[Bis(pyrazolyl)methane]palladium complexes with a carbosilane dendritic structure

Article abstract of DOI:10.1002/ejic.201000076

A series of carbosilane dendritic ligands of general formula Gn-[CH(GiS-Me₂PZ)₂]m and their corresponding palladium(II) complexes Gn-[CH(3,5-Me₂pz)₂Pd(X)C1]_m (X = Cl or Me) containing four (m = 1) or eight (m = 2) terminal bis(pyrazo-lyl)methane moieties, along with their corresponding mono-metallic counterparts (m = 0), have been synthesized. An appropriate choice of poly(pyrazolyl)methane ligand has allowed us to overcome the steric and solubility issues that previously limited the synthesis of polymetallic dendrimers containing (scorpionato) palladium complexes. The evaluation of these complexes as catalyst precursors in the Heck reaction between p-iodotoluene and methyl acrylate is also reported

Full text of DOI:10.1002/ejic.201000076

FULL PAPER
DOI: 10.1002/ejic.201000076
[Bis(pyrazolyl)methane]palladium Complexes with a Carbosilane Dendritic
Structure
Alberto Sánchez-Méndez,[a] Ernesto de Jesús,*[a] Juan C. Flores,*[a] and Pilar Gómez-Sal[a]
Keywords: Dendrimers / N ligands / Palladium / Heck reaction / Heterocycles
A series of carbosilane dendritic ligands of general formula
Gn-[CH(3,5-Me2pz)2]m and their corresponding palladium(II)
complexes Gn-[CH(3,5-Me2pz)2Pd(X)Cl]m (X = Cl or Me)
containing four (m = 1) or eight (m = 2) terminal bis(pyrazo-
lyl)methane moieties, along with their corresponding mono-
metallic counterparts (m = 0), have been synthesized. An ap-
propriate choice of poly(pyrazolyl)methane ligand has al-
lowed us to overcome the steric and solubility issues that pre-
viously limited the synthesis of polymetallic dendrimers con-
taining (scorpionato)palladium complexes. The evaluation of
these complexes as catalyst precursors in the Heck reaction
between p-iodotoluene and methyl acrylate is also reported.
their coordination capability. Furthermore, poor solubility
is a limiting factor commonly found in the synthesis of
higher-generation polymetalated dendrimers.
Introduction
Although a large variety of ligands have been used to
anchor metal complexes to dendrimers,[1,2] [poly(pyrazol-1-
yl)]metal complexes have rarely been used for this purpose.
These ligands are a very versatile and important class of
nitrogen donors in modern day coordination chemistry and
have led to the development of the creative field of scorpi-
onate chemistry.[3] Indeed, recent advances in this area have
shown that poly(pyrazol-1-yl)alkane compounds[4,5] also
have attractive applications in many interdisciplinary
fields.[4,6]
In previous work, we evaluated the possible incorpora-
tion of scorpionate complexes into carbosilane metalloden-
dritic complexes by taking advantage of the facile function-
alization of the bridging methine carbon atom in tris(pyr-
azol-1-yl)methane,[7] as first demonstrated by Reger et al.
in related studies.[8] A different approach to the synthesis of
carbosilane dendrimers with peripheral [bis- or tris(pyraz-
olyl)borato]rhodium complexes was subsequently reported
by Ciriano and Casado and their co-workers.[9]
In subsequent work, we focused on different strategies to
overcome both the steric crowding in the ligand and the
insolubility issue. In our first approach, we targeted a bis-
(pyrazol-1-yl)methane ligand with Fréchet’s dendrons
linked to the methylene bridge {Gn-[HC(3,5-Me2pz)2]}
(Scheme 1, A). These bidentate ligands at the focal point of
the poly(benzyl ether) wedges are more flexible and lead to
monometallic nickel(II)[10] and palladium(II)[11] complexes,
the solubility of which is defined by the dendritic moiety
and enhanced by the methyl substitutions on the pyrazolyl
rings. Molybdenum(VI) and -(0) complexes containing the
same bidentate ligands were also synthesized, and – in ad-
dition – we demonstrated that an –OCH2– spacer between
the poly(benzyl ether) dendrons and the methine carbon
atom in the tris(pyrazol-1-yl)methane ligand (Scheme 1, B)
results in suitable tridentate ligands for the preparation of
either low- or high-oxidation-state molybdenum dendron-
ized complexes.[12]
After our preliminary study, in which we synthesized a
tetranuclear compound with a carbosilane core along with
four [tris(pyrazolyl)methane]molybdenum complexes, we
concluded that a broader use of this type of N-heterocyclic
donor in dendrimer chemistry would require modification
of the ligand to reduce steric crowding and enhance the
solubility of the final metallodendrimer.[7] Sterically de-
manding substituents bonded directly to the methine bridg-
ing carbon atom of tris(pyrazol-1-yl)methane units restrict
the arrangement of the pyrazolyl rings and can suppress
Scheme 1.
These synthetic studies have been complemented by
others that aimed at gaining an understanding of the or-
ganization of the dendritic arms around the metal centers
located at the core or focal point of the dendritic structures.
Because this arrangement might modulate the properties of
[a] Departamento de Química Inorgánica, Universidad de Alcalá,
Campus Universitario,
28871 Alcalá de Henares, Madrid, Spain
Fax: +34-91-885-4683
E-mail: ernesto.dejesus@uah.es
juanc.flores@uah.es
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A. Sánchez-Méndez, E. de Jesús, J. C. Flores, P. Gómez-Sal
In the NMR spectra the SiMe2 resonances shift from δ
FULL PAPER
these metal centers, the catalytic behavior of these metallod-
endrimers has also been studied in processes such as oxi- = 0.4 (1H) and 0.2 ppm (13C) in the starting chlorocarbosil-
dation, polymerization, and other carbon–carbon bond-for- anes to δ ≈ 0.2 (1H) and –3.0 ppm (13C) in 2 and 3. A
mation reactions.[10–12]
unique set of NMR resonances is observed for the pyrazolyl
We describe herein the next step in our ongoing research rings, which are also characterized by a strong νas(C=N)
into dendrimers containing scorpionate complexes by re- IR absorption at around 1554 cm–1. Ligands 2 and 3 gave
porting the preparation of polymetallic carbosilane dendri- satisfactory elemental analyses, and their ESI+-TOF mass
mers decorated with [bis(pyrazol-1-yl)methane]palladi- spectra exhibit a peak corresponding to the protonated mo-
um(II) complexes at their periphery together with their lecular ion [M + H]+.
catalytic performance in the Heck reaction.
Synthesis of Palladium Complexes 4–9
Results and Discussion
ThepalladiumdichloridecomplexesGn-[CH(3,5-Me2pz)2-
PdCl2]m (4–6) were synthesized by displacement of the
diene ligand of [PdCl2(cod)] (cod = η4-1,5-cyclooctadiene)
with 1–3, respectively (Scheme 2). However, whereas the
formation of the mononuclear compound 4 was virtually
quantitative after 2 h in toluene at reflux, the complexation
of 5 and 6 did not go to completion under the same condi-
tions, and further refluxing resulted in the partial decompo-
sition and precipitation of Pd0. These metalations did, how-
ever, go to completion in 3 h, with isolated yields Ն80%,
when the temperature was lowered to 80 °C to avoid decom-
position. Chlorido(methyl) complexes 7 and 8 precipitated
from diethyl ether solutions containing a mixture of ligands
1–3 and [PdClMe(cod)] at room temperature in Ն80%
yield. A partially metalated precipitate was obtained when
dendrimer 3 was treated under the same conditions, but
compound 9 (Figure 1) could be conveniently synthesized
in toluene at 80 °C (80% yield). All compounds were iso-
lated as orange (4–6) or white (7) to pale-grey (8 and 9) air-
stable solids. The general solubility of the chlorido(methyl)
derivatives is slightly superior to that of their dichlorido
counterparts.[11b,13] Thus, complexes 4–6 are soluble in
chlorinated and polar (acetone, acetonitrile) solvents and
insoluble in diethyl ether, toluene, or alkanes, whereas com-
pounds 7–9 are slightly soluble in toluene. As is often the
case with surface-functionalized dendrimers,[13] the solubil-
ity diminishes as the number of metal complexes at the pe-
riphery increases. Note that our attempts to prepare similar
palladium(II) complexes of related carbosilane dendrimers
Synthesis of the Carbosilane Bis(pyrazolyl)methane Ligands
1–3
The same methodology as described previously for the
preparation of Me3SiCH(Me2pz)2 (1; Me2pz = 3,5-dimeth-
ylpyrazol-1-yl) was applied to the synthesis of the dendritic
ligands 2 and 3 (Scheme 2).[10] Thus, the straightforward
functionalization of the bidentate ligand at the methylene
bridge was achieved by treatment of the lithium salt
LiCH(3,5-Me2pz)2 with the appropriate chlorocarbosilane
Me3Si-Cl (G0-Cl), G1-Cl4, or G2-Cl8 in thf. A slight excess
of the lithium salt was added to ensure the complete reac-
tion of the peripheral Si–Cl bonds in the synthesis of com-
pounds 2 and 3. The unreacted lithium salt was readily sep-
arated after hydrolysis by sublimation (10–2 Torr, 50 °C).
Both dendrimers were isolated after workup as air-stable,
yellowish oils in good yield (Ն75%, see the Exp. Sect. for
details) and, as is the case for 1, they were found to be fairly
soluble in all common organic solvents.
containing
terminal
tris(pyrazolyl)methane
ligands
(Scheme 1, B) failed due to the formation of intractable
mixtures of insoluble solids. This observation highlights the
importance of considering the solubility in the ligand de-
sign of metal dendrimers. It is also remarkable that, whereas
chlorido(methyl) complexes usually decompose in chlorin-
ated solvents by Pd–Me/Pd–Cl exchange and concomitant
precipitation of Pd0,[6f,13,14] compounds 7–9 are fairly stable
in such solvents at room temperature.
1
The H and 13C{1H} NMR spectra of the complexes re-
flect the local symmetry around the palladium atoms. Thus,
compounds 4–6 (Cs symmetry) show one set of signals for
the chelate ligand, whereas the absence of a mirror plane in
7–9 (C1 symmetry) means that the two pyrazolyl rings are
nonequivalent. The resonance for the 3-Me protons (δ ≈
2.5 ppm for 4–6) splits into two singles in the spectra of 7–
Scheme 2. Synthesis of carbosilane ligands and complexes. Rea-
gents and conditions (m equiv.): (i) LiCH(3,5-Me2pz)2 in thf; (ii)
[PdCl2(cod)] in toluene or [PdClMe(cod)] in diethyl ether or tolu-
ene.
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Dendritic [Bis(pyrazolyl)methane]palladium Complexes
the Me3Si group occupying an axial position on the bridg-
ing atom C-11, thereby avoiding the steric hindrance that
would arise from the adjacent methyl groups at the 5-posi-
tion of the pyrazolyl ring in the equatorial positions. This
steric repulsion confers rigidity on the metallacycle as no
boat-to-boat conformational exchange is observed in solu-
tion.
Figure 1. Metallodendrimer G2-[CH(Me2pz)2PdClMe]8 (9).
9, with that at higher field (δ ≈ 2.3 ppm) corresponding to
the 3-Me group adjacent to the Pd–Me moiety and that at
lower field (δ ≈ 2.5 ppm) to the 3-Me group adjacent to the
Pd–Cl bond. A similar splitting is observed for the 3-Me
carbon atoms, the 5-Me groups, and, in the case of 9, the
C–H unit at the 4-position of the pyrazolyl rings. Addition-
ally, a lack of symmetry is also observed in the SiMe2 group
bonded to the palladacycles in 8 and 9. Coordination of
Figure 2. ORTEP diagram of the structure of compound 4 with
thermal ellipsoids at the 50% probability level.
Table 1. Selected bond lengths and angles for compound 4.
Bond lengths [Å]
Bond angles [°]
1
the ligands usually shifts the H and 13C resonances of the
Pd–Cl(1)
Pd–Cl(2)
Pd–N(1)
Pd–N(3)
N(1)–N(2)
N(3)–N(4)
N(2)–C(11)
N(4)–C(11)
C(11)–Si(1)
2.2869(11)
Cl(1)–Pd–Cl(2)
N(1)–Pd–N(3)
N(1)–Pd–Cl(1)
N(3)–Pd–Cl(2)
N(1)–Pd–Cl(2)
N(3)–Pd–Cl(1)
N(2)–C(11)–Si(1)
N(4)–C(11)–Si(1)
N(2)–C(11)–N(4)
88.77(5)
87.75(12)
91.70(9)
91.67(9)
177.59(8)
177.35(8)
117.7(2)
118.4(2)
108.3(3)
CH(Me2pz)2 moieties (for instance, ca. 0.5 ppm for the 3-
Me protons) and the SiMe2 or SiMe3 groups (ca. 0.4 ppm)
downfield, whereas a significant upfield shift is observed for
the 13C resonance of the bridging methine carbon atom (ca.
–4 ppm) as a result of the rigidity of the metallacycle
formed.[10–12] Other resonances of the carbosilane frame-
work remain basically unaltered upon coordination.
An absorption corresponding to the νas(C=N) vibration
is found in the IR spectra of complexes 4–9 at around
1560 cm–1. The ESI+ or APCI+ mass spectra of the G0- and
G1-containing molecules (4, 5, 7, and 8) show either the
expected molecular ions or peaks derived from them, often
resulting from the loss of Cl atoms or Me groups. In con-
trast, no peaks assignable to the molecular ions or to simple
fragmentations are observed for the larger dendrimers 6
and 9.
2.2881(11)
2.037(3)
2.032(3)
1.375(4)
1.375(4)
1.460(4)
1.455(4)
1.943(3)
A similar boat-type conformation of the six-membered
metallacycle is found in structures of tetrahedral nickel(II)[10]
and octahedral molybdenum(0)[12] complexes containing re-
lated bis(pyrazolyl)methane chelate ligands, although their
different coordination environments yield broader or nar-
rower N–M–N angles (ca. 94 and 79°, respectively) than
those found in the structure of the square-planar PdII com-
plex in this work (ca. 88°) or in previously reported struc-
tures.[6f,11,14a,15]
Structure of [Me3SiCH(3,5-Me2pz)2PdCl2] (4)
Figure 2 shows an ORTEP representation of the molecu-
lar structure of compound 4 in the solid state, as deter-
mined by single-crystal X-ray diffraction studies; selected
Evaluation of the Pd Dendrimers in the Heck Reaction
Complexes 4–9 were tested as catalytic precursors in the
structural data are given in Table 1. The structural param- Heck coupling reaction of p-iodotoluene and methyl acry-
eters defining the –CH(3,5-Me2pz)2PdCl2 moiety are fairly late. The conversions attained after 23 h at 80 °C are sum-
similar to those reported for other [bis(pyrazolyl)methane]- marized in Table 2 for all the catalysts, and the plots of
palladium(II) complexes[6f,11,14a,15] with the palladium conversion versus reaction time for the dichloride precur-
atoms exhibiting a square-planar geometry. The Pd(NN)2C sors 4–6 are shown in Figure 3 (analogous profiles were ob-
palladacycle adopts a pronounced boat conformation, with tained for 7–9).
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A. Sánchez-Méndez, E. de Jesús, J. C. Flores, P. Gómez-Sal
FULL PAPER
Table 2. Conversion in the Heck reaction of p-iodotoluene with
methyl acrylate catalyzed by 4–9.[a]
Experimental Section
General: All operations were performed under argon by using
Schlenk or dry-box techniques. Unless otherwise stated, reagents
were obtained from commercial sources and used as received. The
ligand Me3Si-CH(3,5-Me2pz)2 (1),[10] carbosilane dendrimers Gn-
Clm,[17] and metallic precursors [PdCl2(cod)] and [PdClMe(cod)][18]
were prepared according to literature procedures. LiCH(3,5-
Me2pz)2 was prepared as a white solid by modifying[10] a previously
reported procedure.[19] All solvents were dried and distilled prior
to use under argon, as described elsewhere.[20] Alternatively, rea-
gent-grade solvents (Baker and SDS) were purified by flash column
chromatography and collected under argon by using an MBraun
MB SPS solvent purification device. NMR spectra were recorded
at room temperature with a Varian Unity VR-300 or -200 spec-
trometer. Chemical shifts (δ) are reported in ppm relative to SiMe4
and are referenced with respect to the 13C and residual 1H reso-
nances of the deuteriated solvents. Coupling constants (J) are given
in Hz. 1H NMR integrated values for dendritic compounds are
given relative to one of the four arms of the molecule. The number-
ing scheme for the pyrazolyl ring atoms is given in Scheme 2. IR
spectra were recorded with a Perkin-Elmer FT-IR Spectrum-2000
spectrophotometer. Elemental analyses were performed by the Mi-
croanalytical Laboratories of the University of Alcalá with a
Heraeus CHN-O-Rapid microanalyzer, and mass spectra were re-
corded with a Thermoquest–Finnigan Automass Multi (APCI) or
an Agilent G3250AA LC/MSD TOF Multi (ESI) mass spectrome-
ter. Heck reactions were performed by using a procedure described
elsewhere[11b] and monitored by GC on a Chrompack CP 9001 gas
chromatograph using a CP-WAX 52 CB FS-capillary column
(15 m, 0.25 mm i.d., 0.25 µm film thickness) under the following
conditions: injector and detector temperatures: 250 and 260 °C,
respectively; oven temperature program: 100 °C for 1 min, 10 °C/
min ramp, 240 °C/10 min.
Compounds
Conversions [%][b]
G0
G1
G2
Gn-[L2PdCl2] 4–6
Gn-[L2PdMeCl] 7–9
61
81
82
90
89
88
[a] Conditions: 5 mL MeCN, n(Pd) = 5 µmol (1 mol-% based on
Pd), [4-iodotoluene] = [methyl acrylate] = [NEt3] = 0.1 ; tr = 23 h;
Tr = 80 °C. [b] Conversions were determined by GC.
Figure 3. Reaction profiles for the Gn-[L2PdCl2]m precursors 4–6
and PdCl2 under the conditions described in Table 2. Conversions
were determined by GC.
Synthesis of Ligands and Complexes
None of these precursors show significant advantages G1-[CH(3,5-Me2pz)2]4 (2): nBuLi (2.9 mL, 1.6  in hexanes,
4.6 mmol) was slowly added from a funnel equipped with a bubbler
to a solution of H2C(3,5-Me2pz)2 (934 mg, 4.6 mmol) in thf
(40 mL) at –78 °C, and the mixture was stirred at that temperature
for 2 h. A solution of carbosilane G1-Cl4 (655 mg, 1.15 mmol) in
thf (20 mL) was then added, and the reaction mixture was warmed
to room temperature and stirred overnight. The resulting solution
was diluted with diethyl ether (30 mL) and washed with water
(40 mL). The aqueous layer was washed with diethyl ether
(2ϫ30 mL), and the combined organic extracts were dried with
over PdCl2 in the absence of the ligand under the same
conditions (dashed line in Figure 3). As we have discussed
previously,[11b] bis(pyrazolyl)methane ligands are barely ef-
ficient in stabilizing the molecular Pd species under the
catalytic conditions and, in fact, precipitation of Pd black
is always observed during the reaction. In any case, the den-
drimer has a positive effect on the conversions, which follow
the trend G2 (6 and 9) Ն G1 (5 and 8) Ͼ G0 (4 and 7). This
result may be related to the observation that polymetallic
MgSO4. The volatiles were removed under vacuum to give com-
1
dendrimers tend often to be more resistant than monome- pound 2 as a yellow oil. Yield: 1.24 g (87%). H NMR (CDCl3): δ
= 0.17 (s, 6 H, SiMe2), 0.41 (m, 2 H, SiCH2), 0.73 (m, 2 H,
CH2SiMe2), 1.16 (m, 2 H, CH2CH2CH2), 1.94 (s, 6 H, 3-Mepz),
2.15 (s, 6 H, 5-Mepz), 5.72 (s, 2 H, 4-Hpz), 5.85 (s, 1 H, CH) ppm.
13C{1H} NMR (CDCl3): δ = –2.8 (SiMe2), 10.9 (5-Mepz), 13.6 (3-
Mepz), 17.2 (CH2), 18.1 (CH2), 19.6 (CH2), 67.9 (CH), 106.1 (C-
tallic complexes towards degradation and metal precipi-
tation in Pd-catalyzed C–C coupling reactions.[16]
Conclusions
4 ), 139.6 (C-5 ), 146.6 (C-3 ) ppm. IR (CsI/Nujol): ν = 1554 (s,
˜
pz
pz
pz
C=N) cm–1. MS (ESI+-TOF, CH2Cl2/MeOH/NH4HCOO 5 m):
m/z = 1241.78 [M + H]+. C64H108N16Si5 (1242.1): calcd. C 61.89,
H 8.76, N 18.04; found C 61.46, H 8.36, N 17.88.
An appropriate choice of poly(pyrazolyl)methane ligand
has allowed us to overcome the steric and solubility issues
that previously limited the synthesis of polymetallic dendri-
mers containing scorpionate palladium complexes. Thus, by
using HC(3,5-Me2pz)2 as a binding motif embedded in car-
bosilane structures, we have been able to synthesise palla-
dium dendrimers up to the second generation, thereby high-
lighting the importance of ligand design in dendrimer
chemistry.
G2-[CH(3,5-Me2pz)2]8 (3):
A solution of G2-Cl8 (470 mg,
0.32 mmol) in thf (10 mL) at –78 °C was added to a suspension of
Li[HC(3,5-Me2pz)2] (544 mg, 2.59 mmol) in the same solvent and
at the same temperature. The reaction mixture was then warmed
to room temperature and stirred overnight. The volatiles were re-
moved under vacuum, the residue extracted with diethyl ether
(2ϫ20 mL), and the resulting solution washed with water
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Dendritic [Bis(pyrazolyl)methane]palladium Complexes
(2ϫ20 mL) and dried with MgSO4. Removal of the solvent gave
compound 3 as a yellow oil. Yield: 670 mg (75%). 1H NMR
pear. The mixture was stirred for 2 h, and then the solvent was
removed under vacuum, and the excess of ligand and cod byprod-
(CDCl3): δ = –0.17 (s, 3 H, SiMe), 0.18 (s, 12 H, SiMe2), 0.47 (m, uct were removed by washing the residue with pentane (2ϫ15 mL).
8
H, SiCH2), 0.74 (m, H, CH2SiMe2), 1.20 (m, H,
4
6
Compound 7 was isolated as a white solid. Yield: 87 mg (96%). 1H
CH2CH2CH2), 1.94 (s, 12 H, 3-Mepz), 2.14 (s, 12 H, 5-Mepz), 5.72 NMR (CDCl3): δ = 0.47 (s, 9 H, SiMe3), 0.88 (s, 3 H, PdMe), 2.26
(s, 4 H, 4-Hpz), 5.86 (s, 2 H, CH) ppm. 13C{1H} NMR (CDCl3): δ (s, 3 H, 3-Mepz aside PdMe) 2.31 (s, 3 H, 5-Mepz), 2.32 (s, 3 H, 5-
= –5.1 (SiMe), –2.7 (SiMe2), 10.8 (5-Mepz), 13.6 (3-Mepz), 17.7
Mepz), 2.47 (s, 3 H, 3-Mepz aside PdCl), 5.78 (s, 2 H, 4-Hpz), 5.91
(CH2), 18.1 (CH2), 18.6 (CH2), 19.1 (CH2), 19.5 (CH2), 67.9 (CH), (s, 1 H, CH) ppm. 13C{1H} NMR (CDCl3): δ = –5.1 (PdMe), –0.2
106.1 (C-4 ), 139.5 (C-5 ), 146.5 (C-3 ) ppm. IR (CsI/Nujol): ν =
(SiMe3), 11.4 (5-Mepz), 12.0 (5-Mepz), 14.1 (3-Mepz), 15.0 (3-Mepz),
˜
pz
pz
pz
1553 (s, C=N) cm–1. MS (ESI+/TOF, CH2Cl2/MeOH/NH4HCOO 63.9 (CH), 106.8 (C-4pz), 107.4 (C-4pz), 137.7 (C-5pz), 139.4 (C-5pz),
5 m): m/z = 2794.70 [M + H]+, 1397.89 [M]2+. C144H252N32Si13 151.4 (C-3 ), 151.5 (C-3 ) ppm. IR (KBr): ν = 1558 (s, C=N)
(2796.9): calcd. C 61.84, H 9.08, N 16.03; found C 61.01, H 9.45,
N 15.45.
˜
pz
pz
cm–1. MS (APCI, MeOH): m/z = 450 [M – Me + MeOH]+, 433
[M]+, 277 [1 + H]+. C15H27ClN4PdSi (433.36): calcd. C 41.57, H
6.28, N 12.93; found C 41.44, H 6.26, N 12.80.
Me3Si-[CH(3,5-Me2pz)2PdCl2] (4): [PdCl2(cod)] (78 mg, 0.27
mmol) and bis(3,5-dimethylpyrazolyl)(trimethylsilyl)methane (1;
83 mg, 0.30 mmol) were placed in a Schlenk tube with toluene
(30 mL), and the resulting yellow suspension was heated at reflux
for 2 h. The orange solution was then cooled to room temperature,
the solvent removed in vacuo, and the residue washed with pentane
(2ϫ15 mL) to give 4 as a clear brownish solid, which was recrys-
tallized from dichloromethane/pentane to give an orange crystal-
G1-[CH(3,5-Me2pz)2PdClMe]4 (8): Compound 8 was synthesized
as described above for 7 starting from 2 (67 mg, 0.054 mmol) and
[PdClMe(cod)] (60 mg, 0.226 mmol) in diethyl ether (20 mL). A
white solid precipitated after a few minutes. Stirring was main-
tained for 3 h, and then the solid was filtered off and washed with
pentane to give compound 5 as a pale-grey solid. Yield: 91 mg
1
(90%). H NMR (CDCl3): δ = 0.38 (m, 2 H, SiCH2), 0.43 (s, 3 H,
1
line solid. Yield: 120 mg (97%). H NMR (CDCl3): δ = 0.68 (s, 9
SiMe2), 0.46 (s, 3 H, SiMe2), 0.85 (s, 3 H, PdMe), 1.10 (m, 4 H,
CH2CH2SiMe2), 2.28 (s, 3 H, 3-Mepz aside PdMe), 2.30 (s, 3 H, 5-
Mepz), 2.33 (s, 3 H, 5-Mepz), 2.45 (s, 3 H, 3-Mepz aside PdCl), 5.79
(s, 2 H, 4-Hpz) 5.93 (s, 1 H, CH) ppm. 13C{1H} NMR (CDCl3): δ
= –5.2 (PdMe), –1.4 (SiMe2), 11.6 (5-Mepz), 12.2 (5-Mepz), 14.2 (3-
Mepz), 15.1 (3-Mepz), 17.0 (CH2), 17.9 (CH2), 20.3 (CH2), 63.5
(CH), 106.8 (C-4pz), 107.5 (C-4pz), 138.0 (C-5pz), 139.8 (C-5pz),
H, SiMe3), 2.32 (s, 6 H, 5-Mepz), 2.58 (s, 6 H, 3-Mepz), 5.85 (s, 1
H, CH), 5.90 (s, 2 H, 4-Hpz) ppm. 13C{1H} NMR (CDCl3): δ =
–0.3 (SiMe3), 11.7 (5-Mepz), 15.3 (3-Mepz), 65.0 (CH), 108.1 (C-
4 ), 140.1 (C-5 ), 153.9 (C-3 ) ppm. IR (KBr): ν = 1557 (s, C=N)
˜
pz
pz
pz
cm–1. MS (APCI, MeOH): m/z = 871 [M2 – Cl]+, 450 [M – Cl +
MeOH]+, 277 [1 + H]+. C14H24Cl2N4PdSi (453.78): calcd. C 37.06,
H 5.33, N 12.35; found C 37.36, H 5.32, N 12.08.
151.2 (C-3 ) ppm. IR (KBr): ν = 1559 (s, C=N) cm–1. MS (ESI+/
˜
pz
TOF, CH2Cl2/MeOH/NH4HCOO 5 m): m/z = 1853.35 [M –
Me]+, 1241.78 [2 + H]+, 905.15 [M – 4 Me]2+. C68H120Cl4N16Pd4Si5
(1869.7): calcd. C 43.68, H 6.47, N 11.99; found C 43.26, H 6.27,
N 11.22.
G1-[CH(3,5-Me2pz)2PdCl2]4 (5): Dendritic compound 5 was syn-
thesized as described above for 4, starting from
2 (67 mg,
0.054 mmol) and [PdCl2(cod)] (65 mg, 0.228 mmol) in toluene
(20 mL). In this case, the reaction mixture was kept in the dark for
3 h, whilst heating at 80 °C. Compound 5 was isolated as an orange
solid after workup. Yield: 92 mg (87%). 1H NMR (CDCl3): δ =
0.37 (m, 2 H, SiCH2), 0.68 (s, 6 H, SiMe2), 1.08 (m, 2 H,
CH2SiMe2), 1.26 (m, 2 H, CH2CH2CH2), 2.35 (s, 6 H, 5-Mepz),
2.54 (s, 6 H, 3-Mepz), 5.88 (s, 1 H, CH), 5.95 (s, 2 H, 4-Hpz) ppm.
13C{1H} NMR (CDCl3): δ = –1.1 (SiMe2), 12.1 (5-Mepz), 15.4 (3-
Mepz), 16.6 (CH2), 17.6 (CH2), 19.6 (CH2), 64.6 (CH), 108.2 (C-
G2-[CH(3,5-Me2pz)2PdClMe]8 (9): Compound 9 was synthesized
as described above for 7, starting from 3 (255 mg, 0.091 mmol) and
[PdClMe(cod)] (194 mg, 0.732 mmol), but in hot toluene (20 mL,
80 °C, 3 h). The volatiles were removed under vacuum, and the
residue was washed with pentane to give compound 9 as a pale-
1
grey solid. Yield: 295 mg (80%). H NMR (CDCl3): δ = –0.19 (s,
3 H, SiMe), 0.44 (s, 6 H, SiMe2), 0.47 (s, 6 H, SiMe2), 0.40 (m, 8
H, SiCH2), 0.85 (s, 6 H, PdMe), 1.11 (m, 10 H, CH2SiMe2 and
CH2CH2CH2 overlapping), 2.28 (s, 6 H, 3-Mepz aside PdMe) 2.30
(s, 6 H, 5-Mepz), 2.33 (s, 6 H, 5-Mepz), 2.44 (s, 6 H, 3-Mepz aside
PdCl), 5.78 (s, 2 H, 4-Hpz), 5.80 (s, 2 H, 4-Hpz), 5.93 (s, 2 H, CH)
ppm. 13C{1H} NMR (CDCl3): δ = –5.4 (PdMe), –5.3 (SiMe), –1.5
(SiMe2), –1.7 (SiMe2), 11.5 (5-Mepz), 12.1 (5-Mepz), 14.0 (3-Mepz),
15.0 (3-Mepz), 17.8 (CH2), 18.5 (CH2), 18.8 (CH2), 20.3 (CH2), 63.4
(CH), 106.8 (C-4pz), 107.5 (C-4pz), 138.1 (C-5pz), 139.9 (C-5pz),
4 ), 140.8 (C-5 ), 153.4 (C-3 ) ppm. IR (KBr): ν = 1559 (s, C=N)
˜
pz
pz
pz
cm–1. MS (ESI+/TOF, CH2Cl2/MeOH/NH4HCOO 5 m): m/z =
1966.16 [M + H2O]+, 1241.78 [2 + H]+, 994.57 [M + K]2+
.
C64H108Cl8N16Pd4Si5 (1951.4): calcd. C 39.39, H 5.58, N 11.48;
found C 40.03, H 5.35, N 10.59.
G2-[CH(3,5-Me2pz)2PdCl2]8 (6): Dendritic compound 6 was syn-
thesized as described above for 4, starting from 3 (200 mg,
0.071 mmol) and [PdCl2(cod)] (163 mg, 0.571 mmol), and was iso-
1559 (s, C=N) cm–1.
1
151.3 (C-3pz) ppm. IR (KBr):
ν =
˜
lated as an orange solid. Yield: 236 mg (79%). H NMR (CDCl3):
C152H276Cl8N32Pd8Si13 (4052.2): calcd. C 45.05, H 6.87, N 11.06;
found C 44.23, H 6.27, N 10.56.
δ = –0.19 (s, 3 H, SiMe), 0.53 (m, 8 H, SiCH2), 0.68 (s, 12 H,
SiMe2), 1.26 (m, 10 H, CH2SiMe2 and CH2CH2CH2 overlapping),
2.37 (s, 12 H, 5-Mepz), 2.54 (s, 12 H, 3-Mepz), 5.92 (br. s, 6 H, 4-
Hpz and CH overlapping) ppm. 13C{1H} NMR (CDCl3): δ = –5.1
(SiMe), –1.4 (SiMe2), 12.2 (5-Mepz), 15.3 (3-Mepz), 17.8 (CH2), 18.4
(CH2), 18.5 (CH2), 19.9 (CH2), 64.5 (CH), 108.2 (C-4pz), 141.1 (C-
X-ray Crystallographic Studies: Single crystals of 4 suitable for X-
ray diffraction studies were obtained by slow diffusion of pentane
into a dichloromethane solution of the palladium complex at room
temperature. A summary of the crystal data, data collection and
refinement parameters is given in Table 3. A suitable crystal was
covered with mineral oil and mounted in the N2 stream of a
Bruker–Nonius Kappa-CCD diffractometer equipped with an area
5 ), 153.4 (C-3 ) ppm. IR (KBr): ν = 1559 (s, C=N) cm–1.
˜
pz
pz
C144H252Cl16N32Pd8Si13 (4215.5): calcd. C 41.03, H 6.03, N 10.63;
found C 40.50, H 6.02, N 9.87.
Me3Si-[CH(3,5-Me2pz)2PdClMe] (7): Diethyl ether (30 mL) was detector and an Oxford Cryostream 700 unit; data were collected
added to [PdClMe(cod)] (56 mg, 0.21 mmol) and ligand 1 (65 mg,
0.30 mmol) in a Schlenk tube at room temperature to give a clear
yellowish solution. After 15 min, a white precipitate started to ap-
by using graphite-monochromated Mo-Kα radiation (λ =
0.71069 Å) at 200 K with an exposure time of 10 s per frame (7 sets;
354 frames; φ and ω scans, 2° scan width). Raw data were corrected
Eur. J. Inorg. Chem. 2010, 1881–1887
© 2010 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.eurjic.org
1885

A. Sánchez-Méndez, E. de Jesús, J. C. Flores, P. Gómez-Sal
FULL PAPER
[4]
[5]
[6]
a) C. Pettinari, R. Pettinari, J. Organomet. Chem. 2005, 249,
663; b) A. Otero, J. Fernández-Baeza, A. Antiñolo, J. Tejada,
A. Lara-Sánchez, Dalton Trans. 2004, 1499.
a) C. Pettinari, R. Pettinari, J. Organomet. Chem. 2005, 249,
525; b) H. R. Bigmore, S. C. Lawrence, P. Mountford, C. S.
Tredget, Dalton Trans. 2005, 635.
For some recent examples in different fields, see: a) A. D. Scho-
field, M. L. Barros, M. G. Cushion, A. D. Schwarz, P. Mount-
ford, Dalton Trans. 2009, 85; b) D. L. Reger, E. A. Foley, M. D.
Smith, Inorg. Chem. 2009, 48, 936; c) T. Godau, F. Platzmann,
F. W. Heinemann, N. Burzlaff, Dalton Trans. 2009, 254; d) L.
Maria, C. Fernandes, R. Garcia, L. Gano, A. Paulo, I. C. San-
tos, I. Santos, Dalton Trans. 2009, 603; e) H.-J. Xu, Y. Cheng,
J.-F. Sun, B. A. Dougan, Y.-Z. Li, X.-T. Chen, Z.-L. Xue, J.
Organomet. Chem. 2008, 693, 3851; f) M. P. Conley, C. T.
Bruns, R. F. Jordan, Organometallics 2007, 26, 6750; g) E. Cav-
ero, S. Uriel, P. Romero, J. L. Serrano, R. Giménez, J. Am.
Chem. Soc. 2007, 129, 11608.
A. Sánchez-Méndez, G. F. Silvestri, E. de Jesús, F. J.
de la Mata, J. C. Flores, R. Gómez, P. Gómez-Sal, Eur. J. Inorg.
Chem. 2004, 3287.
a) D. L. Reger, R. F. Semeniuc, M. D. Smith, J. Organomet.
Chem. 2003, 666, 87; b) D. L. Reger, R. F. Semeniuc, M. D.
Smith, J. Chem. Soc., Dalton Trans. 2002, 476.
a) M. A. Casado, V. Hack, J. A. Camerano, M. A. Ciriano, C.
Tejel, L. A. Oro, Inorg. Chem. 2005, 44, 9122; b) J. A. Cam-
erano, M. A. Casado, M. A. Ciriano, L. A. Oro, Dalton Trans.
2006, 5287.
A. Sánchez-Méndez, J. M. Benito, E. de Jesús, F. J. de la Mata,
J. C. Flores, R. Gómez, P. Gómez-Sal, Dalton Trans. 2006,
5379.
for Lorentzian and polarization effects. The structure was solved
by direct methods, completed by subsequent difference Fourier
techniques, and refined by full-matrix least squares on F2 with
SHELXL-97.[21] Anisotropic thermal parameters were used in the
last cycles of refinement for the non-hydrogen atoms. Hydrogen
atoms were found in the difference Fourier map and refined with
isotropic parameters. All calculations were performed by using the
WinGX program.[22] CCDC-742206 (for 4) contains the supple-
mentary crystallographic data for this paper. These data can be
obtained free of charge from The Cambridge Crystallographic
Data Centre via www.ccdc.cam.ac.uk/data_request/cif.
Table 3. Crystal data and structure refinement for compound 4.
Empirical formula
Formula mass
Color
Temperature [K]
Wavelength [Å]
Crystal system
Space group
Unit cell dimensions
a [Å]
C14H24Cl2N4PdSi
453.76
orange
200.0(2)
0.71069
monoclinic
P21/n
[7]
[8]
[9]
9.152(5)
b [Å]
c [Å]
16.471(5)
13.208(5)
β [°]
90.608(7)
1940.3(14)
4
1.553
1.295
Volume [Å3]
Z
[10]
[11]
Ρcalcd. [g/cm3]
µ [mm–1]
F(000)
920
a) A. Sánchez-Méndez, E. de Jesús, J. C. Flores, P. Gómez-Sal,
Inorg. Chem. 2007, 46, 4793; b) A. Sánchez-Méndez, E.
de Jesús, J. C. Flores, P. Gómez-Sal, Eur. J. Inorg. Chem. 2010,
141.
A. Sánchez-Méndez, A. M. Ortiz, E. de Jesús, J. C. Flores, P.
Gómez-Sal, Dalton Trans. 2007, 5658.
Crystal size [mm]
θ range [°]
Limiting indices
0.54ϫ0.45ϫ0.36
5.08–27.49
–11ՅhՅ11
–21ՅkՅ21
[12]
[13]
[14]
–17ՅlՅ17
Reflections collected/unique
Reflections observed
Completeness to θ [%]
Refinement method
Data/restraints/parameters
Goodness of fit on F2
Final R[a] indices [IϾ2σ(I)]
R indices (all data)
36924/4420 (Rint = 0.1304)
3455 [IϾ2σ(I)]
99.3
J. M. Benito, E. de Jesús, F. J. de la Mata, J. C. Flores, R.
Gómez, Organometallics 2006, 25, 3045.
full-matrix least squares on F2
4420/0/295
a) S. Tsuji, D. C. Swenson, R. F. Jordan, Organometallics 1999,
18, 4758; b) W. de Graaf, J. Boersma, W. J. J. Smeets, A. L.
Spek, G. van Koten, Organometallics 1989, 8, 2907.
a) N. Arroyo, F. Gómez de la Torre, F. A. Jalón, B. R. Man-
zano, B. Moreno-Lara, A. M. Rodríguez, J. Organomet. Chem.
2000, 603, 174; b) G. Minghetti, M. A. Cinellu, A. L. Bandini,
G. Banditelli, F. Demartin, M. Manassero, J. Organomet.
Chem. 1986, 315, 387.
For example, see: a) M. T. Reetz, G. Lohmer, R. Schwickardi,
Angew. Chem. Int. Ed. Engl. 1997, 36, 1526; b) G. S. Smith,
S. F. Mapolie, J. Mol. Catal. A 2004, 213, 187; c) V. Maraval,
R. Laurent, A. M. Caminade, J. P. Majoral, Organometallics
2000, 19, 4025.
1.147
[15]
[16]
[17]
R1 = 0.0378, wR2 = 0.0899
R1 = 0.0583, wR2 = 0.1059
Largest diff. peak and hole [e/Å3] 0.697 and –1.288
2
2
[a] R1 = Σ||Fo| – |Fc||/Σ|Fo|; wR2 = {[Σw(Fo – Fc )]/[Σw(Fo2)2]}1/2
.
Acknowledgments
This work was financially supported by the Ministerio de Ciencia
e Innovación (project CTQ2008-02918/BQU) and the Universidad
de Alcalá (FPI grant to A. S.-M.). P. G.-S. is also indebted to the
“Factoria de Cristalización” (Consolider-Ingenio 2010).
a) A. W. van der Made, P. W. N. M. van Leeuwen, J. Chem.
Soc., Chem. Commun. 1992, 1400; b) B. Alonso, I. Cuadrado,
M. Morán, J. Losada, J. Chem. Soc., Chem. Commun. 1994,
2575; c) D. Seyferth, T. Kugita, A. L. Rheingold, G. P. A. Yap,
Organometallics 1995, 14, 5362.
[18]
[19]
a) D. Drew, J. R. Doyle in Inorganic Syntheses (Ed.: F. A. Cot-
ton), McGraw-Hill, New York, 1972, vol. 13, p. 47; b) R. E.
Rülke, J. M. Ernsting, A. L. Spek, C. J. Elsevier, P. W. N. M.
van Leeuwen, K. Vrieze, Inorg. Chem. 1993, 32, 5769.
a) A. Otero, J. Fernández-Baeza, A. Antiñolo, J. Tejeda, A.
Lara-Sánchez, L. Sánchez-Barba, E. Martínez-Caballero,
A. M. Rodríguez, I. López-Solera, Inorg. Chem. 2005, 44, 5336;
b) A. Otero, J. Fernández-Baeza, A. Antiñolo, J. Tejeda, A.
Lara-Sánchez, L. Sánchez-Barba, A. M. Rodríguez, M. A.
Maestro, J. Am. Chem. Soc. 2004, 126, 1330; c) A. Otero, J.
Fernández-Baeza, A. Antiñolo, F. Carrillo-Hermosilla, J. Te-
jeda, A. Lara-Sánchez, L. Sánchez-Barba, A. M. Rodríguez,
I. López-Solera, Inorg. Chem. 2002, 41, 5193; d) A. Otero, J.
[1] a) G. R. Newkome, C. N. Moorefield, F. Vögtle, Dendrimers
and Dendrons: Concepts, Syntheses, Applications, Wiley-VCH,
Weinheim, 1996; b) J. M. J. Fréchet, D. A. Tomalia, Dendrimers
and other Dendritic Polymers, Wiley, Chichester, 2002.
[2] a) K. Inoue, Prog. Polym. Sci. 2000, 25, 453; b) special issues
on Dendrimers and Nanoscience in D. Astruc, C. R. Chim. 2003,
6, 709–1212; c) J. M. J. Fréchet, J. Polym. Sci., Part A: Polym.
Chem. 2003, 41, 3713; d) special issue on Dendrimers and Den-
dritic Polymers: Design, Properties and Applications in J. P. Ma-
joral, New J. Chem. 2007, 31, 1041–1378.
[3] S. Trofimenko, Scorpionates: The Coordination Chemistry of
Polypyrazolylborate Ligands, Imperial College Press, London,
1999.
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www.eurjic.org
© 2010 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Eur. J. Inorg. Chem. 2010, 1881–1887

Dendritic [Bis(pyrazolyl)methane]palladium Complexes
Fernández-Baeza, J. Tejeda, A. Antiñolo, F. Carrillo-Hermos-
illa, E. Díaz-Barra, A. Lara-Sánchez, M. Fernández-López, J.
Chem. Soc., Dalton Trans. 2000, 2367.
[21] G. M. Sheldrick, SHELXL-97, Program for Crystal Structure
Refinement, University of Göttingen, Göttingen, 1997.
[22] WinGX System: L. J. Farrugia, J. Appl. Crystallogr. 1999, 32,
837.
[20] D. P. Perrin, W. L. F. Armarego, Purification of Laboratory
Chemicals, 3rd ed., Pergamon Press, Oxford, 1988.
Received: January 25, 2010
Published Online: March 18, 2010
Eur. J. Inorg. Chem. 2010, 1881–1887
© 2010 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.eurjic.org
1887