Copolymerization of ethylene and methyl acrylate by cationic palladium catalysts that contain phosphine-diethyl phosphonate ancillary ligands

Article abstract of DOI:10.1021/om5004489

A series of benzo-linked phosphine-diethyl phosphonate (P-PO) and phosphine-bis(diethyl phosphonate) (P-(PO)₂) ligands and the corresponding (P-PO)PdMe(2,6-lutidine)⁺ and (P-(PO) ₂)PdMe(2,6-lutidine)⁺ complexes were synthesized. Cationic (P-PO)PdMe(2,6-lutidine)⁺ complexes are active for ethylene oligomerization/polymerization, with activities of 2 kg mol^-1 h ^-1 for {κ²-1-PⁱPr₂-2-P(O)(OEt) ₂-5-Me-Ph}PdMe(2,6-lutidine)⁺ (3c), 125 kg mol ^-1 h^-1 for {κ²-1-PPh₂-2-P(O) (OEt)₂-5-Me-Ph}PdMe(2,6-lutidine)⁺ (3a), and 1470 kg mol^-1 h^-1 for {κ²-1-P(2-OMe-Ph) ₂-2-P(O)(OEt)₂-Ph}PdMe(2,6-lutidine)⁺ (3b). The polyethylene is highly linear, with over 80% terminal unsaturation and low (230-1890 Da) molecular weight in all cases. 3b copolymerizes ethylene with methyl acrylate, exhibiting highly selective (95%) in-chain (rather than chain-end) acrylate incorporation. The P-(PO)₂ catalyst {κ²-1-P(4-^tBu-Ph)(2-P(O)(OEt)₂-5-Me-Ph)- 2-P(O)(OEt)₂-5-Me-Ph}PdMe(2,6-lutidine)⁺ (3d) is more active for ethylene homopolymerization (2640 kg mol^-1 h ^-1), yielding linear, low-molecular-weight polymer (1280-1430 Da) with predominantly internal olefin placement. In ethylene/methyl acrylate copolymerization, 3d incorporates 2.6 mol % methyl acrylate, 60% of which is in-chain. Both 3b and 3d catalyze ethylene/acrylic acid copolymerization, albeit with low (<10 kg mol^-1 h^-1) activities and acrylic acid incorporation up to 1.1 mol %.

Full text of DOI:10.1021/om5004489

Article
pubs.acs.org/Organometallics
Copolymerization of Ethylene and Methyl Acrylate by Cationic
Palladium Catalysts That Contain Phosphine-Diethyl Phosphonate
Ancillary Ligands
Nathan D. Contrella, Jessica R. Sampson, and Richard F. Jordan*
Department of Chemistry, The University of Chicago, 5735 South Ellis Avenue, Chicago, Illinois 60637, United States
S
* Supporting Information
ABSTRACT: A series of benzo-linked phosphine-diethyl phospho-
nate (P-PO) and phosphine-bis(diethyl phosphonate) (P-(PO)2)
ligands and the corresponding (P-PO)PdMe(2,6-lutidine)+ and (P-
(PO)2)PdMe(2,6-lutidine)+ complexes were synthesized. Cationic
(P-PO)PdMe(2,6-lutidine)+ complexes are active for ethylene
oligomerization/polymerization, with activities of 2 kg mol−1 h−1
for {κ2-1-PiPr2-2-P(O)(OEt)2-5-Me-Ph}PdMe(2,6-lutidine)+ (3c),
125 kg mol−1 h−1 for {κ2-1-PPh2-2-P(O)(OEt)2-5-Me-Ph}PdMe-
(2,6-lutidine)+ (3a), and 1470 kg mol−1 h−1 for {κ2-1-P(2-OMe-Ph)2-2-P(O)(OEt)2-Ph}PdMe(2,6-lutidine)+ (3b). The
polyethylene is highly linear, with over 80% terminal unsaturation and low (230−1890 Da) molecular weight in all cases. 3b
copolymerizes ethylene with methyl acrylate, exhibiting highly selective (95%) in-chain (rather than chain-end) acrylate
incorporation. The P-(PO)2 catalyst {κ2-1-P(4-tBu-Ph)(2-P(O)(OEt)2-5-Me-Ph)-2-P(O)(OEt)2-5-Me-Ph}PdMe(2,6-lutidine)+
(3d) is more active for ethylene homopolymerization (2640 kg mol−1 h−1), yielding linear, low-molecular-weight polymer
(1280−1430 Da) with predominantly internal olefin placement. In ethylene/methyl acrylate copolymerization, 3d incorporates
2.6 mol % methyl acrylate, 60% of which is in-chain. Both 3b and 3d catalyze ethylene/acrylic acid copolymerization, albeit with
low (<10 kg mol−1 h−1) activities and acrylic acid incorporation up to 1.1 mol %.
aggregates through Li−sulfonate interactions involving the
non-Pd-coordinated sulfonate moiety and one oxygen of the
Pd-bound sulfonate. The tetrameric catalyst yields polyethylene
with much higher molecular weight (Mw up to 1 000 000 Da)
and incorporates more vinyl fluoride in copolymerizations
compared to monomeric catalysts A. Sequestration of the Li+
with Crypt211 converts the tetrameric species into a
mononuclear (κ2-P,O-OPO)PdMeL species with a pendant
INTRODUCTION
■
Palladium(II) alkyl complexes that contain ortho-phosphino-
arenesulfonate (PO) ligands (A, Chart 1) polymerize ethylene
to highly linear polyethylene (PE),1 and the catalyst activity and
the polyethylene molecular weight are strongly influenced by
the substituents on the phosphine unit (R) and the lability of
the L ligand.2 These catalysts also copolymerize ethylene with a
wide variety of polar vinyl monomers, yielding functionalized
linear copolymers with both in-chain and chain-end incorpo-
ration of the comonomer.3−8 However, the ethylene polymer-
ization activities and polymer molecular weights exhibited by
(PO)PdMeL catalysts are low compared to those for other
families of single-site catalysts,9 and polar monomers invariably
decrease activities and molecular weights.
The combination of a strong (phosphine) and weak
(sulfonate) donor in the ancillary PO ligand in (PO)PdR
catalysts is believed to suppress β-hydride elimination processes
that can lead to chain walking and branched polymer chains1,10
and β-X eliminations (X = halide, OR, O2CR) that can lead to
catalyst deactivation in copolymerizations.5b,11 Additionally, it
has been proposed that the sulfonate group facilitates cis/trans
isomerization of the catalyst during chain growth via formation
of five-coordinate κ3-P,O,O-PO species that undergo Berry
pseudorotations.1,10
−
ArSO3 group that oligomerizes ethylene with high activity,
suggesting that the pendant arenesulfonate group strongly
accelerates chain transfer.12
Bidentate phosphine-phosphine oxide ligands are similar to
PO ligands in that they contain a combination of strong and
weak donor groups.13 Cationic Pd and Ni complexes with
chelating κ2-P,O-phosphine-phosphine oxide ligands have been
shown to oligomerize ethylene, and the Pd complexes also
catalyze ethylene/CO copolymerization.14 Recently, Nozaki
and co-workers reported a versatile series of such catalysts (C)
that polymerize ethylene to linear PE with low polydispersity
and also copolymerize ethylene with allyl acetate, allyl chloride,
tert-butylvinyl ether, vinyl acetate, and acrylonitrile, but not
with methyl acrylate. Variation of the phosphine and phosphine
oxide substituents (R, R′) yields a broad range of catalyst
activities and product molecular weights, some of which are
comparable to those obtained with the phosphine-sulfonate
The behavior of (phosphine-bis(arenesulfonate))PdMeL
catalysts ((OPO)PdMeL, B, Chart 1) differs dramatically
from that of (PO)PdMeL species A. Phosphine-bis(arene-
sulfonate)PdMeL complexes self-assemble into tetrameric
Received: April 28, 2014
© XXXX American Chemical Society
A
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Chart 1
Scheme 1
reaction of 2a,2b with AgSbF6 in the presence of 2,6-lutidine
yields cationic (P-PO)PdMe(2,6-lut)+ species 3a,3b.
The solid-state structures of 3a and 3b are shown in Figures
1 and 2, respectively. In each case, a square-planar Pd (II)
catalysts.15 Phosphine-dialkyl phosphonate ligands also contain
strong and weak donors.16 Braunstein found that cationic Pd-
alkyl complexes (D) with a chelated phosphine-diethyl
phosphonate ligand undergo CO insertion and subsequent
ethylene or methyl acrylate insertion.17,18
In this paper, we report the synthesis, ethylene polymer-
ization behavior, and ethylene/acrylate copolymerization
characteristics of cationic Pd complexes that contain
phosphine-(diethyl phosphonate) (E) or phosphine-bis(diethyl
phosphonate) (F) ligands. The diethyl arylphosphonate group
is expected to be a weaker donor than a triaryl- or dialkylaryl-
phosphine oxide,2e,19 and the presence of additional oxygen
atoms may facilitate cis/trans isomerization of {phosphine-
(diethyl phosphonate)}PdRL species, which may be important
for chain growth, as proposed for the phosphine-sulfonate
systems. The phosphine-bis(diethyl phosphonate) ligand offers
the possibility of weak interactions of the non-Pd-coordinated
phosphonate group with the metal or a polar comonomer,
which may influence polymerization or copolymerization
behavior, as observed for B. The second phosphonate group
may also prolong catalyst lifetimes if ligand loss is a major
deactivation pathway, or facilitate cis/trans isomerization by
formation of a configurationally labile five-coordinate species.
−
Figure 1. Molecular structure of 3a. Hydrogen atoms and the SbF6
anion are omitted. Bond lengths (Å) and angles (deg): C(1)−Pd(1)
2.020(6), N(1)−Pd(1) 2.110(4), O(1)−Pd(1) 2.170(4), P(1)−Pd(1)
2.2152(16); C(1)−Pd(1)−P(1) 88.36(17), P(1)−Pd(1)−O(1)
96.34(11), O(1)−Pd(1)−N(1) 88.29(16), N(1)−Pd(1)−C(1)
87.1(2).
center is chelated by phosphorus and oxygen donor atoms,
forming a puckered six-membered ring that adopts a boat
conformation in 3a and a twist-boat conformation in 3b. The
angle between the P−C−C−P and O−Pd−P planes is 35.8° in
3a and 33.2° in 3b. In both complexes, the plane of the 2,6-
lutidine ligand is perpendicular to the Pd square plane. The
Pd−C distances of 3a (2.020(6) Å) and 3b (2.021(2) Å) are ca.
0.09 Å shorter than those in analogous neutral phosphine-
sulfonate complexes,5a presumably reflecting the weaker trans
influence of the neutral diethyl phosphonate donor group
compared to the anionic sulfonate group. The PO distance
of 3a (1.477(4) Å) is essentially unchanged from the value
reported for ligand 1a (1.468(3) Å).16i The solution NMR data
for 3a and 3b are consistent with the solid-state structures.
RESULTS AND DISCUSSION
■
Triarylphosphine-Diethyl Phosphonate Complexes.
The benzo-linked phosphine-diethyl phosphonate ligands 1a
and 1b (P-PO, Scheme 1) were synthesized as reported by
Pringle16i and Rieger20 and metalated by reaction with
(COD)PdMeCl, yielding (P-PO)PdMeCl complexes 2a,2b.
The presence of P−P coupling in the 31P NMR spectra of the
complexes is diagnostic of ligand chelation. The free ligands 1a
and 1b do not exhibit P−P coupling, while complexes 2a and
2b show a JPP of 14 and 11 Hz, respectively. Small 3JPH (2a,2b:
2
1
4 Hz) and JPC (2b: 2 Hz) values are observed for the H and
13C PdMe resonances of 2a,2b, consistent with a cis
arrangement of the phosphine and methyl ligands.5a The
Both 3a and 3b exhibit JPP values of 16 Hz and 3JP‑CH values of
4 Hz, indicating κ2-P,O coordination of the P-PO ligand and a
3
B
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Scheme 3
−
Figure 2. Molecular structure of 3b. Hydrogen atoms and the SbF6
anion are omitted. Bond lengths (Å) and angles (deg): C(1)−Pd(1)
2.021(2), N(1)−Pd(1) 2.127(2), O(3)−Pd(1) 2.1639(17), P(1)−
Pd(1) 2.2353(6); C(1)−Pd(1)−N(1) 92.09(9), N(1)−Pd(1)−O(3)
83.08(7), O(3)−Pd(1)−P(1) 97.45(5), P(1)−Pd(1)−C(1) 87.46(8).
cis relationship of the phosphine and methyl groups. The NMR
data for 2a,2b and 3a,3b are consistent with fast inversion of
the chelate rings on the NMR time scale for these species,
which is also observed in (PO)Pd(R)(L) compounds.2a,21
Diisopropylphosphine-Diethyl Phosphonate Com-
plexes. An analogue of 1a,1b with isopropyl substituents on
the phosphine was synthesized by a different route. Diethyl
ortho-bromo-arylphosphonates 4 and 5 were prepared by Pd-
catalyzed P−C coupling22 of the appropriate aryl bromide with
diethyl phosphite by Charette’s procedure (Scheme 2).23
Scheme 2
−
Figure 3. Molecular structure of 3c. Hydrogen atoms and the SbF6
anion are omitted. Bond lengths (Å) and angles (deg): C(1)−Pd(1)
2.011(4), N(1)−Pd(1) 2.111(3), O(1)−Pd(1) 2.118(2), P(2)−Pd(1)
2.2208(14); C(1)−Pd(1)−N(1) 87.04(13), N(1)−Pd(1)−O(1)
87.44(11), O(1)−Pd(1)−P(2) 95.10(8), P(2)−Pd(1)−C(1)
90.57(11).
Diethyl phosphite and triethylamine were used in excess due
to competing dealkylation of the former by the amine.24 5 was
lithiated by metal−halogen exchange and then reacted with
PiPr2Cl, yielding ligand 1c as a waxy solid (Scheme 3).
The reaction of 1c with (COD)PdMeCl affords the neutral
complex 2c. Subsequent chloride abstraction by AgSbF6 in the
presence of 2,6-lutidine yielded cationic complex 3c. Com-
plexes 2c and 3c exhibit P−P coupling in the 31P NMR spectra
(ca. 14 Hz), whereas no P−P coupling is observed in the free
ligand 1c.
synthesized as shown in Schemes 4 and 5. The requisite
ArPCl2 components 6 and 7 were synthesized by lithiation of
Scheme 4
The solid-state structures of 2c (see the Supporting
Information) and 3c (Figure 3) share several characteristics
with the structures of 3a,3b. The phosphine and diethyl
phosphonate moieties chelate a square-planar Pd center. The
methyl group is cis to the phosphine, and the 2,6-lutidine is
perpendicular to the Pd square plane. The chelate ring in 3c is
notably less puckered than those in 3a and 3b and adopts a
half-chair conformation in which the angle between P−C−C−P
and O−Pd−P planes is only 13.8°. The Pd−O distance in 3c
(2.118(2) Å) is significantly shorter than those in 3a (2.170(4)
Å) and 3b (2.1639(17) Å).
the appropriate aryl bromide, reaction with P(NEt2)2Cl, and
treatment with acid (Scheme 4). Dichlorophenylphosphine (8)
was obtained commercially. 6−8 were then coupled with 2
equiv of lithiated 4 or 5 (Scheme 5), yielding a series of
phosphine-bis(diethyl phosphonate) ligands. Only 1d and 1g,
which were expected to best solubilize subsequent Pd
complexes, were used further.
Phosphine-Bis(diethyl phosphonate) Complexes.
Phosphine-bis(diethyl phosphonate) ligands 1d−1g were
The reaction of 1d,1g with (COD)PdMeCl yields neutral (P-
(PO)2)PdMeCl complexes 2d and 2g (Scheme 6). In the solid
C
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Scheme 5
Scheme 6
Figure 4. Molecular structure of 2g. Hydrogen atoms are not shown.
Bond lengths (Å) and angles (deg): C(1)−Pd(1) 2.011(4), Cl(1)−
Pd(1) 2.3486(11), O(1)−Pd(1) 2.152(2), P(1)−Pd(1) 2.1873(11),
P(2)−O(1) 1.467(3), P(3)−O(4) 1.455(3), O(4)−Pd(1) 3.285(3);
C(1)−Pd(1)−Cl(1) 89.47(11), Cl(1)−Pd(1)−O(1) 88.51(7),
O(1)−Pd(1)−P(1) 95.45(7), P(1)−Pd(1)−C(1) 86.70(11).
contains two sets of 2-P(O)(OEt)2-4-Me-Ph resonances, two
2,6-lutidine methyl resonances, and two lutidine H3 resonances
(Figure 5). As the temperature is raised, these corresponding
sets of resonances broaden and coalesce. Similarly, the 31P{1H}
spectrum of 3d at 208 K contains two doublets (J = 20 Hz) at δ
31.8 and 20.5, which are assigned to the phosphine and the Pd-
coordinated phosphonate, and a singlet at δ 16.8, which is
assigned to uncoordinated phosphonate. As the temperature is
increased, the phosphine resonance evolves into a triplet with J
= 9 Hz, and the phosphonate resonances broaden significantly.
The activation barriers determined by line shape analysis of the
1
2-P(O)(OEt)2-4-CH3-Ph H resonance, the lutidine-CH3 1H
resonance, and the 31P resonances are identical (ΔG⧧ = 14 kcal
mol−1 at 272 K), indicative of the operation of a single dynamic
process. Exchange of free and Pd-coordinated phosphonate
groups will produce all of these dynamic NMR effects. Note
that the 2,6-lutidine is expected to be oriented perpendicular to
the Pd square plane, as observed for 3c and 3a,3b, and that the
phosphonate exchange is sufficient to permute the lutidine
methyl groups and the H3 hydrogen atoms.
Ethylene Homopolymerization by Phosphine-Diethyl
Phosphonate and Phosphine-Bis(diethyl phosphonate)
Complexes. Complexes 3a,3b oligomerize/polymerize ethyl-
ene to linear low-molecular-weight PE (Table 1). At 80 °C and
28 atm ethylene, 3a yields a Schulz−Flory distribution of C6−
C22 α-olefins (>95% terminal olefins), with an activity of 125 kg
mol−1 h−1 (entry 1).26 The methoxy substituents in catalyst 3b
significantly alter the polymerization characteristics. Under the
same conditions, for 3b, Mn is increased more than 7-fold to
1760 Da, the activity is increased to 1470 kg mol−1 h−1, and the
selectivity for α-olefin (rather than internal olefin) formation
upon chain transfer is 92% (entry 3). The Tm values for the PEs
produced by 3a (72 °C) and 3b (126 °C) are consistent with
the low molecular weights.27 In comparison, the [(phosphine-
phosphine oxide)PdMe(lut)][SbF6] catalysts (B, Chart 1)
reported by Nozaki exhibit activities ranging from 36 to 340 kg
mol−1 h−1 when run under similar conditions (80 °C, 30 atm, in
toluene), with polymer Mn values between 800 Da and 39
state, 2g adopts a square-planar structure with coordination of
the phosphine and one of the diethyl phosphonate moieties and
a cis arrangement of the phosphine and methyl ligands (Figure
4). The noncoordinated phosphonate oxygen atom is
positioned close to one axial site of the Pd center, but the
P−O distance of 3.285 Å is beyond the sum of the van der
Waals radii of Pd and O (3.15 Å).25 The PO bond length of
the coordinated phosphonate unit (1.467(3) Å) is essentially
equal to that of the noncoordinated unit (1.455(3) Å). The 1H
NMR spectra of 2d and 2g in CD2Cl2 at room temperature
each contain a single set of resonances for the −Ar-P(O)(OEt)2
rings (some are broad). The 31P{1H} NMR spectra for 2d,2g at
room temperature each contain a triplet for the phosphine unit
(JPP = 9) and a single broad resonance for the phosphonate
unit. These results are consistent with fast exchange on the
NMR time scale of the Pd-bound and nonbound phosphonate
units under these conditions.
Complex 2d was converted to the cationic 2,6-lutidine
complex 3d by reaction with AgSbF6 and 2,6-lutidine (Scheme
6). Repeated efforts to crystallize this material were
unsuccessful. However, NMR data establish that 3d, like
2d,2g, contains one Pd-bound and one non-Pd-bound
phosphonate group, which exchange on the NMR time scale
1
at room temperature. At 208 K, the H NMR spectrum of 3d
D
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Figure 5. Variable-temperature NMR spectra of 3d. (a) The phosphine (left) and phosphonate (right) regions of the 31P{1H} spectra. (b) The
1
lutidine-CH3 (downfield) and 2-P(O)(OEt)2-4-CH3-Ph (upfield) regions of the H NMR spectra.
j
Table 1. Ethylene Homopolymerizations
e
e
f
entry
catalyst
pressure (atm)
μmol Pd
activity (kg mol−1 h−1
)
Tm (°C)
Mn (Da)
PDI
% α-olefin
a
g
g
h
1
3a
3b
3b
3c
3c
3c
3d
3d
28
17
28
17
28
28
17
28
10.3
1.00
1.01
11.7
12.9
13.7
0.85
0.88
125
72.1
240
97
84
92
b
2
1150
1470
2.2
125.9
125.5
81.6
1890
1760
1.93
b
3
1.99
h
h
i
4
5
<570
n.d.
h
1.0
83.9
<570
n.d.
n.d.
n.d.
10
c
6
<1
n.d.
n.d.
d
7
d
1030
123.6
123.8
1460
1.86
1.94
8
2640
1430
11
j
a
b
c
d
Conditions: 80 °C, 50 mL of toluene, 2 h. Average of four identical runs. Average of two identical runs. 40 °C. Average of three identical runs.
e
f
g
Determined by GPC, unless otherwise noted. % of olefins that are α-olefins, determined by 1H NMR. Determined by 1H NMR analysis of soluble
h
i
and insoluble polymer fractions. Mn below limit for GPC analysis. Not determined.
a b
,
Table 2. Ethylene/Acrylate Copolymerizations
μmol
Pd
activity
comon. incorp.
(mol %)
comon.
% in chain
d
entry cat.
comon.
(kg mol−1 h−1
)
Tm (°C) Mn (Da) PDI
% α-olefin
c
c
1
2
3
4
3b
3d
3b
3d
methyl acrylate (1.50 M)
methyl acrylate (1.50 M)
acrylic acid (0.75 M)
acrylic acid (0.75 M)
15.2
15.0
15.1
15.5
58
150
1.2
118.0
112.0
123.7
125.9
1500
770
2.36
1.78
3.40
2.46
1.5
95
60
32
68
4
2.6
915
0.45
1.1
87
70
7.1
1465
43
a
b
c
Conditions: 80 °C, 28 atm ethylene, toluene, 50 mL total solution volume. Each entry is the average of two identical trials. With 100 mg BHT.
d
Comon. = comonomer.
kDa.15 The phosphine-diethyl phosphonates reported here,
therefore, span a much broader, generally higher range of
activities, but the polymer molecular weights are lower.
Surprisingly, diisopropylphosphine-diethyl phosphonate
complex 3c exhibited the lowest activity of those tested, less
than 2.2 kg mol−1 h−1 (entries 4−6). The small amount of
polymer produced was found to have a low molecular weight
(Mn < ca. 570 Da).28 In an effort to avoid possible catalyst
decomposition at elevated temperature, a polymerization was
attempted at 40 °C, but no polymer was formed (entry 6).
These results contrast with trends observed in other catalysts.
The most active phosphine-phosphine oxide based catalysts
within the series studied by Nozaki and co-workers were those
with diisopropyl-substituted phosphines. Similarly, in phos-
phine-sulfonate systems, Claverie et al. found that catalysts with
alkyl substituents on the phosphine are typically more active
than those with aryl groups.2d
The phosphine-bis(diethyl phosphonate) complex 3d was
found to be highly active for ethylene polymerization. The
activity exhibits more variation with pressure than observed for
3b, increasing from 1150 kg mol−1 h−1 at 17 atm to 2640 kg
mol−1 h−1 at 28 atm (entries 7 and 8). The PE molecular
weight varies minimally over this pressure range, from 1400 to
1500 Da, with PDI values just under 2. In contrast to
phosphine-mono(diethyl phosphonate) catalysts 3a−3c, 3d
yields a polymer with 87% internal olefins. 13C NMR analysis
shows that 2-olefins are the most common unsaturation (53%,
E:Z approximately 1:1); 1-olefins (13%) and 3+-olefins (34%)
were also identified. When an ethylene polymerization by 3d
was conducted in the presence of 1-heptene, the heptene was
not isomerized, which implies that the internal olefins are
formed during chain growth rather than by isomerization of α-
olefins released by chain transfer. 13C NMR analysis also
revealed that the PE produced by 3d is highly linear (less than 1
branch per 1000 C), with only methyl branches detected. The
E
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Figure 6. H NMR spectra (CDCl2CDCl2, 100 °C) of ethylene/methyl acrylate copolymer produced by catalysts 3b (a) and 3d (b). See the
Supporting Information for additional assignments.
Tm value is consistent with linear PE of the observed molecular
weight.27
phosphine-phosphine oxide complexes, which yielded no
polymer in attempted ethylene/methyl acrylate copolymeriza-
tions.15
The difference in the structures of the PEs produced by
3a,3b (>92% α-olefin) and 3d (>87% internal olefins) provides
insight into differences in the reactivities of the growing metal
alkyl species in these catalysts. For 3a,3b, chain growth and
chain transfer are fast, and either chain walking is not
competitive with growth or the catalyst does not insert
ethylene or undergo chain transfer from an internal alkyl
position so that linear α-olefins are formed. 3d also exhibits fast
chain growth and fast chain transfer, but the predominance of
internal unsaturation and the absence of branching indicate that
chain walking does occur, and the resulting secondary alkyl
species undergo chain transfer preferentially to chain growth.
Ethylene/Methyl Acrylate Copolymerizations. Cata-
lysts 3b and 3d both incorporate methyl acrylate in ethylene
copolymerizations, but with marked differences in the
copolymer structure (Table 2). With both catalysts, at 28 atm
ethylene, 1.50 M methyl acrylate, and 80 °C, the polymer-
ization activity and product molecular weight are decreased
relative to results for ethylene homopolymerization. Under
these conditions, 3b incorporates 1.5 mol % methyl acrylate,29
and notably, the methyl acrylate is selectively (95%)
incorporated in-chain, with only 5% terminating chain-end
placements observed (Figure 6a). Only 5% of terminating end
groups contain MA, suggesting that, after acrylate insertion,
chain growth is highly favored over chain transfer. 3d exhibits
higher activity and acrylate incorporation (2.6 mol %)30 but is
much less selective than 3b for in-chain acrylate placement,
with only 60% incorporated in-chain and 40% incorporated
into terminating chain-end groups (Figure 6b). This result
indicates that, after acrylate insertion, 3d can undergo either
chain growth or chain transfer with approximately equal
probability.
Ethylene/Acrylic Acid Copolymerizations. Both 3b and
3d copolymerize ethylene with acrylic acid (Table 2, entries 3
and 4). However, at 80 °C, 28 atm ethylene, and 0.75 M acrylic
acid, the activity of both catalysts is severely depressed relative
to ethylene homopolymerization. The small amount of polymer
obtained with 3b is highly contaminated with Pd black and
contains 0.45 mol % acrylic acid. The molecular weight (900
Da) is substantially lower than that obtained in ethylene
homopolymerization. 3d yields copolymer containing approx-
imately 1 mol % acrylic acid, with ca. 55% incorporated at chain
ends (entry 4). Interestingly, the molecular weight of the
ethylene/acrylic acid copolymer (1450 Da) is close to the value
observed for ethylene homopolymerization.
CONCLUSIONS
■
Cationic phosphine-diethyl phosphonate complexes of the type
(P-PO)PdMe(lutidine)+ polymerize ethylene to low-molecular-
weight linear PE and copolymerize ethylene with methyl
acrylate and acrylic acid. The polymerization activities of these
catalysts vary widely with the substituents on the ancillary
ligand. In ethylene/methyl acrylate copolymerizations, catalyst
3b is highly selective for in-chain acrylate incorporation.
Catalyst 3d has a higher copolymerization activity and higher
acrylate incorporation, but only 60% of the functionality is
incorporated in-chain, with the remaining 40% as chain-end
groups.
EXPERIMENTAL SECTION
■
General Procedures. All experiments were performed under a
nitrogen atmosphere using drybox or Schlenk techniques. Nitrogen
was purified by passage through columns containing Q-5 oxygen
scavenger and activated molecular sieves. Methylene chloride, diethyl
ether, and THF were dried by passage through columns containing
activated alumina. Pentane was purified by passage through columns of
BASF R3-11 oxygen scavenger and activated alumina. Compounds 1a,
The ability of these phosphine-diethyl phosphonate- and
phosphine-bis(diethyl phosphonate)-based catalysts to incor-
porate methyl acrylate is a major difference from analogous
F
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Organometallics
Article
1b,20 (COD)PdMeCl,31 (TMEDA)PdMe2,32 and bis(diethylamino)-
chlorophosphine33 were prepared by literature procedures. The
following materials were obtained from commercial sources and
used without further purification: PPh3 (Aldrich, 99%), Pd(OAc)2
(Aldrich, 99%), ethanol (Aldrich, anhydrous), 3-bromo-4-iodotoluene
(Oakwood, 98%), NEt3 (Aldrich, 99.5%), nBuLi solution (Aldrich, 1.6
M in hexanes), AgSbF6 (Strem, 98%), 2,6-lutidine (Aldrich, 99+%), 4-
bromotoluene (Aldrich, 98%), HCl solution (Aldrich, 2.0 M in Et2O),
butylated hydroxytoluene (BHT, Aldrich, 99%), and ethylene
(Matheson, polymer grade). Chlorodiisopropylphosphine (Aldrich)
was distilled prior to use. Acrylic acid (Aldrich) and methyl acrylate
(Aldrich) were dried over MgSO4 or CaCl2, respectively, distilled
under reduced pressure, and stored at −40 °C. 1-Heptene (Aldrich)
was dried over Na/benzophenone, transferred under reduced pressure,
and stored in the dark.
δ 161.0 (d, JPC = 3, CL), 137.1 (br d, JPC = 11, CK), 136.8 (dd, JPC = 44,
13, CE), 135.2 (dd, JPC = 15, 2, CD), 133.6 (d, JPC = 2, CI), 133.5 (dd,
JPC = 10, 8, CA), 131.6 (dd, JPC = 7, 3, CC), 130.9 (dd, JPC = 185, 18,
CF), 130.1 (dd, JPC = 13, 2, CB), 121.2 (d, JPC = 11, CJ), 116.5 (d, JPC
=
52, CG), 111.7 (d, JPC = 4, CH), 64.3 (d, JPC = 6, −OCH2CH3), 55.6 (s,
CM), 16.2 (d, JPC = 7, −OCHH2CH3), −1.3 (d, JPC = 2, Pd-CH3).
HRMS (m/z): Calcd for [C25H31P2O5PdCl + Na]+: 637.0266, Found:
637.0273.
3a. A vial was charged with 2a (0.113 g, 0.204 mmol), 2,6-lutidine
(0.077 g, 0.72 mmol), and CH2Cl2 (10 mL). The resulting solution
was added to a second vial containing AgSbF6 (0.070 g, 0.20 mmol).
The resulting suspension was stirred rapidly for 1 h at room
temperature, filtered through Celite, concentrated to ca. 1 mL, layered
with pentane (ca. 5 mL), and allowed to stand at −40 °C overnight.
The resulting white solid was collected by filtration, washed with
pentane (4 × 2.5 mL), and dried. Yield 0.138 g, 70%. X-ray quality
crystals were grown by layering pentane onto a CH2Cl2 solution of 3a
and stored at −40 °C. 31P{1H} NMR (CD2Cl2): δ 30.2 (d, JPP = 16,
Pd-P), 19.6 (d, JPP = 16, PO). 1H NMR (CD2Cl2): δ 7.76−7.20 (m,
17H), 3.87−3.81 (m, 2H, −OCH2CH3), 3.75−3.70 (m, 2H,
−OCH2CH3), 3.10 (s, 6H, Lut-CH3), 1.02 (t, 3H, JHH = 7,
−OCHH2CH3), 0.34 (d, JPH = 4, Pd-CH3). ESI-MS (CH2Cl2, positive
ion), m/z: 626.1 [M]+.
Polymerization reactions were performed in a Parr 300 mL stainless
steel autoclave, which was equipped with a mechanical stirrer,
thermocouple, and water cooling loop and controlled by a Parr
4842 controller.
Elemental analyses were performed by Robertson Microlit
Laboratories. Trace levels of solvents in elemental analysis samples
1
were quantified by H NMR. NMR spectra were acquired on Bruker
DMX-500 or DRX-400 spectrometers at ambient temperatures unless
otherwise indicated. 1H and 13C chemical shifts are reported relative to
3b. A vial was charged with 2b (0.390 g, 0.634 mmol), AgSbF6
(0.219, 0.637 mmol), and 2,6-lutidine (75 μL, 0.643 mmol). CH2Cl2
(10 mL) was added, yielding a suspension of a white solid in a yellow
supernatant, which was stirred at ambient temperature in the dark for
1 h. The mixture was filtered through Celite, and the volatiles were
removed under vacuum, yielding 3b as a fine yellow powder (0.577 g,
98%). This material was rinsed with Et2O and placed under high
1
SiMe4 and are internally referenced to residual H and 13C solvent
resonances. 31P chemical shifts are reported relative to externally
referenced 85% H3PO4. 19F chemical shifts are reported relative to
CFCl3. Coupling constants are reported in Hz. NMR signals for
ligands and complexes are assigned based on COSY, HMQC, HMBC,
1
and H{31P} experiments, as well as trends in chemical shifts and
coupling constants derived from these experiments. 13C and 1H
labeling schemes are provided in the Supporting Information. 1H
NMR integrals are fully consistent with these assignments. NMR
assignments for polymers and copolymers are based on literature
sources.2a,3a,4d,e,34 Mass spectrometry was performed on an Agilent
6224 TOF-MS instrument (high resolution) or an Agilent 6130 LC-
MS (low resolution).
1
vacuum for 18 h. H NMR indicated the presence of 0.015 equiv of
CH2Cl2 and 0.113 equiv of Et2O. X-ray quality crystals were grown by
layering a CH2Cl2 solution with Et2O. 31P{1H} NMR (CD2Cl2): δ
21.8 (d, JPP = 16, P-Pd), 20.8 (d, JPP = 15, PO). 1H NMR (CD2Cl2):
δ 7.85 (dddd, JPH = 14, 4, JHH = 8, 1, Ha), 7.72 (t, JHH = 8, Ho), 7.65
(m, Hb), 7.62 (t, JHH = 9, Hi), 7.59 (t, JHH = 8, Hc), 7.43 (dd, JPH = 18,
JHH = 8, Hd), 7.40 (m, Hk), 7.26 (d, JHH = 8, Hn), 7.07 (t, JHH = 8, Hj),
7.05 (dd, JHH = 8, JPH = 5, Hh), 3.85−3.65 (m, −OCHH2CH3), 3.69
(s, Hq), 3.09 (s, Hp), 1.05 (t, JHH = 7, −OCHH2CH3), 0.17 (d, JPH = 4,
Pd-CH3). 13C NMR (CD2Cl2): δ 161.0 (d, JPC = 3, CL), 158.8 (d, JPC
= 1, CM), 139.3 (s, CO), 136.8 (d, JPC = 11, CK), 135.7 (dd, JPC = 14, 3,
CD), 135.2 (dd, JPC = 46, 11, CE), 134.5 (d, JPC = 2, CI), 133.8 (dd, JPC
= 10, 8, CA), 132.5 (dd, JPC = 7, 3, CC), 130.8 (dd, JPC = 14, 2, CB),
Gel permeation chromatography (GPC) data were obtained on a
Polymer Laboratories PL-GPC 200 instrument at 150 °C with 1,2,4-
trichlorobenzene (stabilized with 125 ppm BHT) as the mobile phase.
Three PLgel 10 μm Mixed-B LS columns were used. Molecular
weights were calibrated using narrow polystyrene standards (ten-point
calibration with Mn from 570 Da to 5670 kDa) and are corrected for
linear polyethylene by universal calibration using the following Mark−
Houwink parameters: polystyrene, K = 1.75 × 10−2 cm3 g−1, α = 0.67;
polyethylene, K = 5.90 × 10−2 cm3 g−1, α = 0.69.
129.5 (dd, JPC = 185, 18, CF), 123.2 (d, JPC = 3, CN), 121.4 (d, JPC
11, CJ), 114.7 (d, JPC = 55, CG), 111.8 (d, JPC = 5, CH), 64.5 (d, JPC
=
=
7, −OCH2CH3), 55.6 (s, CQ), 26.4 (s, CP), 15.9 (d, JPC = 6,
−OCHH2CH3), −1.4 (t, JPC = 2, Pd-CH3). HRMS (m/z): Calcd for
[C32H40P2O5PdN]+ 686.1417, Found: 686.1434. EA: Calcd for
C32H40P2O5PdNSbF6·0.015 CH2Cl2·0.113 Et2O, %: C, 41.82; H,
4.45; N, 1.50. Found: C, 42.03; H, 4.56; N, 1.60.
2a. A flask was charged with 1a (0.200 g, 50.3 mmol),
(COD)PdMeCl (0.133 g, 50.2 mmol), and CH2Cl2 (10 mL). The
mixture was stirred at room temperature for 4 h. Removal of the
solvent under vacuum afforded 2a as an off-white solid (0.278 g, 99%).
31P{1H} NMR (CD2Cl2): δ 31.6 (d, JPP = 14, Pd-P), 19.9 (d, JPP = 13,
Diethyl (2-Bromo-4-tolyl)phosphonate (5). A 1 L Schlenk flask
was charged with triphenylphosphine (6.78 g, 25.9 mmol) and
Pd(OAc)2 (0.573 g, 2.55 mmol). Ethanol (330 mL), 3-bromo-4-
iodotoluene (25.6 g, 86.1 mmol), diethyl phosphite (58.7 g, 425
mmol), and triethylamine (73.8 mL, 530 mol) were added in the order
listed. The resulting suspension of a white solid in a yellow supernatant
was stirred and heated at reflux at 50 h; the mixture became
homogeneous upon warming. The reaction mixture was added to a
separatory funnel with 1 M HCl (aq) (190 mL) and diethyl ether (800
mL). The aqueous layer was extracted with Et2O (200 mL, 160 mL,
160 mL). The combined organic layer was washed with 2.5 M NaOH
(aq) (90 mL), washed with brine (45 mL), and dried over MgSO4.
Removal of solvent under reduced pressure yielded a mixture of 5,
triphenylphosphine, and diethyl phosphite. 5 was purified by silica gel
chromatography, using a 70:29:1 hexanes:acetone:triethylamine
mixture as eluent. 5 was isolated as a pale yellow oil (13.9 g, 53%
1
PO). H NMR (CD2Cl2): δ 7.80 (m, 1H), 7.60−7.40 (m, 12 H),
7.18 (m, 1H), 4.00 (m, 2H, −OCH2CH3), 1.14 (t, 3H, JHH = 7,
−OCHH2CH3), 0.57 (d, 3H, JPH = 4, Pd-CH3).
2b. A flask was charged with 1b (0.503 g, 1.10 mmol),
(COD)PdMeCl (0.277 g, 1.05 mmol), and CH2Cl2 (12 mL). The
pale yellow solution was stirred for 1 h at room temperature. The
volatiles were removed under vacuum, yielding a yellow solid. The
solid was dissolved in minimal CH2Cl2 (approximately 3 mL). A
portion of this solution was used to grow X-ray quality crystals via
vapor diffusion of Et2O. The remaining fraction was layered with
pentane and stored at −40 °C, yielding a white solid after 2 days. The
solid was collected, rinsed with pentane and Et2O, and dried under
high vacuum for 2 h. Yield 0.465 g (72%) of 2b as an off-white solid.
31P{1H}NMR (CD2Cl2): δ 24.1 (d, JPP = 11, Pd-P), 20.6 (d, JPP = 11,
PO). 1H NMR (CD2Cl2): δ 7.79 (dddd, JPH = 13, 4, JHH = 8, 1, Ha),
1
7.54 (m, Hb), 7.53 (t, JHH = 7, Hi), 7.52−7.42 (br, Hk), 7.46 (td, JHH
=
yield). 31P{1H} NMR (CDCl3): δ 16.0. H NMR (CD2Cl2): δ 7.89
7, 1, Hc), 7.34 (m, Hd), 7.01 (t, JHH = 8, Hj), 6.96 (dd, JHH = 8, JPH = 5,
Hh), 4.13−3.93 (m, −OCHH2CH3), 3.62 (s, Hm), 1.18 (t, JHH = 7,
−OCHH2CH3), 0.41 (d, JPH = 4, Pd-CH3). 13C{1H} NMR (CD2Cl2):
(dd, JHH = 8, JPH = 14, Ha), 7.49 (d, JPH = 5, Hd), 7.19 (d, JHH = 8, Hb),
4.25−4 (m, −OCHH2CH3), 2.36 (s, Ar-CH3), 1.34 (t, JHH = 7,
−OCHH2CH3). 13C{1H} NMR (CDCl3): δ 144.6 (d, JPC = 3, CC),
G
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Organometallics
Article
136.2 (d, JPC = 8, CA), 127.7 (d, JPC = 14, CB), 126.1 (d, JPC = 194,
CF), 125.0 (d, JPC = 4, CE), 62.3 (d, JPC = 5, -OCH2CH3), 21.1 (d, JPC
= 1, CG), 16.2 (d, JPC = 7, −OCHH2CH3). ESI-MS (1:1
MeOH:CH2Cl2, positive ion scan): 307.0 ([M + H]+ = 307.1),
615.1 ([2M + H]+ = 615.2). HRMS (m/z): Calcd for [C11H16PO3Br +
H]+: 307.0099, Found: 307.0099.
= 7, JHP = 1, P-CH(CH3)2), 2.52 (s, Hd), 1.35−1.25 (m,
−OCHH2CH3 and −CH(CH3)2), 0.47 (d, JHP = 3, Pd-CH3). 19F
NMR (CD2Cl2): δ −124.5; overlay of 121SbF6 (sextet, JSbF = 1950) and
123SbF6 (octet, JSbF = 1060). 13C NMR (CD2Cl2): δ 158.8 (d, JPC = 1,
CM), 144.7 (dd, JPC = 5,3, CP), 139.3 (s, CF), 134.9 (d, JPC = 15, CC),
134.5 (t, JPC = 9, CA), 132.5 (dd, JPC = 14, 2, CB), 132.2 (dd, JPC = 32,
12, CN), 128.4 (dd, JPC = 186, 13, CO), 123.4 (d, JPC = 3, CE), 65.2 (d,
JPC = 7, −OCH2CH3), 26.6 (d, JPC = 27, P-CH(CH3)2), 26.4 (s, CH),
22.0 (d, JPC = 1, CD), 19.3 (d, JPC = 4, P-CH(CH3)2), 18.5 (s, P-
CH(CH3)2), 16.1 (d, JPC = 7, −OCHH2CH3), −6.7 (dd, JPC = 4, 1, Pd-
1-Diethylphosphonato-2-diisopropylphosphinobenzene
(1c). A 100 mL Schlenk flask was charged with 5 (1.00 g, 3.25 mmol)
and THF (20 mL) and cooled to −78 °C. nBuLi solution (1.6 M, 2.05
mL, 3.28 mmol) was added via syringe, yielding an orange solution
that was stirred for 1 h. A solution of chlorodiisopropylphosphine
(0.530 g, 3.47 mmol) in THF (5 mL) was added via syringe, causing
the orange color to fade. The flask was kept cold for at least 5 h and
was then allowed to warm slowly overnight. The solvent was removed
under reduced pressure, yielding a thick mixture of 1c and LiCl. 25 mL
of CH2Cl2 was added, and the resulting white suspension was filtered
through Celite, yielding a clear solution. The solvent was removed
under reduced pressure, yielding 1c as an oxidatively sensitive, waxy
−
CH3). ESI-MS: (CH2Cl2, positive ion scan): 572.0 ([M − SbF6 ]+,
−
465.0 ([M − lutidine − SbF6 ]+. EA: calcd. for C25H42P2O3NPdSbF6·
0.03 CH2Cl2, %: C, 37.06; H, 5.22; N, 1.73. Found: C, 37.02; H, 5.10;
N, 1.78.
1d. A 500 mL Schlenk flask was charged with 5 (12.02 g, 39.14
mmol) and THF (300 mL). The flask was cooled to −78 °C, and
nBuLi solution (1.6 M, 26.3 mL, 42.1 mmol) was added via syringe,
resulting in a deep orange-brown solution that was stirred for 20 min.
A solution of 7 (4.569 g, 19.4 mmol) in THF (20 mL) was added by
syringe, yielding a pale orange solution. After stirring for 40 min, the
cold bath was removed, and the flask was allowed to warm to room
temperature overnight, with stirring. The reaction mixture was then
concentrated under reduced pressure to an orange oil, which was
added to a separatory funnel with Et2O (300 mL) and H2O (300 mL).
The aqueous layer was extracted with 3 × 100 mL of Et2O. The
combined organic layer was dried over MgSO4, and the solvent was
removed under reduced pressure to yield a viscous yellow oil. The
crude product was loaded onto silica gel packed in ethyl acetate, and
ethyl acetate was run through the column to remove impurities. 1d
was then eluted with a 1:11 methanol:ethyl acetate mixture. Removal
of solvent under reduced pressure yielded a thick, cloudy oil. Heating
at 80 °C for 7 h yielded 1d as a white solid (5.32 g, 44%). 31P{1H}
NMR (CD2Cl2): δ 18.7 (s, PO), −9.9 (s, P). 1H NMR (CD2Cl2): δ
7.94 (ddd, JPH = 4, JHH = 8, JPH = 14, Ha), 7.33 (dd, JHH = 9, JPH = 1,
He), 7.23 (d, JHH = 7, Hb), 7.03 (t, JPH = JHH = 8, Hd), 6.71 (s, Hc),
4.1−3.7 (m, −OCHH2CH3), 2.20 (s, Hj), 1.30 (s, Hi), 1.09 (t, JHH = 7,
−OCHH2CH3), 1.07 (t, JHH = 7, −OCHH2CH3). 13C{1H} NMR
(CD2Cl2): δ 151.9 (s, CQ), 142.5 (d, JPC = 3, CP), 142.5 (dd, JPC = 27,
14, CM), 136.6 (d, JCP = 16, CC), 135.3 (d, JCP = 12, CO), 135.2 (dd,
JPC = 8, 11, CA), 134.2 (d, JCP = 21, CD), 131.1 (dd, JPC = 188, 31, CN),
129.0 (d, JPC = 15, CB), 125.6 (d, JPC = 7, CE), 62.12 (dd, JPC = 6, 2,
−OCH2CH3), 62.07 (dd, JPC = 6, 2, −OCH2CH3), 34.9 (s, CL), 31.4
(s, CI), 21.7 (d, JPC = 2, CJ), 16.29 (d, JPC = 7, −OCHH2CH3), 16.26
(d, JPC = 7, −OCHH2CH3). ESI-MS (1:1 MeOH:CH2Cl2, positive
ion): 619.3 ([M + H]+). EA: Calcd for C32H45P3O6, %: C, 62.13; H:
7.33. Found: C, 62.10; H, 7.33.
white solid (1.02 g, 91%) after several hours. 31P{1H}NMR (CD2Cl2):
1
δ 19.1 (s, PO), 3.2 (s, P). H NMR (CD2Cl2): δ 7.86 (ddd, JPH
=
=
13, JHH = 8, JPH = 3, Ha), 7.46 (dd, JPH = 2.3, 2.2, Hd), 7.22 (ddd, JHH
8, JPH = 2, 1, Hb), 4.12 (m, −OCHH2CH3), 2.09 (sept. of d, JHH = 7,
JPH = 4, P-CH(CH3)2, 1.32 (t, JHH = 7, −OCHH2CH3), 1.15 (dd, JPH
=
14, JHH = 7, P-CH(CH3)2), 0.88 (dd, JPH = 13, JHH = 7, P-CH(CH3)2).
13C{1H} NMR (CD2Cl2): δ 143.9 (dd, JPC = 29, 15, CE), 142.9 (d, JPC
= 3, CC), 135.2 (dd, JPC = 17, 3, CD), 135.1 (dd, JPC = 11, 9, CA), 134.6
(dd, JPC = 191, 32, CF), 130.3 (dd, JPC = 15, 1, CB), 63.1 (dd, JPC = 6,
3, −OCH2CH3), 27.1 (d, JPC = 15, P-CH(CH3)2), 22.6 (d, JPC = 2,
CG), 21.6 (d, JPC = 13, P-CH(CH3)2), 21.4 (d, JPC = 20, P-CH(CH3)2,
17.6 (d, JPC = 7, −OCHH2CH3). HRMS (m/z): Calcd for
[C17H30P2O3 + H]+: 345.1749, Found: 345.1746.
2c. A vial was charged with 1c (0.300 g, 0.870 mmol),
(COD)PdMeCl (0.223 g, 0.841 mmol), and CH2Cl2 (8 mL). The
resulting yellow solution was stirred for 1 h at room temperature and
then filtered through Celite. Removal of the solvent under vacuum
yielded a yellow solid, which was dissolved in 3 mL of CH2Cl2. Several
small portions of this solution were used in attempted crystallizations;
most of the solution was placed in a vial and layered with pentane.
After several days at −40 °C, X-ray quality crystals of 2c had formed in
the vial (structure shown in the Supporting Information). These were
collected on a frit, yielding 2c as a pale yellow powder (0.152 g, 36%).
This material was found to contain 0.33 equiv of CH2Cl2 by 1H NMR.
31P{1H}NMR (CD2Cl2): δ 41.6 (d, 13; P-Pd), 21.8 (d, 14; PO). 1H
NMR (CD2Cl2): δ 7.74 (ddd, JHH = 8, JPH = 8, 3, Ha), 7.54 (t, JPH = 6,
Hd), 7.44 (d, JHH = 7, Hb), 4.35 (m, −OCHH2CH3), 2.54 (sept., JHH
=
7, −CH(CH3)2), 2.46 (s, Hg), 1.39 (t, JHH = 7, −OCHH2CH3), 1.20
(dd, JHH = 7, JPH = 15, −CH(CH3)2), 1.17(dd, JHH = 7, JHP = 18,
−CH(CH3)2), 0.74 (d, JPH = 3, Pd-CH3). 13C{1H} NMR (CD2Cl2): δ
143.4 (dd, JPC = 5,3, CC), 134.1 (d, JPC = 16, CD), 133.5 (t, JPC = 9,
CA), 132.8 (dd, JPC = 29, 13, CE), 131.7 (dd, JPC = 14, 2, CB), 130.2
1g. Compound 1g was prepared analogously to 1d from 7 and 4
and was isolated as a heavy white oil (36% yield). 1H NMR (CD2Cl2):
δ 8.07 (dddd, JHH = 8, 2, JPH = 14,4, Ha), 7.42 (tdd, JHH = 8, 1, JPH = 4,
Hb), 7.37 (tt, JHH = 8, 2, JPH = 2, Hc), 7.34 (dd, JHH = 9, JPH = 1, Hi),
7.05 (t, JHH = JPH = 8, Hh), 6.94 (dt, JHH = 7, JPH = JPH = 4, Hd), 4.05−
3.75 (m, −OCHH2CH3), 1.30 (s, −C(CH3)3), 1.11 (t, JHH = 7,
−OCHH2CH3), 1.10 (t, JHH = 7, −OCHH2CH3). 31P{1H} NMR
(CD2Cl2): δ 17.4 (s, PO), −10.6 (s, P). 13C{1H} NMR (CD2Cl2): δ
151.9 (s, CJ), 142.6 (dd, JPC = 27, 13, CE), 135.9 (d, JPC = 15, CD),
(dd, JPC = 194, 13, CF), 64.6 (d, JPC = 6, −OCH2CH3), 25.7 (d, JPC
=
26, P-CH(CH3)2), 21.9 (d, JPC = 1, CG), 19.0 (d, JPC = 5, P-
CH(CH3)2), 18.5 (s, P-CH(CH3)2), 16.3 (d, JPC = 7, −OCHH2CH3),
−6.3 (d, JPC = 2, Pd-CH3). EA: calcd for C18H33P2O3PdCl·0.33
CH2Cl2, %: C, 41.59; H, 6.40. Found: C, 41.35; H, 6.18.
3c. A vial was charged with 2c (0.129 g, 0.256 mmol), AgSbF6
(0.088 g, 0.255 mmol), 2,6-lutidine (30 μL, 0.258 mmol), and CH2Cl2
(5 mL). The resulting yellow solution was stirred for 40 min at room
temperature. Filtration through Celite yielded a clear yellow solution.
The solvent was removed under vacuum, yielding 3c as a yellow solid
(0.188 g, 91%, crude), which was purified by layering Et2O onto a
THF solution of 3c and storing at −40 °C for 2 days. The resulting
microcrystalline solid was collected on a frit, rinsed with Et2O, and
dried under high vacuum for 18 h. 3c was found to contain 0.03 equiv
135.2 (d, JPC = 12, CG), 135.1 (dd, JPC = 10, 7, CA), 134.4 (dd, JPC
=
186, 31, CF), 134.2 (d, JPC = 21, CH), 132.1 (d, JPC = 3, CC), 128.3 (d,
JPC = 14, CB), 125.7 (d, JPC = 7, CI), 62.2 (dd, JPC = 6, 2,
−OCH2CH3), 62.2 (dd, JPC = 6, 2, −OCH2CH3), 34.9 (s, −C(CH3)3),
31.4 (s, −C(CH3)3), 16.3 (d, JPC = 7, −OCHH2CH3), 16.2 (d, JPC = 7,
−OCHH2CH3). ESI-MS (1:1 MeOH:CH2Cl2, positive ion scan), m/z:
591.1 ([M + H]+), 607.2 ([MO + H]+).
2d. A 50 mL round-bottom flask with a magnetic stir bar was
charged with 1d (1.83 g, 2.95 mmol), (COD)PdMeCl (0.770 g, 2.90
mmol), and CH2Cl2 (20 mL). The resulting yellow solution was
stirred for 45 min, and the solvent was removed under reduced
pressure, yielding a yellow solid. The solid was suspended in a mixture
of Et2O (7 mL) and pentane (13 mL), collected as a white solid, and
rinsed with pentane (2 × 15 mL). Residual solvent was removed under
high vacuum, yielding 2d as a white solid (1.956 g, 87%). 31P{1H}
1
of CH2Cl2 by H NMR. X-ray quality crystals were grown by vapor
diffusion of diethyl ether into a THF solution of 3c. 31P{1H} NMR
1
(CD2Cl2): δ 41.3 (d, JPP = 14, P-Pd), 20.1 (d, JPP = 15, PO). H
NMR (CD2Cl2): δ 7.78 (ddd, JHH = 8, JHP = 8, 4, Ha), 7.72 (t, JHH = 8,
Hf), 7.65 (t, JHP = 7, Hc), 7.54 (dd, JHH = 8, JPH = 1, Hb), 7.25 (d, JHH
=
8, He), 4.06−3.92 (m, −OCHH2CH3), 3.09 (s, Hh), 2.65 (sept d, JHH
H
dx.doi.org/10.1021/om5004489 | Organometallics XXXX, XXX, XXX−XXX

Organometallics
Article
NMR (CD2Cl2): δ 33.1 (t, JPP = 9, P-Pd), 18.4 (br s, PO). 1H NMR
(CD2Cl2): δ 7.78 (ddd, JPH = 13, JHH = 8, JPH = 4, Ha), 8−7.6 (br, Hh),
7.47 (d, JHH = 8, Hi), 7.37 (d, JHH = 8, Hb), 6.87 (d, JPH = 5, Hd), 4.5−
3.6 (br, −OCHH2CH3), 2.26 (s, Hk), 1.32 (s, −C(CH3)3), 1.25 (t, JHH
= 7, −OCHH2CH3), 1.04 (br s, −OCHH2CH3), 0.43 (d, JPH = 4, Pd-
CH3). 13C{1H} NMR (CD2Cl2): δ 155.0 (d, JPC = 2, CJ), 142.7 (d, JPC
= 4, CC), 138−136 (br, CH and CE), 135.3 (d, JPC = 14, CD), 134.8 (br,
= 7, −OCHH2CH3), 15.4 (d, JPC = 8, −OCHH2CH3), 14.6 (d, JPC = 9,
−OCHH2CH3), −6.0 (d, JPC = 4, Pd-CH3). 19F NMR (RT, CD2Cl2):
δ −124.6; overlay of 121SbF6 (sextet, JSbF = 2050) and 123SbF6 (octet,
JSbF = 1110). ESI-MS (1:1 CH2Cl2:MeOH, positive ion, fragmentor
40), m/z: 845.3 [M − SbF6 − H], 738.1 [M − SbF6 − lut − H]. EA:
Calcd for C40H57P3O6NPdSbF6, %: C, 44.36; H, 5.31; N, 1.29. Found:
C, 44.09; H, 5.15; N, 1.36.
Ethylene Homopolymerizations. In a glovebox, a 200 mL glass
autoclave liner was charged with a solution of the catalyst in CH2Cl2
(ca. 1 mL). The solvent was removed under vacuum, and toluene (50
mL) was added. For catalyst loadings larger than 5 μmol, the catalyst
was weighed directly into the liner. The glass liner was placed in a
stainless steel autoclave, which was sealed and removed from the
glovebox. The autoclave was heated to (typically) 80 °C and
pressurized with ethylene while the contents were stirred. After 2 h,
the autoclave was cooled to 25 °C and vented. Acetone (50 mL) was
added to precipitate polymer. The polymer was collected by filtration,
rinsed with acetone, and dried overnight in a vacuum oven. The
oligomer content of the filtrate was determined by GC−MS analysis.
Ethylene Copolymerizations with Methyl Acrylate or Acrylic
Acid. In a glovebox, a 200 mL glass autoclave liner was charged with
catalyst, toluene (50 mL), and, if applicable, BHT (0.100 g).
Comonomer was added, and the liner was placed in a stainless steel
autoclave, which was sealed and removed from the glovebox. Stirring
was initiated, the autoclave was pressurized with ethylene (22 atm),
and the ethylene line was closed. The autoclave was heated to 80 °C,
and the pressure was adjusted to 28 atm with ethylene on demand.
After the listed polymerization time, the autoclave was cooled and
vented. MeOH (200 mL, methyl acrylate copolymerization) or 10%
H2O/90% MeOH solution (200 mL, acrylic acid copolymerization)
was added to precipitate the polymer. The solid was collected by
filtration and washed with the corresponding solvent. For the acrylic
acid copolymerization, the polymer was then washed with MeOH. All
samples were then dried overnight in a vacuum oven.
CA), 130.8 (d, JPC = 14, CB), 128.3 (d, JPC = 160, CF), 127.9 (d, JPC
46, CG), 126.1 (d, JPC = 11, CI), 63.3 (br, −OCH2CH3), 63.0 (d, JPC
=
=
6, −OCH2CH3), 35.1 (d, JPC = 1, −C(CH3)3), 31.1 (s, −C(CH3)3),
21.7 (d, JPC = 2, CK), 16.3 (d, JPC = 6, −OCHH2CH3), 16.0 (br d, JPC
= 7, −OCHH2CH3), −3.4 (s, Pd-CH3). ESI-MS (1:1 CH2Cl2: MeOH,
positive ion), m/z: 739.2 ([M − Cl]+), 771.2 ([M − Cl + MeOH]+).
EA: Calculated for C33H48P3O6PdCl, %: C, 51.11; H, 6.24. Found: C,
50.89; H, 6.33.
2g. A 30 mL Schlenk tube with a magnetic stir bar was charged with
1g (1.007 g, 1.69 mmol), (COD)PdMeCl (0.446 g, 1.68 mmol), and
CH2Cl2 (10 mL). The resulting yellow solution was stirred for 25 min,
and the solvent was removed under reduced pressure, yielding a yellow
solid. The solid was suspended in Et2O (10 mL) and collected as a
white solid, which was then rinsed with Et2O (10 mL) and then
pentane (10 mL). Residual solvent was removed under high vacuum,
yielding 2g as a white solid (0.830 g, 66%). X-ray quality crystals were
grown by slow evaporation of a CH2Cl2 solution of 2g. 31P{1H} NMR
(CD2Cl2): δ 32.9 (t, JPP = 9, Pd-P), 17.5 (br, PO). 1H NMR
(CD2Cl2): δ 7.91 (ddd, J = 13, 8, 4), 7.73 (br), 7.56 (m), 7.48 (td, J =
7.5, 1), 7.10 (br m), 4.4−3.6 (br, −OCHH2CH3), 1.32 (s,
−C(CH3)3), 1.26 (t, J = 7, −OCHH2CH3), 1.04 (br s,
−OCHH2CH3), 0.45 (d, J = 4, Pd-CH3). HRMS (m/z): Calcd for
[C30H41P3O6 + H]+: 591.2195, Found: 591.2192.
3d. A vial was charged with 2d (1.003 g, 1.29 mmol), 2,6-lutidine
(151 μL, 1.29 mmol), and CH2Cl2 (8 mL), yielding a clear solution.
This solution was added to a stirred suspension of AgSbF6 (0.444 g,
1.29 mmol) in CH2Cl2 (35 mL). The resulting suspension of a gray
solid in a yellow supernatant was stirred for 90 min and then filtered
through Celite. Solvent was removed under reduced pressure, and the
resulting solid was further dried on a high-vacuum line for 19 h. Crude
3d was isolated as a yellowish solid (1.397 g, 95%). This compound
was purified by layering Et2O onto a CH2Cl2 solution of 3d and stored
at −40 °C for 5 days. The white precipitate was collected, rinsed with
Et2O, and dried under high vacuum for 18 h. Dynamic solution
behavior of this compound at room temperature required NMR
characterization at low temperature. 31P{1H} NMR (RT, CD2Cl2): δ
32.5 (t, JPP = 9, Pd-P), 19.7 (br s, PO), 15.9 (br s, PO). 31P{1H}
NMR (−60 °C, CD2Cl2): δ 31.8 (d, JPP = 20, Pd-P), 20.5 (d, JPP = 20,
ASSOCIATED CONTENT
* Supporting Information
■
S
Crystal structure report for compounds 2g, 3c, 2c, 3b, and 3a;
synthesis of compounds; NMR labeling scheme; molecular
structure of complex 2c; ethylene homopolymerization data;
Schulz−Flory analysis of oligomers from 3a; 1-heptene
isomerization experiment; ethylene copolymerization data;
variable-temperature NMR spectra of 3d; NMR spectra of
compounds, oligomer fraction, and polymers; and crystallo-
graphic data in CIF format. This material is available free of
charge via the Internet at http://pubs.acs.org.
1
PO-Pd), 16.8 (s, PO). H NMR (RT, CD2Cl2): δ 7.80 (br s),
7.70 (t, JHH = 8, lut), 7.56 (d, J = 7.5), 7.45 (d, J = 7.5), 7.24 (d, J =
7.5), 7.1−6.6 (br), 4.4−3.4 (br, −OCHH2CH3), 3.17 (s, lut-CH3),
2.30 (s, Ar-CH3), 1.36 (s, −C(CH3)3), 1.3−0.4 (br, −OCHH2CH3),
AUTHOR INFORMATION
Notes
The authors declare no competing financial interest.
1
■
0.16 (d, JH−P = 4, Pd-CH3). H NMR (−60 °C, CD2Cl2): δ 8.51 (dd,
JPH = 14, JHH = 8, Hj), 7.79 (ddd, JPH = 13, 4 JHH = 8, Ha), 7.74 (ddd,
JPH = 13, 4, JHH = 8, Ha′), 7.68 (t, JHH = 8, Hd), 7.68 (d, JHH = 8, Hi),
7.43 (d, JHH = 8, Hb), 7.37 (d, JHH = 7, Hb′), 7.32 (d, JHH = 9, Hh), 7.24
(d, JHH = 8, He), 7.17 (d, JHH = 8, Hf), 7.02 (dd, JPH = 11, JPH = 6, Hc′),
6.93 (dd, JPH = 8, JHH = 8, Hg), 6.65 (dd, JPH = 12, 5, Hc), 4.2−3.8 (br
m, −OCHH2CH3), 3.55−3.20 (br m, −OCHH2CH3), 3.10 (s, Hq),
3.01 (s, Hr), 2.40−2.25 (br, −OCHH2CH3), 2.28 (s, Hn), 2.22 (s,
Hn′), 1.25 (s, Hm), 1.30−1.18 (m, −OCHH2CH3), 1.01 (t, JHH = 7,
−OCHH2CH3), 0.48 (t, JHH = 7, −OCHH2CH3), −0.01 (d, JPH = 3,
Pd-CH3). 13C NMR (−60 °C, CD2Cl2): δ 158.3 (s, CO/P), 158.1 (s,
CO/P), 154.3 (s, CK), 143.3 (d, JPC = 6, CS), 142.5 (d, JPC = 8, CS′),
138.4 (d, JPC = 23, CJ), 138.3 (s, CD), 137.0 (dd, JPC = 47, 12, CT),
135.8−135.4 (m, CC), 135.0 (m, CA), 134.0 (d, JPC = 12, CC′), 133.9
(br m, CA′), 132.9 (s, CG), 132.5 (dd, JPC = 51, 16, CT′), 131.1 (d, JPC
= 13, CB), 130.2 (d, JPC = 13, CB′), 126.3 (dd, JPC = 188, 12, CU),
125.9 (d, JPC = 16, CI), 125.8 (s, CH), 125.1 (d, JPC = 49, CV), 123.1
(dd, JPC = 185, 18, CU′), 122.3 (s, CE), 122.2 (s, CF), 62.9 (d, JPC = 6,
−OCH2CH3), 62.7 (d, JPC = 6, −OCH2CH3), 61.5 (d, JPC = 6,
−OCH2CH3), 61.3 (d, JPC = 6, −OCH2CH3), 34.5 (s, CL), 30.2 (s,
CM), 26.2 (s, CQ), 25.8 (S, CR), 21.4 (s, CN), 21.3 (s, CN′), 15.7 (d, JPC
ACKNOWLEDGMENTS
This work was supported by the National Science Foundation
(DGE-1144082, CHE-0911180, and CHE-1048528).
■
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