ) 2750.0(3) Å3, Z ) 2,
Dcalc ) 1.187 Mg/m3, F(000) ) 1044, T ) 295(2) K, Mo KR radiation
(0.71073 Å, µ 0.908 mm-1). 14 021 collected reflections, 8701 unique (Rint
) 0.0390); final R indices [I > 2σ(I)] were R1 ) 0.0512, wR2 ) 0.1095,
R indices (all data): R1 ) 0.0832, wR2 ) 0.1242; data/restraints/parameters
8701/0/578; GoF ) 1.053. Largest peak and hole 0.474 and-0.400 e Å-3
.

Copper(II) Ethylene Polymerization Catalysts
Organometallics, Vol. 27, No. 20, 2008 5335
Scheme 3
Scheme 4
Figure 2. ORTEP plot of 7 at the 50% probability level. The
hydrogen atoms have been omitted for clarity. Selected bond lengths
(Å) and angles (deg): Cl(1)-Cu(2) ) 2.2590(11), Cl(1)-Cu(1) )
2.3020(12), Cu(1)-O(1) ) 1.861(2), Cu(1)-N(1) ) 1.954(3),
Cu(1)-Cl(2) ) 2.2629(10), Cu(2)-Cl(1)-Cu(1) ) 93.77(4),
O(1)-Cu(1)-N(1) ) 94.37(11), O(1)-Cu(1)-Cl(2) ) 164.79(9),
N(1)-Cu(1)-Cl(2) ) 96.07(9), O(1)-Cu(1)-Cl(1) ) 86.99(8),
N(1)-Cu(1)-Cl(1) ) 167.45(10), Cl(2)-Cu(1)-Cl(1) ) 85.22(4).
No attempt to separate 8 from 9 was made; however, the
identity of both species was further confirmed by comparison
to independently synthesized samples of 8 and 9. The (sal)AlMe2
complex, 8, has been previously reported by Gibson and is active
for ethylene polymerization when activated with B(C6F5)3.13c,d
(Sal)Al(Cl)Me (9) is readily synthesized by reaction of the
neutral salH ligand 6 with Me2AlCl in 96% yield (Scheme 3).
Both 8 and 9 were active for ethylene polymerization in the
presence of MAO and have similar activities (Table 1). SalH
ligand 6 was also reacted with 3 equiv of MAO in place of
TMA which resulted in formation of (sal)AlMe2 complex 8 in
95% yield (Scheme 4). Using the phosphine method developed
by Andrew Barron,20 the percentage of the total aluminum
content existing as TMA in the commercially obtained MAO
solution was determined to be 35%. Therefore, 3 equiv of MAO
was employed, resulting in approximately 1 equiv of TMA per
salH ligand. Control polymerization experiments where MAO
was used in the absence of any complex or ligand did not yield
any solid polyethylene (Table 1).
Scheme 2
Having demonstrated that a copper(II) precatalyst of our own
design, upon reaction with TMA or MAO, resulted in facile
ligand transfer to aluminum and that these species were active
for ethylene polymerization in the absence of copper species,
we set about investigating if the same results would be observed
with Gibson’s (R-diimine)CuCl2 complex, 2a.
were also active for ethylene polymerization with similar activity
to that of 7 (Table 1). Thus, it appeared that copper was not
required to initiate ethylene polymerization. To investigate if
ligand transfer was occurring from copper to aluminum,
stoichiometric reactions of 7 with trimethylaluminum (TMA)
were carried out. Commercial MAO solutions contain high
amounts of TMA (30-35%)12 with a significant percentage
remaining present in MAO even after distillation.19 This is due
to the fact that TMA in MAO solutions can exist in two distinct
forms: first as “free” TMA in its dimeric form, Al2Me6, and
second as complexed TMA, associated with the various MAO
chains.12 Upon addition of 2 equiv of TMA to 7 in toluene, the
dark green solution immediately became pale yellow. After
filtration and removal of solvent, a yellow powder was isolated.
Analysis by 1H NMR revealed that the reaction of 7 with TMA
resulted in ligand transfer to aluminum, yielding two products,
(sal)AlMe2 (8) and (sal)Al(Cl)Me (9), in a 1:1 ratio in 85%
isolated yield (Scheme 2). The resulting products showed that
not only does sal ligand transfer occur from copper to aluminum
but chloride/methyl metathesis also occurs between the two
metal centers. The final fate of the copper species was not
ascertained.
In our hands, precatalyst 2a was indeed active for ethylene
polymerization in the presence of MAO, again with very low
activity (Table 1). Addition of the neutral R-diimine ligand 10
to MAO in the absence of any copper species resulted in the
formation of species that were also active for ethylene polym-
erization with similar activity to that of 2a (Table 1). Reaction
of (R-diimine)CuCl2 2a with TMA resulted in formation of
aluminum complex 11; however, rather than having a neutral
diimine coordinated to the aluminum center, alkylation of one
of the imino moieties of the ligand backbone occurred, resulting
in formation of (imino-amido)AlMe2 complex 11 as the major
product (Scheme 5). This reaction did not proceed as cleanly
as the analogous reaction for [(sal)CuCl]2 (7). One other species
was present in the reaction mixture that has not yet been
identified. (Formation of the analogous (imino-amido)Al(Cl)Me
has been ruled out, as it was independently synthesized and
spectral data were compared.) To further confirm the identity
of the major product from Scheme 5, R-diimine 10 (the neutral
(19) Sivaram, S. Macromolecules 1993, 26, 1180.
(20) Barron, A. R. Organometallics 1995, 14, 3581.

5336 Organometallics, Vol. 27, No. 20, 2008
Olson et al.
Scheme 5
Scheme 6
Figure 3. ORTEP plot of 11 at the 50% probability level. The
hydrogen atoms have been omitted for clarity. Selected bond lengths
(Å) and angles (deg): Al(1)-N(1) ) 1.845(2), Al(1)-C(7) )
1.961(3), Al(1)-C(6) ) 1.961(3), Al(1)-N(2) ) 1.980(2),
N(1)-C(1) ) 1.477(3), N(2)-C(2) ) 1.303(4), C(7)-Al(1)-C(6)
) 108.21(15), N(1)-Al(1)-N(2) ) 84.59(10).
ligand from 2a) was reacted with 1 equiv of TMA in toluene,
resulting unequivocally in the formation of 11 in 71% yield
(Scheme 6). The alkylation of an imino moiety of a diimine
ligand, upon reaction with TMA, has previously been observed
1
for both R-diimine and pyridine-diimine ligands.13f,21 The H
to ligand transfer to aluminum, it remains unclear what
the mechanism for polymerization is for aluminum or even if
the aluminum complexes are directly responsible for the
observed catalytic activity.14,23
NMR spectra for 11 indicated a loss of symmetry in the ligand
and formation of a Cs symmetric species with one singlet for
the imino-methyl group at 1.42 ppm integrating for three protons
and another singlet for the two amino-methyl groups at 1.15
ppm integrating for six protons. Characteristic high-field
resonances for the aluminum methyl groups are observed at
-0.40 ppm (s, 6H). Single crystals of 11 were obtained from a
concentrated toluene solution at -25 °C, thus allowing for an
X-ray structure determination (Figure 3).22 The X-ray data
showed that the N1-C1-C2-N2 portion of the imino-amido
ligand is almost planar, with a torsional angle of 3.9°. The
aluminum atom lies within this plane and adopts a distorted
tetrahedral geometry. The Al-Me distances are identical at
1.961(3) Å. As expected, the Al-N bond with the formally
negatively charged amido nitrogen N1 is significantly shorter
at 1.845(2) Å than the neutral imino nitrogen Al-N2 at 1.980(2)
Å.
R-Diimine 10 was also reacted with 3 equiv of MAO in place
of TMA, which again resulted in formation of (imino-ami-
do)AlMe2 complex 11 in 78% isolated yield (Scheme 6).
In conclusion, we have shown in two separate examples of
copper(II) complexes active for ethylene polymerization in the
presence of MAO that the copper itself was not required to
initiate polymerization. In both cases, facile ligand transfer takes
place from the LCu(II) complexes to trimethylaluminum,
resulting in formation of the corresponding LAlMe2 complexes.
The same aluminum species can be generated by simple ligand
addition to MAO in the absence of any copper species, and the
resulting aluminum complexes are all active catalysts for
ethylene polymerization, albeit with low activity.
Experimental Section
General Information. Unless otherwise stated, all reactions were
performed under N2 or vacuum using standard Schlenk techniques
or in a N2-filled drybox. All reaction temperatures for catalytic
reactions refer to the temperature of pre-equilibrated oil baths. All
melting points were recorded on a Gallenkamp melting point
apparatus and are uncorrected. 1H and 13C{1H} NMR spectra were
recorded on a Bruker 500 MHz Avance spectrometer. Chemical
shifts for 1H and 13C NMR are reported in ppm in reference to the
residual 1H and 13C resonances of CDCl3 (1H: δ 7.24; 13C: δ 77.24)
and C6D6 (1H: δ 7.16). Coupling constants are given in Hz.
Elemental analyses were performed on a Perkin-Elmer 2400 CHN
elemental analyzer. Elemental analyses for the air-sensitive alkyl-
aluminum complexes 9 and 11 were performed by Midwest
Microlabs. IR data was collected by diffuse reflectance spectros-
copy. GPC data were obtained from a Viscotek high-temperature
GPC. Methylaluminoxane (10 wt % in toluene), dimethylaluminum
chloride (1.0 M in hexanes), and trimethylaluminum (2.0 M in
toluene) were purchased from the Sigma-Aldrich Chemical Co. The
percentage of the total aluminum content existing as TMA in the
MAO solution was determined to be 35%.20 Salicyaldimine (6),13d
(sal)AlMe2 (8),13d R-diimine (10),2 and (R-diimine)CuCl2 (2a)6
were all synthesized according to literature procedures.
Synthesis of [(sal)CuCl]2 (7). A 100 mL round-bottom flask
was charged with salicylaldimine 6 (0.500 g, 1.27 mmol) and THF
(20 mL). Two equivalents of NaH (0.062 g, 2.56 mmol) was slowly
added, and the suspension was stirred for 1 h and filtered to remove
excess NaH. The filtrate then added to a second round-bottom flask
containing 1.5 equiv of CuCl2 (0.255 g, 1.89 mmol). The yellow
filtrate immediately turned dark brown. The reaction mixture was
allowed to stir 24 h, whereupon it was filtered and the solvent
removed under vacuum, resulting in a dark green solid. The product
was crystallized from a concentrated 1:1 solution of hexane and
toluene at -25 °C (0.462 g, 74%). µeff ) 2.23 µB. IR (KBr, cm-1):
2960 (s), 2906 (s), 2868 (s), 1612 ν(CdN), 1599 (s), 1585 (s),
1551 (s), 1530 (s), 1462 (s), 1442 (s), 1426 (s), 1384 (s), 1362 (s),
1326 (s), 1272 (s), 1255 (s), 1168 (s), 800 (s), 786 (s), 765 (s).
For over a decade now, well-defined aluminum alkyl com-
plexes have been reported to produce polyethylene.13 While it
now appears unlikely that a copper species can be an active
catalyst for ethylene polymerization under mild conditions due
(21) (a) Giezynski, R.; Pasynkiewics, S.; Serwatowska, A. J. Organomet.
Chem. 1974, 69, 345. (b) Knijnenburg, Q.; Smits, J. M. M.; Budzelaar,
P. H. M. Organometallics 2006, 1036.
(22) X-ray structure determination of 11: C31H49AlN2, Mw 476.70,
3
j
colorless, crystal size (0.12 × 0.12 × 0.03 mm ), triclinic, space group P1,
a ) 8.4373(5) Å, b ) 9.7007(5) Å, c ) 19.3460(11) Å, R ) 82.033(4)°,
ꢀ ) 80.769(3)°, γ ) 69.565(3)°, V ) 1458.71(14) Å3, Z ) 2, Dcalc ) 1.085
Mg/m3, F(000): 524, T ) 173(2) K, Mo KR radiation (0.71073 Å; µ 0.090
mm-1). 9900 collected reflections, 5436 unique (Rint ) 0.0631); final R
indices [I > 2σ(I)] were R1 ) 0.0679, wR2 ) 0.1354, R indices (all data):
R1 ) 0.1129, wR2 ) 0.1551; data/restraints/parameters 5436/0/321; GoF
(23) It has been suggested that even ppb levels of transition metals may
significantly affect polymerization results: Budzelaar, P. H. M.; Talarico,
G. Struct. Bonding (Berlin) 2003, 105, 141.
) 1.033. Largest peak and hole 0.613 and-0.266 e Å-3
.

Copper(II) Ethylene Polymerization Catalysts
Organometallics, Vol. 27, No. 20, 2008 5337
Anal. Calcd for C54H76Cl2Cu2N2O2: C 65.97, H 7.79, N 2.85. Found:
C 65.63, H 8.01, N 2.71. Mp: 176-178 °C (dec).
Ligand Transfer between (r-diimine)CuCl2 (2a) and Al-
Me3. A round-bottom flask was charged with toluene (20 mL) and
(R-diimine)CuCl2 2a (0.157 g, 0.291 mmol). Trimethylaluminum
(0.201 mL, 2.0 M in toluene, 0.402 mmol) was added dropwise
via syringe and the solution stirred for 24 h. The initial dark brown
solution changed to a pale orange color upon addition of trimethyl-
aluminum. After stirring, the solution was filtered and the solvent
Synthesis of (sal)Al(Cl)Me (9). A 100 mL round-bottom flask
was charged with salicylaldimine 6 (0.158 g, 0.402 mmol) and
toluene (20 mL). Dimethylaluminum chloride (0.40 mL, 1.0 M in
hexanes, 0.40 mmol) was added dropwise via syringe and the
solution stirred for 24 h at ambient temperatures. The solution was
filtered and excess solvent was removed under vacuum, resulting
1
removed, resulting in formation of an orange solid. The H NMR
1
showed the presence of (imino-amido)AlMe2 (11) as the dominant
species; however one other species was also observed by 1H NMR,
which has not been identified.
in a yellow solid (0.180 g, 96%). H NMR (C6D6): δ 7.90 (s, 1H,
Ar-NdCH-Ar), 7.77 (d, J ) 2.6, 1H, NCAr-H), 7.12-7.08 (m,
3H, NAr-H), 6.92 (d, J ) 2.6, 1H, NCAr-H), 3.53 (sept, J ) 6.7,
1H, CH(CH3)2), 2.97 (sept, J ) 6.7, 1H, CH(CH3)2), 1.58 (s, 9H,
Synthesis of (imino-amido)AlMe2 (11) from r-Diimine 10
and MAO. A 100 mL round-bottom flask was charged with diimine
ligand 10 (0.107 g, 0.265 mmol) and toluene (40 mL). Three
equivalents of methylaluminoxane (0.58 mL, 10 wt % in toluene,
0.86 mmol) was added dropwise via syringe and the solution stirred
for 24 h. After stirring, the solution was filtered and the solvent
was removed under vacuum, resulting in a yellow solid. 1H NMR
showed formation of 11 as the only observed species along with
residual MAO (0.098 g, 78%).
General Ethylene Polymerization Procedure. In a glovebox,
the precatalyst (20 µmol) was dissolved in toluene (20 mL) in a
Fischer-Porter bottle. The bottle was connected to a valve-
polymerization system, sealed, and taken out of the glovebox. The
system was connected to a Schlenk line, purged three times with
N2, and filled with 10 psi of ethylene. A 200 equiv amount of MAO
(10 wt % in toluene) was added via syringe, and the ethylene
pressure increased to 70 psi. The reaction mixture stirred for 24 h
while heating at 70 °C. After stirring, the reaction was quenched
with 1 M acidified methanol and filtered, and the resulting polymer
was washed with 1 M acidified methanol, followed by methanol.
The polymer was dried under vacuum. Molecular weights and Mw/
Mn were determined using a Viscotek high-temperature GPC at
140 °C.
t
tBu), 1.35 (d, J ) 6.7, 3H, CH(CH3)2), 1.22 (s, 9H, Bu), 1.12 (d,
J ) 6.7, 3H, CH(CH3)2), 0.87 (d, J ) 6.7, 3H, CH(CH3)2), 0.70
(d, J ) 6.7, 3H, CH(CH3)2), -0.11 (s, 3H, AlCH3). 13C NMR
(CDCl3): δ 175.49 (CdN), 161.92, 143.61, 142.60, 141.36, 141.10,
134.36, 129.12, 128.78, 125.24, 124.07, 118.21, 35.64, 34.39, 31.39,
29.63, 28.84, 28.39, 26.43, 26.40, 23.54, 22.35. Anal. Calcd for
C28H41AlClNO: C 71.54, H 8.79, N 2.98. Found: C 71.33, H 8.69,
N 2.94. EI-MS (m/z): calcd for C27H38AlClNO [M - CH3]+ 454.2,
found 454.3.
Ligand Transfer between [(sal)CuCl]2 (7) and AlMe3. A 100
mL round-bottom flask was charged with [(sal)CuCl]2 (7) (0.201
g, 0.205 mmol) and toluene (20 mL). Two equivalents of trimethyl-
aluminum (0.23 mL, 2.0 M in toluene, 0.46 mmol) was added
dropwise via syringe, and the solution was stirred for 24 h. Upon
addition of trimethylaluminum, the dark green solution immediately
turned bright yellow. The resulting reaction mixture was filtered
and solvent removed under vacuum, resulting in formation of a
yellow solid (0.179 g, 85% yield based on 1:1 ratio of 8 and 9).
Only two products were observed by 1H NMR, consisting of a 1:1
mixture of (sal)AlMe2 (8) and (sal)Al(Cl)Me (9). Identity of
products was confirmed by comparison to independently synthesized
samples of 8 and 9.
X-ray Structure Determinations. Data were collected at room
temperature for 7 and at -100 °C for 11 on a Nonius Kappa
CCD diffractometer, using the COLLECT program.24 Cell
refinement and data reductions used the programs DENZO and
SCALEPACK.25 SIR9726 was used to solve the structure, and
SHELXL9727 was used to refine the structure. ORTEP-3 for
Windows28 was used for molecular graphics, and PLATON29
was used to prepare material for publication. H atoms were
placed in calculated positions with Uiso constrained to be 1.5
times Ueq of the carrier atom for all methyl H atoms and 1.2
times Ueq of the carrier atom for all other H atoms.
For complex 7, most of the checkCIF ALERTs occur because
the molecule has C atoms that are very rigidly held and others
that have very great vibrational and rotational freedom. Thus,
the first two A ALERTs come from this wide range of rigidity
in the molecule. The third A ALERT (Check Low Ueq as
compared to Neighbors for C42) occurs because C42 is the
central atom of a tert-butyl group and is bonded to a phenyl
ring, but the three attached methyl groups can rotate and vibrate
freely. The first B ALERT occurs because the data were cut at
24.12°. The diffraction pattern became very weak beyond this
angle. The other three B ALERTs occur because of the presence
of isopropyl and tert-butyl groups. The central atom is attached
directly to a phenyl ring and has a small Ueq, whereas the
Synthesis of (sal)AlMe2 (8) from Salicylaldimine (6) and
MAO. A 100 mL round-bottom flask was charged with salicyla-
ldimine 6 (0.104 g, 0.265 mmol) and toluene (20 mL). Three
equivalents of methylaluminoxane (0.51 mL, 10 wt % in toluene,
0.76 mmol) was added dropwise via syringe and the solution stirred
for 24 h. After stirring, the solution was filtered and the solvent
was removed under vacuum, resulting in a yellow solid. 1H NMR
showed formation of 8 as the only observed species along with
1
residual MAO (0.113 g, 95%). H NMR (C6D6): δ 7.86 (s, 1H,
Ar-NdCH-Ar), 7.74 (d, 4J ) 2.4, 1H, NCAr-H), 7.15-7.0 (m, 2H,
4
NAr-H), 7.05 (s, 1H, NAr-H), 6.91 (d, J ) 2.4, 1H, p-NCAr-H),
3.17 (sept, J ) 6.7, 2H, CH(CH3)2), 1.60 (s, 9H, tBu), 1.25 (s, 9H,
tBu), 1.19 (d, J ) 6.7, 6H, CH(CH3)2), 0.81 (d, J ) 6.7, 6H,
CH(CH3)2), -0.24 (s, 6H, Al(CH3)2).
Synthesis of (imino-amido)AlMe2 (11). A round-bottom flask
was charged with toluene (20 mL) and R-diimine ligand 10 (0.170
g, 0.421 mmol). Trimethylaluminum (0.22 mL, 2.0 M in toluene,
0.44 mmol) was added dropwise via syringe and the solution stirred
for 24 h. The initial bright yellow solution of 10 changed to a pale
yellow upon addition of trimethylaluminum. The solution was
filtered and solvent removed under vacuum, resulting in formation
of a white solid. The product was crystallized from a concentrated
1
toluene solution at -25 °C (0.141 g, 71%). H NMR (C6D6): δ
7.25 (m, 3H, Ar-H), 7.10 (m, 3H, Ar-H), 3.93 (sept, J ) 6.7, 2H,
CH(CH3)2), 3.11 (sept, J ) 6.7, 2H, CH(CH3)2), 1.42 (s, 3H,
H3C-CdN), 1.39 (d, J ) 6.7, 6H, CH(CH3)2), 1.31 (d, J ) 6.7,
6H, CH(CH3)2), 1.28 (d, J ) 6.7, 6H, CH(CH3)2), 1.15 (s, 6H,
(CH3)2C-N), 0.96 (d, J ) 6.7, 6H, CH(CH3)2), -0.40 (s, 6H,
Al(CH3)2). 13C NMR (C6D6): δ 199.09, 151.54, 147.53, 143.03,
141.61, 138.74, 125.19, 124.31, 67.84, 28.58, 28.23, 27.99, 25.13,
24.84, 24.63, 24.54, 18.43, -6.53. Anal. Calcd for C31H49AlN2: C
78.10, H 10.36, N 5.88. Found: C 77.82, H 10.05, N 5.57. EI-MS
(m/z): calcd for C30H46AlN2 [M - CH3]+ 461.3, found 461.4.
(24) COLLECT; Nonius BV: Delft, The Netherlands, 1998.
(25) Otwinowski, Z.; Minor, W. In Methods in Enzymology, Vol. 276,
Macromolecular Crystallography, Part A; Carter C. W., Sweet, R. M., Eds.;
Academic Press: London, 1997; pp 307-326.
(26) Altomare, A.; Burla, M. C.; Camalli, M.; Cascarano, G; Giacovazzo,
C.; Guagliardi, A.; Moliterni, A. G. G.; Polidori, G.; Spagna, R. J. Appl.
Crystallogr. 1999, 32, 115–119.
(27) Sheldrick, G. M. SHELXL-97; University of Go¨ttingen: Germany,
1997.
(28) Farrugia, L. J. J. Appl. Crystallogr. 1997, 30, 565.

5338 Organometallics, Vol. 27, No. 20, 2008
Olson et al.
terminal methyl groups have much higher Ueq. C11 is a terminal
methyl in a tert-butyl group. C12 is the central atom of an
isopropyl group, and C25 is the central atom of a tert-butyl
group.
Supporting Information Available: Full crystallographic data
for compounds 7 and 11 are available as CIF files. This material is
available free of charge via the Internet at http://pubs.acs.org.
OM800625F
Acknowledgment. We gratefully thank the Natural Sci-
ences and Engineering Research Council of Canada (NSERC)
for financial support.
(29) Spek, A. L. PLATON; University of Utrecht: The Netherlands, 2001.