Isomeric preference in complexes of palladium(II) with chelating P,n-donor ligands

Article abstract of DOI:10.1002/ejic.200801196

Square-planar complexes [PdCl{K²-(RN = CHC₆H ₄PPh₂)Rj] (R = Cl; R = 4-CH ₃C₆H₄, 1a; R = 2-CH₃OC ₆H₄, 1b;R = 2- HOC₆H₄, 1c;R' =CH₃; R = 4-CH₃C₆H₄, 2a;R = 2-CH₃OC₆H₄, 2b; R = 2-HOC₆H ₄, 2c) have been prepared and characterized. In complexes 2a-c only formation of one isomer was observed. The Pd-methyl bond arranges in a cis position to the phosphane fragment of the P,N chelating ligand. Reaction of complexes 2a-c in acetonitrile with AgBF₄ led to removal of the chlorido ligand and coordination of acetonitrile for 2a. However, for 2b and 2c coordination of the oxygen was observed and the chelating P,N ligands became tricoord- inate. DFT calculations developed on models of the complexes displayed that the isomer with the methyl ligand coordinated in the cis position to the phosphane ligand were harder (or had a bigger HOMO/LUMO gap). Wiley-VCH Verlag GmbH & Co. KGaA.

Full text of DOI:10.1002/ejic.200801196

FULL PAPER
DOI: 10.1002/ejic.200801196
Isomeric Preference in Complexes of Palladium(II) with Chelating P,N-Donor
Ligands
Olga del Campo,[a] Arancha Carbayo,[a] José V. Cuevas,*[a] Gabriel García-Herbosa,[a] and
Asunción Muñoz[a]
Keywords: Isomeric preference / Platinum / Coordination / Density functional calculations / Hardness / Palladium
Square-planar complexes [PdCl{κ2-(RN = CHC6H4PPh2)RЈ}]
(RЈ = Cl; R = 4-CH3C6H4, 1a; R = 2-CH3OC6H4, 1b; R = 2-
HOC6H4, 1c; RЈ = CH3; R = 4-CH3C6H4, 2a; R = 2-CH3OC6H4,
2b; R = 2-HOC6H4, 2c) have been prepared and charac-
terized. In complexes 2a–c only formation of one isomer was
observed. The Pd–methyl bond arranges in a cis position to
the phosphane fragment of the P,N chelating ligand. Reac-
tion of complexes 2a–c in acetonitrile with AgBF4 led to re-
moval of the chlorido ligand and coordination of acetonitrile
for 2a. However, for 2b and 2c coordination of the oxygen
was observed and the chelating P,N ligands became tricoord-
inate. DFT calculations developed on models of the com-
plexes displayed that the isomer with the methyl ligand coor-
dinated in the cis position to the phosphane ligand were
harder (or had a bigger HOMO/LUMO gap)
(© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim,
Germany, 2009)
In this context, the Maximum Hardness Principle
(MHP)[11,12] and antisymbiosis[13–15] can be very useful
tools in order to understand what the most stable isomer is.
In this work we report the syntheses and characterization
of complexes of palladium(II) with P,N-donor ligands. In
some cases these complexes can give rise to cis,trans iso-
mers, but we have found the formation of only one of them.
DFT calculations are used to rationalize this preferential
formation (or others) on the basis of the MHP and are in
good agreement with the antisymbiosis rule.
Introduction
In recent years, phosphorus and nitrogen donor ligands
have been among the most attractive and useful ligands
used in catalysis because of the presence of both soft and
hard donor atoms, which allows for interesting complex-
ation properties.[1,2] Complexes with these kinds of ligands
have found application as catalysts in a wide range of reac-
tions.[2–8]
The properties of a number of P,P- and P,N-donor li-
gands in a variety of chemical environments have been re-
cently studied, building a map of bidentate ligand space
that has potential applications in predictions about novel
or untested ligands.[9] The coordination of P,N-donor che-
lating ligands to synthesize four-coordinate complexes can
give rise to different isomers when the ancillary ligands are
different. This isomeric possibility can be important in cata-
lytic processes, as the activity of each isomer could not be
the same. Schubert et al. have reported the C–Cl/Si–H ex-
change catalyzed by [PtClMe(P,N)] complexes.[10] Despite
the fact that it is possible to propose two isomers, they have
found that only the isomer with the chlorido ligand coordi-
nated cis to the phosphane fragment is the active catalytic
species.
Results and Discussion
Syntheses of the Complexes
The P,N-donor ligands were prepared by simple conden-
sation of the aldehyde 2-diphenylphosphanylbenzaldehyde
with a slight excess of 4-toluidine (a), 2-anisidine (b), or 2-
aminophenol (c) in methanol solution in a similar way to
those previously reported.[16–19] Reactions of equimolar
amounts of ligands (a–c) with [PdCl2(COD)] or
[PdCl(COD)Me] [COD = 1,5-cyclooctadiene] in THF solu-
tion afforded the complexes [PdCl2(P,N)] (1a–c) or
[PdClMe(P,N)] (2a–c), respectively, in high yields
(Scheme 1).
A downfield shift of the phosphane signals (approxi-
mately 30 ppm for dichlorido complexes and 38 ppm for
chloridomethyl complexes) in 31P NMR with respect to the
free ligand reflects the coordination of the phosphane to
the palladium metal. For complexes 2a–c it is possible to
propose the formation of two isomers depending on the ori-
entation of the methyl and chlorido ligands with respect to
[a] Departamento de Química, Facultad de Ciencias, Universidad
de Burgos,
Pza. Misael Bañuelos S/N, 09001 Burgos, Spain
Fax: +34-947-258-831
E-mail: jvcv@ubu.es
Supporting information for this article is available on the
WWW under http://www.eurjic.org or from the author.
2254
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Isomeric Preference in Complexes of Palladium(II)
Scheme 1. Syntheses of complexes 1 and 2.
the phosphane-imine ligand. Nevertheless, the presence of
only one signal in the 31P NMR spectra is indicative of the
formation of only one isomer. The 1H NMR spectrum
shows that the methyl group coordinated cis to the phos-
phorus atom appears as a doublet with a coupling constant
JP-H ≈ 3.4 Hz for complexes 2a and 2b, and 2.7 Hz for com-
plex 2c. These small values for the coupling constants are
indicative of the formation of the isomer in which the phos-
phane fragment and the methyl group are orientated in the
cis position. The observed values for complexes 2a and 2b
are in good agreement with the value reported for a cis ar-
rangement of the methyl group and phosphane in com-
plexes of palladium; however, the observed value for com-
plex 2c is smaller, but not that far off the values of the
related compounds. NOESY experiments showed the pres-
ence of NOE between the methyl group and the aromatic
protons of the phenyl groups bonded to the phosphorus
atom. These experiments confirm the configuration in
which the methyl group is bonded in a cis position to the
phosphorus atom (and trans to the nitrogen atom) of the
chelating ligand. This result is in good agreement with pre-
vious published results of similar complexes.[16,20,21]
Scheme 2. Syntheses of compounds 3.
Structural Characterization of Complex 2b
The slow evaporation of the solvent of a solution of com-
plex 2b in CDCl3 afforded single crystals suitable for X-ray
diffraction studies. The molecular structure of complex 2b
is shown in Figure 1, and selected bond lengths, bond
angles, and torsion angles are given in Table 1.
The reaction of complexes 2a–c with AgBF4 in acetoni-
trile yielded the removal of the chlorido ligand but the re-
sult depends on the coordinating nature of the ligands. For
complex 2a the reaction afforded the substitution of the
chlorido ligand by an acetonitrile ligand keeping the posi-
tion of the methyl group with respect to the chelating ligand
(i.e. the coordinated methyl group remains in a cis position
to the phosphorus atom). For complexes 2b and 2c the
same reaction afforded the removal of the chlorido ligand
without the incorporation of acetonitrile as a ligand. In-
stead of this, we observed the coordination of the oxygen
atom of the methoxy (b) or hydroxy (c) groups, which be-
came terdentate ligands with two chelating rings, as de-
picted in Scheme 2. The terdentate behavior of the ligand
precludes the formation of different isomers and the only
possibility for the methyl group is to remain bonded to the
palladium in a cis position to the phosphorus atom.
Figure 1. Structure of complex 2b. A chloroform molecule of
crystallization is represented. Selected bond lengths and angles are
summarized in Table 1.
The elimination of the halogen to produce cationic com-
plexes moves the signal of the coordinated phosphane to
The chelating ligand binds to the metal through a phos-
lower fields, from 38, 37, or 39 ppm (for 2a, 2b, or 2c, phorus donor P(1) and secondary imine donor N(1). The
respectively) to 40, 44, or 42 ppm (for 3a, 3b, or 3c, respec- P(1)–Pd(1)–N(1) bond angle is 89.09(8)°. The coordination
tively). The chemical shift of the methyl group bonded to around the palladium atom is slightly distorted from plan-
the palladium atom moves to higher fields and this change arity with a torsional angle N(1)–P(1)–C(27)–Cl(1) of
is stronger from complex 2a to 3a (from 0.7 ppm to 10.41°. The six-membered chelating ring is folded and the
0.46 ppm) than in the other complexes.
torsional angle C(14)–P(1)–Pd(1)–N(1) is 38.7°. This non-
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J. V. Cuevas et al.
FULL PAPER
Table 1. Selected bond lengths [Å] and angles [°] for compound 2b. and in all cases this isomer is the one which locates the
methyl group bonded to the palladium atom in a cis posi-
Pd(1)–C(27)
Pd(1)–P(1)
C(8)–C(9)
P(1)–C(14)
N(1)–C(8)
2.054(3)
2.1861(10)
1.463(5)
1.818(4)
1.270(4)
Pd(1)–N(1)
Pd(1)–Cl(1)
C(8)–H(8)
C(9)–C(14)
2.159(3)
2.3843(10)
0.9500
tion to the phosphorus atom of the chelating ligand.
search in the Cambridge Structural Database
A
(CSD,[31,32] version 5.29, November 2007) for structures of
palladium and platinum with a similar coordination envi-
ronment of a phosphorus atom, a nitrogen atom, a carbon
atom, and a halogen restricted to an angle P–Pd–N close
to 90° (see Table 2) displayed 71 hits with 83 structures of
complexes of palladium or platinum with this coordination
environment and in all of them the carbon atom coordi-
nated to the palladium locates in the cis position to the
phosphorus atom as we have found in our complexes. A
similar search replacing a halogen atom for a nitrogen
atom, trying to find similar situations to the complex 3a,
displayed 120 hits with 153 structures. In 149 of the 153
structures the disposition of the atoms was exactly the same
as we found in 3a, and the four structures that do not match
ours have additional chelating rings that impose an alterna-
tive conformation. In three cases a pincer N~C~N chelating
ligand imposes the coordination of the phosphorus atom in
a trans position to the carbon atom.[33] In the fourth outly-
ing case it is a P~N~C chelating ligand that imposes a trans
coordination of the phosphorus and carbon atoms.[34]
1.411(5)
C(27)–Pd(1)–N(1)
N(1)–Pd(1)–P(1)
N(1)–Pd(1)–Cl(1)
C(8)–N(1)–Pd(1)
C(14)–C(9)–C(8)
173.91(12)
89.09(8)
91.94(8)
128.7(2)
126.0(3)
C(27)–Pd(1)–P(1)
C(27)–Pd(1)–Cl(1)
P(1)–Pd(1)–Cl(1)
N(1)–C(8)–C(9)
C(9)–C(14)–P(1)
90.49(11)
89.31(11)
172.00(3)
127.3(3)
122.0(3)
C(27)–Pd(1)–P(1)–C(14) –147.37(16)
Cl(1)–Pd(1)–P(1)–C(14) –58.8(3)
P(1)–Pd(1)–N(1)–C(8)
Pd(1)–N(1)–C(8)–C(9)
N(1)–Pd(1)–P(1)–C(14) 38.70(14)
C(27)–Pd(1)–N(1)–C(8) –117.8(11)
Cl(1)–Pd(1)–N(1)–C(8) 140.4(3)
N(1)–C(8)–C(9)–C(14) 18.5(6)
–31.7(3)
4.5(5)
Pd(1)–P(1)–C(14)–C(9) –34.6(3)
planarity of the six-membered chelating ring gives rise to
twist-boat (δ/λ)[22] chirality in the molecule.[23–30] Taking
into account this source of chirality, it is possible to propose
two enantiomers for these complexes. Figure 2 displays
fragments of the nonplanar chelating rings. Both enantio-
mers crystallize together in the unit cell as required by the
space group P21/c (see Figure 2).
Table 2. CSD results for searches of analogous compounds to 2
and 3a.
This observed structural preference can be interpreted on
the basis of the Maximum Hardness Principle, which states
that “molecules arrange themselves to be as hard as pos-
sible.”[12] Taking into account Koopmans’s theorem, the
chemical hardness (η) is related to the HOMO/LUMO gap
as half the energy gap between the two orbitals.[11,12]
η = (ELUMO – EHOMO)/2
Figure 2. Fragments of the nonplanar chelating rings and packing
in the unit cell (hydrogen atoms and solvent molecules omitted for
clarity).
In order to confirm the relationship between the ob-
served structural preference and the chemical hardness,
theoretical calculations have been developed on simplified
models of our complexes. The models were constructed
considering both possibilities of relative orientation of the
ligands around the metallic center, i.e. the methyl group
Structural Preference
For complexes 2a–c and for the cationic complex of com- bonded to the palladium atom can be orientated cis or trans
pound 3a it is possible to propose two different isomers to the phosphorus atom of the chelating ligand as can be
considering the relative position around the metallic center. seen in Scheme 3.
Nevertheless, the spectroscopic characterization in solution
In the models for the neutral complexes (cis-2 and trans-
of all complexes along with the solid state characterization 2) we found that the HOMO/LUMO gap for the model cis-
for complex 2b indicates that only one isomer was formed 2 is 4.66 eV and for trans-2 the value is 4.11 eV. The bigger
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Isomeric Preference in Complexes of Palladium(II)
the dx2–y2 atomic orbital of the palladium atom and the py
atomic orbital of the carbon. The analogous molecular or-
bital in model trans-3 is LUMO+1, and in this model
LUMO is composed mainly of a π* interaction of the C–N
bond in the imine ligand. In model cis-3 LUMO+1 is com-
posed mainly of a π* interaction of the C–N bond in the
imine ligand, very similar to LUMO in model trans-3. In
brief, we observe the order inversion of LUMO and
LUMO+1 in models cis-3 and trans-3 (Figure 3).
Scheme 3. Simplified models for theoretical calculations of com-
plexes 2 and cations of compounds 3.
gap (with a difference of 0.55 eV or 12.6 kcal/mol) in cis-2
means that cis-2 corresponds to a harder complex and a
more stable configuration for the complexes, according to
the MHP.
Checking the electronic structure of these models, we can
see that in both cases the LUMO has a similar structure
which can be described mainly as a π* (pz–pz) orbital cen-
tered in the double bond C–N. This antibonding orbital
displays a weak π* interaction with the metal which in-
volves a d orbital of the palladium atom. For the model cis-
2, this orbital corresponds to a π* interaction between the
dxz orbital of the palladium atom and the pz atomic orbital
of the chlorido ligand. For the model trans-2 we found that
the HOMO is a molecular orbital with an in plane π* char-
acter built, mainly, by a combination of the atomic orbitals
dz2, dxy, and dx2–y2 of the palladium atom and the py atomic
orbital of the chlorido ligand. For the same model, analyz-
ing HOMO-1 (which is very close in energy to HOMO) we
find now a π* interaction between the dxz orbital of the
palladium atom and the pz orbital of the chlorido ligand
for the model trans-2 (analogous to the HOMO of the
model cis-2). In the case of the model cis-2 HOMO-1 corre-
sponds to a molecular orbital of π* analogous to HOMO
of the model trans-2. Analyzing the shape of the molecular
orbitals for these two models we can state that HOMO and
HOMO-1 have exchanged their order in energies and for
model trans-2 these two levels are very similar in energy.
The phosphorus atomic orbitals have a very small partici-
pation in the frontier orbitals.
Figure 3. Relative energies of frontier orbitals in models 2 (left) and
3 (right).
Conclusions
The square-planar complexes of palladium(II) with P,N-
donor ligands can generate different isomers when the an-
cillary ligands are different. When these two ligands are
chlorido and methyl, the methyl group locates in a cis posi-
tion to the phosphane fragment of the chelating ligand.
This is the only isomer detected in solution. The solid-state
characterization for one of these complexes (2b) is in com-
plete agreement with the facts observed in solution. The
extraction of the chlorido ligand maintains the methyl
group coordinated in a cis position to the phosphorus
atom. This isomeric preference can be understood on the
basis of the Maximum Hardness Principle. DFT calcula-
tions developed for models of the complexes displayed that
the isomer with the methyl ligand coordinated in a cis posi-
tion to the phosphane ligand was harder (or had a bigger
HOMO/LUMO gap). These calculations confirm the pre-
dictions of the antisymbiosis rule.
A similar calculation carried out for models of cationic
complexes (model cis-3 and model trans-3) showed that the
HOMO/LUMO gap for cis-3 is 5.41 eV and for trans-3 the
value is 5.05 eV. As in the neutral complexes, the model cis-
3 corresponds to the more stable configuration, as found in
our complex and in the structural database (the difference
between the gaps is 0.36 eV or 8.40 kcal/mol).
Experimental Section
General Methods: Elemental analyses (C,H,N) were performed with
a LECO CHNS-932 apparatus. 1H NMR spectra were obtained
with a Varian Unity Inova 400-MHz spectrometer with SiMe4 as
internal standard at 25 °C. Ligands b[17,19] and c[17,19] were synthe-
sized as reported in the literature. [PdCl2(1,5-COD)][36] and
[PdMeCl(1,5-COD)][37] were synthesized as reported. Numbering
For both cationic models (model cis-3 and model trans-
3), HOMO has mainly a dz2 character along with a small
participation of orbital py of the methyl carbon. The inter- used for the ligands:
action between both atomic orbitals is σ*, and the partici-
pation of the atomic orbital py is bigger in model trans-3
than in model cis-3. This means that the antibonding inter-
action is stronger and the energy of the HOMO is higher
in model trans-3 than in model cis-3. For cis-3 LUMO is
mainly composed of an antibonding interaction between
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J. V. Cuevas et al.
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Syntheses
off, washed with hexane, and then dried under vacuum. Yield:
1
190.6 mg (89%). H NMR (400 MHz, CDCl3, 20 °C): δ = 0.70 (d,
[C26H22NP] (a): To a solution of 2-diphenylphosphanylbenzal-
dehyde (1082.5 mg, 3.70 mmol) in anhydrous methanol (40 mL)
under N2 was added p-toluidine (907 mg, 8.46 mmol) and the reac-
tion mixture was stirred at room temperature overnight. After that
time the mixture was kept at –18 °C for two hours to induce
crystallization. The product was obtained as a yellow solid col-
lected by filtering through a fritted filter and washed with cold
methanol. Yield: 1053.9 mg (75%). 1H NMR (400 MHz, CDCl3,
20 °C): δ = 2.32 (s, 3 H, -CH3), 6.85 (d, JH,H = 8.40 Hz, 2 H, Ho),
6.92 (m, 1 H, H4), 7.09 (d, JH,H = 8.1 Hz, 2 H, Hm), 7.32 (m, 11
JH,P = 3.3 Hz, 3 H, Pd-CH3), 2.33 (s, 3 H, -CH3), 7.14 (m, 5 H, H6
+ Ha–e + Hb–d), 7.49 (m, 11 H, -Ph2 + H5), 7.62 (m, 2 H, H3
+
H4), 8.19 (d, JH,P = 2 Hz, 1 H, Hi) ppm. 31P NMR (161.92 MHz,
CDCl3, 20 °C): δ = 38.41 ppm. C27H25ClNPPd (536.34): calcd. C
60.46, H 4.7, N 2.61; found C 59.99, H 4.50, N 2.84.
[Pd(C26H22NOP)ClMe] (2b): The same procedure was followed as
for 2a. The compounds used were: complex [PdCl(1,5-COD)Me]
(101.9 mg, 3.84 mmol) and ligand b (153.0 mg, 3.87 mmol). A yel-
low solid was collected as product. Yield: 212.3 mg (93%). 1H
H, -Ph2 + H5), 7.44 (m, 1 H, H3), 8.20 (m, 1 H, H6), 9.08 (d, JH,P NMR (400 MHz, CDCl3, 20 °C): δ = 0.63 (d, JH,P = 3.4 Hz, 3 H,
= 5.2 Hz, 1 H, Hi) ppm. 13C NMR (100.58 MHz, CDCl3, 20 °C.): δ
= 21.23, 76.94, 77.26, 77.57, 109.99, 115.47, 121.14, 128.16, 128.20,
128.85, 128.92, 128.99, 129.15, 129.18, 129.34, 129.83, 129.97,
130.96, 130.97, 133.72, 134.18, 134.21, 134.38, 134.42, 136.03,
136.59, 138.55, 138.74, 139.44, 139.61, 149.29, 158.16, 158.37 ppm.
Pd-CH3), 3.79 (s, 3 H, -OCH3), 6.93 (m, 1 H, H5), 6.97 (m, 1 H,
Hd), 7.05 (dd, JH,H = 1.85, 7.6 Hz, 1 H, Ha), 7.15 (t, JH,H = 8.5 Hz,
1 H, H6), 7.20 (td, JH,H = 1.9, 7.9 Hz, 1 H, Hc), 7.49 (m, 12 H,
-Ph2 + H4 + Hb), 7.62 (m, 1 H, H3), 8.24 (s, 1 H, Hi) ppm. 31P
NMR (161.92 MHz, CDCl3, 20 °C):
δ
=
37.42 ppm.
31P NMR (161.92 MHz, CDCl3, 20 °C): δ = –12.28 ppm. C26H22N C27H25ClNOPPd (552.34): calcd. C 58.71, H 4.56, N 2.54; found
(379.43): calcd. C 82.3, H 5.84, N 3.69; found C 81.99, H 5.55, N
3.88.
C 58.34, H 4.48, N 2.52.
[Pd(C26H23NOP)ClMe] (2c): The same procedure was followed as
[Pd(C26H22NP)Cl2] (1a): Complex [PdCl2(1,5-COD)] (104.0 mg, for 2a. The compounds used were: complex [PdCl(1,5-COD)Me]
3.64 mmol) was dissolved in dichloromethane (15 mL). To this
solution ligand a (140.4 mg, 3.70 mmol) was added. The mixture
was stirred at room temperature for 2 h. The solution was concen-
trated in vacuo and the product was precipitated with diethyl ether.
A yellow solid was filtered off, washed with diethyl ether, and then
(130.1 mg, 4.90 mmol) and ligand c (187.7 mg, 4.92 mmol). A yel-
low solid was collected as product. Yield: 223.3 mg (85%). 1H
NMR (400 MHz, CDCl3, 20 °C): δ = 0.71 (d, JH,P = 2.7 Hz, 3 H,
Pd-CH3), 6.79 (br., -OH), 7.14 (m, 2 H, Hd + H6), 7.19 (m, 1 H,
Hb), 7.46 (m, 10 H, -Ph2), 7.54 (m, 3 H, H4 + H5 + Hc), 7.65 (m,
2 H, H3 + Ha), 8.31 (br., 1 H, Hi) ppm. 31P NMR (161.92 MHz,
CDCl3, 20 °C): δ = 39.38 ppm. C26H23ClNOPPd (538.31): calcd. C
58.01, H 4.31, N 2.60; found C 57.84, H 4.50, N 2.59.
1
dried under vacuum. Yield: 205.6 mg (86%). H NMR (300 MHz,
[D6]DMSO, 20 °C): δ = 2.30 (s, 3 H, -CH3), 7.03 (m, 1 H, H6), 7.16
(d, JH,H = 8.7 Hz, 2 H, Hb,d), 7.35 (d, JH,H = 8.3 Hz, 2 H, Ha,e),
7.58 (m, 10 H, -Ph2), 7.80 (t, JH,H = 7.5 Hz, 1 H, H5), 7.95 (t, JH,H
= 7.4 Hz, 1 H, H4), 8.17 (m, 1 H, H3), 8.64 (s, 1 H, Hi) ppm. 31P
[Pd(MeCN)(C26H26N2P)Me]BF4 (3a): Complex 2a (44.6 mg,
0.083 mmol) was dissolved in dichloromethane (30 mL). To this
solution MeCN (2 mL) and AgBF4 (19.8 mg, 0.102 mmol) were
added. The mixture was stirred for 2 h at room temperature. The
white precipitate of AgCl was removed by filtering through celite.
The solution was concentrated under vacuum and the product was
precipitated by the addition of hexane. A pale yellow solid was
collected as product. Yield: 40.5 mg (90%). 1H NMR (400 MHz,
CDCl3, 20 °C): δ = 0.46 (d, JH,P = 1.8 Hz, 3 H, Pd-CH3), 1.93 (s,
3 H, NCMe overlapped with a small amount of free acetonitrile),
2.36 (s, 3 H, -CH3), 7.15 (m, 3 H, H6 + Ha+e), 7.25 (m, 2 H, Hb+d),
NMR (161.92 MHz, [D6]DMSO, 20 °C):
δ
=
30.31 ppm.
C26H22Cl2NPPd (556.76): calcd. C 56.09, H 3.98, N 2.52; found C
55.97, H 3.89, N 2.71.
[Pd(C26H22NOP)Cl2] (1b): The same procedure was followed as for
1a. The compounds used were: complex [PdCl2(1,5-COD)]
(109.2 mg, 3.82 mmol) and ligand b (154.2 mg, 3.90 mmol). A yel-
low solid was collected as product. Yield: 206.9 mg (94%). 1H
NMR (400 MHz, [D6]DMSO, 20 °C): δ = 3.79 (s, 3 H, -OCH3),
7.00 (t, JH,H = 7.45 Hz, 1 H, Hb), 7.09 (m, 1 H, Hd), 7.14 (m, 1 H,
H6), 7.27 (m, 1 H, Ha), 7.33 (m, 1 H, Hc), 7.65 (m, 10 H, -Ph2), 7.42 (m, 4 H, Ph2), 7.52 (m, 4 H, -Ph2), 7.58 (m, 3 H, -Ph2 + H5),
7.86 (m, 1 H, H5), 7.99 (m, 1 H, H4), 8.20 (m, 1 H, H3), 8.72 (s,
1 H, Hi) ppm. 31P NMR (161.92 MHz, [D6]DMSO, 20 °C): δ =
30.67 ppm. C26H22Cl2NOPPd (572.76): calcd. C 54.25, H 3.87, N
2.45; found C 54.35, H 3.81, N 2.38.
7.77 (t, JH,H = 7.6 Hz, 1 H, H4), 7.90 (m, 1 H, H3), 8.37 (s, 1 H,
Hi) ppm. 31P NMR (161.92 MHz, CDCl3, 20 °C): δ = 40.13 ppm.
C29H28BF4N2PPd (628.74): calcd. C 55.40, H 4.49, N 4.46; found
C 55.02, H 4.65, N 3.98.
[Pd(C25H20NOP)Cl2] (1c): The same procedure was followed as for
1a. The compounds used were: complex [PdCl2(1,5-COD)]
(106.0 mg, 3.71 mmol) and ligand c (145.2 mg, 3.81 mmol). A yel-
low solid was collected as product. Yield: 199.2 mg (96%). 1H
NMR (400 MHz, [D6]DMSO, 20 °C): δ = 6.71 (m, 1 H, Hb), 6.85
[Pd(C26H22NOP)Me]BF4·0.25CH3CN (3b): The same procedure
was followed as for 3a. The compounds used were: complex 2b
(67.4 mg, 0.125 mmol), AgBF4 (27.5 mg, 0.141 mmol), and MeCN
(2 mL). A yellow solid was collected as product. Yield: 30.8 mg
1
(44%). H NMR (400 MHz, CDCl3, 20 °C): δ = 0.56 (s, 3 H, Pd-
(m, 1 H, Hd), 7.10 (m, 1 H, Hc), 7.21 (t, JH,H = 8.95 Hz, 1 H, H5), CH3), 4.22 (s, 3 H, -OCH3), 7.26 (m, 3 H, H6 + Hb + Hd), 7.38
7.35 (d, JH,H = 7.9 Hz, 1 H, Ha), 7.60 (m, 10 H, -Ph2), 7.80 (t, JH,H
= 7.6 Hz, 1 H, H6), 7.94 (t, JH,H = 7.7 Hz, 1 H, H4), 8.21 (m, 1 H,
H3), 8.80 (s, 1 H, Hi), 9.22 (br., OH) ppm. 31P NMR (161.92 MHz,
[D6]DMSO, 20 °C): δ = 30.90 ppm. C25H20Cl2NOPPd (558.73):
calcd. C 53.74, H 3.61, N 2.51; found C 53.53, H 3.52, N 2.66.
(m, 1 H, Hc), 7.44 (m, 8 H, -Ph2), 7.58 (m, 3 H, -Ph2 + H5), 7.83
(m, 1 H, H4), 7.91 (d, JH,H = 8.8 Hz, 1 H, Ha), 8.35 (m, 1 H, H3),
9.20 (s, 1 H, Hi) ppm. 31P NMR (161.92 MHz, CDCl3, 20 °C): δ =
44.12 ppm. C27H25BF4NOPPd·0.25CH3CN (613.96): calcd.
C
53.80, H 4.23, N 2.85; found C 53.95, H 4.28, N 2.78.
[Pd(C26H22NP)ClMe]
(2a):
Complex
[PdCl(1,5-COD)Me]
[Pd(C25H20NOP)Me]BF4·0.25CH3CN (3c): The same procedure
(105.5 mg, 3.98 mmol) was dissolved in dichloromethane (15 mL). was followed as for 3a. The compounds used were: complex 2c
To this solution ligand a (154.6 mg, 4.05 mmol) was added. The
mixture was stirred at room temperature for 5 d. No solid was seen
during this time. The solution was concentrated in vacuo and the
product was precipitated with hexane. A yellow solid was filtered
(51.9 mg, 0.096 mmol), AgBF4 (20.2 mg, 0.104 mmol), and MeCN
(2 mL). A yellow solid was collected as product. Yield: 35.6 mg
1
(68%). H NMR (400 MHz, CDCl3, 20 °C): δ = 0.61 (s, 3 H, Pd-
CH3), 6.74 (br., 1 H, -OH), 7.15 (m, 2 H, -Ph2+Hd), 7.42 (m, 5 H,
2258
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Eur. J. Inorg. Chem. 2009, 2254–2260

Isomeric Preference in Complexes of Palladium(II)
-Ph2 + Hb + H6), 7.50 (m, 8 H, -Ph2 + H5 + Hc), 7.58 (d, JH,H
=
B.04) program suite.[35] Pd and P atoms were described using an
8.2 Hz, 1 H, Ha), 7.70 (t, JH,H = 7.7 Hz, 1 H, H4), 7.87 (m, 1 H, effective core potential (LANL2DZ) for the inner electrons[45,46]
H3), 8.31 (br., 1 H, Hi) ppm. 31P NMR (161.92 MHz, CDCl3,
adding a f-polarization shell for Pd (ζf = 1.472)[47] and a d-polariza-
20 °C): δ = 42.45 ppm. C26H23BF4NOPPd·0.25CH3CN (599.93): tion for P (ζd = 0.387).[48] The basis set for C, N, Cl, and H elements
calcd. C 52.96, H 3.93, N 2.38; found C 52.17, H 4.19, N 2.00.
was split-valence and included polarization functions in all atoms
[abbreviated as 6-31G(d,p)].[49]
X-ray Crystallography: Crystallographic data for compound 2b
were collected with a Bruker SMART CCD area-detector dif-
fractometer with Mo-Kα radiation (λ = 0.71073 Å).[38] Intensities
were integrated[39] from several series of exposures, each exposure
covering 0.3° in ω, and the total dataset being a sphere. Absorption
corrections were applied, based on multiple and symmetry-equiva-
lent measurements.[40] The structure was solved by direct methods
and refined by least-squares on weighted F2 values for all reflec-
tions (see Table 3).[41] All non-hydrogen atoms were assigned aniso-
tropic displacement parameters and refined without positional con-
straints. All hydrogen atoms were constrained to ideal geometries
and refined with fixed isotropic displacement parameters. Refine-
ment proceeded smoothly to give the residuals shown in Table 3.
Complex neutral-atom scattering factors were used.[42] CCDC-
702771 contains the supplementary crystallographic data for this
paper. These data can be obtained free of charge from The Cam-
bridge Crystallographic Data Centre via www.ccdc.cam.ac.uk/
data_request/cif.
Supporting Information (see footnote on the first page of this arti-
cle): Tables of optimized structures for models 2 and 3.
Acknowledgments
The authors gratefully acknowledge the European Commission
(LIFE05 ENV/E/000333) and the Junta de Castilla y León
(BU003B07) for financial support. We also acknowledge the Serv-
icios Centrales de Apoyo a la Investiación (SCAI) of the Uni-
versidad de Burgos for technical support.
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C28H26Cl4NOPPd
671.67
Temperature
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173(2) K
0.71073 Å
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Space group
monoclinic
P21/c
a
b
c
α
11.436(3) Å
14.400(3) Å
17.133(4) Å
90°
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Received: December 9, 2008
Published Online: April 8, 2009
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Eur. J. Inorg. Chem. 2009, 2254–2260