Triazolecarboxamidate Donors as Supporting Ligands for Nickel Olefin Polymerization Catalysts

Article abstract of DOI:10.1021/acs.organomet.7b00807

To increase the structural diversity of dinucleating platforms that are used in the construction of olefin polymerization catalysts, we are exploring new ligand designs that feature non-Alkoxide/phenoxide bridging groups. In the current study, we demonstr

Full text of DOI:10.1021/acs.organomet.7b00807

Article
Cite This: Organometallics XXXX, XXX, XXX−XXX
Triazolecarboxamidate Donors as Supporting Ligands for Nickel
Olefin Polymerization Catalysts
Dawei Xiao and Loi H. Do*
Department of Chemistry, University of Houston, 4800 Calhoun Road, Houston, Texas 77004, United States
*
S Supporting Information
ABSTRACT: To increase the structural diversity of dinucleating
platforms that are used in the construction of olefin polymer-
ization catalysts, we are exploring new ligand designs that feature
non-alkoxide/phenoxide bridging groups. In the current study,
we demonstrate that 1,2,3-triazole-4-carboxamidate donors are
excellent N,N-chelators for nickel and can readily bind secondary
metal ions. We found that sterically bulky nickel triazolecarbox-
amidate complexes are active as ethylene homopolymerization
catalysts and can afford low molecular weight polyethylene with
about 80−130 branches per 1000 carbon atoms. The addition of
zinc salts to our nickel complexes led to catalyst inhibition in
some cases, which we have attributed to the formation of catalytically inactive mixed-metal species. To circumvent this problem,
we anticipate that further elaboration of the triazolecarboxamidate ligand could provide discrete heterobimetallic complexes that
will be useful as single-site catalysts with unique reactivity patterns.
INTRODUCTION
Scheme 1. (A) Proposed Reaction of Methyl Acrylate (MA)
with Bimetallic Catalysts and (B) Our Motivation for the
Study of Nickel Triazolecarboxamidate Complexes To
Prepare Heterobimetallic Catalysts
■
One of the major advantages of coordination−insertion over
other olefin polymerization processes is that it provides precise
control over the continuous enchainment of olefin mono-
1
−4
mers.
Nickel and palladium complexes that promote
coordination−insertion catalysis have even been shown to
copolymerize ethylene and polar vinyl olefins such as acrylic
5
−8
acid, acrylic ester, acrylamide, and vinyl halide. Despite their
broader olefin substrate scope compared to early transition
metal complexes, late transition metal complexes are still far too
slow in the copolymerization of ethylene and polar monomers
to be practical for commercial polymer synthesis. Their poor
performance is believed to be due to the preferential σ
coordination of heteroatoms to the metal catalyst and the
tendency to form metallacyclic intermediates upon polar
monomer insertion. It has been suggested that these problems
could be circumvented by using bimetallic catalysts that take
9
−11
advantage of metal−metal cooperativity.
As shown in
Scheme 1A, it is proposed that the binding of monomers such
as methyl acrylate to a bimetallic complex would engage both
metal centers to yield a metal−π-olefin adduct at the active site
(
1). Upon olefin insertion, the resulting chelated species 2
complexes with the shortest metal−metal bond distances,
which may help to promote cooperative interactions between
both metal centers. To access novel families of type II catalysts,
we are focusing on new ligand frameworks that feature N-
heterocyclic rather than alkoxide/phenoxide bridging do-
could then convert to an open structure 3, which is poised to
accept additional olefins and facilitate more rapid chain growth
compared to 2. This approach appears to be promising based
on work reported by several research groups, including
10,11
9
Takeuchi and Osakada
and Agapie.
17−19
nors.
Expanding the diversity of dinucleating ligands
A wide range of bimetallic motifs has been explored as olefin
polymerization catalysts, including the use of both symmetric
10−16
and asymmetric ligands (Chart 1).
We favor the type II
Received: November 7, 2017
over the type III/IV dinucleating platforms because they give
©
XXXX American Chemical Society
A
DOI: 10.1021/acs.organomet.7b00807
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Article
Chart 1. Depiction of (A) Common Bimetallic Structural
Motifs and (B) Examples of Bimetallic Olefin
Scheme 2. Synthesis of Triazolecarboxamide Ligands 2 and
Their Corresponding Nickel Complexes 3
Polymerization Catalysts Reported in the Literature
26,27
nylnaphthyl (2c).
To obtain the corresponding nickel
complexes 3a−3c, ligand 2 was deprotonated by the addition of
sodium hexamethyldisilazane (NaHMDS) and then reacted
28
with Ni(Br)(Ph)(PPh3)2 to afford the desired products as
yellow solids in moderate yields (55−68%).
To elucidate the structure of Ni(2a)(Ph)(PPh ) (3a), we
analyzed its single crystal by X-ray crystallography. As shown in
Figure 1, complex 3a adopts a square planar arrangement, in
available to assemble bimetallic structures provides us with the
opportunity to fine-tune various catalyst design parameters such
as metal−metal bond distance, metal geometry, and electronic
environment. In the following report, we demonstrate for the
first time that 1,2,3-triazole-4-carboxamidate can be metalated
with nickel to yield discrete mononuclear species that are active
as catalysts for ethylene homopolymerization. We also show
that the nickel triazolecarboxamidate complexes can coordinate
to external zinc ions in solution, suggesting that further
elaboration of the triazolecarboxamidate framework might
afford discrete type II complexes. We anticipate that the
introduction of secondary metal ions to our nickel catalysts
could significantly enhance their polymerization rates as well as
provide access to unique reactivity patterns.
3
RESULTS AND DISCUSSION
■
Nickel Triazolecarboxamidate Catalyst Design. Be-
cause most type II ligands used to prepare olefin polymer-
ization catalyst have either anionic alkoxide or phenoxide
bridges (Chart 1B), we sought to explore other donor groups
such as N-heterocycles that are electronically and geometrically
2
0,21
22
Figure 1. X-ray crystal structure of Ni(2a)(Ph)(PPh ) (3a, ORTEP
3
distinct.
The 1,2,3-triazole-4-carboxamidate group is an
view, displacement ellipsoids drawn at 50% probably level). Hydrogen
atoms and solvent molecules have been omitted for clarity. Bond
lengths (Å): Ni(1)−N(1) = 1.973(3), Ni(1)−N(2) = 1.930(3),
Ni(1)−C(22) = 1.891(4), and Ni(1)−P(1) = 2.165(1). Bond angles
attractive ligand because it can adopt multiple coordination
modes and has the potential to accommodate more than one
metal ions (Scheme 1B). Furthermore, because the triazole ring
can be assembled using click chemistry, accessing the
triazolecarboxamidate scaffold should be synthetically straight-
forward.
23
(
deg): N(1)−Ni(1)−C(22) = 94.48(13), C(22)−Ni(1)−P(1) =
86.91(11), P(1)−Ni(1)−N(2) = 95.91(9), and N(1)−Ni(1)−N(2)
= 82.60(12).
Compounds 2a−2c were prepared starting from the copper-
catalyzed cycloaddition reaction between benzyl azide and
which the nickel center is ligated by the carbon donor of the
phenyl group (Ni−C = 1.89 Å), the phosphorus donor of
triphenylphosphine (Ni−P = 2.16 Å), and the N,N donors of
24
propiolic acid to give compound 1 (Scheme 2). Activation of
1
2
using PCl , followed by the addition of an arylamine, yielded
5
in high purity after a simple workup procedure. We
the triazolecarboxamidate ligand (Ni−N
= 1.97 Å, Ni−
amide
synthesized three ligand variants that differ in their Namide-aryl
substituents, including 2,6-bis(isopropyl)phenyl (2a), 2,6-
N
= 1.93 Å). Similar to the structures of related nickel
triazole
29
complexes, the phosphine group is coordinated trans relative
to the anionic carboxamidate moiety. The β-nitrogen atom of
25
bis(3,5-bis(trifluoromethyl)phenyl)phenyl (2b), and 8-phe-
B
DOI: 10.1021/acs.organomet.7b00807
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Article
the triazole ring is sterically unhindered and should be capable
zinc clusters or oligomers on the NMR time scale. The primary
30−32
of binding external metal ions.
We did not observe the
coordination sphere of the nickel center is unaffected by zinc
33
31
formation of any 1,3-N,O-carboxamidate or 1,4-N,O-triazole-
binding based on the P NMR data, which showed only a
3
4
carboxamidate coordination isomers (Chart S1).
single peak at 31.3 ppm assigned to the nickel-bound
triphenylphosphine ligand. When the 3b/Zn2+ mixture (1:5)
was treated with excess 12-crown-4 ether to remove zinc,
Secondary Metal Ion Binding. Given the propensity of
35
triazole donors to coordinate to transition metal ions, we
expected that our nickel triazolecarboxamidate complexes
would have a high affinity for zinc. When Zn(SO CF ) was
1
further changes in the H NMR spectra were observed (Figure
2B, bottom trace). However, this spectrum did not match that
of 3b (top trace), suggesting that 12-crown-4-ether cannot
reverse zinc binding. Similar results were obtained when NMR
3
3 2
combined with either 3a or 3c in the noncoordinating solvent
1
CDCl , however, the zinc salt did not dissolve. In fact, the H
3
NMR spectra of 3a (Figure S25) and 3c (Figure S26) remained
unchanged after the addition of up to 5 equiv of zinc. In
contrast, when 3b was mixed with up to 10 equiv of
studies were performed using 3b and ZnCl (Figure S24).
Although we could not obtain single crystals of the 3b/Zn
species for X-ray structural analysis, further spectroscopic
2
2
+
2+
Zn(SO CF ) in CDCl (Figure 2), the 3b/Zn mixtures
studies were performed to interrogate the binding of zinc to 3b.
3
3 2
3
2+
We hypothesize that the most likely sites for Zn complexation
are either the β-triazole nitrogen or carbonyl oxygen donors
(
Chart S2). We cannot determine at this time the nuclearity of
the nickel−zinc species in solution. When the infrared (IR)
spectrum of solid 3b was measured, a prominent ν stretch
CO
−1
−1
was observed at 1600 cm , which was shifted by ∼68 cm
lower in frequency compared to that of the free ligand 2b
(
(
Figure S27). Upon the addition of 1−10 equiv of Zn-
−1
SO CF ) to 3b, the signal centered at 1600 cm appeared to
3
3 2
split into multiple peaks. Based on a report on the study of
nickel tetraazamacrocycle complexes, the ν frequency is
CO
−1
expected to undergo a bathochromic shift of about 60 cm
3
6
upon coordination of ZnCl to the diketo moiety. Because the
2
−1
IR features at ∼1600 cm are still observed in the presence of
excess zinc salt, we speculate that Zn2+ binding to the carbonyl
group of 3b is either weak (i.e., exchanges with solvent in
solution) or does not occur. Thus, we propose that the β-
triazole nitrogen donor is the preferred site of coordination,
although further investigations are needed to fully elucidate the
structure of this nickel−zinc adduct.
Ethylene Polymerization with Ni. Next, compounds 3a−
c were tested as possible catalysts for ethylene homopolyme-
3
rization (Table 1). The nickel complexes were dissolved in 5
mL of toluene, treated with 2 equiv of the activator Ni(COD)2
(
COD = 1,5-cyclooctadiene), and then stirred under 100 psi of
ethylene at room temperature (RT) for 1 h (entries 2, 5, and
). Analysis of the reaction products revealed that 3a−3c
afforded polyethylene (PE) with different morphologies. Both
7
3
a and 3b gave polymers with ∼100 branches per 1000 carbon
13
atoms. The presence of sec-butyl groups in their C NMR
spectra (Figure 3A,B) indicated that they have hyperbranched
37
microstructures. Complex 3c, on the other hand, yielded
polymers with 86 branches per 1000 carbon atoms and showed
no detectable hyperbranching (Figure 3C). The tendency of
nickel catalysts to furnish branched polyethylene is typically
1
Figure 2. (A) Reaction of complex 3b with Zn(SO CF ) . (B) H
3
3 2
NMR spectra (CDCl , 600 MHz) of 3b with various equivalents of
3
zinc salt. A tentative structure of the nickel−zinc complex is proposed.
The disappearance of the triazole hydrogen at 7.63 ppm has been
attributed to peak broadening rather than loss of the hydrogen atom.
attributed to facile chain-walking processes and has been well
38,39
documented.
3
In terms of their polymer molecular weights,
3
a and 3c afforded PE with greater M (4.47 × 10 and 3.15 ×
n
3 3
were completely homogeneous and showed clear changes in
their H NMR spectra. For example, the singlet at 7.63 ppm,
which has been assigned to the hydrogen atom of the triazole
ring, broadened upon successive addition of Zn2+ ions and
became nearly undetectable in the presence of 10 equiv of
external salt. The peaks at 7.90 and 8.08 ppm, which
correspond to resonances from the hydrogen atoms of the
10 , respectively) than 3b (0.55 × 10 ). This result was
surprising because the 2,6-bis(3,5-bis(trifluoromethyl)phenyl)-
phenyl substituent in 3b is more sterically encumbered than the
2,6-bis(isopropyl)phenyl substituent in 3a, which usually gives
1
40,41
rise to PEs with higher M in conventional catalyst systems.
n
The PEs from 3a and 3b display relatively narrow
polydispersities, yielding M /M values ranging from about
w
n
2,6-bis(trifluoromethyl)phenyl rings, also showed significant
1.1 to 2.5. In contrast, the gel permeation chromatogram
broadening in the presence of zinc. These spectral changes
suggest that there are dynamic processes occurring in solution,
perhaps due to the interconversion between multiple nickel−
(GPC) of PE from 3c (M /M = 3.2−3.8) is bimodal (Figure
w
n
S30). Although we have not yet identified the reason for this
bimodal distribution, it is possible that the activated 3c complex
C
DOI: 10.1021/acs.organomet.7b00807
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Article
a
Table 1. Ethylene Polymerization Data for 3a−3c
3
b
c
Mn (×103)
c
n
entry
cat.
time (h)
polymer yield (mg)
TOF (×10 g/mol·h)
branches (/1000 C)
C1%
C2%
C3%
C %
4+
M /M
w
1
2
3
4
5
6
7
8
3a
3a
3a
3a
3b
3b
3c
3c
0.5
1
138
266
464
497
158
276
49
11.0
10.6
9.3
102
99
68
69
67
67
78
72
69
84
6
6
7
6
5
6
5
3
4
3
4
3
2
3
4
0
22
22
22
24
15
19
22
13
5.81
4.47
4.11
6.16
0.55
0.46
3.15
2.0
2.5
2.2
1.6
1.5
1.1
3.8
3.2
2
113
108
103
127
86
3
6.6
1
6.3
3
3.7
d
d
1
2.0
3
125
1.7
77
7.01
a
b
Polymerization conditions: nickel precatalyst (25 μmol), Ni(COD) (50 μmol), ethylene (100 psi), 5 mL of toluene, 1 h at RT. The total number
2
1
c
d
of branches per 1000 carbons was determined by H NMR spectroscopy. Determined by GPC in trichlorobenzene at 150 °C. GPC trace shows
two overlapping peaks, suggesting that there are two active catalyst species.
Figure 3. Representative examples of quantitative 13C NMR spectra (TCE-d , 125 MHz, 120 °C) of polymers obtained from the reaction of
2
ethylene/Ni(COD) with catalysts (A) 3a, (B) 3b, and (C) 3c. The peak assignments were based on ref 37.
2
a
Table 2. Homopolymerization Data for 3a−3c with Zn(SO CF3)2
3
Zn2+ (equiv) polymer yield (mg) TOF (×10 g/mol·h) branches (/1000 C) C1% C2% C3% C % Mn (×103) M /M
3
b
c
c
entry
cat.
4+
w
n
1
2
3
4
5
6
7
8
9
3a
3a
3a
3b
3b
3b
3c
3c
3c
0
1
5
0
1
5
0
1
5
203
180
222
157
22
8.1
7.2
8.9
6.3
0.9
0.2
2.0
2.2
3.1
101
113
104
131
79
67
75
80
7
9
6
5
3
6
3
2
11
18
16
13
4.82
0.95
0.52
0.32
2.3
2.0
1.9
1.7
4
d
d
d
51
3.06
3.14
1.81
4.1
3.4
3.4
55
79
a
Polymerization conditions: nickel precatalyst (25 μmol), Ni(COD) (50 μmol), Zn(SO CF ) (various), ethylene (100 psi), 5 mL toluene, 1 mL
2
3
3 2
b
1
c
THF, 1 h at RT. The total number of branches per 1000 carbons was determined by H NMR spectroscopy. Determined by GPC in
trichlorobenzene at 140 °C. GPC trace shows two overlapping peaks, suggesting that there are two active catalyst species.
d
can undergo coordination isomerization to generate multiple
catalytically active constitutional isomers during catalysis.
The polymerization data showed that the activity of our
nickel complexes decreased in the order 3a > 3b > 3c. Their
activity in favor of higher molecular weight polymers compared
to those with 2,6-bis(isopropyl)phenyl groups. In our case,
41
however, both the TOF and M decreased for 3c compared to
n
3a (Table 1, cf. entry 2 vs 7). On the basis of their catalytic
performance, 3a−3c are considerably less active than conven-
3
turnover frequencies (TOFs) are approximately 10.6 × 10 , 6.3
3
3
6
×
(
10 , and 2.0 × 10 g/mol Ni·h for 3a, 3b, and 3c, respectively
Table 1). It has been shown that Pd diimine complexes
featuring 8-phenylnaphthyl groups exhibit reduced catalyst
tional nickel phenoxyimine (TOF = ∼0.1−6 × 10 g/mol Ni·
4
2
6
43
h) and nickel diimine (TOF = ∼0.8−11 × 10 g/mol Ni·h)
catalysts, although the direct comparison of TOFs in some
D
DOI: 10.1021/acs.organomet.7b00807
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Article
cases are not possible because the data reported were obtained
under different polymerization conditions. Despite the
moderate activity of the nickel triazolecarboxamidate com-
plexes, we anticipate that further molecular optimization in
future studies might furnish more robust catalysts.
complexes. Future work will explore the feasibly of this
approach and test further the homo- and copolymerization
behavior of this new class of nickel triazolecarboxamidate
catalysts.
To evaluate the stability of the nickel catalysts, polymer-
ization studies were conducted from 0.5 to 3 h (Table 1, entries
EXPERIMENTAL SECTION
■
General Procedures. Commercial reagents were used as received.
All air- and water-sensitive manipulations were performed using
standard Schlenk techniques or under a nitrogen atmosphere using a
glovebox. Anhydrous solvents were obtained from an Innovative
Technology solvent drying system saturated with argon. High-purity
polymer-grade ethylene was obtained from Matheson TriGas without
1
−8). For all three catalysts 3a−3c, there was a gradual
decrease in the TOF values with increasing reaction time, which
suggests that the catalysts undergo slow decomposition over
4
4
time. Complex 3c appeared to be the most stable, showing
85% activity after 3 h compared to that at 1 h. Since the
∼
polymer morphology and M do not change as a function of
further purification. The precursor Ni(Br)(Ph)(PPh ) was prepared
3 2
28
n
according to a literature procedure. The syntheses of compound 1
and ligands 2a−2c are provided in the Supporting Information.
Characterization Methods. Elemental analyses were performed
by Atlantic Microlab. Trace levels of solvents in elemental analysis
polymerization time, 3a−3c are nonliving catalysts.
Ethylene Polymerization with Ni/Zn. To study the
effects of external cations on ethylene polymerization, we
carried out reactions under 100 psi of ethylene using 3/
1
samples were quantified by H NMR spectroscopy. NMR spectra were
Ni(COD) (1:2) and various equivalents of Zn(SO CF ) salts
2
3
3 2
acquired using JEOL spectrometers (ECA-400, -500, and -600) and
1
9
(
Table 2) in toluene/THF (5:1). The use of THF cosolvent
referenced using residual solvent peaks. F NMR spectra were
31
enhances the solubility of the zinc salt in the reaction mixture.
For catalysts 3a and 3c, the addition of Zn did not
referenced to CFCl , whereas P NMR spectra were referenced to
3
2
+
phosphoric acid. IR spectra were measured using a Thermo Nicolet
Avatar FT-IR spectrometer with diamond ATR. High-resolution mass
spectra were obtained from the mass spectral facility at the University
of Texas at Austin.
Preparation of Complex 3a. Inside the glovebox, a solution
containing 2a (50 mg, 0.14 mmol, 1.0 equiv) and NaHMDS (38 mg,
significantly change their TOFs or PE branching micro-
structures compared to that in the absence of Zn2+ (entries
1
−3 and 7−9). However, their polymer molecular weights
decreased with increasing amounts of Zn(SO CF ) added.
3
3 2
Because our metal titration studies showed that 3a and 3c do
not form adducts with zinc salts (Figures S25 and S26), it is not
surprising that their catalytic properties are largely unaffected
0
.21 mmol, 1.5 equiv) in 10 mL of CH Cl was stirred for 2 h at RT.
2 2
Solid Ni(Br)(Ph)(PPh ) (102 mg, 0.14 mmol, 1.0 equiv) was added
3
2
in small portions. The reaction mixture was stirred for an additional 3
h. The resulting red mixture was filtered through a pipet plug and then
dried under vacuum to give a dark red oil. Upon the addition of
pentane and after being stirred for ∼5 min, a yellow solid formed. The
product was recrystallized by dissolving in CH Cl and then layered
2
+
by the presence of Zn . We believe that the reduction in M
n
observed is due to the zinc cation acting as a chain transfer
3
agent. Interestingly, when similar studies were conducted
using 3b/Ni(COD) /ethylene, the presence of added Zn-
2
2
2
with pentane to afford the final product as yellow crystals (72 mg, 0.09
(
SO CF ) led to significant catalyst inhibition. For example,
3 3 2
1
2
+
mmol, 68%). H NMR (CDCl
3
, 400 MHz): δ (ppm) = 7.68 (s, 1H),
.45 (t, JHH = 9.2 Hz, 6H), 7.34 (m, 6H), 7.22 (m, 6H), 6.90 (d, JHH
.0 Hz, 2H), 6.84 (t, JHH = 7.4 Hz, 1H), 6.76 (d, JHH = 7.4 Hz, 2H),
combining 10 equiv of Zn with 3b led to about a 30-fold
decrease in TOF (cf. entry 4 vs 6). Since our NMR studies
showed that the nickel center of 3b is preserved in the presence
of zinc, we propose that the most likely cause of catalyst
deactivation is the self-assembly of inactive higher nuclearity
structures (Chart S2). These results suggest that the use of
dinucleating ligands that provide well-defined nickel−zinc
species is necessary to form active olefin polymerization
catalysts.
7
7
6
7
=
.58 (d, JHH = 7.3 Hz, 2H), 6.24 (t, JHH = 6.9 Hz, 1H), 6.12 (d, JHH
=
=
.1 Hz, 2H), 5.0 (s, 2H), 3.69 (m, 2H), 1.14 (dd, J = 34.7 Hz, JHH
HH
13
6.4 Hz, 12H). C NMR (CDCl , 100 MHz): δ (ppm) = 163.92,
3
149.88, 149.42, 148.83, 143.62, 142.73, 135.61 (d, JCP = 2.7 Hz),
134.32 (d, JCP = 10.7 Hz), 133.04, 131.58 (d, JCP = 45.4 Hz), 129.89,
1
1
29.22, 128.46, 127.89 (d, JCP = 10.0 Hz), 125.18, 124.15, 122.28,
21.84, 121.10, 55.27, 29.10, 25.42, 23.28. 31P NMR (CDCl , 161
3
MHz): δ (ppm) = 30.03. UV−vis (DCM): λ /nm (ε/cm− M ) =
1
−1
max
−1
3
32 (3906), 415 (516). FT-IR: 3056 (νNH), 1606 (νCO) cm . Mp
CONCLUSIONS
■
(decomp.) = ∼166 °C. Anal. Calcd for C H N NiOP·(CH Cl )0.35:
C, 70.53; H, 5.84; N, 7.10. Found: C, 70.61; H, 5.97; N, 7.30.
Preparation of Complex 3b. A similar procedure was used as
described for 3a. Instead of 2a, ligand 2b (100 mg, 0.14 mmol, 1.0
4
6
45
4
2
2
Toward our ultimate goal of creating cooperative bimetallic
catalysts for olefin polymerization, we sought to design new
type II dinucleating ligands that feature non-oxygen bridging
donors. Although the 1,2,3-triazole-4-carboxamidate unit has
largely been overlooked in coordination chemistry, we have
demonstrated that it serves as an excellent anionic N,N-chelator
for nickel. We successfully synthesized a new family of nickel
triazolecarboxamidate complexes that have sterically bulky N-
carboxamidate substituents. Upon activation by treatment with
equiv) was used. Complex 3b was obtained as a yellow solid (89.4 mg,
1
0
4
.08 mmol, 58%). H NMR (CDCl , 500 MHz): δ (ppm) = 8.09 (s,
3
H), 7.91 (s, 2H), 7.64 (s, 1H), 7.30 (m, 5H), 7.06 (m, 16H), 6.73 (d,
JHH = 6.9 Hz, 2H), 6.29 (t, JHH = 7.0 Hz, 1H), 6.18 (d, J = 7.0 Hz,
H), 6.14 (t, JHH = 7.6 Hz, 2H), 4.94 (s, 2H). C NMR (CDCl , 100
MHz): δ (ppm) = 166.14, 149.62, 149.16, 147.41, 144.17, 143.67,
137.01, 135.21 (d, JCP = 1.6 Hz), 133.93 (d, JCP = 10.7 Hz), 132.95,
131.07, 130.59, 130.53, 130.48 (q, JCF = 32.7 Hz), 130.39, 129.98,
HH
13
2
3
Ni(COD) , the nickel complexes are active as catalysts for
2
ethylene polymerization. Analysis of the polymer products
revealed that their morphologies are highly dependent on the
structures of the nickel catalysts. Interestingly, we showed that
complex 3b binds readily to external zinc ions, most likely via
coordination by the basic β-nitrogen of its triazole ring. We
propose that further modification of the 1,2,3-triazole-4-
carboxamidate framework, such as attachment of a second
metal binding moiety at the γ position of the triazole unit,
would enable the construction of structurally stable bimetallic
129.14, 127.82 (d, JCP = 10.8 Hz), 125.43, 124.80, 123.84 (q, JCF =
3
1
2
72.0 Hz), 122.53, 121.43, 120.07, 55.21. P NMR (CDCl , 161
3
19
MHz): δ (ppm) = 31.30. F NMR (CDCl , 376 MHz): δ (ppm) =
3
−
1
−1
−
62.34. UV−vis (DCM): λmax/nm (ε/cm M ) = 331 (4093), 410
−1
(
°
5
574). FT-IR: 3083 (νNH), 1600 (νCO) cm . Mp (decomp.) = ∼225
C. Anal. Calcd for C H F N NiOP·(C H ) (CH Cl ) : C,
56
37 12
4
5
12 0.2
2
2 1.15
7.64; H, 3.47; N, 4.62. Found: C, 57.52; H, 3.73; N, 4.89.
Preparation of Complex 3c. A similar procedure was used as
described above for 3a. Instead of 2a, ligand 2c (50 mg, 0.12 mmol,
1.0 equiv) was used. Complex 3c was obtained as a yellow solid (53
E
DOI: 10.1021/acs.organomet.7b00807
Organometallics XXXX, XXX, XXX−XXX

Organometallics
Article
1
mg, 0.07 mmol, 55%). H NMR (CDCl , 500 MHz): δ (ppm) = 8.28
(
3
ASSOCIATED CONTENT
Supporting Information
The Supporting Information is available free of charge on the
ACS Publications website at DOI: 10.1021/acs.organo-
met.7b00807.
■
s, 1H), 7.5 (m, 2H), 7.35 (m, 13H), 7.18 (m, 9H), 7.03 (m, 3H), 6.92
d, JHH = 6.8 Hz, 2H), 6.73 (t, JHH = 7.4 Hz, 1H), 6.48 (t, JHH = 7.2
Hz, 1H), 6.37 (m, 2H), 5.86 (s, 2H), 5.56 (s, 1H), 4.85 (s, 2H).
NMR (CDCl , 100 MHz): δ (ppm) = 163.08, 151.69, 151.22, 149.28,
*
S
(
13
C
3
1
46.78, 144.50, 139.76, 136.35, 135.56, 135.12, 134.37 (d, JCP = 10.8
Hz), 133.65, 131.70 (d, JCP = 45.6 Hz), 130.19, 129.73, 129.23, 129.11,
Synthetic procedures, NMR spectra, and X-ray data
1
1
1
29.00, 128.61, 128.22, 127.87, 127.70 (d, JCP = 9.8 Hz), 127.58,
(PDF)
26.99, 126.54, 125.05, 124.64, 124.30, 124.06, 123.44, 123.20, 121.52,
20.46, 54.99. 31P NMR (CDCl , 161 MHz): δ (ppm) = 32.05. UV−
Accession Codes
3
−1
−1
vis (DCM): λmax/nm (ε/cm M ) = 327 (9717), 410 (867). FT-IR:
3
for C H N NiOP·(CH Cl ) : C, 71.86; H, 4.78; N, 6.64. Found: C,
CCDC 1566241 contains the supplementary crystallographic
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
−1
049 (νNH), 1594 (νCO) cm . Mp (decomp.) = ∼195 °C. Anal. Calcd
50
39
4
2
2 0.5
7
1.80; H, 4.77; N, 6.84.
Ethylene Polymerization. Inside the glovebox, the nickel catalyst
25 μmol) was dissolved in 5 mL of toluene in a scintillation vial. Solid
(
1
EZ, UK; fax: +44 1223 336033.
Ni(COD) (50 μmol) was added, and the solution was transferred to a
2
Fischer−Porter glass vessel. A magnetic stir bar was placed inside, and
then the reactor was sealed. The high-pressure apparatus was removed
from the glovebox and then securely fastened on top of a stir plate.
The ethylene line was attached, and the reactor was purged with
ethylene three times by pressurizing with ethylene and then releasing
the pressure. The reactor was then pressurized to 100 psi of ethylene
and stirred at RT for a specified amount of time. The ethylene line was
closed, and the vessel was slowly vented. About 1 mL of HCl(aq) was
added, followed by the addition of 2 mL of MeOH. The aqueous layer
was removed by pipetting, and the organic layer was evaporated to
dryness under vacuum. The resulting material was washed with MeOH
and CH Cl and then dried under vacuum.
AUTHOR INFORMATION
Corresponding Author
*E-mail: loido@uh.edu.
■
ORCID
Loi H. Do: 0000-0002-8859-141X
Notes
The authors declare no competing financial interest.
ACKNOWLEDGMENTS
■
2
2
1
We thank the Welch Foundation (Grant No. E-1894), ACS
Petroleum Research Fund (Grant No. 54834-DNI3), and the
University of Houston New Faculty Startup Grant for funding
this work.
Polymer Characterization. H NMR Spectroscopy. Each NMR
sample contained ∼10−20 wt % of polymer in 0.5 mL of 1,1,2,2-
tetrachlorethane-d (TCE-d ) and was recorded at 500 MHz using
2
2
standard acquisition parameters at 120 °C.
1
3
Quantitative C NMR Spectroscopy. Each NMR sample contained
10−20 wt % of polymer and 50 mM chromium acetylacetonate
∼
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DOI: 10.1021/acs.organomet.7b00807
Organometallics XXXX, XXX, XXX−XXX