Palladium(II)-catalyzed alternating copolymerization of allene with carbon monoxide and the synthesis of terpolymer with alt-allene-carbon monoxide and alt-ethene-carbon monoxide blocks. Synthetic and mechanistic aspects

Article abstract of DOI:10.1021/ja9716620

The alternating copolymerization of 3,3-dimethylallene with carbon monoxide was achieved using [Pd(PPh₃)₂(MeCN)₂](BF₄)₂ as the catalyst. The use of bidentate phosphines resulted in drastically reduced yields. In order to gain insight into the copolymerization mechanism, the stepwise successive insertions of 3,3-dimethylallene and carbon monoxide into palladium-carbon bonds in the complexes, Pd(PPh₃)₂(Me)(Cl), [Pd(PPh₃)₂(C(O)-C₆H₄-Me-p)(MeCN)](BF₄), and [Pd[(Dppp)(Me)(MeCN)](BF₄) (Dppp: 1,3-bis(diphenylphosphino)propane), were studied. These studies, in turn, led to a novel living catalytic system which was used to synthesize a terpolymer with alt-allene-carbon monoxide and alt-ethene-carbon monoxide blocks.

Full text of DOI:10.1021/ja9716620

10028
J. Am. Chem. Soc. 1997, 119, 10028-10033
Palladium(II)-Catalyzed Alternating Copolymerization of Allene
with Carbon Monoxide and the Synthesis of Terpolymer with
Alt-Allene-Carbon Monoxide and Alt-Ethene-Carbon Monoxide
Blocks. Synthetic and Mechanistic Aspects
Smita Kacker and Ayusman Sen*
Contribution from the Department of Chemistry, The PennsylVania State UniVersity,
UniVersity Park, PennsylVania 16802
ReceiVed May 21, 1997X
Abstract: The alternating copolymerization of 3,3-dimethylallene with carbon monoxide was achieved using
[Pd(PPh3)2(MeCN)2](BF4)2 as the catalyst. The use of bidentate phosphines resulted in drastically reduced yields.
In order to gain insight into the copolymerization mechanism, the stepwise successive insertions of 3,3-dimethylallene
and carbon monoxide into palladium-carbon bonds in the complexes, Pd(PPh3)2(Me)(Cl), [Pd(PPh3)2(C(O)-
C6H4-Me-p)(MeCN)](BF4), and [Pd[(Dppp)(Me)(MeCN)](BF4) (Dppp: 1,3-bis(diphenylphosphino)propane), were
studied. These studies, in turn, led to a novel living catalytic system which was used to synthesize a terpolymer
with alt-allene-carbon monoxide and alt-ethene-carbon monoxide blocks.
The alternating copolymers of alkenes with carbon monoxide
porating three different classes of monomers (alkene, allene,
and carbon monoxide).
are of great current interest from scientific as well as techno-
logical standpoints.1 In contrast, the copolymerization of other
unsaturated substrates with carbon monoxide has received far
less attention. The alternating allene-carbon monoxide copoly-
mers would be of particular interest due to the expected high
degree of unsaturation in the backbone which would make the
polymers amenable to further functionalizations. Even simple
hydrogenation would lead to polymers that are otherwise
inaccessible from alkenes and carbon monoxide due to the steric
bulk of the alkene (see below for a specific example). To our
knowledge, the only report of the alternating copolymerization
of an allene with carbon monoxide resides in a patent; however,
the structure of the resultant polymer has not been described.2
Recently, Vrieze and co-workers have published elegant studies
on the stepwise insertions of allene and carbon monoxide into
the palladium-carbon bonds of complexes with a rigid bidentate
nitrogen ligand.3 Not reported, however, was the ability of these
complexes to catalyze the alternating allene-carbon monoxide
copolymerization. Herein, we report the palladium(II)-catalyzed
syntheses of alternating copolymer of allene and carbon
monoxide. In order to gain insight into the copolymerization
mechanism, the stepwise successive insertions of 3,3-dimeth-
ylallene and carbon monoxide into palladium-carbon bonds
in neutral and cationic palladium(II) complexes with mono- and
bidentate phosphines were studied. These studies, in turn, led
to a novel living catalytic system which was used to synthesize
a terpolymer with alt-allene-carbon monoxide and alt-ethene-
carbon monoxide blocks. This is the first synthesis of a
terpolymer consisting of alternating copolymer blocks incor-
Results and Discussion
The Alternating Copolymerization of 3,3-Dimethylallene
with Carbon Monoxide. The catalyst used for the alternating
copolymerization of 3,3-dimethylallene (DMA) with carbon
monoxide was [Pd(PPh3)2(MeCN)2](BF4)2. It was prepared in
situ by dissolving [Pd(MeCN)4](BF4)24 and triphenylphosphine
in a 1:2 molar ratio in a 2:1 (v/v) solvent mixture of ni-
tromethane and methanol. As in previous work on analogous
alkene-carbon monoxide copolymerizations, nitromethane was
needed to dissolve the catalyst precursor while the function of
the methanol was to generate the initial metal hydride.1 The
polymer synthesized was found to have a high degree of
unsaturation with pendant vinylic functionalities present in
conjugation with backbone keto groups. It was characterized
1
by H- and 13C-NMR and IR spectroscopy.
The alternating 3,3-dimethylallene-carbon monoxide (DMA-
CO) copolymer comprised mainly of the repeating units
represented by structure I in Figure 1. The 1H-NMR spectrum
in CDCl3 showed resonances from 1.12 to 1.94 ppm due to the
methyl protons. The CH2 units in the backbone appeared as
multiple peaks from 3.03 to 3.77 ppm. The 13C-NMR spectrum
in CDCl3 showed multiple resonances from 20.0 to 31.1 ppm
due to the methyl carbons. The CH2 carbons in the backbone
appeared from 42.8 to 44.8 ppm as broad peaks. The vinyl
carbons showed resonances from 109.3 to 152.3 ppm, and the
carbonyl group appeared at 203.0 ppm. The IR (CDCl3)
spectrum showed an absorption at 1686 cm-1, characteristic of
conjugated ketones.
Structure I is expected to result from the 1,2-insertions of
DMA into palladium-acyl bonds. However, the presence of
repeat units with structure II (Figure 1) resulting from the 3,2-
insertions of DMA cannot be ruled out. This is mainly because
of the fact that the methyl protons in structure I are allylic and
would not be expected as low as 1.12 ppm in 1H-NMR
spectrum. In order to obtain a copolymer comprising only of
X Abstract published in AdVance ACS Abstracts, October 1, 1997.
(1) (a) Sen, A. Acc. Chem. Res. 1993, 26, 303. (b) Drent, E.; Budzelaar,
P. H. M. Chem. ReV. 1996, 96, 663.
(2) Drent, E. Neth. Appl. 88/1168 (1988); Chem. Abstr. 1990, 113,
24686f.
(3) (a) Delis, J. G. P.; Groen, J. H.; Vrieze, K.; van Leeuwen, P. W. N.
M.; Veldman, N.; Spek, A. L. Organometallics 1997, 16, 551. (b) Groen,
J. H.; Elsevier, C. J.; Vrieze, K.; Smeets, W. J. J.; Spek, A. L.
Organometallics 1996, 15, 3445. (c) Rulke, R. E.; Kliphuis, D.; Elsevier,
C. J.; Fraanje, J.; Goubitz, K.; van Leeuwen, P. W. N. M.; Vrieze, K. J.
Chem. Soc., Chem. Commun. 1994, 1817.
(4) Thomas, R.; Sen, A. Inorg. Synth. 1989, 26, 128; 1990, 28, 63.
S0002-7863(97)01662-4 CCC: $14.00 © 1997 American Chemical Society

Palladium(II)-Catalyzed Copolymerization of Allene
J. Am. Chem. Soc., Vol. 119, No. 42, 1997 10029
Table 1. Yields of the Alternating Copolymer of
3,3-Dimethylallene and Carbon Monoxide as a Function of the
a
Phosphine Added to [Pd(MeCN)4](BF4)2
ligand
yield (g)
PPh3 (2 equiv)
PPh3 (3 equiv)
Dppp
1.00
1.09
0.10
0.15
(R,R)-Me-Duphos
a Reaction conditions: 3.8 × 10-2 mmol of [Pd(MeCN)4](BF4)2 +
ligand in 3 mL of a 2:1 (v/v) mixture of CH3NO2 and CH3OH, 1 g of
3,3-dimethylallene + 500 psi of CO, 2 days at 40 °C.
Figure 1. Possible structures for the alternating copolymer of 3,3-
dimethylallene with carbon monoxide and the corresponding hydro-
genated derivative.
to the keto groups, indicating the loss of conjugation with double
bonds. However, resonances due to unsaturation present in
original DMA-CO copolymer still remained to a small extent.
Further hydrogenation using the same catalysts did not show
any change in the NMR spectra of the copolymer.
The structure of the hydrogenated copolymers (III and IV)
may be alternatively obtained by the copolymerization of
3-methyl-1-butene and 2-methyl-2-butene with carbon monox-
ide. However, attempts to copolymerize these monomers with
carbon monoxide using [Pd(PPh3)2(MeCN)2](BF4)2 or [Pd-
(Dppp)(MeCN)2](BF4)2 (Dppp: 1,3-bis(diphenylphosphino)-
propane) as the catalyst did not yield appreciable amounts of
copolymers. It is clear that the copolymers of allenes and carbon
monoxide can be useful precursors to polymers that are
otherwise inaccessible from alkenes and carbon monoxide due
to the steric bulk of the alkene.
The effect of a chelating ligand on the palladium(II)-catalyzed
copolymerization of DMA with carbon monoxide was studied
using Dppp and (R,R)-Me-Duphos () 1,2-bis(2,5-dimethylphos-
pholano)benzene). It was previously observed that chelating
bidentate phosphines were far superior to monodentate phos-
phines in the copolymerization of alkenes with carbon monox-
ide.1 The results summarized in Table 1, however, show an
opposite trend for the copolymerization of DMA with carbon
monoxide. Triphenylphosphine was found to be significantly
better than either of the bidentate ligands, and, interestingly,
increasing the amount of triphenylphosphine in the reaction
mixture did not affect the yield. The structure of the copolymer
obtained in all cases was the same. The mechanistic origin of
the difference between the reactivities of complexes with
monodentate and bidentate phosphines became apparent during
the study of the successive insertions of DMA and carbon
monoxide into palladium-carbon bonds in the corresponding
neutral and cationic palladium(II) complexes.
Mechanistic Aspects of the Copolymerization of 3,3-
Dimethylallene with Carbon Monoxide. Analogous to the
chain growth mechanism established for the copolymerization
of alkenes with carbon monoxide,1 the copolymerization of
allenes with carbon monoxide would be expected to proceed
by the alternate insertions of allene and carbon monoxide into
a palladium-carbon bond (Scheme 1). However, the insertion
of an allene into a palladium-acyl bond would result in the
formation of a η3-allyl complex, as opposed to a σ-alkyl complex
in the case of the insertion of an alkene into a palladium-acyl
bond: it has been established that the insertion of allene in a
Pd-R complex takes place via migration of the R group to the
central electrophilic carbon atom of the allene.3 In order to
gain further insight into the individual steps in the polymer
chain-growth sequence, the insertions of allene and carbon
monoxide into palladium-carbon bonds in three different kinds
of palladium(II) complexes were studied.
Figure 2. 1H-NMR (CDCl3) spectra of (a) [Pd(PPh3)2(η3-C5H8-C(O)-
C6H4-Me-p)](BF4), 4, and (b) Pd(PPh3)2(η3-C5H8-Me)(Cl), 7.
repeat units represented by structure II, copolymerization of
1,1,3,3-tetramethyl allene (TMA) with carbon monoxide was
attempted using the same catalytic system. The yield of the
TMA-CO copolymer obtained was very low, thereby implying
that the insertion of the substituted end of the allene is not as
1
facile. The H-NMR spectrum of the TMA-CO copolymer in
CDCl3 showed the resonances due to the allylic methyls as broad
peaks centered at 1.81 and 1.62 ppm. The other two methyls
in the backbone appeared as multiple peaks from 0.94 to 1.03
ppm. It can thus be concluded that trace amounts of structure
II are present in the DMA-CO copolymer. The predominant
structure, however, is that represented by I.
The hydrogenation of the highly unsaturated DMA-CO
copolymer was attempted using palladium on carbon and
platinum catalysts. The polymer was dissolved in chloroform
and was exposed to dihydrogen in the presence of the catalyst
for 2 days. The structure of the hydrogenated copolymer would
be expected to be mainly III with trace amounts of IV (Figure
1
1). The H-NMR spectrum of the hydrogenated copolymers
showed new broad resonances around 1.95 and 2.58 ppm due
to the CH units formed. The resonances due to the methyl peaks
shifted upfield from 1.12-1.94 to 0.83-1.76 ppm. The IR
(CDCl3) spectrum now showed an absorption at 1708 cm-1 due
trans-[Pd(PPh3)2(C(O)C6H4-Me-p)(MeCN)](BF4), 1, reacted
with DMA in CDCl3 in 6 h at ambient temperature to form the
η3-allyl complex, 4 (Scheme 2). The 31P-NMR spectrum of 4

10030 J. Am. Chem. Soc., Vol. 119, No. 42, 1997
Kacker and Sen
Scheme 1
8.7 Hz) ppm. The methyl on the central carbon of the allyl
ligand appeared as a singlet at 1.91 ppm. It is clear that the
difference in the reactivities of complexes 1 and 2 arose mainly
due to the anion: complex 1 with a noncoordinating anion was
significantly more reactive than 2.
Complex 2 when heated with a few equivalents of DMA and
200 psi of carbon monoxide for 2 days at 40 °C showed multiple
successive insertions of DMA and carbon monoxide giving a
mixture of two kinds of species, 8 and 9 (Scheme 3).
Complexes 8 and 9 were similar to complexes 5 and 6 obtained
from 1, except the anion was chloride. The 31P-NMR spectrum
in CDCl3 showed a broad resonance at 27.50 ppm for 9
indicative of a cis-η3-allyl complex (cf., compound 7) and a
sharp singlet at 19.27 ppm for 8 ascribable to a trans-Pd-acyl
complex. When 13CO was employed, a singlet at 236.8 ppm
was observed in the 13C-NMR spectrum (CDCl3) due to the
carbonyl group next to the metal in compound 8. The absence
of any 31P-coupling was consistent with a trans structure with
the phosphines cis to the metal-bound organic fragment. The
carbonyl groups in the backbone of compounds 8 and 9 that
are adjacent to the DMA units appeared as multiple resonances
from 201.4 to 206.0 ppm. The η3-allyl ligand of complex 9
in CDCl3 showed two doublets at 24.0 ppm (J ) 43 Hz) and
26.5 ppm (J ) 43 Hz) indicating that the two phosphine ligands
1
are now inequivalent and therefore cis to each other. The H-
NMR spectrum in CDCl3 (Figure 2) showed the two methyl
groups of the allene at 0.78 ppm (dd, J ) 6.3, 9.9 Hz) and 1.53
ppm (t, J ) 5.6 Hz), while the CH2 appeared as a doublet at
3.48 ppm (J ) 8.0 Hz). The methyl of the p-tolyl group
appeared at 2.41 ppm as a singlet. Complex 4, when exposed
to carbon monoxide (50 psi) for 18 h at ambient temperature in
the presence of a few equivalents of DMA, underwent multiple
successive insertions of DMA and carbon monoxide to yield
oligomers of DMA and carbon monoxide still bonded to the
metal. Two different kinds of species, 5 and 6 (Scheme 2),
were present as determined by 31P- and 1H-NMR spectroscopy.
The 31P-NMR spectrum in CDCl3 showed a singlet at 19.36
ppm due to the trans-Pd-acyl species, 5,6 and a pair of doublets
at 23.93 and 26.85 ppm (J ) 41 Hz) due to the cis-η3-allyl
species, 6. The absence of any vinylic protons in the 1H-NMR
spectrum supports a 1,2-insertion of DMA resulting in meth-
ylene units next to carbonyl groups with pendant dC(CH3)2
groups. The CH2 units appeared as multiple singlets between
3.60 and 3.73 ppm. The CH2 unit of the η3-allyl fragment of
6 appeared as a doublet at 3.28 ppm (J ) 8.0 Hz) (similar to
cis-η3-allyl complex 4). The methyl protons derived from DMA
in both species appeared as multiple resonances from 0.72 to
1.98 ppm; the methyl of the p-tolyl fragements appeared as
singlets from 2.36 to 2.41 ppm. This made it difficult to
determine the exact number of DMA molecules (x and y for 5
and 6, respectively) that have inserted; however, integration of
the resonances at 3.60-3.73 versus those at 2.36-2.41 ppm
indicated an average of two DMA units per tolyl group present.
In contrast to complex 1, trans-Pd(PPh3)2(Me)(Cl), 2, reacted
with DMA in CDCl3 only on being heated to 45 °C for 1 day.
The product, 7 (Scheme 3), showed a broad singlet at 27.48
ppm in the 31P-NMR spectrum in CDCl3 at ambient temperature.
However, on lowering the temperature to 233 K, the spectrum
consisted of a pair of doublets at 25.84 and 26.96 (J ) 41 Hz)
ppm. The 31P-NMR parameters are very close to those of
complex 4, thereby indicating that a cationic cis-η3-allyl complex
7 was being formed by displacement of the chloride ion. The
1H-NMR spectrum in CDCl3 (Figure 2) showed a pair of
doublets for the two protons of the methylene unit at 2.76 and
2.92 ppm (J ) 2.1 Hz) and a pair of doublets for the two methyl
groups derived from DMA at 1.51 (J ) 5.9 Hz) and 1.86 (J )
1
showed broad peaks at 2.68 and 2.89 ppm in the H NMR
spectrum in CDCl3 (cf., compound 7). The CH2 units derived
from DMA that were adjacent to carbonyl groups appeared as
multiple singlets from 3.60 to 3.78 ppm. The methyl protons
derived from DMA appeared from 1.73 to 1.97 ppm. Finally,
a broad singlet at 2.24 ppm indicated the presence of a terminal
acetyl group formed by the initial insertion of carbon monoxide
into the starting Pd-methyl bond. Integration of the resonances
at 3.60-3.78 ppm versus that for the terminal acetyl group
indicated an average of five DMA units per acetyl group present.
The effect of a chelating phosphine was examined using
complex 3, [Pd(Dppp)(Me)(MeCN)](BF4). Complex 3 reacted
with DMA in 6 h at ambient temperature to give a η3-allyl
complex, 10a (Scheme 4). The 31P-NMR spectrum in CDCl3
showed a pair of doublets at 8.29 and 10.59 ppm (J ) 63 Hz)
for the two inequivalent cis phosphorus atoms. The resonances
for the two inequivalent protons of the methylene units appeared
at 3.07 (d, J ) 10.0 Hz) and 3.57 (dd, J ) 2.2, 6.0 Hz) ppm in
1
the H-NMR spectrum. The two methyls showed resonances
at 1.12 (dd, J ) 8.0, 10.0 Hz) and 1.22 (t, J ) 6.2 Hz) ppm,
while the methyl on the central carbon of the allyl appeared at
2.01 ppm as a singlet. Complex 10a did not undergo insertion
of a carbon monoxide molecule even on exposure to 200 psi of
carbon monoxide for 1 day. The difficulty associated with the
insertion of carbon monoxide into the palladium-carbon bond
of complex 10a was consistent with poor catalytic activity
exhibited by complexes with bidentate ligands in the alternating
copolymerization of DMA with carbon monoxide.
Analogous insertion reactions carried out with 1,1,3,3-
tetramethylallene (TMA) instead of DMA did not give well-
defined products in good yield with complexes 1 and 2.
Complex 3, however, reacted with TMA at ambient temperature
in 1 day to give a symmetrical η3-allyl complex, 10b (Scheme
4). The 31P-NMR spectrum in CDCl3 showed a singlet at 9.10
ppm for the two equivalent phosphorus atoms. The four methyls
showed resonances as multiplets from 1.24 to 1.35 ppm, while
the methyl on the central carbon of the allyl group appeared at
2.16 ppm as a singlet. The general reluctance of TMA to
undergo insertion into palladium-carbon bonds was consistent
with our inability to form the alternating TMA-carbon monoxide
copolymer in good yields.
(5) Rulke, R. E.; Ernsting, J. M.; Spek, A. L.; Elsevier, C. J.; van
Leeuwen, P. W. N. M.; Vrieze, K. Inorg. Chem. 1993, 32, 5769.
(6) Brumbaugh, J. S.; Whittle, R. R.; Parvez, M. A.; Sen. A. Organo-
metallics 1990, 9, 1735.
Formation of Terpolymer with Alt-Ethene-Carbon Mon-
oxide and Alt-Allene-Carbon Monoxide Blocks. We had

Palladium(II)-Catalyzed Copolymerization of Allene
J. Am. Chem. Soc., Vol. 119, No. 42, 1997 10031
Scheme 2
Scheme 3
Scheme 4
Scheme 5
earlier demonstrated that neutral palladium(II)-acyl complexes
can be used as initiators for the copolymerization of ethene and
carbon monoxide and that the resultant copolymer chain
remains bonded to the metal.7 Also, as described in the
preceding section, neutral palladium(II) complexes undergo
successive insertions of allene and carbon monoxide and the
resultant copolymer chain also remains attached to the metal.
The similarity between the two catalyst systems gave rise to
the possibility of combining these two copolymerizations.
Hence, starting with a neutral palladium complex, an oligomeric
alternating ethene-carbon monoxide (E-CO) block was first
synthesized. The resulting palladium-acyl complex was then
reacted with DMA and carbon monoxide to yield an oligomeric
block of DMA-CO (Scheme 5). The formation of the two
blocks were restricted to oligomeric lengths in order to follow
Complex 2, Pd(PPh3)2(Me)(Cl), when exposed to 100 psi each
of ethene and carbon monoxide at ambient temperature for 2
days gave rise to 11, (PPh3)2Pd[C(O){CH2CH2C(O)}xMe](Cl)
(x ≈ 6). The 31P-NMR spectrum in CDCl3 showed a single
peak at 19.55 ppm indicating the presence of only one kind of
palladium-acyl species and the complete conversion of the
starting complex. When 13CO was employed, the carbonyl
group next to the metal appered at 235.8 ppm, while the rest of
the carbonyl groups in the metal-bound oligomeric chain
exhibited resonances between 206.9 and 208.0 ppm in the 13C-
1
the reactions by 31P-NMR and H-NMR spectroscopy.
(7) Kacker, S.; Sen, A. J. Am. Chem. Soc. 1995, 117, 10591.

10032 J. Am. Chem. Soc., Vol. 119, No. 42, 1997
Kacker and Sen
indicated that cationic palladium(II) complexes with monoden-
tate phosphines show fast successive insertions of allene and
carbon monoxide into an initial palladium-carbon bond. The
poor catalytic activity for the allene-carbon monoxide copo-
lymerization exhibited by palladium(II) complexes with biden-
tate phosphines appears to be due to the difficulty associated
with the insertion of carbon monoxide into the palladium-
carbon bond of the corresponding η3-allyl complexes. Since
the η3-allyl ligand occupies two coordination positions on the
metal, the coordination of carbon monoxide prior to its insertion
(assuming that insertion occurs from a four-coordinate inter-
mediate8) would require either an η3 to η1 isomerization of the
allyl ligand or the dissociation of one of the coordinated
phosphorus atoms. Because of the “chelate effect”, the latter
would be significantly more difficult in the case of the bidentate
phosphines. On the other hand, because Pd-N bonds tend to
be weaker than Pd-P bonds, the corresponding insertion should
proceed more readily in complexes with bidentate nitrogen
ligands as has been reported.3b
Finally, it was possible to design a system that allowed
simultaneously the living alternating copolymerizations of
ethene and carbon monoxide as well as allene and carbon
monoxide. The use of this system led to the synthesis of a
terpolymer with alt-ethene-carbon monoxide and alt-allene-
carbon monoxide blocks. This is the first synthesis of a
terpolymer consisting of alternating copolymer blocks incor-
porating three different classes of monomers (alkene, allene,
and carbon monoxide).
Experimental Section
Materials. C.P. grade chemicals were used as received unless
otherwise stated. Triphenylphosphine, 1,3-bis(diphenylphosphino)-
propane (Dppp), and (-)-1,2-bis((2R,5R)-2,5-dimethylphosphalano)-
benzene ((R,R)-Me-DUPHOS), were purchased from Strem Chemicals.
Pd[(MeCN)4](BF4)2,4 trans-[Pd(PPh3)2(COC6H4-Me-p)(MeCN)](BF4),6
[Pd(Dppp)(Me)(MeCN)](BF4),5 and Pd(PPh3)2(Me)(Cl)5 were prepared
according to the literature methods. Nitromethane and chloroform were
dried over CaH2 and vacuum-transferred. Methanol was dried over
sodium methoxide and vacuum-transferred. 3,3-Dimethylallene (DMA)
and 1,1,3,3-tetramethylallene (TMA) were obtained from Aldrich.
General Methods. All catalyst solutions were prepared in a dry
nitrogen-filled glovebox. The copolymerization of allene and alkene
with carbon monoxide was performed under nitrogen atmosphere. 1H-
and 13C-NMR spectra were recorded on a Bruker AM300 FT-NMR
spectrometer. The chemical shifts of 1H- and 13C-NMR were referenced
to internal tetramethylsilane (TMS) or to the solvent resonance at the
appropriate frequency. IR spectra (CDCl3) were recorded on a Perkin-
Elmer 1600 FT-IR spectrophotometer. Molecular weights of polymers
were measured on a Water Associates liquid/gel permeation chromato-
graph using Microstyragel columns and a differential refractometer.
Polystyrene standards were used to calibrate the instrument.
Copolymerization of 3,3-Dimethylallene with Carbon Monoxide.
To a solution containing 3.8 × 10-2 mmol (17 mg) of [Pd(MeCN)4]-
(BF4)2 and 7.6 × 10-2 mmol (20 mg) of triphenylphoshine in 3 mL of
a 2:1 (v/v) mixture of CH3NO2 and CH3OH was added 1 g of 3,3-
dimethylallene (DMA). The resultant solution was placed in a 125
mL Parr bomb under nitrogen and charged with 500 psi of CO. After
stirring for 2 days at 40 °C, the excess carbon monoxide was released,
and the solution was filtered. The remaining monomer and solvents
were removed under vacuum to obtain 1.0 g of polymer. The polymer
was dissolved in chloroform and run through a short-stem silica gel
column for further purification. It was then dried under vacuum for 1
day.
Figure 3. 1H-NMR (CDCl3) spectra of (a) Pd(PPh3)2[η3-C5H8-
(C(O)CH2CMe2)8(C(O)CH2CH2)6C(O)Me]Cl, 12.
1
NMR spectrum (CDCl3). The H-NMR spectrum in CDCl3
showed the ethene unit nearest to palladium as a set of two
multiplets at 2.33 and 1.27 ppm. The next ethene unit appeared
as multiplets at 2.14 and 2.46 ppm. The rest of the ethene
protons gave a single peak at 2.69 ppm. Additional evidence
that the ethene-CO copolymer chain remains bonded to the metal
in similar complexes are given in a previous publication.7
Complex 11 when placed in the presence of a few equivalents
of DMA and 200 psi of carbon monoxide at 40 °C for 1 day
gave 12, which showed a broad peak at 27.52 ppm in the 31P-
NMR spectrum indicating that it was a cis-η3-allyl complex.
When complex 11, generated using 13CO was used, the 13C-
NMR spectrum (CDCl3) of 12 generated therefrom revealed that
the signal due to the carbonyl group next to the metal had
disappered and was replaced by resonances at 202.5-208.3
ascribable to the presence of a DMA-CO block (cf. compounds
8 and 9). Clearly, the formation of the DMA-CO block was
initiated by the insertion of DMA into the Pd-acyl bond in
compound 11. The 1H-NMR spectrum of 12 in CDCl3 showed
the E-CO block as a broad singlet at 2.69 ppm and the CH2
units in the DMA-CO block at 3.73 ppm (Figure 3). Integration
of these two peaks gave a ratio of repeat units in the two blocks
to be 3:4. The methyls of the DMA-CO block appeared at 1.72
and 1.94 ppm. The methyl group of the starting complex 2
was observed as a singlet at 2.15 ppm indicating an acetyl end-
group.
1H-NMR (CDCl3) (ppm): 1.12-1.94 (br), 3.03-3.77 (m), 5.86 (m).
13C{1H}-NMR (CDCl3) (ppm): 20.0-31.1 (m), 42.8-44.8 (b), 109.3-
152.3 (m), 203.0 (m). IR (CDCl3) (cm-1): 1686. Mp: 4.3 × 103
(MWD ) 3.8), 6.7 × 104 (very broad).
Conclusion
Using [Pd(PPh3)2(MeCN)2](BF4)2 as the catalyst, 3,3-di-
methylallene was successfully copolymerized with carbon
monoxide to form a highly unsaturated polyketone. Studies
(8) Margl, P.; Ziegler, T. J. Am. Chem. Soc. 1996, 118, 7337.

Palladium(II)-Catalyzed Copolymerization of Allene
J. Am. Chem. Soc., Vol. 119, No. 42, 1997 10033
Copolymerization Using Other Ligands. A procedure analogous
to the one described above was used with 3.8 × 10-2 mmol (19 mg)
of Dppp, 11.4 × 10-2 mmol (30 mg) of triphenylphosphine, and 3.8 ×
10-2 mmol (14 mg) of (R,R)-Me-DUPHOS, respectively.
Copolymerization of 1,1,3,3-Tetramethylallene with Carbon
Monoxide. A procedure analogous to the one described for 3,3-
dimethylallene was employed using 0.5 g of 1,1,3,3-tetramethylallene.
At the end of the reaction, the excess gas was released, and the monomer
and solvents were removed under vacuum. Only a trace of copolymer
was obtained.
Hydrogenation of the Copolymer of 3,3-Dimethylallene and Car-
bon Monoxide. 5% Pd/C (100 mg) was added to 10 mL of a solution
containing 300 mg of DMA-CO copolymer in CDCl3. The resultant
solution was placed in a 125 mL Parr bomb and charged with 100 psi
of dihydrogen. After stirring for 2 days at room temperature, the excess
dihydrogen was released. The solution was filtered and run through a
short-stem silica gel column to remove the catalyst.
7.36 (20H, m). 31P-NMR (CDCl3) (ppm): -3.44 (d, J ) 54.8 Hz),
27.20 (d, J ) 54.7 Hz).
[Pd(Dppp)(η3-C5H8-Me)](BF4), 10a. To a solution containing 20
mg (3.0 × 10-2 mmol) of 3 in 0.8 mL of CDCl3 was added 3 × 10-3
mL (3.1 × 10-2 mmol) of DMA. The solution was allowed to stand
at room temperature for 6 h. 1H-NMR (CDCl3) (ppm): 1.12 (3H,
dd, J ) 8.0 Hz), 1.22 (3H, t, J ) 6.2 Hz), 1.68 (2H, m), 1.89 (3H, s),
2.75 (2H, m), 2.95 (2H, m), 3.07 (1H, d, J ) 10.0 Hz), 3.57 (1H,
dd, J ) 2.2, 6.0 Hz), 7.43 (20H, m). 31P-NMR (CDCl3) (ppm): 8.29
(d, J ) 63 Hz), 10.59 (d, J ) 63 Hz). 13C{1H}-NMR (CDCl3)
(ppm): 18.8 (s), 22.0 (s), 23.0 (d, J ) 5.3 Hz), 25.8 (d, J ) 2.8 Hz),
26.1 (d, J ) 2.1 Hz), 26.5 (dd, J ) 4.3, 25.9 Hz), 68.3 (dd, J ) 3.2,
28.3 Hz), 94.2 (s), 101.9 (dd, J ) 6.2, 29.7 Hz), 126.1-133.9 (phenyl
carbons).
Complexes 1 and 2 did not give any well defined products in
appreciable yield with TMA.
[Pd(Dppp)(η3-C7H12-Me)](BF4), 10b. To a solution containing 20
mg (3.0 × 10-2 mmol) of 3 in 0.8 mL of CDCl3 was added 4.0 mg
(4.2 × 10-2 mmol) of TMA. The solution was allowed to stand at
room temperature for 1 day. 1H-NMR (CDCl3) (ppm): 1.24-1.35
(12H, m), 2.16 (3H, s), 2.69 (4H, m), 3.04 (2H, m), 7.40 (20H,
m). 31P-NMR (CDCl3) (ppm): 9.10 (s). 13C{1H}-NMR (CDCl3)
(ppm): 18.5 (s), 20.0 (s), 21.1 (s), 27.5 (s), 27.5 (d, J ) 27 Hz),
96.8 (t, J ) 18 Hz), 118.1 (t, J ) 7 Hz), 127.7-134.71 (phenyl
carbons).
Formation of Terpolymer with Alt-Ethene-Carbon Monoxide and
Alt-Allene-Carbon Monoxide Blocks. Pd(PPh3)2(Me)(Cl) (25 mg, 3.7
× 10-2 mmol) was dissolved in 1.0 mL of CDCl3 and placed in a 125
mL Parr bomb which was then charged with 100 psi each of ethene
and carbon monoxide. After 1 day, the excess gases were released,
and the product 11 was characterized in situ by 1H and 31P-NMR
spectroscopy.
11: 1H-NMR (CDCl3) (ppm): 1.27 (2H, Pd-CO-CH2-CH2-CO-
CH2-CH2-(CO-CH2-CH2)n-CO-Me), 2.14 (5H, Pd-CO-CH2-CH2-CO-
CH2-CH2-(CO-CH2-CH2)n-CO-Me), 2.33 (2H, Pd-CO-CH2-CH2-CO-
CH2-CH2-(CO-CH2-CH2)n-CO-Me), 2.46 (2H, Pd-CO-CH2-CH2-CO-
CH2-CH2-(CO-CH2-CH2)n-CO-Me), 2.69 (16H, Pd-CO-CH2-CH2-CO-
CH2-CH2-(CO-CH2-CH2)n-CO-Me), 7.40 (18H, m), 7.77 (12H, m).
31P-NMR (CDCl3) (ppm): 19.55. See ref 7 for further details.
1H-NMR (CDCl3) (ppm): 0.83-1.76 (br), 1.95 (br), 2.58 (br), 3.57
(m), 4.96 (br), 5.83(m). 13C{1H}-NMR (CDCl3) (ppm): 16.0-30.9
(br,m), 42.0-45.0 (m), 107.3-152.3 (m), 203.0 (m). IR (CDCl3)
(cm-1): 1708.
Hydrogenation was also attempted using Pt instead of Pd/C in the
procedure described above. The results were identical to those obtained
using Pd/C as the catalyst.
Insertion of 3,3-Dimethylallene and Carbon Monoxide into
Palladium-Carbon Bonds. All the reactions were done in NMR
tubes, and the complexes were characterized in situ.
[Pd(PPh3)2(C(O)C6H4-Me-p)(MeCN)](BF4), 1: 1H-NMR (CDCl3)
(ppm): 1.52 (3H, s), 2.2 (3H, s), 6.82 (2H, d, J ) 7 Hz), 7.68 (12H,
m), 7.45 (2H, d, J ) 7 Hz), 7.26 (18H, m). 31P-NMR (CDCl3) (ppm):
20.50.
[Pd(PPh3)2(η3-C5H8-C(O)C6H4-Me-p)](BF4), 4. To a solution
containing 25 mg (2.9 × 10-2 mmol) of 1 in 0.8 mL of CDCl3 was
added 3 × 10-3 mL (3.1 × 10-2 mmol) of DMA. The solution was
allowed to stand at room temperature for 6 h. 1H-NMR (CDCl3)
(ppm): 0.78 (3H, dd, J ) 6.3, 9.9 Hz), 1.53 (3H, t, J ) 5.6 Hz), 2.41
(3H, s), 3.48 (2H, d, J ) 8.0 Hz), 7.37 (24H, m), 7.67 (8H, m), 7.90
(2H, d, J ) 8.0 Hz). 31P-NMR (CDCl3) (ppm): 24.0 (d, J ) 42.7
Hz), 26.5 (d, J ) 43.2 Hz). 13C{1H}-NMR (CDCl3) (ppm): 22.0 (s),
22.1 (d, J ) 5.0 Hz), 22.4 (d, J ) 3.3 Hz), 65.7 (d, J ) 31.1 Hz), 94.2
(s), 112.1 (dd, J ) 4.0, 26.3 Hz), 128.1-146.5 (phenyl carbons), 194.4
(s). IR (CDCl3) (cm-1): 1664.
DMA (12 mg, 0.2 mmol) was added to the above solution of complex
11 in CDCl3, formed in situ from 25 mg (3.7 × 10-2 mmol) of Pd-
(PPh3)2(Me)(Cl). This was placed in a 125 mL Parr bomb and charged
with 200 psi of carbon monoxide. The reaction was allowed to proceed
for 1 day at 40 °C. At the end of this time period excess carbon
monoxide was released, and the product 12 was characterized by
1H- and 31P-NMR spectroscopy.
Pd(PPh3)2(Me)(Cl), 2: 1H-NMR (CDCl3) (ppm): -0.13 (3H, t, J
) 5.9 Hz), 7.42 (30H, m). 31P-NMR (CDCl3) (ppm): 30.93 (s).
Pd(PPh3)2(η3-C5H8-Me)(Cl), 7. To a solution containing 25 mg
(3.7 × 10-2 mmol) of 2 in 0.8 mL of CDCl3 was added 4 × 10-3 mL
(4.1 × 10-2 mmol) of DMA. The solution was allowed to stand at 45
°C for 1 day. 1H-NMR (CDCl3) (233 K) (ppm): 0.84 (3H, b), 1.31
(3H, b), 1.99 (3H, b), 3.12 (1H, b), 3.61 (1H, b), 7.02-7.65 (30H,
m). 31P-NMR (CDCl3) (233 K) (ppm): 25.84 (d, J ) 41 Hz), 26.96
(d, J ) 41 Hz). 1H-NMR (CDCl3) (298 K) (ppm): 1.51 (3H, d, J )
5.9 Hz), 1.86 (3H, d, J ) 8.7 Hz), 1.91 (3H, s), 2.76 (1H, d, J ) 2.1
Hz), 2.92 (1H, d, J ) 2.1 Hz), 7.02-7.65 (30H, m). 31P-NMR (CDCl3)
(298 K) (ppm): 27.48 (b).
1
12: H-NMR (CDCl3) (ppm): 1.72 (24H, bs), 1.94 (24H, bs), 2.15
(3H, s), 2.69 (24H, bs), 3.73 (16H, bs), 7.42 (18H, m), 7.67 (12H, m).
31P-NMR (CDCl3) (ppm): 27.52 (b). IR (CDCl3) (cm-1): 1679 (br).
Acknowledgment. This research was supported by a grant
from the U.S. Department of Energy, Office of Basic Energy
Sciences (DE-FG02-84ER13295).
1
[Pd(Dppp)(Me)(MeCN)](BF4), 3: H-NMR (CDCl3) (ppm): 0.32
(3H, dd, J ) 2.6, 7.3 Hz), 1.79 (3H, s), 1.78 (2H, m), 2.50 (4H, m),
JA9716620