N -Arylcyano-β-diketiminate methallyl nickel complexes: Synthesis, adduct formation, and reactivity toward ethylene

Article abstract of DOI:10.1021/om400847b

The syntheses and structures of new bis-N-phenyl-4-cyano-β- diketiminate (1), bis-N-phenyl-2-cyano-β-diketiminate (2), N-phenyl-4-cyano-N-phenyl-2-cyano-β-diketiminate (3), N-phenyl-4-cyano-N-2, 6-diisopropylphenyl-β-diketiminate (4), N-phenyl-2-cyano-N-2

Full text of DOI:10.1021/om400847b

Article
pubs.acs.org/Organometallics
N‑Arylcyano-β-diketiminate Methallyl Nickel Complexes: Synthesis,
Adduct Formation, and Reactivity toward Ethylene
Oleksandra S. Trofymchuk,† Dmitry V. Gutsulyak,‡ Celso Quintero,† Masood Parvez,‡
Constantin G. Daniliuc,§ Warren E. Piers,*,‡ and Rene S. Rojas*,†
†Departamento de Quimica Inorganica, Facultad de Quimica, Pontificia Universidad Catolica de Chile, Casilla 306, Santiago-22, Chile
‡Department of Chemistry, University of Calgary, 2500 University Drive NW, Calgary, Alberta, Canada T2N 1N4,
§Organisch-chemisches Institut der Universitat Munster, Corrensstrasse 40, 48149 Munster, Germany
̈
̈
S
* Supporting Information
ABSTRACT: The syntheses and structures of new bis-N-
phenyl-4-cyano-β-diketiminate (1), bis-N-phenyl-2-cyano-β-
diketiminate (2), N-phenyl-4-cyano-N-phenyl-2-cyano-β-dike-
timinate (3), N-phenyl-4-cyano-N-2,6-diisopropylphenyl-β-
diketiminate (4), N-phenyl-2-cyano-N-2,6-diisopropylphenyl-
β-diketiminate (5), and methallyl nickel complexes [L1Ni(η3-
methallyl)] (6), [L2Ni(η3-methallyl)] (7), [L4Ni(η3-meth-
allyl)] (8), and [L5Ni(η3-methallyl)] (9) from the reaction of
deprotonated ligands 1/2, 4/5, and methallylnickel chloride
dimer are reported. Subsequent reactions of complexes 6−9
with tris(pentafluorophenyl)boron give rise to new adducts [L1Ni(η3-methallyl)]·2B(C6F5)3 (10), [L2Ni(η3-methallyl)]·
2B(C6F5)3 (11), [L4Ni(η3-methallyl)]·B(C6F5)3 (12), and [L5Ni(η3-methallyl)]·B(C6F5)3 (13), where B(C6F5)3 is coordinated
to the cyano group. New compounds are characterized by NMR, IR, and mass spectrometry techniques, and crystal structures of
most compounds are obtained and described. Complexes 6−9, adducts 10−13, and adducts 10−13 with 5 equiv of B(C6F5)3
have been investigated toward ethylene activation. Complexes 6−9 were inactive toward ethylene even at 60 °C, while adducts
10−13 showed reactivity toward ethylene; adding 5 equiv of B(C6F5)3 to adducts 10−13 leads to an increase in reactivity toward
ethylene. Adducts 10 and 11 alone and with 5 equiv of B(C6F5)3 catalyze the oligomer formation, while adducts 12 and 13 by the
same conditions catalyze the polyethylene formation. Adduct 13 activity is five times higher with respect to 12 at 50 °C and two
times higher at 70 °C. The formation of branched moderate molecular weight PE by 12/B(C6F5)3 and 13/B(C6F5)3 is observed.
INTRODUCTION
■
The discovery of the late-transition-metal polymerization
catalysts has spurred interest in the design of homogeneous
nickel-based polymerization initiators.1 A key feature of these
catalysts lies in the electronic and steric influences of the
supporting ligand system, which can control the process of
olefin polymerization.2 Furthermore, although neutral nickel
polymerization initiators have been successfully developed,
today most catalysts are cationic species generated by addition
of a strong Lewis acid, in the presence or absence of an
alkylating agent, to a neutral organometallic precursor.3
Activation of nickel complexes for polymerization using the
smallest amount of Lewis acid cocatalyst such as MAO,
MMAO, TMA, or B(C6F5)34 improves the economic aspects of
polymerization with this class of catalysts.
Preformed cationic allyl complexes of nickel are stable
initiators for olefin polymerizations, but the initiation process is
generally inefficient, and only a few sites propagate rapidly, in
agreement with reports of initiator systems containing π-allyl
ligands.5 To activate methallyl complexes of nickel, Bazan’s
group has synthesized discrete cationic nickel complexes
(Figure 1) that allow the propagation of the ethylene chain
Figure 1. Example of previously reported cationic nickel complex.
in the presence of various coactivators.6 One reason for
increased polymerization rates in this system was the binding of
a Lewis acid to the carbonyl functionality in the ligand
structure.7 Since most of these examples are cationic
compounds, however, initiation rates remain somewhat
inefficient. We postulated that neutral nickel allyl catalyst
precursors may initiate more readily in the presence of a
suitable Lewis acid and chose to examine nickel diketiminate
methallyl polymerization initiators.
Given the above example of cationic nickel catalyst, we
decided to combine the benefits of both electronic effects and
Received: August 24, 2013
© XXXX American Chemical Society
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Scheme 1. Synthesis of Nickel Methallyl Complexes 6 and 7
Scheme 2. Synthesis of Nickel Methallyl Complexes 8 and 9
steric bulk, and thus our particular interest was in the influence
of electron-withdrawing substituents such as the cyano group
directly linked to the phenyl groups of β-diketimine ligands on
the performance of the resultant catalysts. We therefore
designed a series of substituted ligands differing in electronic
and steric properties and prepared the corresponding neutral
nickel complexes. To activate these complexes for ethylene
propagation, we decided to use B(C6F5)3, which can form
strong coordination bonds with the cyano group8 and further
decrease the electron density on the metal center. Moreover the
presence of the cyano group in the ortho position of the
aromatic ring of the prepared nickel complexes with
coordinated B(C6F5)3 provides steric hindrance near the
metal center.
resonances were seen for complex 7 for the syn and anti allylic
hydrogen atoms: at δ 1.21, 1.22 (Hsyn) and 1.62, 1.98 (Hanti
)
ppm. Interestingly, one of the anti protons of complex 7 is
shifted downfield with respect to the other, perhaps because of
its proximity to the cyano group. The downfield shift of these
signals relative to those of 6 indicate a more electrophilic metal
center in 7 due to the ortho position of the cyano group in the
aromatic ring of this complex.12 The products are therefore
[L1Ni(η3-methallyl)], 6, and [L2Ni(η3-methallyl)], 7, as shown
in a Scheme 1.
Scheme 2 shows the synthesis of [L4Ni(η3-methallyl)], 8,
and [L5Ni(η3-methallyl)], 9, by addition of potassium salt of
ligand 4 and 5 to [Ni(η3-(CH2)2Me)Cl]2, the same procedure
as for 6 and 7, except that to deprotonate 5 the solvent used
was diethyl ether. 1H/13C NMR spectroscopy is consistent with
the molecular structure and N,N-coordination of the
deprotonated ligands 4 and 5. Complex [L4Ni(η3-methallyl)],
8, shows syn and anti allylic hydrogen atoms: at δ 1.14, 1.54
RESULTS AND DISCUSSION
■
Synthesis and Characterization of Ligands. Sym-
metrical N-arylcyano-β-diketiminate ligands 1 (previously
reported9) and 2 employed in this study incorporate the
cyano group in ortho and para position of the aromatic ring, as
well as unsymmetrical ligand 3 (see Figure S-8). Unsymmetrical
N-arylcyano-β-diketiminates 4 and 5 incorporate the bulky 2,6-
diisopropylphenyl group as the substituent on nitrogen and
differ only in the location of the cyano group on the aromatic
ring of the second nitrogen aromatic substituent. Both types of
N-arylcyano-β-diketiminate ligands were synthesized by stand-
ard condensation reaction procedures8c,10 and were charac-
terized by CHN elemental analysis, mass spectrometry, and
spectroscopically; compounds 3, 4, and 5 were also
characterized by X-ray diffraction (for more details see the
Supporting Information).
1
(2H), 1.99 ppm in the H NMR spectrum.
In contrast to 8, complex 9 in the solution exists in the form
of two geometric isomers with the methyl group of the
methallyl either cis or trans to the cyano group of the aromatic
ring, and both isomers, formed with a ratio 50% to 50%, are
exchanging on the NMR time scale by rotation about the N−C
bond and can be differentiated by examining their NMR data
(see Scheme 3 and pages 35 and 36 in the Supporting
Information).
1H NMR analysis of complex 9 shows syn and anti allylic
hydrogen atoms of both isomers: δ 1.19 (2H), 1.41, 1.56, 1.73,
1.94, 2.02, and 2.15.12 One of the possible reasons for the
downfield shift of these signals relative to those of 6, 7, and 8
may be a more sterically hindered nickel center of 9. The IR
Synthesis of Nickel Methallyl Complexes. Deprotona-
tion of ligands 1 and 2 was readily accomplished using KH in
THF. Addition of the ligand potassium salts to [Ni(η3-
Scheme 3. Geometric Isomers of Complex 9
11
(CH2)2Me)Cl]2 yields the target complexes [L1Ni(η3-
methallyl)], 6, and [L2Ni(η3-methallyl)], 7, as yellow and
orange solids in 56% and 60% yields, respectively (Scheme 1).
The 1H and 13C NMR spectra in C6D6 of both complexes are
consistent with the formation of a single isomer containing a
nickel center ligated by N-arylcyano-β-diketiminate and η3-
(CH2)2Me. Compound 6 features separate resonances for the
syn and anti allylic hydrogen atoms: at δ 1.09 and 1.57 ppm.
The presence of these resonances indicates the structural
rigidity of the π-allyl ligand on the NMR time scale. Four
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ν
̃
(CN) cyano band for 6−9 was shifted on average by ν
̃
∼6
nickel center displays a planar environment. As typically
observed in nickel methallyl complexes with bidentate
supporting ligands, the multiple bond of the η3-methallyl lies
in the coordination plane of the complex. Ligand 2 in complex
7 adopts a C2-symmetric conformation, with the cyano groups
trans to each other. Ligand 5 in complex 9 adopts a
conformation with the vector of the cyano group cis with
respect to the methyl group of methallyl. The coordination
around the nickel atom is similar in complexes 7 and 9, in that
Ni−N bond lengths are 2.038(3) and 1.883(3) Å for 7 and
1.903(2) and 1.913(3) Å for 9. However, in complex 7 bonding
of the ligand to the metal is not entirely symmetrical, thus the
coordination in 7 might be more localized than in 9.13 The
N2−Ni1−N1 angle in 7 is 91.94(14)° and N1−Ni1−N1 in 9 is
95.19(10)° due to increased steric hindrance near the nickel
center (see Figure 3) and is close to the average values of
related methallyl nickel complexes.5 Comparison of the C1−
N1−C11−C12 and C3−N2−C21−C26 dihedral angles (see
Supporting Information) of ligand 5 and C1−N1−C11−C12
and C3−N2−C21−C26 dihedral angles (Figure 3) of its nickel
complex 9 shows that the aryl substituent at N2 in 9 is
noticeably more rotated out of the central plane than in the free
ligand 5, possibly due to repulsion with the methyl group of the
η3-methallyl.
Synthesis of B(C6F5)3 Adducts. To promote polymer-
ization by the complexes by remote activation,8a,b tris-
(pentafluorophenyl)borane, B(C6F5)3, was chosen as an
activator because it easily coordinates with the cyano
group.8,14,15 Furthermore, the series of nickel Nacnac
complexes 6−9, with the −CN groups in ortho and para
positions on the N-aryl groups, allow for an assessment of both
electronic (para complexes 6 and 8) and steric/electronic
(ortho complexes 7 and 9) factors associated with B(C6F5)3
activation of these catalyst precursors.
cm−1 to higher wavenumbers compared to the parent ligand
systems 1/2 and 4/5 (see Supporting Information).
Crystal Structure Studies. Single crystals of 7 and 9
suitable for solid-state characterization were obtained by
diffusion of pentane into a toluene solution, and the resulting
structures are shown in Figures 2 and 3. In both 7 and 9 the
Figure 2. View of the molecular structure of complex 7. Hydrogen
atoms are omitted for clarity. Selected bond lengths (Å) and angle
(deg): N2−Ni1, 2.038(3); N1−Ni1, 1.883(3); Ni1−C30, 2.044(19);
Ni1−C32, 2.10(6); Ni1−C31, 2.03(2); N2−Ni1−N1, 91.94(14).
Selected torsion angles (deg): C2−C3−N2−C21, 176.7(3); C2−C1−
N1−C11, 178.4(3).
Symmetrical complexes 6 and 7 were reacted with 2 equiv of
B(C6F5)3, and stirring the reaction mixture for 10 min at room
temperature in toluene yielded the bis-borane adducts 10 and
11, respectively, as orange crystalline solids in 80−85% yields.
Single crystals of 10 and 11 suitable for X-ray structure analysis
were obtained from toluene/pentane and toluene/hexane,
respectively, by the diffusion method (Scheme 4).
Figure 3. View of the molecular structure of complex 9. Hydrogen
atoms are omitted for clarity. Selected bond lengths (Å) and angle
(deg): N1−Ni1, 1.903(2); N2−Ni1, 1.913(3); Ni1−C42, 2.008(3);
Ni1−C40, 2.029(4); Ni1−C41, 2.015(4); N1−Ni1−N2, 95.19(10).
Selected torsion angles (deg): C2−C3−N1−-C11, 173.7(3); C2−
C3−N2−C21, 172.3(3).
̃
The IR ν(CN) band is shifted very characteristically upon
Lewis acid adduct formation from 2223 cm−1 in 6 to 2307 cm−1
in 10 and from 2222 cm−1 in 7 to 2312 cm−1 in 11. This is what
would be expected from simple addition of a nitrile to a strong
Lewis acid: sharing of the nitrogen lone pair with the boron
Scheme 4. Adducts 10 and 11
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Scheme 5. Adducts 12 and 13
Figure 4. View of the molecular structure of the adduct 10. Hydrogen atoms are omitted for clarity. Selected angles (deg): C41−N4−B2, 176.8(3);
C16−N3−B1, 172.9(3).
Figure 5. View of the molecular structure of the adduct 11. Hydrogen atoms are omitted for clarity. Selected angles (deg): C16−N3−B1, 172.7(5);
C41−N4−B2, 177.3(4). Selected torsion angles (deg): C7−C6−N1−C10, 174.6(4); C7−C8−N2−C35, 177.0(4).
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atom effectively reduces the electronic repulsion between
nitrogen and carbon to make the CN triple bond in 10 and
11 slightly stronger.15 Two resonances appear in the H NMR
1
spectrum of 10 for the syn and anti allylic hydrogen atoms,
singlets at δ 0.94 and 1.41 ppm that are shifted upfield with
respect to 6. All four resonances for the syn and anti allylic
hydrogen atoms in 11 are shifted upfield with respect to 7: δ
0.99, 1.00 and 1.54, 1.63 ppm. In 11, the difference in chemical
shift between the two aliphatic “Nacnac” methyls is 0.9 ppm
due to their different chemical environment, whereas in 7 it is
only 0.2 ppm.
Borane ligation to the cyano groups in compound 11 is
indicated by the 11B NMR chemical shift of −9.2 ppm,
16
characteristic of nitrile-coordinated B(C6F5)3. Furthermore,
Δδ (p, m) values of 7.7 and 7.5 ppm in the 19F NMR for
compounds 10 and 11 are consistent with neutral, four-
coordinate borane adducts of B(C6F5)3.17 Finally, the 13C NMR
resonances for the Ar-CN units at 136.60−136.83 (ArCN
-
CH) and 126.43−134.24 (ArCN-CH) ppm for 10 and 11 also
support full borane coordination to both nitrile functions on
the N-aryl groups.
Adducts 12 and 13 incorporate bulky isopropyl groups on
the N-aryl moiety that are known to retard chain transfer and
favor chain propagation.18 Adducts 12 and 13 were synthesized
by adding 1 equiv of tris(pentafluorophenyl)boron B(C6F5)3 to
complexes 8 and 9, respectively, and were purified by the same
procedure as 10 and 11 (Scheme 5).
Figure 6. View of the molecular structure of the adduct 13. Hydrogen
atoms are omitted for clarity. Selected angle (deg): C28−N3−B1,
174.0(3). Selected torsion angle (deg): C7−C8−N2−C22, 176.7(3).
The IR spectrum of the borane adducts 12 and 13 show a
sharp CN stretching band at ν
̃
2310 and 2314 cm−1, which
are shifted by ν
̃
86 and 90 cm−1 to higher wave numbers as
compared to their parent complexes 8 and 9, respectively. As
mentioned above for adducts 10 and 11, the resonances of
allylic hydrogen atoms in the 1H NMR spectra of 12 and 13 are
shifted upfield: δ 0.93, 1.42 and 1.61, 1.75 ppm for 12 and δ
0.91, 1.27, 1.48, 1.62 ppm for 13. 19F and 11B NMR data, as for
adducts 10 and 11, are fully consistent with adduct formation.
Crystal Structure Studies. Single crystals of 10, 11, and 13
suitable for X-ray crystal structure analysis were grown by
layering pentane on a toluene solution of each molecule. As
expected, B(C6F5)3 coordinates end-on with the cyano groups
in 10 (see Figure 4). The C7−C8−N2−C35 and C7−C6−
N1−C10 dihedral angles are 164.0(3)° and 173.4(3)°,
respectively, indicating that both aryl substituents at N2 and
N1 are perpendicularly rotated out of the central plane (Figure
4).
Similarly to 10, B(C6F5)3 coordinates in a linear way with the
cyano groups of 11 (Figure 5), rotating the aryl substituents at
N3 and N4 out of the central plane, which is more than for
analogous dihedral angles of borane-free complex 7 (see Figure
2). The Ni−N bond lengths in 11 are 1.899(3) and 1.906(3) Å,
which is close to the analogous bond lengths of the complex 7;
see Figure 2.
with 0.5 equiv of B(C6F5)3, although exchange is slow on the
NMR time scale, 1D-NOESY exchange experiments20 showed
that exchange between free and bound nickel complexes is
facile (Scheme 6). Thus, cross-peaks between the resonances
for the Nacnac backbone protons in free 9 (5.05 ppm) and that
in the adduct 13 (4.91 ppm) were apparent, indicating
exchange at room temperature, presumably via dissociation of
the nitrile from the borane, followed by recoordination.
Reactivity with Olefins. Benzene-d6 solutions of nickel
complexes 6 and 7, adducts 10 and 11, and adducts 10 and 11
with an additional 5 equiv of B(C6F5)3 were degassed via
freeze−pump−thaw cycles and exposed to one atmosphere of
ethylene. No immediate color changes or precipitation of
polymeric materials were observed, and analysis by NMR
spectroscopy showed essentially no immediate reaction at room
temperature. Only in the case of 10 and 11 with 5 equiv of
B(C6F5)3 could resonances corresponding to the formation of
products be seen over time. Monitoring over the course of 60
min at 60 °C showed that ethylene was being consumed, and
the formation of products having resonances in the olefinic
1
region of the H NMR spectrum was consistent with the
formation of oligomers. Slower oligomer formation was
observed in the experiment in which no excess B(C6F5)3 was
added to 10 and 11, but no reaction between unactivated 6 and
7 was observed under any conditions (Figure 7, Figure S-1). At
the end of each experiment, the major species in solution were
the starting complexes, indicating that only a small amount of
catalyst becomes active in these reactions.
B(C6F5)3 coordinates in a linear manner to the cyano group
of 13, rotating the aryl substituent at N2 out of the central
plane, Figure 6, by more than for the analogous dihedral angle
of complex 9 (see Figure 3). Ni−N bond lengths for 13 are
1.903(3) and 1.907(3) Å, which is close to the analogous bond
lengths of borane-free complex 9.
In all cases, the equilibrium between cyano Nacnac
complexes 6−9, B(C6F5)3, and the adducts 10−13 appears to
favor the adducts almost completely, as judged by the 19F and
11B NMR spectral data discussed above. However, these and
related adducts are known to be labile,19 and when 9 is treated
The procedure described above was applied also to
complexes 8 and 9, adducts 12 and 13, and adducts 12 and
13 with 5 equiv of B(C6F5)3. The main difference in these
series of experiments was the formation of polyethylene. After
approximately the first 20 min at 60 °C it became clear that the
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Scheme 6
1
Figure 7. H NMR spectra after treatment of 11 and 5 equiv of B(C6F5)3 with ethylene. Circle denotes residual protiosolvent.
ethylene was being consumed in the case of 12 and 13 with 5
equiv of B(C6F5)3, while in the absence of added borane,
polyethylene formation was slower. Again, in the unactivated
complexes 8 and 9, no polyethylene formation was observed
during the whole experiment (Figure 8, Figure S-2). We believe
that the presence of the bulky 2,6-diisopropyl N-aryl groups in
adducts 12 and 13 contributes to polymer chain growth,21
while their absence is the reason that 10 and 11 produce
oligomers.
Scaling up the Ethylene Polymerization. A study of the
polymerization of ethylene with the B(C6F5)3 nickel adducts
(10−13) ([Ni] = 3.67 × 10−4 M) “activated” with an additional
5 equiv of B(C6F5)3 was carried out, and the results are
summarized in Table 1. The reactions were performed in a 100
mL autoclave reactor in toluene at an ethylene pressure of 12.5
bar. The reaction was run for 20 min at different temperatures.
In the case of 10/B(C6F5)3 and 11/B(C6F5)3 oligomers22
(butene, hexene) were qualitatively detected by GS-MS at 50
and 70 °C (see Supporting Information) in agreement with
their NMR studies.
Table 1 shows polymerization results using adducts 12 and
13 with an additional 5 equiv of B(C6F5)3 at different
temperatures.
Entries 1 and 2 and 3−5 show the behavior of adducts 12
and 13 with 5 equiv of B(C6F5)3 over a range of temperatures.
A substantial increase in activity for both adducts is observed
when the temperature rises from 50 °C (31 kg/mol h, 149 kg/
mol h) to 70 °C (108 kg/mol h, 209 kg/mol h) for 12 and 13,
respectively, which is consistent with an increase in the rate of
propagation (see Table 1). The activity of adduct 13 is five
times higher with respect to 12 at 50 °C and two times higher
at 70 °C. Clearly, adduct 13 is a significantly more active
polymerization initiator than 12, most likely due to the
interaction between B(C6F5)3 and the ortho CN functionality
nearby nickel active site. This interaction makes the nickel
center more sterically hindered and possibly causes it to be
more electrophilic, resulting in increased activities.
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1
Figure 8. H NMR spectra after treatment of 13 and 5 equiv of B(C6F5)3 with ethylene. Circle denotes residual protiosolvent.
a
Table 1. Selected Ethylene Polymerization Reactions
b
c
c
d
entry
adduct
reaction temperature, °C
activity
Mn
Mw
PDI
Tm
e
1
2
3
4
5
12
12
13
13
13
50
70
50
60
70
31
108
149
206
209
123.1
122.1
128.1
125.0
120.7
12 904
25 419
35 129
20 276
28 467
73 107
60 405
37 654
2.2
2.87
1.72
f
1.86
a
Polymerizations were carried out in a 100 mL autoclave reactor with 10.6 μmol of Ni in 29 mL of toluene and 181 psi of ethylene pressure. The
b
c
d
e
cocatalyst was B(C6F5)3 (5 equiv). Reaction time was 20 min. Activity in kg polymer/(mol Ni × h). ×103 g/mol. In °C. Could not be measured.
f
Bimodal, main fraction Mw = 37 654.
In all cases, the formation of moderate molecular weight PE
is observed. As was expected,23 molecular weights of the
resulting polymers are higher for 13/B(C6F5)3 due to the more
crowded active site. The molecular weight of polymers
produced by 13/B(C6F5)3 decreases from 73 107 to 37 654
(see entries 3−5) when the temperature rises from 50 °C to 70
°C. The polydispersity index for both systems corresponds to a
single-site catalyst (1.72−2.87, entries 2−5). PDI is maintained
at the expected ranges when the temperature increases, but
there is a small fraction (<10%) of higher molecular weight
polymer for system 13/B(C6F5)3 at 70 °C (see Supporting
Information).
Thermal analysis of the polymer products was performed
using differential scanning calorimetry (DSC). Samples were
scanned from 0 to 150 °C at 10 °C/min. In terms of the
thermal polymer properties, 12/B(C6F5)3 produces more
branched polyethylene with slightly lower melting points.
One sharp thermal transition around 123.1 and 122.1 °C,
entries 1 and 2, respectively, is observed for the PE obtained
from the system 12/B(C6F5)3 under study. Variation of the
reaction temperature from 50 to 70 °C almost does not change
the melting point of PE produced by 12/B(C6F5)3, while for
13/B(C6F5)3 a tendency to form more branched polyethylene
is observed with an increase in temperature (see Tm, entries 3−
5). The values of PE melting points of 13/B(C6F5)3 in
comparison with those of 12/B(C6F5)3 are higher due to the
more sterically hindered metal center and thus less branched
polyethylene.
CONCLUSIONS
■
Integrating both electronic and steric effects into the ortho and
para position of the aromatic ring with the cyano group
interacting with tris(pentafluorophenyl)boron in ligands may
have a significant influence on the performance of the catalysts.
Ligands 1−5, complexes 6−9, and their adducts 10−13 were
synthesized with good yields and completely characterized. It
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ethylene line, and the gas was fed continuously into the reactor to the
pressure of 181 psi. The pressurized reaction mixture was stirred at the
corresponding temperature. After 20 min, the ethylene was vented and
acetone was added to quench the polymerization. The precipitated
polymer was collected by filtration and dried overnight.
was observed in NMR spectra at a temperature of 60 °C that
10/11 and 12/13 alone and with 5 equiv of B(C6F5)3 show
activity toward ethylene, while complexes 6−9 do not.
Interestingly, the addition of excess B(C6F5)3 promotes more
rapid interaction with ethylene. Adducts 10 and 11 alone and
with 5 equiv of B(C6F5)3 catalyze the oligomer formation, while
adducts 12 and 13 in the same conditions catalyze polyethylene
formation with comparable or higher catalyst activities with
respect to other diketiminate-based systems.1d−f The most
sterically hindered adduct 13 with an additional 5 equiv of
B(C6F5)3 at 60−70 °C has the highest activity toward ethylene
polymerization of all of these systems (206−209 kg polymer/
(mol Ni × h)), and to our knowledge no other neutral
diketiminate methallyl polymerization initiators are reported
until now. Molecular weights of obtained polymers are in the
moderate range, and their melting points show the formation of
branched polyethylene. PDI of obtained polymers indicates
single-site polymerization catalysts. The higher activity and
polymer molecular weight for 13/B(C6F5)3 with respect to 12/
B(C6F5)3 indicates the importance of the action of Lewis acid
in ortho position of the complex framework.
Preparation of Bis-N-phenyl-4-cyano-β-diketiminate (1). Pen-
tane-2,4-dione (3.37 g, 34 mmol) was mixed with 4-aminobenzonitrile
(10.04 g, 85 mmol) in 150 mL of toluene containing a catalytic
amount of p-TsOH. The solution was refluxed overnight using a
Dean−Stark trap. Removal of volatiles afforded yellow solid of 1. This
was then stirred with 20 mL of methanol and left at −30 °C to
precipitate yellow crystals, which were filtered off, washed with 10 mL
of cold hexane, and dried in vacuo. Yield of 1: 7.21 g (24 mmol, 71%).
1H NMR (400 MHz, CDCl3, 298 K): δ/ppm 2.07 (s, 6H, Me), 5.02 (s,
1H, CH), 6.99 (d, J = 8.5 Hz, 4H, o-Ph), 7.56 (d, J = 8.5 Hz, 4H, r-
Ph), 12.71 (s, 1H, NH). 13C{1H} NMR (100 MHz, CDCl3, 298 K): δ/
ppm 21.80 (Me), 101.01 (CH), 106.49 (a-Ph), 119.48 (CN),
122.02 (o-Ph), 133.49 (r-Ph), 149.95 (c-Ph), 159.50 (CN). HRMS
+
(ESI + H+): m/z calculated (for C19H16N4 ) 300.1375, found
300.1371. IR (KBr): ν
for C19H16N4 (M = 300.1375 g/mol): C 75.98, H 5.37, N 18.65.
̃
/cm−1 2215 (ν
̃
(CN), s). Anal. (%) Calcd
Found: C 75.88, H 5.9, N 18.36.
Preparation of Bis-N-phenyl-2-cyano-β-diketiminate (2). Pen-
tane-2,4-dione (3.37 g, 34 mmol) was mixed with 2-aminobenzonitrile
(8.85 g, 75 mmol) in 100 mL of toluene containing a catalytic amount
of p-TsOH. The solution was refluxed for 86 h using a Dean−Stark
trap. Removal of volatiles afforded a yellow solid of impure 2. This was
then stirred with 20 mL of methanol and left at −30 °C to precipitate
pale yellow crystals of 2, which were filtered off, washed with 10 mL of
cold hexane, and dried in vacuo. Yield of 2: 4.2 g (14 mmol, 64%). 1H
NMR (400 MHz, CDCl3, 298 K): δ/ppm 2.06 (s, 6H, Me), 5.10 (s,
1H, CH), 7.11 (m, 2H, p-Ph), 7.17 (m, 2H, o-Ph), 7.51 (m, 2H, m-
Ph), 7.57 (m, 2H, n-Ph), 12.92 (s, 1H, NH). 13C{1H} NMR (100
MHz, CDCl3, 298 K): δ/ppm 21.31(Me), 100.78 (CH), 106.87 (i-Ph),
117.90 (CN), 123.80 (p-Ph), 123.94 (o-Ph), 133.45 (m-Ph), 133.63
EXPERIMENTAL DETAILS
■
General Considerations. All manipulations were performed
under an inert atmosphere using standard glovebox and Schlenk-line
techniques. All reagents were used as received from Aldrich, unless
otherwise specified. Toluene, THF, ether, and pentane were distilled
from benzophenone ketyl. Tris(pentafluorophenyl)borane (B(C6F5)3)
was doubly sublimed at 65 °C under static vacuum and stored in the
glovebox. All polymerization reactions were carried out in a J. Young
NMR tube and the Parr autoclave reactor as described in the
Supporting Information. The following instruments were used for the
physical characterization of the compounds. NMR spectra were
obtained on Bruker DRX 400, AVANCE 400 MHz, and AVANCE III
400 MHz spectrometers. 1H and 13C {1H} chemical shifts were
referenced to residual proton and naturally abundant 13C resonances
of the deuterated solvent, respectively, relative to tetramethylsilane.
Most NMR assignments were supported by additional 2D experi-
ments. Low- and high-resolution mass spectra were obtained using a
Bruker Esquire 3000 spectrometer operating in electrospray ionization
(ESI) mode. High-resolution mass spectra were also obtained on a
Waters GCT Premier operating at 70 eV in electron impact (EI)
mode. X-ray crystallographic analyses were performed on suitable
crystals coated in Paratone 8277 oil (Exxon). Measurements were
collected on a Nonius Kappa CCD diffractometer by Dr. Masood
Parvez and Dr. Constantin G. Daniliuc; full details can be found in the
independently deposited crystallography information files (cif).
Graphics show thermal ellipsoids at the 50% probability level.
Elemental analyses were performed using a Perkin-Elmer model
2400 series II analyzer by Johnson Li of the Department of Chemistry,
University of Calgary. Nonsolution IR spectra were run as thin films
(NaCl plates) sealed under argon.
(n-Ph), 143.82 (k-Ph), 160.72 (CN). HRMS (ESI + H+): m/z
+
calculated (for C19H16N4 ) 300.1375, found 300.1370. IR (KBr): ν
̃
/
cm−1 2219 (ν(CN), s).
̃
Preparation of N-Phenyl-4-cyano-N-phenyl-2-cyano-β-diketimi-
nate (3). Pentane-2,4-dione (0.5 g, 5 mmol) was mixed with 2-
aminobenzonitrile (0.59 g, 5 mmol) in 80 mL of toluene containing a
catalytic amount of p-TsOH. The solution was refluxed for 72 h using
a Dean−Stark trap. Removal of volatiles afforded a yellow oil mixture
of products, which was then mixed with 1 equiv of 4-amino-
benzonitrile in 80 mL of toluene containing a catalytic amount of p-
TsOH. The solution was refluxed for 24 h using a Dean−Stark trap.
Removal of volatiles afforded a yellow oil mixture of products, which
was then passed through a chromatographic column (eluent: hexane/
diethyl ether as 1:3). As a result 3 was obtained as one of the column
products. Yield of 3: 0.15 g (0.45 mmol, 10%). Single crystals of 3
suitable for X-ray crystal structure analysis were obtained by slow
evaporation of eluent at room temperature. 1H NMR (400 MHz,
CDCl3, 298 K): δ/ppm 2.01 (s, 3H, Me), 2.19 (s, 3H, Me), 5.05 (s,
1H, CH), 6.97 (m, 1H, o-Ph), 7.12 (m, 1H, m-Ph), 7.14 (d, J = 8.7 Hz,
2H, Ar-H), 7.50 (m, 1H, p-Ph), 7.57 (d, J = 8.7 Hz, 2H, Ar-H), 7.63
(m, 1H, k-Ph), 12.83 (s, 1H, NH). 13C{1H} NMR (100 MHz, CDCl3,
298 K): δ/ppm 21.14 (Me), 21.58 (Me), 100.62 (CH), 106.87 (Ar-C),
106.94 (Ar-C), 118.10 (CN), 119.24 (CN), 122.14 (o-Ph),
122.22 (m-Ph), 123.92 (Ar-CH), 132.99 (Ar-CH), 133.15 (p-Ph),
133.20 (k-Ph), 145.83 (n-Ph), 152.23 (Ar-C), 154.15 (CN), 166.29
Ethylene Polymerization and Oligomerization 1H NMR
Experiment. A 2.5 μmol portion of 6−13 (in the case of 10−13
with 5 equiv of B(C6F5)3 12.5 μmol of it was additionally added)
dissolved in C6D6 (ca. 0.5 mL) was added inside a glovebox into an
NMR tube with J. Young valves. The cell was brought out from the
box and assembled on a Schlenk line. The cell was frozen in a dry ice/
acetone bath, and the argon gas was evacuated. Ethylene gas was
charged through the Schlenk line, and the J. Young valve was closed.
1H NMR spectra were recorded at that time.
Ethylene Polymerization and Oligomerization in a Reactor.
Polymerizations were carried out in a Parr autoclave reactor (100 mL),
loaded inside a glovebox with an appropriate amount (μmol) of the
catalyst (10, 11, 12, or 13 with an additional 5 equiv of B(C6F5)3) and
toluene such that the final volume of the solution was 29 mL. The
reactor was sealed inside the glovebox. The reactor was attached to an
(CN). IR (KBr): ν
̃
/cm−1 2220 (ν
̃
(CN), s).
Preparation of N-Phenyl-4-cyano-N-2,6-diisopropylphenyl-β-di-
ketiminate (4). 4-(2,6-Diisopropylphenyl)iminopentan-2-one (0.5 g,
2.5 mmol) was mixed with 4-aminobenzonitrile (0.59 g, 5 mmol) in
100 mL of toluene containing a catalytic amount of p-TsOH. The
solution was refluxed for 48 h using a Dean−Stark trap. Removal of
volatiles afforded a yellow solid of 4. This was then stirred with 20 mL
of methanol and left at −30 °C to precipitate yellow ctrystals, which
were filtered off, washed with 10 mL of cold hexane, and dried in
vacuo. Yield of 4: 0.719 g (2 mmol, 80%). 1H NMR (400 MHz,
H
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Organometallics
Article
CDCl3, 298 K): δ/ppm 1.14 (d, J = 6.8 Hz, 6H, (CH(Me)2), 1.21 (d, J
= 6.8 Hz, 6H, (CH(Me)2)), 1.59 (s, 3H, Me), 1.69 (s, 3H, Me), 3.15
(h, J = 6.8 Hz, 1H, CH(Me)2), 4.84 (s, 1H, CH), 6.57 (d, J = 6.8 Hz,
2H, o-Ph), 7.04 (d, 2H, J = 6.8 Hz, r-Ph), 7.16 (m, 2H, m-Ph), 7.21
(m, 1H, p-Ph), 12.77 (s, 1H, NH). 13C{1H} NMR (100 MHz, C6D6,
298 K): δ/ppm 20.10 (Me), 20.68 (Me), 22.28 (CH(Me)2), 24.17
(CH(Me)2), 28.50 (CH(Me)2), 97.00 (CH), 105.62 (c-Ph), 119.00
(CN), 121.31 (o-Ph), 123.37 (m-Ph), 126.39 (p-Ph), 132.76 (r-Ph),
139.07 (i-Ph), 142.76 (k-Ph), 150.97 (d-Ph), 159.84 (CN), 161.04
(o-Ph), 132.22 (o-Ph), 132.78 (m-Ph), 132.80 (m-Ph), 160.47 (k-Ph),
160.52 (k-Ph), 161.15 (CN), 161.47 (CN). HRMS (ESI + H+):
m/z calculated (for C23H21N4Ni+) 413.1271, found 413.1266. IR: ν
̃
/
cm−1 2222 (ν
̃
(CN), s).
Preparation of Complex 8. A solution of 4 (472 g, 1 mmol) and
KH (4 mg, 1 mmol) was stirred in THF for 12 h. The reaction showed
rapid H2 evolution. The bright orange mixture was filtered.
[(C4H7)NiCl]2 (149 mg, 0.5 mmol) in THF was added in situ to
the filtrate of the potassium salt of 4 in THF and stirred for 4 h at
room temperature. The solution was filtered, and all volatiles were
removed in a vacuum to give a light orange solid, which was washed
several times by pentane and dried 24 h under vacuum. Yield of 8: 274
+
(CN). HRMS (ESI + H+): m/z calculated (for C24H29N3 ) 359.236,
found 359.235. IR (KBr): ν
̃
/cm−1 2220 (ν
̃
(CN), s).
Preparation of N-Phenyl-2-cyano-N-2,6-diisopropylphenyl-β-di-
ketiminate (5). 4-(2,6-Diisopropylphenyl)iminopentan-2-one (0.5 g,
2.5 mmol) was mixed with 2-aminobenzonitrile (0.59 g, 5 mmol) in 50
mL of toluene containing a catalytic amount of p-TsOH. The solution
was refluxed for 96 h using a Dean−Stark trap. Removal of volatiles
afforded a yellow solid of 5. This was then stirred with 20 mL of
methanol and left at −30 °C to precipitate yellow crystals suitable for
X-ray crystal structure analysis, which were filtered off, washed with 10
mL of cold hexane, and dried in vacuo. Yield of 5: 0.45 g (1.25 mmol,
1
mg (0.58 mmol, 58%). H NMR (400 MHz, C6D6, 298 K): δ/ppm
1.10 (d, J = 5.2 Hz, 3H, CH(CH3)CH3), 1.14 (s, 1H, CH2), 1.21 (d, J
= 5.2 Hz, 3H, CH(CH3)CH3), 1.35 (m, 6H, CH(CH3)CH3), 1.45 (s,
3H, Me), 1.54 (s, 2H, CH2), 1.63 (s, 3H, Me), 1.91 (s, 3H,
(CH2)2CCH3), 1.99 (s, 1H, CH2), 3.43 (s, 1H, CH(CH3)CH3), 3.98
(s, 1H, CH(CH3)CH3), 4.98 (s, 1H, CH), 6.42 (d, J = 6.7 Hz, 2H, c-
Ph), 6.87 (d, J = 6.4 Hz, 2H, b-Ph), 7.10 (m, 3H, m-Ph, p-Ph). 13C-
APT{1H} NMR (100 MHz, C6D6, 298 K): δ/ppm 21.77
(CH3(CH2)2), 23.30 (Me), 23.49 (Me), 23.58 (CH(CH3)CH3),
23.87 (CH(CH3)CH3), 23.92 (CH(CH3)CH3), 24.19 (CH(CH3)-
CH3), 27.51 (CH(CH3)CH3), 27.76 (CH(CH3)CH3), 55.45(CH2),
61.64(CH2), 96.89 (CH), 123.17(Ar-CH), 123.61 (Ar-CH), 123.88
(Ar-C), 124.74 (Ar-CH), 125.37 (b-Ph), 132.17 (c-Ph), 138.78 (Ar-C),
140.20 (k-Ph), 153.00 (k-Ph), 157.90 (CN), 161.18 (CN),
162.46 (d-Ph). HRMS (ESI + H+): m/z calculated (for C28H34N3Ni+)
1
50%). H NMR (400 MHz, CDCl3, 298 K): δ/ppm 1.15 (d, J = 6.8
Hz, 6H, (CH(Me)2)), 1.25 (d, J = 6.9 Hz, 6H, (CH(Me)2)), 1.70 (s,
3H, Me), 1.94 (s, 3H, Me), 3.15 (h, J = 6.85, 1H, CH(Me)2), 4.94 (s,
1H, CH), 6.90 (m, 1H, o-Ph), 7.02 (m, 1H, m-Ph), 7.16 (m, 2H, c-Ph),
7.26 (m, 1H, d-Ph), 7.43(m, 1H, p-Ph), 7.55 (m, 1H, k-Ph), 11.86 (s,
1H, NH). 13C {1H} NMR (100 MHz, CDCl3, 298 K): δ/ppm 20.33
(Me), 22.07 (Me), 23.07 (CH(CH3)2), 25.36 (CH(CH3)2), 28.92
(CH(CH3)2), 95.00 (CH), 105.80 (i-Ph), 118.43 (CN), 122.64 (o-
Ph), 122.93 (m-Ph), 123.72 (c-Ph), 128.00 (d-Ph), 133.22 (p-Ph),
133.38 (k-Ph), 136.34 (a-Ph), 146.70 (n-Ph), 155.25 (b-Ph), 158.36
472.2257, found 472.2251. IR (KBr): ν
̃
/cm−1 = 2224 (ν
̃
(CN), s).
Preparation of Complex 9. A solution of 5 (472 mg, 1 mmol)
and KH (4 mg, 1 mmol) was stirred in diethyl ether for 12 h. The
reaction showed rapid H2 evolution. The bright yellow mixture was
filtered. The bright yellow precipitate of the potassium salt of 5 was
separated and washed by diethyl ether. [(C4H7)NiCl]2 (149 mg, 0.5
mmol) in THF was added in situ to the potassium salt of 5 in THF and
stirred for 4 h at room temperature. The solution was filtered, and all
volatiles were removed in a vacuum to give the light orange solid,
which was washed several times by pentane and dried 24 h under
vacuum. Single crystals for X-ray crystallography were grown by
layering pentane onto a toluene solution of compound 9 at room
(CN), 167.86 (CN). HRMS (ESI + H+): m/z calculated (for
+
C24H29N3 ) 359.2361, found 359.2351. IR (KBr): ν
(ν
̃
̃
/cm−1 2216
(CN), s).
Preparation of Complex 6. A solution of 1 (413 mg, 1 mmol)
and KH (4 mg, 1 mmol) was stirred in THF for 12 h. The reaction
showed rapid H2 evolution. The bright orange mixture was filtered.
[(C4H7)NiCl]2 (149 mg, 0.5 mmol) in THF was added in situ to the
filtrate of the potassium salt of 1 in THF and stirred for 4 h at room
temperature. The solution was filtered, and all volatiles were removed
in a vacuum to give a yellow solid, which was washed several times by
pentane and dried 24 h under vacuum. Yield of 6: 231 mg (0.56 mmol,
56%). 1H NMR (400 MHz, C6D6, 298 K): δ/ppm 1.09 (s, 2H, CH2),
1.43 (s, 6H, Me), 1.57 (s, 2H, CH2), 1.80 (s, 3H, CH3(CH2)2), 4.91
(s, 1H, CH), 6.41 (d, J = 5.7 Hz, 4H, b-Ph), 6.91 (d, J = 6.8 Hz, 4H, c-
Ph). 13C-APT{1H} NMR (100 MHz, C6D6, 298 K): δ/ppm 22.18
(Me), 23.44 (2Me), 59.03 (2CH2), 97.40 (CH), 107.56 (a-Ph), 118.42
(CN), 123.50 ((CH2)2CCH3), 124.91 (b-Ph), 132.33 (c-Ph),
159.08 (d-Ph), 161.65 (CN). HRMS (ESI + H+): m/z calculated
1
temperature. Yield of 9: 298 mg (0.63 mmol, 63%). H NMR (400
MHz, C6D6, 298 K): δ/ppm 1.09 (d, J = 6.8 Hz, 3H, (CH(CH3)-
CH3)a), 1.19 (m, 8H, (CH(CH3)CH3)b, (CH2)a, (CH2)b), 1.31 (m,
9H, (CH(CH3)CH3)a), 1.41 (bd, J = 2.8 Hz, 2H, (CH2)b, (CH2)a),
1.51 (d, J = 6.8 Hz, 3H, (CH(CH3)CH3)b), 1.56 (m, 7H, Mea, Meb,
(CH2)b), 1.64 (d, 3H, (CH(CH3)CH3)b), 1.66 (m, 3H, Mea), 1.67 (m,
b
3H, Meb), 1.73 (s, 1H, (CH2)a), 1.94 (s, 3H, CH3(CH2)2 ), 2.02 (s,
a
1H, (CH2)a), 2.15 (s, 4H, CH3(CH2)2 , (CH2)b), 3.40 (h, J = 6.8 Hz,
1H, (CH(CH3)CH3)a), 3.75 (h, J = 6.8 Hz, 1H, (CH(CH3)CH3)b),
3.93 (h, J = 6.8 Hz, 1H, (CH(CH3)CH3)a), 4.39 (h, J = 6.8 Hz, 1H,
(CH(CH3)CH3)b), 5.04 (s, 1H, (CH)a), 5.07 (s, 1H, (CH)b), 6.46 (t,
J = 7.5 Hz, 2H, p-Ph), 6.61 (d, J = 8 Hz, 1H, o-Ph), 6.70 (d, J = 8 Hz,
1H, o-Ph), 6.80 (m, 2H, m-Ph), 7.09 (m, 8H, k-Ph, c-Ph, d-Ph,). 13C-
APT{1H} NMR (100 MHz, C6D6, 298 K): δ/ppm 22.67
(CH3(CH2)2), 22.79 (CH3(CH2)2), 23.83 (CH(CH3)2), 23.92
(CH(CH3)2), 24.12 (CH(CH3)2), 24.17 (CH(CH3)2), 24.27 (CH-
(CH3)2), 24.41 (CH(CH3)2), 24.73 (2Me), 24.87 (CH(CH3)2), 25.10
(CH(CH3)2), 28.24 (CH(CH3)2), 28.48 (CH(CH3)2), 28.67 (CH-
(CH3)2), 28.91 (CH(CH3)2), 57.14 (CH2), 57.73 (CH2), 59.91
(CH2), 60.10 (CH2), 98.41(CH), 98.53 (CH), 123.59 (Ar-CH),
123.88 (p-Ph), 123.90 (p-Ph), 124.04 (Ar-CH), 124.25 (Ar-CH),
124.59 (Ar-C), 124.76 (Ar-CH), 125.50 (Ar-CH), 125.60 (Ar-CH),
125.70 (Ar-C), 125.82 (o-Ph), 127.22 (o-Ph), 132.56 (m-Ph), 132.62
(Ar-CH), 132.81 (m-Ph), 139.14 (Ar-C), 140.55 (Ar-C), 140.75 (Ar-
C), 142.03 (Ar-C), 142.08 (Ar-C), 153.67 (Ar-C), 153.92 (Ar-C),
158.62 (CN), 158.81 (CN), 162.42 (CN), 162.59 (CN),
162.68 (Ar-C), 162.71 (Ar-C). HRMS (ESI + H+): m/z calculated (for
̃
(for C23H21N4Ni+) 413.1271, found 413.1278. IR: ν/cm−1 2223
(ν
̃
(CN), s).
Preparation of Complex 7. A solution of 2 (413 mg, 1 mmol)
and KH (4 mg, 1 mmol) was stirred in THF for 12 h. The reaction
showed rapid H2 evolution. The bright yellow mixture was filtered.
The bright yellow precipitate of the potassium salt of 2 was separated
and washed by THF. [(C4H7)NiCl]2 (149 mg, 0.5 mmol) in THF was
added in situ to the potassium salt of 2 in THF and stirred for 4 h at
room temperature. The solution was filtered, and all volatiles were
removed in a vacuum to give an orange solid, which was washed
several times by pentane and dried 24 h under vacuum. Yield of 7: 248
mg (0.6 mmol, 60%). Single crystals for X-ray crystallography were
grown by layering pentane onto a toluene solution of compound 7 at
1
room temperature. H NMR (400 MHz, C6D6, 298 K): δ/ppm 1.21
(d, J = 3.8 Hz, 1H, CH2), 1.22 (s, 1H, CH2), 1.54 (s, 3H, Me), 1.56 (s,
3H, Me), 1.62 (s, 1H, CH2), 1.98 (s, 1H, CH2), 2.06 (s, 3H, Me), 5.01
(s, 1H, CH), 6.47 (m, 2H, p-Ph), 6.53 (d, J = 7.9 Hz, 1H, o-Ph), 6.70
(d, J = 7.9 Hz, 1H, o-Ph), 6.82 (m, 2H, m-Ph), 7.06 (m, 2H, n-Ph).
13C-APT{1H} NMR (100 MHz, C6D6, 298 K): δ/ppm 22.76 (Me),
23.53 (2Me), 58.02 (CH2), 58.21 (CH2), 99.21 (CH), 109.14 (i-Ph),
110.39 (i-Ph), 117.37 (CN), 117.72 (CN), 123.79 (p-Ph), 123.82
(p-Ph), 124.58 ((CH2)2CCH3), 125.60 (n-Ph), 126.89 (n-Ph), 132.04
C28H34N3Ni+) 472.2257, found 472.2254. IR (KBr): ν
(ν
(CN), s).
Preparation of Adduct 10. Two equivalents of tris-
̃
/cm−1 2224
̃
(pentafluorophenyl)borane (51 mg in 1 mL of toluene, 0.1 mmol)
I
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was added to a toluene solution of 6 (21 mg, 0.05 mmol). The
reaction mixture was stirred for 10 min and filtered, and the volatiles
were removed under vacuum. Compound 10 was isolated as an orange
solid in 80% yield. Single crystals for X-ray crystallography were grown
was added to a toluene solution of 9 (47 mg, 0.1 mmol). The reaction
mixture was stirred for 10 min and filtered, and the volatiles were
removed under vacuum. Compound 9 was isolated as an orange solid
in 85% yield. Single crystals for X-ray crystallography were grown by
1
1
by layering pentane onto a toluene solution of compound 10. H
layering pentane onto a toluene solution of compound 13. H NMR
NMR (400 MHz, C6D6, 298 K): δ/ppm 0.94 (s, 2H, CH2), 1.32 (s,
6H, Me), 1.41 (s, 2H, CH2), 1.67 (s, 3H, CH3(CH2)2), 4.92 (s, 1H,
CH), 6.35 (d, J = 8.0 Hz, 4H, b-Ph), 6.93 (d, J = 8.0 Hz, 4H, c-Ph).
13C-APT{1H} NMR (100 MHz, C6D6, 298 K): δ/ppm 22.07 (Me),
23.64 (2Me), 59.52 (2CH2), 98.37 (CH), 121.29 (CN), 124.19
((CH2)2CCH3), 126.43 (b-Ph), 134.24 (c-Ph), 136.27 (b1-Ph), 138.72
(b1-Ph), 139.42 (d1-Ph), 141.93 (d1-Ph), 147.14 (c1-Ph), 149.62 (c1-
Ph), 159.08 (d-Ph), 161.65 (CN). 19F NMR (564 MHz, C6D6, 298
K): δ −164.7 (m, 4F, m-C6F5), −157 (m, 2F, p-C6F5), −136.5 (m, 4F,
o-C6F5) ppm. 11B NMR (192 MHz, C6D6, 298 K): n.o. HRMS (ESI +
H+): m/z calculated (for C23H21N4Ni+) 413.1271, found 413.1278. IR:
(400 MHz, C6D6, 298 K): δ/ppm 0.91 (m, 1H, CH2), 0.97 (d, J = 6.8
Hz, 3H, (CH(CH3)CH3), 1.14 (m, 6H, (CH(CH3)CH3)), 1.24 (m,
6H, (CH(CH3)CH3)), 1.27 (m, 1H, CH2), 1.31 (m, 9H, (CH(CH3)-
CH3)), 1.37 (m, 3H, Me), 1.48 (bs, 8H, Me, CH2), 1.53 (s, 6H, Me),
1.56 (s, 2H, CH2), 1.62 (s, 1H, CH2), 1.80 (s, 4H, CH3(CH2)2, CH2),
1.84 (s, 3H, CH3(CH2)2), 2.07 (h, 6.9 Hz, 1H, CH2), 3.13 (h, 6.9 Hz,
1H, CH(CH3)CH3)), 3.35 (h, 6.9 Hz, 1H, CH(CH3)CH3)), 3.42 (h,
6.9 Hz, 1H, CH(CH3)CH3)), 3.84 (h, 6.9 Hz, CH(CH3)CH3)), 4.91
(s, 2H, CH), 6.30 (m, 2H, Ar-H), 6.40 (d, J = 8.1 Hz, 2H, Ar-H), 6.54
(d, J = 8.1 Hz, 1H, Ar-H), 6.74 (m, 2H, Ar-H), 7.04 (m, 5H, Ar-H),
7.20 (d, J = 7.9 Hz, 2H, Ar-H). 13C-APT{1H} NMR (100 MHz, C6D6,
298 K): δ/ppm 21.12 (CH3(CH2)2), 21.86 (CH3(CH2)2), 22.95
(CH(CH3)CH3), 23.12 (CH(CH3)CH3), 23.32 (CH(CH3)CH3),
23.34 (CH(CH3)CH3), 23.40 (CH(CH3)CH3), 23.75 (CH(CH3)-
CH3), 23.78 (Me), 23.91 (Me), 24.22 (CH(CH3)CH3), 24.29
(CH(CH3)CH3), 27.46 (CH(CH3)CH3), 27.70 (CH(CH3)CH3),
27.82 (CH(CH3)CH3), 27.97 (CH(CH3)CH3), 57.40 (CH2), 57.99
(CH2), 58.78 (CH2), 58.83 (CH2), 97.43 (CH), 97.88 (CH), 102.06
(Ar-C), 103.55 (Ar-C), 114.02 (Ar-C), 114.35 (Ar-C), 123.12 (Ar-CH),
123.60 (Ar-CH), 123.67 (Ar-CH), 123.99 (Ar-CH), 124.07 (Ar-CH),
124.11 (Ar-CH), 124.97 (Ar-C), 125.18 (Ar-CH), 125.24 (Ar-CH),
126.58 (Ar-CH), 128.26 (Ar-CH), 132.97 (Ar-CH), 133.04 (Ar-CH),
136.19 (b1-Ph), 136.6 (Ar-CH), 136.83 (Ar-CH), 138.18 (Ar-C),
138.64 (b1-Ph), 138.97 (Ar-C), 139.33 (d1-Ph), 139.52 (Ar-C), 140.38
(Ar-C), 141.83 (d1-Ph), 147.06 (c1-Ph), 149.56 (c1-Ph), 152.29 (Ar-
C), 152.45 (Ar-C), 156.46 (CN), 156.94 (CN), 163.65 (CN),
163.72 (CN), 164.69 (Ar-C), 165.3 (Ar-C). 19F NMR (564 MHz,
C6D6, 298 K): δ −164.7 (m, 4F, m-C6F5), −157.7 (m, 2F, p-C6F5),
−135.6 (m, 4F, o-C6F5) ppm. 11B NMR (192 MHz, C6D6, 298 K): δ
−9.84 ppm. Anal. (%) Calcd C46H34BF15N3Ni (M = 984.27 g/mol): C
ν
̃
/cm−1 2307 (ν
Preparation of Adduct 11. Two equivalents of tris-
̃
(CN), s).
(pentafluorophenyl)borane (51 mg, 0.1 mmol in 1 mL of toluene)
was added to a toluene solution of 7 (21 mg, 0.05 mmol). The
reaction mixture was stirred for 10 min and filtered, and the volatiles
were removed under vacuum. Compound 11 was isolated as an orange
solid in 82% yield. Single crystals for X-ray crystallography were grown
by layering hexane onto a toluene solution of compound 11. 1H NMR
(400 MHz, C6D6, 298 K): δ/ppm 0.99 (d, J = 5.2 Hz, 1H, CH2), 1.00
(s, 1H, CH2), 1.28 (s, 3H, Me), 1.37 (s, 3H, Me), 1.54 (s, 1H, CH2),
1.61 (s, 3H, Me), 1.63 (s, 1H, CH2), 4.68 (s, 1H, CH), 6.31 (t, J = 5.2
Hz, 2H, p-Ph), 6.67 (d, J = 8.2 Hz, 2H, o-Ph), 6.88 (dt, J = 19.1, 7.8
Hz, 2H, m-Ph), 7.06 (d, J = 8.2 Hz, 2H, n-Ph). 13C-APT{1H} NMR
(100 MHz, C6D6, 298 K): δ/ppm 21.36 (Me), 22.57 (Me), 22.83
(Me), 58.09 (CH2), 58.81 (CH2), 98.34 (CH), 100.80 (i-Ph), 102.21
(i-Ph), 113.63 (CN), 113.89 (CN), 124.87 (p-Ph), 125.20 (p-
Ph), 125.46 (o-Ph), 125.60 ((CH2)2CCH3), 125.66 (o-Ph), 133.17 (n-
Ph), 133.17 (n-Ph), 136.11 (a-Ph), 137.47 (m-Ph), 137.47 (m-Ph),
138.59 (a-Ph), 139.33 (c-Ph), 141.83 (c-Ph), 147.11(b-Ph), 149.52 (b-
Ph), 161.03 (k-Ph), 161.44 (k-Ph), 162.80 (CN), 163.58 (CN),
n.o. (d-Ph). 19F NMR (564 MHz, C6D6, 298 K): δ −135.69 (m, 4F, o-
C6F5), −157.20 (t, 3JFF = 20.8 Hz, 1F, p-C6F5), −157.40 (t, 3JFF = 20.8
Hz, 1F, p-C6F5), −164.70 (m, 4F, m-C6F5) ppm. 11B NMR (192 MHz,
C6D6, 298 K): δ −9.2 ppm. Anal. (%) Calcd for C59H22B2F30N4Ni·
0.5C6H14 (M = 1480.1880 g/mol): C 50.34, H 1.91, N 3.79. Found: C
56.13, H 3.58, N 4.27. Found: C 55.94, H 3.6, N 4.27. IR: ν
2310 (ν
(CN), s).
̃
/cm−1
̃
ASSOCIATED CONTENT
* Supporting Information
■
S
Text and figures giving further experimental and spectroscopic
details and CIF files giving crystallographic data. This material
is available free of charge via the Internet at http://pubs.acs.org.
50.10, H 2.15, N 3.84. IR: ν
̃
/cm−1 2312 (ν
̃
(CN), s).
Preparation of Adduct 12. One equivalent of tris-
(pentafluorophenyl)borane (51 mg in 1 mL of toluene, 0.1 mmol)
was added to a toluene solution of 8 (47 mg, 0.1 mmol). The reaction
mixture was stirred for 10 min and filtered, and the volatiles were
removed under vacuum. Compound 12 was isolated as an orange solid
in 83% yield. 1H NMR (400 MHz, C6D6, 298 K): δ/ppm 0.93 (d, J =
3.4 Hz, 1H, CH2), 1.05 (d, J = 6.8 Hz, 3H, CH(CH3)CH3), 1.17 (d, J
= 6.8 Hz, 3H, CH(CH3)CH3), 1.30 (d, J = 6.8 Hz, 3H,
CH(CH3)CH3), 1.35 (d, J = 6.8 Hz 3H, CH(CH3)CH3), 1.37 (s,
3H, Me), 1.42 (d, J = 2.3 Hz, 1H, CH2), 1.59 (s, 3H, Me), 1.61 (s, 1H,
CH2), 1.75 (s, 1H, CH2), 1.81 (s, 3H, CH3(CH2)2), 3.35 (h, J = 6.8
Hz, 1H, CH(CH3)CH3), 3.87 (h, J = 6.8 Hz, CH(CH3)CH3), 4.99 (s,
1H, CH), 6.44 (d, J = 8.4 Hz, 2H, r-Ph), 6.92 (d, J = 8.4 Hz, 2H, o-
Ph), 7.05 (m, 1H, p-Ph), 7.09 (m, 2H, k-Ph). 13C-APT{1H} NMR
(100 MHz, C6D6, 298 K): δ/ppm 21.83 (CH3(CH2)2), 23.47
(CH(CH3)CH3), 23.56 (CH(CH3)CH3), 23.78 (Me), 23.91 (CH-
(CH3)CH3), 23.97 (CH(CH3)CH3), 24.24 (Me), 27.68 (CH(CH3)-
CH3), 27.9 (CH(CH3)CH3), 57.44 (CH2), 60.56 (CH2), 97.68 (CH),
115.08(CN), 123.41 (k-Ph), 123.58 (k-Ph), 123.85 (Ar-C), 124.39
(CH3C(CH2)2), 125.19 (p-Ph), 127.27 (r-Ph), 133.92 (o-Ph), 136.26
(a-Ph), 138.6 (a-Ph), 138.72 (Ar-C), 139.43 (c-Ph), 140.07 (Ar-C),
141.78 (c-Ph), 142.97 (Ar-C), 147.21 (b-Ph), 149.55 (b-Ph), 152.54
(Ar-C), 156.47 (CN), 162.52 (CN), 167.12 (m-Ph). 19F NMR
AUTHOR INFORMATION
Notes
The authors declare no competing financial interest.
■
ACKNOWLEDGMENTS
■
Financial support from FONDECYT project Nos. 1100286−
1130077 (to R.S.R.) and NSERC of Canada for a Discovery
Grant (to W.E.P.) is acknowledged. W.E.P. also thanks the
Canada Council of the Arts for a Killam Research Fellowship
(2012−14). O.T. acknowledges funding from Pontificia
Universidad Catolica de Chile via a VRI 2-2012 fellowship
and Ph.D. CONICYT fellowship.
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