Palladium and iridium complexes with a N,P,N-bis(pyridine)phenylphosphine ligand

Article abstract of DOI:10.1039/b919679j

A variety of Pd(ii) complexes containing the neutral N,P,N-ligand bis(2-picolyl)phenylphosphine (N_pyPN_py) have been synthesised and characterized by IR and NMR spectroscopy and X-ray diffraction. The neutral complex [PdCl₂(N_pyPN_py-N,P)] (1) has been selectively obtained in high yield by reaction of [PdCl ₂(NCPh)₂] with the ligand in dichloromethane. The cationic complexes [PdCl(N_pyPN_py-N,P,N)]PF₆ (2) and [Pd(N_pyPN_py-N,P,N)(NCMe)](PF₆)₂ (5) have been prepared from the same reagents by addition to the reaction mixture of one or two equivalents of TlPF₆, respectively. It was found that dynamic exchange of the pyridine rings of 1 occurs on the NMR time-scale and possible mechanisms are discussed. As a by-product of the synthesis of 2, the unexpected dinuclear complex [Pd₂Cl₂(μ-N _pyPN_py)₂](PF₆)₂ (3) has been isolated in 10% yield. Its molecular structure in the solid state reveals the presence of two N_pyPN_py chelating/bridging ligands. The cationic complex [Pd₂Cl₂(μ-N_pyPN _py)₂]²⁺ was then selectively obtained by reaction of cis-[Pd(N_pyPN_py-N,P)₂](BF ₄)₂ (4) with [PdCl₂(cod)]. ¹H- and ³¹P{¹H} NMR studies have demonstrated that 3 converts slowly into 2 in DMSO solution. The Ir(i) complexes [IrCl(cod)(N _pyPN_py)] (6) and [Ir(cod)(N_pyPN _py-N,P,N)]BAr^F (7) have also been prepared, the latter exhibits a trigonal bipyramidal structure with the ligand displaying a facial coordination mode. Compound 7 represents a rare example of an Ir(i) complex bearing a N,P,N-chelating ligand. The Royal Society of Chemistry 2010.

Full text of DOI:10.1039/b919679j

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www.rsc.org/dalton | Dalton Transactions
Palladium and iridium complexes with a N,P,N-bis(pyridine)phenylphosphine
ligand†
Shaofeng Liu,a,b Riccardo Peloso‡a and Pierre Braunstein*a
Received 22nd September 2009, Accepted 10th December 2009
First published as an Advance Article on the web 25th January 2010
DOI: 10.1039/b919679j
A variety of Pd(II) complexes containing the neutral N,P,N-ligand bis(2-picolyl)phenylphosphine
(NpyPNpy) have been synthesised and characterized by IR and NMR spectroscopy and X-ray
diffraction. The neutral complex [PdCl2(NpyPNpy-N,P)] (1) has been selectively obtained in high yield
by reaction of [PdCl2(NCPh)2] with the ligand in dichloromethane. The cationic complexes
[PdCl(NpyPNpy-N,P,N)]PF6 (2) and [Pd(NpyPNpy-N,P,N)(NCMe)](PF6)2 (5) have been prepared from
the same reagents by addition to the reaction mixture of one or two equivalents of TlPF6, respectively.
It was found that dynamic exchange of the pyridine rings of 1 occurs on the NMR time-scale and
possible mechanisms are discussed. As a by-product of the synthesis of 2, the unexpected dinuclear
complex [Pd2Cl2(m-NpyPNpy)2](PF6)2 (3) has been isolated in 10% yield. Its molecular structure in the
solid state reveals the presence of two NpyPNpy chelating/bridging ligands. The cationic complex
[Pd2Cl2(m-NpyPNpy)2]2+ was then selectively obtained by reaction of cis-[Pd(NpyPNpy-N,P)2](BF4)2 (4)
1
with [PdCl2(cod)]. 1H- and 31P{ H} NMR studies have demonstrated that 3 converts slowly into 2 in
DMSO solution. The Ir(I) complexes [IrCl(cod)(NpyPNpy)] (6) and [Ir(cod)(NpyPNpy-N,P,N)]BArF (7)
have also been prepared, the latter exhibits a trigonal bipyramidal structure with the ligand displaying a
facial coordination mode. Compound 7 represents a rare example of an Ir(I) complex bearing a
N,P,N-chelating ligand.
As an extension to N,P,N-tridentate ligands containing oxa-
Introduction
zoline heterocycles, we compared the bonding behaviour of the
The synthesis and coordination chemistry of heterotopic lig-
bis(oxazoline)phenylphosphine (abbreviated below for clarity as
NoxPNoxMe2) and bis(oxazoline)phenylphosphonite ligands (ab-
breviated NOPONMe2) (Scheme 1). It was unexpectedly found
that the former can behave as a N,N-chelate towards Co(II)
ands bearing phosphorus and nitrogen donor atoms represent
increasingly active fields of research owing to the properties that
such ligands confer to their metal complexes in stoichiometric
or catalytic reactions.1-11 The significantly different electronic and
hard–soft properties of the donor functions largely influence their
metal coordination behaviour and account for the observation
of monodentate P- or N-coordination and static or dynamic
(hemilabile) P,N-chelation.2
and Fe(II),17,23 in contrast to the situation in [CoCl2(NOPONMe2
P,N)]23(Scheme 1).
-
In the course of our studies on P,N-ligands in which the P donor
function is of the phosphine, phosphonite or phosphinite-type and
the N donor belongs to a pyridine or an oxazoline heterocycle, we
observed that some of their mononuclear complexes of Ru(II),6,12-15
Ni(II),7,16,17 Co(II)18 and Pd(II)15,19,20 or Fe–Cu21 and Fe–Co22
bimetallic complexes led to active precatalysts for a number of
reactions.
aLaboratoire de Chimie de Coordination, Institut de Chimie (UMR 7177
CNRS), Universite´ de Strasbourg, 4 rue Blaise Pascal, F-67070, Strasbourg
Cedex, France. E-mail: braunstein@unistra.fr
Scheme
1
The ligands NoxPNox
and NOPONMe2 and contrast-
Me2
bKey Laboratory of Engineering Plastics and Beijing National Laboratory for
Molecular Sciences, Institute of Chemistry, Chinese Academy of Sciences,
Beijing, 100190, China
ing bonding modes of the heterofunctional ligands in complexes
[CoCl2(NOPONMe2-P,N)] and [CoCl2(NoxPNoxMe2-N,N)].
† Electronic supplementary information (ESI) available: ORTEP plot
of [PdBr2(NpyPNpy-N,P)] (Fig. S1). CCDC reference numbers 748557–
748562 and 757233. For ESI and crystallographic data in CIF or other
electronic format see DOI: 10.1039/b919679j
‡ current address: Instituto de Investigaciones Qu´ımicas - Departamento
de Qu´ımica Inorga´nica, Universidad de Sevilla - Consejo Superior de
Investigaciones Cient´ıficas, Avda. Ame´rico Vespucio 49, Isla de la Cartuja,
41092 Sevilla, Spain.
As far as bis(oxazoline)phosphine ligands are concerned, only
P,N- or N,P,N-coordination modes have been observed in Pd(II)
complexes (Scheme 2).17,23 We wished to extend these studies to the
corresponding N,P,N-ligand where N represents a pyridine donor
(NpyPNpy) and compare its coordination properties with those of
NoxPNoxMe2, in particular towards Pd(II) complexes.
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and N2 on the NMR time scale (Scheme 4). We shall come back
to this point later in the discussion.
Scheme
2
The complexes [PdCl2(NPNMe2-P,N)] and [Pd(NPNMe2
-
N,P,N)(NCMe)](BF4)2.
For this purpose, the ligand selected was bis(2-picolyl)-
phenylphosphine (NpyPNpy, Scheme 3), a flexible, symmetric
and neutral N,P,N-ligand containing two pyridine arms and a
phosphine-type P donor.24,25 We have also performed preliminary
studies on the coordination chemistry of this ligand to Ir(I)
complexes, in order to investigate its behaviour with a d8 metal
which is more prone to give rise to penta-coordinated complexes.
Moreover, N,N,N-,26 P,C,P-,27 and, very recently, P,N,P-Ir(I)28
chelated complexes have proved to be effective in a number of
challenging catalytic reactions and in C–H bond activation. In
this context, the preparation of new N,P,N-chelated Ir complexes
represents a desirable development of this chemistry.29 Herein,
we report the synthesis and the characterization of Pd(II) and
Ir(I) complexes bearing the neutral bis(2-picolyl)phenylphosphine
(NpyPNpy) ligand.
Scheme 4 Possible mechanisms for the dynamic exchange of the pyridine
rings at the Pd centre in 1.
Although it was not possible to assign all the signals in
the pyridine region, by comparison with the values found for
[PdCl(NpyPNpy-N,P,N)]PF6 (2, vide infra), we suggest that the
H ortho to the coordinated nitrogen in 1 resonates at 9.32 ppm
and that of the non-coordinated pyridine moiety at 8.39 ppm. In
order to better understand this dynamic behaviour, we performed
variable temperature 1H NMR experiments from 25 to 80 ◦C. The
gradual broadening of the eight pyridine resonances resulted in
the coalescence of the signals at 80 ◦C (300 MHz), which gave
rise to four broad peaks at 8.89, 7.86, 7.62, 7.34 ppm. By means
of a line shape analysis, the rates of exchange were estimated
at different temperatures and this allowed us to calculate the
following activation parameters by an Eyring plot: DH‡ = (50
Scheme 3 The NpyPNpy ligand.
Results and discussion
The reaction between [PdCl2(NCPh)2] and an equimolar amount
of NpyPNpy in CH2Cl2 resulted in the formation of a yellow
precipitate, which was characterized by multinuclear NMR and
IR spectroscopy, elemental analysis and X-ray diffraction and
identified as the mononuclear complex [PdCl2(NpyPNpy-N,P)] (1).
The compound is poorly soluble in most organic solvents and only
DMF and DMSO allowed us to prepare concentrated solutions
1
3) kJ mol-1, DS‡ = (-43 8) J mol-1 K-1. As far as the 13C{ H}
NMR spectrum of 1 is concerned, it is worth observing that the
signals of the coordinated picolyl moiety (py2, py6, py4 and CH2)
are downfield shifted with respect to those of the non-coordinated
one. This is likely to result from a decrease of the electron-density
at the pyridine ring upon coordination. The far IR spectrum of the
compound displays two strong absorptions at 337 and 301 cm-1,
which are ascribed to the Pd–Cl stretching vibrations of the
cis-PdCl2 moiety.31,32
of 1. The 31P{ H} NMR spectrum of 1 in DMSO shows a sharp
1
singlet at 49.7 ppm, thus confirming the coordination of the ligand
through the phosphorus atom, whose resonance is downfield
shifted by about 60 ppm with respect to the free ligand. At this
point, we cannot say whether this resonance corresponds to the
neutral complex or, in view of the high donor number (DN = 29.8)
of DMSO,30 to the cation of [PdCl(NpyPNpy-N,P)(DMSO)]Cl
which would form upon dissolution of the neutral complex in
DMSO. The 1H NMR spectrum of 1 at room temperature exhibits
broad signals due to the picolyl moieties of the ligand, whereas
the phenyl protons give rise to sharp signals. In particular, the
presence of eight broad resonances in the pyridine region indicates
the non-equivalence of the two pyridine rings, which are likely to
be involved in a dynamic slow exchange of the nitrogen donors N1
The molecular structure of 1 (Fig. 1) in the solid state confirmed
that the NpyPNpy ligand behaves as a bidentate N,P-chelate, one of
the pyridine rings remaining non-coordinated, as also observed in
the related NoxPNox Pd(II) complex.23 Similarly, it has been previ-
ously observed that a hemilabile bis(oxazoline)phenylphosphonite
acts as a N,P-bidentate ligand in the monohaptyl allyl complex
1
[Pd(h -C3H5)Cl(NOPONMe2)].33 The phosphorus atom becomes a
stereogenic centre upon coordination and both enantiomers are
present in the unit cell. The palladium atom lies in a distorted
square-planar coordination environment, as shown by the bond
angles about the metal, which range from 83.29(8) (N1–Pd1–P1)
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DMSO solution, the conversion being complete after 4 days at
room temperature or 10 h at 80 ◦C. We wondered whether the
formation of the dinuclear complex was due to the heterogeneous
conditions of the synthesis and, consequently, we repeated the
reaction under homogeneous conditions by changing the nature
of the solvent (DMSO instead of THF). As expected, the addition
of one equivalent of TlPF6 to a DMSO-d6 solution of 1, which
forms in the first step of the synthesis of 2 and 3, afforded
1
selectively the mononuclear, cationic complex 2. The 31P{ H}
NMR spectrum of pure 2 in DMSO-d6 exhibits two broad signals
at 83.7 and 56.4 ppm, which are attributed to two different
cationic complexes present in solution, namely [PdCl(NpyPNpy-
N,P,N)]+ and a complex resulting from coordination of a DMSO
molecule and displacement of a pyridine group, [PdCl(NpyPNpy-
N,P)(DMSO)]+ (Scheme 5). The intensities of the two broad
resonances provide an estimate of the molar ratio between the
two species in equilibrium, which is about 3 : 1 ([PdCl(NpyPNpy-
N,P,N)]+/[PdCl(NpyPNpy-N,P)(DMSO)]+).
Fig. 1 ORTEP of complex 1 with ellipsoids drawn at the 50% probability
level. Selected bond distances (A) and angles (deg): Pd1–Cl1 2.3825(9),
Pd1–Cl2 2.2945(9), Pd1–P1 2.200(1), Pd1–N1 2.075(3), N1–Pd1–P1
83.29(8), N1–Pd1–Cl1 94.97(8), Cl1–Pd1–Cl2 92.80(4), Cl2–Pd1–P1
89.02(4).
˚
1
The two broad 31P{ H} NMR resonances (56.4 and 83.7 ppm)
are found in the same region as those exhibited by 1 and the
dicationic complex [Pd(NCMe)(NpyPNpy-N,P,N)](PF6)2 (5, vide
infra), which occurs respectively at 49.7 and 86.6 ppm in DMSO-
d6. So, it seems likely that the peak at 56.4 ppm is due to a complex
where NpyPNpy acts as a bidentate N,P-donor ligand, similarly to 1,
while the peak at 83.7 ppm is due to a complex where it behaves as a
tridentate N,P,N-donor ligand, similarly to [Pd(NCMe)(NpyPNpy-
N,P,N)](PF6)2. This hypothesis is also consistent with the fact that
the 1H NMR spectrum of 2 in DMSO-d6 shows broad signals in
both the pyridine and methylene regions. This is probably caused
by the exchange equilibrium of the two pyridine moieties around
the palladium atom in the [PdCl(NpyPNpy-N,P)(DMSO)]+ species,
to 94.97(8)◦ (N1–Pd1–Cl1). The Pd–Cl bond distances of
˚
˚
2.2945(9) A and 2.3825(9) A, for the positions trans to nitrogen
and trans to phosphorus, respectively, reflect the higher trans
influence of the latter donor.34 The molecular structure of the
analogous complex [PdBr2(NpyPNpy-N,P)] (31P{ H} NMR: d 49.4
1
ppm) was determined for comparison and is very similar to that
of 1 (see ESI†).
Abstraction of a chloride anion from 1 was expected to induce a
tridentate chelating behaviour of the NpyPNpy ligand. The reaction
was performed directly by mixing in THF the palladium complex
[PdCl2(NCPh)2] with the ligand in the presence of one equivalent
of TlPF6, which was added after several hours. The reaction
proceeded heterogeneously because of the formation first of the
insoluble complex 1 and gave rise to a mixture of two complexes,
which were separated by crystallization. The main-product was
the expected complex [PdCl(NpyPNpy-N,P,N)]PF6 (2), whereas the
by-product was shown by X-ray diffraction to be the unexpected
cationic dinuclear complex [Pd2Cl2(m-NpyPNpy)2](PF6)2 (3). The
NMR spectra of the two compounds in DMSO-d6 at room
1
as assumed for compound 1 (see below). In the 13C{ H} NMR
spectrum of 2, two sets of signals are observed, as expected: broad
resonances corresponding to the DMSO substituted species and
sharp resonances due to the [PdCl(NpyPNpy-N,P,N)]+ cation. The
equilibrium constant for the formation of the solvento-complex
in Scheme 5 (Keq = [PdCl(NPN)(DMSO)]/[PdCl(NPN)]) was
calculated at different temperatures, ranging from 25 to 80 ◦C, on
the basis of the molar ratio of the two species in the 31P NMR of
pure 2. Hence, the thermodynamic parameters were estimated by
means of a Van’t Hoff plot. The displacement of one pyridine ring
by DMSO in DMSO solution was found to be slightly endothermic
with DH = (8 1) kJ mol-1 and DS = (21 3) J mol-1 K-1. The far
IR spectrum of 2 exhibits an absorption at 343 cm–1, which is likely
to be due to the Pd–Cl stretching vibration, and a strong band at
556 cm-1 tentatively assigned to the Pd–N stretching vibration.35
The molecular structure of the cationic complex [PdCl(NpyPNpy-
N,P,N)]+ in 2·CH2Cl2 is shown in Fig. 2. Its coordination geometry
approximates to square-planar, the N–Pd–P angles being 83.3(1)◦
1
temperature are different. In particular, the H NMR spectrum
of the dinuclear complex exhibits a doublet at 9.27 ppm due
to two equivalent py6 protons, whereas the py6 protons of the
mononuclear complex 2 resonate at 9.06 ppm. This allowed us
to estimate the molar ratio between the mononuclear and the
dinuclear complexes in the crude, which was found to be about
7/1. Although compound 3 is indefinitely stable in the solid
state, we observed that it converts slowly into compound 2 in
Scheme 5 Dynamic behaviour of 2 in DMSO solution.
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to the complexes 1 and [PdCl(NpyPNpy-N,P)(DMSO)]Cl in slow
exchange on the NMR time-scale.
1
The 31P{ H} NMR spectrum of 3 in DMSO-d6 shows a broad
1
resonance at 47.5 ppm, whereas the H NMR spectrum displays
sharp signals in the aromatic region and broad signals due to the
methylene protons. Consistent with the molecular structure of 3
in the solid state, the two pyridine moieties of each ligand are not
equivalent. Particularly remarkable is the difference between the
resonances of the protons ortho to the nitrogen, which is more
than 1 ppm. As expected for the trans arrangement of the PdCl2
moiety, the far IR spectrum of 3 contains only one absorption at
346 cm-1 for the Pd–Cl stretching vibration.31
The solid-state structure of 3 deserves a more detailed descrip-
tion. It is shown in Fig. 3.
Fig. 2 ORTEP of the cationic complex in 2·CH2Cl2 with ellipsoids drawn
˚
at the 50% probability level. Selected bond distances (A) and angles (deg):
Pd1–Cl1 2.388(2), Pd1–P1 2.171(2), Pd1–N1 2.057(4), Pd1–N2 2.056(4),
N1–Pd1–P1 83.35(13), N2–Pd1–P1 83.71(14), N1–Pd1–Cl1 96.80(13),
N2–Pd1–Cl1 96.42(14), Cl1–Pd1–P1 177.50(5).
and 83.7(1)◦. There is no symmetry element in the molecule.
In spite of the positive charge of the complex, the Pd–Cl bond
˚
distance of 2.388(2) A does not differ significantly from that
˚
observed in 1 (trans to P). The Pd–P (2.171(2) A) and Pd–N
˚
(2.057(4) and 2.056(4) A) bond distances are slightly shorter than
in complex 1.
Let us now come back to the dynamic exchange involving
complex 1. It could formally occur by three different mechanisms:
an associative displacement of N2 for N1, without chloride
dissociation (Scheme 4a), chloride displacement by N1 to give a
cationic complex with a tridentate N,P,N ligand [PdCl(NpyPNpy-
N,P,N)]Cl closely related to 2 (see below) and chloride recoor-
dination and displacement of N2 (Scheme 4b), or dissociation
of 1 in DMSO, nitrogen/DMSO exchange followed by chloride
recoordination (Scheme 4c). In order to check their feasibility,
we mixed equimolar amounts of 1 and 2 in an NMR tube and
Fig. 3 ORTEP of the dinuclear cationic complex in 3·2(CH2Cl2) with
ellipsoids drawn at the 50% probability level. Only the ipso carbons
of the P-phenyl groups are shown for clarity. Selected bond distances
˚
(A) and angles (deg): Pd1–P1 2.224(1), Pd1–P2 2.242(1), Pd1–N1
2.116(3), Pd1–N3 2.123(3), Pd2–Cl1 2.315(1), Pd2–Cl2 2.301(1), Pd2–N2
2.047(3), Pd2–N4 2.020(3), N1–Pd1–P1 81.85(9), N3–Pd1–P2 82.08(9),
N4–Pd2–N2 177.0(1), Cl2–Pd2–Cl1 174.95(4).
1
observed at room temperature a 31P{ H} resonance at 83.7 and
a more intense and broad one at 50.3 ppm. The former corre-
sponds to [PdCl(NpyPNpy-N,P,N)]+ and the latter to the overlap
between those assigned to 1 (49.7 ppm) and to [PdCl(NpyPNpy-
N,P)(DMSO)]+ (56.4 ppm). When the temperature was raised
to 80 ◦C, the resonance at 83.7 ppm disappeared and the other
was found at 49.1 ppm. These experiments suggest that 1 and 2
give rise to a common cationic species in solution and that the
latter exchanges with 2 at higher temperature. This is consistent
with a mechanism such as that shown in Scheme 4c. We verified
independently that the cation in 2, [PdCl(NpyPNpy-N,P,N)]+, reacts
with excess (NMe4)Cl in DMSO to give a single species, according
The cationic complex (Fig. 3) consists of two square-planar
palladium units linked by two bridging NpyPNpy ligands, which
P,N-chelate one palladium centre (Pd1) and act as N donor ligands
towards the other one (Pd2). The coordination environment of
Pd2 is completed by two chlorides in trans position to each
other. Thus, this dinuclear dicationic complex features an unusual
charge differentiation between the two metal centres, Pd1 formally
carrying the doubly positive charge and the Pd2 moiety being
neutral.
The coordination geometry around Pd1 shows a pronounced
distortion from planarity, the P1–Pd2–N3 angle being 161.4(1)◦,
significantly smaller than the related P2–Pd1–N1 of 179.0(1)◦. The
angle between the two mean coordination planes, defined by the
atoms Pd1,P1,P2,N1,N3 and Pd2,Cl1,Cl2,N4,N2 is 13.09(4)◦. The
phosphorus atoms become stereogenic centres upon coordination
and exhibit opposite configurations, the resulting isomer being
the meso diastereoisomer. The Pd2–Cl bond distances are in the
usual range and the Pd1–N bond distances are affected by the
trans influence of the phosphine and are significantly longer than
the Pd2–N bond distances.34 A similar coordination behaviour
1
to 31P{ H} spectroscopy, characterized by a singlet at 49.7 ppm,
which is exactly the value found for 1. Whether this is the dichloro
complex or its solvento derivative (see above), this experiment
demonstrates that a pyridine donor of the tridentate form of the
NpyPNpy ligand can be readily displaced by chloride to give a
complex with a NpyPNpy-N,P chelate. This is again consistent with
a mechanism of the type shown in Scheme 4c. When complex 2
was treated in DMSO with only half an equivalent of (NMe4)Cl,
a sharp resonance was still present at 83.8 ppm, corresponding
to the complex with the tridentate NpyPNpy ligand, and a broad
resonance was observed at 52.3 ppm which could correspond
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of the NpyPNpy ligand has been recently observed in the Ag(I)
24
complex [Ag(NpyPNpy)]2(BF4)2 in which the two metal centres
are additionally linked by an Ag–Ag bond.
The unexpected structure of 3 prompted us to develop a
more straightforward and selective synthesis of this compound.
Looking at the different coordination environments of the two
palladium centres in 3, it seemed convenient to first prepare
a dicationic complex bearing two NpyPNpy ligands, and then
react this complex with a Pd(II) precursor containing the PdCl2
fragment. The reaction between [Pd(NCMe)4](BF4)2 and NpyPNpy
in a 1 : 2 molar ratio in dichloromethane afforded a pale yellow
solid, which was identified by spectroscopy and X-ray diffraction
as the mononuclear complex cis-[Pd(NpyPNpy-N,P)2](BF4)2 (4).
In the molecular structure of 4·2(CH2Cl2) (Fig. 4), a C2
symmetry axis passes through the metal atom and the middle
points of the P ◊ ◊ ◊ P and N ◊ ◊ ◊ N segments. The phosphorus
atoms thus display the same configuration and the complex is
consequently chiral. Both enantiomers are present in the unit cell.
As expected, the Pd–P and Pd–N bond distances in 4 (2.229(1)
Scheme 6 Selective formation of 3 from 4 and [PdCl2(cod)].
As far as the NMR spectra of 5 in DMSO are concerned,
the main difference to be noted with respect to compounds
1–3 is the absence of broad signals. Moreover, the picolyl moieties
1
1
are equivalent as proved by the H and 13C{ H} NMR spectra.
These observations are consistent with a tridentate coordination
behaviour of the ligand, where the pyridine moieties are strongly
bound to the metal and not displaced by the DMSO, at variance
with the situation suggested for compound 2. Nevertheless, the
displacement of the acetonitrile by a dimethylsulfoxide molecule
was established by the presence of the signals of free acetonitrile in
˚
and 2.108(3) A, respectively) are very similar to those observed
in 3. Compound 4 was reacted in DMSO-d6 with an equimolar
1
amount of [PdCl2(cod)]. The 1H- and 31P{ H} NMR spectra of the
resulting solution revealed the selective formation of the dinuclear
cationic complex [Pd2Cl2(m-NpyPNpy)2]2+ of 3 (Scheme 6).
1
1
both 1H- and 13C{ H} NMR spectra. The 31P{ H} NMR spectrum
of 5 displays a sharp singlet at 86.6 ppm. The difference between
this value and that observed for 2 is only 3.3 ppm and suggests
that the phosphorus nuclei in the two complexes lie in a very
similar electronic environment. The increase of the formal charge
of the cationic complex from +1 (for 2) to +2 (for 5) does not
affect significantly the chemical shift of the phosphorus atom but
causes, as expected, a slight downfield shift. As anticipated, the
1H NMR of 5 in DMSO-d6 displays only sharp signals. The ABX
spin system for the CH2P protons was expected to give rise to two
doublet of doublets (2JHH, and two 2JPH). In fact, two triplets are
observed in the methylene region, thus suggesting that the 2JPH are
very similar to the 2JHH. The ABX spin system could be converted
Fig. 4 ORTEP of the cationic complex in 4·2(CH2Cl2) with ellipsoids
31
into an AB spin system by recording the 1H{ P} NMR spectrum
˚
drawn at the 50% probability level. Selected bond distances (A) and
of 5, which showed two doublets at 5.21 and 4.29 ppm with 2JHH
=
angles (deg): Pd1–N1 2.108(3), Pd1–P1 2.229(1), N1–Pd1–N1i 98.4(2),
N1–Pd1–P1 82.21(9), P1–Pd1–P1i 98.65(6). Symmetry operation generat-
ing equivalent atoms (i): -x, y, -z.
17.7 Hz. In the far IR spectrum of 5, the Pd–N stretching vibration
causes a strong absorption at 554 cm–1.35 A view of the molecular
structure of the cationic complex in 5·MeCN is depicted in Fig. 5.
Bond distances and angles in the Pd(NpyPNpy) fragment are in most
cases identical to those observed in 2·CH2Cl2, the main difference
being a shorter Pd–P distance in 5. This is probably due to the
decrease in the overall charge of cation from +1 (in 2) to +2 (in 5).
It appeared interesting to extend our study of the NpyPNpy
ligand to another d8 transition metal system. Since it was
previously reported that NpyPNpy acts as a facial tridentate ligand
in octahedral Fe(II)17 and Cr(III)36 complexes, we wondered which
type of coordination geometry would have been obtained for a
metal cation that can have either a square planar or a trigonal
bipyramidal coordination environment. Ir(I) was expected to be a
good candidate for this purpose. Moreover, although the chemistry
of iridium complexes containing tridentate ligands such as P,C,P-
pincer27 or tris(pyrazolyl)borate ligands26 has been extensively
studied, to the best of our knowledge, only two structurally
Furthermore, the synthesis of a dicationic Pd(II) complex con-
taining the NpyPNpy ligand was realized by extracting both chloride
anions from the coordination sphere of the metal. Thus, the one-
pot 1 : 1 reaction between [PdCl2(NCPh)2] and the NpyPNpy in the
presence of two equivalents of TlPF6 in MeCN afforded selectively
a pale yellow compound in high yield, which was identified as the
expected complex [Pd(NpyPNpy-N,P,N)(NCMe)](PF6)2 (5).
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Fig. 5 ORTEP of the cationic complex in 5·MeCN with ellipsoids drawn
˚
at the 50% probability level. Selected bond distances (A) and angles
(deg): Pd1–P1 2.163(1), Pd1–N1 2.063(4), Pd1–N2 2.051(4), Pd1–N3
2.125(4), N1–Pd1–P1 83.4(1), N2–Pd1–P1 82.6(1), N1–Pd1–N3 97.0(2),
N2–Pd1–N3 97.1(2), N3–Pd1–P1 178.1(1).
Fig. 6 ORTEP of the cationic complex in 7 with ellipsoids drawn at
the 30% probability level. Selected bond distances (A) and angles (deg):
˚
characterized iridium compounds bearing a chelated N,P,N-
ligand have been reported to date.29,37
Ir1–N1 2.150(5), Ir1–N2 2.274(5), Ir1–P1 2.277(2), Ir1–C22/23 2.032(4),
Ir1–C19/26 1.992(4), C22–C23 1.398(10), C19–C26 1.443(9), N1–Ir1–N2
83.9(2), N1–Ir1–P1 81.0(2), N2–Ir1–P1 79.0(1), C22/23–Ir1–C16/C26
85.5(3).
The 1 : 2 reaction between the iridium(I) precursor [Ir(m-
Cl)(cod)]2 and NpyPNpy afforded an air-sensitive orange compound
in high yield. Although the attempts to get crystals suitable
for X-ray diffraction failed, the formation of a new complex of
formula [IrCl(cod)(NpyPNpy)] (6) was inferred from spectroscopic
and elemental analysis data. The coordination of the NpyPNpy
ligand through its phosphorus atom was demonstrated by the
1
31P{ H} NMR spectrum in CDCl3, which consists in a sharp
singlet at 24.7 ppm, 30 ppm downfield shifted with respect to the
free ligand. Differently from that observed for compounds 1–3, all
the signals in the 1H NMR spectrum of 6 are sharp. Moreover, four
sharp signals in the pyridine region and only one ABX spin system
in the CH2 region were detected. These observations are consistent
with a tridentate behaviour of the NpyPNpy ligand, whose picolyl
moieties would be symmetrically coordinated to the metal centre.
As shown in Scheme 7 and Fig. 6, the two P,N-chelating arms are
not equivalent and the fact that only one ABX spin system due to
the CH2P protons is observed (two doublets of doublets at 5.01
Scheme 7 Structures of 6 and 7 based on the X-ray diffraction structure
of 7.
containing cyclooctadiene and phosphine ligands, namely trigonal
bipyramidal and square pyramidal.40-42 In most of them, the metal
centre lies in a distorted trigonal bipyramidal environment, the
double bonds of the cod ligand occupying an equatorial and an
apical position, as shown in Scheme 7.
2
3
and 3.77 ppm with JHH = 17.6 Hz and JPH = 13.5 and 9.7 Hz)
could be due to rapid exchange or to an equilibrium between a
trigonal bipyramidal and a square-base pyramidal coordination
geometry that would render the two P,N arms equivalent. Three
resonances between 3.50 and 1.80 ppm are due to the coordinated
cod ligand. In particular, the protons of the methylene groups
of the cyclooctadiene become non-equivalent upon coordination
It was hoped that the substitution of the chloride anion with a
(tetra)arylborate would promote the crystallization of the complex
and increase its solubility in solvents of low polarity. Therefore,
we reacted [Ir(m-Cl)(cod)]2 with the NpyPNpy ligand and added
two equivalents of NaBArF to the reaction mixture. The yellow
crystalline product, which was isolated in high yield after removing
the NaCl formed, was fully characterized by IR and NMR spec-
troscopic methods, elemental analysis, and X-ray diffraction, and
identified as the cationic complex [Ir(cod)(NpyPNpy-N,P,N)]BArF
1
and give rise to two multiplets. The 13C{ H} NMR spectrum of
6 displays two doublets at 63.0 (2JPC = 8.7 Hz) and 33.0 (3JPC
=
1.8 Hz) ppm, attributed to the CH and the CH2 carbons of the cod,
respectively. IR spectroscopy was very useful to better understand
the molecular structure of 6. In particular, the far IR spectrum
of the compound did not show any strong absorption around
300 cm–1 and this led us to rule out the presence of Ir–Cl bonds.39 In
agreement with the spectroscopic data and the elemental analysis,
we propose that 6 is a penta-coordinated cationic complex. As
far as the coordination environment of the metal is concerned,
two different geometries have been reported for Ir(I) complexes
1
(7). Its 31P{ H} NMR spectrum in CDCl3 displays a sharp singlet
at 24.2 ppm, with a difference of only 0.5 ppm with respect to that
of 6. This suggests a very similar chemical environment around
the phosphorus donor atom. With the exception of the signals
1
due to the counteranion, the 13C{ H} NMR spectra of 6 and 7
are also very similar in terms of chemical shifts and coupling
1
constants. The main difference between the H NMR spectra of
2568 | Dalton Trans., 2010, 39, 2563–2572
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6 and 7 concerns the ABX spin system due to the CH2P protons.
As previously mentioned, the two diastereotopic protons of 6 give
rise to two doublets of doublets at 5.01 and 3.77 ppm. In the case
of 7, instead, they give rise to a multiplet between 3.90–3.80 ppm.
By means of spectral simulation we could estimate the parameters
stated, NMR spectra were recorded at room temperature on
a Bruker AVANCE 300 spectrometer (1H, 300 MHz; 13C,
75.47 MHz; 19F, 282.4 MHz; 31P, 121.5 MHz) or on a Bruker
AVANCE 400 spectrometer (1H, 400 MHz; 13C, 100.60 MHz,
31P, 162.0 MHz) and referenced using the residual proton
solvent (1H) or solvent (13C) resonance. Assignments are based
on DEPT135, COSY, HMQC and HMBC experiments. IR
spectra were recorded in the region 4000–100 cm–1 on a Nicolet
6700 FT-IR spectrometer equipped with a Smart Orbit ATR
accessory (Ge or diamond crystals). Elemental analyses were
performed by the “Service de microanalyse”, Universite´ de
Strasbourg. Yields of the complexes are based on the metal.
[Ir(m-Cl)(cod)]2 and TlPF6 were purchased from UMICORE and
Alfa Aesar and used as received. Bis(2-picolyl)phenylphosphine
of this ABX spin system as dA = 3.86 ppm, dB = 3.84 ppm, 2JAB
=
18.4 Hz, 2JAX = 2.6 Hz and 2JBX = 19.6 Hz. A view of the molecular
structure of the cation [Ir(cod)(NpyPNpy)]+ of 7 in the solid state is
shown in Fig. 6.
The coordination geometry around the metal is best described
as trigonal bipyramidal. Two equatorial (P, N) and one apical
(N) positions are occupied by the donor atoms of the NpyPNpy
ligand, which acts as a facial, tridentate N,P,N-donor. Similarly, in
the octahedral CrIII complex [CrCl3(NpyPNpy-N,P,N)] the ligand
exhibits a facial coordination mode with the phosphorus atom
(NpyPNpy),17
[PdCl2(NCPh)2],43
Na[B(3,5-(CF3)2C6H3)4],44
in an apical position.36 The two C C double bonds of the
[Pd(NCMe)4](BF4)2,45 and [PdCl2(cod)]
were prepared
46
=
cyclooctadiene complete the coordination sphere of the metal.
according to literature methods. Other chemicals were
commercially available and used as received.
˚
The apical Ir–N bond (2.150(5) A) is shorter than the equatorial
˚
one (2.274(5) A).
Synthesis of [PdCl2(NpyPNpy)] (1). Solid [PdCl2(NCPh)2]
(0.722 g, 1.88 mmol) was added to a solution of NpyPNpy
(0.550 g, 1.88 mmol) in dichloromethane (20 mL) to give a yellow
suspension, which was stirred overnight. The solvent was removed
under vacuum affording a yellow powder which was washed with
diethyl ether (2 ¥ 20 mL) and dried in vacuo overnight (Yield:
0.697 g, 1.32 mmol, 79%). Selected IR absorptions (pure, diamond
orbit): 1604 m, 1587 m, 1468 ms, 1436 s, 1107 m, 844 s, 803 s, 785 s,
Conclusions
New coordination complexes of Pd(II) and Ir(I) bearing the
neutral ligand NpyPNpy have been prepared in high yields from
[PdCl2(NCPh)2] or [Ir(m-Cl)(cod)]2 and the ligand. The solid-state
structures of the compounds (1–5 and 7) point out the versatility
of the NpyPNpy molecule, which can act as a N,P-chelating ligand
(in 1 and 4), N,P,N-mer-chelating ligand (in 2 and 5), (N,P)-N
chelating/bridging ligand (in 3), N,P,N-fac-chelating ligand (in 7).
On the basis of NMR experiments in DMSO-d6, the hemilability
of NpyPNpy in 1 has been demonstrated, the two pyridine moieties
being involved in a dynamic exchange in the coordination sphere
of the metal. Dynamic processes in DMSO solution have also been
observed for complex 2 and an equilibrium between the species
[PdCl(NpyPNpy-N,P,N)]+ and [PdCl(NpyPNpy-N,P)(DMSO)]+ has
been inferred. The unexpected dinuclear compound 3 has been
isolated as a by-product of the synthesis of its isomer 2. We have
also demonstrated that, in spite of the stability of 3 in the solid
state, it can be converted into 2 in DMSO solution. A rational,
stepwise preparation of 3 has been described, which involves
the preparation of the dicationic complex cis-[Pd(NpyPNpy-N,P)2]
(BF4)2 (4) and its reaction with [PdCl2(cod)]. Interesting com-
parisons become thus possible between the palladium complexes
of the related NpyPNpy and NoxPNox ligands.38 The Ir(I) cationic
complex [Ir(cod)(NpyPNpy-N,P,N)]BArF (7) is, to the best of our
knowledge, only the third Ir(I) complex containing a N,P,N-
chelating ligand to be structurally characterized.29,37
1
31
744 s, 684 s, 337 m, 301 m cm-1. H{ P} NMR (400.13 MHz,
DMSO-d6): d 9.31 (br, 1H, py6), 8.38 (br, 1H, py6), 8.04 (br, 1H,
3
py4), 7.87 (d, 2H, JHH = 7.5 Hz, o-aryl), 7.81 (br, 1H, py3), 7.71
3
(br, 1H, py4), 7.58 (t, 1H, JHH = 7.4 Hz, p-aryl), 7.51–7.35 (m,
4H, m-aryl, py5 and py3), 7.24 (br, 1H, py5), 4.70 and 4.25 (AB
2
spin system, 2H, JHH = 16.4 Hz, CH2), 4.25 and 4.08 (AB spin
1
system, 2H, 2JHH = 14.4 Hz, CH2) ppm. 13C{ H} NMR (75.5 MHz,
DMSO-d6): d 162.5 (s, coordinated py2), 153.4 (s, uncoordinated
py2), 152.2 (s, coordinated py6), 149.6 (s, uncoordinated py6), 140.8
(s, coordinated py4), 137.5 (s, uncoordinated py4), 132.6 (s, p-aryl),
2
3
132.2 (d, JPC = 10.0 Hz, o-aryl), 129.5 (d, JPC = 11.2 Hz, m-
1
aryl), 127.7 (d, JPC = 52.2 Hz, ipso-aryl), 125.7 (s, py), 124.8 (s,
py), 124.1 (s, py), 122.9 (s, py), coordinated CH2 partially masked
by the solvent resonance, 34.8 (d, 1JPC = 31.3 Hz, uncoordinated
CH2) ppm. 31P{ H} NMR (121.5 MHz, DMSO-d6): d 49.7 (s)
1
ppm. Anal. Calcd for C18H17Cl2N2PPd: C, 46.03; H, 3.65; N, 5.96.
Found: C, 45.53; H, 3.83; N, 5.86. Crystals suitable for X-ray
diffraction were grown by slow cooling of a concentrated solution
of the pure compound in DMF.
Synthesis of [PdCl(NpyPNpy)]PF6 (2) and [Pd2Cl2(l-
NpyPNpy)2](PF6)2 (3). Solid [PdCl2(NCPh)2] (0.690 g, 1.80 mmol)
was added to a solution of NpyPNpy (0.525 g, 1.80 mmol) in
THF (20 mL) to give a yellow suspension, which was stirred
overnight. TlPF6 (0.629 g, 1.80 mmol) was added and the mixture
was stirred for 12 h. The solvent was removed by evaporation
under reduced pressure and the solid residue was extracted in
DMF and the solution was filtered to remove TlCl. Et2O was
added and a yellow solid separated out which was shown by
1H NMR to contain two products (see text). After filtration
and washing of the yellow solid with CH2Cl2 (3 ¥ 10 mL), the
combined filtrates were concentrated to 10 mL under reduced
pressure to give yellow crystals of [Pd2Cl2(m-NpyPNpy)2](PF6)2,
Experimental
General considerations
All operations were carried out using standard Schlenk techniques
under an inert atmosphere. Solvents were dried, degassed, and
freshly distilled prior to use. Et2O and THF were dried over
sodium/benzophenone. Pentane was dried over sodium. CH2Cl2
and acetonitrile were distilled from CaH2. DMF, DMSO-d6 and
˚
CDCl3 were dried over 4 A molecular sieves, degassed by freeze–
pump–thaw cycles and stored under argon. Unless otherwise
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suitable for X-ray diffraction (0.100 g, 0.086 mmol, 10% yield
based on Pd). The insoluble pale yellow residue was identified
as [PdCl(NpyPNpy)]PF6 (0.762 g, 1.32 mmol, 73%). Selected
IR absorptions (pure, diamond orbit) for [PdCl(NpyPNpy)]PF6:
1666w, 1606w, 1474w, 1439w, 1110w, 835vs, 768 m, 688 m,
556 s, 343 m cm-1. The following NMR data correspond to
the sharp signals of the cationic complex [PdCl(NPN)]+. 1H
suspension was stirred overnight, TlPF6 (0.698 g, 2.00 mmol)
was then added and the mixture was further stirred for 12 h.
After filtration and washing of the solid residue with acetonitrile
(3 ¥ 10 mL), the combined filtrates were concentrated to 5 mL,
and Et2O (20 mL) was added affording the precipitation of pure
[Pd(NpyPNpy)(NCMe)](PF6)2 as a pale yellow solid (Yield: 0.584 g,
0.80 mmol, 80%). Selected IR absorptions (pure, diamond orbit):
1609 w, 1476 w, 1437 w, 1111 m, 832 vs, 776 m, 742 m, 689 m,
3
NMR (300.13 MHz, DMSO-d6): d 9.06 (d, 2H, JHH = 4.9 Hz,
py6), 8.25–8.20 (m, 2H, py4), 7.99–7.90 (m, 4H, py3 and o-aryl),
554 s cm-1. H{ P} NMR (400.13 MHz, DMSO-d6): d 8.51 (d,
1
31
2
3
3
4
7.68-7.51 (m, 5H, py5, p- and m-aryl), 5.30–5.19 (m, 2H, JHH
ª
2H, JHH = 5.4 Hz, py6), 8.26 (td, 2H, JHH = 7.9 Hz, JHH
=
2JPH ª 17.3 Hz, CHH), 4.39–4.23 (m, 2H, 2JHH ª JPH ª 17.3 Hz,
1.5 Hz, py4), 8.00 (d, 3JHH = 7.9 Hz, 2H, py3), 7.70–7.67 (m, 3H,
2
CHH) ppm. 13C{ H} NMR (75.5 MHz, DMSO-d6): d 164.9 (s,
py5 and p-aryl), 7.64–7.62 (m, 2H, o-aryl), 7.55–7.51 (m, 2H,
1
py2), 153.6 (s, py6), 142.0 (s, py4), 133.9–124.9 (m, py3,5 and aryl),
m-aryl), 5.21 and 4.29 (AB spin system, JHH = 17.7 Hz, 4H,
2
38.5 (d, JPC = 36.7 Hz, CH2) ppm. 31P{ H} NMR (121.5 MHz,
CH2), 2.07 (s, 3H, free CH3CN) ppm. 13C{ H} NMR (75.5 MHz,
1
1
1
1
DMSO-d6): d 83.7 (br, NpyPNpy), -143.0 (sept, JPF = 712 Hz,
DMSO-d6): d 164.0 (s, py2), 151.6 (s, py6), 142.4 (s, py4), 134.1
-
4
2
PF6 ) ppm. Anal. Calcd for C18H17Cl F6N2P2Pd: C, 37.33; H, 2.96;
(d, JPC = 2.6 Hz, p-aryl), 131.7 (d, JPC = 11.2 Hz, o-aryl),
N, 4.84. Found: C, 37.55; H, 3.06; N, 4.82. Crystals suitable for
X-ray diffraction were grown by cooling a hot dichloromethane
solution of the pure compound to room temperature.
130.4 (d, 3JPC = 12.7 Hz, m-aryl), 126.3 (d, 3JPC = 15.3 Hz, py3),
125.7 (s, py5), 124.4 (d, JPC = 58.6 Hz, ipso-aryl), 118.5 (s, free
1
CH3CN), CH2 partially masked by the solvent resonance, 1.5 (s,
free CH3CN). 31P{ H} NMR (121.5 MHz, DMSO-d6): d 86.6 (s,
1
[Pd2Cl2(l-NpyPNpy)2](PF6)2 (3). Selected IR absorptions (pure,
diamond orbit): 1606 w, 1572 w, 1476 w, 1437 w, 1102 m, 836 vs,
759 m, 746 m, 694 m, 555 s, 346 m cm-1. 1H NMR (300.13 MHz,
DMSO-d6): d 9.27 (d, 2H, 3JHH = 5.4 Hz, py6), 8.20–8.17 (m, 2H,
py), 8.10-8.05 (m, 2H, py4), 7.98–7.93 (m, 2H, py), 7.78–7.67 (m,
8H, py and o-aryl), 7.60–7.51 (m, 6H, py and p-aryl), 7.40–7.34 (m,
4H, m-aryl), 5.66 (br, 2H, CH2), 4.77–4.30 (m, 4H, CH2), 3.94 (br,
1
-
NpyPNpy), –143.0 (sept, JPF = 712 Hz, PF6 ) ppm. Anal. Calcd
for C20H20F12N3P3Pd·CH3CN: C, 34.28; H, 3.01; N, 7.27. Found:
C, 34.21; H, 3.17; N, 6.98. Crystals suitable for X-ray diffraction
were grown by layering Et2O on a concentrated acetonitrile
solution of the pure compound.
Synthesis of [IrCl(cod)(NpyPNpy)] (6). Solid [Ir(m-Cl)(cod)]2
(0.260 g, 0.387 mmol) was added to a solution of the NpyPNpy
ligand (0.220 g, 0.787 mmol) in CH2Cl2 (10 mL). The orange
solution was stirred for 1 h. The solvent was evaporated under
reduced pressure to give an orange solid, which was washed with
pentane (2 ¥ 5 mL) and dried in vacuo (Yield: 0.430 g, 0.684 mmol,
88%). Selected IR absorptions (pure, diamond orbit): 1597 m,
1
2H, CH2) ppm. 31P{ H} NMR (121.5 MHz, DMSO-d6): d 47.5
(br, NpyPNpy), -143.0 (sept, 1JPF = 712 Hz, PF6 ) ppm. We could
-
1
not record the 13C{ H} NMR spectrum of the pure compound
because it isomerises slowly to the monomer in DMSO solution.
Anal. Calcd for C18H17ClF6N2P2Pd: C, 37.33; H, 2.96; N, 4.84.
Found: C, 37.21; H, 3.17; N, 4.72.
1
1472 ms, 1435 ms, 1106 ms, 1011 m, 744 s, 695 s cm-1. H NMR
3
4
Synthesis of [Pd(NpyPNpy)2](BF4)2 (4). Solid [Pd(NCCH3)4]-
(BF4)2 (0.222 g, 0.50 mmol) was added to a solution of NpyPNpy
(0.292 g, 1.00 mmol) in dichloromethane (20 mL). The resulting
yellow suspension was stirred overnight at room temperature.
The solvent was concentrated to 5 mL under reduced pressure
affording a pale yellow powder, which was washed with diethyl
ether (2 ¥ 20 mL) and dried in vacuo overnight (Yield: 0.337 g,
0.39 mmol, 78%). Selected IR absorptions (pure, diamond orbit):
1605 w, 1588 w, 1571 w, 1473 m, 1437 m, 1397 w, 1315 m, 1162 m,
1028 vs, 888 s, 833 m, 752 s, 692 s cm-1. 1H NMR (300.13 MHz,
(300.13 MHz, CDCl3): d 8.76 (dd, 2H, JHH = 5.6 Hz, JHH
=
1.0 Hz, py6), 7.92–7.85 (m, 2H, o-aryl), 7.79 (d, 2H, 3JHH = 7.9 Hz,
py3), 7.70–7.62 (m, 2H, py4), 7.59–7.47 (m, 3H, m-, p-aryl), 7.14–
7.06 (m, 2H, py5), 5.01 and 3.77 (ABX spin system, 4H, JHH
=
2
17.6 Hz,2JPH = 13.5 Hz and 9.7 Hz, PCH2), 3.40 (s, 4H, CH cod),
2.40–2.20 (m, 4H, CH2 cod), 1.95–1.75 (m, 4H, CH2 cod) ppm.
13C{ H} NMR (75.5 MHz, CDCl3): d 161.9 (d, JPC = 6.2 Hz,
1
2
py6), 150.7 (d, 3JPC = 3.5 Hz, py2), 138.3 (s, py4), 131.9 (d, 2JPC
11.2 Hz, o-aryl), 131.3 (d, 4JPC = 2.3 Hz, p-aryl), 129.4 (d, 3JPC
=
=
10.6 Hz, m-aryl), 126.6 (d,1JPC = 49.7 Hz, ipso-aryl), 125.4 (d,
3JPC = 9.7 Hz, py3), 123.9 (s, py5), 63.0 (d, 2JPC = 8.7 Hz, CH cod),
41.8 (d, 2JPC = 28.7 Hz, CH2P), 33.0 (d, 3JPC = 1.8 Hz, CH2 cod)
DMSO-d6): d 8.23 (d, 4H, 3JHH = 5.2 Hz, py6), 7.80 (t, 4H, 3JHH
=
7.7 Hz, py4), 7.71–7.64 (m, 6H, p- and o-aryl), 7.52–7.45 (m, 8H,
py3 and m-aryl), 7.30 (t, 4H, py5), 4.31–4.14 (m, 8H, CH2) ppm.
ppm. 31P{ H} NMR (121.5 MHz, CDCl3): d 24.7 (s) ppm. Anal.
1
1
13C{ H} NMR (75.5 MHz, DMSO-d6): d 155.7 (s, py2), 150.6 (s,
Calcd for C26H29ClIrN2P: C, 49.71; H, 4.65; N, 4.46. Found: C,
49.76; H, 4.93; N, 4.12.
2
py6), 139.7 (s, py4), 133.7 (s, p-aryl), 132.4 (d, JPC = 11.1 Hz, o-
aryl), 129.7 (d, 3JPC = 11.8 Hz, m-aryl), 125.2 (d, 1JPC = 56.3 Hz,
Synthesis of [Ir(cod)(NpyPNpy)]BArF (7). Solid [Ir(m-Cl)(cod)]2
(0.160 g, 0.238 mmol) was added to a solution of the NpyPNpy
ligand (0.142 g, 0.486 mmol) in CH2Cl2 (10 mL). The orange
solution was stirred for 1 h and then NaBArF was added. The
resulting yellow mixture was stirred overnight and filtered to
remove NaCl. The solvent was removed under reduced pressure
and the resulting yellow powder was washed with pentane (2 ¥
5 mL) and dried in vacuo (Yield: 0.440 g, 0.302 mmol, 63%).
Crystals suitable for X-ray diffraction were grown by layering
Et2O and pentane on a concentrated solution of the compound
ipso-aryl), 125.2 (d, 3JPC = 9.3, py3), 124.1 (s, py5), 36.7 (d, 1JPC
=
1
30.2 Hz, CH2) ppm. 31P{ H} NMR (121.5 MHz, DMSO-d6): d
47.0 (s) ppm. Anal. Calcd for C36H34B2F8N4P2Pd C, 50.01; H, 3.96
N, 6.48. Found: C, 49.97; H, 3.86; N, 6.49. Crystals suitable for
X-ray diffraction were grown by layering Et2O on a concentrated
dichloromethane solution of the pure compound.
Synthesis
of
[Pd(NpyPNpy)(MeCN)](PF6)2
(5). Solid
[PdCl2(NCPh)2] (0.384 g, 1.00 mmol) was added to a solution of
NpyPNpy (0.290 g, 1.00 mmol) in acetonitrile (20 mL). The yellow
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in CH2Cl2. Selected IR absorptions (pure, diamond orbit): 1608
6 P. Braunstein, C. Graiff, F. Naud, A. Pfaltz and A. Tiripicchio, Inorg.
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Dalton Trans., 1999, 589.
1
w, 1571 mw, 1354 m, 1277 vs, 1159 s, 1120 vs cm-1. H NMR
(300.13 MHz, CDCl3): 8.86 (d, 2H, 3JHH = 4.8 Hz, py6), 7.80–7.66
(m, 10H, o-aryl, o-BArF), 7.64–7.58 (m, 3H, p-, m-aryl), 7.57–7.44
3
(m, 6H, py4, p-BArF), 7.34 (d, 2H, JHH = 7.8 Hz, py3), 7.08 (t,
3
2H, JHH = 6.2 Hz, py5), 3.90–3.80 (m, ABX spin system, 4H,
2
values from spectral simulation: JHH = 18.4 Hz,2JPH = 19.6 Hz
and 2.6 Hz, PCH2), 3.46 (s, 4H, CH cod), 2.40–2.25 (m, 4H, CH2
1
cod), 1.98-1.88 (m, 4H, CH2 cod) ppm. 13C{ H} NMR (75.5 MHz,
13 P. Braunstein, F. Naud, A. Pfaltz and S. J. Rettig, Organometallics,
2000, 19, 2676.
1
CDCl3): d 161.7 (q, JBC = 49.8 Hz, ipso-aryl BArF), 160.2 (d,
3
2JPC = 7.3 Hz, py2), 151.6 (d, JPC = 4.1 Hz, py6), 138.7 (s, py4),
14 P. Braunstein, F. Naud, C. Graiff and A. Tiripicchio, Chem. Commun.,
4
134.8 (s, o-aryl BArF), 132.2 (d, JPC = 2.6 Hz, p-aryl), 131.0 (d,
2000, 897.
3
2JPC = 11.3 Hz, o-aryl), 129.9 (d, JPC = 10.7 Hz, m-aryl), 128.9
15 P. Braunstein, F. Naud and S. J. Rettig, New J. Chem., 2001, 25, 32.
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2945.
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Trans., 2003, 1601.
(qq, 2JCF = 31.5 Hz, 3JBC = 2.8 Hz, CCF3), 124.7 (s, py5), ipso-aryl
masked, 124.5 (q, 1JCF = 272.5 Hz, CF3), 124.0 (d, 3JPC = 9.5 Hz,
py3), 117.5 (sept,3JCF = 3.8 Hz, p-aryl BArF), 64.3 (d, 2JPC = 8.7 Hz,
CH cod), 42.8 (d, 2JPC = 27.4 Hz, CH2P), 32.9 (d, 2JPC = 1.8 Hz,
1
CH2 cod) ppm. 31P{ H} NMR (121.5 MHz, CDCl3): d 24.2 (s)
ppm.19F NMR (282.4 MHz, CDCl3): -62.8 ppm. Anal. Calcd for
C58H41BF24IrN2P: C, 47.85; H, 2.84; N, 1.92. Found: C, 47.89; H,
2.86; N, 1.82.
23 A. Kermagoret and P. Braunstein, Dalton Trans., 2008, 585.
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Determination of the crystal structures
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47
˚
(l = 0.71073 A) (Table 1). The structures were solved by direct
methods using the SHELX 97 software,47 and the refinement was
by full-matrix least squares on F2. A MULTISCAN absorption
correction was applied on [PdBr2(NpyPNpy-N,P)] and 7.48 All
non-hydrogen atoms were refined anisotropically. The hydrogen
atoms were introduced into the geometrically calculated positions
(SHELXS-97 procedures) and refined riding on the corresponding
parent atoms. In 7, six CF3 groups of the anion were found
disordered. These groups were refined as disordered in two po-
sitions having the carbon atom in common, and with constrained
anisotropic parameters.
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Acknowledgements
We thank the Centre National de la Recherche Scientifique
(CNRS), the Ministe`re de l’Enseignement Supe´rieur et de la
Recherche (Paris) and the Universite´ de Strasbourg for support,
the French Embassy in Beijing for a doctoral grant to S. L.
and Professor Wen-Hua Sun (Institute of Chemistry, Chinese
Academy of Sciences, Beijing) for support. We are grateful
to Drs Lydia Brelot (X-ray structure analyses) and Roberto
Pattacini (X-ray structure analyses and discussions), Dr Weiwei
Zuo for experimental assistance, and Dr Joaqu´ın Lo´pez-Serrano
for helpful discussions on NMR analyses.
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2572 | Dalton Trans., 2010, 39, 2563–2572
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