Synthesis and structure of 1,3-dienolate (CH2C(O)CH=CH2) complex of dipalladium(I) moiety: Contribution of π-olefin co-ordination of enolate to transition metal

Article abstract of DOI:10.1016/S0022-328X(98)00934-6

1,3-Dienolate dipalladium(I) complex [{μ-CH₂C(O)CH=CH₂}Pd₂(PPh₃) ₂(μ-Cl)] (2) is prepared and characterized. Complex 2 is easily protonated to yield 2-hydroxy-1,3-butadiene dipalladium(I) complex [{(μ

Full text of DOI:10.1016/S0022-328X(98)00934-6

Journal of Organometallic Chemistry 574 (1999) 142–147
Synthesis and structure of 1,3-dienolate (CH2C(O)CHꢀCH2) complex
of dipalladium(I) moiety: contribution of y-olefin co-ordination of
enolate to transition metalꢀ
Tetsuro Murahashi, Hideo Kurosawa *
Department of Applied Chemistry, Faculty of Engineering, Osaka Uni6ersity, Suita, Osaka 565-0871, Japan
Received 1 July 1998; received in revised form 3 August 1998
Abstract
1,3-Dienolate dipalladium(I) complex [{v-CH2C(O)CHꢀCH2}Pd2(PPh3)2(v-Cl)] (2) is prepared and characterized. Complex 2 is
easily protonated to yield 2-hydroxy-1,3-butadiene dipalladium(I) complex [{(v-p2:p2-CH2ꢀC(OH)CHꢀCH2}Pd2(PPh3)2(v-
Cl)][BF4] (3). On the basis of the comparative analyses on IR and NMR spectra and X-ray structure analysis, the co-ordination
mode of 1,3-dienolate on PdꢁPd is revealed to involve the resonance between C-bound and y-olefin-bound enolate structures.
© 1999 Elsevier Science S.A. All rights reserved.
Keywords: Enolate; Palladium; Dinuclear
1. Introduction
exhibited different reactivities depending on the co-or-
dination mode of the enolate moiety [2]. In palladium
enolate chemistry, all of the above three types of com-
plexes have been isolated and characterized [3,4], or
proposed as the intermediate of several catalytic pro-
cesses [5]. The authors thought another possible co-or-
dination mode, D, is of great interest, since this is
expected to bring a new entry to enolate transformation
involving the transition metal center, e.g. insertion reac-
tion of enolate into a metal–carbon bond. However, to
the best of the authors knowledge, an enolate complex
of type D is entirely unprecedented. In view of the fact
that mononuclear metal systems generally favor the
types A–C, attention has turned to a dinuclear system,
in which the adjacent metal is expected to assist gener-
ating a new bonding mode of the bridging ligands.
Also noticed was a prominent feature in the type D
enolate complex, namely the zwitterionic structure. The
zwitterionic structure in organometallic complexes has
been recognized as a key factor in changing the electron
density on the metal center, or bringing about the
higher stability of the complex compared with the
Transition metal enolate complexes have been pro-
posed as the important intermediates in several organic
transformations [1]. Previously, three types of enolate
complexes, C-bound form (A), O-bound form (B), and
oxallyl form (C) (Scheme 1) were reported with a wide
variety of early and late transition metals [1]. These
Scheme 1.
ꢀ Dedicated to the late Professor Rokuro Okawara in memory of
his lifetime guidance and encouragement in our research of
organometallic chemistry.
* Corresponding author. Tel.: +81-6-879-7392; Fax: +81-6-879-
7394.
0022-328X/99/$ - see front matter © 1999 Elsevier Science S.A. All rights reserved.
PII: S0022-328X(98)00934-6

T. Murahashi, H. Kurosawa / Journal of Organometallic Chemistry 574 (1999) 142–147
143
corresponding non-ionic complexes [6]. However, the
zwitterionic aggregate through y-bonding, which is
found in the structure of type D, has rarely been observed
in organometallic compounds. Recently, it has been
reported that the zwitterionic structure in the complex 1a
is more stable than the alternative neutral structure 1b
[7]. While the sterically unfavorable cis arrangement of
two phosphine ligands at the mononuclear Pd center
would partially contribute to destabilization of 1b, the
result implies that the zwitterionic structure is a reality
in the p2:p2-diene dipalladium system. Thus, the authors
examined if the 1,3-dienolate anion can analogously
co-ordinate on the Pd2(v-Cl)(PPh3)2 cation in a zwitteri-
onic manner.
Scheme 2.
When the 1,3-dienolate complex, 2, was treated with
one equivalent of HBF4, the protonated product 3 was
generated almost quantitatively (Eq. (3)). The 2-hy-
droxydiene complex 3 was easily deprotonated to re-
generate 2 by treating with base, such as Et3N in
CDCl3.
2. Results and discussion
(3)
v-p2:p2-Dienolate dipalladium(I) complex 2 was pre-
pared by the reaction of an equimolar mixture of Pd(II)
complex [Pd(PPh3)2Cl]2[PF6]2 and Pd(0) complex Pd2(d-
ba)3 with 2-trimethylsiloxy-1,3-butadiene in the presence
of base (Et3N) in 35% isolated yield (Eq. (1)). The dieno-
late dipalladium complex 2 was also prepared by 1,3-di-
ene ligand exchange reaction of [(v-1,3-butadiene)Pd2(P-
Ph3)2(v-Cl)][PF6] [8] followed by desilylation of 2-trimet-
hylsiloxy-1,3-butadiene co-ordinated on the PdꢁPd bond
in the presence of Et3N in 67% isolated yield (Eq. (2)).
As to the 1,3-dienolate co-ordination mode on the
PdꢁPd, there are several possible structures; C-bound
(v-p1:p2) (2-A), O-bound (v-p1:p2) (2-B), v-oxallyl (v-
p3) (2-C), and y-olefin-bound (v-p2:p2) (2-D) as shown
in Scheme 2.
IR and NMR spectroscopic data of 2, 3 and related
enolate complexes are listed in Table 1. 2-B and 2-C
can be ruled out, since no free methylene or vinyl
proton resonances were detected (see Section 4). IR
spectra of 2 showed the CꢀO stretching absorbance at
1596 cm−1, which is approximately 20–40 cm−1 lower
in energy than those of the previously reported Pd(II)
mononuclear enolate complexes [3]. These obviously
indicate that the formal CꢁO bond order in 2 is reduced
from those in the typical C-bound Pd enolate com-
plexes. 13C-NMR spectra of 2 showed a strongly
shielded carbonyl carbon resonance at l 168.9 com-
pared with those of Pd(II) complexes 4–8. As expected,
the carbonyl carbon resonance moved to the still higher
field (140.1 ppm in 3) upon protonation of 2. Since the
chemical shifts of the enolate carbons (especially Ch)
might depend on the electronic effect of the directly
attaching transition metals, little might be deduced
from these shifts. However, the values of JCH and JHH
for the h-CH2 group appear more informative. Com-
parison of these coupling constants between 2 and 4 or
6 suggests that the h-carbon of 2 bears a greater sp2
character than that of 4 and 6. Again, the correspond-
(1)
(2)

144
T. Murahashi, H. Kurosawa / Journal of Organometallic Chemistry 574 (1999) 142–147
Table 1
Relevant spectroscopic data for palladium and nickel enolate complexes
IR
NMR
Reference
w(CꢀO) (cm−1
)
JHaHb
l(CꢁO)
l(Ch) (JCH
)
l(Ck) (JCH
)
l(Cl) (JCH)
2
3
4
5
6
7
8
9
10
1596
–
5.10
1.95
–
–
168.9
140.1
204.5
220.1
207.5
220.8
181.0
182.8
181.0
52.0 (147.9)
52.7 (159.6)
30.5 (135.0)
31.3
40.5
9.85
0.8
0.8
6.48
74.4 (154.6)
73.3 (165.5)
43.9 (157.3)
44.1 (160.2)
This work
This work
[3a]
[3c]
[3a]
[3b]
[3b]
[3b]
[3b]
1624
1670
1643
1634
1682
1675
1682
—
—
—
—
—
—
—
—
—
—
—
—
—
—
10.60
–
–
–
–
ing carbon atom in 3 has a still greater sp2 character, as
judged from larger JCH and smaller JHH. The observed
carbonyl stretching absorbance, chemical shifts for car-
bonyl carbon, geminal JHH on Ch, CꢁH coupling for
ChꢁH of 2 are all in good agreement with the resonance
form between 2-A and 2-D. Akita et al. previously
reported a similar partial contribution of y-bound
structure 11-D in a metalloenolate complex (v-ketene
complex) on the basis of the lower shifted carbonyl
absorbance than the related acyl–Fe complex [9].
oxygen atoms of the bridging dienolate moiety are
disordered to make a precise discussion about the struc-
tural parameters of the dienolate ligand difficult (rela-
tive occupancy for C2ꢁC3ꢁO1/C2%ꢁC3%ꢁO1% was set as
60/40). However, as predicted by the spectroscopic
analyses, the co-ordination mode of dienolate in 2 is
revealed to be 2-A or 2-D but neither 2-B nor 2-C. The
mean dihedral angle between dienolate plane
(C2ꢁC3ꢁC4/C1ꢁC2%ꢁC3%) and dipalladium core plane
(Pd1ꢁPd2ꢁCl1) is 65° [11], which was smaller than that
of y-bound v-butadiene dipalladium complex [(v-
p2:p2-C4H6)Pd2(PPh3)Br(v-Br)] (92°) [8]. This indicates
that the dienolate co-ordination geometry in 2 is not
consistent with the full structural contribution of 2-D.
However, the bond distance between the carbonyl car-
bon and the near Pd atom (Pd1ꢁC2%, Pd2ꢁC3, 2.46(2)
˚
A) is shorter than those of the structurally determined
˚
C-bound enolate complexes (e.g. 2.685 A for 4 and
˚
2.818 A for 6) [3a], again indicating partial contribution
of y-enolate form (2-D). It is noteworthy that the
crystal structure suggests the presence of a relatively
short O···HꢁC contact between the oxygen of the dieno-
late and the hydrogen of the chloroform incorporated
during crystallization. The observed O···C distance
For determining the solid state structure of 2, X-ray
crystal structure analysis was undertaken. The ORTEP
diagram is shown in Fig. 1. The PdꢁPd bond length is
˚
(3.00(1) A for O1ꢁC43 and O1%ꢁC43) is shorter than the
˚
2.6968(6) A, which is in the range of normal PdꢁPd
mean distances of O···C involved in O···HꢁC hydrogen
bond lengths [10]. Unfortunately, the inner carbon and
bonds found from the Cambridge Database search

T. Murahashi, H. Kurosawa / Journal of Organometallic Chemistry 574 (1999) 142–147
145
˚
Fig. 1. ORTEP drawing of 2. Selected bond distances (A) and angles (°): Pd1ꢁPd2, 2.6968(6); Pd1ꢁP1, 2.258(2); Pd2ꢁP2, 2.262(2); Pd1ꢁCl1,
2.379(1); Pd2ꢁCl1, 2.392(1); Pd1ꢁPd2ꢁCl1, 55.36(4); Pd1ꢁPd2ꢁP2, 154.15(4); Pd1ꢁCl1ꢁPd2, 68.64(4); Pd2ꢁPd1ꢁP1, 153.18(4).
˚
(3.32 A) [12]. This hydrogen bonding might be derived
tions were performed under argon atmosphere using
Shlenck techniques.
from the localization of partial anionic charge on the
enolate oxygen atom associated with the structure 2-D.
4.1. Synthesis of [(v-1,3-butadiene)Pd2(PPh3)2
(v-Cl)][PF6]
3. Conclusion
[Pd(PPh3)2Cl]2[PF6]2 was generated from Pd(PPh3)2
Cl2 and AgPF6 in CH2Cl2, and used as a mixture with
two equivalents of AgC1 because of its poor solubility.
1,3-Butadiene gas was bubbled through the suspension
mixture of [Pd(PPh3)2Cl]2[PF6]2 and 2AgCl (134.2 mg,
excess) and Pd2(dba)3 (57.0 mg, 0.0551 mmol) in
CH2Cl2 at r.t.. After bubbling for 0.5 h, the reaction
mixture was filtered, and the volatile materials were
removed in vacuo. The residues were washed with
n-hexane and dried under vacuum. Recrystallization
from CH2Cl2/Et2O gave vivid-orange crystals (51.1 mg,
The authors propose in this work that when 1,3-
dienolate is co-ordinated on the PdꢁPd bond, the co-or-
dination mode is represented by a resonance form
between C-bound enolate (2-A) and y-olefin-bound
enolate (2-D). The spectroscopic and X-ray crystal
structural analyses of 2 were in agreement with this
resonance structure. The new co-ordination geometry
of enolate to transition metal (2-D) has a possibility to
bring a new entry of organometallic transformation of
enolate such as migratory insertion.
1
46% yield). H-NMR (CDCl3), l 7.7–7.5 (30H, m, Ph),
3.61 (2H, br d), 3.46 (2H, br m), 2.98 (2H, br d).
13C-NMR (CDCl3), l 134–129 (Ph), 93.41, 59.42. 31P-
NMR (CDCl3), l −111.33 (s). Anal. Calc. (found) for
C40H36Pd2ClP3F6: C, 49.43 (49.34); 3.73 (3.80).
4. Experimental
Solvents were generally freshly distilled before use:
dichloromethane from calcium hydride; n-hexane from
benzophenone ketyl. Triethylamine was distilled from
calcium hydride. 2-Trimethylsiloxy-1,3-butadiene and
HBF4·Et2O (85%) were purchased and used without
further purification. 1H-, 13C- and 31P-NMR spectra
were recorded using a JEOL GSX-270 (270 MHz) or
JEOL JSX-400 (400 MHz) spectrometer. IR spectra
were recorded using JASCO FT/IR-3. All manipula-
4.2. Synthesis of (v-1,3-dienolate)Pd2(PPh3)2(v-Cl) (2)
To a CH2Cl2 solution of [(v-1,3-butadiene)Pd2(PP-
h3)2(v-Cl)][PF6] (1.00 g, 1.03 mmol), 2-trimethylsiloxy-
1,3-butadiene (272 ml, 1.54 mmol) and Et3N (170 m1,
1.22 mmol) were added and the reaction mixture was
stirred for 1.5 h at r.t. The yellow solution was filtered

146
T. Murahashi, H. Kurosawa / Journal of Organometallic Chemistry 574 (1999) 142–147
and the filtrate was evaporated. The residue was
washed with n-hexane and resolved in CH2Cl2 and the
solution passed through silica gel column (Wakogel
C-200, 50 g) to give a yellow solution. Recrystallization
from CH2Cl2/n-hexane gave yellow crystals of 2 (577
mg, 67% yield). 1H-NMR (CD2Cl2), l 7.7–7.4 (30H, m,
Ph), 3.31 (1H, m, Hd), 3.04 (1H, br d, Hf), 2.55 (2H, br
dd, Hb, He), 2.45 (1H, m, Ha) (for numbering, see Table
1). 31P-NMR (CD2Cl2), l −106.40 (d, J=73 Hz),
−119.52 (d, J=73 Hz). 13C-NMR (CD2Cl2), l 168.9
(CꢀO), 134–129 (Ph), 74.36 (Ck), 52.01 (Ch), 43.92
(Cl). Anal. Calc. (found) for C40H35Pd2ClP2O: C, 57.06
(57.02); 4.19 (4.08).
HBF4·Et2O (13.5 ml, 0.0779 mmol) was added and the
reaction mixture was stirred for 30 min at r.t. The
yellow solution was filtered off, then evaporated and
dried in vacuo. Reprecipitation from CH2Cl2/n-hexane
solution gave orange–yellow powder of 3 (43.8 mg,
60% yield). 1H-NMR (CD2Cl2), l 7.7–7.4 (30H, m,
Ph), 3.66 (1H, br dd, Hb), 3.09 (1H, ddd, Hf), 2.93 (1H,
br ddd, He), 2.65 (1H, dd, Ha), 2.62 (1H, m, Hd).
31P-NMR (CD2Cl2), l −109.60 (d, J=75 Hz), −
112.16 (d, J=75 Hz). 13C-NMR (CD2Cl2), l 140.1
(CꢁO), 134–129 (Ph), 74.3 (Ck), 52.7 (Ch), 44.1 (Cl).
Anal. Calc. (found) for C40H35Pd2ClP2OBF4: C, 51.67
(51.42); 3.90 (4.14).
Alternatively, to a suspension mixture of [Pd(PPh3)2
Cl]2[PF6]2 and two equivalents of AgCl (277 mg, 0.145
mmol), Pd2(dba)3 (100 mg, 0.0966 mmol) was added.
Subsequently, 2-trimethylsiloxy-1,3-butadiene (51.2 ml,
0.290 mmol) and Et3N (27.0 ml, 0.193 mmol) were
added at r.t. After 7 h, the red solution was passed
through silica gel column (Wakogel C-200) to give a
yellow solution. Crystallization gave yellow crystals of
2 (57.7 mg, 35% yield).
4.4. X-ray crystallographic analysis of 2
A yellow prismatic crystal of 2 having approximate
dimensions of 0.30×0.30×0.40 mm3 was mounted
into a glass capillary. All measurements were made on
a
Rigaku AFC5R diffractometer with graphite
monochromated Mo–Kh radiation. Cell constants and
an orientation matrix for data collection corresponded
to a primitive triclinic cell with dimensions listed below.
Based on a statistical analysis of intensity distribution,
and the successful solution and refinement of the struc-
ture of 298 K to a maximum 2q value of 55.1°, the
space group was determined to be P2l/c (No. 14). A
4.3. Synthesis of [(v-p2:p2-2-hydroxy-1,3-dienolate)
Pd2(PPh3)2(v-Cl)][BF4] (3)
To a CH2Cl2 solution of 2 (65.6 mg, 0.0779 mmol),
Table 2
Atomic co-ordinates for [(v-CH2C(O)CHCH2)Pd2(PPh3)2(v-Cl)]·CHCl3
Atom
x
y
z
Atom
x
y
z
Pd(1)
Pd(2)
Cl(1)
Cl(2)
Cl(3)
Cl(4)
P(1)
0.13460(3)
0.17087(3)
0.2188(1)
0.6562(2)
0.6491(2)
0.6066(2)
0.1712(l)
0.2605(1)
0.1607
0.11221(3)
0.05171(3)
−0.06724(9)
−0.0048(2)
0.1586(2)
0.07268(2)
0.04803(2)
C(16)
C(17)
C(18)
C(19)
C(20)
C(21)
C(22)
C(23)
C(24)
C(25)
C(26)
C(27)
C(28)
C(29)
C(30)
C(31)
C(32)
C(33)
C(34)
C(35)
C(36)
C(37)
C(38)
C(39)
C(40)
C(43)
0.3572(5)
0.1390(4)
0.0433(4)
0.0160(4)
0.0824(5)
0.1768(5)
0.2060(4)
0.2352(4)
0.2440(4)
0.2265(5)
0.2021(5)
0.1910(5)
0.2073(5)
0.2625(4)
0.1758(4)
0.1736(5)
0.2567(7)
0.3428(6)
0.3458(5)
0.5403(6)
0.4471(5)
0.3852(4)
0.4173(5)
0.5121(7)
0.5704(6)
0.6771(5)
−0.2049(4)
0.3126(3)
−0.3286(4)
−0.3702(4)
0.3962(4)
0.3788(5)
−0.3385(4)
0.1841(4)
0.2652(4)
0.2791(4)
0.2138(5)
0.1341(4)
0.1193(4)
0.2633(3)
0.3044(4)
0.3852(4)
0.4253(4)
0.3859(5)
0.3049(4)
0.1152(6)
0.1431(5)
0.1250(4)
0.0781(5)
0.0490(7)
0.0661(7)
0.0529(5)
0.1554(4)
0.1561(3)
0.1481(3)
0.2035(4)
0.2680(4)
0.2769(3)
0.2219(3)
−0.01293(8)
0.5654(2)
0.6291(2)
0.7028(1)
0.08333(8)
0.02283(8)
0.2308
0.2329
0.1501(3)
0.116(1)
0.0114(2)
−0.25211(9)
0.15874(9)
0.0286
P(2)
−0.0775(3)
−0.1042(3)
−0.1805(4)
−0.2302(3)
−0.2061(3)
−0.1295(3)
0.0657(3)
0.0575(3)
0.0857(4)
0.1226(4)
0.1317(4)
0.1036(4)
0.0349(6)
0.0115(4)
0.0516(3)
0.1149(5)
0.1392(6)
0.0974(7)
0.6491(4)
O(1)
O(1%)
C(1)
C(2)
C(2%)
C(3)
C(3%)
C(4)
C(5)
C(6)
C(7)
0.1392
−0.0063
0.0570(4)
0.0470(10)
0.090(2)
0.108(1)
0.058(2)
0.1024(5)
0.1246(4)
0.1063(4)
0.0762(5)
0.0654(5)
0.0826(5)
0.1120(4)
0.3009(4)
0.3441(5)
0.4417(6)
0.4975(5)
0.4566(6)
−0.1129(4)
−0.021(1)
−0.030(1)
0.044(1)
0.033(2)
0.1192(4)
−0.3148(3)
−0.2761(4)
0.3220(4)
−0.4082(4)
−0.4477(4)
−0.4010(4)
−0.2628(4)
−0.3281(5)
−0.3349(6)
−0.2778(7)
−0.2124(6)
0.170(1)
0.158(1)
0.104(1)
0.1126(4)
−0.0024(3)
−0.0719(3)
−0.1383(3)
−0.1355(4)
−0.0675(4)
−0.0008(3)
0.1081(3)
0.0814(4)
0.1036(5)
0.1514(5)
0.1783(5)
C(8)
C(9)
C(10)
C(11)
C(12)
C(13)
C(14)
C(15)

T. Murahashi, H. Kurosawa / Journal of Organometallic Chemistry 574 (1999) 142–147
147
B (d) S-E. Bouaoud, P. Braustein, D. Gradjean, D. Matt, D.
Nobel, J. Chem. Soc. Chem. Commun. (1987) 488. (e) Y. Ito, M.
Nakatsuka, N. Kise, T. Saegusa, Tetrahedron Lett. 21 (1980)
2873. Type C (f) N. Yoshimura, S.-I. Murahashi, I. Moritani, J.
Organomet. Chem. 52 (1973) C58.
total of 5855 reflections was collected (I\3|(I)). The
linear absorption coefficient, v, for Mo–Kh radiation
was 12.66 cm−l. The data were corrected for Lorenz
and polarization effects.
[4] All three co-ordination modes were also found in the i-dicar-
bonyl anion (RC(O)CHC(O)R%)–palladium complexes. S.
Kawaguchi, in: H. Yaozeng, A. Yamamoto, B.-K. Teo (Eds.),
New Frontiers in Organometallic and Inorganic Chemistry, Sci-
ence Press, Beijing, 1984, p. 101.
Crystal data for 2·CHCl3: Pd2C41H36Cl4P2O, M=
961.29, monoclinic, space group P2l/c (No. 14), a=
˚
14.581(3),
b=15.724(3),
c=18.458(3)
A,
3
˚
i=107.33(1)°, U=4039(1) A , Z=2, Dcalc. =1.581 g
cm−3, F(000)=1920, v(Mo–Kh)=12.66 cm−l, 652
variables refined with 5855 reflections collected with
I\3|(I) to R=0.050, Rw=0.039. Atomic co-ordi-
nates are listed in Table 2.
[5] (a) J. Ahman, J.P. Wolfe, M.V. Troutman, M. Palucki, S.L.
Buchwald, J. Am. Chem. Soc. 120 (1998) 1918. (b) M. Palucki,
S.L. Buchwald, J. Am. Chem. Soc. 119 (1997) 11108. (c) B.
Hamann, J.F. Hartwig, J. Am. Chem. Soc. 119 (1997) 12382. (d)
H. Muratake, A. Hayakawa, M. Natsume, Tetrahedron Lett. 38
(1997) 7577. (e) H. Muratake, M. Natsume, Tetrahedron Lett.
38 (1997) 7581. (f) A. Satoh, Y. Kawamura, M. Miura, M.
Nomura, Angew. Chem. Int. Ed. Engl. 36 (1997) 1740. (g) M.
Sodeoka, K. Ohrai, M. Shibasaki, J. Org. Chem. 60 (1995) 2648.
(h) J. Nokami, T. Mandai, H. Watanabe, H. Ohyama, J. Tsuji,
J. Am. Chem. Soc. 111 (1989) 4126. (i) J. Tsuji, I. Minami, Acc.
Chem. Res. 20 (1987) 140. (j) Y. Ito, H. Aoyama, T. Saegusa, J.
Am. Chem. Soc. 102 (1980) 4519. (k) Y. Ito, H. Aoyama, T.
Hirao, A. Mochizuki, T. Saegusa, J. Am. Chem. Soc. 101 (1979)
496. (l) Y. Ito, T. Hirao, T. Saegusa, J. Org. Chem. 43 (1978)
1011.
Acknowledgements
Partial support of this work through Grant-in-Aid
for Scientific Research, Ministry of Education, Science
and Culture, and CREST of Japan Science and Tech-
nology Corporation is gratefully acknowledged. T.M.
acknowledges the JSPS research fellowships for young
scientists. Thanks are also due to the Analytical Center,
Faculty of Engineering, Osaka University for the use of
NMR facilities.
[6] For example, H. van der Heijden, B. Hessen, A.G. Orpen, J.
Am. Chem. Soc. 120 (1998) 1112, and references therein.
[7] T. Murahashi, H. Kurosawa, N. Kanehisa, Y. Kai, J.
Organomet. Chem. 530 (1997) 187.
[8] T. Murahashi, N. Kanehisa, Y. Kai, T. Otani, H. Kurosawa, J.
Chem. Soc. Chem. Commun. (1996) 825.
[9] M. Akita, A. Kondoh, T. Kawahara, T. Takagi, Y. Moro-oka,
Organometallics 7 (1988) 366.
References
[1] C.H. Heathcock, in: B.M. Trost (Ed.), Comprehensive Organic
Synthesis, vol. 2, Pergamon, New York, 1991, Chaps. 1.5 and
1.6.
[2] J.G. Stack, J.J. Doney, R.G. Bergman, C.H. Heathcock,
Organometallics 9 (1990) 453.
[3] Type A (a) P. Veya, C. Floriani, A. Chiesi-Villa, C. Rizzori,
Organometallics 12 (1993) 4899. (b) E.R. Burkhardt, R.G.
Bergman, C.H. Heathcock, Organometallics 9 (1990) 30. (c)
R.A. Wanat, D.B. Collum, Organometallics 5 (1986) 120. Type
[10] T. Murahashi, T. Otani, E. Mochizuki, Y. Kai, H. Kurosawa, S.
Sakaki, J. Am. Chem. Soc. 120 (1998) 4536.
[11] This value of dihedral angle reflects the degree of displacement
of carbonyl carbon (C3/C2%) from the plane formed by the other
dienolate carbons, while the mean dihedral angle between
C1ꢁC2ꢁC4/C1ꢁC3%ꢁC4 and Pd1ꢁPd2ꢁCl1 core is 95°, near to
90°.
[12] (a) G.R. Desiraju, J. Chem. Soc. Chem. Commun. (1989) 179.
(b) G.R. Desiraju, Acc. Chem. Res. 29 (1996) 441.
.
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