Synthesis and reactivity of phenoxycarbonyl palladium complex: Relevant to the mechanism of oxidative carbonylation of phenol

Article abstract of DOI:10.1016/S0022-328X(03)00696-X

Phenoxycarbonyl palladium complex was synthesized and its reactivity was investigated relevant to the mechanism of the palladium-catalyzed oxidative carbonylation of phenol to produce diphenyl carbonate (DPC). The phenoxycarbonyl palladium complex PdCl(CO₂Ph) (PPh₃)₂ (1) was synthesized by oxidative addition of phenyl chloroformate to Pd(PPh₃)₄. Complex 1 could be isolated as single crystals and characterized by X-ray crystallography. The thermolysis of 1 resulted in DPC formation, although degradation of the PPh₃ ligand to PhCl and PhCO₂Ph simultaneously occurred. PdCl₂(PPh₃)₂ was a major newly formed palladium species. An efficient DPC formation was observed for the reaction of 1 with phenyl chloroformate. On the other hand, the reaction of 1 with sodium phenoxide (one equivalent) proceeded at -20°C causing the instant formation of a new species assignable to Pd(OPh)(CO₂Ph)(PPh₃)₂ (2) as judged by NMR (¹H, ¹³C{¹H}, and ³¹P{¹H}) spectroscopy; the nucleophilic attack by phenoxide preferentially took place on the palladium center rather than on the carbonyl group. When the reaction mixture was heated, DPC was produced probably via the reductive elimination from 2. These results as well as the previous finding that diaryl carbonate is formed from palladium diaryloxide by carbonylation and subsequent reductive elimination suggest that Pd(OPh)(CO₂Ph) L₂ is the final intermediate toward DPC: the reductive elimination requires a relatively high temperature.

Full text of DOI:10.1016/S0022-328X(03)00696-X

Journal of Organometallic Chemistry 682 (2003) 66ꢃ72
/
www.elsevier.com/locate/jorganchem
Synthesis and reactivity of phenoxycarbonyl palladium complex:
relevant to the mechanism of oxidative carbonylation of phenol
Hiroyuki Yasuda, Noriko Maki, Jun-Chul Choi, Toshiyasu Sakakura *
National Institute of Advanced Industrial Science and Technology (AIST), Tsukuba Central 5, Tsukuba 305-8565, Japan
Received 6 May 2003; received in revised form 10 July 2003; accepted 15 July 2003
Abstract
Phenoxycarbonyl palladium complex was synthesized and its reactivity was investigated relevant to the mechanism of the
palladium-catalyzed oxidative carbonylation of phenol to produce diphenyl carbonate (DPC). The phenoxycarbonyl palladium
complex PdCl(CO2Ph)(PPh3)2 (1) was synthesized by oxidative addition of phenyl chloroformate to Pd(PPh3)4. Complex 1 could be
isolated as single crystals and characterized by X-ray crystallography. The thermolysis of 1 resulted in DPC formation, although
degradation of the PPh3 ligand to PhCl and PhCO2Ph simultaneously occurred. PdCl2(PPh3)2 was a major newly formed palladium
species. An efficient DPC formation was observed for the reaction of 1 with phenyl chloroformate. On the other hand, the reaction
of 1 with sodium phenoxide (one equivalent) proceeded at ꢀ20 8C causing the instant formation of a new species assignable to
/
Pd(OPh)(CO2Ph)(PPh3)2 (2) as judged by NMR (1H, 13C{1H}, and 31P{1H}) spectroscopy; the nucleophilic attack by phenoxide
preferentially took place on the palladium center rather than on the carbonyl group. When the reaction mixture was heated, DPC
was produced probably via the reductive elimination from 2. These results as well as the previous finding that diaryl carbonate is
formed from palladium diaryloxide by carbonylation and subsequent reductive elimination suggest that Pd(OPh)(CO2Ph)L2 is the
final intermediate toward DPC: the reductive elimination requires a relatively high temperature.
# 2003 Elsevier B.V. All rights reserved.
Keywords: Phenoxycarbonyl palladium complex; Oxidative carbonylation of phenol; Diphenyl carbonate
1. Introduction
formation via the reaction of palladium diaryloxide
Pd(OAr)2L2 (ArꢁC6H4-p-t-Bu; L2ꢁTMEDA) with
/
/
Diphenyl carbonate (DPC), a key material for man-
ufacturing polycarbonates by transesterification, is in-
dustrially synthesized by reacting phenol with phosgene
in the presence of bases. Oxidative carbonylation of
phenol with carbon monoxide and oxygen is an
attractive and promising method for synthesizing DPC
without using highly toxic and corrosive phosgene [1].
Various catalytic systems, generally consisting of a
palladium complex, a redox catalyst, and ammonium
halide, have been proposed for the reaction [2]. How-
ever, the catalytic efficiency is still far from the
commercially feasible level. In addition, little has been
known about the DPC formation mechanism for the
palladium-catalyzed oxidative carbonylation of phenol.
We recently confirmed the quantitative diaryl carbonate
carbon monoxide. We also characterized the intermedi-
ate aryloxycarbonyl complex Pd(OAr)(CO2Ar)L2 [3].
Therefore, the formation of palladium diphenoxide
followed by carbonylation and subsequent reductive
elimination is considered to be one of the possible DPC
formation routes (routes a and b in Scheme 1).
The alternative routes involve phenoxycarbonyl pal-
ladium complex PdX(CO2Ph)L2, which may be attacked
by phenol to produce DPC (routes c and b or route d in
Scheme 1). Indeed, it is reported that dimethyl carbon-
ate is formed in an almost quantitative yield through
PdCl(CO2Me)(PPh3)2 by reacting PdCl2(PPh3)2 with
methanol in the presence of trialkylamine and carbon
monoxide [4]. Thus, our interest in the mechanistic study
on the DPC formation led us to synthesize phenox-
ycarbonyl palladium complex as another key intermedi-
ate and investigate its reactivity. Although the
formation of late transition metal aryloxycarbonyl
* Corresponding author. Tel./fax: ꢂ81-29-861-4719.
/
E-mail address: t-sakakura@aist.go.jp (T. Sakakura).
0022-328X/03/$ - see front matter # 2003 Elsevier B.V. All rights reserved.
doi:10.1016/S0022-328X(03)00696-X

H. Yasuda et al. / Journal of Organometallic Chemistry 682 (2003) 66ꢃ
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2. Results and discussion
2.1. Synthesis and structure
The reaction of Pd(PPh3)4 with one equivalent of
phenyl chloroformate at room temperature in toluene
afforded the phenoxycarbonyl palladium complex
PdCl(CO2Ph)(PPh3)2 (1) in 98% yield as a pale yellow
solid (Eq. (1)). Otsuka et al. have previously attempted
the same reaction at 80 8C to give PdCl(PPh3)3 [14]. In
the present study, the lower reaction temperature
enabled the phenoxycarbonyl complex to be isolated.
r:t:
Pd(PPh3)4 ꢂClCO2Ph 0 PdCl(CO2Ph)(PPh3)2
Scheme 1.
(1)
toluene
1
1
The structure of 1 was elucidated by the H-NMR
signals of the phenoxy group at d 5.4ꢃ
those of the phenyl groups in PPh3 at d 7.3ꢃ
the 13C{1H}-NMR signal of the carbonyl group at d
/
6.8 ppm and
complexes is described in the literature [3,5ꢃ13], the
/
/7.8 ppm,
number of the complexes that are isolated and well-
characterized has been very limited. For example, it has
been reported that Ir(OPh)(CO)(PPh3)2 reacts with CO
to form Ir(CO2Ph)(CO)2(PPh3)2 which is characterized
only by IR spectroscopy [5,6]. Pd(pnp)(CO2Ph)Cl
182.2 ppm, the IR absorption of n(CO) at 1686 cmꢀ1
and its elemental analysis. The 31P{1H}-NMR spectrum
showed a singlet at d 18.33 ppm, suggesting a trans
configuration in 1. It is probable that trans-
PdCl(CO2Ph)(PPh3)2 was yielded via isomerization of
cis-PdCl(CO2Ph)(PPh3)2 formed by the oxidative addi-
,
(pnpꢁ/2,6-bis(diphenylphosphinomethyl)pyridine)
is
isolated by the reaction of Pd(pnp)Cl2 with sodium
phenoxide and carbon monoxide [7]. Pt(CO2Ph)2(dppf)
1
tion of phenyl chloroformate to Pd(PPh3)4. In the H-
NMR, the ortho protons in the phenoxy group are
significantly shifted up-field compared with phenyl
chloroformate. No such up-field resonance position is
observed for the ortho protons of the phenyl group in
trans-PdCl(Ph)(PPh3)2 [16]. This characteristic up-field
shift may be due to the influence of the ring current in
the carbonyl group.
(dppfꢁ1,1?-bis(diphenylphosphino)ferrocene) is also
/
isolated in a similar reaction using PtCl2(dppf) [10].
However, the structural information of these complexes
is limited to the elemental analysis and IR spectroscopy.
On the other hand, Kubiak et al. have isolated the
aryloxycarbonyl
phos)(CO2Ar)][PF6] (triphosꢁ
noethyl)phenyl phosphine)
platinum
complexes
bis(2-diphenylphosphi-
by reacting
[Pt(tri-
/
A single crystal of 1 was obtained from a THFꢃ
/
hexane solution at 4 8C. The molecular structure of 1,
as determined by X-ray crystallography, is shown in Fig.
1; selected bond distances and angles are provided in
[Pt(triphos)(OAr)][PF6] with CO and elucidated the first
X-ray structure of an aryloxycarbonyl complex, [Pt(tri-
phos)(CO2C6H4-p-Me)][PF6] [12,13].
Otsuka et al. have previously attempted the synthesis
of PdCl(CO2Ph)(PPh3)2 by oxidative addition of phenyl
chloroformate to Pd(PPh3)4 and concluded that the
complex is unable to be isolated because decarbonyla-
tion readily takes place [14]. Toniolo et al. have reported
although alkoxycarbonyl palladium complexes are
synthesized by reacting PdCl2L2 (Lꢁ
diphenylphosphinoethane) with alcohols under high CO
pressures (10ꢃ50 atm) in the presence of triethylamine,
/
PPh3, L2ꢁ1,2-
/
/
aryloxycarbonyl complexes cannot be obtained by the
similar reaction with phenols [15]. In this work, we
succeeded in isolating the phenoxycarbonyl palladium
complex PdCl(CO2Ph)(PPh3)2 and confirmed the DPC
formation via the reaction of the complex with phenox-
ide or even via simple thermolysis. Here, we report the
synthesis, X-ray crystal structure, and reactivity of
PdCl(CO2Ph)(PPh3)2.
Fig. 1. ORTEP drawing of PdCl(CO2Ph)(PPh3)2 (1). Ellipsoids repre-
sent 30% probability.

68
H. Yasuda et al. / Journal of Organometallic Chemistry 682 (2003) 66ꢃ72
/
Table 1
109.3(3)8 in trans-PdCl(CO2Me)(PPh3)2 and trans-
PdCl(CO2Me)(Ph2Ppy)2, respectively.
˚
Selected bond distances (A) and angles (8) for 1
Bond distances
2.2. Thermolysis
Pd(1)ꢃ
Pd(1)ꢃ
C(1)ꢃ
O(2)ꢃ
/
C(1)
P(1)
1.961(3)
2.3263(8)
1.191(4)
1.409(4)
Pd(1)ꢃ
Pd(1)ꢃ
C(1)ꢃ
/
Cl(1)
P(2)
2.3883(9)
2.3241(8)
1.388(4)
/
/
/
O(1)
/
O(2)
The reactivity of 1 was investigated relevant to the
mechanism of the palladium-catalyzed oxidative carbo-
nylation of phenol. We first examined the thermal
decomposition behavior. When 1 was heated to 100 8C
in toluene, DPC was produced in 30% yield based on
PhO present (Eq. (2)). The 31P{1H}-NMR spectrum of
the resulting mixture showed that 1 was completely
consumed whereas several phosphine-containing species
including 32% based on palladium of PdCl2(PPh3)2 were
formed. Although precise mechanistic discussion is
premature, three possible routes for the DPC formation
are (a) disproportionation of 1 followed by decarbony-
lation and reductive elimination, (b) decarbonylation of
1 followed by transfer of phenoxide to another 1, and (c)
bimetallic reductive elimination of DPC between palla-
dium phenoxide species and 1.
/
C(2)
Bond angles
Cl(1)ꢃPd(1)ꢃ
Cl(1)ꢃPd(1)ꢃ
P(1)ꢃPd(1)ꢃ
Pd(1)ꢃC(1)ꢃ
O(1)ꢃC(1)ꢃO(2)
/
/
P(1)
90.76(3)
Cl(1)ꢃ
Pd(1)ꢃ
Pd(1)ꢃ
Pd(1)ꢃC(1)ꢃ
C(1)ꢃO(2)ꢃC(2)
/
Pd(1)ꢃ
/
P(2)
87.89(3)
178.65(3)
90.34(9)
109.6(2)
118.7(3)
/
/C(1)
177.18(10) P(1)ꢃ
/
/P(2)
/
/
C(1)
91.01(9)
129.6(3)
120.8(3)
P(2)ꢃ
/
/C(1)
/
/
O(1)
/
/O(2)
/
/
/
/
Table 1. This is the first X-ray structure of a neutral
aryloxycarbonyl complex. The complex has a trans
configuration as expected from the 31P{1H}-NMR,
and an approximate square-planar coordination geome-
try around the palladium center: The two trans angles
are Cl(1)ꢃ
P(2) of 178.65(3)8; the cis angles range from P(1)ꢃ
Pd(1)ꢃC(1) of 91.01(9)8 to Cl(1)ꢃPd(1)ꢃP(2) of
/
Pd(1)ꢃ
/
C(1) of 177.18(10)8 and P(1)ꢃ
/
Pd(1)ꢃ
/
/
/
/
/
87.89(3)8. Another feature of the molecular geometry
is that the carbonyl plane in the phenoxycarbonyl ligand
is nearly perpendicular to the palladium coordination
plane, whereas the phenyl ring is rather parallel to the
ð2Þ
coordination plane. The Pd(1)ꢃ
/
C(1) and Pd(1)ꢃCl(1)
/
In the course of the thermolysis, chlorobenzene (7%/
Pd), phenyl benzoate (18%/Pd), biphenyl (2%/Pd), and
phenol (17%/Pd) were produced along with DPC. On
the other hand, the thermolysis of PdCl(CO2Ph)(P(p-
tolyl)3)2 (3) gave p-chlorotoluene, phenyl 4-methyl-
benzoate, 4,4?-dimethylbiphenyl, and phenol, in addi-
tion to DPC. Hence, the formation of chlorobenzene,
phenyl benzoate, and biphenyl in Eq. (2) is assignable to
˚
bond distances in 1 are 1.961(3) and 2.3883(9) A
respectively, almost identical to the values of 1.99(2)
˚
and 2.407(4) A for the methoxycarbonyl analogue trans-
PdCl(CO2Me)(PPh3)2 [17] and those of 1.970(5) and
˚
2.4035(15)
(Ph2Ppyꢁ
age distance of 2.3252(8) A for the Pd(1)ꢃ
Pd(1)ꢃP(2) bonds in 1 is also comparable with the
average Pdꢃ
PdCl(CO2Me)(PPh3)2 and that of 2.332(1) A for trans-
PdCl(CO2Me)(Ph2Ppy)2. The C(1)ꢃO(1) bond distance
of 1.191(4) A is typical for carbonꢃoxygen double
bonds, but fairly longer than the carbonyl distance of
A
for
trans-PdCl(CO2Me)(Ph2Ppy)2
/
2-pyridyldiphenylphosphine) [18]. The aver-
˚
/P(1) and
/
the cleavage of the PꢃC bond in the PPh3 ligand in 1
/
˚
P distance of 2.335(4) A for trans-
/
[24]. When the thermolysis was performed in the
presence of PPh3 (four equivalents), the DPC yield
increased to 44% although the formation of chloroben-
zene, phenyl benzoate, and biphenyl was observed
again. PPh3 possibly stabilizes the resulting unsaturated
palladium(0) complexes. On the contrary, the thermo-
lysis of 1 in the presence of CO (1 atm) produced DPC in
31% yield based on PhO present. Thus, the influence of
CO on the DPC formation was small.
The reactivity of 1 toward electrophiles was also
studied. When 1 was heated in the presence of methyl
iodide (one equivalent), phenyl acetate and anisole were
produced along with DPC in 58 and 4% yields,
respectively (Eq. (3)). The formation of anisole suggests
that the palladium phenoxide species is generated during
the thermolysis [25]. On the other hand, an efficient
DPC formation was observed upon heating of 1 with
one equivalent of phenyl chloroformate (Eq. (4)).
During the reaction, PdCl2(PPh3)2 was the only ob-
servable palladium species as judged by 31P{1H}-NMR.
˚
/
˚
/
˚
1.08(1) A seen for the only structurally characterized
aryloxycarbonyl complex [Pt(triphos)(CO2C6H4-p-
Me)][PF6] [12], in which the artificial shortening of the
bond length is noted. On the other hand, the C(1)ꢃ
˚
bond distance is 1.388(4) A, approximately 0.04 and
/O(2)
˚
˚
0.11 A longer than the average distance of 1.35 A for the
corresponding CꢃO bonds in methoxycarbonyl palla-
dium complexes [17ꢃ
/
/
23] and the corresponding Cꢃ
/O
˚
distance of 1.28(1)
A
in [Pt(triphos)(CO2C6H4-p-
Me)][PF6], respectively. The Pd(1)ꢃ
109.6(2)8 is smaller than the Pd(1)ꢃ
O(1)ꢃC(1)ꢃO(2) angles of 129.6(3)8 and 120.8(5)8,
respectively. Similar tendency is observed for the Ptꢃ
CꢃOAr angle of 110.2(6)8 in [Pt(triphos)(CO2C6H4-p-
Me)][PF6] and the PdꢃCꢃOMe angles of 111(1)8 and
/
C(1)ꢃ/O(2) angle of
/
C(1)ꢃ
/
O(1) and
/
/
/
/
/
/

H. Yasuda et al. / Journal of Organometallic Chemistry 682 (2003) 66ꢃ
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69
The yield of PdCl2(PPh3)2 was nearly quantitative based
on palladium.
ð3Þ
ð4Þ
ð6Þ
On the other hand, when the reaction using three
equivalents of sodium phenoxide was conducted under
otherwise identical conditions DPC was afforded only in
40% yield, which was rather lower than the yield with
one equivalent of sodium phenoxide. Therefore, the
influence of a nucleophilic attack by phenoxide to the
carbonyl group of the phenoxycarbonyl ligand in 2 on
the DPC formation seems small. These results suggest
that in the oxidative carbonylation of phenol DPC is
formed
by
the
reductive
elimination
from
Pd(OPh)(CO2Ph)L2 rather than the nucleophilic attack
of phenoxide to Pd-CO2Ph moiety. This is consistent
with the previous finding that DPC is formed from
palladium diphenoxide followed by carbonylation and
reductive elimination [3].
2.3. Reaction with phenoxide
The reactivity of 1 toward phenol (four equivalents)
was examined in the presence of triethylamine (four
equivalents) in toluene. However, no reaction proceeded
at room temperature judged by 31P{1H}- and H-NMR
In conclusion, we have synthesized the phenoxycar-
bonyl palladium complex 1 and elucidated the X-ray
crystal structure. DPC was formed by the simple
thermolysis of 1, although the yield was not high due
to the simultaneous occurrence of degradation of the
PPh3 ligand to chlorobenzene and phenyl benzoate. The
reaction of 1 with sodium phenoxide at a low tempera-
ture resulted in the formation of a species assignable to
2. Thus, the nucleophilic attack by phenoxide preferen-
tially takes place on the palladium center rather than on
the carbonyl group. On the other hand, a higher DPC
yield than the simple thermolysis was given for the
reaction of 1 with sodium phenoxide. DPC is considered
to be produced via the reductive elimination from 2.
Because the yield of DPC was not improved by the
presence of excess sodium phenoxide, the nucleophilic
attack by phenoxide to the carbonyl group would not be
involved.
1
spectroscopy. When the temperature was raised to
100 8C, DPC was formed in 28%, a similar yield
obtained under simple thermolysis of 1. In other words,
the addition of phenol and amine did not promote the
DPC formation.
The reaction of 1 with sodium phenoxide (one
equivalent) was performed in THF-d8 at ꢀ20 8C. The
/
1H-, 13C{1H}-, and 31P{1H}-NMR data were consistent
with the formation of 2 (Eq. (5)). It is noteworthy that
DPC was not formed at this stage as judged by 13C{1H}-
NMR. Thus, the nucleophilic attack by phenoxide
preferentially takes place on the palladium center rather
than on the carbonyl group in 1, resulting in the
formation of 2. Moreover, the reductive elimination of
DPC from 2 is, if any, very slow at ꢀ20 8C. We
/
attempted the isolation of 2, but did not succeed due
to its instability. When the reaction mixture was heated
to 100 8C, DPC was produced in 56% yield (Eq. (6)).
The DPC yield was higher than the yield for the simple
thermolysis of 1, but still not very high due to
simultaneous occurrence of the decomposition of the
PPh3 ligand as mentioned earlier.
3. Experimental
All manipulations were carried out under a purified
Ar atmosphere using standard Schlenk and glovebox
techniques. Solvents were purified by conventional
means and were distilled immediately prior to use.
Phenyl chloroformate, methyl iodide, triphenylpho-
sphine, and tri-p-tolylphosphine were purchased from
Tokyo Kasei Co. Sodium phenoxide was prepared by
reacting phenol with sodium hydride. Pd(PPh3)4 and
Pd(P(p-tolyl)3)4 were prepared according to the litera-
ture [26]. The 1H-, 13C{1H}-, and 31P{1H}-NMR spectra
ð5Þ

70
H. Yasuda et al. / Journal of Organometallic Chemistry 682 (2003) 66ꢃ72
/
were recorded on a JEOL-LA400WB superconducting
high-resolution spectrometer (400 MHz for 1H).
31P{1H}-NMR spectra were referenced to external 85%
phosphoric acid. IR spectra were recorded on a Shi-
madzu FTIR-8500 spectrometer. The elemental analyses
were carried out using a CE-EA 1110 automatic
elemental analyzer. The reaction products were analyzed
by GC using a capillary column: J&W Scientific DB-1
(60 m) on a Shimadzu GC-14A gas chromatograph
equipped with a flame ionization detector (FID) using
o-terphenyl as the internal standard. The GCMS
analysis was performed using a Shimadzu GC-17A gas
chromatograph connected to a QP-5000 mass spectro-
meter (EI 70 eV). The GC and GCMS analyses of the
product solutions containing 1 were conducted after the
solutions were mixed with excess 30% H2O2 and stirred
3.2. Thermolysis
A solution of 1 (50 mg, 0.063 mmol) in toluene (5 ml)
was heated to 100 8C and stirred at the same tempera-
ture for 2 h. The solution color quickly changed from
yellow to dark brown. After cooling, o-terphenyl (50
mg) was added to the reaction mixture as the internal
standard for GC analysis. Then excess 30% H2O2 was
added to the product solution as mentioned above. The
yield of DPC was 30% on 0.5 Pd by GC. The products
were further identified using GCMS by the comparison
of the retention time and fragmentation pattern with
authentic samples. The thermolysis was also followed by
31P{1H}-NMR. To an NMR tube (5 mm in diameter)
containing 1 (20 mg, 0.025 mmol) was added toluene-d8
(0.5 ml). The NMR tube was sealed under vacuum, and
then heated at 100 8C for 24 h. After cooling, the
31P{1H}-NMR spectrum was recorded at r.t. The
31P{1H}-NMR showed that 1 was completely converted
whereas PdCl2(PPh3)2 was a major palladium species
among several phosphine-containing species. The yield
of PdCl2(PPh3)2 was determined as follows. Because the
solubility of (PPh3)2PdCl2 in toluene is poor, the toluene
was removed under vacuum after the thermolysis and
the products were dissolved in CDCl3. Then, the yield
was measured by 31P-NMR using PMe(CH2CH2CF3)2
sealed in a glass tube as the external standard. The yield
of PdCl2(PPh3)2 thus estimated was 32% based on Pd.
The thermolysis of 1 in the presence of four equivalents
of PPh3 was carried out analogously. The yield of DPC
was 44% on 0.5 Pd. The thermolysis of 1 in the presence
of CO (1 atm) was also carried out analogously. The
yield of DPC was 31% on 0.5 Pd.
for 2ꢃ3 h at room temperature (r.t.): The injection of a
/
solution containing 1 alone in a GC or GCMS instru-
ment brought about the production of DPC resulting
from the decomposition of 1 in the injector port
(200 8C). When excess 30% H2O2 was added to the
solution of 1 followed by stirring for 2 h at room
temperature, 1 was decomposed and no DPC formation
was observed upon injection in the instrument.
3.1. Synthesis of PdCl(CO2Ph)(PPh3)2 (1)
To a solution of Pd(PPh3)4 (1.07 g, 0.93 mmol) in
toluene (60 ml) was added phenyl chloroformate (0.12
ml, 0.93 mmol). After stirring the reaction mixture for 1
h at room temperature, the solvent was evaporated. The
resulting product was repeatedly washed with ether and
dried under vacuum to give a pale yellow solid (0.72 g,
3.3. Reaction with methyl iodide
98% yield). Recrystallization from a THFꢃhexane
/
To a toluene (5 ml) solution of 1 (50 mg, 0.063 mmol)
was added one equivalent of methyl iodide (4.3 ml, 0.069
mmol) at room temperature. The reaction mixture was
then heated to 100 8C and stirred for 2 h. The yields of
phenyl acetate, anisole, and DPC determined by GC
were 58% (on Pd), 4% (on Pd), and 9% (on 0.5 Pd),
respectively.
1
solution at 4 8C gave yellow single crystals of 1. H-
NMR (400 MHz, THF-d8, 25 8C, ppm): d 5.47 (m, 2H,
ortho-H, CO2Ph), 6.76 (m, 3H, meta- and para-H,
CO2Ph), 7.32ꢃ
7.80 (m, 30H, PPh3). 13C{1H}-NMR
/
(100.4 MHz, THF-d8, 25 8C, ppm): d 121.96, 124.27,
128.17, 154.04 (CO2Ph), 128.96, 131.05, 132.74, 135.87
(PPh3), 182.18 (CO). 31P{1H}-NMR (161.7 MHz, THF-
d8, 25 8C, ppm): d 18.33 (s). IR (KBr, cmꢀ1): 1686
(nCO). Anal. Calc.: C, 65.58; H, 4.48; Cl, 4.50. Found: C,
64.94; H, 4.67; Cl, 4.92%.
PdCl(CO2Ph)(P(p-tolyl)3)2 (3) was synthesized in 82%
yield as yellow crystalline solids as described for the
synthesis of 1, but using Pd(P(p-tolyl)3)4 as a starting
material. Complex 3 had a better solubility in ether than
1. 1H-NMR (400 MHz, THF-d8, 25 8C, ppm): d 2.33 (s,
18H, Me), 5.41 (m, 2H, ortho-H, CO2Ph), 6.75 (m, 3H,
meta- and para-H, CO2Ph), 7.14 (d, 12H, meta-H, p-
tolyl), 7.63 (m, 12H, ortho-H, p-tolyl). 31P{1H}-NMR
(161.7 MHz, THF-d8, 25 8C, ppm): d 14.68 (s).
3.4. Reaction with phenyl chloroformate
To a toluene (5 ml) solution of 1 (50 mg, 0.063 mmol)
was added one equivalent of phenyl chloroformate (7.9
ml, 0.063 mmol). The reaction mixture was heated at
100 8C for 2 h. The yield of DPC on Pd was 73% based
on GC. The reaction with phenyl chloroformate was
also followed by 31P{1H}-NMR. To an NMR tube (5
mm in diameter) containing 1 (20 mg, 0.025 mmol) were
added toluene-d8 (0.5 ml) and phenyl chloroformate (3.1
ml, 0.025 mmol). The mixture was heated at 100 8C for 2
h. The 31P{1H}-NMR at room temperature revealed

H. Yasuda et al. / Journal of Organometallic Chemistry 682 (2003) 66ꢃ
/
72
71
that PdCl2(PPh3)2 was the only formed palladium
species. The yield of PdCl2(PPh3)2 estimated in a similar
manner as the thermolysis of 1 was nearly quantitative
based on Pd.
Table 2
Crystallographic data for 1
Formula
C43H35P2O2ClPd
Formula weight
Crystal system
Space group
787.55
Monoclinic
P21/n (No. 14)
9.449(6)
32.637(7)
12.426(5)
100.01(4)
3773(2)
4
3.5. Reaction with phenol and triethylamine
˚
a (A)
˚
b (A)
In an NMR tube (5 mm in diameter), four equivalents
of phenol (9.4 mg, 0.1 mmol) and four equivalents of
triethylamine (14 ml, 0.10 mmol) were added to a
toluene-d8 (0.5 ml) solution of 1 (20 mg, 0.025 mmol).
The 31P{1H}- and 1H-NMR spectra showed that no
reaction proceeded at room temperature. The mixture
was then heated at 100 8C for 2 h. The yield of DPC on
0.5 Pd was 28% based on GC using o-terphenyl (20 mg)
as the internal standard. The same yield was obtained
for the reaction in a Schlenk tube.
˚
c (A)
b (8)
3
V (A )
˚
Z
m (Moꢃ
/
Ka) (cmꢀ1
)
6.83
9355
Number of measured reflections
Number of unique reflections
Rint
9065
0.016
Number of observations (I ꢀ
/
2s(I))
7170
442
Number of variables
Ra
0.044
0.062
b
Rw
a
3.6. Reaction with sodium phenoxide
Rꢁ
Rwꢁ{Sw(½Fo½ꢀ
/
S½½Fo½ꢀ
/
½Fc½½/S½Fo½.
b
/
/
½Fc½)2/SwF2o}1/2
.
In an NMR tube (5 mm in diameter), THF-d8 (0.5 ml)
was vacuum-transferred into a mixture of 1 (20 mg,
0.025 mmol) and one equivalent of sodium phenoxide
(2.9 mg, 0.025 mmol). The NMR tube was sealed under
vacuum with the mixture frozen. When the mixture was
Rigaku AFC 7R diffractometer at 183 K using graphite-
˚
0.710 69 A) and
monochromated Moꢃ
/
Ka radiation (ꢁ
/
the v scan mode (2u 5
/
558). Correction for the Lorentz
and polarization effects and an empirical absorption
correction (C scan) were applied. The full matrix least-
squares refinement was carried out by applying aniso-
tropic thermal factors to all the non-hydrogen atoms.
The hydrogen atoms were located by assuming an ideal
geometry.
thawed at ꢀ
changed from yellow to orange. The 31P{1H}-NMR
spectrum measured at ꢀ20 8C showed the instant
/
20 8C, the color of the solution instantly
/
disappearance of 1 with concurrent growth of a new
singlet at d 9.50 ppm together with a very weak and
broad signal around d 16ꢃ
20 ppm. The 1H- and
/
13C{1H}-NMR spectra revealed the formation of 2. In
1
the H-NMR spectrum, another phenyl group, which
4. Supplementary material
may arise from the phosphine ligands with d 16ꢃ
in 31P{1H}-NMR, was observed at d 7.0ꢃ
7.2 ppm. 2:
1H-NMR (400 MHz, THF-d8, ꢀ
20 8C, ppm): d 5.27 (m,
2H, ortho-H, CO2Ph), 5.74 (t, 1H, para-H, OPh), 5.93
(d, 2H, ortho-H, OPh), 6.16 (t, 2H, meta-H, OPh), 6.76
/
20 ppm
Crystallographic data for the structural analysis of
complex 1 have been deposited with the Cambridge
Crystallographic Data Centre, CCDC no. 200708.
Copies of this information may be obtained free of
charge from The Director, CCDC, 12 Union Road,
/
/
(m, 3H, meta- and para-H, CO2Ph), 7.29ꢃ
/
7.73 (m, 30H,
20 8C,
PPh3). 13C{1H}-NMR (100.4 MHz, THF-d8, ꢀ
/
Cambridge CB2 1EZ, UK (Fax: ꢂ44-1223-336033; e-
/
mail: deposit@ccdc.cam.ac.uk or www: http://
www.ccdc.cam.ac.uk).
ppm): d 153.67 (ipso-C CO2Ph), 167.88 (ipso-C OPh)
181.74 (CO). The other 13C{1H}-NMR peaks due to 2
were not assignable because of contamination of uni-
dentified species. 31P{1H}-NMR (161.7 MHz, THF-d8,
ꢀ
/
20 8C, ppm): d 9.50 (s). The reaction mixture was then
References
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The reaction of 1 (20 mg, 0.025 mmol) with three
equivalents of sodium phenoxide (9.2 mg, 0.079 mmol)
was carried out analogously. The yield of DPC was 40%
on 0.5 Pd.
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