Copolymerization of sterically demanding phosphine-olefins and 1-hexene

Article abstract of DOI:10.1139/V09-120

The copolymerization of 1-hexene with f-Bu₂P(CH ₂)₃CH=CH₂ (1) or f-Bu₂P(CH ₂)₉CH=CH₂ (2) has been achieved using CpMe2Ti(NPt-Bu₃) as the precatalyst and B(C

Full text of DOI:10.1139/V09-120

1620
Copolymerization of sterically demanding
phosphine-olefins and 1-hexene
Jenny S.J. McCahill and Douglas W. Stephan
Abstract: The copolymerization of 1-hexene with t-Bu2P(CH2)3CH=CH2 (1) or t-Bu2P(CH2)9CH=CH2 (2) has been
achieved using CpMe2Ti(NPt-Bu3) as the precatalyst and B(C6F5)3, [Ph3C][B(C6F5)4], or [PhNMe2H][B(C6F5)4] as the acti-
vator. The resulting polymers are shown to incorporate up to 9% of the phosphine comonomer, albeit with reduced catalyst
activity and polymer molecular mass. The cause of the catalyst inhibition is also considered in the light of phosphine–
activator interactions.
Key words: titanium phosphinimide, copolymerization, phosphine-containing polymers, phosphine–activator interactions.
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Resume : On a effectue la copolymerisation du hex-1-ene avec le t-Bu2P(CH2)3CH=CH2 (1) ou le t-Bu2P(CH2)9CH=CH2
´
(2) en utilisant le CpMe2Ti(NPt-Bu3) comme precatalyseur et le B(C6F5)3, [Ph3C][B(C6F5)4], ou [PhNMe2H][B(C6F5)4]
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comme activateurs. On a montre que les polymeres qui en resultent incorporent jusqu’a 9 % du comonomere phosphine,
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avec une reduction de l’activite du catalyseur et du poids moleculaire du polymere. On considere la cause de cette inhibi-
tion du catalyseur en fonction des interactions entre la phosphine et l’activateur.
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Mots-cles : phosphinimide de titane, copolymerisation, polymeres contenant une phosphine, interaction entre une phos-
phine et un activateur.
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[Traduit par la Redaction]
The direct polymerization of functionalized monomers us-
ing group-IV transition-metal catalysts has been limited, as
many polar monomers poison the catalyst by coordination
to the electrophilic metal center. Nonetheless, functionalized
monomers containing Si,6,7 halogens,8 and N7,9 have been
directly polymerized using group-IV catalysts as such
groups afford weak donor interactions.
Previous efforts in our group have shown that activation
of CpMe2Ti(NPt-Bu3) with borane and borate activators af-
fords highly active catalysts for olefin polymerization.
Moreover, the catalytically active cation can be intercepted
with phosphine donors affording species of the form [CpMe-
Ti(NPt-Bu3)(PR3)]+. However, with sterically bulky phos-
phines (R = Cy, t-Bu, and o-tolyl) there was no evidence of
phosphine binding to Ti and the free phosphine was ob-
served in solution by NMR methods.10,11 In this paper, we
exploit this absence of interaction of bulky phosphines to
probe the viability of copolymerization of olefins with ole-
fins containing pendant bulky phosphine fragments.
Introduction
The development of single-site catalysts for the polymer-
ization of ethylene and other a-olefins has been a major
area of research for the past quarter of a century. The spe-
cific tuning of defined metal complexes allows strict control
over the microstructure of polyolefins produced.1,2 This ra-
tional catalyst development, although extensively studied,
continues to be a motivating objective in numerous research
endeavors. A driving force behind some of these investiga-
tions is the expansion of these systems to incorporate func-
tional moieties into the polymer, to enhance or change the
polymer properties and range of applications.
There are two main approaches to the synthesis of func-
tional polyolefins: chain-end functionalization and in-chain
functionalization.3–5 Chain-end functionalization is achieved
through reactivity on unsaturated chain-ends or via function-
alization of polymer terminae. In-chain functionalization is
typically achieved through post-polymerization reactivity,
the use of groups to protect the functionality during the pol-
ymerization, or via direct polymerization. Of these methods
of in-chain functionalization, direct polymerization is pre-
ferred, since it requires no post-polymerization modification.
Therefore, numerous studies have been carried out to incor-
porate the functional moieties directly during the polymer-
ization process. Furthermore, it is desirable to add these
moieties in a controlled manner without compensation of
any desirable properties.
Experimental section
General considerations
All preparations were performed under an atmosphere of
dry O2-free N2 employing either Schlenk-line techniques or
a Vacuum Atmospheres inert atmosphere glovebox. Solvents
were purified employing Grubbs-type column systems man-
Received 28 April 2009. Accepted 13 July 2009. Published on the NRC Research Press Web site at canjchem.nrc.ca on 27 October 2009.
J.S. McCahill and D.W. Stephan.1,2 Department of Chemistry & Biochemistry, University of Windsor, Windsor, ON N9B 3P4, Canada.
1Corresponding author (e-mail: dstephan@chem.utoronto.ca).
2Present address: Department of Chemistry, University of Toronto, 80 St. George St., Toronto, ON M5S 3H6, Canada.
Can. J. Chem. 87: 1620–1624 (2009)
doi:10.1139/V09-120
Published by NRC Research Press

McCahill and Stephan
1621
1
ufactured by Innovative Technologies. Uninhibited THF
purchased from EDM and deuterated benzene, toluene, and
methylenechloride purchased from Cambridge Isotopes Lab-
oratories, were dried, distilled, and freeze-pump-thaw de-
(3): Yield: 0.71 g (51%). H NMR (C6D6) d: 1.27–1.54
3
(m, 8H, CH2), 1.11 (d, 18H, JH–P = 11 Hz, t-Bu), 0.97 (t,
3H, JH–H= 7 Hz, CH3). 13C{1H} NMR (C6D6) d: 34.41 (d,
3
3JC–P = 12 Hz, CH2CH2CH2), 31.56 (d, JC–P = 23 Hz, t-
1
1
gassed (three times) prior to use. H and 13C NMR spectra
2
2
Bu), 31.02 (d, JC–P = 12 Hz, PCH2CH2), 30.19 (d, JC–P
=
=
1
were recorded on Bruker Avance 300 and 500 spectrome-
ters. Trace amounts of protonated solvents were used as
14 Hz, t-Bu), 23.26 (s, CH2CH2CH3) 22.03 (d, JC–P
22 Hz, PCH2), 14.68 (s, CH3). 31P{1H} NMR (C6D6) d:
27.84 (s). Anal calcd. for C14H39P: C 76.45, H 13.17; found:
C 76.13, H 13.13.
1
references, and H and 13C{1H} NMR chemical shifts are re-
ported relative to SiMe4. 31P{1H}, 11B{1H}, and 19F NMR
spectra were referenced to external 85% H3PO4, BF3ÁEt2O,
and CFCl3, respectively. Combustion analyses were per-
formed at the University of Windsor Chemical Laboratories
employing a PerkinElmer CHN Analyzer. Molecular mass
determinations were performed using a Waters Breeze sys-
tem GPC using THF as eluent. The detector used was a
Waters model 410 refractive index detector at 35 8C, and
molecular masses were calibrated using narrow polystyrene
standards (Polymer Laboratories Inc.). High-temperature
GPC data were provided by the technical staff at NOVA
Chemicals Corporation.
Synthesis of t-Bu2P((CH2)9CHCH2)C6F4BF(C6F5)2 (5)
To a solution of B(C6F5)3 (0.254 g, 0.50 mmol) in CH2Cl2
(10 mL) 2 (0.156 g, 0.52 mmol) was added. The solution
was stirred overnight, and the solvent was removed in va-
cuo. The residue was dissolved in 3 mL of CH2Cl2 and hex-
anes were added to precipitate an off-white solid. The solid
was filtered and washed with pentanes several times to give
a white solid. Yield: 0.198 g (50%). H NMR (CD2Cl2) d:
5.74–5.88 (m, 1H, CH=CH2), 4.89–5.01 (m, 2H, CH=CH2),
2.51–2.63 (br m, 2H, CH2), 1.99–2.08 (br m, 2H, CH2),
1
3
HPt-Bu2, Br(CH2)3CHCH2, Br(CH2)4CH3, Br(CH2)9CH3,
and anhydrous MeOH were purchased from Sigma-Aldrich
Chemical Company, and [Me2PhNH][B(C6F5)4] was pur-
chased from Strem Chemical Inc.; all were used as received.
1-Hexene was purchased from Sigma-Aldrich Chemical
Company and distilled from Na/benzophenone. B(C6F5)3,
and [Ph3C][B(C6F5)4] were generously donated by NOVA
Chemicals Corp. CpTiMe2(NPt-Bu3) was prepared via litera-
ture methods.12
1.62–1.79 (br, m, 2H, CH2), 1.51 (d, 18H, JH–P = 13 Hz, t-
Bu2), 1.25–1.36 (br, 12H, CH2). 11B{1H} NMR (CD2Cl2) d:
–0.16 (br). 13C{1H} NMR (CD2Cl2) partial d: 148.41 (dm,
1JC–F = 238 Hz, CF), 139.77 (s, CH=CH2), 139.53 (dm,
1JC–F = 244 Hz, CF), 137.15 (dm, JC–F = 244 Hz, CF),
1
1
114.39 (s, CH=CH2), 38.37 (d, JC–P = 32 Hz, t-Bu), 34.27
(s, CH=CH2), 32.12 (s, CH2), 31.94 (s, CH2), 29.91
(s, CH2), 29.53 (s, CH2), 29.42 (s, CH2), 29.27 (s, CH2),
1
3
27.92 (s, t-Bu2), 20.00 (dd, JC–P = 40 Hz, JC–F = 13 Hz,
CH2). 19F NMR (CD2Cl2) d: –119.93 to –119.73 (m, 1F,
Synthesis of t-Bu2P(CH2)3CH=CH2 (1), t-
Bu2P(CH2)9CH=CH2 (2), t-Bu2P(CH2)4CH3 (3)
C6F4), –125.24 (s, 1F, C6F4), –125.82 (s, 1F, C6F4),
–130.28 to –130.06 (m, 1F, C6F4), –132.54 (t, 4F, JF–F
12 Hz, o-C6F5), –158.28 (t, 2F, JF–F = 20 Hz , p-C6F5),
–163.78 to –163.22 (m, 4F, m-C6F5), –190.87 (br s, BF).
31P{1H} NMR (CD2Cl2) d: 54.98 (s). Anal. calcd. for
C37H39BP: C 54.83, H 4.85; found: C 54.72, H 4.65.
3
=
3
These compounds were prepared in a similar fashion, and
thus only one preparation is detailed. A solution of
Br(CH2)3CH=CH2 (4.829 g 32.40 mmol) in THF (5 mL)
was added to a solution of t-Bu2PLi (4.392g, 28.87 mmol)
in THF (50 mL) cooled to 0 8C. The solution was stirred
and warmed to room temperature for 12 h. The solvent was
removed in vacuo, and hexanes were added to precipitate
LiBr. The solution was filtered through Celite and vacuum-
distilled (58–62 8C) to yield a clear liquid.
Generation of [t-Bu2PH((CH2)3CH=CH2)][B(C6F5)4] (6)
A solution of 1 (0.021 g, 0.100 mmol) in C6D5Br
(0.5 mL) was added to a solution of [Me2PhNH][B(C6F5)4]
(0.079 g, 0.100 mmol) in C6D5Br. Quantitative product for-
mation was observed by NMR. H NMR (C6D5Br) d: 7.22
(t, JH–H = 7 Hz, 2H, Ph), 6.75 (t, JH–H = 7 Hz, 1H, Ph),
6.65 (d, JH–H = 8 Hz, 2H, Ph), 5.50–5.54 (m, 1H,
CH=CH2), 4.96–5.08 (m, 2H, CH=CH2), 4.22 (d, JH–P
444 Hz, PH), 2.69 (s, 6H, Me2), 1.93–1.95 (m, 2H, CH2),
1
1
(1): Yield: 4.89 g (79%). H NMR (C6D6) d: 5.71–5.85
3
3
(m, 1H, CH=CH2), 4.97–5.08 (m, 2H, CH=CH2), 2.13 (q,
3
3
2
2H, JH–H = 7 Hz, CH2CHCH2), 1.65 (sextet, 2H, JH–H
=
1
=
7 Hz, CH2CH2CH2), 1.22–1.33 (m, 2H, PCH2CH2), 1.07 (d,
3
18H, JH–P = 10 Hz, t-Bu). 13C{1H} NMR (C6D6) d: 139.20
3
3
1.29–1.61 (m, 4H, CH2), 0.87 (d, JH–P = 17 Hz, 18H, t-
(s, CH=CH2), 115.39 (s, CH=CH2), 36.06 (d, JC–P = 13 Hz,
Bu). 11B NMR (C6D5Br) d: –16.70 (s). 19F NMR (C6D5Br)
1
CH2CH2CH), 31.66 (d, JC–P = 23 Hz, t-Bu), 30.65 (s,
3
2
1
d: –132.37 (s, 8F, o-C6F5), –162.76 (t, 4F, JF–F = 19 Hz, p-
PCH2CH2), 30.25 (d, JC–P = 15 Hz, t-Bu), 21.46 (d, JC–P
=
C6F5), –166.46 (t, 8F, JF–F = 18 Hz, m-C6F5). 31P NMR
3
22 Hz, PCH2). 31P{1H} NMR (C6D6) d: 27.82 (s). Anal.
calcd. for C13H27P: C 72.85, H 12.70; found: C 72.73, H
12.43.
1
(C6D5Br) d: 53.26 (d, JP–H = 438 Hz).
1
Polymerization procedures
(2): Yield: 2.70 g (66%) H NMR (C6D6) d: 5.73–5.87 (m,
1H, CH=CH2), 4.98–5.09 (m, CH=CH2), 1.99 (q, 2H,
CH2CH=CH2), 1.29–1.66 (m, 14H, CH2), 1.16 (d, 18H,
3JH–P = 11 Hz, t-Bu). 13C{1H} NMR (C6D6) partial d:
139.59 (s, CH=CH2), 114.86 (s, CH=CH2), 34.57 (s, CH2),
A 20 mL vial with a propylene top closure with TFE–
silicone septa was equipped with a magnetic stir bar. 0.673 g
of 1-hexene (8 mmol), 0.015 g of CpMe2Ti(NPt-Bu3)
(0.04 mmol) and 6 mL of toluene were added to the vial.
The vial was then immersed in a bath of desired temperature
and stirred for 5 min at the polymerization temperature. A sy-
ringe containing 0.020 g of B(C6F5)3 (0.04 mmol) dissolved
in 4 mL of toluene was then brought out of the glovebox,
2
1
32.27 (d, JC–P = 13 Hz, CH2), 31.58 (d, JC–P = 23 Hz, t-
1
Bu), 31.56 (s, CH2), 22.13 (d, JC–P = 23 Hz, t-Bu). 31P{1H}
NMR (C6D6) d:27.82 (s). Anal. calcd. for C19H39P: C 76.45,
H 13.17; found: C 76.25, H 13.00.
Published by NRC Research Press

1622
Can. J. Chem. Vol. 87, 2009
and its contents were injected into the vial. After a desired
time interval, polymerizations were quenched by injection of
1 mL of MeOH. Volatiles were removed in vacuo. 1 mL of
toluene was added and 5 mL MeOH was added to precipitate
the polymer. Polymer was washed two times with 5 mL
MeOH and dried in vacuo.
The % P incorporation is based on the relative integrals of
the 13C resonances attributable to methyl groups from the t-
Bu groups on P and methyl groups of the hexene side
chains. While differences in the T1 relaxation times are ex-
pected to be small, a 10 s relaxation delay was employed to
record these spectra. This delay was selected based on previ-
ously determined T1 experiments on polyhexene.13
Results and discussion
In designing an appropriate phosphine-containing mono-
mer for the polymerization with the CpTiMe2(NPt-Bu3)/
B(C6F5)3 system, we noted the previous studies by Way-
mouth and co-workers in which polymerization incorporated
amine-functionalized olefin.7,14 It was shown that the steric
bulk of amine substituents correlated with the resulting ac-
tivity of the catalyst. Similar results were also observed by
Hakala et al. for the copolymerization of oxygen-functional-
ized olefins.15 In addition to the influence of the steric prop-
erties of the functional group, the length of the spacer
between the functional group and the olefinic residue was
also seen to have a profound impact on polymerization. For
example, reducing the spacer to two carbons from three car-
bons to the 4-amino-1-butene, resulted in a decreased poly-
merization activity.14 Gianni et al.16 also observed this trend
for the polymerization of amino-functionalized olefins using
Ziegler catalysts. Lofgren and co-workers have also reported
the increased incorporation of oxygen-functionalized mono-
mers into the polyethylene chain with the increase of the
spacer group.17
In our efforts to incorporate phosphine residues into
polyolefins, these earlier results prompted us to target a steri-
cally encumbered phosphine with the pendant olefinic sub-
stituent, t-Bu2P(CH2)3CH=CH2 (1). This species was readily
prepared via treatment of the corresponding halide derivative
with lithium phosphide (Scheme 1). Employing the same
methodology, the species t-Bu2P(CH2)9CH=CH2 (2) and t-
Bu2P(CH2)4CH3 (3) were also prepared.
Initial attempts to effect the homopolymerizations of the
phosphine-functionalized monomer were unsuccessful as no
polymer was formed. However, copolymerization using 1, 5,
and 10 mol% of (1) with 1-hexene did yield isolable poly-
meric products. In the cases where 5 and 10 mol% of the
phosphine-functionalized monomer were used (Table 1),
this resulted in a marked suppression of yield and molecular
mass of the resulting polymers. The PDI of these polymers
were typical of the single-site phosphinimide catalyst12
used, ranging between 1.0 and 4.2. The degree of comono-
mer incorporation was determined by analysis of the
13C{1H} NMR spectra of the polymers. Specifically, the ra-
tio of the integrals of signal attributable to the terminal
methyl group of the hexyl residue was compared with that
ascribed to the tert-butyl fragment (Fig. 1). The level of co-
monomer incorporation ranges between 3% and 5% with use
of 5–10 mol% of comonomer 1. While these values vary
Published by NRC Research Press

McCahill and Stephan
1623
Fig. 1. 13C NMR spectrum of copolymer of 1-hexene–(1).
Scheme 2. Reactions of olefinic phosphines with activators.
consistent with the presence of a C6F4 fragment in addition
to signals attributable to C6F5 rings. As well, the signal at
–190.87 ppm is attributable to a B–F residue. These data to-
Scheme 1. Synthesis of 1–3.
1
gether with the H and 13C data confirm the formulation of 5
as t-Bu2P((CH2)9CH=CH2)C6F4BF(C6F5)2 (Scheme 2). This
species forms by para-attack on a C6F5 ring by the sterically
encumbered P center. We have previously documented such
reactivity of bulky phosphines with B(C6F5)3.19,20
Such reactions of comonomer with the activator could
compete with the precatalyst and thus account for the lesser
activity observed. Similarly, in the case of the activator
[Ph3C][B(C6F5)4], interactions of phosphines are known
to form traditional acid–base adducts affording the corre-
sponding phosphonium salts. Alternatively, bulky phos-
phines are also known to effect nucleophilic aromatic
substitution of a ring of [Ph3C]+ yielding cations of the
form [R3PC6H4CH(C6H5)2]+.21 In the case of the activator
[Me2PhNH] [B(C6F5)4], it is operative via protonation of
the Ti–Me fragment. Clearly, the basicity of the phosphine
centers in 1 or 2 could compete for this proton, affording
the corresponding phosphonium salt. Indeed, independent
reaction of 1 with [Me2PhNH][B(C6F5)4] generated [t-
Bu2P(H)((CH2)3CH=CH2)][B(C6F5)4] (6) (Scheme 2) and
free amine Me2PhN as evidenced by the NMR data, and in
particular, the 31P NMR signal at 52.5 ppm which exhibits
P–H coupling of 438 Hz. Such phosphonium salts have
been shown ineffective activators. Thus, such competitive
side reactions could also slow catalyst generation.
slightly with co-catalyst used, in general the level of incor-
poration of comonomer into the polymer increase with in-
creased comonomer concentration. Use of
5
mol%
comonomer results in less than 5 mol% incorporation, re-
flecting the differing steric demands of comonomer and hex-
ene. In the case where 10 mol% of 2 is employed,
incorporation rises to 9%, reflecting the decreased steric in-
fluence of the Pt-Bu2 fragment with the increase chain
length in 2. This result is consistent with observations made
for N- and O-containing functional monomers where longer
spacers between the heteroatom and the olefinic fragment
were used.18
Competitive reactions
The yields of polymerizations conducted in the presence
of 1 or 3 were also compared. The yield of polymer gener-
ated, under otherwise identical conditions was significantly
reduced when 1 was employed. This suggests the possibility
that an intramolecular interaction of inserted comonomer
could inhibit catalyst activity. This proposition is consistent
with observations made by Waymouth and co-workers,18
where the aminopentene, iPr2N(CH2)3CHCH2, was found to
be a more potent inhibitor than the amine, iPr2N(CH2)4CH3,
which lacks an olefinic group.18 Nonetheless, the yield was
also seen to decrease with increasing concentration of 3, al-
beit to a lesser extent, suggesting that intermolecular coordi-
nation of the phosphine to the Ti cation could also diminish
polymerization to some extent.
The reduced catalyst activity observed in the presence of
the phosphine-olefin comonomers could be attributed to
competitive and independent interactions of these species
with the activators. For example, the independent reaction
of 1 with B(C6F5)3 has been previously reported to effect ad-
dition of P and B to the olefinic fragment to give the cyclic
phosphonium borate t-Bu2P((CH2)4CHCH2B(C6F5)3 (4). This
yields a cyclic phosphonium borate (Scheme 2). In contrast,
as a result of the longer chain in 2, it is unlikely to undergo
such cyclization. However, reaction of B(C6F5)3 with 2 does
proceed to give a new species 5 in 50% isolated yield. This
species exhibits a 31P{1H} NMR signal at 54.98 ppm. Per-
haps most diagnostic, however, is the 19F NMR data. Here
signals at –119.8, –125.24, –125.82, and –130.1 ppm are
Published by NRC Research Press

1624
Can. J. Chem. Vol. 87, 2009
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(10) Cabrera, L. M. Sc. Thesis, University of Windsor, 2004.
(11) Cabrera, L.; Hollink, E.; Stewart, J. C.; Wei, P. R.; Stephan,
D. W. Organometallics 2005, 24 (6), 1091–1098. doi:10.
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(12) Stephan, D. W.; Stewart, J. C.; Guerin, F.; Courtenay, S.;
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Copolymerization of 1-hexene and phosphine functional-
ized monomers is possible, although the catalyst activity is
diminished. The cause of this diminished reactivity could be
competitive reactions of the comonomer with the activator
or the Ti catalyst. This issue can be mitigated to some extent
by increasing the separation of the functional group from the
double bond. Presumably, increased steric bulk at the heter-
oatom and decreased nucleophilicity would also facilitate
comonomer incorporation.
Acknowledgements
Financial support from the Natural Sciences and Engi-
neering Research Council of Canada (NSERC) and NOVA
Chemicals Corporation is gratefully acknowledged. DWS is
grateful for the award of a Canada Research Chair.
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