Ethylene Polymerization with Ni(II) Diimine Complexes Generated from 8-Halo-1-naphthylamines: The Role of Equilibrating Syn/ Anti Diastereomers in Determining Polymer Properties

Article abstract of DOI:10.1021/acs.organomet.9b00649

A series of 8-halonapthalen-1-amines (6a-d, X = F, Cl, Br, I) were prepared and converted to the α-diimines of 2,3-butanedione (7a-d). The nickel dibromide and zinc dibromide complexes of these diimines (3a-d and 8a-d, respectively) were obtained in good yields from standard precursors. NMR spectroscopic analysis of the zinc diimine complexes show the existence of syn and anti diastereomers with syn/anti ratios of ca. 2:1 (F), 2:1 (Cl), 1:1.5 (Br), and ca. 1:22 (I). Variable temperature NMR spectroscopy was used to calculate barriers to interconversion of these diastereomers which fall in the range 17-18.5 kcal/mol. Activation of nickel dibromide complexes 3a-d with modified methyl alumoxane (MMAO) yields cationic diimine complexes in which the 8-halo substituents lie over the axial coordination sites. Ethylene polymerization using these activated complexes is reported. The anti diastereomer of the diiodo catalyst (10d) in which both axial sites are blocked yields high molecular weight PE (ca. 10⁶ g/mol) as the major fraction with a high turnover frequency at 40 °C. The minor syn diastereomer of 10d in which only one axial site is blocked produces low molecular weight PE as a minor fraction. PE formed from the dichloro catalyst 10b also exhibits a bimodal polymer distribution, but the high molecular weight fraction from the anti diastereomer is minor, while the syn diastereomer produces low molecular weight PE. The dibromo complex (10c) is unique in that interchange of diastereomers is on a time scale such that the PE produced shows a very broad molecular weight distribution (MWD ca. 14), spanning the range from the low to high molecular weight regimes. Catalyst 10a, bearing the small fluoro substituents, yields very low molecular weight PE (ca. 600 g/mol).

Full text of DOI:10.1021/acs.organomet.9b00649

Article
pubs.acs.org/Organometallics
Cite This: Organometallics XXXX, XXX, XXX−XXX
Ethylene Polymerization with Ni(II) Diimine Complexes Generated
from 8‑Halo-1-naphthylamines: The Role of Equilibrating Syn/Anti
Diastereomers in Determining Polymer Properties
Bin Wang, Olafs Daugulis,* and Maurice Brookhart*
Center for Polymer Chemistry, Department of Chemistry, University of Houston, Houston, Texas 77204-5003, United States
*
S Supporting Information
ABSTRACT: A series of 8-halonapthalen-1-amines (6a−d, X
F, Cl, Br, I) were prepared and converted to the α-diimines
=
of 2,3-butanedione (7a−d). The nickel dibromide and zinc
dibromide complexes of these diimines (3a−d and 8a−d,
respectively) were obtained in good yields from standard
precursors. NMR spectroscopic analysis of the zinc diimine
complexes show the existence of syn and anti diastereomers
with syn/anti ratios of ca. 2:1 (F), 2:1 (Cl), 1:1.5 (Br), and ca.
1:22 (I). Variable temperature NMR spectroscopy was used to
calculate barriers to interconversion of these diastereomers
which fall in the range 17−18.5 kcal/mol. Activation of nickel
dibromide complexes 3a−d with modified methyl alumoxane
(
MMAO) yields cationic diimine complexes in which the 8-halo substituents lie over the axial coordination sites. Ethylene
polymerization using these activated complexes is reported. The anti diastereomer of the diiodo catalyst (10d) in which both
axial sites are blocked yields high molecular weight PE (ca. 10 g/mol) as the major fraction with a high turnover frequency at
6
4
0 °C. The minor syn diastereomer of 10d in which only one axial site is blocked produces low molecular weight PE as a minor
fraction. PE formed from the dichloro catalyst 10b also exhibits a bimodal polymer distribution, but the high molecular weight
fraction from the anti diastereomer is minor, while the syn diastereomer produces low molecular weight PE. The dibromo
complex (10c) is unique in that interchange of diastereomers is on a time scale such that the PE produced shows a very broad
molecular weight distribution (MWD ca. 14), spanning the range from the low to high molecular weight regimes. Catalyst 10a,
bearing the small fluoro substituents, yields very low molecular weight PE (ca. 600 g/mol).
INTRODUCTION
■
Since our initial report in 1995 that bulky aryl-substituted α-
diimine complexes of Ni(II) and Pd(II) function as catalysts
for polymerization of ethylene and other α-olefins to high
1
molecular weight polymers, there has been intense interest in
both academic and industrial laboratories in developing late
metal catalysts for a variety olefin homo- and copolymeriza-
tions. Two aspects of these late metal catalysts attracted
particular initial attention. First, since late metal complexes are
more functional group tolerant than early metal complexes,
copolymerizations with polar vinyl monomers appeared as
potentially attractive alternatives to radical-based processes.
Second, as demonstrated early on for the diimine-based
catalysts, microstructures and thus the resulting properties of
polymers produced from late metal catalysts can be quite
different from those generated from early metal catalysts.
The initially investigated structures of the aryl-substituted
diimine complexes are shown in Figure 1A. The key to
generating high polymers from ethylene rather than dimers or
low molecular weight oligomers was the incorporation of ortho
substituents in the aryl rings, typically in these early versions
either methyl or i-propyl groups. Since the aryl rings align
perpendicular to the square coordination plane, these
Figure 1. Group 10 metal-diimine systems.
substituents provide steric blocking in the axial sites. Axial
site blocking greatly retards the rate of associative chain
Received: September 30, 2019
©
XXXX American Chemical Society
A
DOI: 10.1021/acs.organomet.9b00649
Organometallics XXXX, XXX, XXX−XXX

Organometallics
Article
transfer relative to propagation and results in formation of high
polymer. This design feature can be incorporated in a wide
array of bidentate ligands, both neutral and anionic, and as a
result a plethora of new neutral and cationic Ni(II) and Pd(II)
olefin polymerization catalysts bearing [N,N], [N,O], [P,O],
8-substituents over the axial sites of square planar complexes,
we were interested in exploring effects of substituents beyond
the 2-aryl groups in ethylene polymerizations. We targeted the
series of 8-halo derivatives (X = −F, −Cl, −Br, −I) where a
wide variation in size of these monatomic substituents are
available. The atomic radii span values as follows: F = 1.40−
1.47 Å, Cl = 1.73−1.77 Å, Br = 1.84−1.92 Å, and I = 2.01−
2.06 Å. We report here the synthesis of the series of Ni(II)
dibromide complexes, 3a−3d (Figure 1C), and the results of
catalytic ethylene polymerization with the corresponding
catalysts obtained by activation of the dibromides with
modified methyl aluminoxane (MMAO). Results suggest that
the occurrence of syn and anti diastereomers (see Figure 1C)
play a significant role in determining the behavior of these
systems in polymerization.
[
P,N], and [P,P] bidentate ligands have been discovered.
Many of these catalysts can have specific advantageous
properties relative to diimine systems, particularly with respect
to copolymerization of ethylene with certain polar como-
nomers. Numerous reviews of late metal polymerization
catalysts have described these as well as diimine-based catalyst
54
2
−9
systems in detail.
In parallel with design and development of many new
bidentate scaffolds, investigations of diimine-based catalysts
have proceeded with unabated vigor. Such investigations have
been driven by the subtle and intriguing mechanistic attributes
1
0−17
RESULTS AND DISCUSSION
of these systems,
the wide array of modified diimine
■
structures available for study, and the ease of synthesis and
activation of catalyst precursors, particularly the readily
prepared diimineNiBr2 precatalysts. There are numerous
examples of modified nickel aryl diimine systems derived
from incorporating new ortho-aryl substituents into the aryl
diimine structures. Notable reports of such ortho-aryl
Synthesis of Diimine Ligands. 8-Halonaphthalen-1-
amines (6a−d) were prepared according to literature methods
5
5,56
(Scheme 1).
1,8-Diaminonaphthalene (4) was first
Scheme 1. Synthesis of 8-Halonaphthalen-1-amines and the
Corresponding Diimine Ligands
1
8−20
substituents include aryl moieties,
sec-phenethyl sub-
21−23
stituents resulting in C-2 symmetric catalysts,
range of 2,6-diarylhydrylphenyl-substituents
asymmetric variations of these derivatives,
methyl substituents, and nitrogen-containing groups.
a wide
along with
2
4−28
2
9−35
2-menthyl, 6-
36
37,38
A
particularly thorough account of the many modified aryl
diimine catalyst structures including aryl substituent sub-
stitutions, backbone modifications, and binuclear structures
39
has recently appeared.
An innovative strategy for extreme blocking of the axial sites
in nickel and palladium diimine complexes was introduced by
our group and employed 8-arylnaphthyl amines in construction
of the ligands. The general structures of the resulting diimine
complexes (2) are shown in Figure 1B. The naphthyl rings are
oriented perpendicular to the square coordination plane and
the 8-aryl groups lie perpendicular to the naphthyl groups and
thus are positioned over the axial sites of the metal in a
converted to triazine intermediate (5) with isoamyl nitrite in
an acetic acid/ethanol mixture at room temperature. Treating
triazine 5 with excess hydrohalic acid (HX·H O) at room
2
40−42
“sandwich” type structure as shown.
These capping aryl
temperature using copper powder as the catalyst affords 8-
halonaphthalen-1-amines in good yields. A 70%HF/30%
pyridine mixture was used for the synthesis of 8-fluoronaph-
thalen-1-amine to avoid release of dangerous HF gas. Yields for
each step are good and the spectroscopic data of 6a−d match
literature values.
groups are far more effective in blocking axial sites than the
classical ortho-methyl- or ortho-isopropyl substituents of the
aryl ring (Figure 1A) as demonstrated by very large differences
in associative exchange rates of complexed ethylene for free
ethylene in the sandwich palladium methyl ethylene com-
4
1
plex. This property results in much slower chain transfer
relative to propagation in these systems and thus the palladium
sandwich catalyst exhibits living polymerization of ethylene to
yield hyperbranched polymer with very narrow molecular
Direct reaction of 8-halonaphthalen-1-amines 6a−d with
2,3-butanedione in the presence of formic acid led to a mixture
of monoimine, diimine, and other unknown products making
separation and isolation of pure diimines difficult. However,
the desired 8-halonaphthyl-α-diimine ligands 7a−d were
conveniently prepared by the “template method” reported by
4
1
weight distributions and the nickel sandwich catalyst
converts ethylene to higher molecular weight polymer with
more narrow MWDs than the standard i-propyl-substituted
40,57
Rosa and Zhang.
First, dark brown zinc complexes of the
4
0
system under similar conditions. Daugulis and Coates
showed that sandwich nickel complexes enchain higher α-
olefins such as 1-decene primarily in a 1,ω fashion to yield
8-halonaphthyl-α-diimine ligands were synthesized by the
reaction of 2,3-butanedione with 8-halonaphthalen-1-amines
6a−d in the presence of ZnCl . The zinc complexes were
2
“
chain-straightened” semicrystalline poly(α-olefins) exhibiting
subsequently treated with an aqueous solution of potassium
oxalate to give the free 8-halonaphthyl-α-diimine ligands 7a−d
as dark brown viscous oils. Recrystallization from methanol/
methylene dichloride yields bright yellow needle-like crystals in
high purity. The parent α-diimine ligand 7e was prepared as a
reference ligand. Diimine 7e can be prepared either by direct
reaction of naphthalene-1-amine with 2,3-butanedione or by
43,44
low branching densities.
The incorporation of a single 8-
aryl naphthyl group has also been used to enhance molecular
weights of polyethylenes derived from sandwich type
4
5−53
catalysts.
In consideration of the demonstrated unique ability of
diimine ligands generated from 1-naphthyl amines to position
B
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the template method. All of the ligands were fully
Article
5
7
diastereomer. As will be discussed below, NMR evidence
suggests that both syn and anti diastereomers exist in solution
in equilibrium.
1
13
characterized by H and C NMR spectroscopy as well as
high resolution mass spectroscopy (HRMS) (Figures S1−S17
in Supporting Information). The molecular structures of the 8-
bromonaphthyl-α-diimine ligand 7c and 8-iodonaphthyl-α-
diimine ligand 7d were further confirmed by X-ray
crystallography (Figures S25−S26 in Supporting Information).
Synthesis of Nickel Dibromide Precatalysts. The
nickel(II) dibromide complexes 3a−e were readily synthesized
Structures and Dynamics of Diimine Zinc Complexes
8a−d. Anticipating that the behavior of the nickel complexes
in polymerization could be complicated by the existence and
dynamic interconversion of syn/anti diastereomers and
knowing that analysis of diastereomers ratios and dynamics
of the paramagnetic nickel dibromide complexes would be
problematic, we turned to analysis of the zinc complexes, 8a−
d, as models for the nickel complexes. As noted above, the zinc
analogues 8a−d were synthesized by reaction of diimine
from reaction of α-diimine ligands 7a−e with (DME)NiBr
2
(
Scheme 2). Characterization of these complexes is relatively
Scheme 2. Synthesis of Nickel(II) Dibromide Complexes
ligands 7a−d with ZnCl in the presence of glacial acetic acid
Scheme 3). The rigidity of the diimine ligands ensure that the
2
(
Scheme 3. Synthesis of α-Diimine Zinc Complexes
difficult due to their intrinsic paramagnetic properties,
eliminating effective use of NMR spectroscopy. The solubility
of the nickel complexes 3a−e in common solvent decreased
severely as the size of the substituent group in the 8-positon
increased (solubility: 3e ≈ 3a > 3b > 3c > 3d). Purity and
identity were confirmed by elemental analysis as well as X-ray
diffraction analysis. Single crystals of 3a suitable for a
diffraction study were prepared by slow diffusion of pentane
into a methylene dichloride solution of 3a at room temper-
ature. The nickel complex 3a crystallized as a centrosymmetric
dimer in which each nickel atom is coordinated to a diimine
ligand and two bridging bromide atoms (Figure 2). A distorted
tetrahedral geometry is exhibited around each nickel center.
The nickel complex 3a cocrystallized with one molecule of
CH Cl which was verified by elemental analysis. In the single
steric interactions of the halo substituents in the zinc and
nickel systems should be quite similar. Note the N−N
distances in the α-diimine backbone are 2.61 Å in nickel
complex 3a and 2.63 Å in zinc complex 8a. The N−N distance
in the square planar palladium complex 9a is also 2.63 Å (see
below).
The purity and identity of zinc complexes 8a−d were
1
established by H NMR spectroscopy (Figures S18−S22) and
X-ray crystallography. A single crystal of 8a suitable for
diffraction analysis was obtained by slow diffusion of pentane
into a methylene chloride solution of 8a at room temperature.
The ORTEP diagram of 8a is shown in Figure 3. Similar to the
2
2
crystal of 3a the two fluoronaphthyl substituents are oriented
such that the fluorine atoms are on the same side of five-
membered chelate ring. We designate this isomer as the syn
Figure 3. Molecular structure of zinc complex 8a (CCDC number:
1949180). Hydrogen atoms are omitted for clarity. Thermal ellipsoids
are shown in the 50% probability level. Selected bond lengths [Å] and
angles [deg]: Zn(1)−N(2) 2.063(5), Zn(1)−N(1) 2.075(5), Zn(1)−
Cl(2) 2.2044(17), Zn(1)−Cl(1) 2.2070(16); N(2)−Zn(1)−N(1)
78.28(19), N(2)−Zn(1)−Cl(2) 111.64(15), N(1)−Zn(1)−Cl(2)
111.37(15), N(2)−Zn(1)−Cl(1) 116.09(15), N(1)−Zn(1)−Cl(1)
116.93(15), Cl(2)−Zn(1)−Cl(1) 116.66(7).
Figure 2. Molecular structure of nickel complex 3a (CCDC number:
nickel complex 3a, complex 8a adopts a tetrahedral geometry
around zinc in the complex that crystallizes. The two fluorine
atoms are positioned syn to one another (syn diastereomer).
1
949179). Hydrogen atoms are omitted for clarity. Thermal ellipsoids
are shown in the 50% probability level. Selected bond lengths [Å] and
angles [deg]: Ni(1)−N(2) 2.0287(11), Ni(1)−N(1) 2.0671(11),
Ni(1)−Br(1) 2.4775(3), Ni(1)−Br(2) 2. 3991(3);
N(2)−Ni(1)−N(1) 79.12(4), N(2)−Ni(1)−Br(2) 125.21(3),
N(1)−Ni(1)−Br(2) 90.84(3), N(2)−Ni(1)−Br(1) 94.73(3),
N(1)−Ni(1)−Br(1) 92.81(3), Br(2)−Ni(1)−Br(1) 139.808(8).
When crystals of 8a are dissolved in CD Cl at −80 °C and
2
2
1
9
subjected to F NMR spectroscopic analysis, two resonances
are observed at −115.40 ppm and −115.09 ppm and assigned
to anti and syn diastereomers (anti:syn ≈ 1:2) respectively
C
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Organometallics XXXX, XXX, XXX−XXX

Organometallics
Figure S27). (Note, as expected, only one 19F signal is
observed for free ligand 7a.) No significant line broadening
was observed by increasing the temperature from −80 to 0 °C,
indicating there is slow interconversion on the NMR time scale
between the anti and syn diastereomer at these temperatures.
Similarly, anti and syn diastereomers in zinc complexes 8b−d
were also detected, as evidenced by the presence of two signals
for the methyl groups of the backbone (Figure 4 and Figures
Article
(
be estimated on the basis of the slow exchange approximation:
k = πΔw, Δw = (w − w ), where w is line width at half-height
of the resonance and w stands for the line width at half-height
1
0
1
0
of the signal at the slow exchange limit. Since we only see
significant line broadening at 60 and 80 °C (Δw > 2 Hz), we
set the line width of the peak at 25 °C as the slow exchange
‡
line width. The activation energy (ΔG ) was calculated using
the Eyring equation. Data is summarized in Table 1. In the
case on the iodo complex 8d, the fraction of the syn
diastereomer is so small that estimating its change in line
width is very problematic, but note that it does merge with the
major diastereomer resonance upon warming above 40 °C.
The tetrahedral zinc dichloride complexes 8a−d as noted are
good models for the tetrahedral nickel dibromide precatalysts
3
a−d. However, the active species generated from 3a−d in
ethylene polymerizations are square planar cationic nickel
complexes. On the basis of the rigidity of the diimine ligand we
would expect the cross-ring steric interactions to be similar in
the square planar and tetrahedral nickel complexes (the N−N
distances in the α-diimine backbone are 2.61 Å in nickel
complex 3a and 2.63 Å in square planar palladium complex
9
a). Nevertheless, we further examined the diastereomer ratios
in square planar palladium analogue 9a as a model for square
planar nickel intermediates. Complex 9a was prepared by
reaction of diimine ligand 7a with (COD)PdMeCl in CH Cl
Figure 4. 19F NMR spectra of 8a (A) and 1H NMR spectra of 8b−d
2
2
at room temperature as shown below in Scheme 4.
(
B−D, methyl group region) at variable temperatures.
Scheme 4. Synthesis of Palladium Complex, 9a
5
7
S31−S33). The syn diastereomers for 8b−d are assigned to
the lower field resonances. For chloro-substituted 8b the syn/
anti ratio is similar to that for fluoro-substituted 8a and favors
the syn diastereomer by ca. 2:1. For the larger bromo-
substituted system, 8c, the anti diastereomer is now the
favored isomer by ca. 1.5:1. Not surprisingly, the exceptionally
large iodo substituents shift the equilibrium strongly in favor of
the anti diastereomer with only ca. 4.5% of the syn isomer
detected (Figure 4).
1
The purity and structure of 9a were confirmed by H NMR
1
9
and F NMR (Figures S23−24 in Supporting Information) as
well as X-ray diffraction analysis. The molecular structure of 9a
is shown in Figure 5. Like 3a, it exists as the syn form in the
solid state.
While no line-broadening of syn and anti diastereomer
resonances was apparent at temperatures below 40 °C, we
could detect line broadening at 60 and 80 °C which allowed
estimation of the rates of interconversion of diastereomers at
However, upon dissolving crystals of 9a in CD Cl at −80
2
2
19
1
19
these temperatures. The F NMR spectra of 8a and H NMR
°C both syn and anti diastereomers were detected by F NMR
spectroscopy in CD Cl (syn/anti ≈ 1.5:1) indicating that an
spectra of 8b−d were collected at variable temperatures (25 to
2
2
8
0 °C) in tetrachloroethane-d and are shown in Figure 4 (also
equilibrium between the syn and anti diastereomers is
established in solution (Figure S34). In the unsymmetrical
complex 9a, the fluorine atoms are nonequivalent, and thus,
2
see Figures S28−S33). The rate constant for conversion of the
syn to the anti diastereomer (k ) and for the conversion of the
1
1
9
anti to the syn diastereomer (k ) at a given temperature can
unlike 8a−d, each diastereomer shows two F signals. The
−
1
Table 1. Syn/Anti Equilibrium Ratios of 8a−d and Rates and Free Energies of Activation for Isomer Interchange of 8a−c
T = 333 K (60 °C)
T = 353 K (80 °C)
X
anti/syn (60 °C)
k1 (s−1)
k−1 (s−1
)
ΔG‡ (kcal/mol)
ΔG‡ (kcal/mol)
k1 (s−1)
k−1 (s−1
)
ΔG‡ (kcal/mol)
ΔG‡ (kcal/mol)
1
−1
1
−1
F
1:2
1:2
1.5:1
22:1
13
−
−
26
−
−
17.4
−
16.9
−
52
12
36
105
25
24
17.5
19.1
18.3
17.0
18.5
18.6
Cl
Br
I
D
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Article
Figure 6. 19F NMR spectra of palladium complex 9a at variable
temperature (from 25 to 60 °C) in tetrachloroethane-d (500 M). We
2
observe decomposition of 9a at 80 °C.
Figure 5. Molecular structure of palladium complex 9a (CCDC
number: 1949181). Hydrogen atoms are omitted for clarity. Thermal
ellipsoids are shown in the 50% probability level. Note: the Pd atom
site is split to two positions about 0.25 Å apart. Selected bond lengths
Scheme 5. Interconversion of Syn/Anti Isomers in a Ni
Alkyl Ethylene Intermediate
[
2
Å] and angles [deg]: C(25)−Pd(1) 2.026 (5), C(25)−Pd(2)
.057(6), Cl(1)−Pd(2) 2.320(3), Cl(1)−Pd(1) 2.320(3), N(1)−
Pd(2) 2.130(5), N(1)−Pd(1) 2.146(4), N(2)−Pd(1) 2.007(5),
N(2)−Pd(2) 2.096(7); C(1)−N(1)−Pd(2) 114.6(3), C(15)−
N(1)−Pd(2) 124.2(3), C(1)−N(1)−Pd(1) 113.0(3), C(15)−
N(1)−Pd(1) 126.0 (2), N(2)−Pd(1)−C(25) 96.8(2), N(2)−
Pd(1)−N(1) 78.54(16), C(25)−Pd(1)−N(1) 173.09(19), N(2)−
Pd(1)−Cl(1) 174.63(18), C(25)−Pd(1)−Cl(1) 87.65(18), N(1)−
Pd(1)−Cl(1) 96.76(14), C(25)−Pd(2)−N(2) 93.1(3), C(25)−
Pd(2)−N(1) 168.1(6), N(2)−Pd(2)−N(1) 77.0(2), C(25)−
Pd(2)−Cl(1) 89.0(2), N(2)−Pd(2)−Cl(1) 170.1(6), N(1)−
Pd(2)−Cl(1) 99.6(2).
from 25 to 40 °C results in a 1.5 fold increase in TOF (from
5
−1
5
−1
7
.7 × 10 h to 11.9 × 10 h ). TOFs drop quite significantly
major diastereomer exhibits an unusual long-range JF−F
coupling of 17 Hz (Figure S34) which we assign to the syn
isomer since this compound exhibits a much closer F−F
upon further increasing the temperature. The average TOF
5
−1
5
−1
decreases to 6.7 × 10 h at 60 °C and 0.6 × 10 h at 80 °C.
Since complex 10d exhibited highest catalytic activity at 40 °C,
this was the standard temperature employed in other runs.
When the polymerization is carried out for 30 min at 40 °C,
58
distance (3.895 Å) than in the anti diastereomer. Not
surprisingly the syn:anti diastereomer ratio in 9a (1.5:1) is
similar to that in zinc complex 8a. We attempted to observe
5
the TOF drops from 12 to 6.1 × 10 /h, indicating that ca. two-
1
9
F line broadening and isomer interconversion rates at high
thirds of the catalyst has decomposed over 30 min. As
expected, with increasing temperature the branching density
temperatures (25 to 80 °C), but rapid decomposition at 80 °C
precluded reliable data above ca. 60 °C (Figure 6).
1
,3,40
increases and the molecular weight decreases.
Comparing
Ethylene Polymerizations. Ethylene polymerizations
were carried out by activation of dibromides 3a−e in toluene
under ethylene using modified methyl alumoxane (MMAO)
with a 1000:1 Al:Ni ratio. As established in earlier work,
activation with MMAO under ethylene yields active cationic
nickel catalysts illustrated below as alkyl ethylene systems, the
entries 1 and 3, the polymer formed at 25 °C exhibits an M of
n
1030 kg/mol and ca. 5 branches/1000 C while at 60 °C the
polymer shows an M of 458 kg/mol with 15 branches/1000
n
C. Correspondingly, the melting temperature (T ) of the
m
polyethylene decreased from 133.9 to 112.9 °C. Entries 2, 7,
and 8 show only a small ethylene pressure dependence of the
TOF. Upon increasing the pressure 3-fold from 13.6 atm
(entry 2) to 40.8 atm (entry 8) the TOF increases only by a
factor of 1.5. This suggests that the primary resting state is
likely to be an ethylene alkyl complex (which would show no
ethylene dependence) with some contribution from an
ethylene-free nickel alkyl complex which is likely an agostic
1
,10−13
dominant resting states (Scheme 5).
Low catalyst
loadings were used to eliminate mass transport problems.
Catalyst turnover frequencies (TOFs) were calculated as mol
ethylene converted to polymer/mol Ni/time. Branching
1
densities were determined by using H NMR spectroscopy.
Results are summarized in Table 2.
1
,10−13
The effects of varying temperature on catalyst activities and
polymer properties were first investigated by using the nickel
catalyst 10d possessing iodonaphthyl substituents. There is a
significant temperature dependence of the measured TOFs
based on 10 min runs at 13.6 atm (entries 1−4, Table 2). At 25
alkyl complex based on earlier mechanistic studies.
A notable feature of nickel catalyst 10d is the production of
polyethylene with a bimodal distribution of molecular weight
(Figure 7 and Figures S35−S36). We observed two elution
peaks in the gel permeation chromatograph (GPC) which
correspond to a high molecular weight (MW) fraction and a
low MW fraction, respectively. A major molecular weight
fraction is seen with M = 1290 kg/mol (M = 860 kg/mol)
5
−1
°
C, the TOF for 10d is 7.7 × 10 h which is nearly 1 order of
magnitude higher than that observed for the (8-p-tolylnaphth-
yl-α-diimine) nickel catalyst. An increase in temperature
40
p
n
E
DOI: 10.1021/acs.organomet.9b00649
Organometallics XXXX, XXX, XXX−XXX

Organometallics
Article
Table 2. Ethylene Polymerization by (8-Halonaphthyl-α-diimine) Nickel(II) Catalysts
a
TOF (× 10−5 h−1
b
b
c
entry
cat.
T (°C)
ethylene (atm)
t (min)
)
Mn (kg/mol)
MWD
branches (per 1000 C)
Tm (°C)
1
2
3
4
5
6
7
8
9
10d
10d
10d
10d
10d
10d
10d
10d
10c
10b
10a
10e
25
40
60
80
25
40
40
40
40
40
40
40
13.6
13.6
13.6
13.6
13.6
13.6
27.2
40.8
13.6
13.6
13.6
13.6
10
10
10
10
30
30
10
10
10
10
10
10
7.7
12
1030
860
460
110
1560
930
970
1050
58
1.9
1.7
1.8
2.1
1.7
2.0
2.0
1.8
5.4
11
15
25
5.3
11
6.0
4.8
16
20
39
25
133.9
125.6
112.9
6.7
0.6
5.0
6.1
14
f
ND
129.2
117.9
122.0
ND
ND
ND
17
d
8.5
6.1
11
13.6
2.2
−
10
11
12
7.8
0.58
e
ND
ND
e
3.1
0.86
−
a
b
Conditions: Precatalysts 3a−e loading 1.5 μmol, MMAO as activator, Al/Ni = 1000, V(toluene) = 200 mL. Molecular weights and the molecular
c
weight distributions of the high molecular weight fractions determined by GPC in trichlorobenzene at 150 °C. Branching numbers per 1000
1
d
e
carbons determined by H NMR spectroscopy. Broad molecular distribution, see Figure 8. The molecular weight is outside the limits of GPC
1
f
detection; calculated by H NMR spectroscopy. ND = not determined
broad peak (MWD = ca.14) spanning the low molecular to
high molecular weight ranges for the major and minor polymer
fractions produced by 10c.
Figure 7. GPC elution curve of the PE obtained from 3d. Conditions:
1
4
.5 μmol 3d, 1000 equiv. MMAO, pressure = 13.6 atm, temperature =
0 °C, polymerization time = 10 min.
along with a minor low molecular weight fraction, M = 10.6
kg/mol.
p
Figure 8. GPC elution curve of the PE obtained from 3c. Conditions:
1
4
.5 μmol 3c, 1000 equiv. MMAO, pressure = 13.6 atm, temperature =
0 °C, polymerization time = 10 min.
From analysis of the isomer ratios of the zinc complex 8d,
we propose that the active nickel species generated from 3d are
the syn and anti diastereomers of 10d shown in Scheme 5. The
major anti complex gives rise to the major high molecular
weight polymer fraction and the minor syn diastereomer yields
the low molecular weight fraction. In a previous study, we
established that capping one axial site leads to a large reduction
in molecular weight due to an increased rate of chain transfer,
which supports the assignment of the low molecular weight
fraction to the syn diastereomer in which only one axial site is
We propose that the rate of interconversion of the anti and
syn diastereomers falls at the “sweet spot” such that chains of
widely different molecular weights across the full range are
produced. First, we note the ratio of the syn:anti diastereomers
for the Zn analogue of 8c is 1.5, so we expect the active catalyst
10c to show nearly equal populations of syn and anti-isomers.
Second, if the rate of syn/anti diastereomer interconversion of
10c is a reasonable model for the nickel catalyst 3c, then the
rate of interconversion of nickel isomers can be estimated as
4
5
blocked. The large iodo substituents in the anti diastereomer
are capable of effectively blocking both sites and greatly
retarding chain transfer, so very high molecular weight PE is
formed. The fact that two separate molecular weight fractions
are observed suggests that rate of interconversion of
diastereomers is slow relative to the rate of formation of
single chains. If very rapid interconversion was occurring a
single GPC peak would be observed.
‡
ca. 1/sec at 40 °C based on a ΔG of ca. 18.5 kcal/mol for
interconversion of isomers of 10c at 80 °C (see Table 1). An
M ca. 58 kg/mol corresponds to ca. 2100 ethylene units. At a
n
5
TOF of 8.5 × 10 /h, a chain of 2100 ethylene units takes on
average ca. 9 s to grow. An isomer switching rate of 1 s−
1
Polymerization of ethylene using dibromo catalyst 10c
stands in interesting contrast to the behavior of diiodo catalyst
corresponds to one switch every ca. 1 s or, on average, 9
switches per chain of M 58 kg/mol. While this admittedly is a
n
1
0d. Under standard conditions of 40 °C/13.6 atm/10 min,
very crude estimate of the switching frequency in the nickel
catalyst it is nevertheless in the right rate range to produce
chains of intermediate molecular weights, and thus a polymer
exhibiting a broad molecular weight range.
5
the observed TOF of 8.5 × 10 /h and the branching density of
6 branches/1000 C is consistent with data observed for 10d.
However, the GPC trace (Figure 8) shows an exceptionally
1
F
DOI: 10.1021/acs.organomet.9b00649
Organometallics XXXX, XXX, XXX−XXX

Organometallics
Article
Examination of the dichloride catalyst 10b under standard
conditions (40 °C/13.6 atm/10 min) shows the major PE
which the aryl groups are coplanar with the coordination
square plane and above and below the axial sites. These aryl
substituents very effectively block axial coordination sites
leading to retardation of chain transfer rates and very high
molecular weight polymers from polymerization of ethylene.
The aim of this study was to replace the aryl groups in these
sandwich complexes with halo substituents of varying sizes (F,
Cl, Br, I) and gauge the effects of these size changes on the
behavior of these complexes in ethylene polymerization,
particularly the effects on PE molecular weights. Surprisingly,
using 8-halonaphthyl diimine zinc dibromides 8a−d as model
compounds we showed by NMR spectroscopy that these
complexes exist in solution as syn and anti diastereomers with
syn:anti ratios of ca. 2:1 (F), 2:1 (Cl), 1:1.5 (Br) and ca. 1:22
fraction is now in the low molecular weight region with M =
n
7
.8 kg/mol and a PDI of 2.2. A minor high molecular weight
fraction is seen with M = 908 kg/mol (Figure 9).
p
(
I). Dynamic NMR measurements show interconversion of the
diastereomers of 8a−c with free energies of activation barriers
in the range 16.9−18.6 kcal/mol. The behavior of the halo-
substituted catalysts appears to greatly depend on the syn/anti
diastereomer ratios and their rates of interconversion.
Polymerization of ethylene using the activated iodo catalyst
0d yields a major very high molecular weight (ca. 10 kg/
3
1
mol) fraction with a very high turnover frequency but limited
lifetime and a minor PE fraction with low molecular weight
Figure 9. GPC elution curve of the PE obtained from 3b. Conditions:
1
4
.5 μmol 3b, 1000 equiv. MMAO, pressure = 13.6 atm, temperature =
0 °C, polymerization time = 10 min.
(
ca. 10 kg/mol). We assign the high molecular weight fraction
as polymer produced from the major anti diastereomer in
which both axial sites are effectively blocked by the large anti
iodo substituents. The minor low molecular weight fraction
results from the minor syn diastereomer in which only one face
is blocked. The molecular weight observed is consistent with
PE produced from a half-sandwich complex where, like the syn
The dichloro zinc analogues shows a syn/anti ratio of 2 now
favoring the syn diastereomer. The most reasonable inter-
pretation of the these results is that the syn diastereomer of
1
0b produces the major fraction of low molecular weight
45
polymer and the minor high molecular weight material is
produced by the anti isomer of 10b. The low molecular weight
PE observed from the syn diastereomer is consistent with that
seen for polymer generated from the syn diastereomer of the
diiodo catalyst. The minor fraction with high molecular weight
diastereomer, only one face is blocked.
The behavior of the dibromide catalyst is unique in that PE
is produced with an exceptionally broad molecular weight
distribution (MWD = ca. 14) which spans the high and low
molecular weight ranges. Using the rates of syn/anti
diastereomer interconversion of zinc analogue 8c as a model
for the nickel catalyst, we propose that the rates of
interconversion for the nickel catalyst fall in the “sweet spot”
such that chains are formed which span the molecular weight
range expected for individual syn and anti diastereomers. This
appears to be a rare case in which an extremely broad MWD is
not caused by the presence of multiple active species but by a
single catalyst oscillating between two species, one producing
very high M polymer and another one producing low M
(
8
M = 908 kg/mol) from the anti diastereomer shows that an
-chloro substituent in these bis-naphthyl complexes is
p
sufficiently bulky to block the axial site and thus high polymer
is produced by the anti complex in which both axial sites are
blocked. That two molecular weight fractions observed
suggests that, like the iodo case, isomer interconversion is
slow relative to chain growth. The turnover frequency
observed for the dichloro catalyst is in line with that observed
for the diiodo and dibromo catalysts, but the branching density
of polymer formed by 10b, 20 branches/1000 C, is somewhat
higher relative to polymers formed by 10d and 10c.
w
w
polymer, at just the right rate to produce a broad MWD
distribution. On the basis of the zinc analogue 8b, the dichloro
catalyst 10b slightly favors the syn over the anti diastereomer.
PE formed from activation of 3b shows a bimodal distribution.
In contrast to the diiodo system, the major fraction is a low
Complex 10a, possessing the much smaller fluoro
substituents, yields a very low molecular polymer and with
M measured by NMR spectroscopy of 0.58 kg/mol which is
n
quite similar to the Mn of polymer formed from the
unsubstituted bis-naphthyl catalyst, 10e, 0.86 kg/mol (Figure
molecular weight material (M = 7.8 kg/mol) from the syn
n
diastereomer and a minor high molecular weight fraction (Mp
ca. 900 kg/mol) from the anti diastereomer. The difluoro
catalyst system behaves much like the unsubstituted catalyst,
consistent with the small atomic radius of the fluoro
substituent, both of which produce low molecular weight PE.
S37). The turnover frequency of the difluoro complex of 11 ×
5
1
0 /h is ca. 4 fold higher than that of the unsubstituted
complex, possibly due to the electron-withdrawing fluoro
groups generating a more electrophilic nickel center. Branching
in polymers produced by these less hindered systems has
increased further over the dichloride system to 39 branches/
EXPERIMENTAL SECTION
■
1
000 C for polymer from 10a and 25 branches/1000 C from
General Materials and Methods. All manipulations of air- and
moisture-sensitive compounds were carried out using standard
Schlenk, high-vacuum, and glovebox techniques. Diethyl ether,
pentane, dichloromethane and toluene were purified by an MBraun
solvent purification system. Anhydrous methanol was purchased from
Sigma-Aldrich and used without any further purification. Anhydrous
unsubstituted 10e.
CONCLUSIONS
Previous studies have shown that the aryl substituents in 8-
arylnaphthylimine complexes form sandwich-type structures in
■
G
DOI: 10.1021/acs.organomet.9b00649
Organometallics XXXX, XXX, XXX−XXX

Organometallics
Article
dichloromethane-d and 1,1,2,2-tetrachloroethane-d were dried with
8-Halonaphthalen-1-amines (6a−d). The 8-halonaphthalen-1-
2
2
4
Å molecule sieves for 1 week prior to use. 1,8-Diaminonaphthalene,
amines were prepared according to the methods previously
55,56
isoamyl nitrite, and 2,3-butanedione were purchased from Sigma-
reported.
1,8-Diaminonaphthalene (4, 50 g, 316 mmol) was
Aldrich and used as received without further purification. 70%HF/
dissolved in a mixture of acetic acid (100 mL) and ethanol (500 mL)
under nitrogen at room temperature. Isoamyl nitrite (42 mL, 310
mmol) was then added dropwise with the temperature controlled at
about 20 °C by using a cold-water bath. After the addition, the
mixture was stirred at room temperature for 24 h. The red crystalline
solid 5 was collected by filtration and dried under a vacuum without
further purification (43 g, 80%). Compound 5 (10g, 59 mmol) and
Cu powder (10 mol %) was added slowly to excess (30 equiv) of
3
0% Py, hydrochloric acid (37 wt % in H O), hydrobromic acid (48
2
wt % in H O) and hydriodic acid (57 wt % in H O) were purchased
2
2
from Sigma-Aldrich. The MMAO-3A used was a 7 wt % Al solution in
1
13
heptane purchased from Akzo Nobel. H and C NMR spectra of
1
19
ligands were recorded on a 400 MHz JEOL spectrometer. The H,
F
and 13C of the zinc and palladium complexes at variable temperature
were recorded on 500 MHz JEOL spectrometer. High temperature
NMR analysis of polyethylene samples were performed on a 600 MHz
JEOL spectrometer at 120 °C. Elemental analyses of the nickel
complexes were conducted by Altantic Microlabs Inc. (Norcross, GA,
USA). Compounds for HRMS were analyzed by positive mode
electrospray ionization (CI or ESI) using Agilent QTOF mass
spectrometer in the Mass Spectrometry Facility (MSF) of the
Department of Chemistry and Biochemistry of University of Texas-
Austin. High temperature gel permeation chromatography (GPC) was
performed in 1,2,4-trichlorobenzene at 165 °C using a Malvern
OMNISEC instrument with a triple detector. The M and M values
hydrohalic acid solution (HCl: 37 wt % in H O; HBr: 48 wt % in
2
H O; HI: 57 wt % in H O; 70%HF/30% Py was used for the
2
2
synthesis of 8-fluoronaphthalen-1-amine) and the flask was cooled
with an ice/salt bath. The reaction mixture was stirred for 72 h at
room temperature. The reactions were monitored by thin layer
chromatography (TLC). The reaction flasks were cooled in an ice
bath and 50 g of ice chips were added into the reaction mixture. The
mixture was treated with aqueous ammonia (32%, about 150 mL)
until the final pH about 11. The reaction mixture was filtered and the
filtrate was extracted by dichloromethane (3 × 250 mL). After
removing the solvent under a vacuum, the product was purified by
column chromatography using EtOAc/hexane (1:5) as eluent to give
a light brown solid (yields: 80−88%). The spectral data of 6a−d
n
w
were determined using polystyrene standards. The melting temper-
atures (T ) of the polymer samples were measured by DSC on a TA
m
Instruments Q2000 apparatus. Analyses were performed in crimped
aluminum pans under nitrogen and data were collected with the heat
5
5,56
match the literature values.
2
3
N ,N -Bis(8-fluoronaphthalen-1-yl)butane-2,3-diimine (7a).
(
25 to 200 °C)/cool (200 to −100 °C)/heat (−100 to 200 °C) cycles
In a 100 mL round-bottom flask, ZnCl (852 mg, 6.25 mmol), 8-
2
at a heating rate of 10 °C/min.
fluoronaphthalen-1-amine (2.0 g, 12.5 mmol), and 2,3-butanedione
General Procedure for Polymerizations. A 450 mL Parr
autoclave was heated under a vacuum at 100 °C for several hours and
then cooled to 40 °C. After backfilling with ethylene, toluene (200
mL) was added and the autoclave was sealed. The ethylene pressure
was raised to ca. 10 atm and maintained for about 5 min. The
autoclave was then vented, and the nickel catalyst solution (1.5 μmol)
was rapidly added followed by 1.5 mL MMAO (Al:Ni = 1000:1). The
autoclave was sealed and rapidly pressurized to the desired ethylene
pressure with fast stirring. The exotherm of the polymerization was
controlled and the temperature maintained with an ice/water bath.
After 10 min, the reaction was quenched by venting the autoclave
followed by addition of HCl/methanol (5% v/v). The precipitated
polymers were filtered and dried under vacuum overnight.
(
473 mg, 5.5 mmol) were suspended in glacial acetic acid (10 mL).
The reaction mixture was stirred at room temperature for 2 h. The
solid was separated by filtration and washed with acetic acid (3 × 20
mL) and diethyl ether (5 × 20 mL). The zinc complex was then
suspended in methylene chloride (100 mL), and a solution of
potassium oxalate (20 mmol) in water (30 mL) was added. The
mixture was stirred vigorously for 30 min. A white precipitate of zinc
oxalate was generated in the aqueous phase. The two phases were
separated, and the organic layer was washed with water and dried with
MgSO . After filtration, the solvent was removed the under a vacuum
to give a viscous oil. Adding methanol to the flask affords a bright
yellow needle-like solid 7a (yield: 60%, 1.23 g). H NMR (400 MHz,
CDCl , ppm) δ 7.63 (dd, J = 8.5, 7.7 Hz, 4H), 7.52−7.47 (m, 2H),
4
1
3
X-ray Crystallography Analysis. Crystals suitable for X-ray
crystallography were grown by slow diffusion of pentane into a room-
temperature saturated solution of metal complexes in CH Cl .
7
6
.39 (td, J = 7.9, 4.8 Hz, 2H), 7.10 (ddd, J = 12.8, 7.6, 0.9 Hz, 2H),
19
.76 (dd, J = 7.3, 1.0 Hz, 2H), 2.22 (s, 6H). F NMR (376 MHz,
13
2
2
CDCl , ppm) δ −112.54 (t, J = 8.4 Hz). C NMR (101 MHz,
CDCl , ppm) δ 167.8, 159.4 (d, J = 257.6 Hz), 146.0 (d, J = 5.1 Hz),
3
Intensity data were collected on a Bruker APEX-II CCD detector
using Mo Kα radiation with wavelength of 0.71073 Å. The structure
was solved with the olex2 structure solution program using Charge
Flipping and refined using least-squares techniques.
3
1
36.7 (d, J = 3.5 Hz), 126.9, 126.1 (d, J = 9.1 Hz), 124.1 (d, J = 5.0
Hz), 123.5 (d, J = 4.0 Hz), 115.6 (d, J = 10.1 Hz), 114.3, 110.9 (d, J =
+
2
2.2 Hz), 16.0. HRMS (ESI) calculated for C H F N [M + H] :
24 18 2 2
General Procedure for Variable Temperature NMR Studies
at Low Temperature (−80 to 0 °C). An oven-dried NMR tube was
charged with single crystals of (8-fluoronaphthyl-α-diimine)
palladium(II) methyl chloride (9a, 10 mg) in a glovebox. The tube
was capped with a rubber septum, wrapped with parafilm, and
removed from the glovebox. After cooling to −78 °C in a dry ice/
acetone bath, CD Cl was added to the NMR tube via a gastight
3
73.1511, found 373.1518 (Figure S12 in Supporting Information).
The other ligands were synthesized by the same method described
above (Caution: All of these ligands are sensitive to light, and
exposure to light leads to development of a dark color.)
2
3
N ,N -Bis(8-chloronaphthalen-1-yl)butane-2,3-diimine (7b).
1
Yellow solid (yield: 56%, 1.25 g). H NMR (400 MHz, CDCl , ppm)
3
2
2
δ 7.76 (dd, J = 8.2, 0.8 Hz, 2H), 7.63 (dd, J = 8.2, 0.8 Hz, 2H), 7.53−
syringe and the cap was wrapped again with parafilm. The mixture was
briefly shaken to dissolve the materials. The tube was then transferred
to the precooled NMR probe (−80 °C) to collect the spectra. The
7.45 (m, 4H), 7.38−7.32 (m, 2H), 6.74−6.69 (m, 2H), 2.26 (s, 6H).
1
3
C NMR (101 MHz, CDCl , ppm) δ 167.7, 147.5, 136.8, 128.8,
3
1
28.0, 126.6, 125.9, 124.9, 122.7, 122.5, 115.4, 16.6. HRMS (ESI)
1
+
probe was slowly warmed to 0 °C in intervals of 10 °C, and H and
calculated for C H Cl N [M + H] : 405.0920, found 405.0926
2
4
18
2
2
19
F NMR spectra were recorded respectively from −80 to 0 °C.
General Procedure for Variable Temperature NMR Studies
(Figure S13 in Supporting Information).
2
3
N ,N -Bis(8-bromonaphthalen-1-yl)butane-2,3-diimine (7c).
1
at High Temperature (25−80 °C). An oven-dried NMR tube was
charged with single crystals of (8-fluoronaphthyl-α-diimine)
palladium(II) methyl chloride (9a, 10 mg) in a glovebox. The tube
was capped with a rubber septum and removed from the glovebox.
Yellow solid (yield: 50%, 1.36 g). H NMR (400 MHz, CDCl , ppm)
δ 7.83−7.76 (m, 4H), 7.66−7.62 (m, 2H), 7.50−7.44 (m, 2H), 7.26
(t, J = 8.6, 2H), 2.30 (s, 6H). C NMR (101 MHz, CDCl , ppm) δ
168.0, 147.6, 136.8, 132.9, 128.7, 126.5, 126.4, 125.3, 123.7, 118.1,
115.6, 17.0. HRMS (ESI) calculated for C H Br N [M + H] :
3
1
3
3
+
Tetrachloroethane-d was added to the NMR tube via a gastight
2
24 18
2
2
syringe and the cap was wrapped again with parafilm. The mixture was
briefly shaken to dissolve the materials. The tube was then transferred
to the NMR spectrometer. H and F NMR spectra were recorded
494.9891, found 494.9893 (Figure S14 in Supporting Information).
2
3
N ,N -Bis(8-iodonaphthalen-1-yl)butane-2,3-diimine (7d).
1
19
1
Yellow solid (yield: 55%, 1.78 g). H NMR (400 MHz, CDCl3,
respectively at 25, 40, 60, and 80 °C.
ppm) δ 8.21 (t, J = 7.3 Hz, 2H), 7.84 (t, J = 8.2 Hz, 2H), 7.64 (t, J =
H
DOI: 10.1021/acs.organomet.9b00649
Organometallics XXXX, XXX, XXX−XXX

Organometallics
Article
8
.2 Hz, 2H), 7.49−7.42 (m, 2H), 7.11−7.05 (m, 2H), 6.72 (t, J = 7.3
of the backbone were observed at 2.30 (syn) and 2.25 (anti) ppm,
respectively, because both syn and anti diastereomers are present (6H,
syn/anti = 2:1) (Figure S20).
1
3
Hz, 2H), 2.38 (s, 6H). C NMR (101 MHz, CDCl , ppm) δ 168.8,
3
1
1
47.4, 141.3, 136.1, 129.7, 127.1, 126.3, 126.0, 125.4, 115.7, 88.6,
8.1. HRMS (ESI) calculated for C H I N [M + H] : 588.9632,
+
2
3
N ,N -Bis(8-bromonaphthalen-1-yl)butane-2,3-diimine·
2
4
18 2
2
1
found 588.9644 (Figure S15 in Supporting Information).
ZnCl
tetrachloroethane-d
2
(8c). Yellow solid (yield: 75%, 260 mg). H NMR (500 MHz,
, ppm) δ 7.98−7.86 (m, 6H), 7.67−7.55 (m,
2
3
N ,N -Di(naphthalen-1-yl)butane-2,3-diimine (7e). Yellow
2
1
solid (Yield: 65%, 1.2 g). H NMR (400 MHz, CDCl , ppm) δ
7
2
4H), 7.41 (t, J = 7.8 Hz, 5H). Two signals for the methyl groups of
the backbone were observed at 2.28 (syn) and 2.30 (anti) ppm,
respectively, because both syn and anti diastereomers are present (6H,
syn/anti = 1:1.5) (Figure S21).
3
.92−7.88 (m, 2H), 7.83 (d, J = 8.0 Hz, 2H), 7.67 (d, J = 8.2 Hz,
H), 7.58−7.47 (m, 6H), 6.86 (d, J = 7.2 Hz, 2H), 2.32 (d, J = 1.9
13
Hz, 6H). C NMR (101 MHz, CDCl , ppm) δ 169.2, 147.1, 134.2,
3
2
3
1
28.2, 126.4, 125.9, 125.8, 125.6, 124.3, 123.5, 113.1, 16.1. HRMS
N ,N -Bis(8-iodonaphthalen-1-yl)butane-2,3-diimine·ZnCl
2
1
+
(8d). Yellow solid (yield: 82%, 327 mg). H NMR (500 MHz,
(
ESI) calculated for C H N [M + H] : 337.1699, found 337.1705
24 20 2
tetrachloroethane-d , ppm) δ 8.35−8.31 (m, 2H), 7.99 (d, J = 7.7 Hz,
(
Figure S16 in Supporting Information).
2
2
3
2H), 7.92 (dd, J = 7.1, 2.5 Hz, 2H), 7.68−7.62 (m, 4H), 7.23 (t, J =
7.8 Hz, 2H). Two signals for the methyl groups of the backbone were
observed at 2.31 (syn) and 2.17 (anti) ppm, respectively, because both
syn and anti diastereomers are present (6H, syn/anti = 1:22) (Figure
S22)2.
N ,N -Bis(8-fluoronaphthalen-1-yl)butane-2,3-diimine·NiBr
2
(
3a). An oven-dried 50 mL Schlenk tube was charged with diimine
ligand 7a (223.2 mg, 0.6 mmol) and (DME)NiBr (154 mg, 0.5
2
mmol) in an argon-filled glovebox. The tube was connected to a
Schlenk line, and CH Cl (10 mL) was added via syringe. The
2
2
3
reaction mixture was stirred at room temperature for 24 h. The
supernatant liquid was transferred by a syringe and the remaining light
yellow solid was washed with diethyl ether (5 × 5 mL). The solid 3a
was dried under a vacuum at room temperature overnight. Yield: 235
mg (80%). Elem. anal. calculated for C H Br F N Ni·CH Cl : C,
N ,N -Bis(8-fluoronaphthalen-1-yl)butane-2,3-diimine·
PdMeCl (9a). An oven-dried 50 mL Schlenk tube was charged with
59
diimine ligand 7a (223.2 mg, 0.6 mmol) and (COD)PdMeCl (145
mg, 0.55 mmol) under a nitrogen atmosphere. Anhydrous CH Cl
2
2
(
10 mL) was then added via syringe. The reaction mixture was stirred
2
4
18
2
2
2
2
2
at room temperature for 24 h. Then, pentane (10 mL) was added and
yellow solid precipitated from solution. The supernatant liquid was
removed and the solid was washed with additional pentane (3 × 5
mL). The solid was dried under a vacuum at room temperature
4
4.43; H, 2.98; N, 4.15. Found: C, 44.74; H, 3.16; N, 4.34. X-ray
crystallographic data shows one CH Cl molecule bound to 3a.
2
2
Diimine nickel catalysts 3b−3e were synthesized by the method
described above.
1
2
3
overnight. Yield: 227 mg (78%). H NMR (600 MHz, CD Cl , ppm)
N ,N -Bis(8-chloronaphthalen-1-yl)butane-2,3-diimine·
2
2
NiBr (3b). Light brown solid (Yield: 82%, 254 mg). Elem. anal.
calculated for C H Br Cl N Ni·CH Cl : C, 42.37; H, 2.84; N, 3.95.
Found: C, 41.83; H, 3.05; N, 3.84.
δ 7.86−7.70 (m, 4H), 7.64−7.57 (m, 2H), 7.53−7.43 (m, 2H), 7.30−
7.16 (m, 2H), 7.08−7.06 (m, 2H), 0.19 (3H, two peaks, 0.191 and
0.186). Two signals for the methyl groups of the backbone were
observed at 2.10 (syn) and 2.06 (anti) ppm, respectively, because both
syn and anti diastereomers are present (6H, syn/anti = 1.5:1) (Figure
2
24
18
2
2
2
2
2
2
3
N ,N -Bis(8-bromonaphthalen-1-yl)butane-2,3-diimine·
NiBr (3c). Red brown solid (Yield: 85%, 301 mg). Elem. anal.
calculated for C H Br N Ni: C, 40.44; H, 2.55; N, 2.93. Found: C,
3
2
1
9
S23). F NMR (565 MHz, CD Cl , ppm) δ syn −112.35 (t, J = 17.0
24
18
4
2
2
2
9.99; H, 2.54; N, 2.89.
Hz), −112.66 (t, J = 17.0 Hz), anti −113.06 (d, J = 11.3 Hz),
−113.29 (d, J = 11.3 Hz).
2
3
N ,N -Bis(8-iodonaphthalen-1-yl)butane-2,3-diimine·NiBr
2
(3d). Red brown solid (Yield: 80%, 323 mg). Elem. anal. calculated
for C H Br I N Ni: C, 35.73; H, 2.25; N, 3.47. Found: C, 35.12; H,
24
18 2 2
2
ASSOCIATED CONTENT
2
.26; N, 3.45.
■
2
3
N ,N -Di(naphthalen-1-yl)butane-2,3-diimine·NiBr (3e).
2
*
S
Supporting Information
The Supporting Information is available free of charge at
https://pubs.acs.org/doi/10.1021/acs.organomet.9b00649.
Light yellow solid (Yield: 78%, 216 mg). Elem. anal. calculated for
C H Br N Ni·CH Cl : C, 46.93; H, 3.47; N, 4.38. Found: C, 47.31;
2
4
20
2
2
2
2
+
H, 3.38; N, 4.45. HRMS (ESI) calculated for C H N NiO [M −
Br + HCO ] : 439.10, found 439.096. HRMS (ESI) calculated for
2
5
21
2
2
−
+
2
2
NMR spectra of intermediates, α-diimine ligands, zinc
complexes, and palladium complex; molecular structure
of free ligand 7c−d; Characterization and analysis data
of polyethylene (PDF)
+
+
C H N Ni [M − 2Br − H] : 393.10, found 393.090 (Figure S17 in
24
19
2
Supporting Information).
2
3
N ,N -Bis(8-fluoronaphthalen-1-yl)butane-2,3-diimine·
ZnCl (8a). A 50 mL Schlenk tube was charged with diimine ligand
2
7
a (223.2 mg, 0.6 mmol) and ZnCl (75 mg, 0.55 mmol) under a
2
nitrogen atmosphere. Glacial acid (10 mL) was then added via
syringe. The reaction mixture was stirred at room temperature for 2 h.
Yellow solid precipitated during reaction. The solid was collected by
filtration and washed with diethyl ether (5 × 5 mL). The resultant
solid 8a was dried under a vacuum at room temperature overnight.
Yield: 238 mg (85%). Compound 8a was recrystallized three times
Accession Codes
CCDC 1949177−1949181 contain the supplementary crys-
tallographic data for this paper. These data can be obtained
free of charge via www.ccdc.cam.ac.uk/data_request/cif, or by
emailing data_request@ccdc.cam.ac.uk, or by contacting The
Cambridge Crystallographic Data Centre, 12 Union Road,
Cambridge CB2 1EZ, UK; fax: +44 1223 336033.
1
from CH Cl /ether before the NMR dynamic analysis. H NMR (500
MHz, tetrachloroethane-d , ppm) δ 7.90 (d, J = 8.2 Hz, 2H), 7.77 (t, J
2
2
2
=
7.6 Hz, 2H), 7.63 (td, J = 7.8, 3.6 Hz, 2H), 7.56−7.42 (m, 4H),
19
7
.28 (td, J = 13.3, 7.7 Hz, 2H), 2.34 (s, 6H). F NMR (470 MHz,
AUTHOR INFORMATION
■
tetrachloroethane-d , ppm) δ −113.33 to −113.36 (m), −114.08 to
2
Corresponding Authors
*E-mail: olafs@uh.edu.
E-mail: mbrookha@central.uh.edu.
−114.17 (m).
The other zinc complexes 8b−8d were prepared by the same
method described above. Caution: These zinc complexes are sensitive
to moisture and slow hydrolysis of the ligands will occur by exposing
the complexes to air. Keeping them under an inert atmosphere is
highly recommended.
*
ORCID
Bin Wang: 0000-0002-3130-3229
Olafs Daugulis: 0000-0003-2642-2992
2
3
N ,N -Bis(8-chloronaphthalen-1-yl)butane-2,3-diimine·
1
ZnCl (8b). Yellow solid (yield: 80%, 238 mg). H NMR (500 MHz,
2
Notes
tetrachloroethane-d , ppm) δ 7.91 (dd, J = 12.1, 7.8 Hz, 4H), 7.68−
2
7
.60 (m, 4H), 7.54−7.47 (m, 4H). Two signals for the methyl groups
The authors declare no competing financial interest.
I
DOI: 10.1021/acs.organomet.9b00649
Organometallics XXXX, XXX, XXX−XXX

Organometallics
Article
Diimine Nickel Catalysts and Revisiting Formation of Long-Chain
ACKNOWLEDGMENTS
■
Branching. ACS Catal. 2018, 8, 1104−1113.
This research was supported by the Welch Foundation (Grant
E-1893 to M. B. and Chair E-0044 to O. D.). B. W. thanks the
China Scholarship Council for a Visiting Scholar Research
Fellowship (No. 201706255010). We are grateful to Dr. Xiqu
Wang and James D. Korp for collecting the diffraction data and
solving the X-ray structures and to Dr. David Bez
experiments.
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DOI: 10.1021/acs.organomet.9b00649
Organometallics XXXX, XXX, XXX−XXX