Unexpected Precatalyst σ-Ligand Effects in Phenoxyimine Zr-Catalyzed Ethylene/1-Octene Copolymerizations

Article abstract of DOI:10.1021/jacs.9b01445

Recent decades have witnessed intense research efforts aimed at developing new homogeneous olefin polymerization catalysts, with a primary focus on metal-Cl or metal-hydrocarbyl precursors. Curiously, metal-NR₂ precursors have received far less

Full text of DOI:10.1021/jacs.9b01445

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Article
Unexpected Precatalyst #-Ligand Effects in Phenoxyimine
Zr-Catalyzed Ethylene/1-Octene Copolymerizations
Yanshan Gao, Matthew D Christianson, Yang Wang, Jiazhen Chen,
Steve Marshall, Jerzy Klosin, Tracy L. Lohr, and Tobin J. Marks
J. Am. Chem. Soc., Just Accepted Manuscript • DOI: 10.1021/jacs.9b01445 • Publication Date (Web): 24 Apr 2019
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Journal of the American Chemical Society
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Unexpected Precatalyst σ-Ligand Effects in Phenoxyimine Zr-
Catalyzed Ethylene/1-Octene Copolymerizations
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Yanshan Gao, Matthew D. Christianson, Yang Wang, Jiazhen Chen, Steve Marshall, Jerzy
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Klosin, * Tracy L. Lohr, * and Tobin J. Marks *
1
2
Department of Chemistry, Northwestern University, Evanston, IL 60208–3113, USA. Corporate R&D, The Dow
Chemical Company, 1776 Building, Midland, Michigan 48674, USA.
Supporting Information Placeholder
ABSTRACT: Recent decades have witnessed intense research efforts aimed at developing new homogeneous olefin polymerization
catalysts, with a primary focus on metal-Cl or metal -hydrocarbyl precursors. Curiously, metal-NR
attention. In this contribution, the Zr-amido complex FI ZrX (FI = 2,4-di-tert-butyl-6-((isobutylimino)methyl)phenolate, X = NMe
is found to exhibit high ethylene polymerization activity and relatively high 1-octene co-enchainment selectivity (up to 7.2 mol%)
2
precursors have received far less
2
2
2
)
+
°
3 6 5 4
after sequential activation with trimethylaluminum, then Ph C B(C F ) . In sharp contrast, catalysts with traditional X =
hydrocarbyl ligands such as benzyl and methyl give low 1-octene incorporation (0 -1.0 mol%). This unexpected selectivity persists
under scaled/industrial operating conditions and was previously inaccessible with traditional metal-Cl or -hydrocarbyl precursors.
NMR, X-ray diffraction, and catalytic control experiments indicate that in this case an FI ligand is abstracted from FI Zr(NMe ) by
2 2 2
trimethylaluminum in the activation process to yield a catalytically active cationic mono-FIZr- species. Heretofore this process was
believed to serve as only a major catalyst deactivation pathway to be avoided. This work demonstrates the importance of
investigating diverse precatalyst monodentate σ-ligands in developing new catalyst systems, especially for group 4 olefin
polymerization catalysts.
1B),12-13 since these complexes often suffer from low alkylation
INTRODUCTION
7
,
14
12, 15-17
efficiency
and can afford multiple active sites.
Since the pioneering research by Ziegler and Natta on
heterogeneous olefin polymerizations in the 1950s, polyolefins
i
i
Aluminum alkyl reagents such as Al( Bu)
3
or Al( Bu)
However, these AlR
also strong reducing reagents, capable of reducing some
2
H are often
1
8-20
used as alkylating agents.
3
reagents are
1
-
have become some of the most important industrial materials.
2
Over the last three decades, homogeneous polymerization
catalyst systems and methodologies have advanced rapidly,
2
1-22
ancillary ligands (e.g., those with imine moieties).
3
-9
The implementation of phenoxyiminato (FI; Figure 1C)
group 4 metal complexes has afforded significant advances in
post-metallocene homogeneous olefin polymerization
with some produced industrially on a world-scale. These
developments have often focused on the design and
modification of ancillary ligands as well as the effects of the
identity of the central metal ion. Group 4 metal chloride and
hydrocarbyl complexes have primarily been used as catalyst
precursors for such systems due to their straightforward
synthetic accessibility and the ease with which they are
4, 10-11, 23-27
catalysis.
2 2
For example, activated FI Zr(alkyl)
complexes are employed to produce the hard block (PE-rich) of
2
8
Olefin Block Copolymers (OBCs)
via chain shuttling
polymerizations, a process which has been commercialized by
Dow Chemical. However, compared to the chloride and alkyl
7
, 10-11
activated (Figures 1A and 1B).
In contrast, readily
2 2 2
congeners, the corresponding FI Zr(NMe ) complexes have
accessible dialkylamido complexes, which have predominantly
been used only as intermediates in the synthesis of hydrocarbyl
and chloride complexes, have been largely overlooked (Figure
7
not been used as precatalysts. Here we report a novel strategy
for
ii. R abstraction or
A L
C General phenoxyiminate
D
Phenoxyiminate (FI)
catalysts in this study:
protonolysis
L
L
X
X
(FI) catalyst structure
M
M
R A
1
R
L
X = R = Me, Bn
N
X
Precatalyst
R3
N
Active species
X
X
M
M
O
X
O
2
2
R2
L
i. Alkylation
ii.
R
M
M = Ti, Zr, Hf
X = Bn, Cl, Me, etc
FI2Zr(NMe2)2 (1), X = NMe2 FI2ZrMe2 (3), X = Me
FI ZrBn (2), X = Bn
X = Cl, NMe2
R
L
2
2
FI ZrCl (4), X = Cl
2
2
Activated with Me Al, then Ph C B(C F ) (BT)
3
3
6 5 4
B
Bn, Cl, Me
(common precursors)
NMe (rarely studied)
Ancillary Ligand
Design &
Modification
L
L
X
M
X = Cl
X = Bn
X = NMe2
X
2
Inactive
Highly active
Highly active
M = Ti, Zr, Hf
1.0 mol% incorp.
7.2 mol% incorp.
Figure 1. A. Group 4 precatalysts with various monodentate X σ-ligands and their activation pathways for olefin polymerization. B.
Common design approaches to new olefin polymerization catalysts. C. General phenoxyimine catalyst structures. D. This study
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the activation of FI
2
Zr(NMe
2
)
2
complexes to afford highly active
method than the previously reported approach involving the
2
6, 29
1
2
3
4
5
6
7
8
9
1
1
1
1
1
1
1
1
1
1
2
2
2
2
2
2
2
2
2
2
3
3
3
3
3
3
3
3
3
3
4
4
4
4
4
4
4
4
4
4
5
5
5
5
5
5
5
5
5
5
6
catalysts for ethylene/1-octene copolymerization, giving 1-
octene incorporation of up to 7.2 mol%. This result stands in
sharp contrast to the benzyl or methyl analogues, which
achieve only 0-1.0 mol% 1-octene incorporation under the
same reaction conditions. Both advanced NMR spectroscopy
and X-ray diffraction, combined with control experiments
argue that ancillary ligand transfer from Zr to Al occurs during
trimethylauminum (TMA) alkylation. Heretofore this process
was believed to only serve as a major catalyst deactivation
pathway and should be avoided. Instead we report here the
generation and characterization of a mono-FI-Zr catalyst
capable of high comonomer incorporation levels with minimal
loss in polymerization activity.
reaction of FI-MgBr with in situ generated Me
2 2
ZrCl .
Single
crystals suitable for X-ray diffraction were obtained via the
slow cooling of toluene/n-hexane for 1, and toluene for 3 and
4. The Zr centers in all structures (Figure 2) adopt distorted
octahedral geometries with trans-O, cis-Nimine, and cis-X (X =
NMe , Me, or Cl) configurations around the Zr center. This likely
2
reflects both steric and electronic factors, with the Zr-O bond
length shorter than the Zr-Nimine distance (2.04 Å vs. 2.44 Å in
7
, 30
1, 2.00 Å vs. 2.40 Å in 3, and 1.99 Å vs. 2.32 Å in 4, see SI).
To the best of our knowledge, the X-ray structure of 3
represents the first example of the crystallographic
characterization of an FI ZrMe complex.
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
2
2
For polymerization studies, the “alkylation” of amido
complex 1 (FI Zr(NMe ) was performed by adding a
trimethylaluminum (TMA) solution in toluene to a solution of
2
2 2
)
RESULTS AND DISCUSSION
Phenoxyimine Zr precatalysts FI
2
Zr(NMe
2
)
2
(1), FI
2
ZrBn
2
the precatalyst in toluene at 25° C. The reaction mixture was
(
2), FI ZrMe (3), and FI ZrCl (4) were synthesized in good
2
2
2
2
then stirred for 30 min (determined as optimum empirically)
+
yields as shown in Scheme 1. Note that 3 is synthesized by
reacting the free phenoxyimine ligand FI-H (FI-H = 2,4-di-tert-
butyl-6-((isobutylimino)methyl)phenol) with in situ generated
ZrMe . This is a more straightforward and efficient
4
Scheme 1. Synthesis of Zr Precatalysts.
before adding the cocatalyst/activator Ph
3
C B(C
6
F
5
)
4
°
(BT).
Notably, a stirring period of 30 min is critical to effective
alkylation, and shorter alkylation times result in little or no
polymer. Ethylene/1-octene copolymerization reactions were
next carried out under rigorously anhydrous and anerobic
o
conditions at 40 C in a 350 mL glass, semi-batch reactor under
Toluene
2
FI-H + Zr(NMe2)
FI2Zr(NMe2)2 (1), X = NMe2
4% yield
FI2ZrBn2 (2), X = Bn
0% yield
4
a constant ethylene pressure of 4 atm ethylene, 3.56 g of 1-
octene, and 45 mL of toluene, which gives an ethylene/1-octene
molar ratio of 1:1.7 in the liquid phase. Polymerization times
and polymer yields were adjusted to minimize the influence of
rt, 1 h
8
Toluene
rt, 1 h
2
FI-H + ZrBn4
6
4
MeMgBr
2 FI-H
exotherm and mass transfer limitations, as well as significant
ZrCl4
FI ZrMe (3), X = Me
2
2
31-32
o
Toluene, -78 C
o
1-octene
depletion.
Polymerization
results
are
-78 C to r.t.
65% yield
summarized in Table 1. All product polymers are monomodal
with narrow Đ values (<2.9), characteristic of well-defined
single-site behavior. As expected, there is no activity when no
TMA is present for alkylation (Table 1, entry 1). Surprisingly,
however, when 1 is activated by TMA, then BT, it exhibits both
high activity and significantly greater 1-octene incorporation
(7.2 mol%) than TMA, then BT-activated 2 and 3, which, under
identical polymerization conditions, yield 1.0 mol% and 0.9
mol% 1-octene incorporation, respectively (Table 1, entries 2
vs 5 and 8). Interestingly, catalysis with dibenzyl precatalyst 2
or dimethyl precatalyst 3 yields products with 1-octene
incorporation levels all below 1.5 mol% (Table 1, entries 4-9).
Together these results argue that activation of amido
precatalyst 1 with TMA, then BT leads to a different active
species than do precatalysts 2 and 3. Note again that the
polymers produced in all these experiments are monomodal
with narrow Đ, characteristic of well-defined single-site
behavior.
Toluene
rt, 24 h
FI Zr(NMe ) (1) + TMSCl
FI ZrCl (4), X = Cl
2
2 2
2
2
69% yield
tBu
tBu
O
N
X
N
Zr
X
O
tBu
FI ZrX
2
2
tBu
The effects of TMA loading on the polymerization
characteristics were also studied, and strong detrimental
effects of excess TMA on both polymerization activity and 1-
octene incorporation are observed for 1. By increasing the TMA
loading from 40 (Table 1, entries 3 vs. 2) to 120 equiv, the
polymerization activity is reduced by 5.8x for 1; by increasing
the TMA loading from 0.0 (see Table 1) to 120 equiv, the
polymerization activity is reduced by 6.2x for 2, and 2x for 3.
Additionally, 1-octene incorporation is depressed by 2.7x for 1
(Table 1, entry 3 vs. 2); interestingly, however, the 1-octene
incorporation changes are small for 2 and 3 by increasing the
TMA loading from 0.0 to 120 equiv (Figures 3A and 3B, and
Table 1). Note that dichloride complex 4 exhibits no
polymerization activity following reaction with TMA (40
equiv), then BT, likely reflecting the known poor alkylation
Figure 2. Molecular structures of complexes 1, 3, 4, 5, and 6.
Hydrogen atoms are omitted for clarity.
33-34
efficiency of Zr-Cl moieties.
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The detrimental effects of TMA on polymerization activity
may reflect catalyst decomposition induced by large amounts
active, or even inactive dormant species,34,
coordination is too strong (Figure 4A). In this study, a Zr Al
adduct, characteristic of a FI Zr(μ-Me) AlMe moiety, is
confirmed by NMR spectroscopy. NMR studies of FI MX
40-43
if the
…
1
2
3
4
5
6
7
8
9
of TMA or a strong coordination of TMA to the FI
2
Zr- center
2
2
2
…
presumably via μ-Me bonding. The resulting Zr Al adducts are
2
2
thought to act as important intermediates in alkyl/polymeryl
activation chemistry have proven challenging for a number of
reasons, including that alkylation can modify the ancillary
ligand structure and strong, multiple Al coordination modes
9
, 25, 35-39
chain transfer.
However, the adducts may become less
Table 1. Data for ethylene/1–octene copolymerizations mediated by the indicated precatalysts[a]
TMA
equiv
Time
(min)
1-Octene
Incorp.[d]
Act.[b]
Mw[c]
Ð[c]
Entry
Precat.
Poly. (g)
1
2
3
4
5
6
7
8
9
FI
FI
FI
2
2
2
Zr(NMe
Zr(NMe
Zr(NMe
2
2
2
)
)
)
2
2
2
(1)
(1)
(1)
0[e]
40
2.0
2.0
2.0
0.5
0.5
2.0
0.5
0.5
0.5
1.0
6.0
2.0
2.0
2.0
5
0
0
-
6
4
14
5
4
13
4
2
-
-
-
1
1
1
1
1
1
1
1
1
1
2
2
2
2
2
2
2
2
2
2
3
3
3
3
3
3
3
3
3
3
4
4
4
4
4
4
4
4
4
4
5
5
5
5
5
5
5
5
5
5
6
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
3.79
0.66
2.37
1.88
1.53
2.19
1.31
1.03
0
2846
495
7097
5649
1144
6572
3932
3099
0
1.5
1.4
2.0
1.3
1.3
2.2
1.3
1.2
-
7.2
2.7
1.5
1.0
0
120
0[e]
40
FI
2
2
2
ZrBn
ZrBn
ZrBn
2
(2)
(2)
(2)
(3)
(3)
(3)
FI
FI
2
2
120
0[e]
40
FI
FI
FI
2
2
2
ZrMe
ZrMe
ZrMe
2
2
2
1.3
0.9
0.1
-
120
1
1
1
0
1
2
FI
2
ZrCl
2
(4)
(5)
40
FIAlMe
2
0[e]
0[e]
40
0
0
-
-
-
FIZr(NMe
FIZr(NMe
FIZr(NMe
2
2
2
)
)
)
3
3
3
(6)
(6)
(6)
0
0
-
-
-
13
2.42
0.88
0
1812
660
0
9
8
-
1.3
2.9
-
6.3
3.2
-
1
1
1
4
5
6
120
0[f]
40[f]
FI
FI
2
2
ZrMe
ZrMe
2
2
(3)
(3)
0.5
1.24
3720
2
1.3
0.5
[
a] Conditions: precatalyst: 10 µmol; trimethylaluminum (TMA) alkylating agent; Ph
(5 mL); toluene, 45 mL; ethylene, 4 atm, 40 °C; each entry performed in duplicate. [b] Units kg/(mol·h·atm). [c] M
3
C+B(C
6
F
5
)
4
ˉ (BT), 12 µmol; 1-octene, 3.58 g
in units kg/mol;
Ð, dispersity; determined by triple–detection GPC versus polystyrene standards. [d] In mol%, by C NMR, calculated according to
w
1
3
4
4
literature. [e] BT directly added to the precatalyst solution without TMA. [e] Al
2 2 2 4
(NMe ) Me (10 µmol) was added to toluene
solution of precatalyst (entry 15) or precatalyst+40 equiv TMA (entry 16) and stirred for 30 min before BT addition.
to the Zr catalyst,9, 25, 34-43 as well as the general fluxional
concentrations, the rate of chain propagation, and thus
catalytic activity, is depressed or eliminated for many group 4
2
1, 45-47
nature of such FI-based complexes.
well-defined precatalyst 3 (FI ZrMe
Using the preformed,
), in reaction with
1
0, 34, 53-54
2
2
catalysts.
polymer M
Note in the present study that the product
cocatalyst/activator BT, yields a clean NMR spectrum, which
stands in contrast to previous alkylation studies using FI ZrCl
and provides a better understanding of the
activation process via first generating well-defined
species (see SI). The C NMR chemical shift
w
falls with increasing TMA concentrations (Figure
2
2
3C) under all studied conditions, and that terminal double
4
7-49
1
and MAO,
bonds are detected for all the product polymer samples by H
a
NMR (see SI). Thus, chain transfer to Al and β-H
elimination/transfer are both operative chain termination
pathways here (Figure 4A). Note that rapid Zr-polymeryl chain
transfer between Zr and main group metal alkyls is a key
component of the Dow chain shuttling polymerization
+
‾
13
2 6 5 4
FI ZrMe B(C F )
+
of the Zr-Me moiety here is at δ 59.5 ppm (Figure 4B), which
then experiences an upfield shift to δ 23.5 ppm upon the
addition of 5 equiv of TMA (Figure 4C, see SI), indicating
5
0-52
28
formation of μ-methyl groups.
With increasing TMA
process.
w 2 2
Figure 3. Effects of TMA loading (equiv/Zr) on activity (A), 1-octene incorporation (B), and M (C) in FI ZrX -catalyzed ethylene/1-
octene copolymerization.
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(
Figure 5B).11, 48, 57-60, 62-65 Here, the proposed ancillary ligand
As noted above, unexpected precatalyst monodentate σ-
ligand effects (i.e., enhanced 1-octene incorporation) are
1
2
3
4
5
6
7
8
9
1
1
1
1
1
1
1
1
1
1
2
2
2
2
2
2
2
2
2
2
3
3
3
3
3
3
3
3
3
3
4
4
4
4
4
4
4
4
4
4
5
5
5
5
5
5
5
5
5
5
6
abstraction scenario is confirmed by in situ NMR spectroscopy,
precatalyst X-ray diffraction, and catalytic control experiments.
observed when using FI
2 and 3 analogs. FI ZrX
2
Zr(NMe
2 2
) (1) + TMA compared to the
2
2
(X = Bn, Cl, etc)-type precatalysts are
In the reaction of FI
2
Zr(NMe
2
)
2
(1) with TMA, a major set
(5) is
1
known to exhibit very low α-olefin enchainment selectivity in
of new H NMR resonances corresponding to FIAlMe
2
the presence of ethylene, especially for FI ligands having
observed (Figure S22), which suggests ancillary ligand transfer
to Al is a major pathway during the alkylation process (Figure
5C). It is important to note that 5, synthesized and isolated
independently, is not an active polymerization catalyst (Table
1, entry 11). Note also that the reaction of 1 + TMA does not
afford either FI ZrMe (3) or a 3-TMA adduct based on the
2 2
following observations: i) the H NMR features of 3 + TMA do
not match those of 1 + TMA (Figure S23); ii) 3, after activation
6
-7, 55-56
sterically bulky substituents.
Thus, for 1 + TMA + BT it
appears likely that a new active species is formed that exhibits
5
5
enhanced 1-octene incorporation selectivity. It will be seen
below that ancillary ligand transfer occurs during alkylation of
1
by TMA. Ti and Zr complexes having bidentate monoanionic
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
ligands, including those having phenoxyimine ligands, have
previously been reported to undergo ancillary ligand transfer
5
7-61
reactions with trimethylaluminum (TMA),
forming
2
with BT/TMA, forms a cationic FI Zr species (Figure 4C, see SI),
which is a poor 1-octene incorporator (0.9 mol%) vs. 1, which,
as already noted, exhibits increased 1-octene
bidentate monoanionic ligand coordinated Al complexes along
with unidentified group 4 species. Such processes have been
previously associated with catalyst deactivation pathways
A
L
-H
elimination
or transfer
Chain
transfer
Zr R’
Me
Me
MeOH
quench
Me
Me
R
L
L
L
L
L
R
L
L
H
Zr
Zr
Me
+
R
Al
+
Me Al
R
Zr
+
Me
Me Al
Me
R
R = alkyl or polymeryl;
R' = H (-H elimination) or Et (transfer to ethylene)
Intermediate or dormant species
B
0
Ph C B(C F )
6 5 4
3
FI ZrMe
50
2
2
FI ZrMe B(C F )
2
6
5 4
Toluene-d8 /DFB
10/1, v/v)
Zr-Me
(1H), ppm 3.5 3.0 2.5 2.0 1.5 1.0 0.5 0.0 -0.5 -1.0
3
(

C
B(C F )
6
5 4
0
Me
Me
Me
N
Ph C B(C F )
6 5 4
TMA
5 min
3
FI ZrMe
Zr
2
Al
2
2
O
Toluene-d8 /DFB
10/1, v/v)
50
3
Me
(
Zr(
- -
Me) AlMe Me Al( Me) AlMe
 
2
2
2
2
2
7
(1H), ppm 3.5

3.0
2.5 2.0 1.5 1.0 0.5 0.0 -0.5 -1.0
Figure 4. A. FI catalyst chain transfer, termination, and Al coordination processes. B(C
6 5 4
F ) ‾ is omitted for clarity. B and C. A section
1
13
+
o
+
o
of the H- C HSQC spectrum of FI
incorporation (7.2 mol%) (Table 1, entries 8 vs. 2); iii) complex
also undergoes a slow ancillary ligand abstraction in the
presence of 5 equiv of TMA, with ca. 59% conversion to
FIAlMe (5) after 1 day at room temperature (Figure 5C, also
2
ZrMe B(C
6
F
5
)
4
‾ (25 C) (B) and FI
2
Zr (μ-Me)
2
AlMe
2
B(C
6
F
5
)
4
‾ (7) (-50 C) (C).
ZrMe
into the polymerization solution of FI
2
2
(3) in the
3
presence of 0.0 and 40 equiv of TMA, followed by the cocatalyst
BT (Table 1, entries 15 and 16). Note that when no TMA is
present, there is no polymerization activity, presumably
reflecting poisoning effects of Lewis basic Al
However, when 40 equiv of TMA is present, the FI
mediated polymerization proceeds similarly to that without
Al (NMe Me present, in terms of activity, product M , Ð, and
1-octene incorporation (Table 1, entry 16 vs. 8). This control
experiment strongly suggests that the presence of
2
see SI). Using the solution, 3 + TMA (40 equiv), reacted at r.t.
for 1 day, followed by BT addition, as a polymerization catalyst
under otherwise identical conditions to entry 8 of Table 1,
shows significantly decreased activity, 1088 vs. 5433
kg/(mol·h·atm), and similarly very low 1-octene incorporation
2
(NMe
2
)
2
Me
4
.
2
2
ZrMe
2
2
)
2
4
w
(
~0 mol% vs. 0.9 mol%). Thus, 7, which derives from activation
of 3 with BT in the presence of TMA, is likely the active species
Figure 4C); in contrast, the slow ancillary ligand transfer in the
reaction of 3 + TMA ultimately affords an inactive catalyst
Al
2 2 5 2 2 2 4
(NMe )Me and Al (NMe ) Me alkylation by-products
(
cannot account for the observed 1-octene incorporation
differences between FI Zr(NMe ) (1) and FI ZrMe (3)
2 2 2 2 2
under these conditions.
structure which is currently unknown,1
1, 48, 57-60, 62-65
instead of
the formation of a mono-FI-Zr complex observed in the
analogous reaction with 1, which leads to high activity and 1-
octene incorporation.
Based on the above observations, it is reasonable to
propose that the other product resulting from ancillary ligand
transfer to Al in the case of 1 is a cationic mono-FI Zr complex,
most likely in the form of an AlMe
supra). [Zr∙∙∙Al] (8) is the likely structure containing one
coordinated TMA
complexity of this system, however, varied types of AlM
adducts
3
4, 41, 54, 62, 65
Note that one additional factor must be considered when
3
adduct
(vide
comparing the differences between the FI
2
Zr(NMe
(3) derived polymerization catalysts. It is known that
)Me and Al (NMe Me will be present, produced as
catalyst alkylating
Me was prepared
2 2
) (1) and
5
1, 62, 68
FI
Al
2
ZrMe
(NMe
2
(Figure 5C). Considering the
2
2
5
2
2
)
2
4
3
4
0, 50, 69-71
by-products when TMA is used as a Zr-NMe
2
may be present to stabilize the cationic mono-
66
agent. In a control experiment, Al
2 2
(NMe )
2
4
FI Zr moiety. All spectroscopic attempts to clarify the exact
structure of the catalyst were unsuccessful due to the
67
using a modified literature procedure (see SI) and introduced
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Journal of the American Chemical Society
complexity.62, 65 Regarding the possible reason for the different
ligand transfer tendencies, i.e., much faster FI ligand
abstraction for FI Zr(NMe (1) than for FI ZrMe (3), we
hypothesize that this may involve the basic nature of the
neighboring -NMe ligand helping to preorganize the TMA
abstraction process.
instability.72-74 Changing the substituent on the FI imine N from
less bulky aliphatic isobutyl to more bulky aromatic 2,6-
diisopropylphenyl enables preparation of the corresponding
1
2
3
4
5
6
7
8
9
2
2
)
2
2
2
7
5
3
more stable FI"ZrBn complex, however, when activated, this
2
complex gives negligible olefin polymerization activity, making
it a poor control precatalyst for this study (see SI for more
details). Thus, we turned to other mono-FI-Zr precatalysts.
We next focused on the synthesis of mono-FI-Zr-alkyl
complexes, i.e., FIZrMe or FIZrBn , which would be ideal
Fortunately, FIZr(NMe
2 3
) (6) is straightforwardly synthesized
3
3
(
Figure 5A) and characterized spectroscopically and by single
models for comparative studies. However, all attempts to
prepare such complexes were unsuccessful, likely due to their
crystal XRD (Figure 2). Activation of 6 with TMA (40 equiv) +
B(C F )
6 5 4
A
C
1
1
1
1
1
1
1
1
1
1
2
2
2
2
2
2
2
2
2
2
3
3
3
3
3
3
3
3
3
3
4
4
4
4
4
4
4
4
4
4
5
5
5
5
5
5
5
5
5
5
6
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
Me
Me
Me
N
Toluene
0 oC, 3 h
N
TMA
24 h
Ph3C B(C6F5)4
2
FI ZrMe2
Zr
2
Al
+ FIAlMe2 (59%)
FI-H
+
TMA
O
O
Al
Me
Me
3
45% yield
Me
+ unidentified
FIAlMe (5)
2
(41%)
species
7
1088 kg/(molhatm); ~0 mol% 1-octene incorp.
Toluene
N
FI-H + Zr(NMe2)4
xs)
O
NMe2
NMe2
rt, 10 min
Zr
(
8
2% yield
NMe2
FIZr(NMe2)3
Me
Me
Me
Me
N
B
TMA
Ph C B(C F )
Zr
Al
6
3
6
5 4
O
FI Zr(NMe )
2
2 2
FIAlMe2
+
+
L
X
X
30 min
Me
TMA
M
LAlMe2 + unidentified compounds
1
B(C F )
6 5 4
Al (NMe ) Me
8
L
2
2 x
6-x
L = bidentate monoanionic ligand;
x=1 or 2
M = Ti or Zr; X = Cl, NMe , etc.
2
3168 kg/(molhatm); 7.2 mol% 1-octene incorp.
Figure 5. A. Synthesis of key complexes relevant to trimethylaluminum (TMA) alkylation studies. B. Previously reported ancillary
ligand transfer from Ti or Zr to Al as a common catalyst deactivation pathway.
TMA, and proposed cationic active catalysts.
4
8, 57-60, 63-65
C. Reactions of precatalysts 3 and 1 with
catalytic species, reducing the ancillary ligand-engendered
steric bulk, reasonably responsible for the enhanced
comonomer enchainment. Furthermore, buried volume
calculations also confirm the significant differences in
percentage buried volume (%VBur), a measure of steric
encumbrance, for the backbones of FI Zr- and FIZr- catalysts
2
within a radius of 3.5 Å around the Zr center, 77.4 % vs. 58.9 %,
respectively (Figure 6). This indicates that the FIZr- center is
2
less sterically congested than the analogous FI Zr center. Note
that the FI ligand remains intact in both complexes 1 and 6
during TMA-alkylation, since hydrolysis, recovery, and analysis
of the resulting organic mixture gives only FI-H ligands without
74, 78
imine reduction (see SI).
FI Zr
FIZr
2
The above catalysts were also investigated under
conditions more relevant to industrial processes. Ethylene/1-
77.4 %
58.9 %
o
octene copolymerization reactions were carried out at 120 C
in 2L semi-batch reactors under 18.4 atm of ethylene (46 g
ethylene in the liquid phase), 300 g of 1-octene, and 609 g of
mixed alkanes solvent (Isopar E) which gives ethylene/1-
octene molar ratio of 1:2 in the liquid phase. Ethylene was fed
on demand to maintain steady concentration. Two different
alkylation procedures were employed – method [e] (see Table
2
) involved premixing the precatalyst with TMA for 30 min
Figure 6. Steric crowding maps from buried volume
followed by BT addition and injection of the resulting catalyst
mixture into the reactor. In method [f] TMA was only mixed
with precatalyst for less than 1.0 min. Control experiments
with no alkylation step (TMA equiv = 0) also were performed
in which precatalyst was mixed with BT and added to the
reactor within 5 min. Polymerization trends similar to the
effects described above at lower reaction temperatures and
pressures (Table 1) are observed under these conditions. The
activities of precatalysts 2 and 3 are reduced by mixing the
precatalysts with TMA (40 equiv)/BT prior to catalyst addition
7
6
2 2 2 2 3
calculations for FI Zr(NMe ) (1) and FIZr(NMe ) (6) (see
SI).
BT gives activity and 1-octene incorporation statistically
indistinguishable from that of 1 activated the same way, 6.3
and 7.2 mol%, respectively (Table 1, entries 13 vs. 2). The two
precatalysts also behave similarly when 120 equiv of TMA is
7
7
used (Figure 3). These catalytic results strongly argue that
both bis-FI FI Zr(NMe (1) and mono-FI FIZr(NMe (6)
precatalysts form similar if not identical cationic mono-FI-Zr
2
2
)
2
2 3
)
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Journal of the American Chemical Society
Page 6 of 9
to the reactor (Table 2, entries 4, 5, 7 and 8) regardless of the
FI precatalyst 6 which incorporates 12.3 mol% 1-octene (entry
10). As expected, 1 and 6 do not produce polymer when TMA
is not contacted with the precatalyst for a longer period of time.
For example, when TMA is mixed with 6 for less than 2 min, no
1
2
3
4
5
6
7
8
9
1
1
1
1
1
1
1
1
1
1
2
2
2
2
2
2
2
2
2
2
3
3
3
3
3
3
3
3
3
3
4
4
4
4
4
4
4
4
4
4
5
5
5
5
5
5
5
5
5
5
6
TMA premixing method as compared to runs containing no
TMA (entries 3 and 6). Similarly, the comonomer incorporation
for 2- and 3-catalyzed polymerizations remains low, even with
4
0 equiv of TMA, while the dimethylamido precatalyst, 1,
incorporates 4x more 1-octene (10 mol%, entry 2) than does 2
2.5 mol%, entry 4) and 3 (3.1 mol%) under identical
polymerization conditions and behaves very similarly to mono-
Table 2. Ethylene/1–octene copolymerizations at higher temperature and pressure
polymer is produced (Table 2, entry 11). To verify the
5
experimental protocol, a CGCTiMe
2
precatalyst (CGC = [(η -
(
5
C Me
4
-SiMe
2 2
-N-t-Bu)]TiMe ) was evaluated under the same
polymerization
[a]
1
-Octene
Loading (µmol) TMA equiv Time (min) Poly. (g) Act.[b]
M
[c]
Ð[c]
Entry
Precat.
w
Incorp.[d]
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
FI
FI
2
2
Zr(NMe
Zr(NMe
2
2
)
)
2
2
(1)
(1)
1.0
1.0
0.5
0.5
0.5
2.0
2.0
2.0
1.0
1.0
1.0
0.5
0
40[e]
10
10
6
0
0
-
-
-
7.2
2315
19829
2444
6688
3497
193
11
9
4.3
2.2
2.6
3.5
2.5
2.3
5.8
-
10.0
2.3
2.5
2.6
2.5
2.4
3.1
-
FI
2
2
2
ZrBn
ZrBn
ZrBn
2
(2)
(2)
(2)
(3)
(3)
(3)
0
18.5
3.8
FI
FI
2
2
40[e]
40[f]
0
40[e]
40[f]
0
40[e]
40[f]
0
10
10
8
9
10.4
17.4
1.2
12
9
FI
FI
FI
2
2
2
ZrMe
ZrMe
ZrMe
2
2
2
2
10
10
10
10
10
10
10
17
-
10.3
0
1656
0
FIZr(NMe
FIZr(NMe
FIZr(NMe
)
3
3
3
(6)
1
1
1
0
1
2
2
2
)
(6)
(6)
14.2
0
4566
0
30
-
6.9
-
12.3
-
)
CGCTiMe
2
44.2
28426
38
2.5
32.9
C+B(C
–
(BT), 1.2 equiv; 2 L Parr reactor, 120 °C, 18.4 atm, 300 g 1-octene, 609 g Isopar E, 46 g ethylene.
w
in units kg/mol; Ð, dispersity; determined by GPC versus polystyrene standards. [d] In mol%
[
a] Conditions: Ph
3
6
F
5
)
4
[
b] Units kg/(mol·h·atm). [c] M
determined by compositional GPC with IR5 detector [e] Trimethylaluminum (TMA) mixed with a solution of precatalyst for 30 min.
at room temperature followed by addition of BT activator and transfer to the reactor. [f] TMA added to precatalyst solutions followed
by activator and the product added to the reactor within 5 min. CGCTiMe
5
2
= [(η -C
5
Me
4
-SiMe
2
-N-t-Bu)]TiMe
2
.
conditions and shows 1-octene incorporation of 33 mol% as
expected with respect to FI catalysts. These results argue that
the unique alkylation/activation chemistry of the
ASSOCIATED CONTENT
Supporting Information
FI
2
Zr(NMe
2
)
2
precatalyst
is
maintained
under
scaled/industrial operating conditions.
The Supporting Information is available free of charge on the
ACS Publications website. Synthesis of ligand and complexes;
crystal structures (cif.), polymerization procedures;
characterizations of ligand, complexes and polymer products.
CONCLUSIONS
A new phenoxyimine Zr dimethylamido precatalyst is
reported for ethylene/1-octene copolymerizations. By
changing the identity of the precatalyst monodentate -ligands,
as opposed to modifying ancillary ligand structure or changing
the identity of the central metal, the catalyst exhibits
unexpected variations in reactivity in terms of comonomer
incorporation selectivity, without the loss of activity. When
AUTHOR INFORMATION
Corresponding Author
*
*
t–marks@northwestern.edu
tracy.lohr@shell.com
jklosin@dow.com
*
activated with TMA, then BT, mono-FI FIZr(NMe
FI Zr(NMe dimethylamido complexes are shown to
incorporate significantly higher levels of 1-octene than the
corresponding FI ZrMe and FI ZrBn derivatives. Detailed
2 3
) and bis-FI
‡
Current Address: Shell Catalysts & Technologies, Shell
Technology Center Houston, 3333 Highway 6 South, Houston,
Texas, 77082, United States.
2
2 2
)
2
2
2
2
investigation suggests that the distinctive precatalyst
monodentate σ-ligand effects originate in FI ligand abstraction
reactions, which were previously thought to be major catalyst
deactivation pathways. Preliminary studies suggest that in situ
generated mono-FIZr catalysts, which are often inaccessible
through alkyl or chloride precursors, likely account for such
distinctive catalytic properties. Polymerization studies under
scaled/industrial operating conditions also show high catalytic
efficiency and reflect the unique alkylation/activation
Notes
The authors declare no competing financial interests.
ACKNOWLEDGMENT
Financial support by The Dow Chemical Company (Y. G. and Y.
W.) and the National Science Foundation (T. L. L., grant CHE-
1464488) is gratefully acknowledged. We thank Drs. E.
Carnahan and A. Young of The Dow Chemical Company for
helpful discussions. Purchase of the NMR instrumentation at
IMSERC was supported by NSF (CHE–1048773).
Diffractometry experiments were conducted at IMSERC on
2 2 2
chemistry of the FI Zr(NMe ) precatalyst. This report
demonstrates the importance of screening varied precatalyst
monodentate σ-ligands in optimizing new catalysts, especially
for group 4 catalysts in olefin polymerizations.
6
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Journal of the American Chemical Society
Bruker Kappa APEX II instruments purchased with assistance
from the State of Illinois and Northwestern University.
20 Boussie, T. R.; Diamond, G. M.; Goh, C.; Hall, K. A.; LaPointe, A. M.;
Leclerc, M. K.; Murphy, V.; Shoemaker, J. A. W.; Turner, H.; Rosen, R.
K.; Stevens, J. C.; Alfano, F.; Busico, V.; Cipullo, R.; Talarico, G.,
Nonconventional Catalysts for Isotactic Propene Polymerization in
Solution Developed by Using High-Throughput-Screening
Technologies. Angew. Chem., Int. Ed. 2006, 45, 3278-3283.
21 Makio, H.; Prasad, A. V.; Terao, H.; Saito, J.; Fujita, T., Isospecific
Propylene Polymerization with in situ Generated Bis(phenoxy-
amine)zirconium and Hafnium Single Site Catalysts. Dalton Trans.
2013, 42, 9112-9119.
22 Matsui, S.; Mitani, M.; Saito, J.; Tohi, Y.; Makio, H.; Matsukawa, N.;
Takagi, Y.; Tsuru, K.; Nitabaru, M.; Nakano, T.; Tanaka, H.; Kashiwa,
N.; Fujita, T., A Family of Zirconium Complexes Having Two
Phenoxy-Imine Chelate Ligands for Olefin Polymerization. J. Am.
Chem. Soc. 2001, 123, 6847-6856.
1
2
3
4
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Ethylene/1-Octene Copolymerizations
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NMe2 Highly active,7.2 mol% 1-octene incorp.
N
X
Zr
O
2
X
Bn Highly active,1.0 mol% 1-octene incorp.
Activated with
Me3Al
+
Cl
No activity
Ph3C+B(C6F5)4
-
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