Nickel(II) and Palladium(II) Polymerization catalysts bearing a fluorinated cyclophane ligand: stabilization of the reactive intermediate

Article abstract of DOI:10.1021/om900302r

The synthesis and characterization of Ni(II) and Pd(II) α-diimine olefin polymerization catalysts bearing a fluorinated cyclophane-based ligand were performed. Fluorine was placed in such a manner as to interact with the metal center from the axial direct

Full text of DOI:10.1021/om900302r

4452 Organometallics 2009, 28, 4452–4463
DOI: 10.1021/om900302r
Nickel(II) and Palladium(II) Polymerization Catalysts Bearing a
Fluorinated Cyclophane Ligand: Stabilization of the Reactive Intermediate1
Chris S. Popeney,† Arnold L. Rheingold,‡ and Zhibin Guan*,†
†Department of Chemistry, University of California, 1102 Natural Sciences 2, Irvine, California 92697, and
‡Department of Chemistry and Biochemistry, University of California, San Diego, La Jolla,
California 92093-0332
Received April 21, 2009
The synthesis and characterization of Ni(II) and Pd(II) R-diimine olefin polymerization catalysts
bearing a fluorinated cyclophane-based ligand were performed. Fluorine was placed in such a
manner as to interact with the metal center from the axial direction. The catalysts were active in the
polymerization of ethylene, showing substantial differences in both catalytic behavior and polymer
size and structure as compared to their nonfluorinated analogues. Both catalysts afforded polymer of
comparatively low branching density and high molecular weight. The Ni(II) catalysts, from precursor
[Ni(acetylacetonato)(F-Cyc)]+ salts (F-Cyc=fluorinated cyclophane), exhibited enhanced thermal
stability by remaining active after 70 min with little loss in polymerization activity at 105 °C. The Pd-
(II) catalysts from salts of [Pd(F-Cyc)Me(NCR)]+ (NCR=nitrile) afforded polymer of molecular
weights far higher than the nonfluorinated analogue. Additionally, polymerization activity was
directly related to ethylene feed pressure for the Pd(II) system, and NMR analysis could not detect the
presence of bound olefin, indicating that the polymerization proceeded via different kinetics
1
involving an olefin-free 14 e- complex as the catalyst resting state. Furthermore, NMR H-19F
coupling data provide clear evidence that the fluorine atoms were indeed interacting with the metal
axial site. The unusual properties of these new complexes are thus attributed to stabilization of the
highly reactive 14 e- intermediate by donation of the fluorine lone pair to the metal center.
Introduction
catalysts, our laboratories created new Ni(II) and Pd(II)
catalysts bearing a cyclophane-based R-diimine ligand
1 (Chart 1).7,8 The thermal stability of these catalysts,
evident by their relatively high activity, ability to produce
high molecular weight polyethylene at elevated tempera-
tures, and living polymerization for R-olefins at tempera-
tures up to 75 °C,9 is attributed to the influence of the
unique ligand environment of 1. Ligand moieties remain
roughly fixed above the metal center, retarding chain
transfer and limiting deactivation processes. In addition
to their enhanced stability, these catalysts afforded poly-
mers with significantly higher branching densities when
compared to catalysts bearing acyclic ligands, presumably
by facilitating β-hydride elimination/reinsertion with
respect to chain propagation.9,10
Ligand structure has a dramatic effect on the reactivity
of organometallic complexes. This has been especially
evident in the recent development of late transition metal
olefin polymerization catalysts. A major breakthrough
occurred over a decade ago when Ni(II) and Pd(II) cata-
lysts were prepared bearing bulky R-diimine ligands,2-4
which are crucial for blockage of the axial coordination
sites on the metal toward incoming monomer and reduc-
tion of chain transfer. Although the Ni catalysts are highly
active and the Pd catalysts are attractive because of the
unique polymer architectures they afford and their high
functional group tolerance, both systems suffer from
relatively low thermal stability.5,6 In response to the
limitations of existing late transition metal polymerization
During our investigation of the Pd(II) catalysts formed
from 1, it was observed that one pair of ligand aromatic
protons in a position above the metal underwent a significant
*Corresponding author. E-mail: zguan@uci.edu.
(1) This paper has been adapted in part from the following thesis :
Popeney, C. S. Ph.D. Dissertation, University of California, Irvine,
2008.
1
upfield chemical shift of more than 1 ppm in the H NMR
when halide was abstracted from the neutral methyl chloro
complex (NN)PdMeCl to afford a cationic complex of type
(2) Johnson, L. K.; Killian, C. M.; Brookhart, M. J. Am. Chem. Soc.
1995, 117, 6414–6415.
(3) Johnson, L. K.; Mecking, S.; Brookhart, M. J. Am. Chem. Soc.
1996, 118, 267–268.
(4) Ittel, S. D.; Johnson, L. K.; Brookhart, M. Chem. Rev. 2000, 100,
1169–1203.
(5) Gates, D. P.; Svejda, S. A.; Onate, E.; Killian, C. M.; Johnson,
L. K.; White, P. S.; Brookhart, M. Macromolecules 2000, 33, 2320–2334.
(6) Tempel, D. J.; Johnson, L. K.; Huff, R. L.; White, P. S.;
Brookhart, M. J. Am. Chem. Soc. 2000, 122, 6686–6700.
(7) Camacho, D. H.; Salo, E. V.; Ziller, J. W.; Guan, Z. Angew.
Chem., Int. Ed. 2004, 43, 1821–1825.
(8) Camacho, D. H.; Salo, E. V.; Guan, Z. Org. Lett. 2004, 6, 865–
868.
(9) Camacho, D. H.; Guan, Z. Macromolecules 2005, 38, 2544–2546.
(10) Popeney, C. S.; Levins, C. M.; Guan, Z. Manuscript in prepara-
tion.
r
pubs.acs.org/Organometallics
Published on Web 07/06/2009
2009 American Chemical Society

Article
Organometallics, Vol. 28, No. 15, 2009 4453
Chart 1. Cyclophane-Based r-Diimine Ligands 1 and 2 and
Corresponding Ni(II) and Pd(II) Complexes
data provide evidence of direct palladium-fluorine interac-
tions that may contribute to the unusual catalytic properties
for these complexes.
Results
Synthesis and Characterization of F-Cyc Ni(II) and Pd(II)
Catalysts. Preparation of the fluorinated cyclophane ligand
began with the Pd-catalyzed Negishi coupling of acetal 9 to 2,6-
dibromo-4-methylnitrobenzene (10) to afford 11. Following
deprotection to give crude dialdehyde 12, vinyl groups were
installed by Wittig reaction to afford 13. The nitro group was
then subsequently reduced by tin(II) chloride to provide the
divinyl meta-terphenyl aniline 14 (Scheme 2).
Further construction of the complete ligand 2 was performed
in a manner similar to the unsubstituted ligand: diimine con-
densation followed by ring-closing metathesis and hydrogena-
tion (Scheme 3).7,8 Initial attempts at complexation of the
ligand to Ni and Pd appeared to be problematic. Unlike the
unsubstituted cyclophane ligand 1,7 the F-Cyc ligand 2 was
unable to complex to any neutral precursors to afford, for
example, the commonly employed nickel dihalo or palladium
methyl chloride complexes, possibly because of electronic
effects or steric repulsion. Instead, facile preparation of the
Ni(II) complex [(F-Cyc)Ni(acac)]B(C6F5)4 (4, acac = acetyl-
acetonato)19 and Pd(II) nitrile complexes [(F-Cyc)PdMe-
(NCMe)]BAr4 (7, Ar=3,5-bis-(trifluoromethyl)-phenyl)6 and
[(F-Cyc)PdMe(NCAr)]BAr4 (8) was carried out (Scheme 4),
presumably via more reactive cationic intermediates. To allow
for direct comparison, the nonfluorinated analogues of Ni(II)
acetylacetonato and Pd(II) methyl acetonitrile complexes, 3
and 6, were also prepared (Chart 1).
Single crystals of Ni(II) complex 4 were subjected to X-ray
diffraction analysis.20 As expected, complex 4 exhibits
C2v symmetry in the X-ray crystal structure (Figure 1). The
fluorine atoms do not closely approach the nickel atom since
the axial phenyl rings they are attached to lie roughly
perpendicular to the central aniline phenyl rings. In contrast,
the two nonequivalent cis ligands in the Cs-symmetric Pd(II)
complexes impart noticeable deflection of the phenyl-phen-
yl dihedral angle. Although no crystals of Pd complexes of
the F-Cyc ligand were grown of sufficient quality for X-ray
analysis, previous diffraction studies on the nonfluorinated
cyclophane Pd(II) methyl chloride complex Pd(Cyc)MeCl
(15) exhibited such phenyl ring rotation.7 The rings rotate
away from the methyl ligand on the left side of complex 15
but turn inward toward the chloro ligand on the right side,
[(NN)PdMe(L)]+(NN=cyclophane, L=neutral ligand).11 As
elucidated by NOE and 2D NMR, these protons were
found to lie nearest to the exiting chloro and incoming neutral
ligands, suggesting an H-agostic interaction existed with the
more electrophilic metal center of the cationic complexes.10
Prompted by this possibility, we proposed to introduce Lewis
basic groups in this position on the cyclophane ligand for direct
interaction with the metal center through the axial coordination
site. We reasoned that this hemilabile interaction may stabilize
the most reactive 14 e- intermediate in the catalytic cycle and
hence suppress side reactions associated with this species such as
catalyst deactivation (Scheme 1). Binding of an olefin monomer
should afford the less electrophilic 16 e- complex, release the
fluorine interaction, and allow monomer insertion to proceed.
Fluorine was chosen as the Lewis basic group because of
its small size and weakly donating nature. Interactions bet-
ween fluorine and late transition metals are uncommon;12,13
however a reactivity enhancement was recently reported in a
fluorinated Ru metathesis catalyst believed to involve a
metal-fluorine interaction.14 Fluorinated titanium phe-
noxy-imine olefin polymerization catalysts were shown to
afford living polymerizations with a reduction in chain
transfer processes due to direct interaction of β-hydrogen
with fluorine and stabilization toward elimination.15
Although fluorine substituents have been introduced to a
few late metal polymerization complexes,5,16-18 no experi-
mental evidence regarding direct fluorine-metal interac-
tions has been reported. Herein, we describe the synthesis
of Ni(II) and Pd(II) catalysts bearing a fluorinated cyclo-
phane (F-Cyc) ligand 2 and polymerizations with ethylene
(Chart 1). The fluorine atoms are appropriately positioned to
serve as axial ligand donors to stabilize electrophilic polym-
erization intermediates, particularly the important 14 e-
alkyl agostic complex. The new complexes exhibit unusual
polymerization properties. In addition, NMR spectroscopic
(19) Moody, L. S.; Mackenzie, P. B.; Killian, C. M.; Lavoie, G. G.;
Ponasik, J. A., Jr.; Barrett, A. G.; Smith, T. W.; Pearson, J. C. WO 00/
50470, 2002.
(20) Crystals of 4 were grown over several days by slow vapor
diffusion of n-pentane into a dichloromethane solution of the complex
(15 mg/mL). Crystallographic data for 4: C83H39BF28N2NiO2 CH2Cl2:
3
˚
˚
(11) Salo, E. V. Masters thesis, Chapter 2, University of California,
Irvine, 2005.
(12) Mezzetti, A.; Becker, C. Helv. Chim. Acta 2002, 85, 2686–2703.
(13) Grushin, V. V. Chem.;Eur. J. 2002, 8, 1007–1014.
(14) Ritter, T.; Day, M. W.; Grubbs, R. H. J. Am. Chem. Soc. 2006,
128, 11768–11769.
(15) Mitani, M.; Mohri, J.; Yasunori, Y.; Saito, J.; Ishii, S.; Tsuru, K.;
Matsui, S.; Furuyama, R.; Nakano, T.; Tanaka, H.; Kojoh, S.; Matsugi,
T.; Kashiwa, N.; Fujita, T. J. Am. Chem. Soc. 2002, 124, 3327–3336.
(16) Chen, Y.; Qian, C.; Sun, J. Organometallics 2003, 22, 1231–1236.
(17) Ionkin, A. S.; Marshall, W. J.; Adelman, D. J.; Fones, B. B.;
Fish, B. F.; Schiffhauer, M. F. Organometallics 2008, 27, 1147–1156.
(18) Helldorfer, M.; Militus, W.; Alt, H. G. J. Mol. Catal. A: Chem.
2003, 197, 1–13.
red plate, triclinic,Mr=1782.61, P1,a=12.010(3) A,b=14.126(4)A, c=
˚
22.928(6) A, R=103.802(4)°, β=101.778(4)°, γ=100.135(4)°, V=3593.1
3
˚
˚
(16) A , Z=2, T=100(2) K, λ=0.71073 A. The asymmetric unit consists
of one anion, one molecule of the recrystallization solvent, CH2Cl2, and
two half-cations residing on inversion centers; of necessity, while the
outer macrocyclic ring possesses the crystallographically required sym-
metry, the inner Ni coordination sphere does not and is consequentially
fully disordered, but easily modeled based on the planar geometry about
Ni. R1=0.0695, wR2=0.1567 for 12 613 independent reflections. CCDC-
702264 contains the supplementary crystallographic data for this paper.
These data can be obtained free of charge via www.ccdc.cam.ac.uk/
conts/retrieving.html (or from the Cambridge Crystallographic Data
Centre, 12 Union Road, Cambridge CB21EZ, UK; fax: (+44)1223-336-
033; or deposit@ccdc.cam.ac.uk).

4454 Organometallics, Vol. 28, No. 15, 2009
Popeney et al.
Scheme 1. Proposed Hemilabile Interaction between Fluorine and the Metal in the 14 e- Intermediate and Displacement by Incoming
Ethylene
Scheme 2. Synthesis of Aniline 14
allowing two hydrogen atoms to make a relatively close
approach of 2.7 A to the metal center.11 Since all active Ni
˚
with similar magnitude by other nearby fluorine atoms
(FB and FC) (Figure 2). Analogous triplet splitting was also
seen in 13C NMR. Coupling of similar magnitude has been
observed in other rigid complexes containing fluorine and
has been typically attributed to nonbonding, close-contact
interactions.21-24 In complex 7, these interactions were
confirmed by selective 19F decoupling of the four fluorine
resonances, each corresponding to a pair of F atoms lying
(II) and Pd(II) polymerization intermediates, such as the
alkyl olefin and the alkyl agostic complexes, exhibit Cs
symmetry, there should be two fluorine atoms in the corre-
sponding F-Cyc derivatives near the metal at any given time.
1
Furthermore, strong H-19F coupling seen by NMR in
the Pd(II) acetonitrile complex 7 indicated close approach of
the fluorine atoms to the coordination sphere. The reso-
nances of protons on groups that lie in the coordination
plane were noticeably split by fluorine, in addition to the
expected doublets seen for protons ortho to fluorine on the
axial phenyl rings. Most prominently, signals of the methyl
ligand exhibited a triplet pattern split by two nearby fluorine
atoms (FA) with JHF = 4.5 Hz, while protons of the ace-
naphthyl diimine backbone were split in triplet multiplicity
(21) Chambers, R. D.; Sutcliffe, L. H.; Tiddy, D. J. T. Trans. Faraday
Soc. 1970, 66, 1025–1038.
(22) Belt, S. T.; Helliwell, M.; Jones, W. D.; Partridge, M. G.; Perutz,
R. N. J. Am. Chem. Soc. 1993, 115, 1429–1440.
(23) Fornies, J.; Fortuno, C.; Gomez, M. A.; Menjon, B. Organome-
tallics 1993, 12, 4368–4375.
(24) Noveski, D.; Braun, T.; Neumann, B.; Stammler, A.; Stammler,
H. Dalton Trans. 2004, 4106–4119.

Article
Organometallics, Vol. 28, No. 15, 2009 4455
Scheme 3. Synthesis of Fluorinated Cyclophane Ligand 2
Scheme 4. Preparation of Ni(II) acac Complexes 3 and 4 and Pd(II) Nitrile Complexes 7 and 8
above and below the metal coordination plane as expected
from the Cs symmetry of the complex. A summary of the
1H-19F interactions is shown in Figure 2, while the results of
19F decoupling experiments are shown below in Figure 3. In
this manner, it was possible to determine the location of the
fluorine pairs themselves, assuming the observed coupling
arises chiefly from close contact. However, we also observed
weak coupling of the FD fluorines to the acetonitrile methyl
group in 13C NMR and by line broadening of its 1H NMR
signal. The coupling of the acetonitrile methyl group with
fluorine is surprising, given that this group should be too far
away from fluorine for coupling by close contact. Instead, we
believe that a through-bond contribution, mediated by an
F-Pd interaction, is responsible for the observed coupling.

4456 Organometallics, Vol. 28, No. 15, 2009
Popeney et al.
high purity of complex 4 employed, the polymer obtained from
4/TIBA exhibited a bimodal molecular weight distribution, con-
sisting of a high molecular weight major fraction (Mn ≈ 105 g/
mol) and a minor proportion of ultrahigh molecular weight
polymer (Mn>106 g/mol). The main fraction of lower molecular
weight became increasingly dominant at higher polymerization
temperatures, according to GPC analysis (Supporting Informa-
tion, Figure S1). We attribute this behavior to complicated but
temperature-dependent activation kinetics, leading to two active
species. Like other Ni(II) catalysts,5,25 changing the Al/Ni ratio
had no observed effect on the polymer molecular weight dis-
tribution, suggesting that chain transfer to aluminum is negli-
gible. The polymer molecular weight distribution also underwent
little significant change with time (Supporting Information,
Figure S2), indicating that the relative concentrations of both
active species remain constant. To account for changes in
ethylene solubility at different temperatures, TON was also
adjusted for ethylene concentration, as estimated from solubi-
lities in toluene (see Experimental Section and Supporting
Information). This resulted in, overall, a relatively minor
correction due to a reduction of solubility of about 30% from
80 to 120 °C.
Figure 1. X-ray crystal structure of cation 4, [(F-Cyc)Ni(acac)]+
(borate anion and hydrogen atoms omitted for clarity). Selected
interatomic distances (A): Ni1-N1A 1.734(3), Ni1-N1 1.770(3),
˚
Although polymer productivity of 4 is lower than the non-
fluorinated analogue 3, the catalyst exhibits increased thermal
stability. As seen in Figure 4, after 70 min of polymerization at
105 °C, little decrease in activity can be noted. In contrast,
roughly 40% of catalyst 3, itself a dramatic improvement over
the standard acyclic catalyst, had deactivated after 30 min at
80 °C.7 The microstructure of the polymer produced by 4 was
also considerably different than that of 3. Most notably, the
polymer was much more linear, as indicated by a pronounced
decrease in branching density (B, branches per 1000 carbon
atoms). Values of B lie within 30-40 at polymerization tem-
peratures between 80 and 120 °C for polymers obtained from 4,
as compared to the heavily branched polymers obtained from
3 (B>100). The presence of fluorine has a significant inhibiting
effect on the rate of chain walking, likely by reducing the rate of
β-hydride elimination.
Ni1-O26 1.861(3), Ni1-O24 1.897(3), N1-C1 1.434(4), N1A-
C23A 1.498(8), N1-C22A 1.535(8). Selected bond angles (deg):
N1A-Ni1-N1 95.17(13), N1A-Ni1-O26 89.86(15), N1-Ni1-
O26 174.3216, N1A-Ni1-O24 176.47(14), N1-Ni1-O24 88.21
(14), O26-Ni1-O24 86.71(14), C1-N1-C22A 108.9(4), C1-N1-
Ni1 140.1(3), C22A-N1-Ni1 111.0(3), C34-O26-Ni1 132.8(4).
Selected dihedral angles (deg): N1-C22A-C23A-N1A -0.8(6),
C23A-N1A-C1A-C2A 84.4(6), C6-C1-N1-C22A -85.9(6).
The fluorinated Pd(II) cyclophane catalyst exhibited drama-
tically different behavior compared to the nonfluorinated ana-
logue. The addition of ethylene at ambient temperature and
pressure to a solution of Pd(II) F-Cyc acetonitrile adduct 7led to
the formation of negligible polymer. However, at an ethylene
pressure of 88 psi, the catalyst was quite active (Table 2, entry 4).
The catalytic activity of 7 was considerably higher than for the
nonfluorinated acetonitrile catalyst 6 (entries 2 and 3) and
comparable to that of the commonly employed nonfluorinated
ester chelate catalyst 5 (entry 1).7,26 As competitive binding of
the nitrile ligand has been observed to retard polymerization in
the nonfluorinated cyclophane Pd(II) complexes (compare cat-
alysts 5 and 6, entries 1, 2, and 3),27,28 the analogous fluorinated
cyclophane Pd(II) complex bearing the weakly donating
nitrile 3,5-bis(trifluoromethyl)benzonitrile (8) was prepared.29
Figure 2. Diagram of H-F interactions in complex 7. Arrows
indicate 1H and 19F pairs in close proximity by observed J
couplings of 19F with 1H and 13C. Atoms are labeled as assigned
in the characterization provided in the Experimental Section.
Polymerizations with Ni(II) and Pd(II) F-Cyc Catalysts.
Treatment of Ni(II) complex 4 with trialkylaluminum reagents
led to the formation of catalytically active species for the
polymerization of ethylene. The highest yields of polymer were
obtained with triethylaluminum (TEA) and triisobutylalumi-
num (TIBA), while less polymer was produced with trimethyla-
luminum (TMA). Both modified methylaluminoxane (MMAO)
and dimethylaluminum chloride were ineffective. The activity,
expressed as turnover number (TON), of complex 4/TIBA was
low at temperatures below 70 °C. Its activity was increased
significantly at elevated temperature and peaked at 105 °C
(Table 1, entries 4-9), with 1 μmol of 4 yielding 0.35 g of
polyethylene after 10 min upon treatment with 1500 equiv of
TIBA and 200 psi ethylene pressure (entry 4). By comparison,
under otherwise similar conditions, the catalyst 3/TIBA was
roughly 10 times more active than 4/TIBA, but lost activity
rapidly at temperature above 70 °C (entries 1 and 2). Despite the
(25) Meinhard, D.; Wegner, M.; Kipiani, G.; Hearley, A.; Reuter, P.;
Fischer, S.; Marti, O.; Rieger, B. J. Am. Chem. Soc. 2007, 129, 9182–9191.
(26) Popeney, C. S.; Camacho, D. H.; Guan, Z. J. Am. Chem. Soc.
2007, 129, 10062–10063.
(27) Mecking, S.; Johnson, L. K.; Wang, L.; Brookhart, M. J. Am.
Chem. Soc. 1998, 120, 888–899.
(28) Gottfried, A. C.; Brookhart, M. Macromolecules 2003, 36, 3085–3100.
(29) Acetonitrile adduct 7 was synthesized along with an inseparable
unidentified minor product, 70. This was additional motivation for the
synthesis of arylnitrile 8, which could be isolated in high purity. Despite
the impurity, GPC traces of polymer produced by 7 were monomodal,
indicating it was not active toward polymerization.

Article
Organometallics, Vol. 28, No. 15, 2009 4457
Figure 3. Representative NMR spectra for complex 7: (a) 19F NMR and (b) 1H NMR without 19F decoupling. The results of selective
19F decoupling experiments are shown for resonances (c) FA, (d) FB, (e) FC, and (f) FD. While not shown here, decoupling of FD led to a
narrowing of the line width at half-height of the acetonitrile methyl resonance from 1.6 to 1.3 Hz. All resonances are labeled as assigned
in the Experimental Section. For clarity, only the decoupling resonances are labeled in (c)-(f).
Interestingly, the polymerization behavior of 8 (entries 5-9) was
nearly identical to that of 7(entry 4), suggesting any inhibition of
polymerization by nitrile was insignificant for the fluorinated
system. Once ethylene solubility was taken into account, it
appeared that the initial activity of 8 was rather constant from
35 °C up to 80 °C, although significant deactivation took place
with time.
densities of the polymers from the F-Cyc Pd(II) catalysts were
reduced 2-fold. The higher linearity led to a corresponding
increase in polymer crystallinity, as evident by the observation
of strong melting transitions seen in differential scanning
calorimetry.
Discussion
As with the Ni(II) catalyst 4, the fluorinated Pd(II) catalysts
7 and 8 displayed distinctly different polymerization behavior
when compared to its nonfluorinated analogues. First, while
the polymers from cyclophane catalysts 5 and 6 were of low
molecular weight (Table 2, entries 1-3),30 catalysts 7 and 8
affordedpolyethyleneswithover 20-foldincrease inmolecular
weight (Table 2, entries 4-9). Since the turnover frequency of
the fluorinated catalyst was comparable to the nonfluorinated
catalyst, chain transfer processes must have been suppressed
in the former to account for the large molecular weight
increase. Furthermore, as with the Ni system, the branching
Introduction of fluorine onto the cyclophane ligand im-
parts significant effects on the polymerization catalytic
properties for its late transition metal complexes. The fluori-
nated Ni(II) and Pd(II) cyclophane catalysts polymerize
ethylene to give polymers exhibiting much less branching
density than their nonfluorinated counterparts. This, in turn,
imparts crystallinity to the polymers and significantly influ-
ences their macroscopic properties (Tables 1 and 2). Since
polymer branching is introduced by the chain-walking me-
chanism, the presence of fluorine apparently inhibits this
process. On the basis of mechanistic studies by Brookhart
and co-workers,6,31 chain walking results from repetitive
hydride elimination and reinsertion reactions of highly re-
active and electron-deficient alkyl agostic intermediates such
(30) The low molecular weight of polymer produced by the cyclo-
phane Pd(II) catalysts is inconsistent with evidence that suggests a
reduction in associative chain transfer rates (see refs 6, 8). Instead, an
additional chain transfer mechanism, possibly dissociative, may operate
preferentially . Popeney, C. S.; Levins, C. M.; Guan, Z. Manuscript in
preparation.
(31) Shultz, L. H.; Tempel, D. J.; Brookhart, M. J. Am. Chem. Soc.
2001, 123, 11539–11555.

4458 Organometallics, Vol. 28, No. 15, 2009
Table 1. Polymerization Results for Ni(II) Complexes 3 and 4a
Popeney et al.
TON/[C2H4]
(ꢀ 10-3 M-1 d
entry cat. Trxn (°C) time (min) load (μmol)b yield (mg) TON (ꢀ 10-3 c
)
)
Mn (kg/mol)e Mw/Mne
Bf
Tm (°C)g
1
2
3
3
4
4
4
4
4
4
4
4
80
115
80
10
10
10
10
10
20
30
45
70
10
1.0
1.0
4520
920
147
345
174
223
318
476
639
170
160
33
140
38
4.5
13
13
17
24
36
48
267
131
1.9
1.5
104.0 N/Ah
116.7 N/A
33.3 86, 114
33.2 81, 122
N/A
3
4
5
6
7
8
9
10
1.0
1.0
5.2
1664, 166i
159
1.4, 1.3i
2.3
105
105
105
105
105
105
120
12
12
16
23
34
46
0.50
0.50
0.50
0.50
0.50
1.0
197
185
2.9
3.0
N/A
35.6 N/A
N/A
N/A
190
115
2.7
4.1
6.3
7.2
40.2 80, 126
a Polymerization conditions: 1500 equiv of TIBA, 200 psi of ethylene. Solvent = 1,2-dichlorobenzene for runs >80 °C, 4:1 toluene/1,2-
dichlorobenzene for other runs. b Catalyst load. c Turnover number (moles of ethylene per mole of catalyst). d Turnover number adjusted for ethylene
monomer concentration (see Supporting Information). e Determined by size exclusion chromatography in 1,2,4-trichlorobenzene at 140 °C with
polyethylene standard. f Branching density per 1000 carbons by 1H NMR. g Melting temperature of crystalline domains determined by differential
scanning calorimetry. h Amorphous. i Individual distributions could be resolved.
Table 2. Polymerization Results for Pd(II) Catalystsa
catalyst load
(mol-6
TOF
(h-1 b
TOF/ [C2H4]
(h-1 M-1 c
Mn
(kg/mol)d
entry
cat.
Trxn (°C)
time (h)
)
yield (g)
)
)
Mw/Mn
Be
Tm (°C)f
1
2
3
4
5
6
7
8
9
5
6
6
7
8
8
8
8
8
35
35
60
60
35
35
60
60
80
18
18
6
18
6
18
6
18
6
10
10
7.7
10
4.0
4.0
3.0
5.0
4.0
2.28
0.50
0.12
1.79
0.60
0.72
0.28
0.76
0.30
450
100
93
350
890
360
560
300
450
670
150
180
680
1300
530
1100
580
12.9
8.31
3.97
166
264
269
161
134
79.5
1.7
1.2
1.2
1.3
1.3
1.6
1.4
1.5
1.4
106
106
114
N/Ag
N/Ag
N/Ag
64.4
66.5
66.4
63.8
64.7
62.9
55.5
51.3
53.2
56.4
60.8
58.3
1100
a Polymerization conditions: in 100 mL of toluene, 88 psi of ethylene pressure. b Turnover frequency = moles of ethylene per mole of catalyst per hour.
c Turnover frequency adjusted for ethylene monomer concentration (see Supporting Information). d Number-averaged molecular weight determined by
size exclusion chromatography coupled to multi-angle light scattering. e Branching density per 1000 carbon atoms as determined by 1H NMR. f Melting
temperature as determined by differential scanning calorimetry. g Amorphous.
Figure 5. Fluorinated cyclophane complexes: axial F-donation
Figure 4. Polymerization activity of 4/TIBA expressed as turn-
in intermediate I and alkyl agostic intermediate II (M = Ni or
Pd).
over number (TON, mol ethylene polymerized/mol catalyst) at
105 °C.
the H-agosic interaction presumed to occur in the nonfluori-
nated cyclophane catalysts.
as II (Figure 5). Our results from NMR analysis have proven
that the fluorine atoms are close enough to the metal to
interact with groups in the metal coordination plane through
spin-spin coupling and by through-bond coupling facili-
tated by donation to Pd. Therefore, the fluorine atoms seem
appropriately positioned to allow the stabilization of elec-
trophilic species by electron donation to the metal (Figure 5).
On the basis of the molecular model of the ligand geometry,
this interaction should occur through the axial coordination
site on the metal when in a 14 e- state. Unlike the H-agostic
interaction, the interaction with fluorine should occur
by donation from the lone pair on fluorine and not from
the C-F bond, giving rise to an intermediate resembling I.
This interaction with fluorine is expected to be stronger than
Molecular weights of polymers prepared by the fluori-
nated Pd(II) complex are much higher than polymers pre-
pared by the analogous nonfluorinated Pd(II) complexes.
Since the turnover frequency of the fluorinated catalyst is
only slightly higher than the nonfluorinated catalyst (Ta-
ble 2), chain transfer processes must be suppressed in the
former to account for the large MW increase. This suppres-
sion can also be attributed to the stabilization of the highly
active catalytic intermediates through interaction with fluor-
ine. The electronic donation of fluorine from the axial
direction should stabilize the 14 e- alkyl intermediate I,
suppressing β-hydride elimination. The suppression of
β-hydride elimination would reduce the rate of chain transfer,

Article
Organometallics, Vol. 28, No. 15, 2009 4459
Scheme 5. The Presence of the Stabilized Resting State II and the Relative Destabilization of Reactive Alkyl Agostic Complex I Lead to
Reduced Rates of Chain Walking, Chain Transfer, and Decomposition with the F-Cyc Series Ni(II) and Pd(II) Catalysts
which is presumed to operate by associative monomer dis-
placement from the formed olefin hydride intermediate.6,31
This proposal is consistent with the observed reduction in
branching density because β-hydride elimination is critical for
chain walking. Alternatively, as proposed by Ziegler,32 chain
transfer could occur by concerted hydride transfer from the
polymer chain to bound ethylene in the 16 e- alkyl olefin
complex (III). As mentioned previously, in the F-Cyc system
this 16 e- complex is a short-lived intermediate that is not
detectable by NMR. Therefore, the occurrence of chain
transfer by this mechanism would also be suppressed in the
F-Cyc case because of the limited availablility of III.
and catalyst deactivation (thermal stability). The fluo-
rine-stabilized 14 e- alkyl intermediates are less prone to
β-hydride elimination and, hence, less chain walking and less
chain transfer. Because the most reactive 14 e- alkyl agostic
complexes are also key intermediates along the paths of other
processes such as catalyst deactivation, its stabilization may
account for the enhanced thermal stability of the
Ni(II) catalyst.
Conclusions
A significant effect on reactivity and polymer properties
was observed in Ni(II) and Pd(II) olefin polymerization
catalysts bearing a fluorinated cyclophane-based ligand.
Elevated thermal stability was observed for the Ni(II) com-
plex, and significant molecular weight increase was obtained
from the Pd(II) complex. In both metal systems, a large
reduction in chain-branching density was noted, which
suggests a significant reduction in chain-walking isomeriza-
tion. As chain walking was proposed to proceed through
repetitive β-hydride elimination followed by nonregioselec-
tive reinsertion of the hydride, the reduced extent of chain
walking for the fluorinated complexes most likely operates
through restriction of the β-hydride elimination process.
Evidence for interaction between fluorine and Ni(II) and
Pd(II) was gathered by NMR spectroscopy. The strong cou-
pling observed in the NMR between the fluorine atoms and
protons and carbons of coordinating ligands provided evidence
for a direct interaction between fluorine and the metal center.
Lastly, the lack of observation of bound olefin species in the
fluorinated Pd(II) system and the large effect of olefin concen-
tration on polymerization activity implied increased stability of
the 14 e- polymerization intermediates. To the best of our
knowledge, this represents the first example of direct fluorine
interactions with late metal centers in polymerization catalysts
and their positive effects on olefin polymerization.
Another dramatic effect of cyclophane ligand fluorination
is the significant enhancement of thermal stability for the
Ni(II) complex. Although knowledge of the deactivation
processes of Ni(II) catalysts is limited, the alkyl agostic
complex II, being the most reactive intermediate in the
system, is likely involved. Therefore, stabilization of this
intermediate by electronic donation from fluorine could
account for the high thermal stability of the Ni(II) catalyst.
A further interesting observation is that while the polym-
erization activity of Pd(II)-R-diimine catalysts are typically
independent of monomer concentration,2,3,6,31 the produc-
tivity of the fluorinated Pd(II) catalyst (7) was strongly
dependent on the ethylene pressure. In in situ NMR polym-
erization experiments, polyethylene production was ob-
served although bound ethylene signals were not. These
observations suggest that the ethylene trapping step, rather
than monomer insertion,6 is rate limiting and that a 14 e-
species lacking bound olefin is the catalytic resting state.
On the basis of all these observations, we propose that
axial fluorine donation to the metal center helps to stabilize
the 14 e- alkyl intermediates and the olefin-free F-ligated
complex I is the catalytic resting state (Scheme 5). The exact
structure of complex I could involve the interaction of either
one fluorine to form a four-coordinate complex with sig-
nificant tetrahedral distortion33 or two fluorines above
and below the metal coordination plane in a distorted
trigonal-bipyramidal complex.34 The stabilization of the
14 e- reactive catalytic intermediates suppresses a number
of potential pathways as outlined in Scheme 5: chain transfer
(molecular weight), chain walking (branching architecture),
Experimental Section
General Considerations. All catalyst handling was carried out
in a Vacuum Atmospheres glovebox filled with nitrogen. All
moisture- and air-sensitive reactions were carried out in flame-
dried glassware using magnetic stirring under a positive pressure
of nitrogen. Removal of organic solvents was accomplished by
rotary evaporation and is referred to as concentrated in vacuo.
Flash column chromatography was performed using forced
flow on 230-400 mesh silica gel purchased from Dynamic
Adsorbents, Inc. NMR spectra were recorded on Bruker
DRX400, DRX500, and AVANCE600 FT-NMR instruments.
Proton and carbon NMR spectra were recorded in ppm and were
(32) Deng, L.; Woo, T. K.; Cavallo, L.; Margl, P. M.; Ziegler, T. J.
Am. Chem. Soc. 1997, 119, 6177–6186.
(33) Dawson, J. W.; Gray, H. B.; Hix, J. E.Jr.; Preer, J. R.; Venanzi,
L. M. J. Am. Chem. Soc. 1972, 94, 2979–2987.
(34) Antsishkina, A. S.; Porai-Koshits, M. A.; Nivorozhkin, A. L.;
Vasilchenko, I. S.; Nivorozhkin, L. E.; Garnovsky, A. D. Inorg. Chim.
Acta 1991, 180, 151–152.

4460 Organometallics, Vol. 28, No. 15, 2009
Popeney et al.
referenced to the indicated solvents. Fluorine NMR spectra were
recorded in ppm and were referenced to CFCl3. Data were reported
as follows: chemical shift, multiplicity (s = singlet, d = doublet,
t=triplet, q=quartet), integration, and coupling constant(s) in
hertz (Hz). Multiplets (m) were reported over the range (ppm) at
which they appear at the indicated field strength. Elemental
analysis was performed by Atlantic Microlab, Norcross, GA.
High-resolution mass spectrometry (HR-MS) was recorded on a
Micromass LCT or a Micromass Autospec. Infrared spectrometry
was performed by the thin-film method with a Prospect PRS-102
spectrometer from Midac Corp. High-pressure polymerizations
were conducted in a mechanically stirred water-cooled 600 mL
Parr autoclave.
Materials. Toluene, tetrahydrofuran (THF), diethyl ether, and
dichloromethane were purified by passing through solvent purifica-
tion columns and are referred to herein as dry.35 Pentane was dried
by distillation from the solution with sodium benzophenone ketyl.
1,2-Dichlorobenzene was purified by passage through activated
basic alumina under a nitrogen atmosphere. Unless otherwise
stated, all other solvents and reagents were purchased from com-
mercial suppliers and used as received. Grubbs second-generation
catalyst was generously donated by Materia Inc. All catalysts were
stored in a glovebox under a nitrogen atmosphere. The syntheses
and characterization of the nonfluorinated cyclophane ligand 1
and Pd(II) complex 5 can be found in the literature.7,8 2-Dicyclo-
hexylphosphino-20,60-dimethoxybiphenyl (S-Phos)36 and
sodium tetrakis(3,5-bis(trifluoromethyl)phenyl)borate (Na-
BAr4)37 were prepared by known literature procedures. Spectral
data for the BAr-4 anion can be found elsewhere and will not be
repeated in the spectroscopic data below.27
2-(3,5-Difluorophenyl)-1,3-dioxolane (9). 1,3-Propanediol (48.33
mL, 50.89 g, 669 mmol) was added to a solution of 3,5-difluor-
obenzaldehyde (47.53 g, 334 mmol) and 500 mg of p-toluenesul-
fonic acid monohydrate in 100 mL of toluene. The flask was
equipped with a Dean-Stark trap and heated to reflux with
stirring for 4 h, cooled, and poured into 100 mL of water and
100 mL of saturated NaHCO3 solution. The organic phase was
separated, and the aqueous phase was extracted with diethyl ether
(2 ꢀ 100 mL). The organic phases were combined, washed with
water, and concentrated in vacuo. Vacuum distillation afforded 9as
a colorless oil (63.64 g, 95%): 1H NMR (400 MHz, CDCl3) δ 1.42
(d, 1H, J=13.6 Hz), 2.17 (m, 1H), 3.94 (t, 2H, J=12.1 Hz), 4.20 -
4.24 (m, 2H), 5.42 (s, 1H), 6.75 (tt, 1H, JHF=8.8 Hz, J=2.3 Hz),
7.01 (pseudo d, 2H, JHF=8.0 Hz); 13C NMR (125 MHz, CDCl3) δ
25.8, 67.5, 99.88 (d, 4JCF=1.3 Hz), 104.1 (t, 2JCF=23.9 Hz), 109.4
(dd, 2JCF=20.1 Hz, 4JCF=6.3 Hz), 142.7 (t, 3JCF=10.1 Hz), 163.1
(dd, 1JCF=249.0 Hz, 3JCF=12.6 Hz).
113.6, 133.6, 143.3, 149.8. Anal. Calcd for C7H5NO2Br2: C, 28.51;
H, 1.71; N, 4.75. Found: C, 28.59; H, 1.65; N, 4.66.
F-Terphenyl Nitro Diacetal (11). To a solution of 9 (8.38 mL,
9.987 g, 49.89 mmol) in 100 mL of dry THF cooled to -78 °C
was dropwise added 18.86 mL of a 2.86 M solution of butyl-
lithium in hexanes (53.93 mmol). After 1 h, anhydrous zinc
chloride (7.354 g, 53.93 mmol) was added with rapid stirring,
and the mixture was slowly warmed to room temperature over
1 h. The mixture was transferred via cannula to a solution of 10
(6.628 g, 22.47 mmol), S-Phos (185 mg, 0.449 mmol), and
Pd2(dba)3 (206 mg, 0.225 mmol) in dry THF (40 mL), and the
mixture was heated to reflux overnight. The reaction was
cooled, and 200 mL of water and 50 mL of saturated NH4Cl
solution were added. The organic layer was separated and the
aqueous layer extracted twice with diethyl ether (100 mL). The
organic phases were recombined, washed with brine, and dried
over MgSO4. Purification by flash chromatography in 4:1
hexanes/ethyl acetate afforded 11 as a tan solid (6.84 g, 57%):
1H NMR (500 MHz, CDCl3) δ 1.46 (m, 2H), 2.21 (m, 2H), 2.49
(s, 3H), 3.99 (td, 4H, J=12.1, 1.2 Hz), 4.27 (dd, 4H, J=11.5, 4.8
Hz), 5.48 (s, 2H), 7.13 (d, 4H, JHF=7.8 Hz), 7.26 (s, 2H); 13
C
NMR (125 MHz, CDCl3) δ 21.3, 25.6, 67.4, 99.4, 109.5 (dd,
2JCF=21.3 Hz, 4JCF=6.0 Hz), 114.2 (t, 2JCF=20.3 Hz), 124.1,
133.5, 141.76, 142.08 (t, 3JCF=9.1 Hz), 148.2, 159.6 (dd, 1JCF
=
3
249.2 Hz, JCF =6.9 Hz); 19F NMR (376 MHz, CDCl3) δ -
112.14 (d, JHF = 7.8 Hz). Anal. Calcd for C27H23NO6F4: C,
60.79; H, 4.35; N, 2.63. Found: C, 60.11; H, 4.41; N, 2.49.
F-Terphenyl Nitro Dialdehyde (12). A solution of diacetal 11
(5.00 g, 9.37 mmol) in 90 mL of glacial acetic acid and 15 mL of
water was heated to reflux for 1 h, then cooled and concentrated
in vacuo to 20 mL. The mixture was neutralized with saturated
NaHCO3 solution, and water (50 mL) was added and extracted
with diethyl ether (3ꢀ100 mL). The organic layers were com-
bined, washed once with water and once with brine, and dried
over MgSO4. The solution was concentrated in vacuo to 10 mL
and stored at -30 °C for 2 h. The mixture was decanted, and the
remaining crystals were dried in vacuo to afford the dialdehyde
1
12 as pale brown crystals (2.88 g, 74%): H NMR (500 MHz,
CDCl3) δ 2.55 (s, 3H), 7.39 (s, 2H), 7.53 (d, 4H, JHF=6.5 Hz),
9.98 (s, 2H). 13C NMR (125 MHz, CDCl3) δ 21.4, 112.4 (dd, 2J
CF=20.1 Hz, 4JCF=5.0 Hz), 120.2 (t, 2JCF=20.4 Hz), 123.8,
133.8, 141.76, 138.3 (t, 3JCF=7.4 Hz), 142.9, 160.1 (dd, 1JCF
=
252.9 Hz, 3JCF=6.0 Hz), 189.0; 19F NMR (376 MHz, CDCl3)
δ -109.60 (d, JHF=6.2 Hz); HR-MS calcd for [C21H11NO4F4 -
H]- 416.0546, found 416.0544.
F-Terphenyl Nitro Diolefin (13). In a separate flask, a sus-
pension of 8.37 g of methyltriphenylphosphonium bromide
(23.4 mmol) and potassium tert-butoxide (2.98 g, 8.15 mmol)
in 1500 mL of THF was stirred for 1 h at room temperature, then
cooled to -78 °C. A solution of dialdehyde 12 (3.26 g,
7.81 mmol) in 100 mL of THF was added dropwise over
15 min, and the resulting mixture was stirred at - 78 °C for
4 h, then slowly allowed to warm to 0 °C over 1.5 h. The reaction
was quenched with 150 mL of water and 150 mL of saturated
NH4Cl solution, and the organic layer was separated and
concentrated to 200 mL. The aqueous layer was extracted twice
with diethyl ether (50 mL), and the organic layers were com-
bined, washed with brine, and dried over MgSO4. The solvent
was removed in vacuo and the product purified by flash chro-
matography in 9:1 hexanes/ethyl acetate to afford 13 as a light
brown solid (2.46 g, 76%): 1H NMR (500 MHz, CDCl3) δ 2.51
(s, 3H), 5.42 (d, 2H, J=10.8 Hz), 5.81 (d, 2H, J=17.5 Hz), 6.66
(dd, 2H, J=17.5, 10.8 Hz), 7.02 (d, 4H, JHF=8.3 Hz), 7.33 (s,
2H); 13C NMR (125 MHz, CDCl3) δ 21.5, 109.4 (dd, 2JCF=21.4
1,3-Dibromo-5-methyl-2-nitrobenzene (10).38 2,6-Dibromo-4-
methylaniline (22.64 g, 85.5 mmol) and 3-chloroperoxybenzoic
acid (84.26 g, 70 wt %, 342 mmol) were dissolved in 600 mL of
CH2Cl2 and heated to reflux for 6 h. The mixture was cooled in an
ice bath and filtered. Then the filtrate was washed with 1.0 N KOH
solution (4 ꢀ 200 mL). The organic phase was concentrated in
vacuo to afford a tan solid. The residue was redissolved in 350 mL
of glacial acetic acid, and to this was added 120 mL of 30%
hydrogen peroxide solution and 22 mL of concentrated nitric acid.
The mixture was heated to reflux for 2 h, then cooled and poured
into 2.0 L of ice water. The suspension was left to stand overnight,
then filtered, and the solid was washed with water, then dried under
suction. Recrystallization in 99:1 hexanes/methanol afforded 10 as
a pale yellow solid (20.32 g, 81%): 1H NMR (400 MHz, CDCl3)
δ 2.38 (s, 3H), 7.42 (s, 2H); 13C NMR (100 MHz, CDCl3) δ 21.1,
(35) Pangborn, A. B.; Giardello, M. A.; Grubbs, R. H.; Rosen, R. K.;
Timmers, F. J. Organometallics 1996, 15, 1518–1520.
(36) Barder, T. E.; Walker, S. D.; Martinelli, J. R.; Buchwald, S. L. J.
Am. Chem. Soc. 2005, 127, 4685–4696.
(37) Yakelis, N. A.; Bergman, R. G. Organometallics 2005, 24, 3579–
3581.
4
2
Hz, JCF = 6.3 Hz), 113.3 (t, JCF = 21.4 Hz), 117.4, 124.3,
133.7, 134.8, 140.8 (t, 3JCF=10.1 Hz), 141.9, 148.4, 160.1 (dd,
1JCF=247.8 Hz, 3JCF=7.5 Hz); 19F NMR (376 MHz, CDCl3)
δ -112.93 (d, JHF=8.2 Hz). Anal. Calcd for C23H15NO2F4: C,
66.83; H, 3.66; N, 3.39. Found: C, 67.06; H, 3.80; N, 3.27.
(38) Shen, D.; Diele, S.; Pelzl, G.; Wirth, I.; Tschierske, C. J. Mater.
Chem. 1999, 9, 661–672.

Article
F-Terphenyl Aniline Diolefin (14). To a mixture of diolefin
Organometallics, Vol. 28, No. 15, 2009 4461
3JCF=7.4 Hz), 162.5; 19F NMR (376 MHz, CDCl3) δ -113.12
(t, J=7.0 Hz), -109.54 (dd, J=9,1, 6.3 Hz); HR-MS calcd for
[C54H32N2F8 + Na]+ 883.2335, found 883.2359.
13 (2.09 g, 5.06 mmol) and tin(II) chloride dihydrate (6.85 g,
30.4 mmol) in 200 mL of ethanol was added 15 mL of concen-
trated hydrochloric acid. The mixture was heated to reflux and
stirred for 8 h. The organic solvent was removed in vacuo,
200 mL of water was added, and the mixture was made strongly
basic by addition of solid potassium hydroxide. The mixture was
extracted with CH2Cl2, and the organic layer was separated,
washed once with water, and concentrated in vacuo. The residue
was recrystallized in 5:1 ethanol/CH2Cl2 to afford 14 as a
light tan solid identifiable by pale blue fluorescence at 365 nm
[(Cyc)Ni(acac)]B(C6F5)4 (3). 19 A scintillation vial was charged
with diimine 1 (54 mg, 0.075 mmol), trityl tetrakis(pentafluoro-
phenyl)borate (70 mg, 0.075 mmol), and Ni(acac)2 (19 mg,
0.075 mmol). To this was added 2 mL of dry CH2Cl2 and 8 mL
of dry diethyl ether, and the reaction was stirred for 1 h at room
temperature. Pentane (10 mL) was added, the mixture was
decanted, and the solid was washed with 10 mL of diethyl ether
and 10 mL of pentane. The solid was dried for two days in vacuo
to afford 3 as a dark red solid (72 mg, 93%): 1H NMR
(500 MHz, CD2Cl2) δ 1.79 (s, 6H), 2.38 (s, 6 H), 3.03 - 3.22
(m, 8H), 5.56 (s, 1H), 6.44 (d, 4H, J=7.8 Hz), 6.60 (d, 4H, J=
7.8 Hz), 6.85 (d, 2H, J=7.2 Hz), 7.11 (s, 4H), 7.24 (d, 4H, J=
7.8 Hz), 7.30 (d, 4H, J=7.8 Hz), 7.67 (t, 2H, J=8.2 Hz), 8.22 (d,
2H, J=8.0 Hz); 13C NMR (125 MHz, CD2Cl2) δ 21.5, 25.1, 35.2,
102.7, 125.4, 126.84, 127.58, 128.84, 129.68, 130.29, 130.81,
131.83, 132.20, 133.63, 135.85, 135.97, 137.0, 139.3, 140.8,
173.7, 187.8. Anal. Calcd for C83H47N2O2BF20Ni: C, 64.16; H,
3.05; N, 1.80. Found: C, 64.38; H, 3.08; N, 1.74.
1
(1.715 g, 79%): H NMR (500 MHz, CDCl3) δ 2.34 (s, 3H),
3.47 (br s, 2H), 5.42 (d, 2H, J=10.8 Hz), 5.83 (d, 2H, J=17.5
Hz), 6.69 (dd, 2H, J=17.5, 10.8 Hz), 7.03 (s, 2H), 7.07 (d, 4H,
HF=8.0 Hz); 13C NMR (125 MHz, CDCl3) δ 20.4, 109.5 (dd,
J
2JCF=20.1 Hz, 4JCF=5.0 Hz), 114.6 (t, 2JCF=21.7 Hz), 115.4,
116.7, 127.3, 132.6, 134.8, 139.9 (t, 3JCF=9.7 Hz), 140.7, 160.7
1
3
(dd, JCF = 247.8 Hz, JCF = 8.8 Hz); 19F NMR (376 MHz,
CDCl3) δ -111.36 (d, JHF = 7.9 Hz). Anal. Calcd for
C23H17NF4: C, 72.06; H, 4.47; N, 3.65. Found: C, 71.86; H,
4.50; N, 3.62.
19
Open F-Diimine (15). Aniline 14 (1.538 g, 4.01 mmol), ace-
naphthenequinone (329 mg, 1.81 mmol), and 80 mg of pTSA
were reacted in 70 mL of benzene for two days, then purified by
flash chromatography in 6:1 hexanes/ethyl acetate to afford 15
as an orange solid (782 mg, 47%): 1H NMR (500 MHz, CDCl3)
δ 2.43 (s, 3H), 5.25 (d, 4H, J=10.8 Hz), 5.59 (d, 4H, J=17.5 Hz),
6.43 - 6.50 (m, 8H), 6.64 (d, 4H, JHF=9.7 Hz), 6.95 (d, 2H,
J=7.1 Hz), 7.16 (s, 4H), 7.28 (t, 2H, J=8.2 Hz), 7.68 (d, 2H, J=
[(F-Cyc)Ni(acac)]B(C6F5)4 (4). A scintillation vial was
charged with diimine 2 (43 mg, 0.050 mmol), trityl tetrakis
(pentafluorophenyl)borate (46 mg, 0.050 mmol), and Ni(II)
acetylacetonate (13 mg, 0.050 mmol). To this was added
10 mL of dry CH2Cl2, and the reaction was stirred for 1 h at
room temperature. Pentane (10 mL) was added, and the mixture
was decanted. The solid was suspended in 10 mL of diethyl ether
precipitated with 10 mL of pentane, decanted, and dried for two
days in vacuo to afford 4 as a dark red solid (45 mg, 58%):
1H NMR (500 MHz, CDCl3) δ 1.65 (s, 6H), 2.44 (s, 6H), 3.13 -
3.26 (m, 8H), 5.38 (s, 1H), 6.38 (d, 4H, JHF=9.9 Hz), 6.85 (d, 4H,
JHF=9.8 Hz), 7.09 - 7.13 (m, 2H), 7.21 (s, 4H), 7.57 (t, 2H, J=
8.0 Hz), 8.18 (d, 2H, J=8.3 Hz); 13C NMR (125 MHz, CDCl3)
δ 21.2, 23.7, 33.0, 102.0, 111.38 (t, 2JCF=21.7 Hz), 112.37 (dd,
8.2 Hz); 13C NMR (125 MHz, CDCl3) δ 20.8, 108.2 (d, 2JCF
=
2
2
26.4 Hz), 109.2 (d, JCF=23.9 Hz), 115.7 (t, JCF=20.1 Hz),
116.0, 118.9, 127.0, 127.99, 128.36, 130.2, 132.6, 133.5, 135.0,
138.6 (t, 3JCF=10.1 Hz), 139.9, 147.1, 160.3 (dd, 1JCF=245.3,
3JCF = 8.3 Hz), 160.7, 161.6; 19F NMR (376 MHz, CDCl3)
δ -112.88 (dd, J=8.2, 5.6 Hz), -108.18 (dd, J=9.1, 5.6 Hz).
Anal. Calcd for C58H36N2F8: C, 76.31; H, 3.97; N, 3.07. Found:
C, 76.48; H, 4.11; N, 3.02.
2JCF=22.9 Hz, 4JCF=3.2 Hz), 113.24 (dd, 2JCF=22.2 Hz, 4JCF
=
3
3.2 Hz), 122.8, 125.0, 128.2, 129.4 (t, JCF = 7.9 Hz), 130.8,
F-Cyclophane, Unhydrogenated (16). Diimine 15 (257 mg,
0.282 mmol) and Grubbs catalyst (45 mg) were reacted in
280 mL of degassed CH2Cl2 for 3 h, concentrated in vacuo, then
purified by flash chromatography in CH2Cl2 to afford 16 as a
yellow solid (157 mg, 65%): 1H NMR (500 MHz, CDCl3) δ 2.47
(s, 6H), 6.14 (d, 4H, JHF=9.7 Hz), 6.54 (d, 4H, JHF=9.2 Hz),
6.83 (s, 4H), 6.85 (d, 2H, J=7.3 Hz), 7.25 (s, 4H), 7.34 (t, 2H, J=
7.3 Hz), 7.80 (d, 2H, J=8.3 Hz); 13C NMR (125 MHz, CDCl3) δ
133.54, 133.85, 138.57, 139.12, 143.7 (t, 3JCF=9.7 Hz), 159.64
(dd, 1JCF=249.7 Hz, 3JCF=7.9 Hz), 159.75 (dd, 1JCF=248.3 Hz,
3JCF=7.9 Hz), 174.0, 187.2; 19F NMR (376 MHz, CDCl3) δ -
109.45, -108.03. Anal. Calcd for C83H39N2O2BF28Ni: C, 58.72;
H, 2.32; N, 1.65. Found: C, 58.74; H, 2.58; N, 1.66.
[(Cyc)PdMe(NCMe)]BAr4, Ar = 3,5-(CF3)2C6H3 (6). An
oven-dried flask was charged with 26 mg of (Cyc)PdMeCl7
(0.030 mmol) and 27 mg of NaBAr4 (0.030 mmol). To this was
added 5 mL of CH2Cl2 and 1.0 mL of acetonitrile, and the
mixture was stirred overnight at room temperature. The mixture
was filtered through Celite and concentrated in vacuo to 1 mL.
Pentanes (15 mL) were added, the mixture was left to stand for
30 min, and the supernatant was decanted. The solid residue was
dried for 24 h in vacuo to afford 6 as a rust-colored solid (46 mg,
88%). Representative 2D NMR spectra and NOE measure-
ments used during assignment are given in the Supporting
20.8, 111.2 (dd, 2JCF=23.1 Hz, 4JCF=3.2 Hz), 112.8 (dd, 2JCF
23.1 Hz, 4JCF=3.2 Hz), 114.2 (t, 2JCF=21.4 Hz), 118.7, 123.8,
=
127.0, 128.4, 129.2, 130.3, 132.69, 132.85, 133.15, 139.1 (t, 3JCF
10.1 Hz), 140.2, 148.3, 159.26 (dd, JCF = 251.5 Hz, JCF
8.2 Hz), 159.94 (dd, 1JCF=247.8 Hz, 3JCF=7.9 Hz), 162.8; 19
=
=
F
1
3
NMR (376 MHz, CDCl3) δ -112.32 (dd, J = 9.4, 6.2 Hz),
-108.90 (dd, J=8.7, 6.2 Hz); HR-MS calcd for [C54H28N2F8+
H]+ 857.2203, found 857.2202.
F-Cyclophane, Hydrogenated (F-Cyc, 2). Palladium on acti-
vated carbon (20 mg, 10 wt % Pd) was added to a N2-degassed
solution of diimine 16 (133 mg, 0.155 mmol) in 10 mL of
methanol, 10 mL of CH2Cl2, and 0.5 mL of triethylamine. The
mixture was purged with hydrogen for 5 min, stirred under a
hydrogen atmosphere for 1 h at room temperature, filtered
through Celite, and concentrated in vacuo. The residue was
washed with 10 mL of methanol and dried overnight under high
vacuum to afford 2 as a yellow solid (126 mg, 94%): 1H NMR
(500 MHz, CDCl3) δ 2.48 (s, 6H), 2.86 - 3.07 (m, 8H), 6.16 (d,
4H, J=9.5 Hz), 6.57 (d, 2H, J=7.2 Hz), 6.61 (d, 4H, J=9.1 Hz),
1
Information. H NMR (500 MHz, CD2Cl2) δ 0.72 (s, 3H, Pd-
Me), 2.20 (s, 3H, NCMe), 2.45 (s, 3H, Ar-Me), 2.46 (s, 3H, Ar-
Me), 2.81 - 3.22 (m, 8H, N), 6.23 (m, 4H, L/M), 6.50 (d, 1H, J=
7.2 Hz, K), 6.59 (d, 2H, J=7.8 Hz, J), 6.75 (d, 2H, J=7.9 Hz, I),
6.89 (d, 2H, J=7.9 Hz, H), 6.97 (d, 2H, J=7.2 Hz, G), 7.16 (d,
1H, J=8.0 Hz, E), 7.17 (s, 2H, F), 7.19 (s, 2H, F), 7.21 (d, 2H,
J=7.8 Hz, D), 7.26 (d, 2H, J=7.9 Hz, A), 7.57-7.62 (m, 2H,
C), 8.12 (d, 1H, J=8.3 Hz, B0), 8.15 (d, 1H, J=8.3 Hz, B); 13C
NMR (125 MHz, CD2Cl2) δ 3.9 (NCMe), 7.0 (Pd-Me), 21.27
(Ar-Me), 21.33 (Ar-Me), 34.95 (af), 35.01 (af), 121.79 (NCMe),
125.70 (ae), 126.52 (ab), 126.90 (ad), 127.80 (aa), 127.91 (v/ac),
128.66 (y), 128.96 (n), 129.37 (z), 129.56 (x), 129.76 (t), 129.83
(u), 130.01 (w), 130.49 (s), 131.46 (o), 131.88 (m), 131.94 (q),
132.30 (p), 133.09 (r), 135.03 (j/j’), 135.26 (l), 135.42 (k),
138.05 (h), 138.68 (i), 138.81 (d), 140.37 (f/g), 140.41 (f/g),
140.75 (e), 145.25 (c), 169.7 (b), 176.3 (a). Anal. Calcd for
7.19 (s, 4H), 7.33 (t, 2H, J=7.7 Hz), 7.81 (d, 2H, J=8.3 Hz); 13
C
NMR (125 MHz, CDCl3) δ 21.0, 33.6, 111.0 (dd, 2JCF=22.2 Hz,
4JCF=3.2 Hz), 112.5 (dd, 2JCF=22.2 Hz, 4JCF=3.2 Hz), 113.2 (t,
2JCF = 21.7 Hz), 119.0, 125.1, 126.9, 128.30, 128.65, 130.5,
132.71, 133.13, 140.63, 141.28 (t, 3JCF=8.8 Hz), 149.4, 159.67
(dd, 1JCF=250.6 Hz, 3JCF=9.3 Hz), 160.26 (dd, 1JCF=246.5 Hz,

4462 Organometallics, Vol. 28, No. 15, 2009
Popeney et al.
C89H58N3PdBF24: C, 61.34; H, 3.35; N, 2.41. Found: C, 61.64;
H, 3.32; N, 2.39.
and 0.10 mL of 3,5-bis(trifluoromethyl)benzonitrile (140 mg,
0.59 mmol). The mixture was stirred for 10 h at room tempera-
ture, then filtered through Celite. The solution was concentrated
to 1 mL, pentanes were added, and the mixture was left to stand
for 1 h. The supernatant was decanted and the solid residue was
dried in vacuo for 24 h to afford 8 as an orange solid (107 mg,
88%): 1H NMR (500 MHz, CD2Cl2) δ 0.97 (t, 3H, JHF=4.3 Hz),
[(F-Cyc)PdMe(NCMe)]BAr4, Ar = 3,5-(CF3)2C6H3 (7). An
oven-dried flask was charged with 47 mg of Pd(COD)MeCl
(0.18 mmol), 153 mg of diimine 2 (0.18 mmol), and 158 mg of
NaBAr4 (0.18 mmol). To this was added 10 mL of dry CH2Cl2
and 1.0 mL of acetonitrile. The mixture was stirred for 10 h at
room temperature, then filtered through Celite. The solution
was concentrated to 2 mL, pentanes were added, and the
mixture was left to stand for 1 h. The supernatant was decanted,
and the solid residue was dried in vacuo for 24 h to afford 225 mg
(75% yield by weight) of a mixture of 7 (75%) and side product
70 (25%). Anal. Calcd for C89H50N3PdBF32: C, 56.66; H, 2.67;
N, 2.23. Found: C, 57.17; H, 2.71; N, 2.09. The following spectra
are separately given for cations of 7 and 70. Assignments for the
cation 7 were corroborated by HMQC, HMBC, and 1H-de-
2.47 (s, 3H), 2.51 (s, 3H), 3.02 - 3.20 (m, 8H), 6.26 (d, 2H, 3JHF
=
9.8 Hz), 6.39 (d, 2H, 3JHF=9.8 Hz), 6.73 (d, 2H, 3JHF=10.0 Hz),
6.80 (d, 1H, 3JHF=9.9 Hz), 6.88-6.94 (m, 1H), 7.03-7.09 (m,
1H), 7.34 (s, 2H), 7.36 (s, 2H), 7.48-7.56 (m, 2H, obscured by
BAF-), 8.14 (pseudo t, 2H, J=8.3 Hz), 8.20 (s, 1H); 13C NMR
(125 MHz, CD2Cl2) δ 9.5 (t, JCF=9.7 Hz), 20.93, 21.30, 32.88,
2
2
32.97, 111.34 (t, JCF =20.8 Hz), 111.51 (t, JCF = 21.3 Hz),
112.89 (dd, 2JCF=22.6 Hz, 4JCF=2.9 Hz), 113.16 (dd, 2JCF
=
=
4
21.8 Hz, JCF =2.8 Hz), 113.23 (dd, JCF =22.7 Hz, JCF
2
4
19
2
4
coupled F methods. The characterization of side product 70
2.9 Hz), 113.28 (dd, JCF = 22.2 Hz, JCF = 2.9 Hz), 119.22,
119.72, 122.50 (quartet, JCF = 273.3 Hz), 122.59, 123.67 (t,
1
was incomplete because of the small quantities present.
[(F-Cyc)PdMe(NCMe)]BAr4, Ar=3,5-(CF3)2C6H3 (7): Char-
acterization of 7 was aided by 1H NMR with selective 19F
decoupling. Standard 1H pulses were applied over a continuous
weak 19F decoupling signal targeting a single fluorine resonance.
Assignments of carbons were aided by the 2D methods HMQC
JCF=2.3 Hz), 124.22, 124.86 (t, JCF=4.2 Hz), 128.20, 128.26,
128.81 (t, JCF=5.6 Hz), 128.97 (m, obscured by BAF-), 130.00
(t, JCF=6.9 Hz), 133.06 (septet, 3JCF=3.8 Hz), 133.44 (quartet,
3JCF=3.7 Hz), 133.52, 134.17, 134.85, 138.90, 139.64, 141.78,
3
3
142.82, 143.98 (t, JCF = 9.7 Hz), 144.18 (t, JCF = 9.3 Hz),
146.69, 159.46 (dd, 1JCF=246.9 Hz, 3JCF=7.9 Hz), 159.53 (dd,
and HMBC. 1H NMR (500 MHz, CD2Cl2) δ 0.80 (t, 3H, JHF
=
3
1
4.5 Hz, Pd-Me), 2.00 (s, 3H, NCMe), 2.48 (s, 3H, Ar-Me), 2.50
(s, 3H, Ar-Me), 3.02 - 3.24 (m, 8H, HJ), 6.25 (d, 2H, JHF
10.1 Hz, HI), 6.37 (d, 2H, JHF=9.7 Hz, HH), 6.74 (d, 2H, JHF
9.8 Hz, HG), 6.79 (d, 2H, JHF = 9.7 Hz, HF), 6.88 (dt, 1H,
1JCF=245.5 Hz, JCF=7.9 Hz), 160.32 (dd, JCF=249.2 Hz,
2
4
=
=
3JCF =7.8 Hz), 160.35 (dd, JCF =247.8 Hz, JCF =7.4 Hz),
171.55, 177.8; 19F NMR (376 MHz, CD2Cl2) δ -110.54 (m, 2F),
-109.63 (m, 2F), -107.71 (m, 4F), -63.89 (s, 6F). Anal. Calcd
for C96H50N3PdBF38: C, 55.31; H, 2.42; N, 2.02. Found: C,
55.61; H, 2.41; N, 2.15.
JHH=7.3 Hz, JHF=4.6 Hz, HE), 7.00 (dt, 1H, JHH=7.3 Hz,
J
HF=4.2 Hz, HD), 7.29 (s, 2H, HC’), 7.33 (s, 2H, HC), 7.46 - 7.54
(m, 2H, partially obscured by BAF-, HB), 8.11 (d, 1H, J =
Estimation of Ethylene Concentration. The solubilities of
ethylene in this work was estimated from those in toluene
reported by Lee et al.,39 which provided values at 50, 100, and
150 °C at a range of pressures. Solubilities at the desired pressure
(200 psi/13.79 bar or 88 psi/6.07 bar) at these temperatures were
first obtained by a linear fit of the literature data and then
adjusted to other temperatures by quadratic fit. The concentra-
tions were converted from grams of ethylene per gram of solvent
to moles of ethylene per liter of solvent, considering 200 mL of
toluene was used as solvent and assuming the same volume
during the course of the reaction. The calculated values are
shown in the Supporting Information, Table S1, and the quad-
ratic fits are shown in the Supporting Information, Figure S3.
General Procedure for Ni(II)-Catalyzed Polymerizations.
A 600 mL autoclave was heated under vacuum to 120 °C for
2 h, then twice purged with ethylene and adjusted to the desired
polymerization temperature by external oil bath. A flask was
charged with a desired amount of catalyst 3 or 4 under a nitrogen
atmosphere, and to this was added 10 mL of 1,2-dichloroben-
zene. In a separate flask was added 80 mL of dry toluene or 1,2-
dichlorobenzene, the latter solvent if the polymerization was
conducted at a temperature higher than 80 °C, and a suitable
amount of aluminum coactivator solution in toluene ([Al]/[Ni]=
1500). An additional 10 mL of 1,2-dichlorobenzene was set
aside. The solution of Al activator was then transferred into the
reactor by vacuum under nitrogen stream. Ethylene was intro-
duced to a pressure of 200 psi, and the mixture was rapidly
stirred for 10 min and then vented. The catalyst solution was
transferred into the reactor by vacuum under nitrogen stream
and flushed with the final 10 mL of 1,2-dichlorobenzene. The
reactor was filled with ethylene to 200 psi, and the polymeriza-
tion was allowed to proceed for the desired time with rapid
stirring. The reactor was vented, a mixture of 70 mL of acetone,
30 mL of methanol, and 1 mL of concentrated hydrochloric acid
was transferred into the reactor by vacuum, the autoclave was
opened, and the polymer was collected, decanted, and dried
8.3 Hz, HA), 8.13 (d, 1H, J=8.3 Hz, HA ); 13C NMR (125 MHz,
0
CD2Cl2) δ 3.0 (t, JCF=2.3 Hz, NCMe), 8.0 (t, JCF=10.6 Hz, Pd-
Me), 21.14 (Ar-Me), 21.26 (Ar-Me), 32.91 (af), 33.01 (af), 111.22
(t, 2JCF=20.8 Hz, ae), 111.73 (t, 2JCF=21.3 Hz, ad), 112.66 (dd,
2JCF=22.2 Hz, 4JCF=3.4 Hz, ac), 112.86 (dd, 2JCF=21.8 Hz,
4JCF=3.2 Hz, ab), 112.95 (dd, 2JCF=22.2 Hz, 4JCF=3.2 Hz, aa),
113.14 (dd, 2JCF=22.2 Hz, 4JCF=2.3 Hz, z), 121.43 (NCMe),
122.33 (y), 123.96 (t, JCF=2.5 Hz, x), 124.22 (w), 125.03 (t, JCF
=
4.4 Hz, v), 128.09 (t/u), 128.20 (t/u), 128.58 (t, JCF=5.1 Hz, s),
129.76 (t, JCF =6.6 Hz, r), 130.98 (q), 132.64 (p), 133.21 (o),
134.11 (n), 134.77 (m), 138.33 (k/l), 139.38 (k/l), 142.00 (j),
3
3
142.86 (i), 143.87 (t, JCF=9.4 Hz, h/h0), 143.92 (t, JCF=9.4
Hz, h/h0), 146.37 (g), 159.53 (dd, 1JCF=247.8 Hz, 3JCF=8.3 Hz,
2
4
f), 159.61 (dd, JCF=245.6 Hz, JCF=7.9 Hz, e), 160.29 (dd,
2JCF=247.8 Hz, 4JCF=6.0 Hz, d), 160.33 (dd, 2JCF=248.3 Hz,
4JCF = 6.9 Hz, c), 171.2 (b), 177.3 (a); 19F NMR (376 MHz,
CD2Cl2) δ -110.34 (dd, 2F, 3JFH=9.8 Hz, 4JFF=4.9 Hz, FD), -
110.07 (ddd, 2F, 3JFH=9.7 Hz, 4JFF=4.9 Hz, JFH=4.2 Hz, FC),
-107.70 (ddd, 2F, 3JFH=10.1 Hz, JFH=4.6 Hz, 4JFF=3.9 Hz,
3
FB), -107.50 (ddd, 2F, JFH = 9.7 Hz, JFH = 4.5 Hz,
4JFF=3.9 Hz, FA); IR (thin film) 2175.3 cm-1 [ν(CtN)].
Side product (70): 1H NMR (500 MHz, CD2Cl2) δ 2.50 (s, 3H),
2.85 - 3.05 (m, 8H, partially obscured by 7), 6.26 (d, 4H, JHF
=
9.2 Hz), 6.61 (d, 4H, JHF=10.3 Hz), 6.64 (d, 2H, J=7.3 Hz), 7.32
(s, 4H), 7.40 (t, 2H, J=7.8 Hz), 7.94 (d, 2H, J=8.1 Hz); 19F
NMR (376 MHz, CD2Cl2) δ -112.09 (br), -117.79 (br).
[(F-Cyc)PdMe(NCAr)]BAr4, Ar = 3,5-(CF3)2C6H3 (8). An
oven-dried flask was charged with 16 mg of Pd(COD)MeCl
(0.058 mmol), 50 mg of diimine 2 (0.058 mmol), and 52 mg of
NaBAr4 (0.058 mmol). To this was added 10 mL of dry CH2Cl2
(39) Lee, L.-s.; Ou, H.-j.; Hsu, H.-l. Fluid Phase Equilib. 2005, 231,
221–230.

Article
Organometallics, Vol. 28, No. 15, 2009 4463
in vacuo at 80 °C overnight. The reactor was twice cleaned with
boiling toluene before subsequent polymerizations.
measure both the MW and sizes for each fraction of the
polymer eluted from the SEC column.40,41 Both the column
and the differential refractometer were held at 35 °C. A 30 μL
sample of a 2 mg/mL solution was injected into the column.
ASTRA 4.7 from Wyatt Technology was used to acquire data
from the 18 scattering angles (detectors) and the differential
refractometer. The Mn and Mw data were obtained by follow-
ing classical light scattering treatments. All polymers from
Ni(II) catalysts were insufficiently soluble in THF and were
analyzed by SEC in 1,2,4-trichlorobenzene at 140 °C by the
Polymer Characterization Facility at the Cornell Center for
Materials Research, Cornell University, Ithaca, NY. The
Mn and Mw data were obtained by comparison to polyethy-
lene standards. As mentioned above, polymers from the
fluorinated Pd(II) catalyst produced at 60 and 80 °C had their
molecular weights accurately determined by MALS. The
calculated molecular weights of these polymers by GPC using
the polyethylene standards were closer to the actual MALS-
determined value than the values calculated using the more
commonly used polystyrene standards, which were roughly a
factor of 2 larger.
Variable-Temperature Screen. The general procedure for Ni
(II)-catalyzed polymerizations was followed using 1.0 μmol of
catalyst 4 and triisobutylaluminum (TIBA) as the coactivator
(1.5 mL of a 10% w/w solution in toluene, 1.0 M). Polymeriza-
tions were run for 10 min at the desired temperature.
Thermal Stability Study at 105 °C. The general procedure for
Ni(II)-catalyzed polymerizations was followed using 0.5 μmol
of catalyst 4 and TIBA as the coactivator (1.5 mL of a 10% w/w
solution in toluene, 1.0 M). Polymerizations were started at
110 °C, held there for 1 min, then allowed to cool to 105 °C, and
left at that temperature for the duration of the polymerization.
General Procedure for Pd(II)-Catalyzed Polymerizations. A
600 mL autoclave was heated under vacuum to 120 °C for 2 h,
then twice purged with ethylene and adjusted to the desired
polymerization temperature by external oil bath. A flask was
charged with the desired amount of catalyst 5, 6, 7, or 8 under a
nitrogen atmosphere, and to this was added 20 mL of dry
toluene. The catalyst solution was then transferred into the
reactor by vacuum under nitrogen stream followed by toluene
and comonomer, if any, to bring the total volume up to 100 mL.
The reactor was then filled with ethylene to 88 psi, and the
polymerization was allowed to proceed for the desired time at
the desired temperature. The reactor was then vented, the
mixture was concentrated in vacuo, and the polymer was dried
for 24 h under vacuum at 70 °C.
NMR Analysis of Polymers. Branching densities B were
calculated by the ratio of methyl group integration to total
hydrocarbon integration using 1H NMR. Samples were dis-
solved in hot 1,1,2,2-tetrachloroethane-d2, and spectra were
acquired at 140 °C.
SEC Characterization of Polymers. All polymers were char-
acterized by size-exclusion chromatography (SEC). All poly-
mers produced by the Pd(II) catalysts were soluble in THF and
were eluted through a 30 cm size-exclusion column (Polymer
Laboratories PLgel Mixed C, 5 μm particle size) to separate
polymer samples. Measurements were made on highly dilute
fractions eluting from a SEC consisting of a HP Aglient 1100
solvent delivery system/auto injector with an online solvent
degasser, a temperature-controlled column compartment, and
an Aglient 1100 differential refractometer. The mobile phase
was THF, and the flow rate was 1.0 mL/min. A Dawn DSP 18-
angle multiangle light scattering (MALS) detector (Wyatt
Technology, Santa Barbara, CA) was coupled to the SEC to
Acknowledgment. We thank the National Science
Foundation (Chem-0456719, Chem-0723497, and
DMR-0703988) for funding. We thank Materia, Inc. for
the generous donation of Grubbs catalyst. C.P. acknowl-
edges the Allergan Foundation, the UCI Department of
Chemistry, and Joan Rowland for financial support. We
also thank Dr. Phil Dennison for valuable NMR assis-
tance, Chris Levins and Alex Nguyen for aid in ligand
synthesis, Yen Kong and Zach Tolstykia (UCLA) for
DSC assistance, and Dr. Anthony Condo and Jeffrey
Rose of Cornell University for GPC assistance.
Supporting Information Available: Selected GPC traces
of polyethylenes and estimations of ethylene concentration.
This material is available free of charge via the Internet at
http://pubs.acs.org.
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