New cyclometallated precursors of unsubstituted N-phenylpyrazole [{Pd(phpz)(μ-X)}2] (X = AcO or OH) and study of their reactivity towards selected ligands

Article abstract of DOI:10.1039/c0dt00814a

A new acetate-bridged dinuclear palladacycle with unsubstituted N-phenylpyrazole [{Pd(phpz)(μ-AcO)}₂] 1 has been isolated and characterised, including an X-ray diffraction study. A survey of the Cambridge Structural Database (CSD) v. 5.31 looking for analogous dimeric C^N cyclopalladated complexes has been done, exploring the incidence of cisoid/transoid arrangements, the preferred conformation of the eight-membered ring formed in the double bridge, the Pd-Pd distance and the main factors that affect it. The reaction of 1 with NBu₄OH yielded [{Pd(phpz)(μ-OH)} ₂] 2 that has shown to be a complementary precursor of 1 in terms of acid/base reactivity. In this sense, both 1 and 2 are also well differentiated from halide precursors available to date. The preparation of selected complexes with potential applications in several fields, [Pd(phpz)(O^N)] O^N = N-p-chlorophenylsalycilaldiminate (N-pClsal) 3, picolinic acid (pic) 4; 8-hydroxiquinolinate (oxin) 5; 2-pyrrole-carboxaldeydate (2-pcal) 6, [Pd(phpz)(O^O)] O^O = salycilaldehydate (sal) 7 acetylacetonate (acac) 8, [{Pd(phpz)(μ-N^S)}₂] N^S = 2-mercapto-1-methylimidazolate (SMeimz) 11; [{Pd(phpz)(μ-N^O)}₂] N^O = succinimidate (succ) 12; [{Pd(phpz)(μ-N^N)}₂] (N^N = pyrazolate (pz) 13, has been achieved using 1 or 2 as starting materials in acid/base reactions. Dithiocarbamate [Pd(phpz)(S₂CNEt₂)] 9 and dithiophosphate [Pd(phpz){S(S)P(OEt)₂}] 10 derivatives have been synthesised in related reactions, and the reactivity of 1 against neutral phoshine ligands has also been tested with the preparation of [Pd(phpz)(AcO)(PPh₃)] 14. The crystal structures of compounds 7, 9, 11, 12 and 13 (this one obtained from a powder sample using synchrotron radiation) have also been established, and together with 1 are the first examples of complexes containing unsubstituted N-phenylpyrazole as cyclometallated backbone that have been deposited to date on the Cambridge Structural Database.

Full text of DOI:10.1039/c0dt00814a

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PAPER
New cyclometallated precursors of unsubstituted N-phenylpyrazole
[{Pd(phpz)(l-X)}2] (X = AcO or OH) and study of their reactivity towards
selected ligands†
Jose´ Luis Serrano,*a Luis Garc´ıa,a Jose´ Pe´rez,a Eduardo Pe´rez,a Jose´ Miguel Galiana,a Joaqu´ın Garc´ıa,b
Marina Mart´ınez,b Gregorio Sa´nchezb and Ivan da Silvac,d
Received 9th July 2010, Accepted 14th September 2010
DOI: 10.1039/c0dt00814a
A new acetate-bridged dinuclear palladacycle with unsubstituted N-phenylpyrazole
[{Pd(phpz)(m-AcO)}2] 1 has been isolated and characterised, including an X-ray diffraction study. A
survey of the Cambridge Structural Database (CSD) v. 5.31 looking for analogous dimeric CˆN
cyclopalladated complexes has been done, exploring the incidence of cisoid/transoid arrangements, the
preferred conformation of the eight-membered ring formed in the double bridge, the Pd–Pd distance
and the main factors that affect it. The reaction of 1 with NBu4OH yielded [{Pd(phpz)(m-OH)}2] 2 that
has shown to be a complementary precursor of 1 in terms of acid/base reactivity. In this sense, both 1
and 2 are also well differentiated from halide precursors available to date. The preparation of selected
complexes with potential applications in several fields, [Pd(phpz)(OˆN)] OˆN = N-p-chlorophenylsalycil-
aldiminate (N-pClsal) 3, picolinic acid (pic) 4; 8-hydroxiquinolinate (oxin) 5; 2-pyrrole-carboxaldeydate
(2-pcal) 6, [Pd(phpz)(OˆO)] OˆO = salycilaldehydate (sal) 7 acetylacetonate (acac) 8, [{Pd(phpz)(m-
NˆS)}2] NˆS = 2-mercapto-1-methylimidazolate (SMeimz) 11; [{Pd(phpz)(m-NˆO)}2] NˆO =
succinimidate (succ) 12; [{Pd(phpz)(m-NˆN)}2] (NˆN = pyrazolate (pz) 13, has been achieved using 1 or
2 as starting materials in acid/base reactions. Dithiocarbamate [Pd(phpz)(S2CNEt2)] 9 and
dithiophosphate [Pd(phpz){S(S)P(OEt)2}] 10 derivatives have been synthesised in related reactions, and
the reactivity of 1 against neutral phoshine ligands has also been tested with the preparation of
[Pd(phpz)(AcO)(PPh3)] 14. The crystal structures of compounds 7, 9, 11, 12 and 13 (this one obtained
from a powder sample using synchrotron radiation) have also been established, and together with 1 are
the first examples of complexes containing unsubstituted N-phenylpyrazole as cyclometallated
backbone that have been deposited to date on the Cambridge Structural Database.
reactive palladium acetate as the source of the metal, which
Introduction
2-
proved to be a more useful starting material than PdCl4 to
Since the description of the easy cyclopalladation of azoben-
achieve cyclopalladation in some cases, and especially since the
zene upon reaction with tetrachloropalladate in 1965,1 several
resulting acetato-bridged dimers were conveniently soluble in
related organopalladium compounds that incorporated an in-
common organic solvents.4 Thus the availability of both halide and
tramolecular nitrogen atom were soon reported.2 The chloride-
acetate-bridged dinuclear precursor, of for example unsubstituted
bridged compounds were generally insoluble, and at that time
orthometallated backbones such as 2-(2-pyridyl)phenyl or 7,8-
their characterisation usually included the conversion to soluble
benzoquinolyl, owing differentiated properties and reactivity has
mononuclear derivatives with phosphine, pyridine or acetilacet-
revealed to be a powerful synthetic tool extensively employed
onato ligands.3 Initial synthetic interest led to explore the more
to obtain mono- and dinuclear cyclometallates.5,6 Indeed, in
our hands, the use of chloro-, acetate- or hydroxo- bridged
a
´
Departamento de Ingenier´ıa Minera, Geolo´gica y Cartogra´fica. Area de
dimers of those CˆN systems even promoted different coor-
dination modes in phosphine–amide ligands.7 Nowadays the
initial synthetic interest that the cyclometallation reaction3a,8 with
Pd(II) salts attracted has been surpassed by the wide variety
of applications found by cyclometallated compounds acting as
mesogenic and luminescent agents or in different fields like or-
ganic synthesis, organometallic catalysis, medicinal and biological
chemistry.9
Qu´ımica Inorga´nica, 30203, Cartagena, Spain
bDepartamento de Qu´ımica Inorga´nica, Universidad de Murcia, 30071,
Murcia, Spain
cSpLine Spanish CRG Beamline at the ESRF, Grenoble cedex ESRF-BP,
220-38043, France
dInstituto de Ciencia de Materiales de Madrid-ICMM/CSIC, Cantoblanco
Madrid, 28049, Spain
† CCDC reference numbers 783647–783652. For crystallographic data in
CIF or other electronic format see DOI: 10.1039/c0dt00814a
156 | Dalton Trans., 2011, 40, 156–168
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Regarding unsubstituted N-phenylpyrazole, its chloride-
bridged and a few derivatives were reported in the early 70s,10
but surprisingly the analogous acetate complex has not been
synthesised and its chemistry has not been further explored apart
from the excellent NMR study carried out by Caygill and Steel11
on those derivatives previously reported. In fact not even a crystal
structure has been deposited to date on the Cambridge Structural
Database (CSD) v. 5.31 (November 2009 and three updates) and
only a few containing substituted N-phenylpyrazoles have been
reported so far.11b,12
On the other hand, in addition to their interest related to applied
fields such as antitumour activity13 or catalytic processes,14 the
synthetic value of palladium(II) and platinum(II) di-m-hydroxo-
complexes is a subject of continuous study.15 For example, Sharp16
and later others,17 have employed several such complexes as
precursors in the preparation of scarce oxo- and imido- derivatives
that are also relevant to C–O and C–N bond forming reactions
in catalytic processes. The reactivity towards protic substrates of
dinuclear compounds [Pd(m-OH)Ln]2 (Ln = orthometallated imine-
based ligands) provides a general route to obtain mesomorphic
mono- and dinuclear complexes.18 In this sense, during the
last few years we have also been developing the usefulness of
binuclear hydroxo complexes of palladium, some of them with
a cyclometallated backbone,7,19 in the preparation of a wide
variety of new compounds by means of a simple acid–base
reaction.20
acetate]+ and [Pd(phpz)]+. The abundances of the signals around
the pattern ion are consistent with the natural isotopic ones.
The expected solubility of the new precursor allowed its NMR
characterisation. In the experimental section are the two sets of
signals observed in the (CD3)2CO spectra attributed to a 1 : 3
mixture of cis- and trans-isomers. The presence of these isomers in
acetato-bridged cyclometallated dimers is well known,12a,21 and
their distinction has been made on the basis of the methyl-
AcO resonances that appear as one or two singlets for the
trans- or cis-isomer, respectively. In our case the major isomer
corresponds to a trans-arrangement and the assignment has been
done by comparison with reported data for the free ligand and
the acetylacetonate derivative.11a As it was also possible to grow
single crystals of complex 1 suitable for X-ray diffraction, we were
able to unambiguously confirm the molecular structure and the
mentioned conformation, presented in Fig. 1. As mentioned above,
this and the other X-ray structures presented in this paper are
the first examples of complexes containing simple cyclometallated
N-phenylpyrazole reported to date. Selected bond distances and
angles are displayed in Table 1.
In this paper we present the synthesis of the cyclopalladated
acetate dimer [{Pd(phpz)(m-AcO)}2] (phpz = N-phenylpyrazole)
and its characterisation, including the X-ray structure determina-
tion and a comparative structural study with related compounds
previously reported. The easy transformation to the corresponding
di-m-OH precursor is also described. Apart from their intrinsic
interest, the acetate- and hydoxo-complexes of palladium whose
reactivity we present here can offer a convenient and fastest
route in the preparation of compounds that may even not be
accessible using classical halide precursors. Specifically we explore
here the reactivity of [{Pd(phpz)(m-X)}2] (X = AcO or OH)
towards several protic electrophiles, related reactions like that
against amines in the presence of carbon disulfide or also neutral
ligands, all selected to yield complexes that have shown interesting
structural features/physical properties with other orthometallated
backbones similar to N-phenylpyrazole.
Fig. 1 ORTEP diagram of complex 1 with the atom numbering scheme;
thermal ellipsoids are drawn at the 50% probability level.
A survey of the Cambridge Structural Database (CSD) v.
5.31 (November 2009 and three updates) reveals that the trans-
arrangement is also preferred in the solid state and that a
folded shape, commonly known as open-book structure, is always
adopted. The CSD was searched for all the structures of dimeric
CˆN cyclopalladated complexes containing a double carboxylate
bridge with a total of 86 refcodes matching the search, 15 of them
have a six membered cyclopalladated CˆN ring and the resting 71
have a five membered ring. It was not until 2002 that the first crystal
structure of a cisoid-acetate bridged dinuclear cyclometallated
complex was reported (refcode XUHVAX).22 A selected iminic
backbone 2,3,4-(MeO)3C6H2C(H) NCH2CH2OH with small
steric hindrance at the N-atom was claimed to direct the adoption
of this conformation, that can be determined without ambiguity
due to the geometry of the iminic ligand itself. Since then only
two structures with refcodes NOGKUG23 and XEMQIQ0124 and
simple unsubstituted backbones have appeared as cisoid at the
Results and discussion
Synthesis and characterisation
The acetato-bridged cyclometallated dimer [{Pd(phpz)(m-AcO)}2]
1 was readily prepared in good yield by the classical method
that involves reacting N-phenylpyrazole with Pd(AcO)2 in hot
acetic acid. The infrared spectra of 1 displayed the characteristic
absorptions around 1512 and 750 cm-1 corresponding to C
N
absorption of the cyclometallated ligand and the out-of-plane
C–H bending in disubstituted arenes, respectively. A strong
broad band of carbonyl stretching centered in 1561 cm-1 is the
main feature of the spectra that allows fast monitoring of the
reactions explored with this precursor. Support for the proposed
dinuclearity of complex 1 comes from the mass spectrometry, as
can be implied by the m/z values for the observed fragments [M+-
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◦
˚
Table 1 Selected bond lengths (A) and angles ( ) for complexes 1, 11, 12 and 13 (structure solved by powder X-ray diffraction)
1
11
Pd(1)–C(1)
Pd(1)–N(1)
Pd(1)–O(1)
Pd(1)–O(2)
C(1)–Pd(1)–N(1)
C(1)–Pd(1)–O(1)
C(1)–Pd(1)–O(2)
N(1)–Pd(1)–O(1)
N(1)–Pd(1)–O(2)
O(1)–Pd(1)–O(2)
Pd(1)–Pd(2) 2.8421(3)
12
1.966(3)
1.983(3)
2.040(2)
2.120(2)
80.86(13)
94.33(12)
175.70(12)
173.91(10)
94.86(11)
89.96(9)
Pd(2)–C(12)
Pd(2)–N(3)
Pd(2)–O(3)
Pd(2)–O(4)
C(12)–Pd(2)–N(3)
C(12)–Pd(2)–O(3)
C(12)–Pd(2)–O(4)
N(3)–Pd(2)–O(3)
N(3)–Pd(2)–O(4)
O(3)–Pd(2)–O(4)
1.963(3)
1.999(3)
2.132(2)
2.037(2)
81.44(12)
175.02(11)
93.49(12)
95.46(10)
174.92(10)
89.61(9)
Pd(1)–C(1)
Pd(1)–N(1)
Pd(1)–N(7)
Pd(1)–S(1)
C(1)–Pd(1)–N(1)
C(1)–Pd(1)–N(7)
C(1)–Pd(1)–S(1)
N(1)–Pd(1)–N(7)
N(1)–Pd(1)–S(1)
N(7)–Pd(1)–S(1)
Pd(1)–Pd(2) 2.9621(4)
13
1.999(3)
2.042(3)
2.118(3)
2.2985(9)
80.84(13)
174.18(13)
92.85(10)
93.82(12)
173.49(9)
92.55(8)
Pd(2)–C(14)
Pd(2)–N(3)
Pd(2)–N(5)
Pd(2)–S(2)
C(14)–Pd(2)–N(3)
C(14)–Pd(2)–N(5)
C(14)–Pd(2)–S(2)
N(3)–Pd(2)–N(5)
N(3)–Pd(2)–S(2)
N(5)–Pd(2)–S(2)
2.006(3)
2.121(3)
2.031(3)
2.2925(10)
173.86(13)
81.03(14)
92.11(11)
95.05(12)
91.74(9)
173.12(9)
Pd(1)–C(1)
Pd(1)–N(1)
Pd(1)–N(3)
Pd(1)–O(2)
C(1)–Pd(1)–N(1)
C(1)–Pd(1)–N(3)
C(1)–Pd(1)–O(2)
N(1)–Pd(1)–N(3)
N(1)–Pd(1)–O(2)
N(3)–Pd(1)–O(2)
Pd(1)–Pd(2) 2.9106(4)
1.974(3)
2.010(3)
2.037(3)
2.165(2)
81.31(12)
94.10(12)
172.49(11)
175.24(11)
93.67(10)
91.02(10)
Pd(2)–C(14)
Pd(2)–N(4)
Pd(2)–N(6)
Pd(2)–O(1)
C(14)–Pd(2)–N(4)
C(14)–Pd(2)–N(6)
C(14)–Pd(2)–O(1)
N(4)–Pd(2)–N(6)
N(4)–Pd(2)–O(1)
N(6)–Pd(2)–O(1)
1.968(3)
1.994(3)
2.026(3)
2.151(2)
81.56(13)
94.21(13)
175.23(12)
175.77(11)
93.67(11)
90.56(11)
Pd(1)–C(1)
Pd(1)–N(1)
Pd(1)–N(5)
Pd(1)–N(7)
1.966
2.058
2.064
2.060
79.35
Pd(2)–C(10)
Pd(2)–N(3)
Pd(2)–N(6)
Pd(2)–N(8)
C(10)–Pd(2)–N(3)
2.079
2.087
2.063
2.154
76.73
C(1)–Pd(1)–N(1)
N(5)–Pd(1)–N(7)
92.83
N(6)–Pd(2)–N(8)
82.69
Pd(1)–Pd(2) 3.569
˚
CSD, although the authors have not even commented it in the
articles. A survey of the data available at the CSD for NOGKUG
and XEMQIQ01, paying special attention to the trans influence
associated with an aromatic carbon and with an aromatic nitrogen,
that produce bond distances trans to C significantly longer than
trans to N, revealed a mistake in the assignment of C/N atoms
around one palladium that would make these structures also
transoid. It seems that the differentiated trans influence would
favour the preferred trans geometric isomer in solid state, in which
alternated long/short Pd–O distances are found in the double
bridge (C2), formed in this case by two identical units of bridge.
Cisoid-isomer would involve two different units instead that fit
worse, a side of the bridge with short Pd–O distances opposite to
a side with long Pd–O distances (Cs).
distance = 2.924; min. = 2.823; max. = 3.281 A, 55 refcodes once
excluded those with errors, disorder or not availability of 3D
coordinates). When working with the more recent data set29 the
˚
value of 1.39(6) A for Pd covalent radius takes the complexes of the
low part of the list close to a single bond. The distance in 1 is quite
short, as it is for the 11 complexes that contain a cyclometallated
backbone formed by a set of 6 (including the C bonded to Pd) and
5 membered rings like N-phenylpyrazole (mean Pd–Pd distance =
˚
2.874, min. = 2.831; max. = 3.159 A). In fact only the complex
JEPVEF,30 that has the maximum distance of 3.159 A with the
˚
hindering 2-(4¢,4¢-dimethyl-2-oxazolinyl)phenyl backbone, is up
to 2.88 A in this group. Other planar backbones with a set of two 6
membered rings like 2-phenylpyridine produce 8 complexes in the
similar range of Pd–Pd distances, all below 2.90 A. Azobencenes
˚
˚
The geometric isomer does not affect the conformation of
the eight-membered ring formed in the double bridge. We have
developed methods for the conformational classification of these
rings.25 From this perspective the Pd1–O1–C10–O3–Pd2–O4–
C21–O2 ring in complex 1 displays a boat–boat conformation
(BB = 0.9864; S = 0.0136 for s = 10◦) deformed 39◦. The same
distribution appears in 66 from 182 total fragments.
and imine based ligands (23 refcodes: mean Pd–Pd distance =
2.980; min. = 2.834; max. = 3.281 A) that bear freely rotating
groups on the N atom bonded to Pd, together with N,N dimethyl
benzylamine and related systems are the cyclometallating ligands
˚
˚
prone to give Pd–Pd distances up to 2.90 A in the family of
complexes under study. We grouped separately complexes with
a palladacycle of six members that have longer Pd–Pd distances
˚
The surrounding of the Pd atoms in 1 may be described as
planar and their deviation from the planar coordination has been
quantified by measures of improper torsion angles, with values
of w1 = -0.06◦ and w2 = -2.44◦ for Pd(1) and w1 = -2.62◦ and
w2 = 0.05◦ for Pd(2).26 These values correspond respectively to
a tetrahedral and pyramidal square distortion from the ideal
square-plane. The N–Pd–C angle, 80.86(13)◦ and 81.44(12)◦,
is similar to that found in related complexes with substituted
(mean Pd–Pd distance = 2.987; min. = 2.888; max. = 3.113 A).
Thus, in complexes with a double carboxylate bridge, it seems that
the number of atoms in the palladacycle, the bulky substituents
on key positions and the planarity of the cyclometallated ligands
(with potential interactions between faced groups) are the main
factors that would control the Pd–Pd distance.
Complex 1 displays an interesting arrangement of the two phpz
ligands, nearly parallel but not eclipsed with centroid-plane and
centroid–centroid distances compatible with a face-to-face sliced
intramolecular p–p interaction. (Fig. 2)
The cyclometallated precursor [{Pd(phpz)(m-OH)}2] 2 was
conveniently prepared by the smooth reaction of the acetate-
bridged complex with NBu4OH in acetone. The IR spectrum of the
new complex exhibited a clean carbonyl region and the expected
N-phenylpyrazoles.11b,12 Pd(1)–Pd(2) distance of 2.8421(3) A is
˚
well in the generally accepted range for a Pd–Pd intramolecular
27
˚
interaction (< 3.00 A). Some authors claimed that this
˚
interaction should not be considered a bond up to 2.62 A (taking
it as the sum of square planar palladium covalent radius),28 which
would exclude all the structures surveyed here (mean Pd–Pd
158 | Dalton Trans., 2011, 40, 156–168
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ligands are displayed in Scheme 1 and specific conditions followed
for each of them are collected in the Experimental.
In the excellent review carried out by Ghedini and coworkers,9a
they have pointed out the relationship between molecular ge-
ometries, types of ligands and important physical properties of
dinuclear and mononuclear cyclometallated derivatives containing
OˆO or OˆN complementary ligands. Thus, the authors have
studied the effects exerted by different bridging groups on the
spectroscopic and liquid-crystal properties of complexes type
[{Pd(CˆN)(m-X)}2] (X = halide, azido, thiocyanate, oxalate or
acetate),31 or the presence of an asymmetric coordination around
palladium as a key aspect for photophysical properties, well exem-
plified by complexes [Pd(phpy)(oxin-R)] that emit in solution at
room temperature.32 Cyclopalladated acetylacetonate complexes
have also been thoroughly studied, showing again the importance
of the orthometallated backbone and the substituents on the acac
moiety in the fine tuning of properties.33 As a whole these results
suggest that related complexes can be candidates for the above
mentioned practical applications.
Our new precursors react with weak protic acids H(LˆL) to give
mono- or binuclear species depending on whether the deproto-
nated acid (LˆL)- is exo- or endo-bidentate. These reactions can be
viewed as an initial proton abstraction by 1–2 that provides (LˆL)-
and the metal substrate, subsequently trapped by the anion to form
the new complexes of general formula [Pd(phpz)(LˆL)] (3–10) or
[{Pd(phpz)(m-NˆX)}2] (11–13) respectively. It is worth noting that
the synthesis of the acac complex 8 has been previously reported by
reacting [{Pd(phpz)(m-Cl)}2] with an excess of Na(acac) prepared
in advance.11b Longer reaction times (24 h) and a different work-up
in the reported procedure in comparison with the straightforward
route that we present here, allow one to envisage the general
usefulness of our precursors when reacting with other substrates.
Thus a 30 min reaction at room temperature with selected
H(OˆO) or H(OˆN) ligands was enough to obtain mononuclear
complexes 3–8 when the hydroxo-complex 2 was employed as
starting material. With the exception of 6 and 7, that even under
reflux and excess of ligand produced mixtures with 1, the new
compounds can be prepared from the di m-acetate precursor in
the same smooth conditions. The derivatives are air-stable yellow
or white solids and their infrared spectra show the characteristic
absorptions of the cyclometallated ligand, partially overlapped
Fig.
distances.
2
Intramolecular arrangement in 1 displaying centroid-plane
bands for the cyclometallated backbone, together with a 3371 cm-1
absorbance due to the n(OH) stretching. The H NMR data of
1
2 are collected in the experimental section and include a con-
clusive high field resonance characteristic of palladium hydroxo-
complexes.19 Further evidence of the proposed coordination is
obtained with mass spectrometry, with a fragmentation pattern
similar to that shown by 1.
As mentioned above, complexes containing the {Pd(m-X)}2
(X = AcO or OH) core are good synthetic precursors, as their
reactions towards protic electrophiles have allowed the isolation
of numerous compounds in good yields. The reactions explored
in this paper using 1 and 2 as precursors against a selection of
Scheme 1 Reactivity of the acetato and hydroxo-complexes under study.
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Table 2 Selected bond lengths (A) and angles ( ) for complexes 7 and 9
7
9
Pd(1)–C(1)
Pd(1)–N(1)
Pd(1)–O(1)
Pd(1)–O(2)
C(1)–Pd(1)–N(1)
C(1)–Pd(1)–O(1)
C(1)–Pd(1)–O(2)
N(1)–Pd(1)–O(1)
N(1)–Pd(1)–O(2)
O(1)–Pd(1)–O(2)
1.967(5)
1.984(4)
2.088(4)
1.992(3)
80.91(19)
174.43(17)
92.52(17)
93.63(16)
172.61(16)
92.86(14)
Pd(2)–C(17)
Pd(2)–N(3)
Pd(2)–O(3)
Pd(2)–O(4)
C(17)–Pd(2)–N(3)
C(17)–Pd(2)–O(3)
C(17)–Pd(2)–O(4)
N(3)–Pd(2)–O(3)
N(3)–Pd(2)–O(4)
O(3)–Pd(2)–O(4)
1.961(5)
1.996(4)
2.105(4)
2.005(4)
81.16(19)
175.23(17)
91.72(17)
94.37(16)
171.98(16)
92.63(14)
Pd(1)–C(1)
Pd(1)–N(1)
Pd(1)–S(1)
Pd(1)–S(2)
C(1)–Pd(1)–N(1)
C(1)–Pd(1)–S(1)
C(1)–Pd(1)–S(2)
N(1)–Pd(1)–S(1)
N(1)–Pd(1)–S(2)
S(1)–Pd(1)–S(2)
2.004(3)
2.045(2)
2.2906(7)
2.3961(7)
80.77(10)
98.55(8)
172.88(8)
178.68(7)
105.14(7)
75.46(2)
in some cases with those of the incoming ligands. However the
disappearance of hydroxo or carbonyl stretching gives unequivocal
monitoring of the reaction, in agreement with the 1H NMR spectra
that show no methyl (reactions with 1) or high field (reactions with
2) resonances.
Although mononuclear complexes can exist as two isomers
depending on the relative positions of the CˆN/OˆO or CˆN/OˆN
chelating systems, the presence of only one isomer was observed
1
by H NMR except for 4 that displayed two sets of resonances
with 1 : 3 relative proportion. M+ and/or M+ + 23 signals in the
mass spectra support the proposed formulation.
The preparation of the dithiocarbamate complex 9 should in-
volve a first step of amine deprotonation, followed by nucleophilic
attack of Et2N- to carbon disulfide to form the dithiocarbamate
anion in a well known reactivity of hydroxo complexes34,19d,20c that
have allowed the preparation of new mesomorphic mononuclear
orthometallated palladium complexes.18b Characteristic dithiocar-
bamate vibrations were found in the n(CN) and n(CS) regions.
The presence of only one band in the latter at 1075 cm-1
supports the bidentate coordination of the dithio- ligand.35 As
found in other cyclopalladated systems, the alkyl groups on
the dithiocarbamate are equivalent and give one set of NMR
resonances for NEt2 protons.19d The considerable nucleophilicity
of the bridging groups of 1 and 2 make them also reactive towards
ammonium O,O¢-dimethyldithiophosphate, yielding complex 10
with the concomitant release of NH3 and H2O. The 31P NMR of
10 shows a single resonance for the coordinated dithiophosphate
ligand at the usual range.
Fig. 3 ORTEP diagram of complex 7 with the atom numbering scheme;
thermal ellipsoids are drawn at the 50% probability level.
Suitable crystals of 7 (two molecules in the asymmetric unit)
and 9 were grown from CH2Cl2–hexane, enabling their molecular
structures to be confirmed by X-ray single crystal diffraction
(Fig. 3 and 4, respectively, and Table 2).
The deviation from the planar coordination has been quan-
tified by measurements of improper torsion angles.26 The
values are 0.99◦ (C1O2O1Pd1), -2.36◦ (N1O1O2Pd1), 1.37◦
(C17O4O3Pd2), -2.62◦ (N3O3O4Pd2) in 7, while they are 2.39◦
(C1S1S2Pd1) and -0.68◦ (N1S2S1Pd1) in 9. Thus, the coordina-
tion around Pd is essentially planar in the two complexes, with
a slight square pyramidal distortion. The bite angle that involves
the CˆN ligand is also close to 81◦.
Fig. 4 ORTEP diagram of complex 9 with the atom numbering scheme;
thermal ellipsoids are drawn at the 50% probability level.
from neighbour pairs associated by means of CH-p interaction.
This packing can be observed in Fig. 5(a), and also the very similar
one found in complex 9 (Fig. 5(b)).
As mentioned in the introduction, the reactivity of di-m hydroxo
complexes towards protic substrates has provided a general route
to other dinuclear complexes with double and mixed bridges. An
interesting reaction explored here has been that of 1 or 2 against
2-mercapto-1-methyl imidazole that yields dinuclear complex 11.
We have recently prepared37 cyclometallated palladium complexes
with heterocyclic thiones that exhibited an exceptional behaviour
The planar molecules of 7 are packed in pairs with the salicylate
of one of them in front of the orthometallated ligand of the other.
˚
A distance of 3.419 A between the planes defined by these ligands
corresponds to intermolecular p–p face to face sliced interaction.36
Furthermore the planes of a pair of molecules are located at 71◦
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Fig. 5 Crystal packing found in 7 (a) and 9 (b).
since intense photoluminescence was found in both solid state and
in solution, at room temperature or 77 K, supporting the crucial
role played for those auxiliary ligands in the luminescent properties
of palladacycles suggested by other authors.9a Characterisation
data of the new complex 11 in solid state and solution are collected
in the Experimental section. In this case its dinuclear head to tail
nature, the most common arrangement in this type of complexes,38
has also been confirmed by single crystal X-ray analysis. It is
noticeable that no equilibrium in solution with the head to head
configuration was detected by 1H NMR, and only one sharp singlet
for the –Me protons was observed.
expected to be stabilised as dimers.39 Complex 11 exhibits S1–C10–
N3 and S2–C23–N7 angles of 128.2(3)◦ and 129.6(3)◦ respectively,
in the range of those previously reported for related Pd complexes.
Regarding the cyclometallated ligands, an anti-arrangement of
identical donor atoms is found with bite angles again close to 81◦
and this time the conformation of the eight-membered ring Pd1–
S1–C10–N3–Pd2–S2–C23–N4 is twist-boat deformed 41◦. Like in
complex 1 an open-book geometry is adopted, accompanied by a
˚
Pd(1)–Pd(2) distance of 2.962(4) A, within the generally accepted
value for a Pd–Pd intramolecular interaction although longer than
that found in 1. The geometry around the palladium centres is
almost planar with values of w1 = 1.41◦ and w2 = 0.90◦ for Pd(1)
(tetrahedral distortion) and w1 = -3.11 and w2 = 0.76◦ for Pd(2)
(pyramidal square distortion). Also in common with complex 1
is the arrangement of the two phpz ligands described above, that
suggest a face to face sliced intramolecular p–p interaction. In
complex 11 we have also found relevant intermolecular CH/p
interactions (with short H ◊ ◊ ◊ C distances in the range 2.413–
The corresponding ORTEP drawing is shown in Fig. 6, while
the relevant bond lengths and angles are reported in Table 1.
˚
2.792 A) and bond lengths and angles that suggest likely H ◊ ◊ ◊ Pd
anagostic interactions40,41 and weak hydrogen bonding (Fig. 7).
On the other hand, during the last few years we have devoted our
effort to understand, control and exploit the diverse functions and
role of imidate anionic ligands (rather unusual pseudohalides with
a subtle blend of s-donating and p-accepting ability)42 in topical
and important Pd-catalysed cross-coupling reactions.43 From
the discovery of the useful precatalyst44 [Pd(Br)(N-succ)(PPh3)2]
(Sigma-Aldrich; Cat. No. 643742) for Stille reaction to its re-
cent application for Suzuki–Miyaura cross-couplings of benzylic
halides,45 we have explored different synthetic routes to get second
generation imidato precatalysts. Among them, binuclear cyclomet-
allated palladium(II) complexes and mononuclear phosphine
adducts have been evaluated in Stille,46 Suzuki and Sonogashira
reactions,47 and later phosphine-free anionic dinuclear imidate
complexes48 containing a palladacyclopentadiene backbone have
shown superb performance in Stille couplings. We decided then
to prepare a sample imidate complex 12 that suggests that a
new chemistry of phenylpyrazole complexes in the fields above
mentioned could be explored. Again important differences were
found between precursors 1 and 2 when reacted against suc-
cinimide. Thus straightforward reaction with 2 takes place at
room temperature in 30 min while the acetate precursor could
not deprotonate succinimide even in excess of it and keeping
Fig. 6 ORTEP diagram of complex 11 with the atom numbering scheme;
thermal ellipsoids are drawn at the 50% probability level.
The influence of the N–C–S bond angle on the stability of
heterocyclic-2-thiolate dipalladium complexes has been studied.
Complexes containing a five-membered heterocyclic ring such
11 have larger angles than those of six-membered ones and are
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Fig. 7 Details of the interactions in 11.
the reaction under continued reflux. The IR spectra of the new
complex exhibited the expected bands for the cyclometallated
backbone, together with two strong bands in the carbonyl region
characteristic of a bridging –NCO– coordination of the imidate
ligand. Also mass spectrometry and X-ray analysis support the
proposed dinuclearity of complex 12, whose structure is displayed
in Fig. 8 and selected bond lengths and angles are collected in
Table 1.
the faced cyclometallates. In 12 molecules the atoms of the
orthometallated rings overlap in major extent than in 1 or 11 and
the angle of phpz planes opens to 29◦. Fig. 9 shows the packing of
molecules with parallel intermolecular phpz planes separated in
˚
alternating 3.424 and 3.440 A. Both Pd atoms display a tetrahedral
distortion (w1 = 3.67◦ and w2 = 0.55◦ for Pd(1) and w1 = 0.07◦ and
w2 = 0.11◦ for Pd(2)) and the conformation of the eight-membered
ring Pd1–N3–C10–O1–Pd2–N6–C23–O2 is twist-boat deformed
42◦.
Our last test of reactivity against acidic ligands of 1 and 2
allowed the preparation of the di-m-pyrazolate complex 13 from
both precursors. A large area of coordination and supramolecular
chemistry has been developed around pyrazole and pyrazolate
anions.50 As an example, homoleptic pyrazolate complexes have
been widely studied because of their potential use as liquid
crystals,51 antimicrobial drugs52 or phosphorescent materials.53
The bridging pyrazolate in cyclometallated Pt(II) complexes have
shown to control the degree of metal–metal interaction and thus
the nature of excited states.54
We have recently reported the similar solid state arrangement of
“interlocked dimers” following a herringbone-like pattern found
in all neutral dinuclear square-planar complexes having m-pz or
related bridges and planar aromatic ligands completing the coor-
dination spheres.40 There we confirmed this extent with the crystal
structures of three pseudopolymorphs of the 2-phenylpyridine
complex [{Pd(ppy)(m-pz)}2], two of which were elucidated by pow-
der X-ray diffraction, and the support of DFT-based calculations.
Due to the scarce solubility of 13, that nevertheless allowed spec-
troscopic characterisation (see Experimental), and also to avoid
the perturbation of the crystallisation process, we have elucidated
its structure by powder diffraction using synchrotron radiation.
Fig. 10 shows the expected packing of “dimers” where the N-
phenylpyrazole ligands overlap with a distance between planes of
Fig. 8 ORTEP diagram of complex 12 with the atom numbering scheme;
thermal ellipsoids are drawn at the 50% probability level.
In accordance with all the dinuclear imidate compounds
reported to date, an anti-arrangement of identical donor atoms,
and an open-book geometry is found in 12.42,49
˚
A slightly shorter Pd(1)–Pd(2) distance of 2.9106(4) A than
those found in the analogous di-m-succinimidate compounds with
42
49a
˚
˚
N-phenylbenzaldimine (2.9793 A) phenylpyridine (2.9544 A)
49d
˚
˚
3.577 A, and Table 1 collects selected crystallographic data.
or the bulkier 2-dimethylaminomethyl(ferrocenyl) (3.040 A) as
orthometallated backbones should give account of its different
steric requirements and the interactions established between
˚
The Pd ◊ ◊ ◊ Pd separation shows a value of 3.569 A within the
range of related compounds.40 The central six-membered ring
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Fig. 9 Crystal inter- and intramolecular packing in succinimidate complex 12.
Fig. 10 “Dimers” of [{Pd(phpz)(m-pz)}2], 13.
consisting of the two Pd atoms and the four pyrazolyl N atoms has
a boat-shaped conformation with mean Pd–Npz distances of 2.085
parent dinuclear acetate precursor 1 in dichloromethane. The
reaction against such neutral ligands has been explored with other
cyclometallated backbones to prepare mononuclear derivatives
that improve the catalytic activity of the starting materials in
cross-coupling reactions.55 The presence of phosphine ligands
in monomeric cyclometallated halo-complexes has also revealed
crucial to increase growth inhibitory activity against murine
leukaemias.56 The IR spectra of the new complex exhibited the
bands for the cyclometallated backbone, together with those
attributed to the incoming phosphine ligand and one strong
carbonyl band around 1600 cm-1. The 31P NMR spectrum of the
◦
˚
A and N–Pd–N mean angle of 87.76 between the two pyrazolate
groups. This conformation creates an “open book” disposition for
the square-planar environment of the two Pd atoms, the (phpz)Pd1
and (phpz)Pd2 planes forming a dihedral angle of 81.35◦.
As mentioned in the introduction, the conversion to soluble
mononuclear derivatives with phosphine or pyridine has been a
typical reaction of dinuclear precursor since the early advances
in this field. In our case, the triphenylphosphine adduct 14 was
synthesised in good yield by reaction of this ligand and the
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complex shows characteristic singlet resonance at 43.60 ppm, in
the expected range for Pd(II) complexes.
pressure. Addition of water followed by vigorous stirring and
filtration afforded a white solid which was air dried. (0.041 g, 68%).
Anal. calc. for C18H16N4O2Pd2: C, 40.6; H, 3.0; N, 10.5. Found: C,
40.6; H, 3.1; N, 10.6%). IR (cm-1): n(OH) 3371, n(phpz) 1515 m,
750m. 1H NMR (300 M Hz, CDCl3): d (SiMe4)(ppm): 8.02 (d, 2H,
H5¢, J = 2.1 Hz), 7.62 (d, 2H, H3¢, J = 2.1 Hz), 7.56 (m, 1H, H6),
7.41 (m, 2H, H5), 7.13 (m, 4H, H3, H4), 6.06 (m, 2H, H4¢), -0.15
(s, 2H, OH). Positive MS: m/z: 516 [Pd2 (phpz)2 (OH)]+.
Conclusion
We have synthesised two new versatile precursors bearing AcO or
OH bridges with simple N-phenylpyrazole acting as an orthomet-
allated backbone. The exploration of their reactivity against
selected ligands to yield twelve new complexes with potential
applications is also presented. The scarcity of complexes with this
orthometallated ligand is stated by the fact that the six crystal
structures reported here, one of them elucidated from a powder
sample using X-ray synchrotron radiation, are the first to be
deposited at the CSD. A survey of this database about dimeric CˆN
cyclopalladated complexes with a carboxylate bridging core like 1
reveals the most frequent ligands that produce them, the preferred
conformations adopted in complexes and the main factors that
seem to control the Pd–Pd distance.
Preparation of complexes [Pd(phpz)(OˆN)] OˆN
= N-p-
chlorophenylsalycilaldiminate (N-pClsal) 3, picolinic acid (pic) 4;
8-hydroxiquinolinate (oxin) 5; 2-pyrrole-carboxaldeydate (2-pcal)
6, [Pd(phpz)(OˆO)] OˆO = salycilaldehydate (sal) 7 and acety-
lacetonate (acac) 8; [{Pd(phpz)(l-NˆS)}2] (NˆS = 2-mercapto- 1
methylimidazolate (SMeimz) 11; [{Pd(phpz) (l-NˆN)}2] NˆO =
succinimidate (succ) 12; [{Pd(phpz)(l-NˆN)}2] (NˆN = pyrazolate
(pz) 13. With the exception of complexes 6, 7 and 12 that require
the use of di-m-hydroxo complex 2 as starting material, the new
complexes were obtained by treating an acetone solution (20 mL)
of the precursor 1 (0.07 g; 0.136 mmol) with the corresponding
protic ligand (HLˆL) (molar ratio 1 : 2). The reaction was stirred at
room temperature for 30 min and then it was concentrated under
reduced pressure until ca. one fifth of the initial volume. Slow
addition of diethyl ether caused the formation of the complexes,
which were filtered off, washed with diethyl ether and air-dried.
The compounds were recrystallised from dichloromethane–diethyl
ether.
Experimental
Materials and physical techniques
All chemicals were of reagent grade and were used without
further purification. Solvents were dried and distilled by general
methods before use. C, H, and N analyses were carried out with
a microanalyzer Carlo Erba model EA1108. IR spectra were
recorded on a Perkin-Elmer 16F PC FT-IR spectrophotometer
using Nujol mulls between polyethylene sheets. ESI-MS analyses
were performed on an Agilent VL mass spectrometer. The ioniza-
tion mechanism used was electrospray in positive and negative ion
full scan mode using acetonitrile as solvent and nitrogen gas for
desolvation. The NMR spectra of CDCl3 solutions were recorded
on a Bruker spectrometer (AC 200E or AC 300E).
[Pd(phpz)(NpClphsal)] 3. (0.087 g, 79%). Anal. calc. for
C22H16ClN3OPd: C, 55.0; H, 3.4; N, 8.8. Found: C, 55.0; H, 3.4;
N, 8.7%). IR (cm-1): n(NpClphsal) 1610 vs, 1530 vs, n(phpz) 1515
br, 753 s. 1H NMR (300 MHz, CDCl3): d (SiMe4)(ppm): 8.38 (d,
1H, H5¢, J = 2.7 Hz), 8.26 (s, 1H, CH-iminic), 7.87 (m, 1H, H3¢),
7.44 (m, 4H, NpClphsal), 7.13 (m, 2H, NpClphsal), 7.06 (d, 1H,
H6, J = 8.7 Hz), 6.56 (m, 4H, NpClphsal), 6.31 (m, 1H, H4), 5.67
(m, 1H, H4¢). Positive MS: m/z: 503 [Pd (phpz) (NpClphsal)]+ +
23, 249 [Pd (phpz)]+.
Synthesis of precursors [{Pd(phpz)(l-AcO)}2] and
[{Pd(phpz)(l-OH)}2] (1 and 2)
[Pd(phpz)(pic)] 4. (0.069 g, 81%). Anal. calc. for
C15H11N3O2Pd: C, 48.5; H, 3.0; N, 11.3. Found: C, 48.6; H,
3.0; N, 11.3%). IR (cm-1): n(pic) 1649 vs, 1602 s, n(phpz) 1515 s,
[{Pd(phpz)(l-AcO)}2] 1. Palladium acetate (500 mg (2.22
mmol) and excess phenylpyrazol (0.3 mL) were suspended in
glacial acetic acid (80 mL) and the mixture was heated on oil
bath (50 ◦C, 4 h). Still hot it was filtered through Celite to remove
palladium black and the solution was then concentrated under
vacuum to ca. 3 mL, layered with 15 mL acetone and stored at
5 ◦C for 24 h. The yellow product was then isolated by filtration,
washed with acetone and air dried. (0.445 g, 65%). Anal. calc. for
C22H20N4O4Pd2: C, 42.8; H, 3.3; N, 9.1. Found: C, 42.9; H, 3.4;
1
750 m. H NMR (300 MHz, CDCl3): d (SiMe4)(ppm): 8.94 (d,
1H, pic, J = 5.6 Hz), 8.62 (d, 1H, H5¢, J = 2.8 Hz), 8.29 (d, 1H, H3¢,
J = 2.4 Hz), 8.25 (m, 1H, pic), 8.14 (d, 1H, pic, J = 7.6 Hz), 7.84
(m, 1H, pic), 7.64 (dd, 1H, H3, J = 1.6 Hz, J* = 7.4 Hz), 7.44 (dd,
1H, H6, J = 1.2 Hz, J* = 7.8 Hz), 7.16 (m, 1H, H5), 7.05 (m, 1H,
H4), 6.75 (m, 1H, H4¢). Positive MS: m/z: 395 [Pd (phpz) (pic)]+ +
23, 249 [Pd (phpz)]+.
1
N, 9.2%). IR (cm-1): n(CO) 1561 s, n(phpz) 1512 m, 750 m. H
NMR (300 MHz, CDCl3): d (SiMe4)(ppm): 8.07 (d, H5¢cis, J = 2.7
Hz), 7.95 (d, 2H, H5¢, J = 2.7 Hz), 7.36 (d, H3¢cis, J = 2.1 Hz), 7.09
(d, 2H, H3¢, J = 2.1 Hz), 6.95 (d, 2H, H6, J = 1.8 Hz), 6.91 (m,
4H, H5, H3, H6cis), 6.78 (m, 2H, H4, H5cis), 6.68 (d, H3cis, J = 1.2
Hz), 6.59 (m, H4cis), 6.31 (m, H4¢cis), 6.03 (m, 2H, H4¢), 2.10 (s, 6H,
CH3). Positive MS: m/z: 640 [{Pd (phpz) (mAcO)}2]+ + 23, 558
[Pd2(phpz)2(AcO)]+, 249 [{Pd(phpz)]+.
[Pd(phpz)(oxin)] 5. (0.072 g, 80%). Anal. calc. for
C18H13N3OPd: C, 54.9; H, 3.3; N, 10.7. Found: C, 54.9; H, 3.3;
N, 10.8%). IR (cm-1): n(oxin) 1571 s, 1501 s, n(phpz) 1512 m, 750
1
m. H NMR (300 MHz, CDCl3): d (SiMe4)(ppm): 8.29 (dd, 1H,
oxin, J = 1.2 Hz, J* = 4.6 Hz), 8.60 (d, 1H, H5¢, J = 2.8 Hz), 8.41
(dd, 1H, oxin, J = 1.6 Hz, J* = 8.4 Hz), 8.30 (d, 1H, H3¢, J = 2.0
Hz), 7.82 (dd, 1H, H6, J = 1.2 Hz, J* = 7.4 Hz), 7.57 (m, 1H, H5),
7.43 (m, 1H, H3), 7.38 (d, 1H, oxin, J = 8.0 Hz), 7.14 (m, 1H, oxin),
7.06 (m, 1H, H4), 6.97 (m, 2H, oxin), 6.74 (m, 1H, H4¢). Positive
MS: m/z: 416 [Pd (phpz) (oxin)]+ + 23, 393 [Pd (phpz) (oxin)]+ +
249 [Pd (phpz)]+.
[{Pd(phpz)(l-OH)}2] 2. To
a
solution of [{Pd(phpz)(m-
AcO)}2] (70 mg, 0.114 mmol) in 10 mL acetone was added 20%
NBu4OH (aq.) (0.3 mL, 0.227 mmol). After 1 h stirring at room
temperature the solvent was partially evaporated under reduced
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[Pd(phpz)(2pcal)] 6. The general procedure was followed,
using 0.07 g, 0.131 mmol of the di-m-hydroxo complex 2 as starting
material instead of 1. (0.049 g, 62%). Anal. calc. for C14H11N3OPd:
C, 48.9; H, 3.2; N, 12.2. Found: C, 48.9; H, 3.2; N, 12.2%).
(200 MHz, CDCl3): d (SiMe4)(ppm): 7.96 (d, 1H, H5¢, J = 2.6 Hz),
7.70 (d, 1H, H3¢, J = 2.0 Hz), 7.29 (m, 1H, H6), 7.16 (m, 2H, H3,
H5), 7.01 (m, 1H, H4), 6.49 (m, 1H, H4¢), 3.89 (s, 3H, CH3), 3.81 (s,
3H, CH3). 31P NMR (200 MHz, CDCl3): d (H3PO4)(ppm): 111.85.
Positive MS: m/z: 406 [Pd(phpz){S2P(OMe)2}]+, 249 [Pd(phpz)]+.
1
IR (cm-1): n(2pcal) 1570 vs, n(phpz) 1512 m, 765 m. H NMR
(300 MHz, CDCl3): d (SiMe4)(ppm): 8.77 (d, 1H, CH), 8.56 (d,
1H, H5¢, J = 2.6 Hz), 7.95 (d, 1H, H3¢, J = 1.2 Hz), 7.62 (m, 2H,
2pcal), 7.49 (m, 1H, H6), 7.22 (m, 2H, H3, H5), 7.11 (m, 1H, H4),
6.69 (s, 1H, H4¢), 6.36 (d, 1H, 2pcal, J = 3.2 Hz). Positive MS: m/z:
366 [Pd (phpz) (2pcal)]+ + 23, 249 [Pd (phpz)]+.
[{Pd(phpz)(l-SMeimz)}2] 11. (0.069 g, 83%). Anal. calc. for
C26H24N8Pd2S2: C, 43.0; H, 3.3; N, 15.5. Found: C, 42.9; H, 3.4; N,
15.4%). IR (cm-1): n(CS) 1585 s, n(phpz) 1516 m, 746 m. 1H NMR
(300 MHz, CDCl3): d (SiMe4)(ppm): 7.88 (d, 2H, H5¢, J = 2.4 Hz),
7.29 (dd, 2H, SMeimz, J = 1.2 Hz, J* = 7.8 Hz), 7.04 (d, 2H, H3¢,
J = 1.5 Hz), 6.87 (dd, 2H, H6, J = 1.2 Hz, J* = 7.8 Hz), 6.75 (m,
6H, H5, H3, SMeimz), 6.56 (m, 2H, H4), 6.32 (m, 1H, H4¢), 3.55 (s,
6H, CH3) Positive MS: m/z: 613 [Pd2(phpz)2(SMeimz)]+.
[Pd(phpz)(sal)] 7. The general procedure was followed, using
0.07 g, 0.131 mmol of the di-m-hydroxo complex 2 as starting
material instead of 1. (0.059 g, 60%). Anal. calc. for C16H12N2O2Pd:
C, 51.8; H, 3.3; N, 7.6. Found: C, 51.8; H, 3.2; N, 7.5%). IR (cm-1):
n(CO) 1610 s, 1547 vs, n(phpz) 1512 s, 745 m. 1H NMR (300 MHz,
CDCl3): d (SiMe4)(ppm): 9.36 (s, 1H, CH), 8.52 (d, 1H, H5¢, J =
0.9 Hz), 7.89 (s, 1H, H3¢), 7.61 (m, 2H, H6, H3), 7.40 (m, 2H, sal),
7.14 (m, 1H, H5), 7.06 (m, 1H, H4), 6.96 (d, 1H, sal, J = 8.7 Hz),
6.65 (m, 1H, H4¢), 6.59 (m, 1H, sal). Positive MS: m/z: 392 [Pd
(phpz) (sal)]+ + 23, 249 [Pd (phpz)]+.
[{Pd(phpz)(l-suc)}2] 12. The general procedure was followed,
using 0.07 g, 0.131 mmol of the di-m-hydroxo complex 2 as
starting material instead of 1. (0.054 g, 68%). Anal. calc. for
C26H22N6O4Pd2: C, 44.9; H, 3.2; N, 12.1. Found: C, 45.0; H, 3.3;
N, 12.1%). IR (cm-1): n(suc) 1742 s, 1610 vs, n(phpz) 1515 s, 745
1
m. H NMR (300 MHz, CDCl3): d (SiMe4)(ppm): 7.88 (d, 2H,
H5¢, J = 2.8 Hz), 7.14 (d, 2H, H3¢, J = 2 Hz), 6.95 (d, 2H, H6, J =
6 Hz), 6.82 (m, 1H, H3), 6.60 (m, 4H, H4, H5), 6.00 (m, 2H, H4¢),
2.80 (m, 8H, succ). Positive MS: m/z: 717 [{Pd(phpz)(suc)}2]+ +
23, 696 [{Pd(phpz)(suc)}2]+, 598 [Pd2(phpz)2(suc)]+.
[Pd(phpz)(acac)] 8. (0.045 g, 56%). Anal. calc. for
C14H14N2O2Pd: C, 48.2; H, 4.1; N, 8.0. Found: C, 48.2; H, 4.0;
N, 8.0%). IR (cm-1): n(acac) 1577 vs, 1547 vs, n(phpz) 1518 s,
767 s. 1H NMR (300 MHz, CDCl3): d (SiMe4)(ppm): 8.50 (d, 1H,
H5¢, J = 2.7 Hz), 7.82 (d, 1H, H3¢, J = 1.8 Hz), 7.47 (dd, 1H, H6,
J = 1.2 Hz, J* = 7.35 Hz), 7.40 (d, 1H, H3, J = 7.5 Hz), 7.15
(m, 1H, H5), 7.03 (m, 1H, H4), 6.64 (m, 1H, H4¢), 5.44 (s, 1H,
CH), 2.04 (s, 3H, CH3), 2.09 (s, 3H, CH3). Positive MS : m/z: 598
[Pd2(phpz)2(acac)]+, 372 [Pd (phpz) (acac)]+ + 23, 249 [Pd (phpz)]+.
[{Pd(phpz)(l-pz)}2] 13. (0.051 g, 70%). Anal. calc. for
C24H20N8Pd2: C, 45.5; H, 3.2; N, 17.7. Found: C, 45.5; H, 3.3;
1
N, 17.6%). IR (cm-1): n(pz) 1590 s, n(phpz) 1515 s, 753 m. H
NMR (300 MHz, CDCl3): d (SiMe4)(ppm): 8.51 (d, 2H, H5¢, J =
2.8 Hz), 7.63 (m, 4H, H3¢, pz), 7.44 (d, 2H, pz, J = 2.4 Hz), 7.43
(m, 2H, H6), 7.11 (m, 2H, H5), 7.06 (m, 2H, H4), 6.93 (m, 2H,
H3), 6.58 (m, 2H, H4¢), 6.34 (m, 2H, pz). Positive MS: m/z: 633
[{Pd(phpz)(pz)}2]+, 566 [Pd2(phpz)2(pz)]+, 317 [Pd(phpz)(pz)]+.
[Pd(phpz)(S2CNEt2)] 9. To an acetone solution (20 mL) of
the different precursors (1 or 2) (0.07 g) was added Et2NH,
(molar ratio 1 : 2) and a slight excess of carbon disulfide. Once the
suspension was dissolved (ca. 30 min) it was concentrated under
reduced pressure until ca. one fifth of the initial volume. Slow
addition of diethyl ether caused the formation of the complexes,
which were filtered off, washed with water, diethyl ether and air-
dried. The compound was recrystallised from dichloromethane–
diethyl ether. (0.068 g, 75%). Anal. calc. for C14H17N3S2Pd: C, 42.3;
H, 4.3; N, 10.5; S, 16.1. Found: C, 42.2; H, 4.3; N, 10.7, S, 16.2%).
[Pd(phpz)(AcO)(PPh3)] 14. To a dichloromethane (20 mL)
solution of 1 (0.07 g; 0.136 mmol) was added triphenylphosphine
in 1 : 2 ratio. The solution was stirred for 30 min at room
temperature, then concentrated until ca. one fifth of the initial
volume. Slow addition of diethyl ether completed the precipitation
of the complex, which was filtered off, washed with ether and air-
dried. (0.083 g, 64%). Anal. calc. for C29H25N2O2PPd: C, 61.1; H,
4.4; N, 4.9. Found: C, 61.3; H, 4.6; N, 5.1%). IR (cm-1): n(AcO)
1600 vs. n(PPh3) 534 s, 517 s, 490 s. n(phpz) 1514 s, 755 s. 1H NMR
(200 MHz, CDCl3): d (SiMe4)(ppm): 7.97 (d, 1H, H5¢, J = 2.2 Hz),
7.83 (m, 6H, Ph), 7.66 (m, 1H, H3¢), 7.40 (m, 8H, H6, H5 + Ph),
7.09 (m, 1H, H3), 6.94 (m, 1H, H4), 6.46 (m, 4H, H4¢ + Ph), 1.42 (s,
3H, CH3). 31P NMR (200 MHz, CDCl3): d (H3PO4)(ppm): 43.60.
Positive MS: m/z: 511 [Pd(phpz)(PPh3)]+, 249 [Pd(phpz)]+.
1
IR (cm-1): n(S2CNEt2) 1580 s, 1075 s. n(phpz) 1503 s, 753 s. H
NMR (300 MHz, CDCl3): d (SiMe4)(ppm): 7.96 (d, 1H, H5¢, J =
2.4 Hz), 7.63 (d, 1H, H3¢, J = 2.0 Hz), 7.16 (m, 3H, H6, H3, H5),
7.01 (m, 1H, H4), 6.46 (m, 1H, H4¢), 3.85 (q, 4H, CH2, J = 7.2 Hz),
1.35 (m, 6H, CH3). Positive MS: m/z: 397 [Pd(phpz)(S2CNEt2)]+,
249 [Pd(phpz)]+.
[Pd(phpz){S2P(OMe)2}] 10. The new complex was obtained
by treating an acetone solution (20 mL) of the different pre-
cursors (1 or 2) (0.07 g) with the corresponding amount of
[NH4][S(S)P(OMe)2] (molar ratio 1 : 2). Once the suspension was
dissolved (ca. 30 min) it was concentrated under reduced pressure
until ca. one fifth of the initial volume. Slow addition of diethyl
ether caused the formation of the complexes, which were filtered
off, washed with water, diethyl ether and air-dried. The compound
was recrystallised from dichloromethane–diethyl ether. (0.059 g,
64%). Anal. calc. for C11H13N2O2PS2Pd: C, 32.5; H, 3.2; N, 6.9;
S, 15.7. Found: C, 32.7; H, 3.3; N, 7.1, S, 15.9%). IR (cm-1):
Crystallographic data and structure determination
Crystals of 1, 7, 9, 11 and 12 suitable for a single crystal diffraction
study were prepared by slow diffusion of dichloromethane into
hexane. Diffraction data were measured on a Bruker SMART
˚
APEX using Mo-Ka radiation (l = 0.71073 A). The structures
were solved by direct methods57 and refined by full-matrix least-
squares techniques using anisotropic thermal parameters for non-
hydrogen atoms.
For 13, high resolution X-ray powder diffraction patterns were
collected at the SpLine beamline (BM25A) of the Spanish CRG at
1
n(S2P(OMe)2) 1020 vs, 811 vs. n(phpz) 1509 s, 749 s. H NMR
This journal is
The Royal Society of Chemistry 2011
Dalton Trans., 2011, 40, 156–168 | 165
©

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Table 3 Crystal data and structure refinement for complexes 1, 7, 9, 11, 12 and 13
1
7
9
11
12·CH2Cl2
13
Empirical formula
C22H20N4O4Pd2
617.22
100(2)
0.71073
Trigonal
P3121
11.7292(3)
11.7292(3)
27.8342(13)
90
90
120
3316.2 (2)
6
1.854
C16H12N2O2Pd
370.68
100(2)
0.71073
Monoclinic
P21/a
14.4947(10)
12.1565(9)
15.8097(11)
90
99.4880(10)
90
2747.6(3)
8
1.792
1.356
C14H17N3PdS2
397.83
100(2)
0.71073
Monoclinic
C26H24N8Pd2S2
725.45
100(2)
0.71073
Orthorhombic
Pbca
11.1797(5)
17.5215(7)
26.8062(11)
90
90
90
5250.9(4)
8
1.835
C27H24Cl2N6O4Pd2 C24H20N8Pd2
M
780.22
100(2)
633.2
298
T/K
˚
l/A
0.71073
Triclinic
P1
Crystal system
Space group
Monoclinic
P21/a
¯
P21/n
˚
a/A
8.8527(7)
12.4569(10)
13.7577(11)
90
8.9145(4)
10.8879(4)
15.3871(8)
103.0790(10)
90.5410(10)
107.2350(10)
1384.71(11)
2
23.3603(5)
8.95252(17)
11.5684(2)
90
104.0736(14)
90
2346.74(8)
4
1.797
˚
b/A
˚
c/A
a/◦
b/◦
g /◦
95.1880(10)
90
1510.9(2)
4
1.749
1.497
800
2.21 to 28.61
18 234
3
˚
V/A
Z
Dc/Mg m-3
m/mm-1
F(000)
1.871
1.663
1824
1.562
2880
2.29 to 28.17
57 537
1.538
772
1.36 to 28.23
15 980
1472
1.31 to 28.68
32 760
q range for data collection/◦ 2.00 to 28.23
Reflections collected
38 625
Independent reflections
Goodness-of-fit on F2
Final R indices [I > 2s(I)]
5225
1.064
R1 = 0.0260
wR2 = 0.0578
R1 = 0.0267
wR2 = 0.0582
6649
1.217
R1 = 0.0590
wR2 = 0.1362
R1 = 0.0627
wR2 = 0.1385
3674
1.096
6240
1.209
R1 = 0.0419
wR2 = 0.0901
R1 = 0.0451
wR2 = 0.0915
6209
0.911
R1 = 0.0343
wR2 = 0.0856
R1 = 0.0368
wR2 = 0.0876
R1 = 0.0336
wR2 = 0.0816
R1 = 0.0338
wR2 = 0.0817
3.652 and -0.956
R indices (all data)
-3
˚
Max/min Dr/e A
0.714 and -0.396 6.025 and -0.864
1.325 and -0.597 3.154 and -0.620
the European Synchrotron Radiation Facility (ESRF, Grenoble)
ments. We would like to thank the SpLine staff at the ESRF for
their valuable help in the study by synchrotron radiation.
˚
with a fixed wavelength of 0.826924 A at room temperature.
Powdered samples were placed inside a 0.5 mm-diameter capillary,
which was rotated during exposure. Data collection was done in a
continuous 2q-scan mode with 0.015◦ step and 2 s acquisition time
per point. The diffracted beam was detected using a scintillation
counter. The incoming beam was also monitored to normalise the
decay of the primary beam.
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