Alternating copolymerization of fluoroalkenes with carbon monoxide

Article abstract of DOI:10.1021/ja055862k

The palladium-catalyzed alternating copolymerization of fluoroalkenes, represented as CH₂= CH-CH₂-C_nF_2n+1, with CO was performed using (R,S)-BINAPHOS (2e) as a ligand. The CH ₂-C_nF_2n+1 group is the most electronegative substituent ever reported for the copolymerization (Taft's σ* value of 0.90 for CH₂CF₃). The copolymer obtained from CH ₂=CH-CH₂-C₈F₁₇ (1a) existed as a mixture of polyspiroketal and polyketone, while that from CH₂=CH- CH₂-C₄F₉ (1b) was a pure polyspiroketal, as was revealed by infrared and ¹³C-CP/MAS NMR spectroscopies. The terminal structure of the polymer from 1b was confirmed by MALDI-TOF MS spectrometry. Detailed NMR studies suggested that the much higher reactivity with (R,S)-BINAPHOS (2e) than that with the conventional ligand DPPP (2a) can be attributed to the unique 1,2-insertion of the fluoroalkene into acylpalladium species. The existence of an electronegative substituent on the α-carbon of the palladium center is successfully avoided in the 1,2-insertion mechanism.

Full text of DOI:10.1021/ja055862k

Published on Web 01/20/2006
Alternating Copolymerization of Fluoroalkenes with
Carbon Monoxide
Tomoyuki Fujita, Koji Nakano, Makoto Yamashita, and Kyoko Nozaki*
Contribution from the Department of Chemistry and Biotechnology, Graduate School of
Engineering, The UniVersity of Tokyo, 7-3-1 Hongo, Bunkyo-ku, Tokyo 113-8656, Japan
Received August 25, 2005; E-mail: nozaki@chembio.t.u-tokyo.ac.jp
Abstract: The palladium-catalyzed alternating copolymerization of fluoroalkenes, represented as CH2d
CH-CH2-CnF2n+1, with CO was performed using (R,S)-BINAPHOS (2e) as a ligand. The CH2-CnF2n+1
group is the most electronegative substituent ever reported for the copolymerization (Taft’s σ* value of
0.90 for CH2CF3). The copolymer obtained from CH2dCH-CH2-C8F17 (1a) existed as a mixture of
polyspiroketal and polyketone, while that from CH2dCH-CH2-C4F9 (1b) was a pure polyspiroketal, as
was revealed by infrared and 13C-CP/MAS NMR spectroscopies. The terminal structure of the polymer
from 1b was confirmed by MALDI-TOF MS spectrometry. Detailed NMR studies suggested that the much
higher reactivity with (R,S)-BINAPHOS (2e) than that with the conventional ligand DPPP (2a) can be
attributed to the unique 1,2-insertion of the fluoroalkene into acylpalladium species. The existence of an
electronegative substituent on the R-carbon of the palladium center is successfully avoided in the 1,2-
insertion mechanism.
Scheme 1. Ideal Catalytic Cycle of the Alternating
Copolymerization of Electron-Deficient Olefins and Carbon
Introduction
Electron-deficient olefins, such as methyl acrylate,1,2 vinyl
acetate,3,4 and vinyl chloride,5 are reported to be unfavorable
for the alternating copolymerization with carbon monoxide. As
shown in Scheme 1, the copolymerization would proceed via
olefin coordination to acylpalladium (AfB), intramolecular
olefin insertion (BfC), carbon monoxide coordination (CfD),
and intramolecular CO insertion (DfA). In this scheme, there
are several disadvantages of the olefins bearing electron-
withdrawing groups. The coordination of electron-deficient
olefins (AfB) is less favorable as compared to ethene or simple
1-alkenes.6-9 Nevertheless, for acetylpalladium complexes, the
olefin insertion (BfC) was reported to proceed for X )
COOMe,1,2 OCOCH3,3,4,7 and Cl.5,8,10,11 The insertion undergoes
via the predominant 2,1-insertion in all of the reported examples.
Alkylpalladium C thus produced has an electron-withdrawing
group on the R-carbon of palladium. The electron-withdrawing
group in C was reported to cause the stronger five-membered
Monoxide
chelation of the carbonyl oxygen to the metal center.5 This
chelation was anticipated to obstruct the subsequent CO
insertion, which requires the replacement of the intramolecular
ketone-coordination by the intermolecular CO-coordination
(CfD). In addition, the electronegative substituent on the
R-carbon in D should retard the subsequent CO insertion to the
metal-carbon bond (DfA) by lowering the nucleophilicity of
the migrating R-carbon atom.5,12-15 For example, in a carbonyl
complex L2Pd(CO)R where L2 is a bidentate sp2-nitrogen ligand,
the CO insertion takes place when R is CH2Cl12 or CH2-
(1) Rix, F. C.; Brookhart, M.; White, P. S. J. Am. Chem. Soc. 1996, 118, 4746-
4764.
OCOCH3,7 but does not undergo when R is CHCl2 or n-C3F7
12
(2) Braunstein, P.; Frison, C.; Morise, X. Angew. Chem., Int. Ed. 2000, 39,
2867-2870.
(L2 is dppp for the last example). As a result, all of the attempted
examples for the alternating copolymerization of electron-
deficient olefins with CO ended up at the stage of complex C
when started from an acetylpalladium corresponding to A.
In contrast, palladium-catalyzed copolymerization with CO
is reported for monomers represented as CH2dCH-EWG,
(3) Reddy, K. R.; Chen, C. L.; Liu, Y. H.; Peng, S. M.; Chen, J. T.; Liu, S. T.
Organometallics 1999, 18, 2574-2576.
(4) Reddy, K. R.; Surekha, K.; Lee, G. H.; Peng, S. M.; Chen, J. T.; Liu, S. T.
Organometallics 2001, 20, 1292-1299.
(5) Shen, H.; Jordan, R. F. Organometallics 2003, 22, 1878-1887.
(6) Kang, M. S.; Sen, A.; Zakharov, L.; Rheingold, A. L. J. Am. Chem. Soc.
2002, 124, 12080-12081.
(7) Williams, B. S.; Leatherman, M. D.; White, P. S.; Brookhart, M. J. Am.
Chem. Soc. 2005, 127, 5132-5146.
(8) Philipp, D. M.; Muller, R. P.; Goddard, W. A.; Storer, J.; McAdon, M.;
Mullins, M. J. Am. Chem. Soc. 2002, 124, 10198-10210.
(9) Mecking, S.; Johnson, L. K.; Wang, L.; Brookhart, M. J. Am. Chem. Soc.
1998, 120, 888-899.
(12) Foley, S. R.; Shen, H.; Qadeer, U. A.; Jordan, R. F. Organometallics 2004,
23, 600-609.
(13) Blake, D. M.; Vinson, A.; Dye, R. J. Organomet. Chem. 1981, 204, 257-
266.
(10) Michalak, A.; Ziegler, T. J. Am. Chem. Soc. 2001, 123, 12266-12278.
(11) von Schenck, H.; Stromberg, S.; Zetterberg, K.; Ludwig, M.; Akermark,
B.; Svensson, M. Organometallics 2001, 20, 2813-2819.
(14) Blake, D. M.; Winkelman, A.; Chung, Y. L. Inorg. Chem. 1975, 14, 1326-
1332.
(15) Koga, N.; Morokuma, K. J. Am. Chem. Soc. 1986, 108, 6136-6144.
9
1968
J. AM. CHEM. SOC. 2006, 128, 1968-1975
10.1021/ja055862k CCC: $33.50 © 2006 American Chemical Society

Alternating Copolymerization of Fluoroalkenes with CO
A R T I C L E S
Scheme 2. The Alternating Copolymerization of Olefins and
Carbon Monoxide Catalyzed by the Palladium Complexes Bearing
a Bidentate Ligand
Table 1. The Alternating Copolymerization of Fluoroalkenes 1a,
1b, or 1-Hexene (1c) with COa
fluoroalkene
(R
ligand
L1-L2
PCO
yieldb
(%)
run
))
(MPa)
time
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
CH2-n-C8F17 (1a)
CH2-n-C8F17 (1a)
CH2-n-C8F17 (1a)
CH2-n-C8F17 (1a)
CH2-n-C8F17 (1a)
CH2-n-C8F17 (1a)
CH2-n-C8F17 (1a)
CH2-n-C8F17 (1a)
CH2-n-C8F17 (1a)
CH2-n-C8F17 (1a)
CH2-n-C8F17 (1a)
CH2-n-C8F17 (1a)
CH2-n-C4F9 (1b)
n-C4H9 (1c)
2a
2a
2b
2c
2d
2e
2e
2e
2e
2f
2f
2f
2e
2e
2e
2e
3.0
8.0
3.0
3.0
3.0
3.0
5.0
8.0
8.0
3.0
5.0
8.0
8.0
8.0
2.0
5.0
24 h
24 h
17 h
40 h
24 h
24 h
24 h
24 h
84 h
24 h
24 h
24 h
84 h
3 h
3
3
2
0
5
27
49
54
81c
8
27d
34d
27e
71
40f
58f
n-C4H9 (1c)
n-C4H9 (1c)
45 min
45 min
a Pd (0.020 mmol), alkene (5.2 mmol) in CH2Cl2 (2 mL) at 60 °C
(palladium complexes were prepared by the reaction of (cod)PdMeCl with
ligands 2a-2f in toluene and then with Na[B(3,5-(CF3)2C6H3)4] in MeCN/
CH2Cl2; the resulting cationic palladium complex and alkene 1 were
dissolved in CH2Cl2, transferred into an autoclave, and treated with CO at
60 °C). b Calculated by assuming the polymeric materials were poly(alkene-
alt-CO). c 4 mL of CH2Cl2 was used for the reaction. d 2.6 mmol of alkene
was used for the reaction. e Low yield may be due to the impurity of alkene.
f 6 mmol of alkene was used for the reaction.
whereEWGisCH2CH2OH,16 CH2COOH,16 CH2OR,17 CH2C6F5,18
and CH2CH2C4F9.19 It is of interest to compare the substituents
based on their electronegativity. As an index to compare the
electronegativity of substituents, Taft’s σ* value may be
referred.20 When the monomers did not copolymerize with CO,
Taft’s σ* values of the substituents were 2.26 (-COOEt), 2.51
(-OCOCH3), and 2.94 (-Cl). On the other hand, the values
were 0.21 (-CH2CH2OH), 0.82 (-CH2COOEt), 0.58 (-CH2-
OEt), and 0.32 (-CH2CH2CF3) for the substituents that were
applicable to the copolymerization.
Here in this paper, we report the alternating copolymerization
of fluoroalkenes represented as CH2dCH-CH2-CnF2n+1 with
CO. Taft’s σ* value of 0.90 for -CH2CF3 is the highest value
ever reported for substituents of olefins that copolymerize with
CO using palladium catalysts.21 By using the Pd-(R,S)-
BINAPHOS (2e) system as a catalyst, the alternating copolymer
of CH2dCH-CH2-C8F17 and CO was obtained in up to 81%
yield. The use of DPPP ()1,3-bis(diphenylphosphino)propane,
2a), instead of 2e, resulted in a much lower yield. The higher
reactivity with 2e is attributed to the unique 1,2-insertion of
the fluoroalkene into acylpalladium species, producing Pd-CH2-
CH(EWG)- instead of Pd-CH(EWG)-CH2-.22
and CH2dCHCH2-n-C4F9 (1b) were treated with cationic
palladiumcomplexesrepresentedas[Pd(CH3)(NCCH3)(2)]+[BArF]-,
where [BArF]- is [B(3,5-(CF3)2C6H3)4]-. The results are sum-
marized in Table 1. The polymer obtained from 1a (runs 1-12
in Table 1) was not soluble in any of the common organic
solvents. Thus, the materials obtained in Table 1 were character-
ized by solid-state IR and solid-state NMR spectroscopies and
MALDI-TOF mass spectrometry, as will be discussed in the
next section. It should be noted that the copolymer forms not
only a polyketone structure but also a spiroketal structure, a
structural isomer of the polyketone, depending on the substit-
uents and the reprecipitation conditions (Scheme 2).16,19
As is shown in run 1, the weight of the residue after
evaporation of the solvent and monomer corresponded to 3%
yield of the polyketone using the conventional ligand 1,3-bis-
(diphenylphosphino)propane (DPPP, 2a). Elevation of the CO
pressure did not affect the result (run 2). Only negligible
amounts of nonvolatiles were given using nitrogen-based ligands
2b and 2c, both of which are effective for styrene/CO copo-
lymerization (runs 3 and 4).23,24 In contrast, the yield was slightly
improved with 2d (JOSIPHOS), which provides isotactic poly-
(propene-alt-CO), effectively (run 5).25 A higher yield of 27%
was achieved with 2e (BINAPHOS) (run 6). The yield was
improved at the higher CO pressure (runs 6-8), and the highest
yield of 81% was achieved under CO pressure of 8.0 MPa in
84 h (run 9). A similar pressure effect was observed with
MeDuPHOS (2f), which was previously reported as an effective
ligand for polymerization of CH2dCHCH2C6F5,18 although the
yields were slightly lower than those with 2e (runs 10-12).
Fluoroalkene CH2dCHCH2-n-C4F9 (1b) bearing a shorter
fluoroalkyl-chain was similarly copolymerized with CO (run
Results and Discussion
The Reaction of CH2dCH-CH2-Rf with CO Catalyzed
by Various Pd-Complexes. First, the palladium-catalyzed
reaction of CH2dCHCH2-n-CnF2n+1 with CO was carried out
using several ligands under various conditions (Scheme 2).
Under CO pressure, fluoroalkenes CH2dCHCH2-n-C8F17 (1a)
(16) Kacker, S.; Jiang, Z. Z.; Sen, A. Macromolecules 1996, 29, 5852-5858.
(17) Lee, J. T.; Alper, H. Chem. Commun. 2000, 2189-2190.
(18) Murtuza, S.; Harkins, S. B.; Sen, A. Macromolecules 1999, 32, 8697-
8702.
(19) Nozaki, K.; Shibahara, F.; Elzner, S.; Hiyama, T. Can. J. Chem. 2001, 79,
593-597.
(23) Brookhart, M.; Rix, F. C.; Desimone, J. M.; Barborak, J. C. J. Am. Chem.
Soc. 1992, 114, 5894-5895.
(20) Brandstrom, A. J. Chem. Soc., Perkin Trans. 2 1999, 1855-1857.
(21) Korenaga, T.; Kadowaki, K.; Ema, T.; Sakai, T. J. Org. Chem. 2004, 69,
7340-7343.
(24) Aeby, A.; Gsponer, A.; Consiglio, G. J. Am. Chem. Soc. 1998, 120, 11000-
11001.
(22) Nozaki, K.; Komaki, H.; Kawashima, Y.; Hiyama, T.; Matsubara, T. J.
Am. Chem. Soc. 2001, 123, 534-544.
(25) Gambs, C.; Chaloupka, S.; Consiglio, G.; Togni, A. Angew. Chem., Int.
Ed. 2000, 39, 2486-2488.
9
J. AM. CHEM. SOC. VOL. 128, NO. 6, 2006 1969

A R T I C L E S
Fujita et al.
Figure 1. 13C CP/MAS spectra of the polymers obtained from 1a (run 9 in Table 1, left) and from 1b (run 13 in Table 1, right).
13). It should be noted that the fluoroalkenes 1a and 1b are
much less active than simple aliphatic 1-alkenes. As is shown
in runs 14-16, 1-hexene (1c) copolymerizes with CO in a much
shorter time of 45 min otherwise under the same conditions.
Characterization of the Polymeric Products. The materials
obtained in Table 1 were characterized by IR and NMR
spectroscopies, MALDI-TOF mass spectrometry and thermal
analysis. The IR spectrum of the polymer from 1a (Table 1,
run 9, KBr pellet) showed a weak carbonyl vibration at 1718
cm-1, suggesting that the copolymer is in a polyketone form or
is a mixture of polyketone and polyspiroketal. Heating the
copolymer at 200 °C for 10 min led to no change of IR
spectrum. On the other hand, the IR spectrum of polymeric
material obtained from 1b (Table 1, run 13) showed no carbonyl
vibration, indicating that the material has a complete spiroketal
form. The melting point of the polymer obtained in run 9 was
determined by DSC analysis to be 182-183 °C.26 Above the
melting point, loss of weight (decomposition) of the polymer
started as determined by TGA.26 It is notable that the material
obtained in run 2 also exhibited a carbonyl absorption at 1716
cm-1 but it melted at 89-94 °C, at much lower temperature.
Either higher molecular weight or higher stereoregularity for
the polymer in run 9 is implied.
The low solubility of these polymers in common organic
solvents, unlike the reported polymer made from CO and CH2d
CHCH2C6F5,18 prevented us from analysis of their solution state.
Thus, the 13C CP/MAS NMR spectra were recorded for the
products obtained at runs 9 and 13 (Figure 1). The spectrum of
copolymer from 1a exhibited peaks at the carbonyl region
accompanied with spinning sidebands, which were confirmed
by changing rotational frequency. A peak at δ 116 overlapped
with the carbons of the perfluoroalkyl group should be assigned
to the quaternary carbon of the spiroketal structure. In sharp
contrast, exclusive formation of the spiroketal is manifested for
the copolymer obtained from 1b by the absence of the carbonyl
carbon and by the existence of a large peak of the spiroketal
quaternary center. The difference between the copolymers from
1a and that from 1b may be explained in that the longer
perfluoroalkyl group caused the aggregation of fluorous groups
Figure 2. MALDI-TOF mass spectrum of poly(1b-alt-CO) obtained in
run 13 of Table 1. Open circles (O) describe a series of m/z ) 559 + 288
× n (n ) 6-15). Solid circles (b) describe a series of m/z ) 314 + 288
× n (n ) 6-15). Both estimated structures are drawn at the top right (Rf
) n-C4F9).
overcoming the demand by the main-chain to form the spiroketal
structure.19 However, there might be even further factors that
control the ratio of spiroketal and ketone structures. For example,
Sen reported that the alternating copolymer made from CO and
CH2dCHCH2C6F5 was a pure polyketone, while that from
CH2dCHCH2C6H4-4-CF3 was a pure spiroketal.18 Currently,
no clear explanation for their difference has been given.
The higher solubility of the copolymer from 1b allowed us
subject the material to MALDI-TOF mass spectrometry. As is
shown in Figure 2, there were two series of polymers whose
repeating units were all 288 corresponding to the unit -CH2-
CH(CH2C4F9)-C(dO)-. The peak-series with lower intensity
can be characterized as poly(spiroketal) initiated by the CO
insertion to the original methylpalladium complex resulting in
the formation of two dihydrofuran rings at the head and end
groups. The peak-series with the higher intensity is assigned as
poly(spiroketal) initiated by the olefin insertion to a Pd-H bond.
The generation of these two series of polymers may be explained
by the mechanism shown in Scheme 3. The catalyst precursor,
a cationic methylpalladium complex [Pd(CH3)(NCCH3)(2e)]+-
(26) See the Supporting Information.
9
1970 J. AM. CHEM. SOC. VOL. 128, NO. 6, 2006

Alternating Copolymerization of Fluoroalkenes with CO
A R T I C L E S
Scheme 3. A Possible Mechanism for the Chain Propagation and Chain Transfer, Consistent with the Results of the MALDI-TOF Mass
Spectrum
[BArF]-, reacts with CO to form the corresponding acylpalla-
dium complex, and then the insertion of the olefin into the acyl-
palladium bond affords the alkyl complex. After several chain
propagation cycles, the acylpalladium complex may isomerize
to a palladium enolate by a hydride migration. Nucleophilic
attack of the enolate oxygen atom to the neighboring carbonyl
group leads to the tandem acetalization to form the spiroketal
skeleton. Elimination of hydroxide gives the first series of
polymer, which was detected with the lower intensities in
MALDI-TOF mass spectra. The generated palladium hydroxide
may be reduced to form a hydridopalladium complex, possibly
via the hydroxide migration to the coordinated carbonyl to form
a hydroxycarbonylpalladium and followed by a â-hydride
elimination producing carbon dioxide.27
NMR Studies on the Reaction of Acetylpalladium with
CH2dCHCH2C8F17 (1a). To clarify the polymerization mech-
anism, the reaction of acetylpalladium [CH3C(dO)Pd(NC-
Me)(2)]+[BArF]- with CH2dCHCH2C8F17 (1a) in the absence
of CO was monitored by NMR spectroscopy using DPPP (2a),
BINAPHOS (2e), or MeDuPHOS (2f) as a ligand (Scheme 4).
Characterization of the alkyl complexes 3, which were generated
by mixing acetylpalladium complexes with 10 equiv of 1a at 0
°C, was performed by 1H, 13C, 19F, and 31P NMR experiments
and 2D NMR techniques at 0 °C. In the case of using ligand
2a, alkyl complex 3a(2,1) was observed as a single product via
the 2,1-insertion of 1a. In contrast, 31P NMR spectra of the alkyl
complex bearing 2e showed six pairs of doublets (six doublets
for phosphine and six doublets for phosphite); three pairs of
them were detected as separated peaks, and the other three pairs
were overlapping each other. The ratio of the six pairs was 54%,
11%, 8% for the separated three pairs and 27% for the sum of
the three overlapped pairs. The major two pairs of doublets were
assigned to isomers of the 1,2-adducts; these are 3e(1,2)OP-
trans-CO (for the peak of 54%) and 3e(1,2)OP-cis-CO (for the
peak of 11%) by 31P NMR22 (OP-trans-CO and OP-cis-CO
explains the stereochemistry between phosphite moiety and the
carbonyl ligand). The structure of the major species 3e(1,2)-
OP-trans-CO was further confirmed by 2D-NMR technique (see
Experimental Section for details). The other minor peaks were
not fully characterized, but, most probably, they are either 2,1-
complexes or diastereomers of 3e(1,2)OP-trans-CO or 3e(1,2)-
OP-cis-CO due to the opposite configuration at the R-position
of the CH2Rf group. Using MeDuPHOS (2f), the corresponding
acetylpalladium complex was not quantitatively converted to
the corresponding alkyl complex.28
Because the NMR experiments were carried out in the
absence of CO pressure, the subsequent CO-insertion did not
occur. Instead, appearance of R,â-unsaturated ketones was
detected as a result of the â-hydride elimination from 3. After
144 h, CH2dC(COCH3)CH2C8F17 (4) and its reduced compound
4′ were produced with 2a.29 On the other hand, with 2e, a
mixture of CH3COCHdCHCH2C8F17 (5) and 4′ (5/4′ ) 82/18,
1
estimated by H NMR spectra) was given accompanied by a
trace amount of 4 in 14 days at room temperature. The total
yield of 5 and 4′ was 85% when the acetylpalladium
[CH3C(dO)Pd(NCMe)(2e)]+[BArF]- was treated with an equimo-
lar amount of 1a. Thus, it is further confirmed that the 1a
(27) For the platinum complex, the reaction from metal hydroxide to hydride
via CO insertion and â-hydrogen elimination was suggested. Torresan, I.;
Michelin, R. A.; Marsella, A.; Zanardo, A.; Pinna, F.; Strukul, G.
Organometallics 1991, 10, 623-631. For the palladium complex, an
insertion reaction of CO to hydroxide complex to form the corresponding
hydroxycarbonylpalladium complex by using a PCP pincer-type ligand was
reported. Campora, J.; Palma, P.; del Rio, D.; Alvarez, E. Organometallics
2004, 23, 1652-1655.
(28) Before consumption of the added 1equivalent of fluoroalkene 1a, the
acetylpalladium complex completely disappeared accompanied by a new
unidentified peak (δP 108.4)
(29) Disproportionation reaction of alkylpalladium complexes to form both
â-hydride eliminated product and reduced product was reported. Albeniz,
A. C.; Espinet, P.; Lopez-Fernandez, R. Organometallics 2003, 22, 4206-
4212.
9
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A R T I C L E S
Fujita et al.
Scheme 4. The Reactions of Acetylpalladium Complexes 2 with 1 equiv of CH2dCHCH2C8F17 (1a)a
a Counteranions (BArF) are omitted for clarity.
Scheme 5. Characteristic 1,2-Insertion of Styrene into Acetylpalladium Complex Bearing a BINAPHOS Ligand
insertion exclusively takes place via 2,1-insertion with 2a. In
sharp contrast, it is indicated that the 1a insertion proceeds via
both 1,2- and 2,1-fashion with 2e, the 1,2-insertion being the
major pathway. Using 2f as a ligand, a mixture of 5 and 4 was
given in a ratio of 85:15, suggesting the preferential 1,2-insertion
similarly to the results with 2e.
polymerization underwent from 6e(1,2) until finally the catalyst
ends up with 2,1-insertion.30 From the 2,1-adduct, the â-hydride
elimination eventually underwent to give the R,â-unsaturated
ketones. Here in the present study with fluoroalkene 1a, again
the 2,1-product such as 3a(2,1) seems to be the “dead end” that
is not involved in the further polymerization. Thus, the higher
yield of 1a/CO copolymerization with 2e than that with 2a
should be attributed to the selective formation of the 1,2-adduct
3e(1,2).
The Factors That Enabled the 1a/CO Copolymerization.
As mentioned above, the 1a/CO copolymerization proceeded
smoothly with 2e and the unique 1,2-insertion of 1a to
acylpalladium species was detected with 2e. Here, we will
discuss the results in relation to our previous studies. We
reported the selective 1,2-insertion of styrene to acyl complex
[CH3C(dO)Pd(NCMe)(2e)]+[BArF]- (Scheme 5).22 The pal-
ladium-catalyzed styrene/CO copolymerization usually requires
the use of bidentate sp2-nitrogen ligands, and ligand 2e is the
only exception of bidentate phosphorus ligands in terms of its
effectiveness for the styrene/CO co-oligomerization.22,30 We
proposed that the bulky ligand 2e preferred the 1,2-insertion to
the 2,1-, so that the steric repulsion between the ligand and the
phenyl group of styrene would be avoided. The unique styrene/
CO co-oligomerization with 2e was thus attributed to the facile
CO insertion in the 1,2-adduct 6e(1,2). In fact, the high-pressure
NMR studies under 2.0 MPa of CO revealed that, under the
polymerization process, the 6e(2,1) was visible but not 6e(1,2).
The result suggests that (1) no further polymerization took place
once the 2,1-insertion occurred to give 6e(2,1) while (2) further
The different reactivity between the 1,2-adduct and the 2,1-
adduct should come from either the step C to D (carbonyl
coordination) or the step D to A (carbonyl insertion) in Scheme
1. Alkylpalladium C bearing CH2-n-C8F17 on the R-carbon to
palladium ()2,1-adduct) is likely to form a stronger five-
membered chelation by lowering the electron density of the
palladium center.5 The CO-coordination CfD should become
less favorable with the stronger chelation. In addition, the
electron-deficient R-carbon in D should retard the subsequent
CO insertion to the metal-carbon bond (DfA) by lowering
the nucleophilicity of the migrating R-carbon atom.5,12 As is
shown in Scheme 6, such electronic disadvantage of the CH2-
n-C8F17 group is successfully avoided in the 1,2-adduct. That
means that the electron-withdrawing substituent is on the
â-position of the palladium and the R-carbon is less electron
deficient.
Thus, using 2e, the alternating copolymerization of 1a with
CO was managed to take place. However, the polymerization
was much slower than that of 1-hexene (Table 1, compare runs
(30) Iggo, J. A.; Kawashima, Y.; Liu, J.; Hiyama, T.; Nozaki, K. Organometallics
2003, 22, 5418-5422.
9
1972 J. AM. CHEM. SOC. VOL. 128, NO. 6, 2006

Alternating Copolymerization of Fluoroalkenes with CO
A R T I C L E S
Scheme 6. Proposed Catalytic Cycle Containing the Advantageous 1,2-Insertion of Fluoroalkene into the Acylpalladium Complex
ThermoPlus TG 8120 at a scanning rate of 10 °C min-1. â-Eliminated
olefinic products were separated by using a recycling preparative HPLC
7 and 14). This should be attributed to the disfavorable olefin
coordination A′fB′. Noteworthy is that the equilibrium between
C′ and D′ also affected the rate as was demonstrated in the
higher yield under the higher CO pressure (Table 1, runs 6-8).
Summarizing the above observations, it seems that there exist
three pre-equilibriums C′-D′, D′-A′, and A′-B′ before the
rate-determining step B′ to C′.
(LC-928, Japan Analytical Industries, 60 cm × 20φ Jaigel-1H and 2H,
CHCl3 eluent). Chemicals were purchased from Wako Pure Chemical
Industries Ltd., Strem Chemicals Inc., and were used without further
purification unless otherwise specified. Solvents were purified by
distillation under argon after drying over standard drying agents. Carbon
monoxide (99.9%) was obtained from Senda-gas Co. Na[B{3,5-
(CF3)2C6H3}4],31 Pd(Me)(Cl){(R,S)-BINAPHOS},32 and Pd(Me)(Cl)-
Conclusion
(dppp)‚0.5Εt2O33 were prepared according to the literature.
The palladium-catalyzed alternating copolymerization of
Synthesis of Fluorinated Olefin 1b. To a 200 mL three-necked
fluoroalkenes represented as CH2dCH-CH2-CnF2n+1 with CO
was successfully achieved using (R,S)-BINAPHOS (2e) as a
ligand. The copolymer obtained from CH2dCH-CH2-C8F17
(1a) existed as a mixture of polyspiroketal and polyketone, while
that from CH2dCH-CH2-C4F9 (1b) was a pure polyspiroketal.
Detailed NMR spectroscopic studies demonstrated that the
higher reactivity with (R,S)-BINAPHOS (2e) than that with the
conventional ligand DPPP (2a) can be attributed to the unique
1,2-insertion of the fluoroalkene to acylpalladium species with
2e. Taft’s σ* value of 0.90 for -CH2CF3 is the highest value
ever reported for the olefin substituents involved in the
copolymerization.
It is well-known that the chain-running of a late transition
metal, such as palladium or nickel, becomes a problematic issue
in the homopolymerization of olefins bearing functional groups.
That is, the metal often migrates on an alkyl complex to form
complexes that are either stabilized by coordination of the
functional group to the metal center7,9 or ready to get decom-
posed, for example, via â-heteroatom elimination.8 Thus, even
if the original olefinic bond is separated from the functional
group by methylene spacers, the isomerization takes place to
deactivate the metal center without waiting for the next
monomer to insert. In this viewpoint, it is of interest to note
that the alkyl complex is protected from the rapid chain-running
in the copolymerization with CO because of the stable five-
membered chelate C′ in Scheme 6. As a result, the CH2Rf group
in C′ was kept at the â-position without migrating to the
R-position of the metal center.
round-bottom flask filled with nonafluorobutyl iodide (30.0 mL, 174
mmol) and (PhCOO)2 (1.22 g, 5.00 mmol) was added allyl acetate (21.5
g, 0.200 mmol) dropwise at 70 °C. The resulting reaction mixture was
stirred several hours at 70 °C until nonafluorobutyl iodide was
consumed. The reaction mixture was added dropwise to refluxing
methanol suspended with zinc dust (15.3 g, 210 mmol), and the whole
mixture was stirred under reflux for an hour. After filtration through
Celite, the upper layer of the resulting filtrate was separated and washed
with water. The resulting liquid was kept under molecular sieves 13X,
and was distilled through a Vigreaux column over CaH2. A colorless
liquid (14 g, 54% yield) was obtained. The product was almost pure
but contains about 1% of impurity, which could not be separated; bp
82 °C. The spectroscopic data were in agreement with the reported
data.34
General Procedure for Copolymerization of Olefins 1 with CO.
To a 1 mL toluene solution of (cod)PdMeCl (5.3 mg, 0.020 mmol)
was added 1 mL of a toluene solution of ligand 2 (0.020 mmol), and
the mixture was stirred for several hours (1-20 h) at ambient
temperature. The solvent was removed in vacuo, and the residue was
dissolved in CH2Cl2. To this solution was added an acetonitrile solution
of Na{B[3,5-(CF3)2C6H3]4} (18.0 mg, 0.020 mmol), and the mixture
was stirred for an hour at room temperature. After removal of the
solvents, the residue was dissolved in CH2Cl2 (2.0 mL) and olefin 1
(5.2 mmol) was added. The solution was degassed by three freeze-
pump-thaw cycles and transferred into an autoclave. The autoclave
was pressurized with CO, and the solution was stirred with a stirring
bar at 60 °C. After CO gas was released, methanol was added to the
mixture. After evaporation of the volatiles, the mixture was dried under
vacuum, and then the resulting products were collected in runs 1-5
and 10-16. For the experiments in runs 6-9, addition of methanol to
the reaction mixture provided the polymeric product as solid precipi-
tates. The solid products were collected by filtration and dried under
vacuum. Product in run 2, IR (KBr) 1716 cm-1, mp 89-94 °C; run
11, IR (KBr) 1718 cm-1; run 12, mp 182-183 °C.
Experimental Section
General. All manipulations involving the air- and moisture-sensitive
compounds were carried out using standard Schlenk techniques or in
a glove box under argon. All NMR spectra except CP-MAS were
recorded using JEOL JNM-ECP500 spectrometer. CP/MAS NMR
spectra were recorded using JEOL JNM-ECA920 spectrometer. CHCl3
(1H) and H3PO4 (31P) were employed as internal and external standards,
respectively. Matrix-assisted laser desorption/ionization time-of-flight
mass spectrometry (MALDI-TOF-MS) was performed on an Applied
Biosystems BioSpectrometry Workstation model Voyager-DE STR
spectrometer using dithranol as a matrix. Melting points were measured
on a Yanagimoto micro melting point apparatus MP-500D and are
uncorrected. Thermal characterizations were conducted with a Mettler
DSC 30 system at a scanning rate of 10 °C min-1 and a Rigaku
Under the conditions of run 9, the use of 2.37 g of 1a resulted in
2.04 g (80.6%) of white solids. The thermal property of the product
was analyzed via DSC and TGA. The obtained DSC curve showed the
melting point was 182-183 °C, and the TGA curve showed that the
(31) Brookhart, M.; Grant, B.; Volpe, A. F. Organometallics 1992, 11, 3920-
3922.
(32) Nozaki, K.; Sato, N.; Tonomura, Y.; Yasutomi, M.; Takaya, H.; Hiyama,
T.; Matsubara, T.; Koga, N. J. Am. Chem. Soc. 1997, 119, 12779-12795.
(33) Dekker, G.; Elsevier, C. J.; Vrieze, K.; Vanleeuwen, P. Organometallics
1992, 11, 1598-1603.
(34) Hu, C. M.; Qing, F. L.; Huang, W. Y. J. Org. Chem. 1991, 56, 2801-
2804.
9
J. AM. CHEM. SOC. VOL. 128, NO. 6, 2006 1973

A R T I C L E S
Fujita et al.
product decomposed at the same or a little higher temperature than the
melting point. IR (KBr): 1718 cm-1, mp 182-183 °C. Under the
conditions of run 13, 200 mg of gray solid was obtained. The MALDI-
TOF-MS spectrum of the product was shown in Figure 1. IR (KBr):
to make an NMR sample. The 31P NMR spectrum of this sample
showed six pairs of doublets (six doublets for phosphine and six
doublets for phosphite); three pairs were detected as separated peaks,
and the other three pairs were overlapping each other. The ratio of the
six pairs was 54%, 11%, 8% for the separated three pairs and 27% for
the sum of the overlapped three pairs.26 Comparison of the obtained
31P NMR spectra with those of previously reported [Pd(CH2CH(CH3)-
COCH3)(2e)][B{3,5-(CF3)2C6H3}4]32 and [Pd(CH2CH(Ph)COCH3)(2e)]-
[B{3,5-(CF3)2C6H3}4]22 enabled us to assign the major isomer as
3e(1,2)OP-trans-CO, which resulted via the 1,2-insertion of 1a to the
acetylpalladium complex. Similarly, the second largest pair of peaks
was assigned as the isomeric 1,2-insertion complex (3e(1,2)OP-cis-
CO). Characterization of the other minor peaks was not completed,
but some of the peaks are possibly due to the 2,1-products judging
from the following results.
1718 cm-1
.
Insertion of 1a into [Pd(COMe)(CH3CN)(2a)]{B[3,5-(CF3)2C6H3]4}
To Afford Alkyl Complex 3a(2,1). A solution of Na[B{3,5-
(CF3)2C6H3}4] (93.0 mg, 0.105 mmol) in CH3CN (2.0 mL) was added
to a solution of Pd(Me)(Cl)(2a)‚0.5Εt2O (61.0 mg, 0.100 mmol) in
CH2Cl2 (2.0 mL). After the solution was stirred for an hour at ambient
temperature, solvent was removed in vacuo. Dichloromethane was
added and removed in vacuo three times to reduce the remaining MeCN.
The resulting solid was dissolved in CH2Cl2 (2 mL), and 1a (0.60 mL,
2.1 mmmol) was added to this solution. After the solution was bubbled
with CO, the mixture was stirred for 7 h at 0 °C. Solvents were removed
in vacuo, and the residue was washed with hexane (10 mL) twice at 0
°C, and then dissolved in CH2Cl2. The solids were removed by filtration
through a Celite pad at 0 °C, and the solvent was evaporated. The crude
product was washed with hexane (10 mL) twice and dried in vacuo at
0 °C. Formation of the 2,1-product 3a(2,1) as a single product was
judged by NMR spectroscopy: 31P NMR (CDCl3, 202 MHz, 0 °C) δ
26.8 (d, J ) 61 Hz), -4.9 (d, J ) 61 Hz); 1H NMR (CDCl3, 500 MHz,
0 °C) δ 7.75-7.28 (m, 32H, Ar), 3.30-3.14 (m, 2H), 2.61 (m, 3H),
2.33 (s, 3H), 2.26 (m, 2H), 1.83 (brs, 1H), 1.69 (m, 1H), 1.49 (m, 2H);
a part of 13C NMR (CDCl3, 125 MHz, 0 °C, Rf moiety could not be
characterized) δ 234.6 (d, J ) 10 Hz, COCH3), 161.6 (q, J ) 100 Hz,
ipso to B atom in -BAr4), 134.7-126 (m, Ar), 55.8 (s, CH2), 40.6 (dd,
J ) 93 Hz, 5 Hz, CH), 32.8 (t, J ) 21 Hz, CF2CH2), 28.6 (s, CH3CO),
27.4 (dd, J ) 35 Hz, 9 Hz, PCH2), 26.1 (d, J ) 24 Hz), 18.4 (s,
CH2CH2P); 19F NMR (CDCl3, 470 MHz, 0 °C) δ -62.2 (s, 24F,
ArCF3), -80.7 (s, 3F, CF3), -108.8(d, J ) 274 Hz, 1F, CH2CFF),
-115.3 (d, J ) 274 Hz, 1F, CH2CFF), -121.8 (s, 2F, CF2), -122 (s,
4F, CF2), -122.9(s, 2F, CF2), -123.3 (s, 2F, CF2), -126.2(s, 2F, CF2).
After the solution was kept for 144 h at room temperature, â-hydride
elimination from 3a(2,1) afforded R,â-unsaturated ketone 4 and
saturated ketone 4′. Because 4 could not be isolated, 4 was partly
3e(1,2)OP-trans-CO. 31P NMR (CDCl3, 202 MHz) δ 139.2 (d, J )
65 Hz), 14.1 (d, J ) 65 Hz); 1H NMR (CDCl3, 500 MHz) δ 3.40 (br,
1H, Hc), 2.98 (br, 1H, Hb), 2.72 (br, 2H, Hd and He), 2.52 (br, 1H, Ha),
2.19 (s, 3H, CH3), H-H COSY experiment revealed the spin-spin
coupling between Ha,Hb and Hc, and Hc and Hd,He (spectra are in the
Supporting Information); 13C NMR (CDCl3, 125 MHz, Rf and
BINAPHOS moiety could not be characterized) δ 237.8 (d, J ) 9.2
Hz, COCH3), 53.3 (CH), 35 (br, CF2CH2, PdCH2), 28.1 (CH3). 3e-
(1,2)OP-cis-CO. 31P NMR (CDCl3, 202 MHz) δ 148.9 (d, J ) 61 Hz),
29.7 (d, J ) 61 Hz). The other four small pairs of doublets could not
be completely assigned. 31P NMR (CDCl3, 202 MHz) δ 137.98 (d, J
) 61.0 Hz), 137.87 (d, J ) 61.0 Hz), 137.80 (d, J ) 65.4 Hz), 136.18
(d, J ) 65.4 Hz), 16.85 (d, J ) 65.4 Hz), 15.18 (d, J ) 61.0 Hz),
14.65 (d, J ) 65.4 Hz), 14.01 (d, J ) 65.4 Hz).
1
assigned by the H NMR spectrum of the mixture of 4 and 4′. 4′ was
completely characterized by isolation from the following experiment
with 3e. 4: 1H NMR (CDCl3, 500 MHz) δ 6.69 (dt, J ) 16, 7 Hz, 1H,
CHdCHCO), 6.29 (d, J ) 16 Hz, 1H, CHdCHCO), 3.03 (td, J ) 18,
7 Hz, 2H, CF2CH2), 2.30 (s, 3H, COCH3).
Leaving the NMR samples for 14 days at ambient temperature
resulted in the decomposition of the complex and formation of â-hydride
eliminated product (5 and a trace amount of 4) and protonated product
1
Insertion of 1a into [Pd(COMe)(CH3CN)(2e)]{B[3,5-(CF3)2C6H3]4}
To Afford Alkyl Complexes 3e. Cationic methylpalladium species was
prepared from Pd(Me)(Cl)(2e) (92.6 mg, 0.10 mmol) in the same
procedure as that from Pd(Me)(Cl)(2a). To its CH2Cl2 (2 mL) solution,
1a (1.5 mL, 5.1 mmmol) was added and CO was bubbled through the
solution. After the solution was stirred for 8 h at ambient temperature,
the volatiles were removed in vacuo. The crude product was dissolved
in CH2Cl2, and the solid materials were removed by filtration through
a Celite pad. The filtrate was dried in vacuo, and the residue was washed
with hexane (10 mL) five times. The residue was dissolved in CDCl3
(4′) as was observed by H NMR spectroscopy (5/4′ ) 82/18). The
major olefinic product 5 was purified by silica gel column chroma-
tography (Et2O/hexane ) 1/1, Rf ) 0.6) and recycling preparative
HPLC and characterized by NMR and IR spectroscopies and mass
spectrometry, although a trial for the isolation of pure 5 was not
successful due to its high volatility. 5: 1H NMR (CDCl3, 500 MHz) δ
6.39 (s, 1H, CdCHH), 6.17 (s, 1H, CdCHH), 3.17 (t, J ) 19 Hz, 2H,
CF2CH2), 2.41 (s, 3H, COCH3); 13C NMR (CDCl3, 125 MHz, italicized
peaks of Rf moiety were assigned by independently measured 13C-
{19F} NMR spectrum) δ 197.3 (CO), 138.0 (CdCH2), 131.4 (CdCH2),
9
1974 J. AM. CHEM. SOC. VOL. 128, NO. 6, 2006

Alternating Copolymerization of Fluoroalkenes with CO
A R T I C L E S
117.1, 117.0, 111.1, 111.0, 110.8, 110.7, 110.2, 108.4, 30.3 (t, J ) 22
Hz, CF2CH2), 25.2 (COCH3); 19F NMR (CDCl3, 470 MHz) δ -80.6
(s, 3F, CF3CF2), -113.1 (s, 2F, CF2), -121.5 (s, 2F, CF2), -121.8 (s,
4F, CF2), -122.6 (s, 2F, CF2), -123.0 (s, 2F, CF2), -126.0 (s, 2F,
CF2); GC-MS m/z 501.3 (M), 486.1 (M - Me), 482.3 (M - F). 4′:
1H NMR (CDCl3, 500 MHz) δ 2.57 (t, J ) 7 Hz, 2H, COCH2), 2.17
(s, 3H, COCH3), 2.09 (m, 2H, CF2CH2), 1.90 (m, 2H, CH2CH2CH2);
13C{1H} NMR (CDCl3, 125 MHz, italicized peaks of Rf moiety were
assigned by independently measured 13C{19F} NMR spectrum) δ 207.1
(CO), 118.4, 117.1, 111.1, 111.0, 110.8, 110.7, 110.2, 108.4, 42.1, 29.9,
29.9 (t, J ) 21 Hz, CF2CH2), 14.5; 19F NMR (CDCl3, 470 MHz) δ
-80.6 (s, 3F, CF3CF2), -114.3 (s, 2F, CF2), -121.6 (s, 2F, CF2),
-121.8 (s, 4F, CF2), -122.6 (s, 2F, CF2), -123.4 (s, 2F, CF2), -126.0
(s, 2F, CF2); GC-MS m/z 503.3 (M), 488.3 (M - Me), 484.3 (M -
F).
corresponded to more than 85% of the initial acetylpalladium complex,
as was determined by using CH2Cl2 as an internal standard.
Acknowledgment. We thank the Asahi Glass Co. Research
Collaboration Project and Grant-in-Aid for Scientific Research
on Priority Areas “Advanced Molecular Transformations of
Carbon Resources” from MEXT, Japan for financial support.
The authors are grateful to Prof. Y. Uozumi and Ms. M. Nakano
for their help in measuring the solid-state 13C NMR spectra
recorded on a JEOL JNM-ECA920 at Institute for Molecular
Science sponsored by Nanotechnology Support Project of the
MEXT. The authors also thank Prof. T. Kato and Dr. M. Yoshio
(The University of Tokyo) for DSC measurement.
Supporting Information Available: DSC and TGA charts of
Estimation of the Yield of 5 and 4′ from [Pd(COMe)(CH3CN)-
(2e)][B{3,5-(CF3)2C6H3}4] and 1a. A CH2Cl2 (2 mL) solution of [Pd-
(COMe)(CH3CN)(2e)][B{3,5-(CF3)2C6H3}4] (0.020 mmol) was prepared
according to the procedure described above. To this was added 1a
(0.029 mL, 0.020 mmol), and the mixture was warmed to 50 °C. After
22 h, the existence of 5 and 4′ with a ratio of 82:18 was detected via
the 1H NMR spectrum. The sum of these two olefinic products
poly(1a-alt-CO), 31P and 13C NMR spectra of 3a(2,1), and 31
P
NMR and H-H COSY spectra of the isomeric mixture of 3e.
This material is available free of charge via the Internet at
http://pubs.acs.org.
JA055862K
9
J. AM. CHEM. SOC. VOL. 128, NO. 6, 2006 1975