Reactivity of diaryloxy palladium complex with TMEDA (N,N,N′,N′-tetramethylethylenediamine) ligand toward carbon monoxide and carbon dioxide

Article abstract of DOI:10.1021/om010877m

The reactivity of the diaryloxy palladium complex toward carbon monoxide was investigated relevant to the mechanism of the palladium-catalyzed oxidative carbonylation of phenol to produce diphenyl carbonate (DPC). (TMEDA)Pd(OC₆H₄-p-t-Bu)₂ (1) reacted at high CO pressures (10-80 atm) at 100 °C to give the di(p-tert-butyl)phenyl carbonate. The yield of the carbonate increased with the increase in the CO pressure and with the addition of triphenylphosphine. The ¹³C{¹H} NMR and IR spectroscopic studies at room temperature under high CO pressure (50 atm) revealed that CO inserts into one of the Pd-0 bonds in 1. Thus, the formation of palladium phenoxide followed by carbonylation and subsequent reductive elimination is considered to be one of the possible DPC formation routes in the oxidative carbonylation of phenol; the reductive elimination is slower than the carbonylation. The reactivity of 1 with carbon dioxide was also examined relating to the DPC synthesis from carbon dioxide and phenol. The reaction of 1 with CO₂ led to the formation of a palladium carbonate complex, (TMEDA)Pd(η²-CO₃) (2), whose molecular structure was determined by X-ray crystallography.

Full text of DOI:10.1021/om010877m

1216
Organometallics 2002, 21, 1216-1220
Rea ctivity of Dia r yloxy P a lla d iu m Com p lex w ith TMEDA
(N,N,N′,N′-Tetr a m eth yleth ylen ed ia m in e) Liga n d tow a r d
Ca r bon Mon oxid e a n d Ca r bon Dioxid e
Hiroyuki Yasuda, J un-Chul Choi, Sang-Chul Lee, and Toshiyasu Sakakura*
National Institute of Advanced Industrial Science and Technology (AIST), Tsukuba Central 5,
Tsukuba 305-8565, J apan
Received October 5, 2001
The reactivity of the diaryloxy palladium complex toward carbon monoxide was investigated
relevant to the mechanism of the palladium-catalyzed oxidative carbonylation of phenol to
produce diphenyl carbonate (DPC). (TMEDA)Pd(OC6H4-p-t-Bu)2 (1) reacted at high CO
pressures (10-80 atm) at 100 °C to give the di(p-tert-butyl)phenyl carbonate. The yield of
the carbonate increased with the increase in the CO pressure and with the addition of
triphenylphosphine. The 13C{1H} NMR and IR spectroscopic studies at room temperature
under high CO pressure (50 atm) revealed that CO inserts into one of the Pd-O bonds in 1.
Thus, the formation of palladium phenoxide followed by carbonylation and subsequent
reductive elimination is considered to be one of the possible DPC formation routes in the
oxidative carbonylation of phenol; the reductive elimination is slower than the carbonylation.
The reactivity of 1 with carbon dioxide was also examined relating to the DPC synthesis
from carbon dioxide and phenol. The reaction of 1 with CO2 led to the formation of a palladium
carbonate complex, (TMEDA)Pd(η2-CO3) (2), whose molecular structure was determined by
X-ray crystallography.
In tr od u ction
Oxidative carbonylation of phenol to produce diphenyl
carbonate (DPC), which is a raw material for the
production of aromatic polycarbonates by the melt-
polymerization process, has attracted considerable at-
tention as one of the environmentally benign synthetic
routes for DPC without using toxic and corrosive phos-
gene.1 Various catalytic systems2-8 have been proposed
for the oxidative carbonylation of phenol, generally
involving palladium-based redox catalysts. However, the
catalytic performances are still unsatisfactory, and
fundamental studies on the DPC formation mechanism
are very limited (Figure 1).
F igu r e 1. Possible catalytic cycle for the oxidative carbo-
nylation of phenol.
* Corresponding author. Tel: +81-298-61-4719. Fax: +81-298-61-
4719. E-mail: t-sakakura@aist.go.jp.
(1) (a) Shaikh, A. G.; Sivaram, S. Chem. Rev. 1996, 96, 951. (b) Ono,
Y. Appl. Catal. A 1997, 155, 133. (c) Komiya, K.; Fukuoka, S.; Aminaka,
M.; Hasegawa, K.; Hachiya, H.; Okamoto, H.; Watanabe, T.; Yoneda,
H.; Fukawa I.; Dozono, T. ACS Symp. Ser. 1996, 626, 20; (d) Chem.
Br. 1994, 30, 970; (e) Eur. Chem. News 1998, 21, 29.
(2) (a) Hallgren, J . E.; Matthews, R. O. J . Organomet. Chem. 1979,
175, 135. (b) Hallgren, J . E.; Lucas, G. M. J . Organomet. Chem. 1981,
212, 135.
(3) Moiseev, I. I.; Vargaftik, M. N.; Chernysheva, T. V.; Stromnova,
T. A.; Gekhman, A. E.; Tsirkov, G. A.; Makhlina, A. M. J . Mol. Catal.
A 1996, 108, 77.
(4) Takagi, M.; Miyagi, H.; Yoneyama, T.; Ohgomori, Y. J . Mol.
Catal. A 1998, 129, L1.
One of the key steps in the catalytic cycle of the
palladium-catalyzed oxidative carbonylation of phenol
would be the carbonylation of the palladium phenoxide
complex. However, no clear evidence has yet been
obtained for carbon monoxide insertion into the Pd-O
bond in palladium aryloxides.9 For example, aryloxo-
palladium(II) hydrides [Pd(PCy3)2(H)(OAr)]‚ArOH (Ar )
Ph, C6F5) react with CO to give polynuclear palladium
carbonyls via reductive elimination of ArOH.10 For the
(5) (a) Goyal, M.; Nagahata, R.; Sugiyama, J .; Asai, M.; Ueda, M.;
Takeuchi, K. Catal. Lett. 1998, 54, 29. (b) Ishii, H.; Goyal, M.; Ueda,
M.; Takeuchi, K.; Asai, M. J . Mol. Catal. A 1999, 148, 289.
(6) (a) Vavasori, A.; Toniolo, L. J . Mol. Catal. A 1999, 139, 109. (b)
Vavasori, A.; Toniolo, L. J . Mol. Catal. A 2000, 151, 37.
(7) Yin, G.; J ia, C.; Kitamura, T.; Yamaji, T.; Fujiwara, Y. Catal.
Lett. 2000, 69, 89.
(9) It is known that carbon monoxide inserts into the metal-oxygen
bond in iridium and platinum aryloxides, see: (a) Rees, W. M.;
Churchill, M. R.; Fettinger, J . C.; Atwood, J . D. Organometallics 1985,
4, 2179. (b) Ni, J .; Kubiak, C. P. In Homogeneous Transition Metal
Catalyzed Reactions; Moser, W. R., Slocum, D. W., Eds.; Advances in
Chemistry Series; American Chemical Society: Washington, DC, 1992;
Vol. 230, p 515. (c) Dockter, D. W.; Fanwick, P. E.; Kubiak, C. P. J .
Am. Chem. Soc. 1996, 118, 4846.
(8) Song, H. Y.; Park, E. D.; Lee, J . S. J . Mol. Catal. A 2000, 154,
243.
10.1021/om010877m CCC: $22.00 © 2002 American Chemical Society
Publication on Web 02/08/2002

Reactivity of Diaryloxy Palladium Complex
Organometallics, Vol. 21, No. 6, 2002 1217
Ta ble 1. Rea ction of 1 w ith Ca r bon Mon oxid ea
dinuclear palladium aryloxides, Pd2L2(OAr)2 (L ) dmpm,
dppm; Ar ) Ph, OC6H3-2,6-Me), CO insertion predomi-
nantly occurs at the Pd-Pd bond, although the pos-
sibility of CO insertion into the Pd-O bond is also
suggested.11 Methylpalladium(II) phenoxides, L2Pd(Me)-
(OPh) (L2 ) (PMe3)2, dppe, tmeda, bpy), react with CO
to produce phenyl acetate, MeCO2Ph.12 In this reaction,
however, L2Pd(COMe)(OPh) rather than L2Pd(Me)(CO2-
Ph) is assumed to be the intermediate. Indeed, the
acylpalladium(II) aryloxide, (PEt3)2Pd(COMe)(OC6H4-
p-CN), is isolated by reacting (PEt3)2Pd(Me)(OC6H4-p-
CN) with CO.13
entry
no.
pressure of CO
(atm)
yield of carbonateb
(%)
additive
1
2
3
4
1
10
10
80
80
80
80
none
none
PPh3
none
PPh3
PPh3
PPh3
tr.
25.3
42.0
61.8
94.5
95.5
99.9
5
6c
7d
a
Reaction conditions: 1 (0.58 mmol), p-tert-butylphenol (2.30
b
mmol), additive (1.15 mmol), 24 h at 100 °C. Yield of di(p-tert-
butylphenyl) carbonate based on 1. c After 48 h. p-tert-Butylphenol
d
was not added.
In this study, we investigated the reactivity of the
diaryloxy palladium complex toward carbon monoxide
relevant to the mechanism of the palladium-catalyzed
oxidative carbonylation of phenol to produce DPC. We
present here evidence for the insertion of CO into the
Pd-O bond in the palladium aryloxide to yield the
aryloxycarbonyl palladium complex, followed by the
formation of the diaryl carbonate via reductive elimina-
tion. We also examined the reactivity of the palladium
diaryloxide with carbon dioxide relating to a possible
DPC synthesis from carbon dioxide and phenol. We
reported the analogous dimethyl carbonate synthesis
from carbon dioxide and methanol (or methanol deriva-
tives) catalyzed by tin dimethoxides.14
Table 1. The reaction with CO (10 atm) gave 25.3% of
the carbonate (entry 2). When triphenylphosphine (2
equiv) was added to the reaction system, the yield
increased to 42.0% (entry 3). The increase in the CO
pressure from 10 to 80 atm also resulted in an increase
in the yields to 61.8% in the absence of PPh3 and to
94.5% (95.5% after 48 h) in the presence of PPh3. The
absence of p-tert-butylphenol produced a similar yield
(entry 7), indicating almost no influence by the addition
of p-tert-butylphenol on the carbonate formation. Briefly,
di(p-tert-butyl)phenyl carbonate was quantitatively
formed from 1 by reacting with CO at a pressure of 80
atm at 100 °C in the presence of PPh3. The reason the
addition of PPh3 promotes the carbonate formation is
not clear, but PPh3 presumably contributes to the
stabilization of the palladium(0) complex formed by
reductive elimination of the diaryl carbonate. Another
possible explanation is that the PPh3-ligated palladium
diaryloxide such as (PPh3)2Pd(OAr)2 and/or (TMEDA)-
(PPh3)Pd(OAr)2 is produced during the reaction,16 and
CO insertion and/or subsequent reductive elimination
are accelerated because the three-coordinate palladium
diaryloxide species, which is assumed to be the inter-
mediate in both reactions,17 would form more easily
from the palladium diaryloxides with monodentate
ligands than from palladium diaryloxides with a biden-
tate ligand like TMEDA.
The efficient formation of diaryl carbonate stated
above allows us to assume that the palladium aryloxy-
carbonyl complex acts as an intermediate. Thus, the
insertion of CO into 1 was investigated by high-pressure
NMR spectroscopy. For the reaction of 1 with CO (10-
50 atm) at -30 °C in CD2Cl2, the 13C{1H} NMR spectra
of the reaction mixture were the same as the spectra of
1 except for the appearance of the signal arising from
free CO at 184.67 ppm. The 13C{1H} NMR spectrum at
50 atm is shown in Figure 2a. When the temperature
was increased to 20 °C, a signal due to the carbon of
PdCOO appeared at 185.69 ppm in 13C{1H} NMR
(Figure 2b). In addition, the apparent splittings of
signals due to aromatic carbons (110-170 ppm), NCH2
and NCH3 in TMEDA (40-70 ppm), as well as C(CH3)3
and C(CH3)3 in tert-butyl groups (30-40 ppm) were
Resu lts a n d Discu ssion
The diaryloxy palladium complex with the
TMEDA (N,N,N′,N′-tetramethylethylenediamine) ligand
(TMEDA)Pd(OC6H4-p-t-Bu)2 (1) was prepared by react-
ing palladium acetate with 2 equiv of sodium p-tert-
butylphenoxide at room temperature in the presence of
TMEDA according to the method reported by van Koten
et al.15 Recrystallization from a CH2Cl2-ether solution
gave an orange crystalline solid of 1 in 82% yield.
Elemental analysis and NMR (1H and 13C{1H}) spec-
troscopy confirmed the formation of the complex 1.
Rea ctivity w ith Ca r bon Mon oxid e. The reactivity
of 1 toward CO was investigated at 100 °C in the
presence of p-tert-butylphenol (4 equiv). The reaction
of 1 with atmospheric CO hardly proceeded, whereas 1
reacted with highly pressurized CO (10-80 atm) to
produce di(p-tert-butyl)phenyl carbonate (eq 1).
The yield of di(p-tert-butyl)phenyl carbonate based on
the palladium complex after 24 h is summarized in
(10) Bugno, C. D.; Pasquali, M.; Leoni, P.; Sabatino, P.; Braga, D.
Inorg. Chem. 1989, 28, 1390.
(11) (a) Kullberg, M. L.; Kubiak, C. P. Organometallics 1984, 3, 632.
(b) Krafft, T. E.; Hejna, C. I.; Smith, J . S. Inorg. Chem. 1990, 29, 2682.
(12) (a) Kim, Y.-J .; Osakada, K.; Takenaka, A.; Yamamoto, A. J . Am.
Chem. Soc. 1990, 112, 1096. (b) Kapteijn, G. M.; Dervisi, A.; Verhoef,
M. J .; van den Broek, M. A. F. H.; Grove, D. M.; van Koten, G. J .
Organomet. Chem. 1996, 517, 123.
(13) Komiya, S.; Akai, Y.; Tanaka, K.; Yamamoto, T.; Yamamoto,
A. Organometallics 1985, 4, 1130.
(14) (a) Choi, J .-C.; He, L.-N.; Yasuda, H.; Sakakura, T. Manuscript
in preparation. (b) Choi, J .-C.; Sakakura, T.; Sako, T. J . Am. Chem.
Soc. 1999, 121, 3793.
(15) (a) Kapteijn, G. M.; Grove, D. M.; Kooijman, H.; Smeets, W. J .
J .; Spek, A. L.; van Koten, G. Inorg. Chem. 1996, 35, 526. (b) Alsters,
P. L.; Baesjou, P. J .; J anssen, M. D.; Kooijman, H.; Sicherer-Roetman,
A.; Spek, A. L.; van Koten, G. Organometallics 1992, 11, 4124.
(16) The reaction of 1 with 2 equiv of PPh3 was done at room
temperature in an NMR tube. The resulting 31P{1H}, 1H, and 13C{1H}
NMR spectra showed the formation of several phosphine-containing
species accompanied by the partial liberation of TMEDA, suggesting
the substitution of the rather weakly coordinating TMEDA by PPh3.
(17) (a) Gillie, A.; Stille, J . K. J . Am. Chem. Soc. 1980, 102, 4933.
(b) Ozawa, F.; Ito, T.; Nakamura, Y.; Yamamoto, A. Bull. Chem. Soc.
J pn. 1981, 54, 1868. (c) Ozawa, F.; Yamamoto, A. Chem. Lett. 1981,
289.

1218 Organometallics, Vol. 21, No. 6, 2002
Yasuda et al.
elimination of CO from the aryloxycarbonyl palladium
species is, if any, very slow at room temperature (eq 2).
CO insertion into the Pd-OR bond in the palladium
alkoxides has been reported by several groups.12,18 For
the nitrogen-ligated methylpalladium methoxide,18d CO
(1 atm) first inserts into the Pd-OMe bond at -60 °C
and then into the Pd-Me bond at -25 °C. On the other
hand, the present study shows that CO insertion into
the Pd-OAr bond in the TMEDA-ligated palladium
diaryloxide requires a higher CO pressure and temper-
ature. This is consistent with the previous findings that
CO insertion preferentially takes place at the Pd-Me
bond in the methylpalladium aryloxides.12,13
If these results are taken into account, the carbonyl-
ation of palladium diphenoxide at one of the phenoxy
ligands followed by reductive elimination is considered
to be a plausible DPC formation route in the palladium-
catalyzed oxidative carbonylation of phenol. On the
other hand, the influence of a nucleophilic attack by
phenol on the carbonyl group of the phenoxycarbonyl
ligand on the DPC formation seems to be small, seeing
that the addition of phenol does not promote the diaryl
carbonate formation (Table 1). It is noteworthy that the
reductive elimination of DPC from L2Pd(CO2Ph)(OPh)
is slower than the carbonylation of L2Pd(OPh)2 since we
could observe L2Pd(CO2Ar)(OAr) at room temperature
without any subsequent reductive elimination. There-
fore, it is thought that the acceleration of reductive
elimination together with reoxidation of the palladium-
(0) complex is important in the catalytic cycle of the
oxidative carbonylation of phenol.
F igu r e 2. 13C{1H} NMR spectra of (TMEDA)Pd(OC6H4-
p-t-Bu)2 (1) in CD2Cl2 in the presence of CO (50 atm) (a) at
-30 °C and (b) at 20 °C.
Rea ctivity w ith Ca r bon Dioxid e. The direct reac-
tion of carbon dioxide with phenol is a very ideal
synthetic process for DPC. Alkyltin dimethoxides can
catalyze the analogous reaction of dimethyl carbonate
synthesis from carbon dioxide and methanol (or meth-
anol derivatives).14 Therefore, it is interesting to
investigate the CO2 insertion into the metal-oxygen
bond in diaryloxide complexes. Darensbourg et al.
have reported that [Et4N][W(CO)5OAr] (Ar ) Ph,
C6H4-m-Me) inserts CO2 into the tungsten-oxygen bond
to produce tungsten pentacarbonyl aryl carbonate,
W(CO)5OCO2Ar-, which has been characterized by
NMR (1H and 13C) and IR spectroscopies.19 Thus, we
further examined the reactivity of the diaryloxy pal-
ladium complex toward CO2. The reaction of 1 with
CO2 was attempted at room temperature and monitored
by NMR and IR spectroscopies. However, no evidence
for the CO2 insertion into the Pd-O bonds in 1 was
obtained even at 200 atm. On the other hand, when
F igu r e 3. IR spectra of (TMEDA)Pd(OC6H4-p-t-Bu)2 (1)
in CH2Cl2 at room temperature (a) in the absence of CO,
(b) in the presence of CO (50 atm), and (c) in the presence
of CO (1 atm) after CO was released from 50 to 1 atm.
observed. The result indicates the asymmetry of the
formed aryloxycarbonyl complex. In other words, the
insertion of CO occurs only at one of the Pd-O bonds
in 1 (eq 2). This is the first clear evidence for the
insertion of CO into the Pd-O bond in the palladium
aryloxide. The insertion of CO was also confirmed by
high-pressure IR spectroscopy. Figure 3a shows the
IR spectrum of 1 in CH2Cl2 in the absence of CO.
When the solution was pressurized with CO (50 atm)
at room temperature, the absorption band assignable
to the ν(CO) of the palladium aryloxycarbonyl species
appeared at 1655 cm-1 with a shoulder around 1676
cm-1 (Figure 3b). In addition, the ν(CO) band almost
remained when CO was released from 50 to 1 atm
(Figure 3c). This result clearly demonstrates that the
(18) (a) Kim, Y.-J .; Osakada, K.; Sugita, K.; Yamamoto, T.;
Yamamoto, A. Organometallics 1988, 7, 2182. (b) To´th, I.; Elsevier,
C. J . J . Chem. Soc., Chem. Commun. 1993, 529. (c) Smith, G. D.;
Hanson, B. E.; Merola, J . S.; Waller, F. J . Organometallics 1993, 12,
568. (d) Kapteijn, G. M.; Verhoef, M. J .; van den Broek, M. A. F. H.;
Grove, D. M.; van Koten, G. J . Organomet. Chem. 1995, 503, C26.
(19) (a) Darensbourg, D. J .; Sanchez, K. M.; Rheingold, A. L. J . Am.
Chem. Soc. 1987, 109, 290. (b) Darensbourg, D. J .; Sanchez, K. M.;
Reibenspies, J . H.; Rheingold, A. L. J . Am. Chem. Soc. 1989, 111, 7094.

Reactivity of Diaryloxy Palladium Complex
Organometallics, Vol. 21, No. 6, 2002 1219
Exp er im en ta l Section
Gen er a l Com m en ts. All manipulations were carried out
under a purified argon atmosphere using standard Schlenk
techniques. Solvents were purified by conventional means
and were distilled immediately prior to use. N,N,N′,N′-Tetra-
methylethylenediamine (TMEDA), palladium acetate, p-tert-
butylphenol, and triphenylphosphine were purchased from
Tokyo Kasei Co. Sodium p-tert-butylphenoxide was prepared
by reacting p-tert-butylphenol with sodium hydride. Carbon
monoxide (Takachiho Co., Toyko, purity over 99.9%, water
content less than 0.01%) and carbon dioxide (Showa Tansan
Co., Kawasaki, purity over 99.99%) were used without further
purification. The elemental analyses were carried out using
a CE-EA 1110 automatic elemental analyzer. The 1H and
13C{1H} NMR spectra were recorded on a J EOL-LA400WB
superconducting high-resolution spectrometer (400 MHz for
1H). IR spectra under high CO and CO2 pressures were
measured on a J ASCO FT/IR-5300 spectrometer using an IR
cell with zinc sulfide windows. The inner volume of the cell
was about 5 mL, and the thickness of the sample solution was
0.5 mm at the optical path. The reaction products were
analyzed by GC using a capillary column: GL Science TC-1
(15 m) on a Shimadzu GC-14A gas chromatograph equipped
with a flame ionization detector (FID) using o-terphenyl as
the internal standard. The GC-MS analysis was performed
using a Hewlett-Packard HP-5890 gas chromatograph con-
nected to a HP-5971A mass spectrometer (EI 70 eV).
Syn th esis of (TMEDA)P d (OC6H4-p-t-Bu )2 (1). (TMEDA)-
Pd(OC6H4-p-t-Bu)2 (1) was synthesized according to the lit-
erature method.15 To a Schlenk tube containing Pd(OAc)2
(1.17 g, 5.21 mmol) were added CH2Cl2 (100 mL), N,N,N′,N′-
tetramethylethylenediamine (0.624 g, 5.37 mmol), and sodium
p-tert-butylphenoxide (10.6 mmol, 0.53 M in THF solution).
After stirring for 1 h at room temperature, the reaction
mixture was fully evaporated to dryness. The crude product
was extracted with CH2Cl2, filtered through Celite, and fully
evaporated to dryness. The resulting product was repeatedly
washed with ether and hexane and dried under vacuum.
Recrystallization from a CH2Cl2-ether solution gave an orange
crystalline solid of 1 (2.23 g, 82% yield). 1H NMR (400 MHz in
CDCl3 at 25 °C): δ 1.20 (s, 18H, C(CH3)3), 2.23 (s, 4H, N-CH2),
2.31 (s, 12H, N-CH3), 6.94 (d, J ) 8.6 Hz, 4H, aromatic-H),
7.05 (d, J ) 8.6 Hz, 4H, aromatic-H). 13C{1H} NMR (100 MHz
in CDCl3 at 25 °C): δ 31.78 (C(CH3)3), 33.58 (C(CH3)3),
49.70 (N-CH3), 61.37 (N-CH2), 118.65, 125.40, 136.38, 165.10
(aromatic-C). Anal. Calcd for C26H42O2N2Pd: C, 59.93; H, 8.12;
N, 5.38. Found: C, 59.71; H, 8.06; N, 5.41.
Rea ction of 1 w ith CO. (1) Au tocla ve Rea ction . In a
stainless steel autoclave (20 mL inner volume), CO was added
to a mixture of 1 (0.58 mmol), p-tert-butylphenol (2.30 mmol),
triphenylphosphine (1.15 mmol), and THF (5 mL) at room
temperature. The autoclave was heated in an oil bath, and
the initial pressure was adjusted to a desired value (10-80
atm) at 100 °C. After stirring for 24 h and then cooling,
o-terphenyl (50 mg) was added to the reaction mixture as an
internal standard in order to determine the product yields by
GC. Products were further identified using GC-MS by the
comparison of retention times and fragmentation patterns with
authentic samples. A similar reaction of 1 with CO (1 atm)
was also done in a Schlenk tube.
(2) NMR Tu be Rea ction . In a sapphire NMR tube (10 mm
in diameter), CO (50 atm) was added to a CD2Cl2 (2.25 mL)
solution of 1 (100 mg, 0.19 mmol), and the 13C NMR spectrum
was recorded at 20 °C. Similar measurements were also carried
out at -30 °C and lower CO pressures (10-50 atm). 13C{1H}
NMR (100 MHz in CD2Cl2 at 25 °C and 50 atm of CO): δ 31.64,
31.95 (C(CH3)3), 33.92, 34.64 (C(CH3)3), 49.50, 49.97 (N-CH3),
60.53, 61.98 (N-CH2), 118.84, 122.33, 125.65, 126.18, 136.82,
147.48, 151.30, 165.66 (aromatic-C), 184.67 (free CO), 185.69
(CO).
F igu r e 4. ORTEP drawing of (TMEDA)Pd(η2-CO3) (2).
Ellipsoids represent 50% probability.
Ta ble 2. Selected Bon d Dista n ces (Å) a n d An gles
(d eg) for 2
Distances
Pd(1)-O(1)
O(1)-C(4)
2.001(4)
1.318(8)
Pd(1)-N(1)
O(2)-C(4)
2.053(6)
1.20(1)
Angles
O(1)-Pd(1)-O(1*) 65.4(3) O(1)-Pd(1)-N(1)
170.0(4)
O(1)-Pd(1)-N(1*) 104.8(2) N(1)-Pd(1)-N(1*) 84.9(4)
Pd(1)-O(1)-C(4)
O(1)-C(4)-O(2)
92.0(5)
124.5(5)
O(1)-C(4)-O(1*)
110.2(10)
the reaction mixture with CO2 (4 equiv) in an NMR
tube was left for a long time at room temperature, pale
yellow single crystals of the TMEDA-ligated palladium
carbonate complex (TMEDA)Pd(η2-CO3) (2) were formed
along with the evolution of p-tert-butylphenol. The
molecular structure of 2, as determined by X-ray
crystallography, is shown in Figure 4; selected bond
distances and angles are provided in Table 2. The
molecule lies on a 2-fold rotation axis in the crystal. The
carbonate ligand is bound to palladium in a chelating
manner, and the geometry around the palladium center
is regarded as distorted square-planar. The Pd(1)-O(1)
bond distance (2.001(4) Å) is comparable to the corre-
sponding distances in the palladium carboxylates (1.99-
2.12 Å).20 The distance of O(2)-C(4) (1.20(1) Å) is
shorter than that of O(1)-C(4) (1.318(8) Å), being
characterized by a carbon-oxygen double bond. It has
been reported that W(CO)5OCO2Ar- is readily converted
into W(CO)4(η2-CO3) in the presence of water.19 It seems
likely that the formation of 2 also proceeds through the
reaction with water and CO2.21 The reaction of 1 with
CO2 (4 equiv) in the presence of water (2 equiv)
immediately gave 2 in 97% yield, thus supporting this
assumption.
In conclusion, we have shown that diaryl carbonate
is quantitatively formed by reacting the diaryloxy
palladium complex (TMEDA)Pd(OAr)2 with carbon mon-
oxide. We have also succeeded in characterizing the
aryloxycarbonyl complex (TMEDA)Pd(CO2Ar)(OAr) as
an intermediate. In the reaction of the diaryl carbonate
formation, reductive elimination from (TMEDA)Pd(CO2-
Ar)(OAr) is slower than the carbonylation of (TMEDA)-
Pd(OAr)2.
(20) Mehrotra, R. C.; Bohra, R. Metal Carboxylates; Academic
Press: London, 1983; p 284.
(21) Ganguly, S.; Mague, J . T.; Roundhill, D. M. Inorg. Chem. 1992,
31, 3831.

1220 Organometallics, Vol. 21, No. 6, 2002
Yasuda et al.
Ta ble 3. Cr ysta llogr a p h ic Da ta for 2
(3) IR Cell Rea ction . In an IR cell, a CH2Cl2 (4.0 mL)
solution of 1 (94 mg, 0.18 mmol) was placed under an argon
atmosphere followed by the introduction of CO (50 atm). After
stirring for 6 h at room temperature, the IR spectrum was
measured. Afterward CO was released from 50 to 1 atm, and
the IR spectrum was then measured again.
Rea ction of 1 w ith CO2. (1) NMR Tu be Rea ction . In
an NMR tube (5 mm in diameter), CO2 (0.17 mmol) was
vacuum-transferred into a CDCl3 (0.5 mL) solution of 1
(22 mg, 0.042 mmol). The resulting 1H and 13C{1H} NMR
spectra recorded at room temperature were the same as the
spectra of 1, indicating that no insertion of CO2 occurs. After
the reaction mixture was left for a long time at room temper-
ature, pale yellow single crystals of (TMEDA)Pd(η2-CO3) (2)
were deposited.
formula
fw
C7H16O3N2Pd
282.64
cryst size (mm)
cryst syst
space group
a (Å)
0.20 × 0.20 × 0.30
orthorhombic
Cmc21 (No. 36)
8.438(2)
15.230(3)
8.603(2)
1105.6(4)
8
b (Å)
c (Å)
V (Å3)
Z
T (K)
λ (Å)
223
0.71069
1.866
16.77
624.00
0.029
dcalcd (g cm-3
)
µ(cm-1
F(000)
R
)
(2) IR Cell Rea ction . In an IR cell, a CH2Cl2 (4.0 mL)
solution of 1 (203 mg, 0.39 mmol) was placed under an argon
atmosphere and pressurized with CO2 (10-200 atm) at room
temperature. The IR spectra were recorded with increasing
CO2 pressure from 10 to 100 and 200 atm and after stirring
for 4-5 h at each pressure. However, no evidence for the CO2
insertion into the Pd-O bonds in 1 was obtained even at 200
atm; we did not observe the absorption band due to ν(CO) in
a
Rw
0.035
no. of variables
64
no. of observations (I > 3σ(I))
598
w ) [σ(Fo)]-2
.
a
X-r a y Cr ysta llogr a p h ic Stu d y. The data collection and
refinement parameters for 2 are summarized in Table 3. The
data were collected using a Rigaku AFC 7R diffractometer
at 223 K with graphite-monochromated Mo KR radiation
()0.710 69 Å) and the ω scan mode (2θ e 55°). Correction for
the Lorentz and polarization effects and an empirical absorp-
tion correction (Ψ scan) were applied. The full matrix least-
squares refinement was carried out by applying anisotropic
thermal factors to all the non-hydrogen atoms. The hydrogen
atoms were located by assuming an ideal geometry.
the range 1600-1800 cm-1
.
Syn th esis of (TMEDA)P d (η2-CO3) (2). (TMEDA)Pd(η2-
CO3) (2) could also be synthesized in the presence of water.
To a Schlenk tube containing 1 (78 mg, 0.15 mmol) were added
THF (8 mL), water (5.4 µL, 0.30 mmol), and CO2 (0.60 mmol).
After stirring for 1 h at room temperature, hexane (15 mL)
was added. The resulting pale yellow precipitate of 2 was
collected by filtration and dried under vacuum (41 mg, 97%
1
yield). H NMR (400 MHz in CD2Cl2 at 25 °C): δ 2.67 (s, 4H,
Su p p or tin g In for m a tion Ava ila ble: Crystallographic
data of 2. This material is available free of charge via the
Internet at http://pubs.acs.org.
N-CH2), 2.80 (s, 12H, N-CH3). 13C{1H} NMR (100 MHz in
CD2Cl2 at 25 °C): δ 51.19 (N-CH3), 61.62 (N-CH2), 167.80
(CO3). Anal. Calcd for C7H16O3N2Pd: C, 29.75; H, 5.71; N, 9.91.
Found: C, 29.77; H, 5.63; N, 9.80.
OM010877M