?-Allylic Rhodium Complex Catalyzed Living Copolymerization of Arylallenes with Carbon Monoxide To Give Structurally Regulated Polyketones

Full text of DOI:10.1021/ja971856f

12390
J. Am. Chem. Soc. 1997, 119, 12390-12391
π-Allylic Rhodium Complex Catalyzed Living
Copolymerization of Arylallenes with Carbon
Monoxide To Give Structurally Regulated
Polyketones
Kohtaro Osakada,* Jun-chul Choi, and
Takakazu Yamamoto*
Research Laboratory of Resources Utilization
Tokyo Institute of Technology, 4259 Nagatsuta
Midori-ku, Yokohama 226, Japan
ReceiVed June 6, 1997
Figure 1. ORTEP drawing of Rh[η3-CH(Ar)C{C(dCHAr)-
CH2C(dCHAr) CH2CH2CHdCHAr}CH2](PPh3)2 (Ar ) C6H4OMe-p)
(1) with 30% thermal ellipsoidal levels. Hydrogens are omitted for
simplicity.
Palladium-catalyzed copolymerization of alkenes with carbon
monoxide attracts considerable attention arising from the
structure of the produced polymer with a high density of
carbonyl functions and from potential utility as photodegradable
materials.1 This reaction has been recently extended to copo-
lymerization of several dienes with carbon monoxide to give
the corresponding polyketones shown in Chart 1.2 A catalyst
based on Pd compounds and chelating diamine has been reported
to initiate copolymerization of 1,2-propadiene and CO to give
the corresponding polyketone, (CH2-C(dCH2))n.3 Control of
structure and molecular weights in preparation of the polymers
derived from 1,2-dienes and CO is of a significant interest since
it has a unique enone structure in the repeating unit and can be
converted into further functionalized derivatives. Here, we
report the use of a new π-allylic rhodium complex for the first
living copolymerization of 1,2-dienes with carbon monoxide
to give new polyketones with a highly regulated structure.
The polymerization catalyst, Rh[η3-CH(Ar)C{C(dCHAr)-
CH2C(dCHAr) CH2CH2CHdCHAr}CH2](PPh3)2 (Ar ) C6H4-
OMe-p) (1), is obtained from reactions of RhH(PPh3)4 with (4-
methoxyphenyl)allene in 1:4 and 1:5 molar ratios at room
temperature. Complex 1 is isolated in high yields (>80%)
Chart 1
starting complex.5 The NMR (1H, 13C, 31P, 1H-1H COSY, and
1H-13C COSY) spectra in solution are consistent with the
crystallographic structure of the molecule.
Copolymerization of phenylallene and of (4-methoxyphenyl)-
allene with CO in the presence of a catalytic amount of 1
converts the monomers into polyketones [-CO-CH2-C(dCHPh)-
]n (2) and [-CO-CH2-C(dCHC6H4OMe-p)-]n (3), respectively.6
The 1H NMR spectrum of 2 shows signals due to the repeating
among many possible complexes that could result from the
reaction of (4-methoxyphenyl)allene with RhH(PPh3)4.4 Figure
1 shows the molecular structure of 1 which possesses the
π-allylic ligand formed through consecutive insertion of four
(4-methoxyphenyl)allene molecules into the Rh-H bond of the
unit formed through completely alternating insertion of pheny-
lallene and carbon monoxide (Figure 2).7 Measurement using
ROESY technique has revealed a cis orientation of the Ar and
carbonyl groups in the repeating unit. The absence of structural
unit from 1,2-polymerization and narrow peak width of the
signals indicate highly regulated structure of the polymer chain.
Small peaks at δ 3.6-3.8 are assigned to OMe hydrogens of
the polymer end derived from 1. The peak area relative to those
of hydrogens in the repeating unit gives rise to Mn, which is
(1) For recent reviews and leading references, see: (a) Sen, A. Acc. Chem.
Res. 1993, 26, 303. (b) Drent, E.; Budzelaar, P. H. M. Chem. ReV. 1996,
96, 663. (c) Drent, E.; van Broekhoven, J. A. M.; Budzelaar, P. H. M.
Recl. TraV. Chim. Pays-Bas. 1996, 115, 263. (d) Abu-Surrah, A. S.; Rieger,
B. Angew. Chem., Int. Ed. Engl. 1996, 35, 2475. (e) Bronco, S.; Consiglio,
G.; Hutterm, R.; Batistini, A.; Suter, U. W. Macromolecules 1994, 27, 4436.
(f) Bronco, S.; Consiglio, G.; DiBenedetto, S.; Fehr, M.; Spindler, F.; Togni,
A. HelV. Chim. Acta 1995, 78, 883. (g) Brookhart, M.; Rix, F. C.; DeSimone,
J. M.; Borborak, J. C. J. Am. Chem. Soc. 1992, 114, 5894. (h) Brookhart,
M.; Wagner, M. I.; Balavoine, G. G. A.; Haddou, H. A. J. Am. Chem. Soc.
1994, 116, 3641. (i) Rix, F. C.; Brookhart, M.; White, P. S. J. Am. Chem.
Soc. 1996, 118, 4746. (j) Brookhart, M.; Wagner, M. I. J. Am. Chem. Soc.
1996, 118, 7219. (k) Jiang, Z.; Adams, S. E.; Sen, A. Macromolecules 1994,
27, 2694. (l) Jiang, Z.; Sen, A. J. Am. Chem. Soc. 1995, 117, 4455. (m)
Nozaki, K.; Sato, N.; Takaya, H. J. Am. Chem. Soc. 1995, 117, 9911. (n)
Margel, P.; Ziegler, T. J. Am. Chem. Soc. 1996, 118, 7337.
(2) (a) Drent, E. Eur. Pat. Appl. 504,985, 1992; Chem. Abstr. 1993, 118,
103023 (b) Borkowsky, S. L.; Waymouth, R. M. Macromolecules 1996,
29, 6377. (c) Nozaki, K.; Sato, N.; Nakamoto, K.; Takaya, H. Bull. Chem.
Soc. Jpn. 1997, 70, 659.
(3) Maatschappij, B. V. Neth. Appl. 1988, 88 01168; Chem. Abstr. 1990,
113, 24686f.
(4) Insertion of four (4-methoxyphenyl)allene molecules into the Rh-H
bond occurs rapidly at room temperature to give 1 selectively in the reactions
of RhH(PPh3)4 and (4-methoxyphenyl)allene in 1:4 and 1:5 molar ratios.
Once formed 1 does not react further with additional phenylallene or (4-
methoxyphenyl)allene at this temperature. Formation of other complexes
than 1 and RhH(PPh3)4 is not noted in the reaction mixture.
(5) X-ray data of 1: triclinic, P1h(No. 2), a ) 14.132(3) Å, b ) 18.519-
(7) Å, c ) 12.177(5) Å, R ) 102.13(3)°, â ) 95.35(3)°, γ ) 95.60(2)°,V
) 3079 Å3, Z ) 2, Dcalcd ) 1.308 g cm-3, F(000) ) 1268, µ(Mo KR) )
3.80 cm-1 for monochromated MoKR radiation (λ ) 0.710 69 Å). The
structure was solved by direct methods and refined by full-matrix least-
squares calculations. R (Rw) ) 0.062 (0.044) for 7100 reflections with I >
3σ(I) among 10709 unique reflections.
(6) The polymer products in this study have been treated with a large
excess amount of MeOH before isolation and characterization in order to
remove Rh and PPh3 and are free from the metal and ligand.
(7) For insertion of CO into a π-allyl-palladium bond and for insertion
of allene into a Pd-C bond, see: Yamamoto, A. Bull. Chem. Soc. Jpn.
1995, 68, 433 and references cited therein. Ru¨lke, 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. Groen, J. H.; Elsevier, C.
J.; Vrieze, K.; Smeets, W. J. J.; Spek, A. L. Organometallics 1996, 15,
3445. Delis, J. G. P.; Groen, J. H.; Vrieze, K.; van Leeuwen, P. W. N. M.;
Veldman, N.; Spek, A. L. Organometallics 1997, 16, 551.
S0002-7863(97)01856-8 CCC: $14.00 © 1997 American Chemical Society

Communications to the Editor
J. Am. Chem. Soc., Vol. 119, No. 50, 1997 12391
Figure 2. 1H NMR spectrum of (CH2-C(dCHPh)-CO)n-I (2, n ) 50)
where I denotes the polymer end group derived from 1. Decrease in
the relative intensity of OCH3 hydrogens of I caused by increase in
the monomer/catalyst ratios is shown in inset.
Table 1. Results of Copolymerization of Phenylallene and CO
Initiated by 1
Figure 4. 1H NMR spectra of block copolyketone 4 and random
copolyketone 5. Positions of the vinylic hydrogen signals are shown
with arrows.
conditionsa
productb
c
[CH2dCdCHPh]0/[1] 10-3Mn (GPC)c Mw/Mn 10-3Mn (NMR)d
Chart 2
50
100
150
200
7.9
17.1
25.6
35.0
1.08
1.09
1.14
1.10
7.2 (7.8)
14.6 (15.0)
23.0 (22.2)
e (29.4)
a Polymerization was carried out under CO (1 atm) in THF using
0.050 mmol of 1 at room temperature. b Polyketone 2 is obtained
quantitatively in each reaction. c Determined by GPC using polystyrene
1
standards. d Determined from H NMR peak area ratio between the
OCH3 and CH2 hydrogens, based on the molecular formula H-[(CH2C-
(dCHPh))-CO]n-CH2C{dCH(Ar)}-C(dCHAr)CH2C(dCHAr)-
CH2CH2CHdCHAr (Ar ) C6H4OMe-p). Calculated molecular weights
assuming quantitative efficiency of the initiator 1 are shown in
parentheses. e Not determined due to small peak intensity of the OCH3
hydrogens.
to the resulting mixture afford block copolyketone 4, whose
structure is shown in Chart 2.8 An equimolar mixture of
phenylallene and (4-methoxyphenyl)allene reacts with carbon
monoxide to give 5 containing units A and B randomly. Figure
1
4 compares the H NMR spectra of 4 and 5. Copolymer 4
shows two sharp peaks due to vinyl hydrogens of the blocks
AAA‚‚‚A (δ 7.82) and BBB‚‚‚B (δ 7.80). The corresponding
vinylic hydrogen of 5 appears at δ 7.7-7.9 as three peaks, which
are resulted from random sequence of the structural units A
and B.9
All of the above results, including narrow molecular weight
distribution of 2 during the polymerization reaction and forma-
tion of the block copolymer 4, indicate that 1 catalyzes living
copolymerization of the arylallenes with carbon monoxide to
afford new polyketones under mild conditions.
Figure 3. Change in Mn and Mw/Mn of growing polymer during
polymerization of phenylallene (55 mol/1) and CO initiated by 1. A
small portion of the solution obtained by a syringe is quenched by
MeOH and analyzed by GPC (polystyrene standards) for each plot.
The final molecular weight of the product is consistent with the initial
molar ratio of phenylallene and 1.
Acknowledgment. This work was financially supported by a Grant-
in-Aid for Scientific Research from the Ministry of Education, Science,
Culture, and Sports, Japan.
Supporting Information Available: Full experimental details,
crystallographic data of complex 1, and NMR, GPC, and DSC data of
the polymers (30 pages). See any current masthead page for ordering
and Internet access instructions.
close to that from GPC using polystyrene standards. Molecular
weights of 1 increase with increase in the monomer/catalyst
ratio without significant change of polydispersity (Mw/Mn )
1.08-1.14) as summarized in Table 1. Figure 3 depicts change
in molecular weight of the growing polymer during the reaction.
Molecular weight of the polymer increases with narrow mo-
lecular weight distribution (Mw/Mn < 1.11) until consumption
of phenylallene. The above results imply that the copolymer-
ization proceeds without any chain transfer reaction.
JA971856F
(8) GPC analyses of the reaction mixture in preparation of the block
copolyketone show unimodal patterns with narrow molecular weights
distribution (Mw/Mn ) 1.09-1.10) before addition of the second monomer
((4-methoxyphenyl)allene) and after consumption of both monomers.
(9) The three 1H NMR peaks of 5 at δ 7.7-7.9 in a 1:2:1 area ratio can
be assigned to the triads ABA (and BAB), ABB (AAB, BAA, and BBA),
and AAA (and BBB), respectively. ABB and BBA as well as AAB and
BAA are equal to each other.
Copolymerization of phenylallene with carbon monoxide
catalyzed by 1 and ensuing addition of (4-methoxyphenyl)allene