Synthesis of [(π-cyano-P-nacnac)Cp] and [(π-cyano-nacnac)Cp]- zirconium complexes, and their remote activation for ethylene polymerization

Article abstract of DOI:10.1039/c1dt11261a

In this contribution the synthesis and characterization of two distinct, yet similar, zirconium complexes, [(π-P-nacnac-CN)Cp] and [(π-nacnac-CN)Cp] zirconium dichloride were discussed. In addition to the complexes, Lewis acid adducts [B(C₆F

Full text of DOI:10.1039/c1dt11261a

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PAPER
Synthesis of [(p-cyano-P-nacnac)Cp] and [(p-cyano-nacnac)Cp]-zirconium
complexes, and their remote activation for ethylene polymerization†
Rene S. Rojas,*a Alan R. Cabrera,a Brian C. Peoples,a Kirsten Spannhoff,b Mauricio Valderrama,a
Roland Fro¨hlich,‡b Gerald Kehrb and Gerhard Erker*b
Received 1st July 2011, Accepted 6th October 2011
DOI: 10.1039/c1dt11261a
In this contribution the synthesis and characterization of two distinct, yet similar, zirconium complexes,
[(p-P-nacnac-CN)Cp] and [(p-nacnac-CN)Cp] zirconium dichloride were discussed. In addition to the
complexes, Lewis acid adducts [B(C6F5)3] of the complexes were isolated and characterized as well. It
was found that while structurally similar, the complexes behave distinctly upon adduct formation and in
their ethylene polymerizations.
would be synthesized: the first would take into consideration the
change in steric bulk of the diimine ligand, while the second would
explore the use of diphosphinimine ligands.13
Introduction
The ability to control the electronic and steric environments of
polymerization catalysts has been shown to be very important,
when trying to manipulate the activity and resulting polymer
properties. Late transition metal systems in particular are largely
dependent on the steric bulk of the ligands, where the presence of
bulky groups converts what would otherwise be an oligomerization
catalyst into a system which can produce high molecular weight
materials.1–5 Metallocene based systems are also sensitive to the
modification of their steric environments; however, in their cases
the modification tends to affect the stereochemistry of the resulting
materials (for instance syndio vs. isotactic polypropylene) rather
than the molecular weight of the materials.6–8 Recently, we reported
on the design and synthesis of new zirconium systems bearing
a cyclopentadienyl ring as well as a bidentate imine ligand.
These systems were shown to be active in polymerization and
copolymerization of ethylene at relatively low concentrations of
MAO. Additionally it was shown that the polymerization activity
of these systems could be increased via the action of a Lewis acid on
a functional group located remotely on the complex backbone.9–12
These results while significant, left several questions unan-
swered, in particular the effect of the steric bulk of the diimine
ligand on the activity and polymer properties and the general
applicability of the remote activation through the exocyclic func-
tionality. For these reasons it was decided that two new complexes
The nacnac class of ligands has been extensively used in
organometallic chemistry as bidentate ligands for the stabilization
of both early and late transition metal complexes. These com-
pounds allow for the use of a common ligand framework, while at
the same time introducing groups which can effect the steric and
electronic properties of the ligand.14
A structurally similar class of ligands, the C1-bridged chelate
phosphinimines, are relatively unknown in organometallic chem-
istry, and were just recently reported.15–21
We recently described the adduct chemistry and subsequent
thermolysis of cyano substituted ‘nacnac’ and ‘P-nacnac’ com-
pounds with HB(C6F5)2.22,23 As expected, the cyano function
preferentially binds the borane. Thermolysis yields the reduced
imine and, in the case of the ‘P-nacnac’ complex, a rearrangement
occurs to give a new heterocycle (see Scheme 1).24
Based on the similar behavior of ‘nacnacH-CN’ and ‘P-nac-
nacH-CN’ toward adduct formation with Lewis acids, it was
thought that a comparison of the two ligand classes under
similar conditions would be interesting. Therefore (P-nacnac-
CN)CpZrCl2 and the corresponding (nacnac-CN)CpZrCl2 were
synthesized and characterized and their ethylene polymerization
activity investigated.
Results and discussion
aDepartamento de Qu´ımica Inorga´nica, Facultad de Qu´ımica, Pontificia
Universidad Cato´lica de Chile, Casilla 306, Santiago-22, Chile. E-mail:
rrojasg@uc.cl; Fax: (+56-2) 354 4744; Tel: (+56-2) 354 7557
The nacnac based compound 2 was prepared using the well known
compound 1 as a starting material.25 A nitrile was added to the
ligand backbone of compound 1 using recently reported synthetic
techniques as outlined in Scheme 2, resulting in the generation
of compound 2 in 70% yield. Compound 2 was characterized
by CHN elemental analysis, spectroscopically and by X-ray
diffraction. The characteristic NMR and IR data are given in
Table 1. The NMR signals are consistent with typical enamino
bOrganisch-Chemisches Institut, Universita¨t Mu¨nster, Corrensstrasse 40,
48149, Mu¨nster, Germany. E-mail: erker@uni-muenster.de; Fax: +49 251
83-36503
† Electronic supplementary information (ESI) available: further exper-
imental and spectroscopic details. CCDC reference numbers 847631–
847635. For ESI and crystallographic data in CIF or other electronic
format see DOI: 10.1039/c1dt11261a.
‡ X-Ray single crystal structure analyses.
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Scheme 1 Hydroboration of nacnac and P-nacnac ligands.
Table 1 Selected spectroscopic parameters of the nacnac-CN and P-
nacnac-CN systems 2, 3, 4, 6 and 7a
2a
3a
4a
6a
7a
d
13C
170.1
69.0
n.o
C
N
N
165.8
82.3
122.2
168.4
74.3
n.o
—
7.9
n.o
119.5
CCN
C
—
—
—
Cp
118.8
119.8
1
d H
Cp
Me
—
2.27
6.19
2.26
6.19
5.82
—
5.86
—
2.16
d
31P
—
—
—
28.1
27.6
IR [cm-1]
2261
n(CN)
2190
2209
2177
2260
Scheme 2 Synthesis of compounds 2–4.
a In CD2Cl2 solution.
heterocarbonyl systems. The 13C NMR signal of the cyano carbon
appears at 122.2 ppm, while the CCN signal appears at 82.3 ppm.
The IR n(CN) band of compound 2 is found at 2190 cm-1. These
results are consistent with the previously reported nacnacH-CN
systems.9
The X-ray crystal structure of 2 shows the expected U-shaped
C3N2 core with the N5–C4 bond distance slightly shorter than
N1–C2, while the bond length of C4–C3 is longer than C3–C2
which is in agreement with the double bond character of its bond
due to the hydrogen being located on the N1 atom. The N–H
vector is oriented inward in the direction of N5, with which it
likely forms a hydrogen bridge. Both phenyl groups, on N1 and
N5, are orientated perpendicularly to the core plane (see Table 2
and Fig. 1).
1
complex 3 was isolated as yellow crystals in a yield of 84%. H
NMR characterization of complex 3 (see Table 1) shows a singlet
at 2.26 ppm (Me) and a singlet at 6.19 (C5H5). In the 13C NMR
spectrum the Cp signal is observed at 118.8 ppm. The signal at
74.3 ppm can be assigned to the quaternary carbon CCN. This
resonance is shielded in comparison to that of the free ligand (82.3
ppm). We attribute this effect to metal–carbon (C3) interactions
(see below). Such behaviour was previously observed for a series
of other zirconium complexes including the (nacnac-CN) ligand.9
Single crystals of 3 suitable for the X-ray crystal structure
analysis were obtained via the diffusion method (THF/pentane).
The X-ray crystal structure of compound 3 (see Fig. 2) shows
that the nacnac-CN ligand is bound in a U-shaped form, similar
to previously reported complexes.9 It appears that the Zr atom
has interactions with all five members of the ligating ring, making
it metallocene-like. As the substituents on the imines are the
Compound 2 was deprotonated by treatment with KH and from
the light brown ligand salt obtained in quantitative yield, NMR
analysis of the salt indicated complete deprotonation. The salt
was transmetallated using CpZrCl3(dme)26–28 (THF, rt, 12 h) and
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Table 2 Selected structural parameters of the nacnac-CN systems 2, 3
and 4a (values take from molecule A)
same (Ph), the complex shows a high symmetry, with a
mirror plane containing the C3–C7–N8 vector, dividing the Cp
ring and bisecting the Cl–Zr–Cl angle. The Zr–N bond lengths
2
3
4
˚
2.224(2) A indicate a strong interaction with the nitrogen atoms
˚
while the Zr–C3 bond length of 2.747(3) A (see Table 2 and Fig.
Zr–N1
Zr–C3
Zr–N5
Zr–C2
Zr–C4
Zr–Cl1
Zr–Cl2
C2–N1
C2–C3
C3–C4
C4–N5
C3–C7
C7–N8
—
—
—
—
—
—
—
1.319(2)
1.411(2)
1.441(2)
1.304(2)
1.426(2)
1.146(2)
2.224(2)
2.747(3)
—
2.796(2)
—
2.469(1)
—
1.309(3)
1.438(3)
—
2.250(3)
2.690(3)
2.241(3)
2.809(4)
2.766(4)
2.439(1)
2.447(1)
1.286(5)
1.462(5)
1.452(5)
1.295(4)
1.409(5)
1.141(4)
2), shows a substantially weaker interaction in comparison with
the previously reported unsymmetrical (nacnac-CN)CpZrCl2
9
˚
example (Zr–C3, 2.658(3) A).
However, the Zr–C3 interaction is sufficiently strong to produce
the typical deviation of the nacnac-CN ligand in complex 3 from
planarity into the direction of a boat-shaped arrangement.9,14
The adduct formation with 3 proceeded smoothly upon treat-
ment with 1 molar equivalent of B(C6F5)3, yielding compound
[(C6F5)3B-NC-nacnac]CpZrCl2 (4) in 77% yield (see Scheme 2). 1H
NMR characterization of the complex reveals the characteristic
singlets associated with the Cp ring (6.19 ppm) and the methyl
groups (2.16 ppm) both of which are shifted slightly upfield
compared to complex 3. The 13C NMR spectrum shows the
expected signals for the imine carbons (C N) at 170.1 ppm, the
Cp ring at 119.8 ppm, and the CCN carbon at 69.0 ppm. The
CCN resonance is shifted in comparison to that of the complex 3
(74.3 ppm). We attribute this effect to the inductive effects resulting
—
1.423(5)
1.144(5)
N1–C2–C3
C2–C3–C4
C3–C4–N5
C3–C7–N8
Cl1–Zr–Cl2
C2–N1–C11–C12
C4–N5–C21–C22
118.7(2)
125.5(2)
118.9(2)
179.7(2)
—
135.2(2)
56.2(3)
118.2(2)
122.6(3)
—
179.2(4)
89.0(1)
-102.0(3)
—
116.1(3)
123.8(3)
116.9(3)
177.4(4)
90.3(1)
-89.6(5)
99.7(4)
a
˚
Bond lengths in A, angles and dihedral angles in degrees.
from the coordination of the Lewis acid B(C6F5)3 to the C
N
group. The 11B NMR spectrum features a typical four-coordinate
boron resonance (d -10.6) which is supported by a small Dd(p,m)
chemical shift difference29 in the 19F NMR spectrum [d -134.1 (o),
-157.6 (p), -164.4 (m)].
The IR spectrum of the borane adduct 4 shows a sharp C
N
-1
-1
˜
˜
stretching band at n = 2261 cm which is shifted by Dn = 71 cm
to higher wave numbers as compared to its parent ligand system
2. 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 atom effectively reduces the electronic repulsion between
nitrogen and carbon to make the C N triple bond in 4 slightly
stronger.30
In the solid state the Zr atom has an interaction with all five
members of the “nacnac” ring, the Zr–N1 and Zr–N5 bond
˚
˚
lengths of 2.250(3) A and 2.241(3) A are longer while the Zr–
˚
C3 bond length of 2.690(3) A is shorter than the respective length
Fig. 1 Molecular structure of compound 2.
in compound 3 (see Table 2 and Fig. 3), this indicates a strong
metal carbon interaction which produces the more pronounced
boat configuration. However, we find a symmetry disruption
due to the bulkiness of the Lewis acid, attached to the C
N
˚
functionality, the bond length (C7–N8) of 1.141(4) A is not
significantly different from that found in the direct precursor 3
˚
(C7–N8: 1.144(5) A). B(C6F5)3 coordinates in a linear fashion
to the NC-nacnac ligand in 4 (C7–N8–B1: 170.8(4)◦, N8–B1:
˚
1.589(5) A). The C7–N8–B1(C6F5)3 unit is oriented toward the
open side of the pseudometallocene wedge in 4. In the projection
the C3–C7 vector almost bisects the Cl1–Zr–Cl2 angle (see Fig. 3
and Table 2).
Transmetallation of [P-nacnacK-CN]
The cyano-substituted bis-phosphinimine system 5 was prepared
starting from the cyano substituted dppm-CN system as pre-
viously described.13,31 Metallation with KH gave the previously
reported P-nacnac-CN potassium salt, (analogous to the lithium
salt32), subsequent transmetallation with one molar equivalent of
Fig. 2 Molecular structure of compound 3.
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Fig. 4 A view of the molecular structure of the adduct 6.
does not share the high crystallographic symmetry observed in
complex 3 (see Fig. 4). This can be observed in the Zr–N (Zr–
˚
˚
N1 of 2.226(4) A vs. Zr–N2 of 2.288(4) A) and Zr–P (Zr–P1 of
˚
˚
3.151(1) A vs. Zr–P2 of 3.182(1) A) distances which indicate that
one side of the molecule is shifting slightly (see Table 3). This is
most likely a result of the large steric requirements of the phenyl
groups attached to the phosphine. This can also be observed in the
angles between the phenyl groups when observed along the P1–P2
vector, where the phenyl groups are shifted approximately 15◦ out
of alignment. The overall conformation of the six-membered P-
nacnac-CN framework strongly deviates from planarity (see Fig.
4). It exhibits a pronounced boat-shaped conformation similar to
that of compounds 3 and 4 as well as previously observed in Rh
and Ir complexes with this ligand.32
Fig. 3 A view of the molecular structure of the adduct 4.
Table 3 Selected structural parameters of the P-nacnac-CN systems 6
and 7a
6
7
Zr–CCp
Zr–N1
Zr–P1
Zr–C1
Zr–P2
Zr–N2
Zr–Cl1
Zr–Cl2
P1–N1
P1–C1
C1–P2
P2–N2
C1–C2
C2–N3
N3–B1
2.492(6)–2.539(6)
2.226(4)
3.151(1)
2.793(5)
3.182(1)
2.288(4)
2.501(2)
2.493(1)
1.621(4)
1.785(5)
1.759(5)
1.623(4)
1.431(6)
1.151(6)
—
2.493(3)–2.525(3)
2.268(2)
—
2.839(2)
—
2.271(2)
2.467(1)
2.465(1)
1.616(2)
1.791(2)
1.791(3)
1.619(2)
1.388(3)
1.148(3)
1.567(3)
Scheme 3 Synthesis of compounds 5–7.
CpZrCl3(dme) (THF, rt, 12 h) gave the (P-nacnac-CN)CpZrCl2
complex 6, isolated as a light yellow solid in 85% yield
(see Scheme 3).
˜
The complex 6 shows a n(C N) stretching band (n = 2177
cm-1) that is shifted to higher wave numbers as compared to
-1 13
˜
its free precursor 5 (n = 2157 cm ). Compound 6 features
a singlet 31P NMR resonance at d 28.1 ppm and it shows a
singlet for the 13C NMR Cp signal at d 119.5 ppm, while the
1
CCN signal is observed at d 79 ppm (t, JPC = 91.7 Hz) (see Table
1
1). In the H NMR spectrum of 6 there are two sets of phenyl
N1–P1–C1
N2–P2–C1
C1–C2–N3
Cl1–Zr–Cl2
B1–N3–C2
P1–N1–C11–C12
P2–N2–C21–C22
103.7(2)
100.8(2)
178.7(6)
83.4(1)
—
78.6(5)
-69.5(5)
101.8(1)
101.4(1)
178.8(3)
84.9(1)
174.9(2)
114.7(3)
-112.8(3)
groups for the P–Ph (in an integral ratio of 1 : 1 approximately)
and one for the N–Ph (see the Supplementary Information†)
and the respective singlet corresponding to the Cp ring at
5.82 ppm.
Single crystals of 6 suited for the X-ray crystal structure analysis
were obtained from a CH2Cl2/pentane solution at -35 ◦C via
the gas diffusion method. This analysis shows that complex 6
a
˚
Bond lengths in A, angles and dihedral angles in degrees.
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As was observed in 5, the Lewis acid, B(C6F5)3, added to the ni-
trile nitrogen atom (see Fig. 5). The boron atom has taken up a dis-
torted tetrahedral coordination geometry in the adduct, featuring
bond angles of 104.7(2)◦ (N3–B1–C71), 111.4(2)◦ (N3–B1–C81),
107.0(2)◦ (C71–B1–C81), 114.7(2)◦ (C91–B1–C81) and 115.8(2)◦
˚
(C91–B1–C71). The N3–B1 bond length is found to be 1.567(3) A.
˚
The C2–N3 triple bond is short (1.148(3) A) and the C1–B1 moiety
◦
˚
is linear (C1–C2 1.388(3) A, angles C1–C2–N3 178.8(3) , C2–N3–
B1 174.9(2)◦). It is interesting to note that the central N2P2C unit
is not delocalized. It exhibits similar N1–P1, N2–P2 bonds lengths
˚
˚
of 1.616(2) A and 1.619(2) A, respectively, while the P1–C1, P2–C1
˚
bond lengths (1.791(2–3) A) are even longer than the adjacent N–
P linkages, indicating their single bond character (see Fig. 5 and
Table 3).
The adduct formation produced changes in the structure of
complex 7 when compared to complex 6. In particular the Zr–N
distances are interesting. Whereas in complex 6 there is significant
˚
difference between the Zr–N1 and Zr–N2 distances of 0.062 A,
in complex 7 the difference in the Zr–N distances is reduced to
˚
only 0.013 A. In addition, the Zr–Cl bond distances decrease
˚
significantly (ca. 0.03 A), indicating a slight strengthening of these
bonds (see Table 3).
The adduct 7 shows a n(C N) stretching band (n = 2260 cm )
-1
˜
Fig. 5 A view of the molecular structure of the adduct 7.
that is shifted to higher wave numbers as compared to its free
-1
-1
˜
˜
ligand 5 (n = 2157 cm ) and precursor 6 (n = 2177 cm ). The
adduct 7 features a 11B NMR resonance at d -12.0 ppm and
shows a single 31P NMR resonance at d 27.6 ppm. In the 1H NMR
spectrum a singlet for the C5H5 resonance was observed at d 5.86
ppm (see Table 1).
˚
˚
The P–N bond lengths of 1.621(4) A and 1.623(4) A are
longer than the corresponding C N imine bond lengths, but are
consistent with a phosphorus–nitrogen double bond. This larger
P
N bond length results in the formation of a larger “boat”, and
˚
as a result the Zr–C1 bond length of 2.793(5) A is longer than that
˚
observed in complex 3 (2.747(3) A).
Ethylene polymerization
The phosphorus atoms in complex 6 are pseudo-tetrahedrally
coordinated (angles N1–P1–C1: 103.7(2)◦, C1–P1–C41: 113.1(2)◦,
N2–P2–C1: 100.8(2)◦, C1–P2–C61: 112.4(2)◦). The coordination
geometry of carbon atom C1 deviates considerably from trigonal-
planar (angles P2–C1–P1: 119.0(3)◦, C2–C1–P1: 115.7(3)◦, C2–
C1–P2: 114.3(3)◦, total: 349.0◦). The CN group, however, main-
tains its alignment and continues to bisect the Cl1–Zr–Cl2, the
A series of ethylene polymerization reactions were carried out
using compounds 3, 4, 6 and 7 under various reaction conditions,
with MAO used as the co-activator. The results are summarized
in Table 4.
In comparison to the previously reported nacnac-CN system
(Entry 1) which had an asymmetric ligand (diisopropylphenyl on
one side with only a phenyl ring on the other) an increase in
activity is observed, most likely due to a reduction in the steric
environment around the zirconium metal center. In both cases a
linear polyethylene with a narrow polydispersity is obtained, with
a small decrease in melting point observed (2 ◦C) in materials
produced by compound 3.
Comparison of entries 2–4 details the effect of MAO concen-
tration on the polymerization activity and molecular weight of
the materials produced by compound 3. There appears to be a
small effect of the MAO on the activity of the polymerization,
with increased MAO concentration producing a slight increase in
polymerization activity. The molecular weight of the materials
produced show almost no variation as a function of MAO
content. The melting point of the polymers are all very similar at
133 ◦C. The B(C6F5)3 adduct of compound 3 (compound 4) shows
behaviour similar to previously reported results, with compound
4 showing a higher polymerization activity when using the same
MAO concentrations (entries 3, 5 and 4, 6). The molecular weight
of the polymers produced by the complexes 3 and 4 changes as
well, with the B(C6F5)3 adduct 4 producing materials which have
molecular weights which are ca. 40 000 g mol-1 higher than the
˚
CN bond length 1.151(6) A is slightly longer than that observed
˚
in complex 3 (1.144(5) A) (see Fig. 4 and Table 3).
Compound 6 was reacted with one molar equivalent of B(C6F5)3
at room temperature (one hour) yielding adduct 7 in a yield of 87%.
Single crystals of 7 suitable for X-ray crystal structure analysis were
obtained from a CH2Cl2/pentane solution at room temperature
via the gas diffusion method. In the solid state (see Fig. 5) the
coordination sphere around the zirconium atom is defined by
the Cp carbons atoms, two chloride and the two phosphinimine
˚
˚
nitrogen atoms (Zr–N1 2.268(2) A and Zr–N2 2.271(2) A). A
six-membered metallacycle (N1–P1–C1–P2–N2–Zr) is formed by
the ligand and the zirconium atom in 7. The ring maintains a
twist boat conformation (similar to compound 6) in which the
central carbon (C1) atom and the zirconium atom are displaced
from the N2P2 least-square plane. A long interaction between the
methine carbon atom (C1) and the zirconium atom of 2.839(2)
˚
A is observed (see Table 3). This distance is longer than the
˚
Zr–C1 length in compound 6 [2.793(5) A]. As mentioned above,
the observed conformation of the six-membered metallocycle of
compound 6 and 7 is typical for bis(phosphinimino)methanides16
as well as the nacnac-methanide complexes.9
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Table 4 Selected ethylene polymerization reactionsa
Tf/◦Cd
c
c
Entry
Pre-catalyst
Ratio Al/Zr
Ab
Mn
Mw
PDI
1
2
3
4
5
6
7
8
Ref. 9
500
1000
500
250
500
250
1000
500
250
500
250
1520
2063
1910
1689
2826
1944
4258
3246
883
99
85
80
80
101
106
73
77
51
67
47
175
154
147
146
182
190**
137
146
93
1.76
1.8
1.8
1.8
1.8
5.6*
1.9
1.9
1.8
1.9
1.8
135
133
133
133
134
133
133
134
134
134
133
3
3
3
4
4
6
6
6
7
7
9
10
11
3635
641
128
83
a Polymerizations were carried out in a 100 mL autoclave reactor with 6.8 mm◦ol of Zr in 30 mL of toluene and 12 bar of ethylene pressure. The co-catalyst
was MAO. Duration of the reaction was 10 min. Temperature of reaction 75 C. b Activity in kg polymer/(mol Zr ¥ h). c ¥103 g mol-1. d In ◦C. * Bimodal
distribution, ** Value obtained from GPC trace by the integration of the main fraction (see the Supporting Information†).
materials produced by 3 under similar conditions. In addition,
at low MAO concentrations a low molecular weight shoulder is
noticed in the GPC curves, which may be an indication of catalyst
decomposition (see Supplementary Information†). This increase
in molecular weight is not uncommon in polymerization catalysts
which have large groups coordinated to the backbone, either in the
form of supports or through Lewis acid interactions. The polymer
properties of all the materials are very similar with the melting
point varying less than 1 ◦C in any sample.
The coordination of the P-nacnac-CN to the zirconium (6) has
a substantial effect on the ethylene polymerization activity. Com-
parison of entries 7 and 2 shows that the P-nacnac-CN supported
ligand has an activity which is more than double that obtained
with the nacnac-CN alone. At lower MAO concentrations the
effect is reduced (compare entries 3 and 8) with a ca. 60% increase
in activity observed in the P-nacnac-CN system. At even lower
MAO concentrations, the P-nacnac-CN systems begins to falter,
with the activity reducing significantly, which may be an indication
of it sensitivity.
The B(C6F5)3 adduct of compound 6 (compound 7), (entries 10
and 11) has a higher activity than the B(C6F5)3 free compound 6
as well as the compound 4 under similar reaction conditions. It is
Fig. 6 GPC traces of polymers produced using complexes 3, 4, 6 and 7
using 500 equiv. MAO.
interesting to note, that while the activity of this complex increases
compared to the B(C6F5)3-free complex 6, the increase is less than
that observed between complexes 3 and 4. It is thought that the
increased activity of the P-nacnac-CN complexes is a result of
the increased steric congestion of the phenyl rings. The phenyl
rings are unable to rotate in the presence of the bulky phenyl rings
attached to the phosphorus in the backbone. This forced planar
arrangement has previously been shown to increase activity in Ni
catalysts.33
Comparison of the GPC curves (see Fig. 6) of the four complexes
under the same reaction conditions (500 equiv. MAO) reveals that
the B(C6F5)3-free complexes (3 and 6), (entries 3, 8) produced
materials of a nearly identical molecular weight and dispersity.
When the B(C6F5)3 adducts of the complexes (4 and 7) (entries
5, 10) are used the molecular weight of the materials change
in opposite ways with the polymer produced by 7 possessing a
lower molecular weight than that produced by 4. This suggests
two things: the first is that the B(C6F5)3 is remaining attached to
the cyano functionality throughout the process, the logic being
that if the B(C6F5)3 was displaced by the excess MAO, then the
molecular weight of the materials produced by the complexes with
and without B(C6F5)3 would be the same, the second is that as
the B(C6F5)3 is affecting the catalysts in different ways there must
be competing effects produced by the presence of the B(C6F5)3.
The effects of B(C6F5)3 are normally two-fold, it can reduce the
electron density at the metal center and can also introduce steric
bulk. As the ability of B(C6F5)3 to remove electron density via the
nacnac-CN set of ligands has previously been demonstrated in this
and other groups, the question was what was happening in the P-
nacnac-CN system. The P-nacnac-CN system, however, provides a
convenient spectroscopic handle in the presence of the phosphines
in the ligand backbone. It was suspected that the action of the
Lewis acid upon the ligand would produce a significant change in
the 31P NMR spectrum. The 31P NMR shifts of 28.1 ppm (6) and
27.6 ppm (7) respectively indicate that the B(C6F5)3 is having only
a limited effect on the electronic environment of the phosphorus
in the ligand backbone. The B(C6F5)3 however is having a great
effect on the geometry of the chelate ring, with the Zr–N and
N–P bond lengths becoming nearly identical for both sides. In
addition, it is interesting to note that the N1–P1–C1 bond angles
1248 | Dalton Trans., 2012, 41, 1243–1251
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©

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become nearly equivalent at 101.41◦ and 101.84◦. Finally, perhaps
the most important factor which would affect the polymerization
is the bite angle of the N1–Zr–N2 which changes dramatically
from 90.11◦ to 84.47◦ in 6 and 7 respectively. This is a substantial
change which affects the size and nature of the open site, (in 3 and
4 the difference is 1◦).
were used as received from Aldrich unless otherwise specified.
Ethylene was purchased from Matheson Tri-Gas (research grade,
99.99% pure). Toluene, THF, ether and pentane were distilled from
benzophenone ketyl. All polymerization reactions were carried
out in a Parr autoclave reactor as described below. Toluene for
polymerization was distilled from sodium benzophenone. The
following instruments were used for the physical characterization
of the compounds. NMR experiments: Varian Inova 500 (1H: 500
MHz; 13C: 126 MHz; 19F: 470 MHz; 11B: 160 MHz), Bruker Unity
Plus 600 (1H: 600 MHz; 31C: 151 MHz; 19F: 564 MHz; 11B: 64 MHz)
and Bruker Avance 400. Most NMR assignments were supported
by additional 2D experiments. FT-IR spectra were recorded on
a Bruker Vector-22 Spectrophotometer using KBr pellets, and in
solution using C6D6 as solvent. X-Ray crystal structure analyses:
data sets were collected with a Nonius KappaCCD diffractometer,
equipped with a rotating anode generator. Programs used: data
collection COLLECT (Nonius B.V., 1998), data reduction Denzo-
SMN (Z. Otwinowski and W. Minor, Methods Enzymol., 1997,
276, 307–326), absorption correction Denzo (Z. Otwinowski,
D. Borek, W. Majewski and W. Minor, Acta Crystallogr., Sect.
A, 2003, 59, 228–234), structure solution SHELXS-97 (G. M.
Sheldrick, Acta Crystallogr., Sect. A, 1990, 46, 467–473), structure
refinement SHELXL-97 (G. M. Sheldrick, Acta Crystallogr., Sect.
A, 2008, 64, 112–122), graphics XP (BrukerAXS, 2000). Graphics
show the thermal ellipsoids with 50% probability, R values are
given for the observed reflections, wR2 values for all reflections.†
Comparison of the materials obtained using lower concen-
trations of MAO (250 equiv.) afford similar conclusions for the
materials produced using complex 3 and 4, which give materials
which were more or less identical to those obtained using 500
equiv. of MAO. The materials produced by complexes 6 and 7
had molecular weights which were ca. 35% less than the materials
formed with 500 equiv. MAO. This could be an indication that
the catalyst is not completely activated, or is undergoing a
decomposition process at the lower MAO ratios. Complexes 3 and
4 show low molecular weight shoulders which decrease in size with
increasing MAO concentrations. As this occurs in both complexes,
it is thought that the complex is undergoing a decomposition
process. The primary signal in the GPC (high molecular weight)
can be accurately fitted using a Flory–Shultz distribution; however,
the lower molecular weight material cannot be fitted even using
multiple peaks, this indicates that the material is being produced
by a decomposing species. These shoulders are not observed in any
of the materials produced by complexes 6 and 7, suggesting that
the low molecular weight materials generated by these systems are
a result of a different type of decomposition process.
Conclusions
3-Cyano-2-(phenyl)aminopent-2-en-4-(phenyl)imine (2)
The zirconium complexes 3, 4 and 6, 7 were successfully synthe-
sized and characterized. In general the complexes were structurally
similar except that the phosphinimine complexes showed an
increased ring size and also a tendency to form distorted six-
membered rings. In all cases the imine or phosphinimine group
coordinated to the zirconium metal in a boat like conformation,
similar to that previously reported. All of the complexes were
found to be active for ethylene polymerization with high activity,
and produced linear materials with high molecular weights and
low PDI. The ability to remotely remove electron density via
the formation of a Lewis acid adduct [B(C6F5)3] proved useful,
in particular for the complex 4 which showed substantial in-
creases (ca. 40%) over the B(C6F5)3 free complex. The analogous
phosphinimine complex, 7, showed an increase as well over the
B(C6F5)3 free complex 6; however, it was much smaller (only 10%)
than that observed in the imine complex. We suspect that this
is a result of changes in the geometry of the complex due to
the interaction of the B(C6F5)3 on the ligand backbone, and not
necessarily due to direct withdrawal of electron density from the
metal center. The results with the phosphinimine illustrate that the
effects of Lewis acids on remote sites can be multifaceted and can
include both electronic (as observed in imine based ligands) and
steric/geometric effects.
n-BuLi (5.7 mL, 1.6 M, 9.0 mmol) was added drop-wise to
a stirred solution of 2-(phenyl)aminopent-2-en-4-(phenyl)imine
(1)25 in THF (30 mL) (1.6 g, 6.5 mmol) at -78 ◦C. The reaction was
allowed to warm to room temperature over 2 h to afford the lithium
salt. The resulting yellow suspension was then cooled to -78 ◦C,
and p-toluenesulfonylcyanide (1.4 g, 7.7 mmol) in THF (20 mL)
was added. The reaction mixture was again allowed to warm to
room temperature over 24 h. From this mixture, all volatiles were
removed under vacuum, and the residue was dissolved in CH2Cl2
(50 mL). This was washed with brine (2 ¥ 100 mL), dried over
Na2SO4 and filtered. The solvent was subsequently removed under
vacuum to yield a light brown solid. Precipitation from methanol
provided a light yellow solid of 3-cyano-2-(phenyl)aminopent-2-
en-4-(phenyl)imine (2) in 70% yield (1.23g. 4.5 mmol). Anal. Calcd
for C18H17N3: C, 78.52; H, 6.22; N, 15.26. Found: C, 78.36; H, 6.15;
-1
1
˜
N, 15.30%. IR (KBr): n/cm = 2190 (n(C N)). H NMR (400
MHz, CD2Cl2, 298 K): d (ppm) = 14.42 (s, 1H, NH), 7.36 (t,
4H, m-Ph), 7.18 (t, 2H, p-Ph), 6.99 (d, 4H, o-Ph), 2.27 (s, 6H,
N
1
CMePh). 13C{ H} NMR (100 MHz, CD2Cl2, 298 K): d (ppm) =
165.8 (C NPh), 144.1 (i-Ph), 129.6 (m-Ph), 125.7 (p-Ph), 123.9
(o-Ph), 122.2 (C N), 82.3 (CCN), 19.9 (N CMePh).
X-Ray crystal structure analysis of 2: C18H17N3, M = 275.35,
¯
triclinic, P1(No. 2), a = 11.3372(2), b = 11.4394(2), c = 13.2279(3)
◦
˚
A, a = 90.974(1), b = 109.646(1), g = 110.002(1) , V = 1501.23(5)
A , Dc = 1.218 g cm , m = 0.074 mm , F(000) = 584, Z = 4, l =
0.71073 A, T = 223(2) K, 13 598 reflections collected ( h, k, l),
[(sinq)/l] = 0.66 A , 6933 independent (Rint = 0.045), and 5590
Experimental section
3
-3
-1
˚
˚
General information
-1
˚
All manipulations were performed under an inert atmosphere
using standard glovebox and Schlenk-line techniques. All reagents
observed reflections [I ≥ 2s(I)], 389 refined parameters, R = 0.063,
wR2 = 0.149, GoF = 1.063.
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The Royal Society of Chemistry 2012
Dalton Trans., 2012, 41, 1243–1251 | 1249
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[(3-Cyano-2-(phenyl)aminopent-2-en-4-(phenyl)imine)](g5-
[Bis(N-phenyldiphenylphosphinimino)acetonitrile] potassium (5¢)
C5H5)ZrCl2 (3)
Compound 5 (100 mg, 0.17 mmol) and KH (15 mg, 0.37 mmol)
were stirred in THF for 6 h. The reaction showed rapid gas
evolution. The slightly cloudy mixture was filtered through Celite
and THF was removed under vacuum, washed with pentane
and dry under vacuum. A dark yellow powder corresponding
3-Cyano-2-(phenyl)aminopent-2-en-4-(phenyl)imine (2) (100 mg,
0.36 mmol) and KH (22 mg, 0.54 mmol) were stirred in THF
for 12 h. The reaction showed rapid gas evolution. The slightly
cloudy mixture was filtered through Celite and added dropwise to
CpZrCl3(dme) (116 mg, 0.33 mmol) in THF. The reaction mixture
was stirred for 12 h. The resulting yellow solution was filtered
over Celite. The solvent volume was reduced, pentane and ether
were added separately to wash the solid. A light brown powder
corresponding to compound 3 was isolated in 84% yield (153 mg,
to compound 5¢ ¥ 1 THF was isolated in 86% yield (102 mg,
-1
0.15 mmol). IR (KBr): n/cm = 2134 (n(C N)). 1H NMR (500
˜
MHz, CD2Cl2, 298 K): d (ppm) = 7.74 (m, 4H, o-PhP), 7.33 (m,
2H, p-PhP), 7.24 (m, 4H, m-PhP), 6.87 (m, 2H, m-PhN), 6.53 (m,
1H, p-PhN), 6.38 (m, 2H, o-PhN), 3.66 (m, 6H, THF), 1.81 (m,
1
0.31 mmol). Anal. Calcd for C23H21Cl2N3Zr: C, 55.08; H, 4.22; N,
6H, THF). 13C{ H} NMR (126 MHz, CD2Cl2, 298 K): d (ppm) =
-1
152.6 (broad, i-PhN), 135.4 (broad m, i-PhP), 134.6 (Br, i-PhP),
132.6 (m, o-PhP), 131.0 (broad, p-PhP), 129.5 (m-PhN), 128.4 (m,
m-PhP), 122.9 (broad, o-PhN), 117.1 (broad, p-PhN), 68.1 (THF),
˜
8.38. Found: C, 55.03; H, 4.36; N, 8.05%. IR (KBr): n/cm = 2209
(n(C N)). 1H NMR (400 MHz, CD2Cl2, 298 K) d (ppm) = 7.51
(m, 4H, m-Ph), 7.37 (m, 2H, p-Ph), 7.12 (broad, 4H, o-Ph), 6.19 (s,
5H, Cp), 2.26 (s, 6H, Me). 13C{ H} NMR (100 MHz, CD2Cl2, 298
25.9 (THF), n.o. (CCN, CN). 31P{ H} NMR (202 MHz, CD2Cl2,
1
1
K): d = 168.4 (C N), 148.8 (i-Ph), 130.0 (m-Ph), 127.3 (p-Ph),
123.8 (o-Ph), 118.8 (Cp), n.o. (C N), 74.3 (CCN), 21.3 (Me).
X-Ray crystal structure analysis of 3: C23H21Cl2N3Zr, M =
298 K): d (ppm) = 12.0 (n1/2 ~ 30 Hz).
[Bis(N-phenyldiphenylphosphinimino)acetonitrile](g5-C5H5)ZrCl2
(6)
501.55, orthorhombic, Pnma (No. 62), a = 7.6639(1), b =
3
˚
˚
Bis(N-phenyphosphinimino)acetonitrile (5)13 (50 mg, 0.085 mmol)
and KH (5 mg, 0.13 mmol) were stirred in CH2Cl2 for 12 h. The
reaction showed rapid gas evolution. The slightly cloudy mixture
was filtered through Celite and added dropwise to CpZrCl3(dme)
(30 mg, 0.085 mmol) in CH2Cl2. The reaction mixture was stirred
for 12 h. The resulting yellow solution was filtered over Celite.
The solvent volume was reduced, pentane and ether were added
separately to wash the solid. A light yellow solid corresponding to
compound 6 was isolated in 85% yield (59 mg, 0.072 mmol). Anal.
13.2857(2), c = 25.1922(5) A, V = 2565.08(7) A , Dc = 1.299 g
-3
-1
˚
cm , m = 0.649 mm , F(000) = 1016, Z = 4, l = 0.71073 A, T =
223(2)K, 14 370 reflections collected ( h, k, l), [(sinq)/l] = 0.66
-1
˚
A , 3123 independent (Rint = 0.044), and 2818 observed reflections
[I ≥ 2s(I)], 140 refined parameters, R = 0.041, wR2 = 0.119, GoF =
1.015.
[(3-Cyano-2-(phenyl)aminopent-2-en-4-(phenyl)imine)tris-
(pentafluorophenyl)borate](g5-C5H5)ZrCl2 (4)
Calcd for C43H35Cl2N3P2Zr: C, 63.15; H, 4.31; N, 5.11. Found: C,
-1
62.99; H, 4.12; N, 4.98%. IR (KBr): n/cm = 2177 (n(C N)). 1H
˜
1 Equiv. of tris(pentafluorophenyl)borane (51 mg, 0,099 mmol in
1 mL of CH2Cl2) was added to a CH2Cl2 solution of 3 (50 mg,
0.099 mmol). The reaction mixture was stirred for 1 h at room
temperature, filtered through Celite and the volatiles were removed
under vacuum and washed with pentane. Compound 4 was
isolated as light yellow solid in 77% yield (77.8 mg, 0.077 mmol).
NMR (600 MHz, CD2Cl2, 298 K): d (ppm)t = 7.90 (4H, o), 7.54
(2H, p), 7.35 (4H, m) (each broad, PPh), 7.35 (4H, o), 7.17 (2H, p),
6.97 (4H, m) (each broad, PPh¢), 7.23 (4H, m), 7.12 (4H, o), 7.08
(2H, p) (each broad, NPh), 5.82 (s, 5H, Cp). Ligand (ca. 30%):
7.74 (4H, o), 7.55 (2H, p), 7.40 (m, 4H) (each broad, PPh), 7.03
(2H, m), 6.80 (2H, o), n.o. (1H, p) (each broad, NPh). [t tentative
Anal. Calcd for C41H21Cl2F15N3Zr: C, 48.59; H, 2.09; N, 4.15.
1
assignment] 13C{ H} NMR (151 MHz, CD2Cl2, 298 K): d (ppm)t =
-1
˜
Found: C, 48.73; H, 2.18; N, 4.03%. IR (KBr): n/cm = 2261
(n(C N)). 1H NMR (500 MHz, CD2Cl2, 298 K): d (ppm) = 7.55
(m, 4H, m-Ph), 7.42 (m, 2H, p-Ph), 7.14 (broad, 2H, o-Ph), 6.19
137.0 (o), 133.4 (p), 132.9 (m), n.o. (i) (each broad, PPh), 132.4 (p),
128.7 (m, m), 127.1 (o), n.o. (i) (each broad, PPh¢), 149.0 (i), 129.0
(m), 128.7 (m, o), 124.9 (p) (each broad, NPh), 119.5 (Cp), 7.9 (t,
1JPC = 91.7 Hz, PCP), n.o (CN). Ligand: 133.2 (o), n.o. (i, p), 129.2
(m) (each broad, PPh), 129.3 (m), 121.4 (o), n.o. (i, p) (each broad,
(s, 5H, Cp), 2.16 (s, 6H, Me). 13C{ H} NMR (126 MHz, CD2Cl2,
1
298 K): d (ppm) = 170.1 (C N), 148.3 (dm, 1JFC ~ 241 Hz, C6F5),
1
1
147.9 (i-Ph), 140.6 (dm, JFC ~ 250 Hz, C6F5), 137.5 (dm, JFC
~
1
NPh). [t tentative assignment] 31P{ H} NMR (243 MHz, CD2Cl2,
250 Hz, C6F5), 130.3 (m-Ph), 128.0 (p-Ph), 123.5 (broad, o-Ph),
119.8 (Cp), 116.3 (broad, i-C6F5), n.o. (C N), 69.0 (CCN), 21.7
(Me). 19F NMR (470 MHz, CD2Cl2, 298 K): d (ppm) = -134.1 (m,
2F, o-C6F5), -157.6 (t, 3JFF = 20.3 Hz, 1F, p-C6F5), -164.4 (m, 2F,
298 K): d (ppm) = 28.1 (n1/2 ~ 2 Hz).
X-Ray crystal structure analysis of 6: C43H35Cl2N3P2Zr·
2CH2Cl2, M = 987.65, monoclinic, P21/c (No. 14), a = 10.2317(2),
◦
˚
1
m-C6F5). 11B{ H} NMR (160 MHz, CD2Cl2, 298 K): -10.6 ppm
b = 22.4233(4), c = 20.5016(5) A, b = 98.196(1) , V = 4655.61(17)
3
-3
-1
˚
A , Dc = 1.409 g cm , m = 0.684 mm , F(000) = 2008, Z = 4, l =
0.71073 A, T = 223(2)K, 26 608 reflections collected ( h, k, l),
[(sinq)/l] = 0.67 A , 10 825 independent (Rint = 0.051), and 8637
(n1/2 ~ 300 Hz).
˚
X-Ray crystal structure analysis of 4: C41H21BCl2F15N3Zr·
-1
˚
¯
C5H12, M = 1085.68, triclinic, P1 (No. 2), a = 10.7744(2), b =
observed reflections [I ≥ 2s(I)], 514 refined parameters, R = 0.080,
˚
12.2695(3), c = 18.4381(4) A, a = 101.946(1), b = 99.864(1), g =
wR2 = 0.199, GoF = 1.051.
◦
3
-3
-1
˚
91.168(2) , V = 2345.47(9) A , Dc = 1.537 g cm , m = 0.445 mm ,
˚
F(000) = 1088, Z = 2, l = 0.71073 A, T = 223(2)K, 20 491
reflections collected ( h, k, l), [(sinq)/l] = 0.67 A , 10 883
independent (Rint = 0.047), and 9090 observed reflections [I ≥
2s(I)], 615 refined parameters, R = 0.067, wR2 = 0.175, GoF =
1.096.
[(Bis(N-phenyldiphenylphosphinimino)acetonitrile)-tris-
(pentafluorophenyl)borate]-(g5-C5H5)ZrCl2 (7)
-1
˚
1 Equiv. of tris(pentafluorophenyl)borane (50 mg, 0.098 mmol in
1 mL of CH2Cl2) was added to a CH2Cl2 solution of 6 (80 mg,
1250 | Dalton Trans., 2012, 41, 1243–1251
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©

View Article Online
0.098 mmol). The reaction mixture was stirred for 2 h, filtered
through Celite and the volatiles were removed under vacuum,
washed with pentane. Compound 7 was isolated as light yellow
solid in 87% yield (113 mg, 0.085 mmol). The realization of NMR
experiments of compound 7 was difficult due to the poor solubility
of 7 in CD2Cl2. Additionally, the dynamic behavior of 7 in solution
resulted in complex NMR spectra (for details see the Supporting
Information†). Anal. Calcd for C61H35BCl2F15N3P2Zr: C, 55.09;
A.R.C. acknowledges Ph.D. CONICYT fellowship. G.E. ac-
knowledges support of this work by the Deutsche Forschungs-
gemeinschaft.
Notes and references
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H, 2.65; N, 3.16. Found: C, 54.96; H, 2.73; N, 3.36%. IR (KBr):
-1
˜
n/cm = 2260 (n(C N)).
X-Ray crystal structure analysis of 7: C61H35BCl2F15N3P2Zr·
¯
CH2Cl2, M = 1414.72, triclinic, P1 (No. 2), a = 11.2880(1), b =
˚
˚
13.1301(2), c = 20.3011(3) A, a = 87.214(1), b = 81.712(1), g =
◦
3
-3
-1
6 W. Kaminsky, A. Funck and H. Hahnsen, Dalton Trans., 2009, 8803–
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78.068(1) , V = 2912.57(7) A , Dc = 1.613 g cm , m = 0.520 mm ,
˚
F(000) = 1416, Z = 2, l = 0.71073 A, T = 223(2)K, 25 213 reflections
collected ( h, k, l), [(sinq)/l] = 0.67 A , 13 644 independent
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-1
˚
(Rint = 0.048), and 12 320 observed reflections [I ≥ 2s(I)], 793
refined parameters, R = 0.055, wR2 = 0.151, GoF = 1.052.
Typical homopolymerization of ethylene
Polymerizations were carried out in a Parr autoclave reactor
(100 mL), loaded inside a glovebox with an appropriate amount
(6.8 mmol) of the pre-catalyst (3, 4, 6 or 7) and the corresponding
MAO with toluene, such that the final volume of the toluene
solution was 30 mL. The reactor was sealed inside the glovebox
(when is indicated, MAO was put into the addition funnel).
The reactor was attached to an ethylene line and the gas was
fed continuously into the reactor to the pressures of 12.5 bar.
The pressurized reaction mixture was stirred at temperature of
75 ◦C. After 10 min, the ethylene was vented and acetone was
added to quench the polymerization. The precipitated polymer
was collected by filtration and dried overnight.
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Acknowledgements
Financial support from FONDECYT project N◦ 1100286,
Alexander von Humboldt Foundation auspices, through Experi-
ence Research Program to R.S.R. are gratefully acknowledged.
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This journal is
The Royal Society of Chemistry 2012
Dalton Trans., 2012, 41, 1243–1251 | 1251
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