High-pressure NMR studies on the alternating copolymerization of propene with carbon monoxide catalyzed by a palladium(II) complex of an unsymmetrical phosphine-phosphite ligand

Article abstract of DOI:10.1021/om990985x

When high-pressure NMR techniques are employed, the following two facts are revealed. (1) The cis/trans isomerization from (SP-4-4)-[Pt(CH₃)(CO)(L¹)][BAr₄] (8a; L¹ = (R,S)-BINAPHOS; Ar = 3,5-(CF₃)₂C₆H₃) to the more stable SP-4-3 isomer (8b) is faster than CO insertion into either 8a or 8b, the CO insertion being reversible. (2) For the Pd¹¹-L¹-catalyzed copolymerization of propene and CO, there exist at least two major resting states, most probably acylpalladium, (SP-4-3)-[Pd(COR)(L²)(L¹)][BAr₄] (3; L² = CH₃CN, CO), and alkyl-palladium, [Pd{CH₂CH(CH₃)C(=O)R}(L¹)][BAr₄] (5a).

Full text of DOI:10.1021/om990985x

Organometallics 2000, 19, 2031-2035
2031
High -P r essu r e NMR Stu d ies on th e Alter n a tin g
Cop olym er iza tion of P r op en e w ith Ca r bon Mon oxid e
Ca ta lyzed by a P a lla d iu m (II) Com p lex of a n
Un sym m etr ica l P h osp h in e-P h osp h ite Liga n d
Kyoko Nozaki* and Tamejiro Hiyama
Department of Material Chemistry, Graduate School of Engineering, Kyoto University,
Yoshida, Sakyo-ku, Kyoto 606-8501, J apan
Smita Kacker and Istva´n T. Horva´th†
Corporate Research Laboratory, Exxon Research & Engineering Company,
Annandale, New J ersey 08801
Received December 13, 1999
When high-pressure NMR techniques are employed, the following two facts are revealed.
(1) The cis/trans isomerization from (SP-4-4)-[Pt(CH3)(CO)(L1)][BAr4] (8a ; L1 ) (R,S)-
BINAPHOS; Ar ) 3,5-(CF3)2C6H3) to the more stable SP-4-3 isomer (8b) is faster than CO
insertion into either 8a or 8b, the CO insertion being reversible. (2) For the PdII-L1-catalyzed
copolymerization of propene and CO, there exist at least two major resting states, most
probably acylpalladium, (SP-4-3)-[Pd(COR)(L2)(L1)][BAr4] (3; L2 ) CH3CN, CO), and alkyl-
palladium, [Pd{CH2CH(CH3)C(dO)R}(L1)][BAr4] (5a ).
In tr od u ction
BINAPHOS to be an efficient catalyst for the asym-
metric copolymerization of propene (3 atm) with carbon
monoxide (20 atm). Highly isotactic polyketone with
high enantioselectivity was obtained using [Pd(CH3)(CH3-
CN){(R,S)-BINAPHOS}][B{3,5-(CF3)2C6H3}4] (1).4 The
ligand is an unsymmetrical cis-bidentate phosphine-
phosphite, and accordingly, two nonequivalent coordi-
nation sites are available for reactions on the tetraco-
ordinated palladium species. Mechanistic aspects of the
copolymerization were studied in detail, and the com-
plexes marked “observed” in Scheme 1 were detected
by stepwise NMR studies under ambient pressure.
Namely, treatment of the methylpalladium compound
1 with CO in the absence of propene gave the acylpal-
ladium species 3-I, and exposure of 3-I to propene
afforded a 4:1 mixture of alkylpalladium complexes 5a -I
and 5b-I. Further, formation of the second-generation
acyl complex 3-II was detected after pressurize-depres-
surize treatment of a mixture of 5a -I and 5b-I with 20
atm of CO, and the second-generation acyl complex 5a -
II was given as an exclusive product by exposure of 3-II
to propene.
The work was then focused on the reaction pathways
between the observed complexes, such as 1 f 3-I and
3-I f 5-I in Scheme 1. The platinum complex [Pt(CH3)-
(CH3CN){(R,S)-BINAPHOS}][B{3,5-(CF3)2C6H3}4] (7)
was studied as an analogue of palladium complex 1.
Methylplatinum carbonyl 8a was obtained under 1 atm
of CO as a result of CO-acetonitrile exchange. After a
pressurize-depressurize cycle with 20 atm of CO, 8a
was transformed into 8b , the cis/trans isomer of 8a
Alternating copolymerization of olefins with CO has
attracted much attention from both academia and
industry due to the easy availability of starting materi-
als and the engineering plastic type novel properties of
the product.1 The polymerization process includes two
of the representative reactions of a palladium complex:
(1) CO insertion into an alkyl-Pd bond and (2) an olefin
insertion into an acyl-Pd bond; thus, intensive efforts
have been devoted to mechanistic studies of the reaction
by both experimental2 and theoretical approaches.3
We previously reported a cationic Pd(II) complex with
the unsymmetrical chiral phosphine-phosphite (R,S)-
† Present address: Department of Organic Chemistry, Eotvos Lo-
rand University, Pazmany Peter setany 1/A, H-1117 Budapest, Hun-
gary.
(1) (a) Drent, E.; Budzelaar, P. H. M. Chem. Rev. 1996, 96, 663. (b)
Sen, A. Acc. Chem. Res. 1993, 26, 303. (c) Nozaki, K.; Hiyama, T. J .
Organomet. Chem. 1999, 576, 248.
(2) (a) Cavell, J . K. Coord. Chem. Rev. 1996, 155, 209. (b) Yamamoto,
A. Organometallics 1995, 14, 337. (c) Brookhart, M.; Rix, F. C.;
DeSimone, J . M. J . Am. Chem. Soc. 1992, 114, 5894. (d) Rix, F. C.;
Brookhart, M.; White, P. S. J . Am. Chem. Soc. 1996, 118, 4746. (e)
Dekker, G. P. C. M.; Buijs, A.; Elsevier, C. J .; Vrieze, K.; van Leeuwen,
P. W. N. M.; Smeets, W. J . J .; Spek, A. L.; Wang, Y. F.; Stam, C. H.
Organometallics 1992, 11, 1937. (f) To´th, I.; Elsevier, C. J . J . Am.
Chem. Soc. 1993, 115, 10388. (g) van Asselt, R.; Gielens, E. E. C. G.;
Ru¨lke, R. E.; Vries, K.; Elsevier, C. J . J . Am. Chem. Soc. 1994, 116,
977. (h) van Leeuwen, P. W. N. M.; Roobeek, C. F.; van der Heijden,
H. J . Am. Chem. Soc. 1994, 116, 12117. (i) Markies, B. A.; Kruis, D.;
Rietveld, M. H. P.; Verkerk, K. A. V.; Boersma, J .; Kooijman, H.; Lakin,
M. T.; Spek, A. L.; van Koten, G. J . Am. Chem. Soc. 1995, 117, 5263.
(j) Markies, B. A.; Wijkens, P.; Dedieu, A.; Boersma, J .; Spek, A. L.;
van Koten, G. Organometallics 1995, 14, 5628. (k) Bianchini, C.; Lee,
H. M.; Meli, A.; Moneti, S.; Vizza, F.; Fontani, M.; Zanello, P.
Macromolecules 1999, 32, 4183. (l) Bianchini, C.; Lee, H. M.; Barbaro,
P.; Meli, A.; Moneti, S.; Vizza, F. New J . Chem. 1999, 23, 929. Related
studies with Pt: (m) To´th, I.; Ke´gl, T.; Elsevier, C. J .; Kolla´r, L. Inorg.
Chem. 1994, 33, 5708. (n) Ke´gl, T.; Kolla´r, L.; Radics, L. Inorg. Chim.
Acta 1997, 265, 249.
(4) (a) Nozaki, K.; Sato, N.; Tonomura, Y.; Yasutomi, M.; Takaya,
H.; Hiyama, T.; Matsubara, T.; Koga, N. J . Am. Chem. Soc. 1997, 119,
12779. (b) Nozaki, K.; Sato, N.; Takaya, H. J . Am. Chem. Soc. 1995,
117, 9911. (c) Nozaki, K.; Yasutomi, M.; Nakamoto, K.; Hiyama, T.
Polyhedron 1998, 17, 1159.
(3) (a) Svensson, M.; Matsubara, T.; Morokuma, K. Organometallics
1996, 15, 5568. (b) Margl, P.; Ziegler, T. J . Am. Chem. Soc. 1996, 118,
7337. (c) Margl, P.; Ziegler, T. Organometallics 1996, 15, 5519.
10.1021/om990985x CCC: $19.00 © 2000 American Chemical Society
Publication on Web 04/14/2000

2032 Organometallics, Vol. 19, No. 10, 2000
Nozaki et al.
Sch em e 1
(Scheme 2). On the basis of the isomerization, the
process 1 f 2a f 2b f 3-I was proposed. Theoretical
approaches cleared the 3-I f 5-I process. In the previous
study, however, success at determining the structures
of complexes has been limited due to the difficulty in
detecting in situ species which may exist only under
high pressures. Hence, here we report further studies
on the Pt and Pd complexes related to the copolymeri-
zation, employing high-pressure NMR techniques.5 Two
subjects will be presented: (1) the reaction of alkyl-
platinum 7 with CO and (2) observation of the chain
growth of propene-CO copolymer initiated by cationic
palladium 1.
in an immediate transformation to acyl complex 3-I and
no intermediate complexes were detectable (Scheme 1).
In contrast, when methylplatinum 7 was treated with
1 atm of CO, only a ligand displacement was observed
from acetonitrile to CO to give 8a (Scheme 2). After a
pressurize (up to 20 atm)-depressurize (down to 1 atm)
cycle, the predominant product was 8b, in which the
methyl group and the coordinated carbonyl isomerized.
Acyl complex (9 in Scheme 3) was not detected. Here,
in this work, the reaction of 7 with CO was carried out
in a sapphire tube under 22 atm of CO pressure and was
followed by 31P NMR. When the reaction was allowed
to start at -50 °C, peaks were detected at δ 122.5 for
the phosphite and δ 15.4 for the phosphine, showing 8a
to be essentially the single product (part i of Figure 1).
No change was observed below -25 °C. When the mix-
ture was warmed to 25 °C, peaks due to isomer 8b ap-
peared at δ 148.6 for the phosphite and δ 15.0 for the
phosphine (part ii of Figure 1). After 4 h at 25 °C,
another set of peaks appeared at δ 112.8 for the phos-
phite and δ 6.9 for the phosphine (part iii of Figure 1).
To determine the structure of this new species, the
same experiment was repeated using 13CO. Broad peaks
were detected by 31P NMR for the new species, and the
existence of an acyl group attached to the platinum was
confirmed by the peak at δ 215.0 in 13C NMR. To get a
better resolution, the solution was cooled to -50 °C. At
Sch em e 2
(5) For examples of high-pressure NMR studies on homogeneous
carbonylation process, see: (a) Roe, D. C. Organometallics 1987, 6,
942. (b) Horva´th, I. T.; Millar, J . M. Chem. Rev. 1991, 91, 1339. (c)
Horva´th, I. T.; Kiss, G.; Cook, R. A.; Bond, J . E.; Stevens, P. A.; Ra´bai,
J .; Mozeleski, E. J . J . Am. Chem. Soc. 1998, 120, 3133. See also ref
2f,j-n.
Resu lts a n d Discu ssion
Rea ction of Alk ylp la tin u m Com p lex 7 w ith Ca r -
bon Mon oxid e. As we previously reported,4a treatment
of methylpalladium complex 1 with 1 atm of CO resulted

Copolymerization of Propene with CO
Organometallics, Vol. 19, No. 10, 2000 2033
F igu r e 1. Treatment of alkylplatinum 7 in CD2Cl2 with
CO in a sapphire NMR tube, followed by 31P NMR: (i) at
-50 °C and 22 atm of CO pressure, alkylplatinum 8a being
formed via immediate replacement of CH3CN of 7 by CO;
(ii) after the sample in (i) was warmed to 25 °C, the cis-
trans isomerization 8a f 8b taking place to some extent;
(iii) after 4 h at 25 °C, a new set of peaks appearing at δ
112.8 (phosphite) and δ 6.9 (phosphine) (the peaks will be
assigned as acylplatinum 9 in Figure 2).
F igu r e 2. Reaction of alkylplatinum 7 with CO carried
out using 13CO in CD2Cl2: (i) 31P NMR under 22 atm of
13CO at -50 °C, the three species [Pt(CH3)(13CO){(R,S)-
BINAPHOS}][B{3,5-(CF3)2C6H3}4] (8a -13C and 8b-13C)
and [Pt(13COCH3)(13CO){(R,S)-BINAPHOS}][B{3,5-(CF3)2-
C6H3}4] (9-13C) being shown (in 9-13C, J P-C is 172 Hz for
the phosphite (δ 112.8) and 71 Hz for the phosphine (δ 6.9));
(ii) 13C NMR under 56 atm of 13CO at -50 °C. In the
carbonyl region, the sp2 carbon of the acylplatinum exhibits
a peak at δ 215.0 with J P-C ) 71 Hz. Next to the large
peak of free 13CO, a broad peak is found at δ 182.8 due to
the coordinated 13CO. Putting all the observations together,
acylplatinum 9 in which acyl is trans to the phosphine is
suggested as the new species.
Sch em e 3
this temperature, the new species exhibited P-C cou-
pling constants in 31P NMR of 172 Hz for the phosphite
and 71 Hz for the phosphine (part i of Figure 2).
Elevation of the 13CO pressure to 56 atm increased the
concentration of the new species. Again at -50 °C, one
of the J P-C couplings, 71 Hz, was detected in 13C NMR
for the sp2 carbon of the acetylplatinum at δ 215.0, as
can be seen in part ii of Figure 2. In addition, there is
a broad peak at δ 182.8 due to the coordinated 13CO.
When all the observations are put together, acylplati-
num 9 in which acyl is trans to the phosphine is
suggested as the new species.
The formation of acylplatinum 9 from 7 is a reversible
process. When CO was removed from the sample of part
iii of Figure 1 by freeze-thaw cycles, 9 and 8a disap-
peared and two new sets of peaks appeared at δ 114

2034 Organometallics, Vol. 19, No. 10, 2000
Nozaki et al.
and 24 and at δ 115 and 10.6 The former set of peaks
are attributed to the decarbonylated complex 7. The
latter could not be characterized. When the NMR tube
is charged with CO again, the equilibrium between 8a
and 8b is established and the cycles of events described
above can be repeated.
The studies may be summarized as follows. (1) High-
pressure NMR showed the appearance of 8b followed
by that of acyl complex 9. Thus, the cis/trans isomer-
ization from 8a to 8b is a faster process than the CO
insertion.7 (2) Considering that the isomerization of 8a
to 8b is reversible, the increasing content of 8b com-
pared to 8a (Figure 1: (i) f (ii) f (iii)) suggests the
thermally more stable nature of 8b than 8a . The energy
difference arises most probably from the stabilization
of the coordinated CO in 8b than in 8a , as was shown
by the IR spectra in our previous study.4a The energy
gain at the carbonyl-Pt bond in 8b overcomes the
energy loss at the methyl-Pt bond, which is less stable
in 8b than in 8a . Thus, in 8b, the methyl was suggested
to be more activated for a nucleophilic migration to the
carbonyl and the carbonyl is less active toward the
electrophilic attack to the methyl. Here, we may say
safely that the present study gives no information about
the origin of 9, either/both from 8a or/and 8b but that,
at least, the 8a f 8b isomerization is a faster process
than the CO insertion. The chemistry presented here
is valid only for the Pt(II)-(R,S)-BINAPHOS system.
Nevertheless, it is of interest to compare the result with
the recent work by Luinstra et al., who showed the cis/
trans isomerization was slower than the CO insertion
in their alkylpalladium-(phosphine-amine) complexes.8,9
The difference might be attributed to the metal, either
Pt or Pd, or the ligand, phosphine-phosphite or phos-
phine-amine.
F igu r e 3. 31P NMR of the copolymerization of propene (3
atm) with CO (20 atm) initiated by palladium complex 3-I
(CD2Cl2, 25 °C). Three pairs of peaks are observed in the
region of δ 138.3-139.4 (phosphite) and 7.0-7.3 (phos-
phine) with J P-P ) 104-105 Hz, which may be assigned
as 3-I, 3-II, 3-III, .... The peaks at δ 140.3 (phosphite) and
12.9 (phosphine) with J P-P ) 67 Hz are characterized as
alkyl complexes 5a -I, 5a -II, 5a -III, .... One more set of
peaks at δ 131.3 and 25.2 (broad) are unassignable.
not proceed under these conditions. Next, we examined
the same process under high pressure (propene, 3 atm;
CO, 20 atm), which was employed for the real copolym-
erization. Polymer formation was observed by 13C NMR.
By 31P NMR, three pairs of peaks were observed in the
region of δ 138.3-139.4 (phosphite) and 7.0-7.3 (phos-
phine) with J P-P ) 104-105 Hz (Figure 3). The fact that
the chemical shifts and coupling constants resemble
those of acyl complexes 3-I and 3-II allows us to assign
the peaks to 3-I, 3-II, 3-III, .... In addition, peaks
observed at δ 140.3 (phosphite) and 12.9 (phosphine)
with J P-P ) 67 Hz were in the region of and alkyl
complexes 5a -I, 5a -II, 5a -III, .... One more set of peaks
at δ 131.3 and 25.2 (broad) were unassignable.
Apparently, the acyl complexes 3-I, 3-II, 3-III, ... (L
) CH3CN, CO) are waiting for the olefin insertion. Thus,
it is suggested that either the replacement of CO by
propene or the transition state for the propene insertion
ts(4-5b) is one of the highest energy barriers to go over.
Alkyl complexes 5a -I, 5a -II, 5a -III, ... are another
resting state of the catalytic cycle. This implies that the
ring opening of cyclic alkyl complex 5a to open alkyl
complex 6b is another high-barrier step, regardless to
the pathway from 5a to 6b, either ring opening-
isomerization or isomerization-ring opening. Thus, the
present observation does not allow us to determine the
rate-determining step unambiguously. Nevertheless, it
seems that there are two major energy barriers in the
catalytic cycle instead of simply just one. The results
agree with the comparable activation energies for 3-I
f 5-I and 5-I f 3-II reported in our previous study.
Alter n a tin g Cop olym er iza tion of P r op en e w ith
CO In itia ted by 1. The palladium-catalyzed alternat-
ing copolymerization involves two major steps: namely
the propene insertion into acylpalladium 3-I and the CO
insertion into alkylpalladium 5-I. To investigate the
rate-determining step, the reaction rates 3-I f 5-I and
5-I f 3-II were measured in our previous study.4a
Unfortunately, however, both rates were close to each
other, and the difference was buried in the range of
experimental errors. Here in this study, the polymeri-
zation process was followed by NMR, with the expecta-
tion that the species right before the rate-determining
step might be observable. First, the cationic acylpalla-
dium species 3-I was treated under ambient pressure
(propene, 0.5 atm; CO, 0.5 atm). In this case, only alkyl
complexes 1, 5a -I, and 5b-I were observed in a 4:4:1
ratio by 31P NMR. No polymeric or oligomeric products
1
were observed by H and 13C NMR. The results can be
interpreted as follows. (1) The decarbonylation from 3-I
to 1 could not be suppressed under 0.5 atm of CO. (2)
The insertion of CO into cyclic alkyl complexes 5-I does
Con clu sion
By employing high-pressure NMR techniques, we
studied two subjects as described above. Acylplatinum
9, which was invisible under 1 atm of CO, was detected.
The cis/trans isomerization from 8a to the more stable
isomer 8b is proven to be a faster process than the CO
insertion to give 9. The whole process from 7 to 9 is
reversible. For the palladium-catalyzed copolymeriza-
tion of propene with CO, the existence of at least two
major resting states, most probably acylpalladium 3-I,
(6) 31P NMR spectra for the experiments described in this paragraph
are attached as Supporting Information.
(7) (a) Anderson, G. K.; Cross, R. J . Acc. Chem. Res. 1984, 17, 67.
(b) Anderson, G. K.; Cross, R. J . Chem. Soc. Rev. 1980, 9, 185. (c)
Anderson, G. K.; Clark, H. C.; Davies, J . A. Organometallics 1982, 1,
64. See also ref 2m,n.
(8) Luinstra, G. A.; Brinkmann, P. H. P. Organometallics 1998, 17,
5160. See also ref 2e.
(9) With unsymmetrical bisphosphine ligands: van Leeuwen, P. W.
N. M.; Roobeek, K. F. Recl. Trav. Chim. Pays-Bas 1995, 114, 73. See
also ref 2h.

Copolymerization of Propene with CO
Organometallics, Vol. 19, No. 10, 2000 2035
with 21 atm of 13CO at 25 °C. The peaks corresponding to 8a -
13C, 8b-13C, and 9-13C (not yet characterized) were detected
by 31P NMR. Differing from nonlabeled peaks, the phosphite
peak of 8a -13C and the phosphine peak of 8b-13C were
broadened due to the P-C couplings. Probably, the exchange
between the coordinated 13CO and free 13CO caused the
broadenings. Although the full characterization of 9-13C
should wait for the next step, the existence of an acylpalladium
species was suggested by the 13C NMR peak at δ 215.0 (J P-C
) 71 Hz) at this moment. The peaks were sharpened at -50
°C, and the couplings were read as J P-C ) 162 Hz for the
phosphite of 8a -13C and 132 Hz for the phosphine of 8b-13C.
The sample was warmed again to 25 °C, and the 13CO
pressure was raised to 58 atm. The sample was kept at 25 °C
for 12 h. To get a better resolution, the solution was then cooled
to -50 °C in the NMR probe. Finally, 31P and 13C NMR of
9-13C clearly showed the following peaks which enabled the
3-II, 3-III, ... (L ) CH3CN or CO) and alkylpalladium
5a -I, 5a -II, 5a -III, ..., was suggested by high-pressure
NMR. The results are in sharp contrast to the observa-
tion under low pressure of CO; alkyl complexes 1, 5a -I,
and 5b-I were the predominant species.
Exp er im en ta l Section
Gen er a l Con sid er a tion s. All NMR experiments were
performed with an Oxford Instruments 400 MHz magnet with
a Varian Associates Unity 400 system and VNMR version 5.3
software for data collection and analysis and a Varian Associ-
ates 10 mm multinuclear broad-band probe: 13C, 100 MHz;
1H, 400 MHz; 31P, 160 MHz. High-pressure NMR was carried
out in sapphire tubes. Tetramethylsilane and H3PO4 were used
as internal and external standards. Dichloromethane, aceto-
nitrile, and CD2Cl2 were obtained from Aldrich and purified
by distillation under argon after drying over CaH2. 13CO (99%)
was obtained from CIL and propene, and 12CO was obtained
from MG Industries (research grade).
characterization. 9-13C: 31P NMR δ 112.8 (phosphite, J P-P
)
49 Hz, J P-C ) 172 Hz, J Pt-P ) 6714 Hz) and 6.9 (phosphine,
J P-C ) 71 Hz, J Pt-P ) 1342 Hz); 13C NMR δ 215.0 (sp2 carbon
of the acetyl-Pt, J P-C ) 71 Hz, J Pt-C ) 509 Hz), 182.8 (broad,
the coordinated 13CO to Pt). The fact that J P-C ) 71 Hz was
observed for the acyl carbon and the phosphine suggests that
these two groups are trans to each other.
Stu d ies on th e Rea ction of (SP -4-3)-[P t(CH3)(CH3CN)-
{(R,S)-BINAP HOS}][{3,5-(CF 3)2C6H3}4B] (7) w ith CO. As
in our previous report, a solution of Pt(CH3)(Cl){(R,S)-BINA-
PHOS} (0.020 mmol) in dichloromethane (3 mL) and a solution
of NaB{3,5-(CF3)2C6H3}4 (0.020 mmol) in acetonitrile (2 mL)
were mixed at 25 °C and stirred to form 7.4a After 1 h, the
solvents were removed under reduced pressure, and the
remaining solids were dissolved in 2.2 mL of CD2Cl2. This
solution was transferred to a sapphire tube, which was placed
in the NMR probe and cooled to -50 °C. It was then taken
out of the probe, charged with 22 atm of CO, and placed back
into the probe immediately. This was done so that the solution
was at 25 °C for a very brief time period and the isomerization
could be slowed considerably. At this temperature, the 31P
NMR spectra showed the presence of mostly 8a : δ 122.5
(phosphite, J P-P ) 36 Hz, J Pt-P ) 6022 Hz), 15.4 (phosphine,
J Pt-P ) 1564 Hz). There was a trace amount of 8b present,
evident by a peak at δ 148.6 (J P-P ) 40 Hz; J Pt-P could not be
read). The assignments of 8a and 8b were previously reported.4a
Warming the solution to -25 °C did not change the nature of
the species. The solution was warmed to 25 °C and was
followed by 31P NMR. Isomerization of 8a to 8b resulted in
increasing the concentration of 8b without showing any
intermediate species. 8b: δ 148.6 (phosphite, J P-P ) 40 Hz,
J Pt-P 3029 Hz), 15.0 (phosphine, J Pt-P 3265 Hz). After about 4
h, a third species, which will be assigned as 9 in the next
paragraph, appeared at δ 112.8 (phosphite) and 6.9 (phos-
phine) with J P-P ) 50 Hz. At this point, the pressure was
released. Disappearance of 8a was observed and two new sets
of peaks appeared at δ 114 and 24 and at δ 115 and 10. The
former can be assigned as the decarbonylated complex 7, but
the latter was unassignable. The concentration of both sets of
peaks increased on repeated freeze-thaw degassing cycles.
When the NMR tube is charged with CO again, the equilib-
rium between 8a and 8b is established and the cycles of events
described above can be repeated.
Alter n a tin g Cop olym er iza tion of P r op en e w ith CO
In itia ted by (SP -4-3)-[P d (COCH3)(CH3CN){(R,S)-BINA-
P HOS}][{3,5-(CF 3)2C6H3}4B] (3-I). Methylpalladium 1 was
prepared from Pd(CH3)(Cl){(R,S)-BINAPHOS} (0.020 mmol)
and NaB{3,5-(CF3)2C6H3}4 (0.020 mmol) and then transformed
into cationic acylpalladium species 3-I in CDCl3 (1.0 mL) by
treatment with CO (1 atm).4a The atmosphere was replaced
by a mixture of propene (0.5 atm) and CO (0.5 atm) and kept
for 12 h at 25 °C. Only alkyl complexes 1, 5a -I, and 5b-I were
observed at δ 143.0 and 13.1 (J P-P ) 64 Hz), δ 141.0 and 13.5
(J P-P ) 66 Hz), and δ 150.3 and 30.3 (J P-P ) 66 Hz),
respectively, by 31P NMR (see ref 4a for the full characteriza-
tion of these species). No polymeric or oligomeric products were
1
observed by H and 13C NMR. Next, 3-I (0.020 mmol) in CD2-
Cl2 (1.5 mL) was treated under pressures of propene (3 atm)
and CO (21 atm) at 25 °C. After a short time, three pairs of
peaks were observed by 31P NMR at δ 138.3 and 7.3 (J P-P
)
104 Hz), δ 138.8 and 7.0 (J P-P ) 104), and δ 139.4 and 7.8
(J P-P ) 105), which resemble the reported values of acyl
complexes 3-I (when X ) CH3CN: δ 133.8, 10.3, J P-P ) 113
Hz, in CDCl3) and 3-II (when X ) CH3CN: δ 137.0, 9.7, J P-P
) 108 Hz, in CDCl3). In addition, peaks were observed at δ
140.3 and 12.9 (J P-P ) 67 Hz), which correspond to the
reported data for alkyl complex 5a -I (δ 142.4, 13.0, J P-P ) 66
Hz, in CDCl3) and 5a -II (δ 142.0, 13.1, J P-P ) 67 Hz, in CDCl3).
A set of peaks at δ 25.2 and 131.3 (broad) was unassignable.
Ack n ow led gm en t. This work was partially sup-
ported by a Grant-in-Aid for Scientific Research on
Priority Areas (No. 283 and No. 403) from Monbusho.
Su p p or tin g In for m a tion Ava ila ble: 31P NMR spectra of
the sample in part iii of Figure 1. This material is available
free of charge via the Internet at http://pubs.acs.org.
Ch a r a cter iza tion of (SP -4-4)-[P t(13COCH3)(13CO){(R,S)-
BINAP HOS}][{3,5-(CF 3)2C6H3}4B] (9-13C). Methylplatinum
7 was prepared as mentioned above and dissolved in 2.2 mL
of CD2Cl2. In a sapphire NMR tube, the solution was charged
OM990985X