A new synthesis for thermolabile low-valent palladium complexes by electron transfer reactions from nickel(0) to palladium(II) compounds

Article abstract of DOI:10.1016/j.jorganchem.2006.08.015

The nickel(0) complex [Ni(bpy)(cod)] (bpy: 2,2′-bipyridine, cod: cycloocta-1,5-diene) was used as a mild reducing reagent for the synthesis of the extremely reactive low-valent palladium complexes [Pd₂X₂(cod)₂] (1: X = Cl, 2: X = Br), Pd(cod)₂ (3) and Pd(norbornene)₃ (4). The X-ray analysis of 1 showed that the two [Pd(cod)(Cl)] moieties are only connected by a short Pd(I)-Pd(I) bond (bond length: 2.5379(4) ?) with the chloride ions as monodentate ligands. The X-ray structure of 3 which is also known to be an extremely reactive compound could be determined by X-ray diffraction. As expected, the Pd(0) centre is surrounded by the two cod ligands to form a PdC₄ tetrahedron with typical Pd-C bond lengths. The crystal structure of 3 shows it to be very similar to the closely related complexes M(cod)₂ (M: Ni, Pt). The X-ray structure of 4 displays that the Pd(0) centre is in a trigonal planar environment of the three olefin groups. According to ¹H NMR measurements the complexes have the same structure in solution as found in the solid state.

Full text of DOI:10.1016/j.jorganchem.2006.08.015

Journal of Organometallic Chemistry 691 (2006) 4868–4873
www.elsevier.com/locate/jorganchem
A new synthesis for thermolabile low-valent palladium complexes
by electron transfer reactions from nickel(0)
to palladium(II) compounds
*
Matthias Schwalbe, Dirk Walther , Heike Schreer, Jens Langer, Helmar Gorls
¨
Institut fu¨r Anorganische und Analytische Chemie der Friedrich-Schiller-Universita¨t Jena, August-Bebel-Straße 2, 07743 Jena, Germany
Received 23 March 2006; received in revised form 2 August 2006; accepted 9 August 2006
Available online 18 August 2006
Abstract
The nickel(0) complex [Ni(bpy)(cod)] (bpy: 2,20-bipyridine, cod: cycloocta-1,5-diene) was used as a mild reducing reagent for the syn-
thesis of the extremely reactive low-valent palladium complexes [Pd2X2(cod)2] (1: X = Cl, 2: X = Br), Pd(cod)2 (3) and Pd(norbornene)3
(4). The X-ray analysis of 1 showed that the two [Pd(cod)(Cl)] moieties are only connected by a short Pd(I)–Pd(I) bond (bond length:
˚
2.5379(4) A) with the chloride ions as monodentate ligands. The X-ray structure of 3 which is also known to be an extremely reactive
compound could be determined by X-ray diffraction. As expected, the Pd(0) centre is surrounded by the two cod ligands to form a PdC4
tetrahedron with typical Pd–C bond lengths. The crystal structure of 3 shows it to be very similar to the closely related complexes
M(cod)2 (M: Ni, Pt). The X-ray structure of 4 displays that the Pd(0) centre is in a trigonal planar environment of the three olefin groups.
1
According to H NMR measurements the complexes have the same structure in solution as found in the solid state.
ꢀ 2006 Elsevier B.V. All rights reserved.
Keywords: 1,5-Cyclooctadiene; Norbornene; Palladium(I) complexes; Palladium(0) complexes; Redox reactions
1. Introduction
of the thermolabile and extremely reactive low-valent pal-
ladium(I) and palladium(0) complexes [Pd2X2(cod)2] (1:
X = Cl, 2: X = Br), Pd(cod)2 (3) and Pd(norbornene)3 (4)
by using [Ni(bpy)(cod)] as reducing reagent. Furthermore,
we describe the X-ray structures of 1, 3, and 4.
Recently we have found that [Ni(bpy)(cod)] reduced
Pt(cod)Cl2 to form Pt(cod)2 which could be isolated in good
yields [1]. From this finding the question arises whether this
type of electron transfer reaction may have a more general
preparative value for the formation of low-valent transition
metal complexes which often require very sophisticated
reaction conditions, particularly if the resulting reduced
products are very reactive. Generally, transition metal com-
plexes as reductands offer some advantages compared with
other reducing reagents such as the possibility of tuning
their redox properties and the controlling of their kinetic
behaviour by choosing suitable ligands.
2. Results and discussion
Dimeric Pd(I) complexes have been intensively investi-
gated due to their importance in homogeneous catalytic
reactions, as model complexes for clusters and for metallic
surfaces [2–18]. Dimeric Pd(I) complexes, however, consist-
ing only of the Pd2Cl2 core and olefins (e.g. cod) as addi-
tional ligands are hitherto unknown, although they
would be of great interest as starting material for the syn-
thesis of other Pd(I) compounds with variable stabilizing
ligands and as potential homogeneous catalysts, also in
combination with additional controlling ligands.
Therefore we continued our investigations in this area
and here we report on new procedures for the formation
*
Corresponding author. Tel.: +49 3641 9 48110; fax: +49 3641 9 48102.
E-mail address: cdw@uni-jena.de (D. Walther).
0022-328X/$ - see front matter ꢀ 2006 Elsevier B.V. All rights reserved.
doi:10.1016/j.jorganchem.2006.08.015

M. Schwalbe et al. / Journal of Organometallic Chemistry 691 (2006) 4868–4873
4869
Our attempts for preparing the cod complexes were car-
ried out below ꢀ20 ꢁC, since the cod complexes of Pd(I)
were expected to be thermically instable. For reducing
Pd(II) a suspension of Pd(cod)Cl2 in THF containing a
small amount of anthracene or 1,3-butadiene which pre-
vented fast decomposition of the reaction products was
slowly treated with a THF solution of [Ni(bpy)(cod)].
Upon addition of 0.5 equiv of the nickel(0) complex to
the reaction mixture, an immediate colour change from yel-
low to red-violet was observed and upon workup complex
1 was isolated as a red compound. Single crystals of 1 were
grown by layering a toluene solution of 1with heptane. Its
mass spectrum (FAB-MS) showed one major peak at m/
z = 498 corresponding to the composition [Pd2Cl2(cod)2].
This suggests that a redox reaction has occurred in which
two electrons were transferred from Ni(0) to two Pd(II)
centres accompanied by the exchange of cod and two chlo-
ride ligands (Eq. (1)):
It is interesting to note that the known dimeric Pd(I)
complexes usually contain strong ligands with P- or N-
donor atoms or mixed N–P chelate ligands [2–18]. In many
of them the Pd centres are connected by bridging ligands.
The 1H NMR spectrum of 1 in THF-d8 at ꢀ20 ꢁC
showed the typical singlet for the CH protons at 6.15 ppm
(integrated to four protons) and two resonances for the
CH2 protons at 2.86 and 2.57 ppm (each integrated to four
protons). This splitting into two signals indicated that the
solid state structure of 1 is stable as well in solution.
The compound 2 containing bromide in place of chlo-
ride was prepared in analogy to the synthesis of 1 starting
with Pd(cod)Br2. Mass spectroscopic and NMR measure-
ments display that 2 has the same composition and struc-
ture as observed for 1. The FAB-MS showed an envelope
of peaks at m/z = 588 corresponding to the dimeric com-
1
plex [Pd2Br2(cod)2] and in the H NMR spectrum the CH
protons were observed at 6.27 ppm and the CH2 protons
resonated at 2.74 and 2.46 ppm; each of these signals cor-
responded to four protons.
[Ni(bpy)(cod)] + 2Pd(cod)Cl2
! ½Pd2Cl2ðcodÞ2ꢁ þ NiðbpyÞCl2 þ cod
ð1Þ
Compounds 1 and 2 are extremely air and moisture sen-
sitive compounds which decomposed above ꢀ15 ꢁC as well
in solution as in the solid state resulting in the formation of
elementary palladium. It is noteworthy that attempts to
isolate 1 and 2 using sodium/naphthalene as reducing agent
failed so far. Under these conditions palladium black was
formed as main product together with a very small amount
of the Pd(I) complexes. Furthermore, the conproportiona-
tion reaction between Pd(dba)2 and Pd(cod)Cl2 in the pres-
ence of an excess of cod was unsuccessful as well. This
demonstrates that [Ni(bpy)(cod)] is indeed a valuable mild
agent for reducing organometallic compounds which may
offer numerous other applications.
Fig. 1 shows the solid state structure of 1 determined by a
low-temperature X-ray analysis and contains relevant bond
lengths and angles in the caption. Complex 1 is a bimetallic
˚
Pd(I) complex with a Pd–Pd bond of 2.5379(4) A. Each Pd
ion is in a planar environment created by cod acting as
bidentate chelate ligand, one monodentate chloride ligand
and the other Pd(I). The Pd–C bond lengths are unsymmet-
rical due to the strong trans influence of the Pd(I)–Pd(I)
bridge [19]. The two Cl–Pd–Pd angles are 83.72(3)ꢁ and
81.11(3)ꢁ. Furthermore, the two planar coordination polye-
ders form an angle of 82.4ꢁ.
To prove this potential we investigated the electron
transfer reaction between the Ni(0) centre and Pd(II) com-
plexes in order to form Pd(0) complexes and succeeded in
preparing Pd(cod)2 (complex 3) by careful tuning the reac-
tion conditions. Compound 3 is known to be an extremely
sensitive compound which decomposes very easily. It was
obtained by metal atom synthesis [20], by reducing Pd(II)
with Mg(anthracene) [21] in relatively low yields and by
reacting Pd(cod)Cl2 with cyclooctatetraendiyl lithium
[22,23] in good yields; however in the latter reaction the
use of liquid propene was required. To the best of our
knowledge neither the solid state structure of 3 nor its
NMR data are known.
The reaction to form 3 was carried out as follows: In the
presence of an excess of 1,3-butadiene [Ni(bpy)(cod)] and
Pd(cod)Cl2 were reacted at ꢀ20 ꢁC and 3 could be obtained
as light yellow crystals according to Eq. (2). For the success
of the synthesis the presence of 1,3-butadiene was essential.
In the absence of added butadiene [Ni(bpy)(cod)] failed to
afford 3, and 1 together with palladium black was obtained.
Fig. 1. Molecular structure of complex 1 (H-atoms are omitted for
clarity). Selected bond distances (A) and bond angles (ꢁ): Pd1–Pd2
˚
2.5379(4), Pd1–Cl1 2.3293(9), Pd1–C4 2.327(4), Pd1–C5 2.338(4), Pd1–C1
2.209(4), Pd1–C8 2.194(4), Pd2–Cl2 2.3218(9), Pd2–C9 2.206(3), Pd2–C16
2.205(4), Pd2–C12 2.311(4), Pd2–C13 2.307(4), Pd1–X1 2.090(1), Pd1–X2
2.232(1), Pd2–X3 2.095(1), Pd2–X4 2.208(1) Cl1–Pd1–Pd2 81.11(3), Cl1–
Pd1–X1 175,5(1), Cl1–Pd1–X2 98.2(1), X1–Pd1–Pd2 94.9(1), X1–Pd1–X2
85.9(1), X2–Pd1–Pd2 175.2(1), Cl2–Pd2–Pd1 83.72(3), Cl2–Pd2–X3
177.8(1), Cl2–Pd2–X4 95.8(1), X3–Pd2–Pd1 94.4(1), X3–Pd2–X4 86.1(1),
X4–Pd2–Pd1 178.4(1) (centroids: X1 (C1–C8), X2 (C4–C5), X3 (C9–C16),
X4 (C12–C13)).
[Ni(bpy)(cod)] + Pd(cod)Cl2 ! Pd(cod)2 + Ni(bpy)Cl2
ð2Þ
The EI mass spectrum showed an envelope of peaks at
m/z = 322 that match well with the isotopic distribution

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M. Schwalbe et al. / Journal of Organometallic Chemistry 691 (2006) 4868–4873
calculated for the ion [Pd(cod)2]+. In addition, the 1H
NMR spectrum in THF-d8 at ꢀ20 ꢁC showed the expected
simple pattern for two symmetrically bonded cod ligands at
5.50 ppm for the CH protons and at 2.33 ppm for the sig-
nals of the CH2 groups.
Single crystals were grown from toluene at ꢀ25 ꢁC and
the crystal structure of 3 has been solved by X-ray diffrac-
tion analysis. Its molecule structure is displayed in Fig. 2
containing relevant bond lengths and angles in the caption.
The crystal structure of 3 shows it to be very similar to
the closely related M(cod)2 complexes of Ni(0) and Pt(0)
[1,24] with the Pd(0) centre in a tetrahedral environment
of the centroids of the olefin groups of the two chelating
cod ligands. The Pd–C bond distances lie in the range usu-
ally observed for this type of bonding and need therefore
no further discussion.
The use of [Ni(bpy)(cod)] for reducing Pd(II) complexes
is not restricted to the synthesis of cod containing com-
plexes. For example, the reaction of [Ni(bpy)(cod)] with
Pd(cod)Cl2 in the presence of norbornene afforded the
complex Pd(norbornene)3 (4) (Eq. (3)):
Fig. 3. Molecular structure of complex 4 (H-atoms are omitted for
˚
clarity). Selected bond distances (A) and bond angles (ꢁ): Pd–C1 2.207(2),
[Ni(bpy)(cod)] + Pd(cod)Cl2 + 3 norbornene
Pd–C2 2.210(3), Pd–C8 2.214(3), Pd–C9 2.224(2), Pd–C15 2.212(3),
Pd–C16 2.207(3), Pd–X1 2.098(3), Pd–X2 2.108(3), Pd–X3 2.098(3),
X1–Pd–X2 119.7(1), X1–Pd–X3 121.9(1), X2–Pd–X3 118.2(1) (centroids:
X1 (C1–C2), X3 (C8–C9), X3 (C15–C16)).
! PdðnbnÞ3 þ NiðbpyÞCl2 þ 2cod
ð3Þ
Compound 4 has been prepared earlier by Stone by using
cyclooctatetraendiyl lithium as reducing agent and the
compound was found to be isomorphous with the structur-
ally elucidated Pt(nbn)3 [23]. We succeeded in obtaining
single crystals of 4 by slow crystallization of the complex
from hexane/diethyl ether. Fig. 3 displays the molecular
structure determined by X-ray diffraction and relevant
bond lengths and angles are listed in the figure caption.
The Pd(0) centre is in a trigonal planar environment of
three olefin groups and its structure is very similar to the
related platinum complex [23].
For the electron transfer reaction between the Ni(0) com-
plex and the Pd(II) compounds, two competitive pathways
may be envisioned (Scheme 1): the first one would start with
the formation of a 1:1 complex A as an intermediate in
Ni(bpy)(cod)
+
Pd(cod)X2
- cod
X
Pd(cod)
+
-
Pd(cod)X2
Pd(cod)X2
X
X
X
X
(bpy)Ni
(bpy)Ni
Pd(cod)
Pd(cod)
X
A
B
- Ni(bpy)X2
"Pd(cod)"
+ butadiene
-
Ni(bpy)X2
Pd(cod)X2
+
Pd2(cod)2X2
(cod)
Pd(butadiene)
n
-
products
1, 2
Fig. 2. Molecular structure of complex 3 (H-atoms are omitted for
˚
C
clarity). Selected bond distances (A) and bond angles (ꢁ) : Pd–C1 2.148(6),
Pd–C8 2.160(6), Pd–C4 2.151(6), Pd–C5 2.158(6), Pd–C11 2.146(6), Pd–
C12 2.144(6), Pd–C15 2.163(6), Pd–C16 2.188(5), Pd–X1 2.040(6), Pd–X2
2.040(6), Pd–X3 2.037(6), Pd–X4 2.063(6), X1–Pd–X2 88.4(2), X1–Pd–X3
117.0(2), X1–Pd–X4 125.4(2), X2–Pd–X3 126.6(2), X2–Pd–X4 115.8(2),
X3–Pd–X4 87.7(2) (centroids: X1 (C1–C8), X2 (C4–C5), X3 (C11–C12),
X4 (C15–C16)).
+ cod
Pd(cod)2
3
Scheme 1. Possible pathways for generating 1, 2 and 3.

M. Schwalbe et al. / Journal of Organometallic Chemistry 691 (2006) 4868–4873
4871
which the (bpy)Ni fragment and Pd(cod)X2 are bridged by
two halogenide ligands. Subsequent two-electron transfer
could then result in the formation of the instable ‘‘Pd(cod)’’
fragment followed by a fast conproportionation reaction of
this intermediate with a Pd(cod)X2 molecule to generate 1
or 2.
Alternatively, A may react with a further molecule
Pd(cod)X2 to form B in equilibrium with A. Subsequent
electron transfer from the Ni(0) centre in B to two Pd cen-
tres and elimination of Ni(bpy)X2 may result in 1 or 2 as
well.
In the presence of an excess of 1,3-butadiene, however,
complex 3 was obtained. We assume therefore that the
fragment ‘‘Pd(cod)(0)’’ may react under these conditions
with the diene to form a butadiene Pd(0) complex C which
is transformed into 3 in the last step. When the reaction
was carried out in the presence of deuterium-labelled buta-
diene the deuterated product of the composition C16D24Pd
was detected. This suggests that in the course of the reac-
tion an oxidative coupling of two butadienes to form
allyl-Pd species as intermediates could play a role [25,26]
which may undergo reductive elimination to form 3. How-
ever, this assumption needs further support by mechanistic
investigations.
to use, tetrahydrofurane, toluene, n-alkanes and diethyl
ether were dried over potassium hydroxide and distilled
over Na/benzophenone. Dichloromethane was distilled
over CaH2. Pd(cod)Cl2and Pd(cod)Br2 were prepared
according to literature procedures [27,28]. Compounds 1–
4 are extremely reactive and decompose above ꢀ20 ꢁC.
4.1.1. [Ni(bpy)(cod)]
The starting complex [Ni(bpy)(cod)] was synthesized in
a procedure similar to that described in Refs. [29,30]:
Ni(cod)2 (2.75 g, 10 mmol) and 2,20-bipyridine (1.64 g,
10.5 mmol) were dissolved in 120 ml THF at 20 ꢁC. The
mixture was stirred for 3 h to give a deep blue solution.
After filtration the solvent of the filtrate was evaporated
under vacuum and the remaining residue was treated with
80 ml diethyl ether. The deep blue precipitate of [Ni(bpy)-
(cod)] was filtered off and washed with diethyl ether and
with n-pentane. Yield: 2.94 g (91%). After drying under
vacuum this product was used for the reduction of the
Pd(II) complexes to form 1–4. Alternatively, a 1:1 mixture
of Ni(cod)2 and 2,20-bipyridine can be used giving the same
reduction products.
4.1.2. [Pd2Cl2(cod)2] (1)
A solution of [Ni(bpy)(cod)] (0.16 g, 0.5 mmol) or a
freshly prepared mixture of Ni(cod)2 and 2,20-bipyridine
(1:1) in 10 ml of THF was added drop wise into a suspen-
sion of Pd(cod)Cl2 (0.29 g, 1.0 mmol) and anthracene
(18 mg, 0.1 mmol) in a mixture of 10 ml of THF and 1 ml
of cod at ꢀ25 ꢁC. It was crucial that the temperature was
kept below ꢀ20 ꢁC during the reaction time and work up
to avoid fast decomposition of the product. The blue violet
colour of the [Ni(bpy)(cod)] should always disappear before
adding the next portion to the reaction mixture. When the
addition was completed the deep red violet suspension
was stirred for further 2 h. All insoluble parts were then fil-
tered off over Celite and washed with 10 ml of THF. The
formed red solution was concentrated under reduced pres-
sure whereupon a solid appeared which was washed with
hexane. The red solid obtained was dried i.V. Yield:
0.075 g (30%); C16H24Cl2Pd2 (500.1). Due to the extreme
thermolability of 1 only its chloride content was be deter-
mined by volumetric titration. Calc.: Cl, 14.18. Found: Cl,
14.05%; MS-FAB (in dmba) m/z: 498 [M]+, 463 [MꢀCl]+;
1H NMR (200 MHz, THF-d8, ꢀ20 ꢁC): d = 2.57 (m, 4H,
CH2), 2.86 (m, 4H, CH2), 6.15 (s, 4H, CH) ppm. Crystals,
suitable for the X-ray diffraction, were obtained from a dif-
fusion of heptane into a solution of toluene.
3. Conclusions
In this work we have demonstrated that [Ni(bpy)(cod)]
could be used for the reduction of Pd(II) centres resulting
in the extremely sensitive low-valent Pd complexes
[Pd2Cl2(cod)2], [Pd2Br2(cod)2], Pd(cod)2 or Pd(norborn-
ene)3, depending on the reaction conditions. We suggest
that three factors contribute to the ability of the Ni(0) com-
plex to act as a mild reagent for such reactions: First, bpy
increases the reducing power of the Ni(0) centre compared
with other neutral ligands due to its relatively strong r-
donor-behaviour. Second, Ni forms stable (bpy)Ni frag-
ments in both oxidation states 0 and +2. Third, the final
product Ni(bpy)X2 is sparingly soluble in most organic sol-
vents which allow easy separation of this reaction product
by filtration. Since Ni(cod)2 and bpy are commercially
available and a combination of both substances in situ
can also be used as reducing agent this method may find
a number of other applications for preparing very sensitive
low-valent metal complexes.
4. Experimental
4.1. General procedures
4.1.3. [Pd2Br2(cod)2] (2)
1H NMR spectra were recorded at low temperature on a
Bruker AC 200 MHz spectrometer. All spectra were refer-
enced to TMS or deuterated solvent as an internal stan-
dard. Mass spectra were recorded using a Finnigan MAT
SSQ 710. FAB-Measurements were made using dmba as
a matrix. All manipulations were carried out by using
Schlenk techniques under an atmosphere of argon. Prior
The compound was prepared analogously to 1. Higher
yields of the product were obtained by using dichlorometh-
ane instead of THF for the reaction suspension and work
up. Yield: 0.20 g (70%)
– using dichloromethane;
C16H24Br2Pd2; (589.0); Calc.: C, 32.63; H, 4.11. Found:
C, 32.82; H, 4.21%; MS-FAB (in dmba) m/z: 588 [M]+,
508 [MꢀBr]+; 1H NMR (200 MHz, THF-d8, ꢀ20 ꢁC):

4872
M. Schwalbe et al. / Journal of Organometallic Chemistry 691 (2006) 4868–4873
d = 2.46 (m, 4H, CH2), 2.74 (m, 4H, CH2), 6.27 (s, 4H,
CH) ppm.
extracted with heptane and analysed by mass spectroscopy.
C16D24Pd; MS-EI m/z: 346 [M]+, 286 [MꢀC4D6]+, 226
[MꢀC8D12]+. It decomposes very rapidly above ꢀ20 ꢁC.
4.1.4. [Pd(cod)2] (3)
A solution of [Ni(bpy)(cod)] (0.24 g, 0.75 mmol) or a
freshly prepared mixture of Ni(cod)2 and 2,20-bipyridine
(1:1) in 10 ml of THF was added drop wise into a suspen-
sion of Pd(cod)Br2 (0.37 g, 1.0 mmol) or Pd(cod)Cl2,
respectively, in a mixture of 15 ml of THF, 1 ml of cod
and 3 ml of 1,3-butadiene at ꢀ25 ꢁC. It was important to
keep the temperature below ꢀ20 ꢁC during the synthesis
to avoid fast decomposition of the product. The blue violet
colour of the [Ni(bpy)(cod)] should always disappear
before adding the next portion to the reaction mixture.
When the addition was completed the deep red-violet sus-
pension was further allowed to stir for 2 h. All insoluble
parts were filtered off over Celite and washed with 10 ml
of THF. Then the remaining yellow solution was concen-
trated under reduced pressure. For further preparative
use it is recommended to use the Pd(cod)2 as its THF solu-
tion. For isolation all liquids were removed under reduced
pressure and the yellowish white solid was recrystallized
from toluene or hexane to give a white solid. Yield:
0.05 g (20%); C16H24Pd (322.8); Calc.: C, 59.53; H, 7.50.
Found: C, 59.44; H, 7.74%; MS-EI m/z: 322 [M]+, 268
[MꢀC4H6]+, 214 [MꢀC8H12]+; 1H NMR (200 MHz,
THF-d8, ꢀ20 ꢁC): d = 2.33 (m, 8H, CH2), 5.50 (m, 4H,
CH) ppm. Crystals, suitable for the X-ray diffraction, were
obtained from a solution of toluene at ꢀ25 ꢁC.
5. Crystal structure determination
The intensity data for the compounds were collected on
a Nonius Kappa CCD diffractometer, using graphite-
monochromated Mo-Ka radiation. Data were corrected
for Lorentz and polarization effects, but not for absorption
effects [31,32].
The structures were solved by direct methods (SHELXS
[33]) and refined by full-matrix least squares techniques
against F 2o (SHELXL-97 [34]). All hydrogen atoms were
included at calculated positions with fixed thermal param-
eters. All nonhydrogen atoms were refined anisotropically
[34]. XP (SIEMENS Analytical X-ray Instruments, Inc.)
was used for structure representations.
5.1. Crystal data for 1
C16H24Cl2Pd2 C H , Mr = 592.19 g molꢀ1 orange
*
7
prism, size 0.02 · 0.02 ·80.02 mm3, monoclinic, space group
˚
P2/n, a = 15.7960(3), b = 6.9767(1), c = 20.9746(5) A, b =
3
˚
103.965(1)ꢁ, V = 2243.16(8) A , T = ꢀ90 ꢁC, Z = 4, qcalc
=
1.754 g cmꢀ3
,
l(Mo-Ka) = 18.47 cmꢀ1
,
F(000) = 1184,
15187 reflections in h(ꢀ19/20), k(ꢀ8/9), l(ꢀ27/25), mea-
sured in the range 2.66ꢁ 6 H 6 27.48ꢁ, completeness
H
max = 99.2%, 5101 independent reflections, Rint = 0.042,
4153 reflections with Fo > 4r(Fo), 244 parameters, 0
restraints, R1 obs = 0.034, wR2 obs = 0.076, R1 all = 0.050,
4.1.5. [Pd(norbornene)3] (4)
A solution of [Ni(bpy)(cod)] (0.097 g, 0.30 mmol) or a
freshly prepared mixture of Ni(cod)2 and 2,20-bipyridine
(1:1) in 5 ml of THF was added drop wise into a suspension
of Pd(cod)Cl2 (0.094 g, 0.33 mmol) and norbornene (0.42 g,
4.5 mmol) in a mixture of 5 ml THF, 1 ml 1,3-butadiene at
ꢀ30 ꢁC. When the addition was completed the orange sus-
pension was allowed to stir for further 2 h. All insoluble
parts were filtered off over Celite and washed with 5 ml
of THF. Then the remaining yellow solution was concen-
trated under reduced pressure. The yellowish white solid
was washed with a small portion of hexane and dried in
vacuum. Recrystallization can be made using hexane to
give a white solid. Yield: 0.064 g (50%); C21H30Pd
(388.87); the spectroscopic properties of the compound
wR2 all = 0.082, GOOFꢀ=3 1.027, largest difference peak and
˚
hole: 0.793/ꢀ0.790 e A
.
5.2. Crystal data for 3
C16H24Pd, Mr = 322.75 g molꢀ1, colourless prism, size
3
ꢀ
0.03 · 0.03 · 0.02 mm , triclinic, space group P1, a =
˚
7.3858(2), b = 9.2342(2), c =10.7138(4) A, a = 72.015(1),
3
˚
b = 84.375(1), c = 69.717(1)ꢁ, V = 651.87(3) A , T =
ꢀ90 ꢁC, Z = 2, qcalc = 1.644 g cmꢀ3, l(Mo-Ka) = 13.99
cmꢀ1, F(000) = 332, 4591 reflections in h(ꢀ9/9), k(ꢀ11/
11), l(ꢀ11/13), measured in the range 2.46ꢁ 6 H 6 27.46ꢁ,
completeness Hmax = 98.9%, 2953 independent reflections,
Rint = 0.038, 2767 reflections with Fo > 4r(Fo), 155 parame-
1
were identical with those of an authentic sample [23]. H
ters, 0 restraints, R1 obs = 0.051, wR2 obs = 0.130, R1 all =
NMR (200 MHz, toluene-d8, ꢀ40 ꢁC): d = 3.80 (s, 2H,
@CH), 2.81 (s, 2H, CH), 1.38 (m, 4H, CH2), 0.27 (m,
2H, CH2bridge) ppm. Crystals, suitable for the X-ray dif-
fraction, were obtained from a solution of pentane/diethyl
ether at ꢀ40 ꢁC.
0.054, wR2 all = 0.133, GOOF = 1.075, largest difference
ꢀ3
˚
peak and hole: 2.207/ꢀ2.177 e A
.
5.3. Crystal data for 4
C21H30Pd, Mr = 388.85 g molꢀ1, colourless prism, size
0.03 · 0.03 · 0.03 mm3, orthorhombic, space group P212121,
4.1.6. Reaction of [Ni(bpy)(cod)] and Pd(cod)Cl2 in the
presence of 1,3-butadiene-d6
The reaction was carried out as stated above for the
preparation of Pd(cod)2 in the presence of 1,3-butadiene-
d6 instead of 1,3-butadiene. The crude white product was
˚
a = 5.5943(1), b = 10.7699(2), c = 28.5210(4) A, V =
3
1718.39(5) A , T =ꢀ 90 ꢁC, Z = 4, qcalc= 1.503 g cmꢀ3
,
˚
l(Mo-Ka) = 10.75 cmꢀ1, F(000) = 808, 12,292 reflections
in h(ꢀ7/7), k(ꢀ13/12), l(ꢀ36/37), measured in the range

M. Schwalbe et al. / Journal of Organometallic Chemistry 691 (2006) 4868–4873
4873
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2.86ꢁ 6 H 6 27.47ꢁ, completeness
Hmax = 99.8%, 3925
independent reflections, Rint = 0.034, 3582 reflections with
Fo > 4r(Fo), 199 parameters, 0 restraints, R1 obs = 0.026,
wR2 obs = 0.053, R1 all = 0.032, wR2 all = 0.056, GOOF =
1.022, Flack-parameter ꢀ0.07(3), largest difference peak
ꢀ3
˚
and hole: 0.415/ꢀ0.590 e A
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Crystallographic data for the structural analysis have
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These data can be obtained free of charge via www.ccdc.
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