Synthesis and structure of new palladium complexes with the ligand 2-(diphenylphosphino)-1-methylimidazole: Evidence of hemilability

Article abstract of DOI:10.1016/j.jorganchem.2006.11.045

Several Pd(II) complexes containing the potentially bidentate ligand 2-(diphenylphosphino)-1-methylimidazole, dpim, have been synthesized and characterized: [PdCl₂(dpim)]_n (1), [PdCl₂(H₂O)(dpim-κP)] (2), [PdClMe(μ-dpim-κP,κN)]₂ (3) (previously described), [PdClMe(dpim-κP)₂] (4), [Pd(C₆F₅)₂(dpim-κP)₂] (5) and [Pd(η³-2-Me-C₃H₄)(μ-dpim-κP,κN)]₂[PF₆]₂ (6). The highly insoluble complex 1 dissolves in wet DMSO-d₆ to give the water adduct 2 in which a hydrogen bond is established between one of the water hydrogens and the imidazolyl nitrogen. Two types of coordination mode have been found for the dpim ligand in these derivatives, with the ligand behaving as P monodentate and also as a P,N bridge. The transformations between 3 and 4 demonstrate the hemilability of the dpim ligand. Complex 6 was obtained as a mixture of two pairs of enantiomers (R,S)/(S,R) and (R,R)/(S,S). Analysis of the fluxional behaviour of 6, in which the allyl group acts as a reporter ligand , indicates that Pd-N bond rupture takes place - again providing evidence of the hemilabile character of the dpim ligand.

Full text of DOI:10.1016/j.jorganchem.2006.11.045

Journal of Organometallic Chemistry 692 (2007) 1482–1495
www.elsevier.com/locate/jorganchem
Synthesis and structure of new palladium complexes with the ligand
2-(diphenylphosphino)-1-methylimidazole: Evidence of hemilability
a
a
b
b,
*
´
´
´
´
Virginia Dıez , Gustavo Espino , Felix A. Jalon , Blanca R. Manzano
,
a
Mercedes Perez-Manrique
a
Departamento de Quı´mica, Facultad de Ciencias, Universidad de Burgos, Pza Misael Ban˜uelos s/n., 09001-Burgos, Spain
Departamento de Quı´mica Inorga´nica, Orga´nica y Bioquı´mica, Universidad de Castilla-La Mancha, 13071-Ciudad Real, Spain
b
Received 7 July 2006; received in revised form 14 November 2006; accepted 30 November 2006
Available online 6 December 2006
This paper is dedicated to Professor Victor Riera on the occasion of his 70th birthday.
Abstract
Several Pd(II) complexes containing the potentially bidentate ligand 2-(diphenylphosphino)-1-methylimidazole, dpim, have been syn-
thesized and characterized: [PdCl2(dpim)]n (1), [PdCl2(H2O)(dpim-jP)] (2), [PdClMe(l-dpim-jP,jN)]2 (3) (previously described),
[PdClMe(dpim-jP)2] (4), [Pd(C6F5)2(dpim-jP)2] (5) and [Pd(g3-2-Me–C3H4)(l-dpim-jP,jN)]2[PF6]2 (6). The highly insoluble complex
1 dissolves in wet DMSO-d6 to give the water adduct 2 in which a hydrogen bond is established between one of the water hydrogens
and the imidazolyl nitrogen. Two types of coordination mode have been found for the dpim ligand in these derivatives, with the ligand
behaving as P monodentate and also as a P,N bridge. The transformations between 3 and 4 demonstrate the hemilability of the dpim
ligand. Complex 6 was obtained as a mixture of two pairs of enantiomers (R,S)/(S,R) and (R,R)/(S,S). Analysis of the fluxional behav-
iour of 6, in which the allyl group acts as a ‘‘reporter ligand’’, indicates that Pd–N bond rupture takes place – again providing evidence of
the hemilabile character of the dpim ligand.
ꢀ 2006 Elsevier B.V. All rights reserved.
Keywords: Palladium; Hemilabile ligands; N,P ligands; Allyl ligands; Fluxionality; Coordination modes
1. Introduction
which would probably have a less pronounced effect on
the stability of the catalyst. A bidentate PN ligand, when
monocoordinated by the phosphorus atom, also offers a
free nitrogen that, as a basic centre, could participate in
the activation of the substrates. In the presence of OH
groups the formation of hydrogen bridges would be feasi-
ble and this could favour some sort of activation. Braun-
stein and Naud [1] differentiated three types of hemilabile
behaviour: type I involves the spontaneous formation of
a vacant coordination site after partial dissociation of the
hemilabile ligand. In type II hemilability, there is intramo-
lecular competition with another donor function while in
type III hemilability the coordination of an external ligand
takes place. It was also suggested that the reversibility of
the process is necessary to assign the hemilabile character
to a ligand. These concepts have been applied in palladium
Hemilabile ligands and their coordination chemistry [1]
have received increasing attention in recent years. Applica-
tions of these compounds as sensors have been described
[2] but the main interest lies in their potential as auxiliaries
in catalytic processes [3]. Theoretical studies concerned
with this application have been performed [4]. In many of
the catalytic cycles, steps occur that involve dissociation
of monodentate ligands to allow the coordination of sub-
strates. A theoretical alternative to the complete dissocia-
tion of a ligand such as a tertiary phosphine is the partial
dissociation of a bidentate and hemilabile phosphine,
*
Corresponding author. Tel.: +34 926295300; fax: +34 926295318.
E-mail address: Blanca.Manzano@uclm.es (B.R. Manzano).
0022-328X/$ - see front matter ꢀ 2006 Elsevier B.V. All rights reserved.
doi:10.1016/j.jorganchem.2006.11.045

V. Dı´ez et al. / Journal of Organometallic Chemistry 692 (2007) 1482–1495
1483
chemistry by Ros et al. [5]. The chemistry and catalytic
applications [6]of the ligand 2-(diphenylphosphino)pyri-
dine have been widely explored. In this context, another
interesting hemilabile ligand is 2-(diphenylphosphino)-1-
methylimidazole, dpim, which was first reported in 1993
[7] (see Scheme 1). A more convenient method of synthesis
was published by Nishikawa et al. in 2001. This work also
included the formation of dinuclear complexes of Cu(I),
Ag(I) and Pd(I) with the dpim ligand acting as a bridge
and also of [PdCl2(dpim)2] [8]. The dichloro, chloromethyl
and methylacetonitrile palladium(II) complexes of the
dpim ligand have also been described [9] and a dimeric
head-to-tail structure with dpim bridges has been pro-
posed. Complexes of gold(I) and silver(I), some of which
are luminescent, have recently been reported with dpim
[10,11]. A similar ligand with a t-Bu group in the 4-position
of the imidazole ring (t-Budpim) has been used in the syn-
thesis of the complex [RuCp(t-Budpim)2(H2O)]Otf [12]. It
has also been reported the preparation of Pd(0) and Pd(II)
complexes with new bulky imidazolylphosphines [13]. In a
previous paper we also described the synthesis and charac-
terization of new Ru derivatives that contain the dpim
ligand in the three possible coordination modes: monoden-
tate, bidentate chelate and bridging [14]. In the work
described here we decided to explore the coordination pos-
sibilities of the dpim ligand in palladium complexes in an
effort to obtain information about its hemilabile behaviour.
We were also interested in analyzing the chelate versus
bridging coordination of the ligand when the dpim:Pd ratio
is 1:1. Complexes with monodentate or bidentate bridging
coordination for the dpim ligand were obtained, including
a complex with coordinated water and an allyl derivative
whose fluxionality was analysed. The hemilabile behaviour
of the ligand was demonstrated.
dpim. In both cases an orange solid, 1, was formed. This
product is not soluble in common organic solvents such
as acetone, dichloromethane or chloroform. A mass spec-
trum (MALDI) of the product was obtained and the most
intense peak corresponded to a fragment with two palla-
dium atoms. However, a peak clearly due to a fragment
with three palladium atoms was also observed. A small
peak that could correspond to a fragment with four palla-
dium atoms was detected but, in this case, the low intensity
prevented a reliable assignment (see Section 4). Higher
mass peaks were not observed. Consequently, the nuclear-
ity of complex 1 can not be unambiguously established.
The reaction between [PdCl2(cod)] and dpim has been pre-
viously reported [9]. It is proposed that the obtained com-
plex is a dimmer of formulae [PdCl2(dpim)]2.
Compound 1 was treated with wet DMSO-d6 and heated
at 70 ꢁC, a process that gave rise to a different species, 2,
which was soluble in this solvent (see Eq. (1)).
DMSO-d6/H2O
dpim
[PdCl2(PhCN)2]
[PdCl2(dpim)(H2O)]
1/n [PdCl2(dpim)]n
or
CH3COCH3
or
CH2Cl2
[PdCl2(cod)]
(1)
(2)
ð1Þ
The 31P{1H} NMR spectrum of the freshly prepared
sample in DMSO-d6 at room temperature (see Table 1
and Fig. 1) showed two singlets at 16.2 and 89.6 ppm.
When this solution was heated to 70 ꢁC the first signal
almost disappeared while the intensity of the second
increased. This observation is consistent with a chemical
evolution in situ, with the first signal corresponding to
the initial sparingly soluble species (or an intermediate evo-
lution product) and the second to derivative 2, which seems
to be the final product. The process was found to be irre-
versible because when the sample was cooled down to
room temperature the spectrum did not change.
2. Results and discussion
1
The H NMR (DMSO-d6, 70 ꢁC) spectrum of the sam-
2.1. Preparation and characterization of neutral and cationic
complexes
ple after the evolution outlined above (see Table 1) exhib-
ited the expected resonances for the ligand. In addition,
two other signals were observed at 12.40 (sharp) and 11.2
(broad) ppm, which integrate as one proton each.
The reaction of [PdCl2(PhCN)2] with two equivalents of
dpim has already been explored [8] and gives rise to a mix-
ture of cis- and trans-[PdCl2(dpim-jP)2]. The similar deriv-
atives cis- and trans-[PdCl2(PPh2py)2] have also been
described [15]. Given the possibility of synthesizing a deriv-
ative containing a chelate phosphine ligand, we carried out
the reaction of either [PdCl2(PhCN)2] or [PdCl2(cod)]
(cod = 1,5-cyclooctadiene) with only one equivalent of
NOE experiments were carried out in order to identify
these low field signals and clarify the structure of 2 (see
Scheme 2). An NOE was found between the methyl group
0
0
and the signal of H4 or H5 (7.07 ppm, isochronous nuclei
by coincidence). Moreover, when the signal at 7.07 ppm
was irradiated, a positive effect was observed in the reso-
nance at 12.40 ppm. On the basis of these data, we propose
the structure shown in Scheme 2, in which a molecule of
water is coordinated to the palladium centre and a hydro-
gen bond is established between the imidazolyl nitrogen of
the ligand and one of the water hydrogens (Hb). In this sit-
uation the two water protons become inequivalent.
H
H
'
4
N
N
P
Ph
'
Ph
5
A FAB+experiment confirmed our proposal for 2. In this
regard, DMSO was added to a sample of 1 and the resulting
suspension was analysed by FAB+ mass spectrometry. Two
CH
3
dpim
Scheme 1.

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V. Dı´ez et al. / Journal of Organometallic Chemistry 692 (2007) 1482–1495
Table 1
1H and 31P{1H} NMR data for the dpim ligand and complexes 2–6a
Deriv.
dpimb
1H NMR dpim
1H NMR Other groups
31P NMR
0
0
H4
H5
Me
Ho
Hm + p
7.25 (dd)
JHP ¼ 2:3
JHH ¼ 0:9
7.07 (m)
7.03 (d)
JHH ¼ 0:9
3.79 (s)
7.56–7.44 (m)
7.38–7.28 (m)
ꢀ32.20 (s)
2c
7.07 (m)
3.66 (s)
7.65 (m)
7.2 (m)
12.40 (s) Hb
89.6 (bs)
11.2 (bs) Ha
3Md
4b
7.35 (m)
7.32 (s)
6.70 (m)
7.08 (s)
3.23 (s)
3.97 (s)
8.25 (m)
7.22 (m)
7.35 (m)
7.46 (m)
0.97 (d), JHP ¼ 3:2 Pd–Me
ꢀ0.01 (t), JHP ¼ 6:1
Pd–Me
24.09 (s)
15.34 (s)
5d
7.01 (s)
6.67 (s)
6.94 (s)
7.61 (s)
3.55 (s)
3.23 (s)
7.32 (m)
7.42 (m)
7.24(t) J = 6.91 Hp
7.1 (m) Hm
7.74–7.64 (m)
4.19 (s)
6Mb
4.77 (dd) JHP ¼ 7:1,
JHsyn1–Hsyn2 ¼ 3:1, Hsyn2
3.92 (d) JHP ¼ 11:2, Hanti2
3.48 (d) Hsyn1
10.83e (s)
3.47 (s) Hanti1
2.24 (s) Me-allyl
a
Room temperature. o, ortho; m, meta; p, para. M, major isomer; m, minor isomer. See Section 4 for more data of complex 6M and those of 6m.
CD3COCD3.
b
c
DMSO-d6.
CDCl3.
d
e
The resonance of the PFꢀ6 group appears at ꢀ141.37 ppm (spt;1JFP ¼ 707:4).
20 °C
120
110
100
90
80
70
60
50
40
30
20
10
0
-10
-20
-30
-40
40 °C
120
110
100
90
80
70
60
50
40
30
20
10
0
-10
-20
-30
-40
70 °C
120
110
100
90
80
70
60
50
40
30
20
10
0
-10
-20
-30
-40
Fig. 1. 31P{1H} NMR spectra at the temperatures given for the treatment of complex 1 with wet DMSO-d6 that gives 2.
spectra were recorded, the first one at room temperature
and the second after heating the same sample at 70 ꢁC –
at this point the sample readily dissolved. The first spectrum
showed peaks corresponding to dimeric fragments m/z =
853 while the second spectrum exhibited a very informative
peak at m/z = 427, which corresponds to the monocationic
fragment [PdCl(dpim)(H2O)]+. In addition, the base peak
appears at m/z = 389, a value that is consistent with the

V. Dı´ez et al. / Journal of Organometallic Chemistry 692 (2007) 1482–1495
1485
hydrogens of benzylamine coordinated to a palladium cen-
tre and the free nitrogens of two monodentate imidazolyl-
phosphine ligands [13].
Ha
NOE
O
Hb
Cl
H4´
The reaction of [PdClMe(cod)] with the ligand dpim in
1:1 and 1:2 molar ratios, either in acetone or THF, at room
temperature gave rise to the products [PdClMe(l-dpim-
jP,jN)]2 (3) and [PdClMe(dpim-jP)2] (4), respectively
(see Scheme 3). The reaction of the dinuclear complex 3
with two equivalents of the dpim ligand gave the mononu-
clear derivative 4. Furthermore, the reaction of 4 with one
equivalent of [PdClMe(cod)] gave 3, among other prod-
ucts. These transformations demonstrate the type III
hemilabile behaviour of the dpim ligand in these derivatives
[1].
Pd
N
N
Cl
P
Ph
H5´
Ph
H3C
NOE
Scheme 2. Proposed structure for 2 and the most important NOEs
observed (arrows).
fragment [Pd(OH)(dpim)]+. Furthermore, the intensity of
the peak at 853 decreased markedly in the second spectrum.
We considered the possibility that complex 2 could contain
coordinated DMSO and the water could be hydrogen
bonded to both it and the imidazole nitrogen. However,
in the mass spectra we did not observe peaks due to species
containing DMSO. This complex was isolated and com-
pletely characterized by elemental analysis, NMR and IR
spectroscopy (see Section 4).
Complex 2 has strong similarities with the previously
reported derivative [RuCp(t-Budpim)2(H2O)]OTf [12]. In
the Ru complex, the two protons of the water molecule
are equivalent (d = 9.1 ppm) because each one participates
in the formation of a hydrogen bond with the free nitrogen
of one of the two ligands. This complex is very active as a
precursor in the catalytic hydration of terminal alkynes to
give aldehydes selectively. The process that leads to com-
plex 2 is a sort of water activation and, although at this
stage the process is not reversible, it has some similarities
with processes described for other complexes containing
hemilabile ligands, which behave as humidity sensors
[2b]. Hydrogen bonds have also been found between the
The synthesis of derivative 3 has been previously
reported [9] as a mixture of two isomers. We performed
the reaction in order to demonstrate the hemilabile behav-
iour of the ligand by means of the 3 $ 4 transformation.
To complement the characterization of this derivative, we
also performed a 13C{1H} NMR spectrum and a HSQC
experiment. We agree with Cavell et al. that the most rea-
sonable structure for this derivative is that with two HT
dpim bridges. A trans HT disposition of the ligands has
also been observed in homodinuclear systems and in the
majority of the heterodinuclear derivatives with the PPh2py
ligand [16,17]. They proposed that the difference between
the major and minor isomers concerns the relative disposi-
tion of the chloride and methyl ligands on the two metal
centres (‘‘cisoid’’ or ‘‘transoid’’). The NMR data do not
allow the unequivocal assignment of the major isomer to
one of the two structures. However, we tentatively propose
the ‘‘transoid’’ structure on the basis that this is the type of
structure found in similar complexes [18–20].
The 31P{1H} NMR (CD3COCD3) spectrum of 4 exhib-
its one singlet (see Table 1), which indicates that the two
2 PdClMe(cod)
2 dpim
4 dpim
Me
N
Ph
N
Ph
Pd
PPh2
Me
N
Me
P
2dpim
Cl
P
Cl
Cl
N
2
N
Pd
Me
Pd
N
PdClMe(cod)
Me
Me
Ph2P
N
Ph
Ph
4
N
3
Me
Scheme 3.

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V. Dı´ez et al. / Journal of Organometallic Chemistry 692 (2007) 1482–1495
F
ical shifts of derivatives of the type [PdR2(PMe3)2]
F
(R@C6BrF4) which, depending on the starting material
used, have been obtained both in the cis and trans forms.
The resonances of the cis isomers appear at lower frequen-
cies than those of the trans forms [23]. The corresponding
1H NMR (dichloromethane-d2) spectrum of 5 confirms
that both phosphines are equivalent. The 19F NMR spec-
trum shows the three expected types of F atoms: ortho,
meta and para (see Section 4). The expected three-bond
couplings were observed in a 19F–19F COSY spectrum.
The existence of single resonances for the Fortho and Fmeta
atoms indicates that there is free rotation around the Pd–
C bonds and/or that a symmetry plane exists in the complex
that makes the two halves of the C6F5 groups equivalent.
It is worth noting the different behaviour of the
‘‘PdClMe’’ and ‘‘Pd(C6F5)2’’ fragments against the dpim
ligand. When two dpim ligands are coordinated, the Cl
and Me are situated in a mutually trans disposition while
the two pentafluorophenyl groups prefer to be in a cis ori-
entation. This is again in accordance with the trans influ-
ence, being bigger for the aryl groups than for the
phosphines (some authors have proposed the term ‘‘trans-
phobia’’ to explain this type of behaviour. The transphobia
of two aryl groups would be bigger than that of two phos-
phines) [21a,21b,21c]. Another difference is that in the case
of the pentafluorophenyl derivative the adoption of a
bidentate coordination through the formation of a dinu-
clear complex is not favoured. A plausible explanation is
that, considering the preference for a mutual cis deposition
of the two aryl groups, the formation of a dinuclear species
would lead to a high steric hindrance.
F
N
N
F
P
P
F
Pd
F
F
F
F
F
5
Scheme 4.
phosphorus atoms must be in a trans disposition. The
chemical shift (15.34 ppm) is lower than that for 2,
although in both cases the ligand is only coordinated by
the P atom. This difference may be ascribed to the distinct
r donor character of the groups in the trans position. In the
1H NMR (CD3COCD3) spectrum (see Table 1), resonances
for only one type of dpim ligand were observed. A triplet at
ꢀ0.01 ppm (3JPH = 6.1 Hz, coupling demonstrated by 31P
decoupling experiments) for the corresponding methyl-Pd
group is also observed. The low value of the coupling con-
stant confirms the cis disposition between the methyl group
and the phosphorus atoms. The relative disposition of
these groups is in accordance with the high trans influence
of the methyl group, which prevents the presence of a
strong donor ligand such as a phosphine in a trans disposi-
tion to it [21]. Complexes of the type trans-[PdClMe(L)2]
have been described in which L = different derivatives of
PPh2py [6e].
We also performed the reaction of the allyl derivative
[Pd(g3-2-Me–C3H4)Cl]2 with the ligand dpim. It was
carried out in two steps according to the procedure
described by Pregosin and coworkers [24] (see Eq. (2)). Com-
plex 6, {[Pd2(g3-2-Me–C3H4)2(l-dpim-jN, jP)2][PF6]2}, was
obtained.
The reaction of [Pd(C6F5)2(cod)] with dpim, in both 1:1
and 1:2 molar ratios, gave the product [Pd(C6F5)2(dpim-
jP)2] (5). It is noteworthy that the formation of 5 takes
place even when one equivalent of ligand per palladium
was used. In this case, the excess of the starting palladium
S
½Pdðg3-2-Me–C3H4ÞClꢁ2 þ 2AgPF6 ! 2½Pdðg3-2-Me–C3H4ÞS2ꢁPF6 þ 2AgCl
# 2dpim
ð2Þ
S ¼ acetone
½Pdðg3-2-Me–C3H4Þ2ðdpimÞ2ꢁ½PF6ꢁ26
compound remains in solution. The IR spectrum in the X–
C6F5 sensitive region [22] shows two bands at 770 and
780 cmꢀ1, a finding consistent with the presence of two pen-
tafluorophenyl groups in a cis disposition (see scheme 4).
The 31P{1H} NMR (dichloromethane-d2) spectrum shows
a singlet at 4.19 ppm. This chemical shift is of lower fre-
quency than expected considering the monodentate coordi-
nation mode of the phosphines, but this could be
interpreted as being the result of the r-donor character
of the pentafluorophenyl ligands trans to the phosphorus
atoms. This r-donor character is reflected in the 31P chem-
Different peaks observed in the FAB mass spectrum are
indicative of a dinuclear structure for 6. For example, a
peak at m/z = 1001 Da corresponding to {[Pd2(C4H7)2-
(dpim)2]PF6}+ is observed (see Section 4 for more
information).
Complex 6 in solution was studied by multinuclear
NMR and the results show the presence of two isomers
in very different proportions; 6M:6m = 10:1 (M = major
isomer, m = minor isomer). The major isomer gives rise
to one singlet in the 31P{1H} NMR spectrum along with
the septet due to the PFꢀ6 , an observation that is consistent

V. Dı´ez et al. / Journal of Organometallic Chemistry 692 (2007) 1482–1495
1487
1
with the presence of two equivalent dpim ligands. The H
and 13C{1H} NMR spectra of 6M both reflect the existence
of a single type of dpim ligand and one type of asymmetric
allyl group. The assignment of the allyl 1H NMR
(CD3COCD3) resonances (see Table 1) was made on the
basis of characteristic chemical shifts and coupling con-
stants for allyl derivatives with PN ligands [25] and with
the help of some NOESY experiments (both 1- and 2-D).
NOEs were found between the methyl resonance and both
Hsyn protons, between Hsyn2 and Hanti2 (see Scheme 5 for
the atom numbering scheme) and also between both Hanti
The minor isomer, 6m, exhibits two singlets in the
31P{1H} NMR spectrum and resonances corresponding
to two different dpim ligands and two asymmetric allyl
1
groups in the H NMR spectrum. In fact, in CD3COCD3
two different methyl resonances for the dpim ligand and
at least 6 allylic protons are detected (some of which have
been assigned). In 1,10,2,20-tetrachloroethane-d2 seven
allylic protons and the two methyl allylic groups are also
clearly seen (see Section 4).
When the different structural possibilities for this
dimeric allyl derivative are considered, it is useful to
remember that square-planar allyl palladium complexes
with PN bidentate ligands show chirality. Both Faller [27]
and Hayashi [28] have tried to improve on the previous
nomenclature based on the exo and endo prefixes to estab-
lish a more general system that is effective when there is no
reference to assign these prefixes. We decided to use the
system proposed by Faller because it is similar to that pro-
posed for other gn donor ligands [29]. This method
involves extending the Cahn, Ingold and Prelog (CIP) rules
to describe the absolute configuration of both enantiomers.
Faller et al. chose to view the Pd system as one would a chi-
ral pyramidal phosphorus atom, considering the allyl as an
18-electron (6 · 3) pseudoatom [30] located at the centroid
of the allyl group (the Pd system is seen from the side of the
coordination plane where the methyl group is pointing). In
the case of dinuclear allylic complexes there are two differ-
ent chiral palladium atoms and, therefore, four diastereo-
mers grouped into two pairs of enantiomers: on the one
hand (R,S) and (S,R) and on the other (R,R) and (S,S)
(see Scheme 7). In principle, it is also possible to consider
another (R,R) and (S,S) pair of enantiomers, i.e., those that
have the two allyl groups with the methyl fragments
oriented towards the inside of the molecule (cisoid orienta-
tion of the allyl methyl groups) (see Scheme 7). Strictly
speaking, both pairs of (R,R) and (S,S) cisoid and transoid
enantiomers could interconvert into each other by a boat-
to-boat interconversion similar to that found in derivatives
containing bis(pyrazol-1-yl)methane ligands [31]. However,
this interconversion is much less common in eight-mem-
bered cycles and the presence of the phenyl substituents
on the phosphorus atom makes this process very unlikely
in our system. In any case, this cisoid orientation of the
methyl groups would lead to a high level of steric hindrance
and this pair of enantiomers is probably not formed in our
case and will not be considered in the following discussion.
The pair of enantiomers (R,S) and (S,R) contain two
different dpim ligands and two inequivalent and asymmet-
ric allyl groups, which fits well with the minor isomer 6m.
On the other hand, the C2 axis present in the enantiomers
(R,R) and (S,S) implies that the two dpim and the two allyl
groups are equivalent and consequently these correspond
to the major isomer 6M.
protons. The arrangement in which Hsyn2 is trans to phos-
0
phorus was deduced from the NOE between Hsyn2 and H4 ,
as well as by the NOE between Hsyn1 and some phenyl pro-
tons (ortho and meta) (see Scheme 6). (Intraligand NOEs in
the dpim ligand were also observed. Others NOEs detected
between allylic protons and the dpim ligand will be consid-
ered below). As expected, higher chemical shifts are
observed for the terminal protons and the carbon trans
to phosphorus [25], a situation that is consistent with the
higher trans influence of this donor atom [26]. The coupling
with phosphorus (in the case of the protons, higher for
H
H
anti) is only observed for the trans nuclei. A small
syn1–Hsyn2 coupling is also detected. A particularly low
chemical shift is found for the Hsyn1 proton that is cis to
phosphorus. This observation can be attributed to the
shielding effect of the phenyl rings. The existence of two
types of phenyl rings can also be deduced from the
13C{1H} NMR spectrum.
Hsyn 2
Hsyn 1
Hanti 2
Hanti 1
Pd
P
N
Scheme 5.
2+
Me
Hs1
H4´
P
H5´
Pd
N
Hs2
Ha2
N
Ha1
N
CH3
P
Pd
Having established the structure for 6M, it is interesting
to consider the NOEs found between the allylic methyl
group and different protons of the dpim ligand (see Scheme
6). Indeed, we found NOEs with phenylic ortho and meta
Scheme 6. Some of the NOEs (arrows) found in complex 6M.

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V. Dı´ez et al. / Journal of Organometallic Chemistry 692 (2007) 1482–1495
N
P
P
P
P
N
Pd
Pd
Pd
Pd
Pd
Pd
Pd
Pd
Pd
N
N
P
P
N
N
N
N
P
N
N
P
P
Pd
P
N
P
P
Pd
Pd
S,R
N
R,S
S,S
R,R
R,R
S,S
6m
6M
transoid
cisoid
Scheme 7. Possible structures for complex 6.
0
protons and, more interestingly, with the H4 proton of the
imidazole ring. This last NOE is strongly consistent with a
dimeric structure and it would not be very likely to occur in
a monomeric structure with a chelate dpim ligand. In this
case, the plane of the imidazolyl ring should be approxi-
mately parallel to the coordination plane.
6M and 6m. However, this experiment does enable three
important facts to be deduced: (i) There is chemical inter-
change between Hsyn2(6m) and Hsyn2(6M); (ii) There is
0
interchange between Hanti2(6m) and Hanti2 (6m) and (iii)
there is no interchange between Hsyn1(6M) and Hsyn2(6M).
Point (i) indicates that interconversion between the two iso-
mers is possible and that the observed interchange takes
place without changing the nature of the allylic protons
(syn and trans to P) – although in this regard point (ii) is
more conclusive. Besides, there is interchange between
the two allylic groups of 6m but without a change in the
nature of the allylic protons: i.e., syn and trans to P. This
implies that we are observing neither a process of apparent
allyl rotation nor a g3-g1-g3 dynamic process. Even a
selective g3-g1-g3 process can be discarded because if it
existed – bearing in mind that electronic effects should be
operating (high steric effects are not expected) – this would
lead to opening of the carbon trans to phosphorus due to
its higher trans influence and, consequently, an Hsyn2–Hanti2
interchange should be observed.
Once studied the NMR characteristics of the new deriv-
atives, we have analysed whether the chemical shift of the
imidazolic Me resonance was sensitive to the nitrogen coor-
dination. On comparing our Pd complexes with the previ-
ously described compounds of the same metal [8,9], it
was observed that when the ligand is monodentate the
chemical shift of this group is above 3.5 ppm, while a
bidentate coordination gives rise to chemical shifts below
this value (2.7–3.5 ppm). The only exception is the dichlo-
ride derivative reported by Cavell et al. where a dinuclear
structure with dpim bridges is proposed [9].
2.2. Fluxional behaviour of complex 6
Considering the rich fluxional behaviour usually exhib-
ited by allyl palladium complexes [32], we attempted to
study the dynamics of 6. Processes involving apparent allyl
rotation that would interchange the two terminal allylic
groups (syn-syn0 or anti-anti0 interconversion) have been
described [31a,31b,32a,33,34]. Also common are g3-g1-g3
interconversion processes [24b,32,33e,35,36]. Such a pro-
cess is sometimes selective and in the g1 intermediate only
one of the two terminal carbons remains bonded to the
metal [24b,33e,36]. If electronic factors govern the process,
the carbon that opens up would be the one situated trans to
the stronger donor ligand. The g3-g1-g3 process would
lead to an Hsyn–Hanti interconversion on the carbon (or car-
bons) that retains the r bond to Pd. In the case of complex
6 changes were not observed in the 1H- and 31P NMR spec-
tra at low temperature (ꢀ80 ꢁC). When solutions of 6
(CD3COCD3) were heated up to 50 ꢁC a slight broadening
of the proton signals was observed. It seems that the pro-
cess or processes that may be in operation are of higher
energy than that required for study by the coalescence
method. In order to detect possible interchange processes
of higher energy we performed a phase-sensitive 2D-
NOESY experiment in CD3COCD3. Some cross-peaks
could not be taken into account because they involve reso-
nances for which there is partial overlap between signals of
When the phase-sensitive 2D-NOESY was recorded in
1,10,2,20-tetrachloroethane-d2 only cross-peaks correspond-
ing to NOEs were detected but there were not observed any
interchange. This is consistent with the fact that when the
1,10,2,20-tetrachloroethane-d2 solution was heated up to
130 ꢁC, it was not observed a broadening of the resonances.
Consequently, there is a clear effect of the solvent possibly
due to its coordinating ability.
The hemilabile character of the dpim ligand provides a
possible fluxional process to explain the behaviour
observed in solution through the transient formation of
the monomeric [Pd(g3-allyl)(dpim-jP)(S)]+ intermediate,
probably stabilized by the coordination of acetone. The
observation in the mass spectra of the base peak at
427 Da that correspond to [Pd(C4H7)(dpim)]+ is consistent
with our proposal. The interconversion between the two
different allyl groups in 5m is represented in Scheme 8.
Pd–N bond rupture is followed by rotation about the
Pd–P bond and a change in the relative disposition of the
two metallic fragments leads to the aforementioned inter-
change through reformation of the Pd–N bonds. Similarly,
the formation of these monomeric metallic fragments and
recombination in a different way, as outlined in Scheme
9, can explain the 6M–6m interconversion. If the solvent
participates in the formation of the transient intermediate,

V. Dı´ez et al. / Journal of Organometallic Chemistry 692 (2007) 1482–1495
1489
N
PA
PA
I
I
I
PA
Pd
R
S
Pd
Pd
S
Pd
+2S
N
N
S
N
N
PB
S
Pd
Pd
S
PB
II
PB
II
N
R,S
II
6m
S
PB
Pd
II
S
Pd
N
II
N
PB
PA
N
PA
R
Pd
-2S
N
S
Pd
I
I
S,R
6m
Scheme 8. Proposed mechanism for the interchange of the two allyl fragments in 6m.
According to the mechanism proposed for this deriva-
tive, it is the allyl group that offers information about the
hemilabile behaviour of the dpim ligand. The allyl moiety
behaves as a kind of ‘‘reporter ligand’’. This concept has
been used in allyl-derivatives to refer to an accompanying
ligand that, usually by means of NOE studies, can give
information about the stereochemistry and selective distor-
tions of the allylic moiety [32b,34a]. Interestingly, in our
case, the concept of the reporter ligand can be used in
the other sense and the NMR data for the allyl group allow
the detection of the dynamic behaviour of the other ligand
at the coordination centre.
S
S
S
S
R
R
R
R
6M
R
S
S
R
6m
Scheme 9. 6M/6m interconversion.
the hemilabile behaviour in this case, as in the chloro-
methyl derivatives 3 and 4, is also of type III. The equilib-
rium between the dimeric l-PN and the j1 species seems to
be fast even at ꢀ80 ꢁC because, at this temperature, split-
2.3. X-ray diffraction study for 6
Crystals of complex 6 were obtained from a mixture of
acetone and hexane by slow diffusion and its structure
was determined by X-ray diffraction analysis. The mono-
crystal corresponded to the isomer 6m. Despite having
obtained crystals on three separate occasions, we always
found the same complex 6m. Consequently, although 6M
is thermodynamically more stable in solution, it is 6m that
always crystallizes better. A selection of bond distances and
angles are gathered in Table 2 and the crystallographic
data are given in Table 3. The asymmetric unit of this crys-
tal shows two slightly different (S,R) stereoisomers for the
cationic dinuclear complex of 6m, (S,R)a and (S,R)b, which
differ from each other in some structural features. The cor-
responding enantiomers (R,S)a and (R,S)b, were generated
1
ting of the H NMR signals is not observed. Faller et al.
recently pointed out that the effects of j2–j1 interconver-
sions, although they can be hidden or subtle, may be
important in certain fluxional processes observed in allyl
complexes containing hemilabile ligands [27]. Processes
involving Pd–N bond rupture have been widely described
[24b,27b,33b,33c,33j,36c,37,38]. A case with a certain sim-
ilarity to our example was reported by Espinet et al., [39]
who described a cisoid/transoid interconversion through
cleavage of both bridges and statistical rearrangement in
dimeric allyl-palladium derivatives with two aryl bridges.
It is worth noting that in our proposed process for the
observed interchanges, the absolute configuration of each
metallic fragment does not change throughout the dynamic
process. We must emphasize that although we did not
observe the apparent allyl rotation or the g3-g1-g3 pro-
cesses in our study, they could be present as higher energy
processes.
ꢀ
through the inversion center that has the space group P1.
In consequence the unit cell consist of two pairs of enanti-
omers (R,S) and (S,R). From this point on, and to make
clear which enantiomer is designated by using the descrip-
tors R and S we have adopted the following criterion. The

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V. Dı´ez et al. / Journal of Organometallic Chemistry 692 (2007) 1482–1495
Table 2
Table 3
˚
Selected bond distances (A) and angles (ꢁ) for 6m
Crystal data and structure refinement for 6m
Bond lengths
(S,R)a
Empirical formula
Formula weight
Temperature (K)
Wavelength (A)
Crystal system
Space group
C40H44F12N4P4Pd2
1145.47
293(2)
0.71073
Triclinic
Pd(1)–C(21)
Pd(1)–C(22)
Pd(1)–C(23)
Pd(1)–N(3)
Pd(1)–P(1)
2.085(8)
2.216(9)
2.185(8)
2.140(6)
2.318(2)
Pd(2)–C(19)
Pd(2)–C(18)
Pd(2)–C(17)
Pd(2)–N(1)
Pd(2)–P(2)
2.081(8)
2.191(9)
2.175(9)
2.116(6)
2.288(2)
˚
ꢀ
P1
˚
a (A)
13.6354(14)
17.1523(18)
19.653(2)
86.086(2)
82.525(2)
88.826(2)
4546.3(8)
4
1.674
1.016
2288
0.15 · 0.15 · 0.10
˚
b (A)
(S,R)b
˚
c (A)
Pd(3)–C(57)
Pd(3)–C(58)
Pd(3)–C(59)
Pd(3)–N(7)
Pd(3)–P(1)
2.079(8)
2.179(9)
2.190(8)
2.132(6)
2.2900(19)
Pd(4)–C(63)
Pd(4)–C(62)
Pd(4)–C(61)
Pd(4)–N(5)
Pd(4)–P(4)
2.094(8)
2.214(8)
2.185(8)
2.133(6)
2.314(2)
a (ꢁ)
b (ꢁ)
c (ꢁ)
3
˚
Volume (A )
Z
Dcalc (Mg/m3)
Bond angles
(S,R)a
C(21)–Pd(1)–C(23)
N(3)–Pd(1)–P(1)
C(21)–C(22)–C(23)
Absorption coefficient (mmꢀ1
F(000)
)
67.2(4)
97.32(16)
115.8(9)
C(19)–Pd(2)–C(17)
N(1)–Pd(2)–P(2)
C(17)–C(18)–C(19)
66.0(3)ꢁ
96.21(17)ꢁ
113.8(10)
Crystal size (mm)
h Range for data collection (ꢁ) 1.05–26.00
Index ranges
ꢀ16 6 h 6 16, ꢀ21 6 k 6 21,
(S,R)b
ꢀ24 6 l 6 24
C(57)–Pd(3)–C(59)
N(7)–Pd(3)–P(3)
C(59)–C(58)–C(57)
66.6(4)
97.08(17)
114.1(10)
C(63)–Pd(4)–C(61)
N(5)–Pd(4)–P(4)
C(61)–C(62)–C(63)
67.0(4)
96.22(17)
116.2(9)
Reflections collected
Independent reflections [Rint
Completeness to h = 26.00ꢁ
(%)
48,328
]
17,752 [0.0754]
99.3
Absorption correction
Maximum and minimum
transmission
Refinement method
Data/restraints/parameters
Goodness-of-fit on F2
R indices [for 10,871
reflections with I > 2rðIÞ]
R indices (for all 17752 data)
Weighting scheme
Semi-empirical from equivalents
0.903 and 0.792
first absolute descriptor in between the brackets refers to
the Pd atom whose allylic methyl group points outwards
the eight-membered metallacycle, meanwhile the second
refers to the Pd atom with its methyl group pointing
inwards the same dipalladium cycle. Moreover, we have
added a and b subscripts to the absolute configuration to
distinguish between the structural isomers. The corre-
sponding ORTEP diagrams for the two (S,R) stereoiso-
mers are shown in Fig. 2.
Full-matrix least-squares on F2
17,752/0/1125
S = 0.995
R1 ¼ 0:0672, wR2 ¼ 0:1676
R1 ¼ 0:1157, wR2 ¼ 0:2006
2
wꢀ1 ¼ r2ðF 2oÞ þ ðaPÞ þ ðbPÞ, where
P ¼ ½maxðF 2o; 0Þ þ 2F 2c ꢁ=3 a = 0.101400,
b = 0.0000
The molecular structure of each (S,R) enantiomer can be
described as a dimeric molecule with square planar envi-
ronments for both Pd atoms although distortions from
the ideal geometry are significant due to the small bite
angle of the allyl group (C–Pd–C). The N–Pd–P angle in
each coordination plane is slightly bigger than the ideal
value of 90ꢁ. The dpim ligands coordinate to the metal
atoms in a bridged bidentate ‘‘head-to-tail’’ arrangement,
Largest difference in peak and 1.105 and ꢀ0.914
ꢀ3
˚
hole (e A
)
forming an eight-membered metallacycle with a ‘‘boat’’
conformation. The allyl groups are planar and form angles
of more than 90ꢁ with the metallic coordination planes,
although both angles are slightly different in the same
Fig. 2. ORTEP diagram for both (S,R) enantiomers of 6m found in the same unit cell. Counteranions, as well as phenyl groups and hydrogen atoms have
been omitted for clarity.

V. Dı´ez et al. / Journal of Organometallic Chemistry 692 (2007) 1482–1495
1491
(S,R) isomer, with average values for the two stereoisomers
being 105.67ꢁ and 139.11ꢁ. The two allylic methyl groups
have the same relative orientation. It is worth noting that,
in contrast to the situation found in 6m, in all X-ray struc-
tures of dinuclear palladium g3-allyl derivatives with eight-
membered metallacycles described to date, both allyl
groups have the central carbon pointing outward from
the molecule. In other words, both methyl groups have
opposite orientations [40]. We found only one exception
to this trend – an example in which the allyl group pos-
sesses a large steroid substituent that makes the usual dis-
position impossible [41]. The two coordination planes in
each enantiomer are not completely parallel, with a dihe-
dral angle of 17.49ꢁ (average for the two enantiomers).
As expected, the Pd–C bonds trans to the N atoms are,
in all cases, shorter than the Pd–C bonds trans to the P
atoms and this is due to the higher trans influence of the
P-donor atom. The Pd–N and Pd–P bond distances are
in the expected range. The Pd–Pd distances are Pd(1)–
Pd(2) = 3.1896(8) and Pd(3)–Pd(4) = 3.2046(8). Finally,
four octahedral PFꢀ6 counterions were found between each
pair of cationic enantiomers. We verified that the distances
between protons that showed an NOE in the NMR studies
at room temperature (ꢂ22 ꢁC), unless otherwise stated, on
a VARIAN UNITY INOVA-500, on a VARIAN UNITY-
300 or on a VARIAN INOVA-400 spectrometers. Chemi-
cal shifts (ppm) are relative to TMS (1H, 13C NMR),
1
H3PO4 (85%) (31P NMR) and CFCl3 (19F NMR). H–1H
COSY spectra: standard pulse sequence with an acquisition
time of 0.214 s, pulse width 10 ms, relaxation delay 1 s,
number of scans 16, number of increments 512. The
NOE difference spectra were recorded with 5000 Hz, acqui-
sition time 3.27 s, pulse width 90ꢁ, relaxation delay 4 s, irra-
diation power 5–10 dB. NOESY spectra for 6 (VARIAN
INOVA-500) standard parameters: relax delay 1.000 s,
mixing 1.00 s, acquisition time 0.128 s, width 7996.0 Hz,
2D width 7996.0 Hz, 16 repetitions, 2 · 256 increments,
DATA PROCESING Gauss apodization 0.059 s, F1
DATA PROCESING Gauss apodization 0.030 s.
19F–19F-COSY spectra: standard pulse gCOSY sequence,
standard parameters: VARIAN INOVA-400, relax delay
1.000 s, acquisition time 0.181 s, width 22624.4 Hz, 2D
width 22624.4 Hz, single scan, 128 increments, Sq sine bell
0.091 s. HSQC, VARIAN INOVA-400 Temp = 40 ꢁC,
Relax. delay 1.000 s, Acq. time 0.211 s,Width 4861.4 Hz,
2D Width 20110.6 Hz, 128 repetitions, 2 · 256 increments.
For variable temperature spectra, the probe temperature
( 1 K) was controlled by a standard unit calibrated with
a methanol reference. IR spectra were recorded on a Nico-
let Impact 410 spectrophotometer as KBr pills, or on a
Jasco FT/IR – 6300 type A (630–150 cmꢀ1 range) in Nujol
mulls, or on a Perkin–Elmer 883 (4000–200 cmꢀ1 range) in
Nujol mulls. Elemental analyses were performed in a
LECO CHNS932 microanalyser. FAB+ mass spectra were
recorded in a VG AutoSpec using a ionization Liquid Sec-
ondary Ion Mass Spectrometry (LSMIS+) and Cs and
NBA ions as the matrix and in a 4700 Proteomics Analyzer
(MALDI-TOFTOF) of Applied Biosystems (dry sample
preparation with dithranol). The ligand dpim [8] and the
complexes [PdCl2(cod)] [42], [PdCl2(PhCN)2] [43],
[PdClMe(cod)] [44], [Pd(g3-2-Me–C3H4)Cl]2 [45] and
[Pd(C6F5)2(cod)] [46] were prepared as previously
described. o = ortho, m = meta, p = para, d = doublet,
m = multiplet, s = singlet, b = broad.
˚
are in the range 3.346–3.732 A.
3. Conclusions
We have synthesised several palladium complexes con-
taining the hemilabile ligand 2-(diphenylphosphino)-1-
methylimidazole (dpim) and different modes of coordination
have been found (P monodentate and P,N bridge). It has
been found that small changes in the other ligands present
in the complexes influence the type of coordination of the
dpim ligand. An unexpected coordination of water to the
palladium centre has been achieved in one complex. For
the chloromethyl derivatives, the transformations between
mononuclear and dinuclear species demonstrate the exis-
tence of type III hemilability. The allyl derivative that is
present as a mixture of two pairs of enantiomers exhibits
double HT dpim bridges with a relative cis disposition.
In the minor isomer whose structure has been determined
by X-ray diffraction the two allylic methyl groups have
the same relative orientation, a very unusual fact for dinu-
clear palladium g3-allyl derivatives with eight-membered
metallacycles. A solvent dependent fluxional process that
involves Pd–N bond rupture has been found for this deriv-
ative. The dynamic process implies that the allyl group acts
as a reporter ligand and shows the hemilabile behaviour of
the dpim ligand.
4.2. Synthesis of [PdCl2(dpim)]n Æ n/2CH2Cl2 (1)
The ligand dpim (74.56 mg, 0.28 mmol) was added to a
solution of [PdCl2(cod)] (80 mg, 0.28 mmol) in CH2Cl2
(20 mL). The mixture was stirred at room temperature.
After 15 min an orange precipitate was formed and one
hour later this orange solid (1) was filtered, washed with
diethylether (2 · 10 mL) and dried under vacuum. Yield:
102.4 mg (0.22 mmol, 79%). Note. Alternatively the reac-
tion can be carried out using [PdCl2(PhCN)2] as the start-
ing material in acetone or THF. PdCl2(dpim) Æ 1/2CH2Cl2,
4. Experimental
4.1. General remarks
C16.5H16Cl3N2PPd (486.06): calcd. C, 40.77; H, 3.32; N,
All manipulations were carried out under Ar using stan-
dard Schlenk techniques. Solvents (Merk) were dried and
distilled under N2 prior to use. NMR spectra were recorded
5.76. Found: C, 40.61; H, 3.57; N, 5.81%. MALDI
mass spectra: m/z = 598 Da, [PdCl(dpim)2–C6H5]+; 675 Da,
[PdCl(dpim)2]+; 781 Da [Pd2Cl(dpim)2]+; 816 Da, [Pd2Cl2-

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V. Dı´ez et al. / Journal of Organometallic Chemistry 692 (2007) 1482–1495
(dpim)2]+; 853 Da (base peak), [Pd2Cl3(dpim)2]+; 895 Da,
[Pd2Cl5(dpim-Me)2]+; 1034 [Pd3Cl6(dpim-Me)2]+; 1214 Da,
tentatively assigned to: [Pd4Cl8(dpim-CH2)2]+.
NMR (75.432 MHz, CD3COCD3, 298 K): d = 135.3 (d,
1
2JPC = 10.3, 8C, Co–Ph), 131.4 (d, JPC = 46.3, 4C, Cipso
–
4
Ph), 130.7 (d, JPC = 2.6, 4C, Cp–Ph), 129.3 (d,
0
1JPC = 41.2, 2C, C2 –Im), 129.8 (s, 2C, CH–Im), 128.3 (d,
3JPC = 10.3, 8C, Cm–Ph), 125.7 (s, 2C, CH–Im), 35.39 (s,
2C, Me–Im), 1.5 (s, 1C, Me–Pd) ppm.
4.3. Synthesis of [PdCl2(H2O)(dpim-jP)] (2)
Complex 1 was solved at 70 ꢁC in wet DMSO-d6 to give
a yellow solution of complex 2 which was characterized by
NMR. The solid was isolated as follows: the solvent was
removed by heating the solution under vacuum. The oily
residue was then solved in THF and precipitated with
diethylether. The resulting yellowish-white solid was dried
under vacuum and completely characterized. C16H17Cl2N2-
OPPd (461.62): calcd. C, 41.63; H, 3.71; N, 6.07. Found: C,
41.20; H, 3.78; N, 6.16%. IR (KBr pellet, cmꢀ1), m(O–H,
H2O and C–H, aromatic) = 3201 (b), 3163, 3134, 3113,
3056, 3028; far-IR (nujol mull, cmꢀ1), m(Pd–O) = 490;
4.6. Synthesis of [Pd(C6F5)2(dpim-jP)2] (5)
The ligand dpim (83.5 mg, 0.32 mmol) was added to a
solution of [Pd(C6F5)2(cod)] (86 mg, 0.16 mmol) in dichlo-
romethane (30 mL). The mixture was stirred at room tem-
perature for 30 min and then the solvent was removed
under vacuum. The residue was washed with pentane
(2 · 10 mL) and dried under vacuum. A pale yellow solid
of complex 5 was obtained. Yield: 126.63 mg (0.13 mmol,
83%). C44H30F10N4P2Pd (973,09): calcd. C, 54.31; H,
3.11; N, 5.76. Found: C, 54.25; H, 3.01; N, 5.96%. IR
(KBr, cmꢀ1), 1500, 1057, 958, 780 and 770 (C6F5). See
1
m(cis-PdCl2) = 293, 306. See Table 1 for the H and 31P
NMR data.13C{1H} NMR (DMSO-d6, 75.432 MHz,
298 K): d = 139.6 (d, JPC = 41.3, 1C, C2 0–Im), 130.8 (m,
Table 1 for the H and 31P NMR data. 13C{1H} NMR
1
1
3
6C, Co,p-Ph), 127.8 (d, JPC = 11.1, 4C, Cm-Ph), 122.0 (s,
(100.577 MHz, CDCl3, 298 K): d = 133.1, 130.4, 130.3,
128.2 and 125.5 (Ph+Im), 36.04 (s, 1C, Me–Im) ppm. 19F
NMR (376.308 MHz, CDCl3, 298 K): d = ꢀ114.92 (d,
1C, CH–Im), 119.5 (s, 1C, CH–Im), 36.5 (s, 1C, Me–Im)
1
ppm. It was confirmed that the H NMR spectra of the
3
solid obtained is the same than that observed after solving
1 in DMSO-d6. FAB+ mass spectra: m/z = 427 Da,
[PdCl(H2O)(dpim)]+; m/z = 389 Da, [Pd(OH)(dpim)]+.
3JFF = 21.56, 4F, Fortho, C6F5), ꢀ161.91 (t, JFF = 21.56,
2F, Fpara, C6F5), ꢀ162.95 (m, 4F, Fmeta, C6F5) ppm.
FAB+ mass spectrum: m/z = 372 Da [Pd(dpim)]+, 433 Da
[(dpim)(C6F5)]+ꢀ (base peak), 539 Da [Pd(C6F5)(dpim)]+,
639 Da [Pd(dpim)2+H]+, 746 Da [Pd2(dpim)2]+, 805 Da
[Pd(C6F5)(dpim)2]+, 913 Da [Pd2(C6F5)(dpim)2]+.
4.4. Synthesis of [PdClMe(l-dpim-jN,jP)]2 (3)
The ligand dpim (57 mg, 0.21 mmol) was added to a
solution of [PdClMe(cod)] (55 mg, 0.21 mmol) in THF
(15 mL). The mixture was stirred for 30 min at room tem-
perature. A pale yellow precipitated was formed that was
filtered, washed with diethylether (2 · 10 mL) and dried
under vacuum. Yield: 81.68 mg (0.19 mmol, 93%).
C17H18ClN2PPd (423.18): calcd. C, 48.25; H, 4.29; N,
6.62. Found: C, 47.93; H, 4.32; N, 6.72%. IR (nujol mull,
cmꢀ1), m(Pd–Cl) = 311. See Table 1 for the 1H and 31P
NMR data. FAB+ mass spectrum: m/z = 811 Da [Pd2Cl-
4.7. Synthesis of [Pd(g3-2-Me–C3H4)(dpim-
jN,jP)]2[PF6]2 (6)
AgPF6 (160.5 mg, 0.5 mmol) was added to a solution of
[Pd(C4H7)Cl2]2 (100 mg, 0.25 mmol) in acetone (100 mL).
The mixture was stirred for 3 h in the absence of light
and the resulting yellow solution was filtered and the solid
residue, AgCl, washed with acetone (2 · 5 mL) to extract
some additional palladium complex. The washing liquor
was added to the yellow solution and both together treated
with dpim, (135.2 mg, 0.5 mmol). This mixture was stirred
1.5 h and then the solvent was removed under vacuum. The
resulting oil became a white solid after treatment with pen-
tane (20 mL) and drying under vacuum. Yield: 106.1 mg
(0.19 mmol, 73%). C20H22N2P2PdF6 (572.75): calcd. C,
41.94; H, 3.87; N, 4.89. Found: C, 41.84; H, 3.92; N,
5.11%. IR (KBr, cmꢀ1): m(P–F) = 835, d(FPF) = 557, 547
Me2(dpim)2]+ (base peak). 13C{1H} NMR (100.577 MHz,
1
DMSO-d6, 298 K): d = 139.4 (d, JPC = 74.2, 2C, Cipso
–
1
Ph); 136.3 (d, JPC = 74.22, 2C, Cipso–Ph); 134–125 (m,
Ph+Im); 36.9 (d, JPC = 29.4, 2C, Me–Im); 11.2 (d,
2JPC = 72.9, 2C, Me–Pd).
4.5. Synthesis of [PdClMe(dpim-jP)2] (4)
1
The ligand dpim (114 mg, 0.42 mmol) was added to a
solution of [PdClMe(cod)] (55 mg, 0.21 mmol) in THF
(15 mL). The mixture was stirred for 30 min at room tem-
perature and afterwards the solvent was removed under
vacuum. The resulting pale yellow solid was washed with
diethylether (2 · 10 mL) and dried under vacuum. Yield:
137.4 mg (0.2 mmol, 96%). C33H33ClN4P2Pd (689.46):
calcd. C, 57.49; H, 4.82; N, 8.13. Found: C, 57.21; H,
4.79; N, 8.41%. IR (nujol mull, cmꢀ1), m(Pd–Cl) = 304.
See Table 1 for the 1H and 31P NMR data. 13C{1H}
(PF6). H NMR (500 MHz, CD3COCD3, 293 K): 6m: the
0
following signals have been identified: 7.20 (s, 1H, H5 –
0
Im), 6.75 (s, 1H, H4 –Im), 5.03 (m, 1H, Hsyn2), 4.74 (m,
0
1H, Hsyn2 ), 4.37 (d, JPH = 8.8, 1H, Hanti2), 3.82 (d,
0
JPH = 10.7, 1H, Hanti2 ), 3.74 (m, 1H, Hallyl), 3.37 (bd,
1H, Hsyn1), 3.23 (s, 3H, Me–Im), 3.19 (s, 3H, Me–Im)
1
ppm. H NMR (500 MHz, 1,10,2,20-tetrachloroethane-d2,
293 K): 6M: 7.6 (m, 12H, Hmeta and Hpara), 7.3 (m, 4H,
0
H
ortho), 7.12 (s, 2H, H5 –Im), 7.0 (m, 4H,0 Hortho, protons
situated near to Me–Im), 6.12 (s, 2H, H4 –Im), 4.40 (dd,

V. Dı´ez et al. / Journal of Organometallic Chemistry 692 (2007) 1482–1495
1493
2H, JHsyn2–Hsyn1 = 2.9, JHP = 6.8, Hsyn2), 3,45 (d, 2H,
Acknowledgements
JHP = 11.2, Hanti2), 3.26 (d, 2H, Hsyn1), 3.06 (s, 6H, Me–
Im), 2.96 (s, 2H, Hanti1), 2.04 (s, 6H, Me-allyl). 6m: the fol-
lowing signals have been identified: 6.72 (s, 1H, CH–Im),
6.23 (s, 1H, CH–Im), 4.56 (m, 1H, Hsyn2), 4.36 (m, 1H,
0
We are grateful to the Spanish DGES/MCyT (Project
No. CTQ2005-01430/BQU) for financial support. Thanks
to Dr. Jacinto Delgado from SCAI of University of Burgos
for sample analysis. We also thank to Prof. Mariano Lagu-
H
syn2 ), 3.90 (d, 1H, JHP = 8.8, Hanti2), 3.30 (d, 1H,
0
´
JHP = 10.7, Hanti2 ), 3.19 (bs, 1H, Hallyl), 3.14 (bs, 1H, Hallyl),
3.04 (s, 3H, Me–Im), 2.99 (s, 3H, Me–Im), 2.92 (s, 1H,
na from the Instituto de Ciencia de Materiales de Aragon
for carrying out the mass spectra.
H
allyl), 1.98 (s, 3H, Me–allyl), 1.93 (s, 3H, Me-allyl).
13C{1H}–NMR (75.432 MHz, CD3COCD3, 298 K, 6M):
Appendix A. Supplementary material
0
d = 139.8 (d, JPC = 5.0, 2C, C4 –Im), 138.7 0 (d, JPC
=
3
1
0
61.8, 2C, C2 –Im), 133.0 (d, JPC = 14.6, 2C, C5 –Im), 132.0
CCDC 607744 contains the supplementary crystallo-
graphic data for this paper. These data can be obtained free
of charge via http://www.ccdc.cam.ac.uk/conts/retriev-
ing.html, or from the Cambridge Crystallographic Data
Centre, 12 Union Road, Cambridge CB2 1EZ, UK; fax:
(+44) 1223-336-033; or e-mail: deposit@ccdc.cam.ac.uk.
Supplementary data associated with this article can be
found, in the online version, at doi:10.1016/j.jorganchem.
2006.11.045.
3
2
(d, JPC = 9.5 Hz, 4C, Co-Ph), 131.9 (s, 2C, Cp–Ph), 131.6
(d, 4C, JPC = 12.9 Hz, Co–Ph), 130.5 (d, JPC = 10.3 Hz,
4C, Cm–Ph), 130.3 (s, 2C, Cp–Ph), 130.2 (d, JPC = 9.3 Hz,
4C, Cm–Ph), 128.2 (d, JPC = 44.0, 2C, Cipso–Ph), 125.0 (d,
2
3
3
1
1JPC = 45.0, 2C, Cipso–Ph), 78.4 (d, JPC = 31.2, 2C, C2-
allyl), 64.4 (s, 2C, C1-allyl), 36.8 (s, 2C, Me–Im), 23.2 (s,
2C, Me-allyl) ppm. 31P{1H} NMR (121 MHz,
CD3COCD3, 293 K, 6m): d = 10.43 (s, 1P), 9.93 (s, 1P)
ppm. FAB+ mass spectrum: m/z = 1001 Da {[Pd2(C4H7)2-
(dpim)2]PF6}+, m/z = 801 Da [Pd2(C4H7)- (dpim)2]+, m/
z = 746 Da [Pd2(dpim)2]+, m/z = 427 Da [Pd(C4H7)-
(dpim)]+ (base peak), m/z = 372 Da [Pd-(dpim)]+, m/z =
265 Da [(dpim-H)]+.
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1494
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