Heteropolymetallic complexes linked to a 9,10-dihydroanthracenyl frame. Ruthenium as active spectator for palladium reactivity

Article abstract of DOI:10.1021/om5001502

New monometallic Pd(II) (3, 4) and heteropolymetallic Pd(II)/Ru(II) complexes (5, 6) linked to an original 9,10-dihydroanthracenyl-pyrrolidine scaffold were synthesized and fully characterized. For monometallic complexes, exo-3 and endo-4 conformers were exclusively obtained from Pd(OAc)₂ and [PdCl₂(COD)], respectively. The formation of the sterically hindered endo-4 was justified by the positive noncovalent intramolecular Cl-π interaction, observed by X-ray diffraction. The reaction of endo-4 with 1 and 2 equiv of [RuCp(NCMe)₃]PF₆ led to complexes 5 and 6, respectively. It is worth noting that lower conversions in the Suzuki-Miyaura coupling were found using 5 and 6 as catalysts, in comparison to those with monometallic palladium complexes. This behavior could be related to the higher stabilization of Pd(II) species for the heteropolymetallic complexes, as proven by electrochemical analyses.

Full text of DOI:10.1021/om5001502

Article
pubs.acs.org/Organometallics
Heteropolymetallic Complexes Linked to a 9,10-Dihydroanthracenyl
Frame. Ruthenium as Active Spectator for Palladium Reactivity
Ielyzaveta Bratko,†,‡ Sonia Mallet-Ladeira,§ Emmanuelle Teuma,†,‡ and Montserrat Gomez*,†,‡
́
†UPS, LHFA, Universite
́
de Toulouse, 118 route de Narbonne, 31062 Toulouse Cedex 9, France
‡LHFA UMR 5069, CNRS, 31062 Toulouse Cedex 9, France
§Institut de Chimie de Toulouse, FR 2599, Universite
́
Paul Sabatier, 118 route de Narbonne, 31062 Toulouse Cedex 9, France
S
* Supporting Information
ABSTRACT: New monometallic Pd(II) (3, 4) and heteropolyme-
tallic Pd(II)/Ru(II) complexes (5, 6) linked to an original 9,10-
dihydroanthracenyl−pyrrolidine scaffold were synthesized and fully
characterized. For monometallic complexes, exo-3 and endo-4
conformers were exclusively obtained from Pd(OAc)2 and
[PdCl2(COD)], respectively. The formation of the sterically
hindered endo-4 was justified by the positive noncovalent intra-
molecular Cl−π interaction, observed by X-ray diffraction. The
reaction of endo-4 with 1 and 2 equiv of [RuCp(NCMe)3]PF6 led to
complexes 5 and 6, respectively. It is worth noting that lower
conversions in the Suzuki−Miyaura coupling were found using 5 and
6 as catalysts, in comparison to those with monometallic palladium
complexes. This behavior could be related to the higher stabilization of Pd(II) species for the heteropolymetallic complexes, as
proven by electrochemical analyses.
selectivity of the Pd-catalyzed catalytic process in relation to the
related Mn-free monometallic palladium complex.6 A similar
behavior was observed in Ru-catalyzed alkene metathesis
reactions upon π coordination of “Cr(CO)3” to the
monometallic complex.8b
INTRODUCTION
■
Catalysis represents the key approach to convert raw materials
into valuable products. Mimicking nature seems to be the
elegant way to conceive polyfunctional assemblies leading to
“synergic” catalysts. Imitating biocatalysts, several research
groups have developed polymetallic catalysts, finding cooper-
ative effects between the different metal centers.1 The design of
versatile bimetallic catalysts containing robust ancillary frames
seems to be an appropriate strategy for cooperative purposes.2
The successful design of polymetallic catalysts, most of them
bimetallic, where metals are linked to the same structure ligand,
has been accomplished, proving their positive cooperative effect
in a large number of organic transformations.3 In this context,
N-heterocyclic carbenes appear as suitable ligands.4 In the last
years, the Peris group has developed homo- and hetero-
bimetallic complexes containing the straightforward 1,2,4-
trimethyltriazolyldiylidene ligand acting as a Janus-type
skeleton, able to coordinate two different metals.5 Electro-
chemical studies proved weak electronic coupling between the
two metal centers.5e
However, π interactions between the ligand and metals are
hardly represented.6−8 Among them, the most relevant
bimetallic systems are those described by the Marks group,
which are constituted by constrained binuclear complexes;7 the
metal is coordinated to an indenyl or cyclopentadienyl moiety
by π coordination and a nitrogen atom by a dative bond. An
interesting effect was also observed by the fragment “Mn-
(CO)3” coordinated through a π interaction to a palladium
phosphino oxazoline complex, increasing both the activity and
In particular, we have been intrigued by structures containing
both aromatic groups able to favor metal π coordination and
flexible frameworks assisting metal−ligand dative interactions,
with the aim to prepare heteropolymetallic complexes for
cooperative effects in catalysis. Triptycene, a rigid molecule
containing three aromatic rings, has attracted attention from a
coordination standpoint since the pioneering work of Pohl and
Willeford in 1970,9 followed by the independent studies of
Mislow10 and Toyota11 reporting the first X-ray crystal
structures of mono-, bi-, and trimetallic complexes through π
interactions with metal fragments such as Cr(CO)3 and
Co4(CO)9;12 triptycene complexes containing [RuCp*]+
moieties have been previously described, without a full
structural characterization.13 More recently, triptycene-based
phosphane and seleno ligands, able to coordinate transition
metals (Pd, Pt, Ir), have found interesting applications in
catalysis.14 The versatility of triptycene led us to consider
dihydroanthracene−dicarboximides as appropriate candidates
for coordination chemistry purposes, where one of the aromatic
groups is replaced by a five-membered ring which allows an
easy functionalization.
Received: February 10, 2014
Published: March 20, 2014
© 2014 American Chemical Society
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We have reported the first studies concerning the
coordination chemistry of functionalized 9,10-dihydroanthra-
cene ligands15 and their applications in catalysis. Therefore,
Pd(II) and Rh(I) monometallic complexes containing chiral
phosphite or NHC moieties have been successfully applied in
asymmetric Pd-catalyzed allylic alkylations and Rh-catalyzed
hydroformylation reactions16a and in Rh-catalyzed conjugate
additions of unsaturated carbonyls.16b Concerning polymetallic
complexes, we have been initially interested in the study of the
π coordination of these multifunctional ligands, offering
different ways to link metallic fragments.17 Selective synthesis
of mono-, bi-, and trimetallic Ru complexes by π coordination
was effectively achieved using the organometallic precursor
[RuCp(NCMe)3]PF6, known for its affinity toward η6
coordination.18 These studies encouraged us to design
heteropolymetallic complexes based on novel scaffolds allowing
different coordination modes, in order to search for positive
catalytic cooperative effects. In the present work, we describe
the synthesis of Pd(II)/Ru(II) polymetallic complexes 5 and 6
starting from the monometallic Pd(II) complex endo-4 and
their effect on Pd-catalyzed Suzuki−Miyaura C−C cross-
coupling.
Scheme 2. Synthesis of Monometallic Pd(II) Complexes 3
and 4 and Pd(II)/Ru(II) Heteropolymetallic Complexes 5
and 6
the corresponding complexes 3 and 4 in high yields (73 and
90%, respectively). Both complexes gave only one isomer,
according to the NMR and X-ray diffraction analyses. The
corresponding crystal structures showed a distorted-square-
planar geometry around the palladium as expected. The torsion
angles between the two five-membered cycles connected by the
nitrogen atoms of these structures are 83.46 and 75.89° for 3
and 4, respectively; the difference observed can be attributed to
the steric hindrance for 3 being higher than that for 4. The
structure of 3 showed that the five-membered palladacycle
formed by coordination of the two nitrogen atoms of ligand 2
to the palladium atom points out of the 9,10-dihydroanthra-
cenyl backbone, adopting an exo arrangement (Figure 1). This
RESULTS AND DISCUSSION
■
Synthesis of Ligands. The diamine ligand 2 was prepared
by a two-step sequence on the basis of published method-
ologies (Scheme 1).15b Therefore, the imide 1 was first
Scheme 1. Synthesis of 9,10-Dihydroanthracene-Based
a
Compounds 1 and 2
a
For 2, the molecular view is given (ellipsoids drawn at the 50%
probability level), where hydrogen atoms are omitted for clarity.
prepared by a [4 + 2] cycloaddition of 9,10-diethoxyanthracene
with the N,N-dimethylethylenemaleimide A in toluene under
thermal conditions (68% yield). Imide 1 was then reduced by
LiAlH4, giving the pyrrolidine 2 in high yield (89%).
Compounds 1 and 2 were fully characterized both in solution
(by means of NMR and high-resolution mass spectrometry)
and the solid state. Suitable crystals for an X-ray diffraction
analysis were obtained for 2 from a diisopropyl ether solution.
The heterocycle adopts an envelope conformation, where the
nitrogen atom presents an unambiguous pyramidalization
(∑°N = 332°). Ethoxide groups of the dihydroanthracenyl
skeleton point out of the pyrrolidine cycle (Scheme 1).
Synthesis of Complexes. With the goal of preparing
heteropolymetallic complexes, we started by the coordination
of Pd(II) precursors to the diamine fragment of 2 by dative
nitrogen−metal interactions (complexes 3 and 4, Scheme 2),
pursuing the coordination of RuCp+ fragments to the 9,10-
dihydroanthracenyl frame to lead to the corresponding bi- and
trimetallic complexes 5 and 6, respectively (Scheme 2). All of
the complexes were fully characterized in solution (NMR) and
in the solid state (X-ray diffraction).
Figure 1. Molecular views (ellipsoids drawn at the 50% probability
level) of palladium monometallic complexes 3 (left) and 4 (right).
Hydrogen atoms and molecules of solvent are omitted for clarity. For
4, the dashed line indicates the noncovalent Cl−π interaction: the
Cl−π bond length is 3.528(4) Å, and the angle of the Cl−centroid axis
to the plane of the ring is 80.2°.
exo conformer is also confirmed in solution by NOE NMR
experiments (Figure S1 in the Supporting Information). The
exo arrangement precludes the formation of a trimetallic
complex. The calculated relative energy for the two plausible
isomers (DFT level, B3LYP 6-31G*), exo-3 and endo-3,
indicated that the exo form is the most stable conformation,
probably due to steric reasons (Figure 2).
We then envisaged the use of a less hindered ligand, chlorine
instead of acetate, favoring the formation of the desired endo
conformation. Actually, the endo-4 conformer was exclusively
First, we isolated monometallic palladium complexes by
reaction of ligand 2 with Pd(OAc)2 and [PdCl2(COD)], giving
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complex 5 was obtained as a mixture of two isomers in a ca. 7/3
ratio (determined by 1H NMR; see Figure S3 in the Supporting
Information). The interaction of 1 equiv of RuCp+ with the
complex 4 could lead to three isomers, depending on the
coordination to the dissymmetric 9,10-dihydroanthracenyl
skeleton. On the basis of the corresponding calculated
structures (Figure S4 in the Supporting Information), the two
low-energy complexes could be associated with the observed
isomers. The most stable isomer corresponds to that observed
by X-ray diffraction analysis.
The coordination of the diamine fragment to the metal was
proven by {1H,15N}-HMBC NMR experiments at natural
abundance of the 15N isotope for the ligand 2 and complexes 4
and 5 (unfortunately, complex 6 was not soluble enough for
this kind of experiment). As reported for Pd(II) complexes
containing N-donor ligands,19 the nitrogen chemical shifts for
complexes are shielded (by ca. 5−7 ppm) in relation to the free
ligand (Figure S5 in the Supporting Information).
The spatial arrangements of the three structures having the
same metallacycle, 4−6, are quite similar with regard to the
palladium coordination, as proven by the relative angle between
the two five-membered cycles in the spiro frame (75.89, 75.25,
and 78.23° for 4−6, respectively) and the noncovalent Cl−π
interaction.
Actually, complexes 4−6 seem to exhibit noncovalent
intramolecular Cl−π interactions (see above), showing Cl−π
distances in the range 3.52−3.73 Å with angles of the Cl−
centroid axis to the plane of the ring between 78.9 and 80.2°,
comparable to those reported for intermolecular interactions
between chloride anion and pyridine rings in polymetallic
copper complexes (3.46−3.69 Å, 75−82°).20 However, the
interactions observed for complexes 4−6 are weaker than those
observed involving electron-deficient aromatic rings such as
triazine21 or imidazolyl rings22 but similar to those observed for
the intramolecular Cl−π interaction, where the aromatic ring is
a pentafluorophenoxide group (Cl−π distance 3.725 Å).23
The noncovalent Cl−π interactions are proposed to occur
from a negatively charged species (in our case the chloride
ligand) to an electron-deficient aromatic ring (for us, the six-
membered ring of the 9,10-dihydroanthracenyl frame) by
Coulombic attraction.24 Calculations of charges (natural atomic
population, NAP, by DFT M06 6-31G*) of the aromatic ring
close to the chloride ligand indicated that, even for the
monometallic complex 4, the net charge of the six-membered
ring is positive (NAP data: for 4, +0.0260; for 5, +0.2403; for 6,
+0.2817), proving the electron-deficient character of this
moiety and consequently favoring the Cl−π contact.
Figure 2. Calculated structures (DFT, B3LYP 6-31G*) for the
conformers exo-3 and endo-3. Hydrogen atoms are omitted for clarity.
Energy values are relative to the most stable isomer.
obtained when ligand 2 reacted with [PdCl2(COD)], as proven
by its crystal structure (Figure 1); in solution, only one isomer
was also observed (Figure S2 in the Supporting Information).
In addition, the X-ray diffraction analysis revealed an
intramolecular interaction between one of the chlorine atoms
linked to the metal center and one of the aromatic rings of the
9,10-dihydroanthracenyl skeleton. This interaction could be the
responsible for the stabilization of the endo conformer in
relation to the exo form (see below for a more detailed
discussion).
Due to the different coordination behavior between both
palladium complexes 3 and 4, only that adopting the endo
conformation is appropriate to synthesize bi- and trimetallic
complexes (through π interactions between the aromatic rings
of the 9,10-dihydroanthracenyl backbone and the electrophilic
metallic moiety RuCp+). On the basis of our previous work on
the synthesis of homopolymetallic π complexes,17 we decided
to treat 4 with 1 and 2 equiv of [RuCp(NCMe)3]PF6 to give
the corresponding Pd(II)/Ru(II) heteropolymetallic complexes
(Scheme 2). Therefore, the palladium complex 4 reacted with
[RuCp(NCMe)3]PF6 under reflux of dichloromethane to
selectively afford the bi- (5) and trimetallic (6) complexes, in
high yields (ca. 80%). These two complexes were fully
characterized both in solution and in the solid state, in
particular by XRD on single crystals (Figure 3). The bimetallic
Palladium Reactivity. With the aim of analyzing the effect
of RuCp+ fragments in the palladium reactivity, we evaluated
the catalytic activity of complexes 3−6 in the Suzuki−Miyaura
cross-coupling between 4-bromoanisole and phenylboronic acid
as a benchmark reaction, in toluene at 65 °C using 1 mol % of
Pd (Table 1). Monometallic complexes 3 and 4 showed a
similar catalytic behavior, giving high conversions (91−99%)
after 2.5 and 5 h, respectively (entries 1 and 2). While complex
4 exclusively gave the desired product B (entry 2), complex 3
led to the formation of byproducts (up to 6% of anisole and
biphenyl) together with the major cross-coupling product, B
(entry 1).
Figure 3. Molecular views (ellipsoids drawn at the 50% probability
level) of the cations corresponding to bimetallic 5 (left) and trimetallic
6 (right) complexes. Hydrogen atoms and molecules of solvent are
omitted for clarity. Dashed lines indicate the noncovalent Cl−π
interactions. For 5the Cl−π distance is 3.731(3) Å and the angle of the
Cl−centroid axis to the plane of the ring is 79.8°; for 6, the Cl−π
distance is 3.628(2) Å and the angle of the Cl−centroid axis to the
plane of the ring is 78.9°.
Heteropolymetallic complexes 5 and 6 with one and two Ru
fragments, respectively, exhibited lower conversions than 4
(entries 3 and 4). After 5 h of reaction, 27% and 11% of
conversion were respectively achieved. Longer times did not
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Table 1. Pd-Catalyzed Suzuki−Miyaura Cross-Coupling
Reactions Using Complexes 3−6 as Catalytic Precursors
a
b
b
entry
complex
conversn (%)
B/biphenyl/anisole (%)
c
1
3
4
5
6
99
99
27
11
94/4/2
100/0/0
100/0/0
98/2/0
d
2
3
4
a
Reaction conditions: 4-bromoanisole/PhB(OH)2/Na2CO3/Pd =
100/150/200/1, 2 mL of toluene, 0.5 mL of H2O, 65 °C, 5 h.
Determined by H NMR. Catalytic data for 2.5 h. For 2.5 h, 60%
b
c
d
Figure 5. Cyclic voltammogram for the oxidation region (glassy-
carbon electrode; scan rate 200 mV s−1) for complex 8 in acetonitrile
(top) and a schematic representation of the generated species
(bottom).
1
conversion.
improve the catalytic activity. These results are in contrast with
those previously reported using pincer ferrocene and
ruthenocene bimetallic catalysts25a,b and pincer Pd/Ru
complexes applied as catalytic precursors in cross-coupling
reactions.25c
The observed reactivity trend seems to indicate a higher
stabilization of Pd(II) species in relation to the corresponding
Pd(0) species, when RuCp+ moieties are present. This fact
could consequently trigger a catalytic activity decrease in the
studied cross-coupling reaction. Following this reasoning, the
reduction of Pd(II) to Pd(0) could turn more difficult in the
presence of ruthenium fragments. In order to make this
behavior clearer, we decided to analyze by voltammetry the
different species involved.
the CpRu−Ph bond, the ligand being shifted by acetonitrile,
used as solvent. In addition, in the reduction potential region,
two irreversible waves were observed (at −1.72 and −2.05 V
corresponding to Ru(II)/Ru(I) and Ru(I)/Ru(0) processes,
respectively), closer to those exhibited by the precursor
[RuCp(NCMe)3]PF6 (see Figure S6 in the Supporting
Information). However, complex 7, coordinated to the ligand
through the aromatic moiety of the 9,10-dihydroanthracenyl
ligand, showed two irreversible reduction waves, corresponding
to Ru(II)/Ru(I) (at −1.76 and −2.1 V), and one irreversible
oxidation wave at +2.6 V, associated with the oxidation of the
ligand (Figures S7 and S8 in the Supporting Information). No
metal deposition was observed. These facts point to a higher
stabilization of the Ru(II) species and also a higher robustness
of the Ru−(aromatic cycle) η6 bond when the metal is
coordinated to the 9,10-dihydroanthracenyl fragment complex
7 rather than through the phenyl group as in complex 8 (see
Figure S9 in the Supporting Information for comparisons
among 7, 8, and the precursor [RuCp(NCMe)3]PF6).
Electrochemical Studies. We decided to study the
electrochemical behavior of complexes 4−6. In order to
evaluate the effect of the ligand skeleton on both metals, we
first considered the monometallic palladium complex 4 and
monometallic ruthenium complexes 717 and 8 (Figure 4), for
With regard to palladium, both the precursor [PdCl2(COD)]
and the monometallic complex 4 only exhibited one wave
corresponding to the Pd(II)/Pd(0) reduction (at −0.44 and
−1.30 V, respectively);27 actually, this reduction becomes more
difficult upon coordination to the ligand 2 (see Figure S10 in
the Supporting Information). For both complexes, palladium
deposition occurred.
For the heteropolymetallic complexes 5 and 6, as expected,
three irreversible reduction waves were observed corresponding
to Pd(II)/Pd(0), Ru(II)/Ru(I), and Ru(I)/Ru(0), at potentials
close to those observed for 4 and 7 (Figure 6; see Figure S11 in
the Supporting Information for the full electrochemical study of
complexes 5 and 6). However, no palladium deposition was
observed. In addition, with regard to the Pd(II)/Pd(0)
reduction, the waves were broader than those observed for 4,
pointing to a higher stabilization of the Pd(II) oxidation state
when the RuCp+ fragment is present in the corresponding
complexes. The NAP calculated charges on metal, nitrogen, and
chlorine atoms remain practically unchanged for complexes 4−
6, in agreement with the similar potentials observed (Table S1
in the Supporting Information).
Figure 4. Monometallic Ru(II) complexes 7 and 8.
comparative purposes. Monometallic ruthenium complexes
permitted us to analyze the stability of the involved species
when Ru is linked to different kinds of six-membered neutral
aromatic rings through metal−π interactions: complex 7
coordinated to an aromatic cycle of the 9,10-dihydroanthra-
cenyl skeleton and complex 8 to a phenyl group present as a
substituent of the pyrrolidine heterocycle.
The cyclic voltammogram of complex 8 exhibited an
irreversible Ru(II)/Ru(III) oxidation wave at +1.6 V. After
the oxidized Ru(III)−8 species was generated, a reversible wave
at +1.1 V was observed, which corresponds to the Ru(III)/
Ru(II) process of the organometallic precursor [RuCp-
(NCMe)3]PF6 (Figure 5) (for the cyclic voltammogram
corresponding to [RuCp(NCMe)3]PF6, see Figure S6 in the
Supporting Information).26 This fact evidences the lability of
This electrochemical behavior is in agreement with the low
catalytic reactivity observed for the C−C cross-coupling when 5
and 6 were involved as catalytic precursors in relation to 4,
because the Pd(II) oxidation state is more stable toward
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Irvine, CA 92612, USA). Calculations were carried out with density
functional B3LYP or M06 using the basis set 6-31G*.
Synthesis of Maleimide A. To a solution of maleic anhydride
(999.1 mg, 10.195 mmol) in toluene (120 mL) was added N,N-
dimethylethylenediamine (1.1 mL, 10.195 mmol). The solution was
refluxed over molecular sieves for 24 h. The reaction mixture was then
cooled to room temperature and filtered. After the evaporation of the
solvent, compound A was isolated as a yellow solid (904.2 mg, 5.382
mmol, 53%).
1H NMR (300 MHz, CDCl3): δ 6.67 (s, 2H, CH), 3.62 (t, 3JH−H
=
6.6 Hz, 2H, CH2), 2.47 (t, 3J = 6.6 Hz, 2H, CH2), 2.24 (s, 6H, CH3).
13C{1H} NMR (75 MHz, CDCl3): δ 170.8 (CO), 134.1 (CH), 57.0
(CH2), 45.4 (CH3), 35.8 (CH2).
Synthesis of 1. To a solution of 9,10-diethoxyanthracene (408.0
mg, 1.534 mmol) in toluene (80 mL) was added maleimide A (258.0
mg, 1.534 mmol). The solution was refluxed for 96 h. After
evaporation of the solvent the crude reaction mixture was purified
by column chromatography (eluent dichloromethane/methanol, from
100/0 to 98/2, Rf = 0.3). The compound was isolated as a white solid
(449.3 mg, 1.035 mmol, 68%). For NMR labeling, see Figure S12 in
the Supporting Information.
Figure 6. Electrochemical study of the oxidation potential region of
complexes 5 and 6: (top) scanning voltammogram (Pt electrode; 20
mV s−1) for complex 5; (bottom) cyclic voltammogram (glassy-carbon
electrode; 5000 mV s−1) for complex 6.
1H NMR (300 MHz, CDCl3): δ 7.53 (m, 2H, Harom), 7.41 (m, 2H,
Harom), 7.21 (m, 2H, Harom), 7.14 (m, 2H, Harom), 4.59 (dq, 3JH−H = 7.0
Hz, 2JH−H = 8.6 Hz, 2H, H23(a), H25(a)), 4.15 (dq, 3JH−H = 7.0 Hz, 2JH−H
= 8.6 Hz, 2H, H23(b), H25(b)), 3.69 (s, 2H, H15, H16), 3.17 (m, 2H,
H20), 2.09 (s, 6H, H21, H22), 1.62−1.67 (m, 8H, H19, H24, H26).
13C{1H} NMR (75 MHz, CDCl3): δ 173.7 (C17, C18), 141.3 (C11, C12
or C13, C14), 138.3 (C11, C12 or C13, C14), 126.7 (CHarom), 126.4
(CHarom), 121.4 (CHarom), 121.3 (CHarom), 79.4 (C9, C10), 61.0 (C23,
C25), 55.2 (C19), 46.4 (C15, C16), 45.1 (C21, C22), 35.8 (C20), 15.3
(C24, C26). IR (KBr, υ cm−1): 3072, 3026 (C−H), 2971, 2942, 2861,
2825 (C−H), 1701 (CO), 1458 (CC), 1150 (C−N), 1077 (C−
O). High-resolution mass spectrometry (CI, CH4, CH2Cl2): calcd
mass 435.2284, found mass 435.2287 (C26H31N2O4).
reduction and then the formation of Pd(0) active catalytic
species turns more difficult.
CONCLUDING REMARKS
■
In this work, we have described the synthesis of new
monometallic palladium complexes (exo-3 and endo-4), linked
to the ligand 2 containing a 9,10-dihydroanthracenyl−
pyrrolidine skeleton. The endo-4 conformer was exclusively
formed, probably due to the presence of a positive noncovalent
intramolecular Cl−π interaction, observed by X-ray diffraction
analyses. This complex 4 led selectively to the formation of bi-
and triheteropolymetallic complexes (5 and 6). The catalytic
activity of 5 and 6 was compared to that observed using
monometallic complexes 3 and 4, in Suzuki−Miyaura cross
coupling, in order to analyze the effect of the RuCp+ fragment
on the Pd-assisted reactivity. Heteropolymetallic complexes
showed catalytic activity lower than that observed using
monometallic palladium systems. It seems that a higher
stabilization of the Pd(II) center occurs in the presence of
electrophilic RuCp+ moieties in the complex, as proven by the
electrochemical study. The coordination of RuCp+ in the frame
increases the stability of Pd(II) species, and consequently the
reduction to give Pd(0) catalytically active species becomes
more difficult.
Synthesis of 2. This compound was prepared according to a
previously reported procedure.15b To a solution of compound 1 (449
mg, 1.035 mmol) in THF (55 mL) at 0 °C was added LiAlH4 (590
mg, 15.52 mmol) in small portions. The reaction mixture was then
refluxed for 24 h. The reaction mixture was then cooled to 0 °C,
diethyl ether (40 mL) was added, and then Na2SO4 aqueous saturated
solution was added dropwise. The formed precipitate was filtered off
and the filtrate washed three times with water. The combined organic
layers were dried on anhydrous Na2SO4 and filtered off and the solvent
evaporated, leading to a white powder (372.1 mg, 0.916 mmol, 89%).
Single crystals suitable for X-ray analysis were obtained from a
diisopropyl ether solution of 2. For NMR labeling, see Figure S12 in
the Supporting Information.
1H NMR (300 MHz, CDCl3): δ 7.48 (m, 2H, H5, H8), 7.31 (m, 2H,
H1, H4), 7.12−7.16 (m, 4H, H2, H3, H6, H7), 4.11 (dq, 3JH−H = 7.0 Hz,
3
2
2JH−H = 8.6 Hz, 2H, H23(a), H25(a)), 3.84 (dq, JH−H = 7.0 Hz, JH−H
=
8.6 Hz, 2H, H23(b), H25(b)), 3.19 (m, 2H, H15, H16), 3.01 (m, 2H,
H17(a), H18(a)), 2.22 (m, 4H, H19, H20), 2.15 (s, 6H, H21, H22), 1.65 (m,
Further studies concerning heteropolymetallic complexes to
be applied in multistep catalytic processes looking for
cooperative effects are currently under way.
3
2H, H17(b), H18(b)), 1.52 (t, JH−H = 7.0 Hz, 6H, H24, H26). 13C{1H}
NMR (75 MHz, CDCl3): δ 143.6 (C11, C12 or C13, C14), 140.9 (C11,
C12 or C13, C14), 125.6 (C2, C3 or C6, C7), 125.5 (C2, C3 or C6, C7),
121.9 (C5, C8), 120.7 (C1, C4), 80.9 (C9, C10), 60.0 (C23, C25), 57.9
(C19), 56.3 (C17, C18), 54.2 (C20), 45.7 (C21, C22), 45.2 (C15, C16),
15.7 (C24, C26). IR (KBr, υ cm−1): 3065, 3037 (C−H), 2970, 2925,
2876, 2805 (C−H), 1449 (CC), 1142 (C−N), 1074 (C−O). High-
resolution mass spectrometry (CI, CH4, CH2Cl2): calcd mass
407.2699, found mass 407.2693 (C26H35N2O2). Anal. Calcd for
C26H34N2O2 (406.26): C, 76.81; H, 8.43; N, 6.89. Found: C, 76.60; H,
8.35; N, 6.70.
Synthesis of 3. This compound was prepared according to a
previously reported procedure.15b Ligand 2 (200.5 mg, 0.4938 mmol)
was dissolved in 30 mL of toluene, and Pd(OAc)2 (110.8 mg, 0.4938
mmol) was then added. This mixture was stirred for 1 h at 70 °C. The
solvent was then evaporated to give a green solid. Recrystallization
from dichloromethane/diethyl ether (1/5) at 4 °C afforded the
complex 3 as yellow crystals (226.2 mg, 0.359 mmol, 73%). Single
EXPERIMENTAL SECTION
General Information. All manipulations were carried out under
■
argon using standard Schlenk techniques and high vacuum, unless
otherwise stated. Anhydrous solvents were dried using a solvent
purification system (SPS, MBraun). All other reagents were used as
received from commercial suppliers. NMR spectra were recorded on
300 or 500 MHz spectrometers at room temperature unless otherwise
stated. IR spectra were recorded on a FTIR instrument. Elemental
analyses were carried out at the University of Barcelona. The mass
spectra were recorded on instruments to analyze the samples by
−
chemical ionization or electrospray; for all metallic complexes, PF6
was detected as a single counteranion. Theoretical studies were carried
out using the following software: SPARTAN′14 for Windows and
Linux (Wavefunction, Inc. 18401 Von Karmaan Avenue, Suite 307,
1816
dx.doi.org/10.1021/om5001502 | Organometallics 2014, 33, 1812−1819

Organometallics
Article
crystals suitable for X-ray analysis were obtained by cooling a
dichloromethane/diethyl ether (1/5) solution of 3. For NMR labeling,
see Figure S12 in the Supporting Information.
H
arom), 6.20 (m, 2H, Harom), 5.70 (s, 5H, Cp), 4.00 (m, 4H, H23, H25),
3.68 (m, 2H, H20), 3.53 (m, 2H, H15, H16), 3.06 (m, 4H, H17, H18),
2.83 (m, 2H, H19), 2.73 (s, 6H, H21, H22), 1.52 (t, 3JH−H = 6.9 Hz, 6H,
H24, H26). 13C{1H} NMR (75 MHz, (CD3)2CO): δ 145.5 (C11 or
C14), 144.7 (C11 or C14), 127.7, 124.2, 123.9 (C1, C2, C3, C4), 110.0
(C12, C13), 89.1, 87.3, 87.1, 84.6 (C5, C6, C7, C8), 83.5 (Cp), 80.6 (C9,
C10), 64.9 (C17, C18), 63.0 (C23, C25), 61.2 (C19), 60.8 (C20), 52.5
(C21, C22), 44.5 (C15, C16), 16.9 (C24, C26).
1H NMR (500 MHz, CDCl3): δ 7.48 (m, 2H, Harom), 7.26 (m, 2H,
3
2
Harom), 7.11−7.16 (m, 4H, Harom), 4.16 (dq, JH−H = 6.9 Hz, JH−H
=
8.6 Hz, 2H, H23(a), H25(a)), 4.08 (m, 2H, H17(a), H18(a)), 3.87 (dq, 3JH−H
= 6.9 Hz, 2JH−H = 8.6 Hz, 2H, H23(b), H25(b)), 3.50 (m, 2H, H15, H16),
2.62 (s, 6H, H21, H22), 2.37 (m, 2H, H20), 2.26 (m, 2H, H19), 1.89 (s,
3H, CH3−COO), 1.79 (s, 3H, CH3−COO), 1.67 (m, 2H, H17(b)
,
Synthesis of 6. To a solution of 2 (20 mg, 0.034 mmol) in 5 mL of
degassed dichloromethane was added [RuCp(NCMe)3]PF6 (29.8 mg,
0.068 mmol). The resulting mixture was refluxed overnight. After the
evaporation of the solvent the resulting complex was isolated as a
brown solid (31.8 mg, 0.026 mmol, 77%). Single crystals suitable for
X-ray analysis were obtained from an acetone solution of 6. For NMR
labeling, see Figure S12 in the Supporting Information.
H18(b)), 1.52 (t, JH−H = 6.9 Hz, 6H, H24, H26). 13C{1H} NMR (125
MHz, CDCl3): δ 178.4 (CH3−COO), 178.3 (CH3−COO), 141.9
(C11, C12 or C13, C14), 140.2 (C11, C12 or C13, C14), 126.0 (CHarom),
125.9 (CHarom), 122.4 (CHarom), 120.9 (CHarom), 80.5 (C9, C10), 63.3
(C17, C18), 62.5 (C20), 61.7 (C19), 60.5 (C23, C25), 50.7 (C21, C22),
44.7 (C15, C16), 23.0 (C28), 22.9 (C30), 15.5 (C24, C26). IR (KBr, ν
cm−1): 3447 (C−H), 2973, 2928 (C−H), 1617, 1600 (CO),
1451 (CC), 1073, 1024 (C−O). Anal. Calcd for C30H40N2O6Pd
(631.5): C, 57.01; H, 6.33; N, 4.44. Found: C, 56.86; H, 6.51; N, 4.49.
Synthesis of 4. Ligand 2 (100 mg, 0.246 mmol) was dissolved in
15 mL of toluene, and [PdCl2(COD)] (70.2 mg, 0.246 mmol) was
then added. This mixture was stirred for 15 h at 70 °C. The solvent
was then evaporated, and the obtained solid was washed with diethyl
ether. After it was dried under vacuum, the complex was isolated as a
yellow solid (129.2 mg, 0.222 mmol, 90%). Single crystals suitable for
X-ray analysis were obtained from a dichloromethane/diethyl ether
(1/2) solution of 4. For NMR labeling, see Figure S12 in the
Supporting Information.
3
1H NMR (300 MHz, (CD3)2CO): δ 6.36 (m, 4H, Harom), 6.30 (m,
2H, Harom), 6.27 (m, 2H, Harom), 5.50 (s, 10H, Cp), 4.11 (m, 4H, H23,
H25), 3.67 (m, 2H, H20), 3.10 (m, 2H, H19), 2.78 (m, 6H, H15, H16,
3
H17, H18), 2.70 (s, 6H, H21, H22), 1.52 (t, JH−H = 6.9 Hz, 6H, H24,
H26). 13C{1H} NMR (75 MHz, (CD3)2CO): δ 153.8, 131.7 (C11, C12,
C13, C14), 89.1 (CHarom), 87.3 (CHarom), 86.6 (CHarom), 85.2
(CHarom), 84.2 (Cp), 80.7 (C9, C10), 65.6 (C17, C18), 63.1 (C23,
C25), 61.5 (C19), 60.9 (C20), 52.1 (C21, C22), 44.5 (C15, C16), 16.7
(C24, C26). 31P{1H} NMR (121.4 MHz, (CD3)2CO): δ −144.5 ppm.
IR (KBr, ν cm−1): 3479 (C−H), 2974, 2928 (C−H), 1459 (CC),
1065 (C−O), 842 (P−F). High-resolution mass spectrometry (ES+,
methanol): calcd mass 1005.3069, found mass 1005.3076
(C36H44N2O2ClPdRu2PF5). High-resolution mass spectrometry (ES−,
methanol): calcd mass 144.9642, found mass 144.9642 ([PF6]−).
Synthesis of 8. To a solution of the corresponding aniline ligand17
(20 mg, 0.049 mmol) in 3 mL of degassed dichloroethane was added
[RuCp(NCMe)3]PF6 (21 mg, 0.049 mmol). The resulting mixture
was refluxed overnight. After the evaporation of the solvent the
resulting solid was purified by recrystallization in a dichloromethane/
diethyl ether mixture (1/2). Yield: 20 mg (61%).
1H NMR (300 MHz, CDCl3): δ 7.48−7.51 (m, 2H, Harom), 7.14−
3
2
7.19 (m, 6H, Harom), 4.10−4.18 (dq+m, JH−H = 6.9 Hz, JH−H = 8.6
3
Hz, 4H, H23(a), H25(a) and H17(a), H18(a)), 3.76−3.86 (dq+m, JH−H
6.9 Hz, JH−H = 8.6 Hz, 4H, H23(b), H25(b) and H15, H16), 2.76 (s, 6H,
=
2
H21, H22), 2.42 (m, 2H, H20), 2.14 (br, 2H, H19), 1.95 (m, 2H, H17(b)
,
3
H18(b)), 1.53 (t, JH−H = 6.9 Hz, 6H, H24, H26). 13C{1H} NMR (75
MHz, CDCl3): δ 141.9 (C11, C12 or C13, C14), 140.4 (C11, C12 or C13,
C14), 129.0 (CHarom), 128.2 (CHarom), 126.1 (CHarom), 125.3
(CHarom), 80.9 (C9, C10), 65.1 (C17, C18), 63.7 (C20), 63.4 (C19),
60.7 (C23, C25), 51.8 (C21, C22), 45.8 (C15, C16), 15.5 (C24, C26). IR
(KBr, ν cm−1): 3447 (C−H), 2974, 2928 (C−H), 1459 (CC),
1078, 1025 (C−O). High-resolution mass spectrometry (ES+,
methanol): calcd mass 547.1351 [M − Cl]+, found mass 547.1353
[M − Cl]+ (C26H34ClN2O2Pd). Anal. Calcd for C26H34Cl2N2O2Pd·
CH2Cl2 (667.486): C, 48.54; H, 5.39; N, 4.19. Found: C, 49.78; H,
5.70; N, 3.90.
1H NMR (300 MHz, (CD3)2CO): δ 7.59 (m, 2H, Harom), 7.41 (m,
2H, Harom), 7.19−7.23 (m, 4H, Harom), 5.95 (m, 3H, Harom), 5.72 (m,
2H, Harom), 5.11 (s, 5H, Cp), 4.20 (m, 2H, CH2−CH3), 3.92 (m, 2H,
CH2−CH3), 3.59 (m, 2H, CH2−N), 2.90 (m, 4H, CH and CH2−N),
1.55 (t, 3JH−H = 6.9 Hz, 6H, CH2−CH3). 31P{1H} NMR (121.4 MHz,
(CD3)2CO): δ −143.7 ppm. IR (KBr, ν cm−1): 3113 (C−H), 2973,
2927 (C−H), 1551, 1468 (CC), 1070 (C−O), 836 (P−F).
Procedure for Pd-Catalyzed Suzuki−Miyaura Cross-Cou-
pling. Palladium complex (1 mol %), phenylboronic acid (91.5 mg,
0.75 mmol), and Na2CO3 (106 mg, 1.0 mmol) dissolved in 0.5 mL of
deoxygenated water were dissolved in 2 mL of dried toluene. 4-
Bromoanisole (93.5 mg, 0.5 mmol) was then added. The mixture was
heated to 65 °C for the corresponding time. A 15 mL portion of
diethyl ether was added, and the organic phase was consecutively
washed with a NaOH aqueous solution (1 M) and water. The organic
phase was dried on Na2SO4, filtered, concentrated under vacuum, and
Synthesis of 5. To a solution of 2 (25 mg, 0.043 mmol) in 5 mL of
degassed dichloromethane was added [RuCp(NCMe)3]PF6 (18.6 mg,
0.043 mmol). The resulting mixture was refluxed overnight. After
evaporation of the solvent the resulting complex was isolated as an
orange solid (29.9 mg, 0.033 mmol, 78%). Single crystals suitable for
X-ray analysis were obtained from an acetone solution of 5. For NMR
labeling, see Figure S12 in the Supporting Information.
31P{1H} NMR (121.4 MHz, (CD3)2CO): δ −144.5 ppm. IR (KBr,
ν cm−1): 3481 (C−H), 2976, 2930 (C−H), 1458 (CC), 1068
(C−O), 841 (P−F). High-resolution mass spectrometry (ES+,
methanol): calcd mass 750.0480, found mass 750.0475
(C31H39Cl2N2O2PdRu). High-resolution mass spectrometry (ES−,
methanol): calcd mass 144.9642, found mass 144.9644 ([PF6]−).
Anal. Calcd for C31H39Cl2F6N2O2PPdRu·CH2Cl2 (979.923): C, 39.19;
H, 4.18; N, 2.86. Found: C, 39.83; H, 4.59; N, 2.40.
1
analyzed by gas chromatography and H NMR.
Electrochemical Measurements. Experiments were performed
at room temperature in a homemade airtight three-electrode cell
connected to a vacuum/argon line. The reference electrode consisted
of a saturated calomel electrode (SCE) separated from the solution by
a bridge compartment. The counter electrode was a platinum wire of
ca. 1 cm2 apparent surface or a glassy-carbon disk 1 mm in diameter.
The solutions used during the electrochemical studies were typically
10−3 mol L−1 in complex compound and 0.1 mol L−1 in supporting
electrolyte. The supporting electrolyte (nBu4N)[PF6] (Fluka, 99%
electrochemical grade) was used as received and simply degassed
under argon. Acetonitrile was used from the MBraun SPS-800 solvent
purification system. Before each measurement, the solutions were
degassed by bubbling Ar and the working electrode was polished with
a polishing machine (Presi P230). Potentials are given vs the Fc+/Fc
couple as internal standard (E1/2 = 0.4 V/SCE).
Data for maj-5 (70%) are as follows. 1H NMR (300 MHz,
(CD3)2CO): δ 7.48 (m, 2H, Harom), 7.23 (m, 2H, Harom), 7.17 (m, 2H,
Harom), 6.32 (m, 2H, Harom), 5.49 (s, 5H, Cp), 4.13 (m, 4H, H23, H25),
3.65 (m, 2H, H20), 3.55 (m, 2H, H15, H16), 2.96 (m, 4H, H17, H18),
3
2.83 (m, 2H, H19), 2.70 (s, 6H, H21, H22), 1.48−1.56 (t, JH−H = 6.9
Hz, 6H, H24, H26). 13C{1H} NMR (75 MHz, (CD3)2CO): δ 142.0
(C11 or C14), 139.0 (C11 or C14), 129.7, 127.9, 127.5, 122.7 (C1, C2,
C3, C4), 113.6 (C12, C13), 87.3 (CHarom), 83.2 (Cp), 83.0, 82.9, 82.0
(CHarom), 80.5 (C9, C10), 66.3 (C17, C18), 61.9 (C23, C25), 61.4 (C19),
60.8 (C20), 52.0 (C21, C22), 44.8 (C15, C16), 16.8 (C24, C26).
X-ray Diffraction Data Collection and Structure Solution
Refinement. The X-ray data (see the Supporting Information, Table
S2) for single crystals of ligand 2 and complexes 3−6 were obtained at
Data for min-5 (30%) are as follows. 1H NMR (300 MHz,
(CD3)2CO): δ 7.57 (m, 2H, Harom), 7.35 (m, 2H, Harom), 6.52 (m, 2H,
1817
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a temperature of 193(2) K, using a 30 W air-cooled microfocus source
with focusing multilayer optics and Mo Kα radiation (λ = 0.71073 Å).
ψ and ω scans were used. The data were integrated with SAINT, and
an empirical absorption correction with SADABS was applied.28 The
structures were solved by direct methods, using SHELXS-97 and
refined using the least-squares method on F2 with SHELXL-97.29 All
non-H atoms were treated anisotropically. The hydrogen atoms were
fixed geometrically and treated as a riding model.
CCDC-967241 (2), CCDC-967240 (3), CCDC-967244 (4),
CCDC-967242 (5), and CCDC-967243 (6) contain supplementary
crystallographic data. These data can be obtained free of charge from
The Cambridge Crystallographic Data Centre via www.ccdc.cam.ac.
uk/data_request/cif.
(7) (a) Li, L.; Metz, M. V.; Li, H.; Chen, M.-C.; Marks, T. J.; Liable-
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131, 3974.
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I. L.; Marks, T. J. J. Am. Chem. Soc. 2009,
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1878.
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ASSOCIATED CONTENT
* Supporting Information
■
S
Tables S1 and S2, Figures S1−S12, and CIF files giving NMR,
electrochemical, theoretical, and crystallographic data for 2−6.
This material is available free of charge via the Internet at
http://pubs.acs.org.
(14) (a) Grossman, O.; Azerraf, C.; Gelman, D. Organometallics
2006, 25, 375. (b) Azerraf, C.; Gelman, D. Organometallics 2009, 28,
6578. (c) Nakata, N.; Uchiumi, R.; Yoshino, T.; Ikeda, T.; Kamon, H.;
Ishii, A. Organometallics 2009, 28, 1981. (d) Musa, S.; Filippov, O. A.;
Belkova, N. V.; Shubina, E. S.; Silantyev, G. A.; Ackermann, L.;
Gelman, D. Chem. Eur. J. 2013, 19, 16906.
AUTHOR INFORMATION
Corresponding Author
*M.G.: tel, +33 561557738; fax, + 33 561558204; e-mail,
gomez@chimie.ups-tlse.fr.
Notes
■
(15) (a) Sanhes, D.; Favier, I.; Saffon, N.; Teuma, E.; Gom
Tetrahedron Lett. 2008, 49, 6720. (b) Sanhes, D.; Raluy, E.; Retory, S.;
Saffon, N.; Teuma, E.; Gomez, M. Dalton Trans. 2010, 39, 9719.
(c) Bratko, I.; Mallet-Ladeira, S.; Saffon, N.; Teuma, E.; Gom
́
ez, M.
The authors declare no competing financial interest.
́
́
ACKNOWLEDGMENTS
This work was financially supported by the Centre National de
la Recherche Scientifique (CNRS) and the Universite
Sabatier. The authors thank Prof. A. Lledos
discussions concerning the theoretical study, A. Saquet and A.
Moreau for their contributions to the electrochemical study,
and P. Lavedan for his help in the NMR studies. I B. is grateful
́
ez, M.
■
Acta Crystallogr., Sect. E 2012, E68, m1313.
(16) (a) Sanhes, D.; Gual, A.; Castillon, S.; Claver, C.; Gom
Teuma, E. Tetrahedron: Asymmetry 2009, 20, 1009. (b) Bratko, I.;
́
́
ez, M.;
́
Paul
for the fruitful
́
Guisado-Barrios, G.; Favier, I.; Mallet-Ladeira, S.; Teuma, E.; Peris, E.;
Gom
(17) Bratko, I.; Mallet-Ladeira, S.; Saffon, N.; Teuma, E.; Gom
Dalton Trans. 2013, 42, 1136.
́
ez, M. Eur. J. Org. Chem. 2014, DOI: 10.1002/ejoc.201301220.
́
ez, M.
̀ ́
to the Ministere de l′Enseignement Superieur et de la Recheche
(18) Deeming, A. J. In Comprehensive Organometallic Chemistry;
Wilkinson, G., Stone, F. G. A., Abel, E. W., Eds.; Pergamon Press:
Oxford, U.K., 1982; Vol. 4, p 475.
for a Ph.D. grant.
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