Synthesis and structure of bifunctional zirconocene/borane complexes and their activation for ethylene polymerization

Article abstract of DOI:10.1021/om200536z

The potassium salt of 1 was transmetalated by reaction with (Cp-allyl)ZrCl₃(dme), yielding the complex (NC-nacnac)Cp- allylZrCl₂ (2). Addition of 1 molar equiv of B(C₆F ₅)₃ gave [(C₆F₅

Full text of DOI:10.1021/om200536z

Article
pubs.acs.org/Organometallics
Synthesis and Structure of Bifunctional Zirconocene/Borane
Complexes and Their Activation for Ethylene Polymerization
Rene S. Rojas,*,† Brian C. Peoples,† Alan R. Cabrera,† Mauricio Valderrama,† Roland Frohlich,‡,⊥
̈
Gerald Kehr,‡ Gerhard Erker,*,‡ Thomas Wiegand,§,∥ and Hellmut Eckert§,∥
†
́
́
Departamento de Quımica Inorganica, Facultad de Quımica, Pontificia Universidad Católica de Chile, Casilla 306, Santiago 22, Chile
́
‡Organisch-Chemisches Institut, Universitat Munster, Corrensstrasse 40, D-48149 Munster, Germany
§Institut fur Physikalische Chemie and Graduate School of Chemistry, Universitat Munster, Corrensstrasse 28/30, D-48149 Munster,
̈
̈
̈
̈
̈
̈
̈
Germany
S
* Supporting Information
ABSTRACT: The potassium salt of 1 was transmetalated by
reaction with (Cp-allyl)ZrCl3(dme), yielding the complex
(NC-nacnac)Cp-allylZrCl2 (2). Addition of 1 molar equiv of
B(C6F5)3 gave [(C6F5)3B-NC-nacnac]Cp-allylZrCl2 (3), and
the subsequent addition of 1 molar equiv of HB(C6F5)2 to 3
gave the hydroborated species [((C6F5)3B-NC-nacnac)Cp-(CH2)3-B(C6F5)2]ZrCl2 (4). The hydroboration of 2 with 1 molar
equiv of HB(C6F5)2 gave an insoluble product. This product was fully characterized by 11B and 13C solid-state NMR and IR,
which showed that the hydroboration followed by intermolecular adduct formation (R−B(C6F5)2- - -NC- - -R′) occurs, resulting
in an organometallic polymer (5). In addition to the CN-free [nacnac]Cp-allylZrCl2 (6), the hydroborated derivative
[(nacnac)Cp-(CH2)3-B(C6F5)2] (7) was also prepared. Complexes 2−7 were activated with methylaluminoxane (MAO) and
gave active catalysts for ethylene polymerization. The polymers produced were linear and had high molecular weight, with
polydispersities (PDI) of less than 2, indicating that the catalysts are single site. The presence of the allyl group on the Cp ring
was found to increase the molecular weight of the materials produced. In addition to discrete complexes, an organometallic
polymer (5) was formed. This compound is air stable and, while not very soluble, polymerizes ethylene with good activity.
Chart 1
INTRODUCTION
■
Homogeneous metallocene Ziegler−Natta catalysis1 and various
types of related “post-metallocene” catalysts usually require
specific activation by strongly Lewis acidic cocatalysts.2 The
most commonly applied activating reagents are methylaluminox-
anes. They usually serve two purposes, namely nucleophilic
methylation at the metal center combined with electrophilic
removal of a methyl anion equivalent generating a reactive alkyl
metal cation salt or ion pair, respectively, that starts the olefin
polymerization chain upon exposure to the olefin monomer. A
variety of related reagents were employed alternatively, including
at a simple catalyst precursor. We chose the complex system 4 (see
Scheme 1), which is closely related to III.12,13 It contains a B(C6F5)3
function coordinated to a cyano substituent at a conjugated position
of a nacnac ligand at zirconium combined with a −B(C6F5)2
function tethered to the adjacent Cp ring.14,15 We will see how the
combination of steric and electronic effects of these different boron-
centered functionalities will affect the olefin polymerization process
taking place after suitable activation.
3
4,5
B(C6F5)3 or various very bulky [R3C+][B(C6F5)4 ] salts.
−
Some Lewis acidic components can, however, carry out
additional functions, except direct activation, when added to a
suitable molecular Ziegler−Natta polymerization catalyst precur-
sor.6 They can be added to a Lewis base function at the metal
complex. This may make the metal center more electrophilic and
result in a more active catalyst at the activated stage but at the same
time serve as bulky substituents and influence the catalytic process
by that property. Complexes I in Chart 1 are typical examples.7−9
Lewis acidic centers can alternatively be covalently attached at the
core of the catalyst precursor by a suitable tether.10 Complex II in
Chart 1 is a typical example. The intramolecular Lewis acid may
become actively involved in the activation step but again may also
serve as a bulky substituent at the catalyst periphery. In this study
we have introduced both of these Lewis acid derived functionalities
RESULTS AND DISCUSSION
■
The synthesis of [π-(NC-nacnac)-η 5-allylcyclopentadienyl]-
zirconium dichloride types of precursors for reaction with boranes
was straightforwardly accomplished using commonly employed
transmetalation, hydroboration, and addition reactions, as outlined
in Scheme 1. The precursor [η5-(2-propenyl)cyclopentadienyl]-
zirconium trichloride dimethoxyethane was synthesized using
Received: June 22, 2011
Published: November 14, 2011
© 2011 American Chemical Society
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a
Scheme 1.
a
Legend: (i) n-BuLi, C4H8O; (ii) p-toluenesulfonyl cyanide, C4H8O; (iii) KH, C4H8O; (iv) (Cp-allyl)ZrCl3(dme), CH2Cl2, room temperature, 65%;
(v) B(C6F5)3, CH2Cl2, room temperature, 86%; (vi) HB(C6F5)2, CH2Cl2, room temperature, 87%; (vii) HB(C6F5)2, CH2Cl2, room temperature,
78%; (viii) KH, C4H8O; (ix) (Cp-allyl)ZrCl3(dme), CH2Cl2, room temperature, 85%; (x) HB(C6F5)2, toluene, room temperature, 87%.
Table 1. Selected Spectroscopic Parameters of the NC-nacnac Systems 2−7
2
3
4
5
6
7
δ(13C)
a
a
CNPh
168.0
72.7
171.6
63.9
170.8
63.9
170.9
161.7
161.3
a
CCN
64.4
CNAr
171.1
35.4
170.8
35.4
171.4
33.5
170.9
168.3
35.4
168.0
33.7
a
−CH2−(C6)
−CHCp‑allyl(C7)
CH2Cp‑allyl(C8)
33.6
137.0
116.4
136.5
116.7
137.7
115.8
δ(1H)
-CHCp‑allyl(7H)
CH2Cp‑allyl(8H)
HCiPr
6.01
5.05
3.36
2.76
2.27
2.30
1.33
1.20
1.17
0.91
5.97
6.02
5.05/5.03
3.21
5.03/5.01
3.63
3.26
2.58
1.88
1.81
1.25
1.15
0.92
0.59
3.90
2.72
1.76
1.56
1.44
1.18
1.01
0.72
2.78
2.69
MePh
MeAr
MeiPr
2.20
2.03
2.22
2.06
1.31
1.35
1.23
1.20
1.21
1.14
0.96
0.92
IR (cm−1
)
ν(CN)
2213
2280
2284
2279
a
From solid state NMR.
literature procedures.16 Subsequently, transmetalation with
1 molar equiv of the previously reported NC-nacnac
potassium salt12 (CH2Cl2, room temperature, 4 h) gave the
(NC-nacnac)Cp-allylZrCl2 complex 2, isolated as a light yellow
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Table 2. Selected Structural Parameters of the NC-nacnac Systems 2−4 and 6
2
3
4
6
Bond Distances (Å)
Zr−N(1)
Zr−C(3)
Zr−N(5)
Zr−C(2)
Zr−C(41)
Zr−C(4)
Zr−Cl(1)
2.286(2)
2.631(2)
2.220(2)
2.823(3)
2.525(2)
2.699(2)
2.4607(6)
2.4939(6)
1.298(3)
1.462(3)
1.439(3)
1.313(3)
1.438(3)
1.136(3)
2.322(3)
2.307(4)
2.688(5)
2.246(5)
2.867(5)
2.479(5)
2.763(5)
2.431(2)
2.454(2)
1.289(7)
1.473(7)
1.442(7)
1.301(7)
1.398(8)
1.143(7)
1.574(8)
1.531(13)
1.499(9)
1.486(10)
1.463(13)
2.270(2)
2.717(2)
2.154(2)
2.843(2)
2.543(3)
2.657(2)
2.4881(6)
2.5096(6)
1.305(3)
1.437(3)
1.396(3)
1.345(3)
-
2.611(3)
2.258(3)
2.869(3)
2.512(3)
2.721(3)
2.4740(9)
2.4372(9)
1.288(4)
1.482(4)
1.444(4)
1.310(4)
1.405(4)
1.143(4)
1.577(4)
Zr−Cl(2)
C(2)−N(1)
C(2)−C(3)
C(3)−C(4)
C(4)−N(5)
C(3)−C(7)
C(7)−N(8)
N(8)−B(1)
C(48)−B(2)
C(41)−C(46)
C(46)−C(47)
C(47)−C(48)
1.505(4)
1.478(4)
1.271(5)
1.501(6)
1.483(8)
1.145(12)
1.512(5)
1.420(6)
1.292(6)
Bond Angles (deg)
Cl(1)−Zr−Cl(2)
N(1)−C(2)−C(3)
C(2)−C(3)−C(4)
C(3)−C(4)−N(5)
C(3)−C(7)−N(8)
C(7)−N(8)−B(1)
Zr−C(41)-C(46)
C(41)−C(46)−C(47)
86.60(2)
117.1(2)
123.4(2)
116.9(2)
178.7(3)
87.95(3)
115.7(3)
86.80(6)
117.1(5)
123.8(5)
116.6(5)
178.2(6)
176.0(6)
122.7(4)
111.9(6)
85.22(2)
119.2(2)
125.2(2)
120.0(2)
121.8(3)
115.5(3)
175.8(4)
167.2(3)
121.0(2)
113.2(2)
120.7(3)
123.7(2)
115.0(3)
113.6(5)
Dihedral Angles (deg)
91.8(7)
C(42)−C(41)−C(46)−C(47)
C(41)−C(46)−C(47)−C(48)
C(46)−C(47)−C(48)−B(2)
88.2(4)
−92.8(9)
50.9(14)
175.6(4)
121.4(5)
−118.7(4)
−2.3(15)
−175.2(10)
solid in 65% yield. The 1H NMR spectrum features allyl signals
(−CH and CH2) as multiplets centered at δ 6.01 and
5.05 ppm (13C 137.0 and 116.4 ppm), respectively, and a pair
of MePh/MeAr resonances from the unsymmetrically substituted
NC-nacnac ligand core at δ 2.27/2.30 ppm (13C 21.8/
23.6 ppm). The isopropyl groups of the diisopropyl substituent
at N1 are different, giving rise to a pair of CHMe2 methine 1H
Scheme 2. Typical Pattern of Metal−nacnac
1
NMR resonances and a total of four corresponding H NMR
CH3 doublets. For further details see Table 1 and the
Supporting Information. The IR ν(CN) band of compound
2 was found at 2213 cm−1.
the exocyclic functionality (C−CN) oriented toward the
open-boat side of the (lig)ZrCl2 geometry. The plane that
contains the CN functionality is symmetrically located between
the Zr−Cl(1)/Zr−Cl(2) vectors.
Single crystals of complex 2 suitable for X-ray crystallography
were obtained by pentane diffusion into a toluene solution at
room temperature. The molecular connectivity shows a η5-like
coordination of the NC-nacnac ligand in an U-shaped form,
similar to the previously reported (NC-nacnac)CpZrCl2
complex.12 The Zr−N(1) bond (2.286(2) Å) is slightly longer
than the Zr−N(5) bond (2.220(2) Å) due to the substituted
phenyl ring on N(1). The Zr−C(3) bond distance of 2.631(2) Å
indicates a marked interaction. Moreover, the adjacent
Zr−C(2)/Zr−C(4) bond lengths are longer (see Table 2)
and, consequently, these interactions are considered weaker. This
typical pattern of metal−C/N bond length results in
a typical deviation of the NC-nacnac ligand from planarity
(see Scheme 2)17,3c,11a,c into the boat-shaped configuration in
complex 2 (see Figure 1) with the C(3)−C(7)−N(8) vector of
The allylcyclopentadienyl unit shows a typical η 5-Cp
coordination similar to that in the well-known constrained-
geometry compounds. Due to the allyl functionality, the Zr−
C(41) bond length of 2.525(2) Å is 0.036 Å longer than the
average of the unsubstituted Zr−CCp linkages ((NC-nacnac)-
CpZrCl2).12 In the projection the C(41)−C(46) vector bisects
the Zr−Cl(1)/Zr−Cl(2) angle in the σ-ligand plane.
Adduct formation proceeded smoothly upon treatment of 2 with
1 mol equiv of B(C6F5)3 to give [(C6F5)3B−NC-nacnac]Cp-allylZrCl2
(3) (see Scheme 1). Compound 3 was isolated in 86% yield.
NMR-scale experiments indicated that the adduct formation
occurred rapidly, essentially upon the mixing of the reagents.
This was shown by the immediate shift of, for example, the
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1H NMR (−CHCp‑allyl, CH2Cp‑allyl at δ 5.97 and 5.05/5.03 ppm,
respectively) and the complete dissolution of the normally only
partially soluble borane. As expected, the pair of C6F5 groups
on the tricoordinate planar boron atom (B2) (Figure 3)
Figure 3. 19F NMR (564 MHz, C6D6, 298 K) spectrum of
compound 4.
behaves in a symmetry-equivalent fashion in solution,
producing a single set of o-, p- and m-19F NMR resonances
at δ −130.3, −147.1, and −160.9 ppm, respectively. A single set
of C6F5 resonances at δ −133.8 (o), −156.2 (p), and −163.4
ppm (m) was observed for the B(C6F5)3 group coordinated to
the nitrile function (Figure 3).
Figure 1. Molecular structure of complex 2.
characteristic HCiPr and MeiPr resonances of the isopropyl
group in the 1H NMR (see Table 1 and the Supporting
Information). The ν(CN) IR band is shifted upon the
formation of the Lewis acid adduct from 2213 cm−1 in 2 to
2280 cm−1 in 3, as is typically observed in such a situation.12,18
The X-ray crystal structure analysis of 3 showed that the
B(C6F5)3 group is coordinated in a linear fashion to the NC-
nacnac ligand, with a C(7)−N(8)−B(1) bond angle of
167.2(3)°. The C(7)−N(7)−B(1)(C6F5)3 vector is oriented
toward the open side of the pseudo-metallocene wedge in 3
(see Figure 2).
Compound 4 was isolated by precipitation from a
concentrated toluene solution by the addition of pentane and
collected as a white solid in ca. 86% yield. Compound 4 is stable
at room temperature but is highly susceptible to coordination by
1 equiv of any Lewis base present in the system, and so donor
solvents are to be avoided when handling this compound.19
Single crystals suitable for the X-ray crystal structure
determination of 4 were obtained by diffusion of CH2Cl2/
pentane into a toluene solution at room temperature. In the solid
state, the (C6F5)3B−NC-nacnac fragment in complex 4 follows
the same coordination mode and boat-shaped configuration (see
Figures 4 and 5) as previously observed in this type of com-
pound,12 including compounds 2 and 3 (see Figures 1 and 2).
However, there are substantial increases in the Zr−C(2)/C(3)/
C(4) bond lengths compared to those in compounds 2 and 3,
consistent with a more crowded metal center (see Table 2).
Due to the geometric constraints in this type of system, the
attached −(CH2)3B(C6F5)2 side chain is oriented away from the
metal center with the trimethylene moiety resting in a position
which roughly bisects the Cl−Zr−Cl angle in the projection
(Figure 5). The −(CH2)3B(C6F5)2 chain is fully extended to
maximize the distance between the Zr center and the bulky
B(C6F5)2 group (see Figures 4 and 5). This orientation of the
−(CH2)3B(C6F5)2 fragment generates a B−Zr−B plane which
roughly bisects the bidentate ligand and the Cp ring. This
extended conformational arrangement is characterized by the
corresponding dihedral angles C(42)−C(41)−C(46)−C(47) =
−92.8(9)°, C(41)−C(46)−C(47)−C(48) = 50.9(14)°, and
C(46)−C(47)−C(48)−B(2) = −175.2(10)°.
Figure 2. Molecular structure of complex 3.
The allyl moiety on the Cp ring bisects the Cl(1)−Zr−Cl(2)
angle (see Figure 2) similar to that observed in 2. The Zr−C(3)
and Zr−C(41) distances in compound 3 are slightly shorter
compared to those in compound 2, while the Cl(1)−Zr−Cl(2)
angle is slightly larger. The double bond of the allyl
functionality is oriented perpendicular to the Cp plane.
Hydroboration of the olefinic group in the [(C6F5)3B-NC-
nacnac]Cp-allylZrCl2 (3) substrate with the HB(C6F5)2
reagent14d,e proceeds to completion essentially upon mixing
of the reagents, as indicated by the immediate disappearance of
characteristic olefinic resonances of the 2-propenyl group in the
The bifunctional complex 2 was reacted with 1 molar equiv
of [BH(C6F5)2]n in toluene or CH2Cl2 at room temperature
(see Scheme 1).20,14 The reaction took place rapidly and
proceeded to completion essentially upon mixing of the
reagents. After a few minutes a white solid precipitated,
which was collected by filtration and washed with fresh solvent
(CH2Cl2), to give 5 in a yield of 78%. The IR ν(CN) band of
compound 5 is found at 2279 cm−1, which suggests that the
boron interaction with the CN functionality is similar to that
observed for compounds 3 and 4. Unfortunately, the product of
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Figure 4. Molecular structure of complex 4.
this reaction was not soluble in organic solvents, which made
direct characterization by high-resolution spectroscopy in
solution or single-crystal X-ray crystallography impossible.
Therefore, the structure of polymer 5 was mainly characterized
by 11B and 13C solid-state NMR spectroscopy. Parts a and b of
Figure 6 show the 13C{1H} CPMAS spectra of the polymer 5
without and with dipolar dephasing, respectively. In the dipolar
dephasing (DD) experiments (see the Supporting Information,
Figure S9), only quaternary and methyl carbon atoms are
detected. On the basis of this spectral editing method, the
resonances of polymer 5 in the 23−34 ppm range are assigned
straightforwardly to various aliphatic CH3, CH2, and CH moieties.
Furthermore, the signal near ∼171 ppm is assigned to the imino
carbon atoms CNAr and CNPh, whereas the peak at 64 ppm
can be assigned to the quaternary carbon atom linked to the nitrile
group (CCN). The strong shielding of this signal in comparison to
that of the free ligand (82.1 ppm)12 can be attributed to strong
metal−carbon interactions and inductive effects resulting from the
intermolecular coordination of the Lewis acid −B(C6F5)2 to the
CN group. Such behavior had previously been observed for a
series of other zirconium complexes including the NC-nacnac
ligand, where it was also found that Zr complex formation leads to
a low-frequency shift of the discussed resonance that is enforced
by coordination of a Lewis acid to the nitrile group,12 as was
observed when the HB(C6F5)2 forms an adduct with the NC-
nacnac ligand (75.6 ppm).14a On the basis of the IR and NMR
results, we therefore conclude that dominant intermolecular Lewis
acid/base interactions are also present in this polymer constituting
the structural backbone of this material.
Figure 5. Side view of the slightly boat-shaped central core of complex 4.
The assignment of the CN resonance is, for example, based
on quantum-chemical calculations of chemical shifts on the
structurally comparable compound 3 (where in liquid-state
NMR (solvent CD2Cl2) the nitrile group could not be observed),
which reveal that the ipso carbons of the C6F5 ligand and the
nitrile carbons have very similar chemical shifts of about 117 ppm.
Moreover, the spinning sideband pattern in a slow-spinning
DD-CPMAS experiment (see Figure 7) clearly indicates that
this signal is composed of two contributions: one resonance at
120 ppm assigned to the ipso carbons of the C6F5 ligand and a
second contribution centered near 117 ppm, assigned to a nitrile
carbon having a nearly axially symmetric chemical shielding
anisotropy tensor. The individual principal axis components
extracted from simulations of the MAS NMR spinning sideband
intensity profiles are given in Table 3 and are in agreement with
previously reported CSA tensor elements for nitrile groups21 (i.e.
|Δσ| = 310 ppm for benzonitrile21b). Additional slow-spinning
DD-CPMAS studies and ab initio calculations of the CSA tensor
Figure 6. Comparison of the 13C{1H} CPMAS spectrum (9.4 T,
spinning frequency 10 kHz) of polymer 5 (a), the spectrum obtained
with dipolar dephasing for 56 μs (1/(2νrot)) (b), and the 13C{1H}
CPMAS spectrum of reference compound 3 (c). Spinning sidebands
are marked by asterisks.
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Figure 8. (a) (bottom) Experimental 11B MAS NMR spectrum
measured for polymer 5 at 9.4 T with H decoupling (TPPM-15)
Figure 7. 13C{1H} slow-spinning DD-CPMAS spectrum (d) of polymer
5 using a spinning speed of 4 kHz. The spectrum was acquired at 9.4 T.
Spinning sidebands for the resonance of interest at about 120 ppm are
marked with an asterisk. The simulated spinning sideband pattern (c)
indicates two contributions given in (a) and (b): the two ipso carbon
atoms of the C6F5 ligand at 120 ppm (a) and the nitrile carbon at
117 ppm (b). Simulated spectra are based on |Δσ| = 135.0 ppm and η =
0.35 for (a) and |Δσ| = 262.5 ppm and η = 0.05 for (b).
1
using a sample spinning frequency of 14 kHz and (top) simulation of
the central transition line shape, using δcs −7.4 ppm, CQ = 1.9 MHz,
and η = 0.58. (b) (bottom) Experimental 11B MAS NMR spectrum
measured for reference compound 3 at 11.7 T with a sample spinning
frequency of 14 kHz and (top) simulation of the central transition line
shape, using δcs −11.1 ppm, CQ = 1.7 MHz, and η = 0.16.
strongly distorted by three different types of ligands. The low-frequency
shift of the boron resonance also suggests a partially negatively
charged 4-fold-coordinated boron species and consequently argues
in favor of the formation of a Lewis acid/base adduct with the
nitrile group. Previous work has shown that trigonal alkyl boron
compounds obtained by hydroboration of several alkene substrates
with HB(C6F5)2 resonate typically near 70 ppm14,15 and that the
isotropic shifts for tricoordinated boron range between 0 and
120 ppm.23 In comparison, the more symmetric bonding in the
four-coordinated reference compound 3 leads to an EFG tensor
components for model compound 3 confirm these assignments
(see Table 3 and Figure S6).
Table 3. Experimental CSA Parameters Extracted from the
Slow-Spinning DD-CPMAS Spectrum Using the DMFIT22
a
Software
assignt
δ(13C) (ppm)
|Δσ| (ppm)
262.5a
η
5
5
3
3
3
3
3
CN 117.0a
i-C6F5 120.0a
CN 120.8a
i-C6F5 120.0a
i-C6F5 119.0a
CN 117.7b
0.05a
0.35a
0.04a
0.10a
0.30a
0.03b
135.0a
270.0a
181.0a
159.3a
247.4b
that is much closer to axially symmetric (δ cs −11 ppm, CQ
=
1.7 MHz, η = 0.16) (see Figure 8b). DFT calculations at a GGA
level yield CQ and η values of 1.8 MHz and 0.07, respectively, in
reasonable agreement with the experimental data. Nevertheless,
also in the case of compound 3 a distortion from axial symmetry is
observed due to the Lewis acid/base adduct formation, which
highlights the remarkable sensitivity of 11B MAS NMR to small
changes in the local environments of the boron nuclei.
i-C6F5 114.6b/115.1b/116.8b 145.7b/140.2b/146.4b 0.04b/0.14b/0.16b
a
Experimental (a) and theoretical DFT CSA parameters (b). The fol-
lowing convention is used: Δσ = σ33 − 1/2(σ11+ σ22), η = (σ22 − σ11)/
(σ33 − σiso), and |σ33 − σiso| > |σ11 − σiso| > |σ22 − σiso|. The
calculated values for the axiality of the CSA values are slightly
underestimated, presumably as a consequence of the chosen GGA level.
In principle, the strongly Lewis acidic borane might have
been able to form an adduct with the nitrile group. However,
on the basis of the insolubility of the final product, the
hydroboration of the pendant CC double bond takes
place first, followed by the intermolecular adduct formation
with the nitrile group, giving the organometallic polymer 5, as
shown in Scheme 1 and verified by 11B and 13C solid-state
NMR spectroscopy.
The related CN-free system (nacnac)Cp-allylZrCl2 (6) was
prepared for comparison. This complex was obtained by
deprotonation of the nacnacH ligand precursor with potassium
hydride followed by the reaction with Cp-allylZrCl3(dme) in
CH2Cl2 at ambient temperature (see Scheme 1). The complex
(nacnac)Cp-allylZrCl2 (6) was isolated as a pale yellow solid in
85% yield (see the Experimental Section and the Supporting
Information for its characterization).
The proposed peak assignments can be justified further by
comparison with the structurally related compound 3, for which
the 13C NMR peak assignment has been successfully achieved
by liquid-state NMR, solid-state NMR, and ab initio calculations
of magnetic shieldings (see Table S3 and Figure S4, Supporting
Information). In addition to small changes in the chemical shifts
for some carbon sites (e.g., the central carbon of the conjugated
enamino heterocarbonyl system; see Figure 6c) a significant
broadening of the 13C peaks is observed in case of polymer 5,
presumably resulting from a lower degree of crystallinity as often
observed in polymeric systems.
1
The 11B MAS NMR spectrum acquired with H TPPM-15
decoupling of polymer 5 (see Figure 8a) shows a single resonance
affected by anisotropic second-order quadrupolar perturbations.
The simulation of this spectrum yields an isotropic chemical shift
of −7.4 ppm, a quadrupolar coupling constant CQ of 1.9 MHz,
and an electric field gradient asymmetry parameter η of 0.58,
indicating a four-coordinated boron atom whose environment is
Complex 6 was characterized by X-ray diffraction. It features
a typical constrained geometry with independent Cp-propenyl
and nacnac ligands bound to the Zr center. The −CH2CH
CH2 unit was found oriented toward the front side of the bent
nacnac/Cp wedge. The observed conformational arrangement
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Organometallics
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a
of the propenyl unit in the crystal is almost coplanar with
the Cp ring, with the ZrCl2 side spatially open (see Figure 9;
Table 4. Selected Ethylene Polymerization Reactions
b
c
c
d
entry
complex no.
activity
Mn
Mw
PDI
Tm
1
2
3
4
5
6
7
8
9
ref
2
1520
1109
1061
1037
966
99
185
144
157
161
144
172
171
175
342
295
302
306
282
310
313
1.8
1.8
2.1
1.9
1.9
2.0
1.8
1.8
135
136
135
135
135
135
135
136
135
3
4
5
e
5
1080
1115
630
f
5
6
7
780
a
Polymerizations were carried out in a 100 mL autoclave reactor with
6.8 μmol of Zr in 30 mL of toluene and 178 psi of ethylene pressure.
The cocatalyst was MAO (the Al/Zr ratio was 500/1). The duration of
the reaction was 10 min, and the temperature of the reaction was
b
c
d
75 °C. Activity in kg of polymer/((mol of Zr) h). 103 g/mol. In °C.
e
Exposed to the air as a solid for 17 h, before addition into the reactor
Exposed to the air as a solid for 28 h, before addition into the reactor.
f
Surprisingly, the molecular weight of the materials increased
significantly, which may be an indication that the presence of the
allyl or the alkyl-B(C6F5)2 functionalities retard termination of the
growing polymer chain. Under these conditions all of the
complexes show similar polymerization activities and molecular
weights of the materials produced (entries 2−4). In addition all of
the complexes have a PDI less than 2, which is an indication that
the systems are single site. No additional effect was observed in the
polymerizations of the presence of the alkyl-B(C6F5)2 group on
the Cp ring (hydroborated complex 4) (entry 4) that has an
activity and molecular weight distribution which is similar to
that observed in complexes 2 and 3. The polymerization
behavior of complex 5 shows perhaps the most interesting
behavior of all the complexes. Using the same conditions as for
the other complexes, it gave similar activities and molecular
weights. When the complex was exposed to air prior to the
polymerization reaction (for 17 or 28 h), there was no change
in the polymerization activity or in the molecular weight of the
polymer produced, whereas when the other complexes were
exposed to air, no polymer was produced. This is most likely
due to the polymeric nature of the complex due to the R−
B(C6F5)2- - -NC- - -R′ intermolecular interactions, which stabil-
izes the structure and prevents side reactions at boron. In
addition, the structure likely limits oxygen access to the Zr
metal center, hindering the decomposition process.
Figure 9. Molecular structure of complex 6.
dihedral angles C(42)−C(41)−C(46)−C(47) = 175.6(4)° and
C(41)−C(46)−C(47)−C(48) = 121.4(5)°).
The nacnac ligand is in a boat conformation, as was observed
in compounds 2−4. However, the C(3) (methine unit in Figure 9)
is 0.086 Å farther away from the zirconium in comparison with
the case for complex 2 (Zr−C(3) = 2.717(2) and 2.631(2) Å,
respectively).
Hydroboration of 6 proceeded smoothly upon treatment with
1 equiv of HB(C6F5)2,14 yielding compound 7 (Scheme 1). Like
the hydroboration of other olefinic substrates including
compounds 2 and 3 with HB(C6F5)2, the reaction proceeded to
completion essentially upon mixing of the reagents, as indicated by
the immediate disappearance of characteristic olefinic resonances
1
Cp‑allyl
of the 2-propenyl group in the H NMR, −CH
and 
CH2Cp‑allyl at 6.02 and 5.03/5.01 ppm, respectively (for more
details see the Supporting Information). Complex 7 shows a
broad 11B NMR resonance at ca. δ +74 ppm, which is
characteristic for trigonal alkyl boron compounds obtained by
hydroboration of alkene substrates,10d,e and three typical 19F NMR
signals corresponding to the pair of symmetry-equivalent C6F5
substituents at boron (δ −130.1 (o), −147.8 (p), −161.1 ppm (m)).
1
The H/13C NMR spectra show the presence of two non-
Entries 8 and 9, which refer to reactions with complexes 6
and 7, respectively, illustrate the importance of the CN in the
ligand backbone. Comparison of entry 8 with entry 2 shows
that the presence of the CN increases the polymerization
activity significantly (ca. 470 kg of polymer/((mol of Zr) h)).
At the same time, entry 9 allows the evaluation of the effect of
the −(CH2)3−B(C6F5)2 interaction on the polymerization
activity, which resulted in an increase of ca. 150 kg of polymer/
((mol of Zr) h) over entry 8. These results indicate that, while
the bidentate imine ligand has a dominant effect on the
electronic environment of the catalyst system, the Cp allyl
ligand has a marked effect on the molecular weight.
equivalent isopropyl groups of the diisopropylphenyl substituent
1
at N1, giving rise to a pair of CHMe2 methine H NMR
resonances at δ 3.90/2.72 ppm (13C 27.6/27.4 ppm) and a total
1
of four corresponding H NMR CH3 doublets. For further
details see Table 1 and the Supporting Information.
Ethylene Polymerization. A series of ethylene polymer-
ization reactions were carried out using compounds 2−7 under
specific reaction conditions, with MAO as the coactivator
(Table 4). In all cases, one observes the formation of high-
molecular-weight PE with a melting point of ca. 136 °C,
indicating that the material is linear. Entry 1 shows the behavior
of the (NC-nacnac)CpZrCl2/MAO system under these reaction
conditions. Comparison with complexes 2−4 under the same
conditions (entries 2−4) shows that the addition of the allyl
substituent to the cyclopentadienyl ring results in a decrease in
activity of ca. 20%. This was not unexpected as the allyl (2) and
alkyl-B(C6F5)2 moieties increase the steric environment around
the zirconium metal center, reducing the rate of polymerization.
CONCLUSION
■
In this contribution, zirconium complex 2 bearing both a
nacnac-CN and a Cp-allyl ligand was synthesized and
characterized. As this compound bears two functional groups
which are available for reaction with Lewis acids, it was decided
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compound 2 suitable for X-ray crystal structure analysis were grown by
diffusion of pentane into toluene at room temperature. Anal. Calcd for
C32H37Cl2N3Zr (M = 625.79): C, 61.42; H, 5.96; N, 6.71. Found: C,
to explore the modification of the compound via the controlled
reaction with soluble Lewis acids. Derivatives of 2 selectively
bearing a Lewis acid function tethered to the Cp ring or
coordinated to the nacnac-CN ligand or both were isolated. In
addition an organometallic polymer was obtained upon the
selective hydroboration of the allyl functionality in 2. A detailed
analysis of these complexes was undertaken, and single-crystal
X-ray crystal structures were obtained for all complexes except
5, which was characterized by solid-state MAS NMR spectros-
copy. The solid-state NMR spectra of 5 show that the
organometallic monomers are connected by interaction of the
Cp-tethered B(C6F6)2 Lewis acid with the cyano functionality
in the nacnac-CN ligand backbone. These complexes were
activated for ethylene polymerization by MAO. In addition, it
was found that the organometallic polymer showed an unusual
stability in air and was able to polymerize ethylene even after
exposure to air for 28 h. The presence of the two distinct
functionalities and the ability to selectively form Lewis acid
adducts allowed for the evaluation of the effect of these
groups on the polymerization activity and polymer properties.
It was found that the Cp group affected the molecular weight
of the materials more so than the bis-imine ligand, whereas
changes to the bis-imine ligand were found to affect the
polymerization activity more than changes to the Cp ligand.
Finally, we are particularly intrigued by the air stability of the
organometallic polymer 5, and future work will be conducted
using this complex to evaluate how this stability can best be
taken advantage of.
1
61.77; H, 6.09; N, 6.58. IR (KBr): ν
̃
NMR (600 MHz, CD 2 Cl 2 , 298 K): δ/ppm 7. 51
(m, 2H, m-Ph), 7.37 (m, 1H, p-Ph), 7.36 (m, 2H, p,m-Ar), 7.24 (m,
1H, m′-Ar), 7.19 (br, 2H, o-Ph), 6.36 (m, 1H, 2-H), 6.31 (m, 1H,
5-H), 6.01 (m, 1H, 7-H), 5.90 (m, 1H, 4-H), 5.71 (m, 1H, 3-H), 5.05
(m, 2H, 8-H), 3.63 (m, 2H, 6-H), 3.36 (hept, 3J = 6.8 Hz, 1H,
HCiPr(o)), 2.76 (hept, J = 6.7 Hz, 1H, HCiPr(o′)), 2.30 (s, 3H, MeAr),
3
2.27 (s, 3H, MePh), 1.33 (d, J = 6.8 Hz, 3H, MeiPr(o)), 1.20 (d, J =
3
6.8 Hz, 3H, MeiPr(o)′), 1.17 (d, J = 6.7 Hz, 3H, MeiPr(o′)), 0.91 (br d,
3
3J = 6.7 Hz, 3H, MeiPr(o′)′). 13C{1H} NMR (151 MHz, CD2Cl2, 298
K): δ/ppm 171.1 (CNAr), 168.0 (CNPh), 148.6 (i-Ph), 143.2
(i-Ar), 143.1 (o-Ar), 140.7 (o′-Ar), 137.0 (C7), 135.8 (C1), 129.8
(m-Ph), 128.5 (p-Ar), 127.2 (p-Ph), 126.3 (m-Ar), 124.5 (m′-Ar),
124.0 (br, o-Ph), 119.0 (C2), 118.8 (C5), 118.5 (C3), 116.6 (C4),
116.4 (C8), 72.7 (CCN), 35.4 (C6), 28.1 (HCiPr(o′)), 27.8 (HCiPr(o)),
25.9 (MeiPr(o)), 25.1 (MeiPr(o′)′), 24.5 (MeiPr(o)′), 23.6 (MeAr), 22.8
(MeiPr(o′)), 21.8 (MePh), n.o. (CN).
Compound 3. One equivalent of tris(pentafluorophenyl)borane
(147 mg in 1 mL of CH2Cl2, 0.29 mmol) was added to a CH2Cl2
solution of 2 (180 mg, 0.29 mmol). The reaction mixture was stirred
for 4 h and filtered over Celite, and the volatiles were removed under
vacuum, washed with 10 mL of toluene/pentane (1/1), and then
washed with pentane (5 mL). Compound 3 was isolated as a colorless
solid in 86% yield (281 mg, 0.247 mmol). Single crystals suitable for
X-ray crystal structure analysis were grown by evaporation of a C6H6
solution of compound 3 at room temperature. IR (KBr): ν̃
/cm−1 2280
(ν(CN), s). Anal. Calcd for C50H37BCl2F15N3Zr (M = 1137.77): C,
1
52.78; H, 3.28; N, 3.69. Found: C, 52.60; H, 3.76; N, 3.83. H NMR
(500 MHz, CD2Cl2, 298 K): δ/ppm 7.55 (m, 2H, m-Ph), 7.42 (m, 1H,
p-Ph), 7.40 (m, 2H, m-, p-Ar), 7.29 (m, 1H, m′-Ar), 7.20 (br, 2H,
o-Ph), 6.36 (m, 1H, 2-H)t, 6.33 (m, 1H, 5-H)t, 5.97 (m, 1H, 7-H), 5.93
(m, 1H, 4-H)t, 5.75 (m, 1H, 3-H)t, 5.05 (dm, 3J = 10.1 Hz, 1H, 8-H),
5.03 (dm, 3J = 16.8 Hz, 1H, 8-H), 3.60 (m, 2H, 6-H), 3.21 (hept, 3J =
EXPERIMENTAL SECTION
■
General Remarks. 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. 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: 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, 192 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
Nonius KappaCCD diffractometers, in the case of Mo radiation
equipped with a rotating anode generator. Programs used: data
collection COLLECT,31 data reduction Denzo-SMN,32 absorption
correction SORTAV33 and Denzo,34 structure solution SHELXS-97,35
structure refinement SHELXL-97,36 graphics XP37 and SCHAKAL.38
R1 values are given for the observed reflections and wR2 values for all
reflections. CCDC 818691−818694 contain the supplementary
crystallographic data for this paper. These data can be obtained free
of charge at www.ccdc.cam.ac.uk/conts/retrieving.html (or from the
Cambridge Crystallographic Data Centre, 12 Union Road, Cambridge
CB2 1EZ, U.K.; fax, (internat.) +44(1223)336-033; e-mail, deposit@
ccdc.cam.ac.uk).
3
6.8 Hz, 1H, HCiPr(o)), 2.78 (hept, J = 6.8 Hz, 1H, HCiPr(o′)), 2.22 (s,
3
3H, MeAr)t, 2.20 (s, 3H, MePh)t, 1.31 (d, J = 6.8 Hz, 3H, MeiPr(o)),
1.23 (d, 3J = 6.8 Hz, 3H, MeiPr(o′)), 1.21 (d, 3J = 6.8 Hz, 3H, MeiPr(o)′),
0.96 (d, 3J = 6.8 Hz, 3H, MeiPr(o′)′), (t, tentative assignment). 13C{1H}
NMR (126 MHz, CD2Cl2, 298 K): δ/ppm 171.6 (CNPh)t, 170.8
1
1
(CNAr)t, 148.3 (dm, JFC ≈ 243 Hz), 140.5 (dm, JFC ≈ 250 Hz),
1
137.5 (dm, JFC ≈ 248 Hz) (C6F5), 147.4 (i-Ph), 142.7 (o-Ar), 142.0
(i-Ar), 140.1 (o′-Ar), 137.1 (C1), 136.5 (C7), 130.2 (m-Ph), 129.2
(p-Ar), 128.0 (p-Ph), 126.7 (m-Ar), 124.7 (m′-Ar), 123.4 (br, o-Ph),
119.8 (C2,5)t, 119.6 (C3)t, 117.5 (C4)t, 116.7 (C8), 116.4 (br,
i-C6F5), 63.9 (CCN), 35.4 (C6), 28.4 (HCiPr(o′)), 28.0 (HCiPr(o)), 26.1
(MeiPr(o)), 25.4 (MeiPr(o′)′), 24.1 (MePh), 23.8 (MeiPr(o)′), 22.5
(MeiPr(o′)), 22.2 (MeAr), n.o. (CN) (t, tentative assignment). 19F
NMR (564 MHz, CD2Cl2, 298 K): δ/ppm −134.1 (m, 2F, o-C6F5),
3
−157.8 (t, JFF = 20.3 Hz, 1F, p-C6F5), −164.5 (m, 2F, m-C6F5),
(Δδ(19Fm,p) = 6.8). 11B{1H} NMR (192 MHz, CD2Cl2, 298 K): δ/
ppm −10.6.
Compound 4. One equivalent of bis(pentafluorophenyl)borane
(50 mg in 1 mL of toluene, 0.14 mmol) was added to a toluene
suspension of 3 (160 mg, 0.14 mmol). The reaction mixture was
stirred for 4 h, and then the volatiles were removed under vacuum,
washed with pentane (10 mL), and removed; fresh pentane was added
(10 mL), and this mixture was stirred for 12 h. After this time, the
solid was decanted, more fresh pentane was added (10 mL), and
this mixture was stirred for an additional 12 h. A white solid
(182 mg, 0.123 mmol) corresponding to compound 4 was recovered
by filtration in 87% yield. Single crystals suitable for X-ray crystal
structure analysis were grown by diffusion of CH2Cl2 / pentane into
Compound 2. A solution of the potassium salt of 1 (910 mg,
1.94 mmol) in CH2Cl2 (5 mL) was added to trichloro(η 5-allyl-
cyclopentadienyl)zirconium−dme (dme = dimethoxyethane) (760 mg,
1.93 mmol) in CH2Cl2. The reaction mixture was stirred for 4 h. The
resulting orange solution was filtered over Celite. The solvent volume
was reduced, and pentane and ether were added separately to wash the
solid. A light yellow powder corresponding to compound 2 was
isolated in 65% yield (815 mg, 1.25 mmol). Single crystals of
a toluene solution at room temperature. IR (KBr): ν
̃
/cm−1 2284
(ν(CN), s). Anal. Calcd for C62H38B2Cl2F25N3Zr (M = 1483.71):
1
C, 50.19; H, 2.58; N, 2.83. Found: C, 50.58; H, 2.90; N, 3.03. H
NMR (600 MHz, C6D6, 298 K): δ/ppm 7.07 (m, 1H, m-Ph), 7.02
(m, 2H, m-, p-Ar), 6.96 (m, 3H, p-, o-Ph), 6.87 (m, 1H, m′-Ar), 6.21
(m, 1H, 2-H)t, 6.14 (m, 1H, 5-H)t, 5.71 (m, 1H, 4-H)t, 5.53 (m, 1H,
6379
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3-H)t, 3.26 (hept, 3J = 6.6 Hz, 1H, HCiPr(o)), 2.85 (m, 2H, 6-H), 2.58
(s, 3H, MePh), 1.56 (s, 3H, MeAr), 1.44 (d, 3J = 6.7 Hz, 3H, MeiPr(o)),
1.18 (d, 3J = 6.7 Hz, 3H, MeiPr(o)′), 1.01 (d, 3J = 6.8 Hz, 3H, MeiPr(o′)),
3
(hept, J = 6.8 Hz, 1H, HCiPr(o′)), 1.88 (s, 3H, MePh), 1.81 (s, 3H,
3
0.72 (d, J = 6.8 Hz, 3H, MeiPr(o′)′). 13C{1H} NMR (126 MHz, C6D6,
3
MeAr), 1.76 (m, 2H, 8-H), 1.70 (m, 2H, 7-H), 1.25 (d, J = 6.6 Hz,
298 K): δ/ppm 168.0 (CNAr), 161.3 (CNPh), 150.3 (i-Ph), 144.7
(i-Ar), 143.7 (o-Ar), 141.3 (o′-Ar), 135.7 (C1), 129.1 (m-Ph), 127.7
(p-Ar), 126.2 (p-Ph), 125.8 (m-Ar), 124.5 (br, o-Ph), 124.0 (m′-Ar),
117.2 (C2), 116.8 (C5), 116.6 (C3), 114.8 (C4), 90.9 (CH), 33.7 (C-6),
32.2 (br, C-8), 27.6 (HCiPr(o)), 27.4 (HCiPr(o′)), 26.1 (C-7), 25.9
(MeiPr(o)), 24.8 (MeiPr(o′)′), 24.5 (MeiPr(o)′), 23.4 (MeAr), 23.2
3H, MeiPr(o)), 1.15 (d, 3J = 6.6 Hz, 3H, MeiPr(o)′), 0.92 (d, 3J = 6.8 Hz,
3H, MeiPr(o′)), 0.59 (d, 3J = 6.8 Hz, 3H, MeiPr(o′)′) (t, tentative
assignment). 13C{1H} NMR (151 MHz, C6D2, 298 K): δ/ppm 171.4
(CNAr), 170.8 (CNPh), 147.3 (i-Ph), 142.7 (o-Ar), 141.8 (i-Ar),
139.6 (o′-Ar), 138.2 (C1), 129.7 (m-Ph), 129.0 (p-Ar), 127.6 (p-Ph),
126.6 (m-Ar), 124.1 (m′-Ar), 123.1 (o-Ph), 118.8 (C5), 118.79,
118.78 (C2,3), 116.4 (C4), 63.9 (CCN), 33.5 (C6), 31.6 (br, C8),
27.9 (HCiPr(o′)), 27.8 (HCiPr(o)), 26.1 (MeiPr(o)), 25.9 (C7), 25.2
(MeiPr(o′)′), 23.5 (MeiPr(o)′), 23.3 (MeAr), 22.2 (MeiPr(o′)), 21.5 (MePh),
n.o. (CN) (C6F5 not listed). 19F NMR (564 MHz, C6D6, 298 K):
(MeiPr(o′)), 22.9 (MePh) (C6F5 not listed). 19F NMR (470 MHz,
3
C6D6, 298 K): δ/ppm −130.1 (m, 2F, o-(C6F5)), −147.8 (t, JFF
=
19.4 Hz, 1F, p-(C6F5)), −161.1 (m, 2F, m-(C6F5)) (Δδ(19Fm,p) =
13.4).
3
Homopolymerization of Ethylene. Polymerizations were car-
ried out in a Parr autoclave reactor (100 mL), loaded inside a glovebox
with an appropriate amount (6.8 μmol) of the precatalyst (2−7) 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. The reactor was attached to an ethylene line, and the gas was
fed continuously into the reactor to a pressure of 178 psi. The
pressurized reaction mixture was stirred at 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.
δ/ppm −130.3 (m, 4F, o-F), −147.1 (t, JFF = 20.4 Hz, 2F, p-F),
−160.9 (m, 4F, m-F) (B(C6F5)2) (Δδ(19Fm,p) = 13.8), −133.8 (m, 6F,
3
o-F), −156.2 (t, JFF = 20.7 Hz, 3F, p-F), −163.4 (m, 6F, m-F)
(B(C6F5)3) (Δδ(19Fm,p) = 7.2).
Compound 5. One equivalent of bis(pentafluorophenyl)borane
(83 mg in 1 mL of CH2Cl2, 0.24 mmol) was added to a solution of 2
in CH2Cl2 (150 mg, 0.24 mmol). After a few minutes a white solid
started to precipitate, and the reaction mixture was stirred for 4 h. A
white solid corresponding to compound 5 was recovered by filtration
and washed several times with fresh CH2Cl2; 78% yield (181 mg, 0.186
mmol). Compound 5 was insoluble in noncoordinating solvents. IR
/cm−1 2279 (ν(CN), s). Anal. Calcd for C62H38
Polymer Characterization. Polymers were dried overnight under
vacuum, and the polymerization activities were calculated from the
mass of product obtained. These values were to within 5% of the
calculated mass determined by measuring the ethylene consumed by
use of a mass flow controller. The polymers were characterized by gel
permeation chromatography (GPC). GPC analysis was performed on
a Waters Alliance GPC 2000 system equipped with a refractive index
detector. Samples were run at 150 °C in spectrophotometric grade
1,2,4-trichlorobenzene (TCB), stabilized with BHT (0.5 g of BHT/4 L
of solvent). Molecular weights were calculated by using a universal
calibration from narrow polystyrene standards in the molecular weight
range of 580−7 500 000. Mark−Houwink parameters of a = 0.7 and
k = 47.7 were utilized to correct for polyethylene. Polymer melting
points were measured on a TA Instruments differential scanning
calorimeter (model DSC 2920) at a rate of 10 °C/min for two cycles
in the temperature range 25−200 °C.
(KBr): ν
̃
B2Cl2F25N3Zr (M = 1483.71): C, 54.39; H, 3.94; N, 4.32. Found: C,
52.07; H, 3.65; N, 4.05.
Compound 6. The potassium salt of 2-(2,6-diisopropylphenyl)-
aminopent-2-en-4-(phenyl)imine (200 mg, 0.45 mmol) in 5 mL of
CH2Cl2 was added to trichloro(η5-allylcyclopentadienyl)zirconium−
dme (dme = dimethoxyethane; 177 mg, 0.45 mmol) in CH2Cl2.
The reaction mixture was stirred for 4 h at room temperature.
The resulting orange solution was filtered over Celite. The solvent
volume was reduced, and pentane and ether were added separately
to wash the solid. A light yellow powder corresponding to compound
7 was isolated in 85% yield (230 mg). Single crystals suitable for
X-ray crystal structure analysis were obtained by slow diffusion of
pentane into CH2Cl2 at room temperature. Anal. Calcd for
(C31H38Cl2N2Zr)3CH2Cl2 (M = 2488.04): C, 59.82; H, 6.20; N,
4.45. Found: C, 59.40; H, 6.14; N, 4.46. 1H NMR (500 MHz, CD2Cl2,
298 K): δ/ppm 7.46 (m, 2H, m-Ph), 7.32 (m, 2H, m-, p-Ar), 7.30 (m,
1H, p-Ph), 7.22 (br, 2H, o-Ph), 7.20 (m, 1H, m′-Ar), 6.32 (m, 1H, 2-
H), 6.26 (m, 1H, 5-H), 6.02 (ddt, 3JH,H = 16.9, 10.2, 6.5 Hz, 1H, 7-H),
5.88 (m, 1H, 4-H), 5.74 (m, 1H, 3-H), 5.67 (s, 1H, CH), 5.03 (dm,
Solid-State MAS NMR Spectroscopy. 11B and 13C{1H} CPMAS
spectra were recorded at resonance frequencies of 160.5 MHz (128.4
MHz) and 100.6 MHz, respectively, on Bruker DSX 500 and
BRUKER Avance DSX 400 spectrometers, equipped with a 4 mm
NMR double-resonance probe operating at MAS rotation frequencies
of 4−14 kHz. Typical acquisition parameters for single-pulse and
CPMAS measurements: 0.6 μs (30° flip angle) for 11B and 5 μs for 1H
(90° flip angle) with a contact time of 5 ms within the CP step; recycle
3
3JH,H = 16.9 Hz, 1H, 8-H), 5.01 (dm, JH,H = 10.2 Hz, 1H, 8-H), 3.63
3
(hept, 3J = 6.6 Hz, 1H, HCiPr(o)), 3.61 (m, 2H, 6-H), 2.69 (hept, J =
6.8 Hz, 1H, HCiPr(o′)), 2.06 (s, 3H, MeAr), 2.03 (s, 3H, MePh), 1.35 (d,
3J = 6.6 Hz, 3H, MeiPr(o)), 1.20 (d, 3J = 6.6 Hz, 3H, MeiPr(o)′), 1.14 (d,
3J = 6.8 Hz, 3H, MeiPr(o′)), 0.92 (d, 3J = 6.8 Hz, 3H, MeiPr(o′)′).
13C{1H} NMR (126 MHz, CD2Cl2, 298 K): δ/ppm 168.3 (CNAr),
161.7 (CNPh), 150.0 (i-Ph), 144.6 (i-Ar), 143.6 (o-Ar), 141.6
(o′-Ar), 137.7 (C7), 134.2 (C1), 129.4 (m-Ph), 127.8, 126.4 ((p-Ar,
p-Ph), 125.8 (m-Ar), 124.6 (br, o-Ph), 124.3 (m′-Ar), 118.0 (C2),
117.4 (C5), 117.1 (C3), 115.8 (C8), 115.5 (C4), 90.4 (CH), 35.4
(C-6), 27.8 (HCiPr(o′)), 27.7 (HCiPr(o)), 25.8 (MeiPr(o)), 25.0 (MeiPr(o′)),
24.6 (MeiPr(o)′), 24.1 (MeAr), 23.29 (MePh), 23.27 (MeiPr(o′)′).
1
delay 4 s for 11B and 5 s in the 13C{1H} CPMAS experiments. H
decoupling was achieved by applying the TPPM-15 decoupling
scheme.24 11B and 13C{1H} NMR chemical shifts are referenced to a
BF3·Et2O standard and to TMS, respectively, in the latter case using
adamantane (δ(CH2) 38.56 ppm for the methylene resonance as a
secondary standard). For more experimental details see the Supporting
Information.
DFT Calculations. All computations have been performed
using the program packages TURBOMOLE25 and GAUSSIAN.26
13C magnetic shieldings and CSA tensor elements were calculated on a
GGA level of theory by using the BP-86 functional27 and the def2-
TZVP28 basis set (for zirconium the all-electron basis set
TZVPPalls229 was applied). EFGs were calculated with the B97-D30
functional and a slightly modified def2-TZVP basis set. For more
technical details of the computations see the Supporting Information.
Compound 7. One equivalent of bis(pentafluorophenyl)borane
(58 mg in 1 mL of toluene, 0.17 mmol) was added to a toluene
suspension of 6 (100 mg, 0.17 mmol). The reaction mixture was
stirred for 4 h, and then the volatiles were removed under vacuum and
the residue washed with pentane. A 137 mg amount of a light yellow
1
solid corresponding to compound 7 was collected in 87% yield. H
NMR (500 MHz, C6D6, 298 K): δ/ppm 7.29 (br, 2H, o-Ph), 7.16 (m,
2H, m-Ph), 7.13 (dd, 3J = 7.7 Hz, 4J = 1.6 Hz, 1H, m-Ar), 7.07 (t, 3J =
7.7 Hz, 1H, p-Ar), 6.99 (m, 1H, p-Ph), 6.95 (dd, 3J = 7.7 Hz, 4J = 1.6
Hz, 1H, m′-Ar), 6.50 (m, 1H, 2-H), 6.38 (m, 1H, 5-H), 5.92 (m, 1H,
ASSOCIATED CONTENT
■
S
* Supporting Information
Text, figures, and CIF files giving further experimental and
spectroscopic details and crystallographic data. This material is
available free of charge via the Internet at http://pubs.acs.org.
3
4-H), 5.79 (m, 1H, 3-H), 5.22 (s, 1H, CH), 3.90 (hept, J = 6.7 Hz,
1H, HCiPr(o)), 3.21 (m, 2H, 6-H), 2.72 (hept, 3J = 6.8 Hz, 1H,
HCiPr(o′)), 2.03/1.96 (each m, each 1H, 7-H), 1.96 (m, 2H, 8-H), 1.76
6380
dx.doi.org/10.1021/om200536z|Organometallics 2011, 30, 6372−6382

Organometallics
Article
Sobolev, A. N.; White, A. H.; Keim, W. J. Organomet. Chem. 1997, 544,
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Bochmann, M. Organometallics 2005, 24, 3792. (f) Rojas, R. S.; Galland,
G. B.; Wu, G.; Bazan, G. C. Organometallics 2007, 26, 5339. (g) Song,
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AUTHOR INFORMATION
Corresponding Author
*E-mail: rrojasg@uc.cl (R.S.R.); erker@uni-muenster.de
(G.E.).
■
Author Contributions
⊥X-ray crystal structure analyses.
̃
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Author Contributions
∥Solid-state NMR.
ACKNOWLEDGMENTS
■
Financial support from the FONDECYT Project No. 1100286,
Alexander von Humboldt Foundation auspices, through
Experience Research Program, to R.S.R. is gratefully acknowl-
edged. B.C.P. acknowledges funding from Pontificia Uni-
versidad Catolica de Chile via VRI No. 2 2010. A.R.C.
acknowledges a Ph.D. CONICYT fellowship. We thank
Professor Stefan Grimme for his support with the DFT
calculations. T.W. thanks the NRW Graduate School of
Chemistry for additional support and the Fonds der
Chemischen Industrie for a personal fellowship. G.E. acknowl-
edges the support of this work by the Deutsche Forschungsge-
meinschaft.
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