Frechet-type pallado-dendrimers containing bis(pyrazolyl)methane ligands

Article abstract of DOI:10.1002/ejic.200900869

Neutral and cationic {bis(3,5-dimethylpyrazol-l-yl)methane}palladium(II) complexes of general formula [PdClX[RCH(3,5Me₂pz)₂}] (X = Cl or Me) or [PdMe(MeCN)[RCH(3,5-Me₂pz)₂}][BAr ^f₄], where

Full text of DOI:10.1002/ejic.200900869

FULL PAPER
DOI: 10.1002/ejic.200900869
Fréchet-Type Pallado-Dendrimers Containing Bis(pyrazolyl)methane Ligands
Alberto Sánchez-Méndez,[a] Ernesto de Jesús,*[a] Juan C. Flores,*[a] and Pilar Gómez-Sal[a]
Keywords: Dendrimers / N ligands / Palladium / Heck reaction / Pyrazolyl ligands
Neutral and cationic {bis(3,5-dimethylpyrazol-1-yl)methane}-
palladium(II) complexes of general formula [PdClX{RCH(3,5-
methods in some cases. These palladium complexes have
been evaluated as catalyst precursors in the Heck reaction
Me2pz)2}](X=ClorMe)or[PdMe(MeCN){RCH(3,5-Me2pz)2}]- between para-iodotoluene and methyl acrylate. The active
[BArf4], where R is a benzyl or benzyloxycarbonyl group or a
poly(aryl ether) Fréchet-type dendron, have been synthe-
sized and fully characterized, including by X-ray diffraction
catalytic species formed from these precursors are apparently
not coordinated to the bis(pyrazolyl)methane ligands.
sado used a different approach to synthesize carbosilane
dendrimers with bis- or tris(pyrazolyl)borate rhodium com-
plexes.[17]
The application of dendrimers containing transition
metal atoms in catalysis has been stimulated by the possibil-
ity of catalyst recovery, especially by using nanofiltration
techniques,[18,19] and the likelihood of obtaining specific
dendrimer effects.[3,20] A stable dendritic ligand–metal coor-
dination is usually a prerequisite for most of these applica-
tions. We recently reported the X-ray structures of the
Introduction
The incorporation of transition metal atoms into dendri-
mers has attracted much attention in the light of possible
applications in advanced materials, biomedicine, and cataly-
sis.[1–4] Metal binding is achieved by means of a large vari-
ety of anchoring ligands, which themselves modulate the
steric and electronic properties of the first coordination
sphere of the metal centers. Our recent work in this field
has focused on metal–dendrimer linkages based on N-do-
nor ligands, such as diketiminato,[5] imido,[6] or (pyridin-2-
yl)methanimine.[7]
Poly(pyrazol-1-yl)borates and related compounds consti-
tute an important and versatile class of N-donor ligands
with an extensively developed coordination chemistry.[8]
Their neutral and isoelectronic counterparts, poly(pyrazol-
1-yl)alkanes, have also received significant attention during
the last few years[9] encouraged by synthetic advances[10]
and a wide range of attractive applications.[11,12] Despite
their availability, however, poly(pyrazolyl) ligands have ra-
rely been used in the chemistry of dendrimers or related
compounds. We have combined scorpionato ligands with
dendrimers according to the strategy used by Reger and
co-workers to prepare multitopic ligands and polynuclear
compounds by taking advantage of the facile functionaliza-
tion of the methine bridging carbon atom in tris(pyrazol-1-
yl)methanes.[13,14] According to a similar strategy, we func-
tionalized the bridging methylene carbon atom of bis(pyr-
azol-1-yl)methanes with poly(aryl ether) dendrons (Fréchet
dendrons) and used these ligands to form monometallic
nickel(II)[15] or molybdenum complexes.[16] Ciriano and Ca-
{bis(pyrazol-1-yl)methane}palladium
complexes
4–6
(Scheme 1), which differ in the size of the poly(aryl ether)
substituents (zeroth, first, and second generation, respec-
tively).[21] As the accessibility of metal centers varies with
the size of the dendritic ligand coordinated to them, we
reasoned that these complexes might be useful for examin-
ing the stability of bis(pyrazol-1-yl)methane coordination
to palladium under the reductive conditions of a Heck reac-
tion. The results of this study are reported herein together
with full details of the synthesis and characterization of 4–
6 and other related neutral and cationic palladium(II) com-
plexes.
Results and Discussion
Synthesis of Ligands and Palladium Compounds
The (benzyl)bis(3,5-dimethylpyrazol-1-yl)methane ligand
I and the related first- to third-generation Fréchet dendrons
II–IV used in this work were obtained by alkylation of the
bromobenzyl derivatives Gn-Br[22] with LiCH(3,5-Me2pz)2,
as reported elsewhere (Scheme 1).[15] Ester 1 was synthe-
sized from benzyl bromide and the carboxylate Na[CH(3,5-
Me2pz)2(COO)] in a reaction which took 2 d to complete in
refluxing thf. In contrast, formation of the G1 analogue 2
was not possible under the same conditions, and the maxi-
[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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The solubility of these compounds in the above solvents
increases with the molecular size of the dendritic substitu-
ent.
The neutral methyl complexes 8–12 are fairly stable in
chlorinated solvents despite the tendency of methylpalla-
dium complexes to decompose in such solvents by Pd–Me/
Pd–Cl exchange, with concomitant precipitation of black
Pd0.[7c,23] Cationic methyl complexes 13–16 are somewhat
less stable under such conditions and, for instance, complex
13 partially decomposes after several weeks in CDCl3 to
give a complex mixture of products from which single crys-
tals of the dimer 17 were obtained. The molecular structure
of 17 was obtained by X-ray diffraction methods and is
discussed below. The formation of this dimer probably oc-
curs via an intermediate similar to that proposed in
Scheme 2. Indeed, a new group of two resonances, as would
be expected for the two nonequivalent CH2 protons of the
proposed intermediate, were found to appear at δ = 4.80
2
3
2
[dd, JH,H = 13.5, JH,H = 7.2 Hz] and 5.08 (dd, JH,H
=
3
1
13.5, JH,H = 7.5 Hz) ppm in the H NMR spectrum of
samples of 13 in CDCl3 after 2–3 weeks.
Scheme 1. Synthesis of the palladium complexes.
Scheme 2. Proposed pathway for the formation of the dimetallic
complex 17 by decomposition of 13 in [D1]chloroform (counter-
anion = [BArf4]–).
mum yield of this ligand (21%) was achieved after 4 d in
refluxing acetone. Moreover, compound 2 was always iso-
Both pyrazolyl rings are equivalent in the 1H and
lated contaminated with small amounts of the carboxylic 13C{1H} NMR spectra of the dichlorido complexes 3–7 but
acid CH(3,5-Me2pz)2(COOH). In view of these results, the give rise to two sets of resonances in monomethyl deriva-
preparation of higher-generation analogues of ligands 1 and tives 8–16 due to the absence of a mirror plane in the latter
2 was not attempted.
complexes. Thus, the resonance for the Me3 protons at δ ≈
The palladium(II) dichloride complexes 3–7 were synthe- 2.5 ppm in 3–7 is split into two singlets in 8–16, with that
sized by treating the corresponding bis(pyrazolyl)methanes at higher field corresponding to the Me3 group adjacent to
with 1 equiv. of [PdCl2(COD)] in warm toluene, whereas the the Pd–Me (δ ≈ 2.3 ppm) or Pd–NCMe groups (δ ≈
chlorido(methyl)palladium(II) complexes 8–12 were ob- 2.1 ppm). For the same reason, the methylene protons of
tained from [PdClMe(cod)] at room temperature in diethyl the benzyl group or their analogues in the Gn dendrons are
ether (cod = η4-1,5-cyclooctadiene; Scheme 1). The ad- diastereotopic in the asymmetrically substituted complexes
dition of Na[BArf4] [Arf = 3,5-(CF3)2C6H3] to dichloro- 8–16. The chemical shifts corresponding to the dendron nu-
methane solutions of 9–12 in the presence of acetonitrile clei remain basically unmodified upon coordination of the
afforded the cationic methyl(acetonitrile) complexes 13–16 free ligands to the metal center, with the exception of those
by chloride abstraction. All these complexes were obtained belonging to the most internal moieties [–ArCH2CH(3,5-
in good to excellent yields as air-stable, hygroscopic, yellow- Me2pz)2 or >–CH2OC(O)CH(3,5-Me2pz)2]. The most sig-
orange (3–7 and 13–16) or white solids (8–12). They are nificant changes involve the 3-Me (∆δ ≈ +0.5 ppm), methyl-
insoluble in alkanes, scarcely soluble in diethyl ether, solu- ene (∆δ ≈ +1.7 ppm), and ortho-protons of the inner benzyl
ble in aromatics, and very soluble in chlorinated solvents. group (∆δ ≈ +0.5 ppm), and the methylene (∆δ ≈ +3 ppm),
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Fréchet-Type Pallado-Dendrimers Containing Bis(pyrazolyl)methane Ligands
methine (∆δ ≈ –3 ppm), pz-C5 (∆δ ≈ +2 ppm), pz-C3 (∆δ ≈ Crystal Structures of 3–6 and 17
+5 ppm), and ipso-carbon atoms of the same benzyl group
The molecular structures of the G0–G2 series of PdCl2
(∆δ ≈ –3 ppm) for 4–7 and 9–16, respectively. These changes
are more pronounced for the dichlorido complexes and are
attributed to a combination of deshielding and anisotropic
effects caused by the chlorido ligand and the positioning
upon coordination of the pyrazolyl rings, respectively.
The anisotropy resulting from the increasing number of
aryl groups surrounding the metal center in a G0–G3 series
of complexes also has a small effect on the chemical shifts
of nuclei situated at the focal point of the molecules. The
general trend is a small, but steady and consistent, shift of
the proton and carbon resonances to higher field, as can be
seen, for instance, for the Me3 group of the G0–G3 series
complexes 4–6 have been reported previously[21] and data
are given here for comparative purposes only. The molecu-
lar structure of 3 consists of discrete monometallic mole-
cules (Figure 1), whereas that of 17 contains a cationic di-
mer (Figure 2). The structural parameters defining the
[CH(3,5-Me2pz)2]PdCl2 moieties are fairly similar for the
five complexes compared in Table 1 (3–6 and 17), with the
palladium atoms exhibiting rather square-planar geome-
tries. The Pd[(NN)2C] palladacycles adopt pronounced boat
1
4–7: δaverage = 2.59, 2.57, 2.52, and 2.51 ppm for H and
δaverage = 15.4, 15.3, 15.3, and 15.2 ppm for 13C.
Compounds 1–16 were also characterized by IR spec-
troscopy, where an intense νas(C=N) absorption at around
1560 cm–1 was observed, and mass spectrometry (APCI+/
MS for 1–6 and 8–11, ESI+/MS for 7, and ESI+-TOF/MS
for 12–16). However, whereas the molecular cation [M –
BArf4]+ was detected in the case of the ionic compounds
12–16, only typical fragmentation patterns of [L2PdXY]
complexes were observed for the neutral complexes 3–11.
For instance, dichlorido complexes 3–7 fragmented by loss
of one or two chloro atoms, followed in some cases by coor-
dination of methanol or by recombination to give dimetallic
halide-bridged structures such as [M2 – Cl]+ or [{M – Cl}2 –
Cl]2+. Chlorido(methyl) derivatives 8–12 produced compar-
able fragments by loss of methyl groups or chloro atoms. In
addition, peaks corresponding to the bis(pyrazolyl) ligands
and their fragmentation by loss of a pyrazolyl ring were
generally observed for all palladium complexes.
Figure 1. Molecular structure of [PdCl2{PhCH2OC(O)CH(3,5-
Me2pz)2}] (3).
Figure 2. Molecular structure of [(Pd(µ-Cl){PhCH2CH(3,5-Me2pz)2})2][BArf4]2 (17). The BArf4– ions have been omitted for clarity.
Eur. J. Inorg. Chem. 2010, 141–151
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FULL PAPER
Table 1. Selected bond lengths [Å] and angles [°] for compounds 3–6 and 17.
3
4
5
6
17[a]
Pd–Cl(1)
Pd–Cl(2)
2.2734(9)
2.2894(9)
2.2883(16)
2.2797(16)
2.281(2)
2.292(2)
2.2826(12)
2.2852(15)
2.3419(12)
Pd–Cl(1i)
Pd(1)···Pd(1i)
Pd–N(1)
Pd–N(3)
C(11)–N(2)
C(11)–N(4)
Cl(1)–Pd–Cl(2)
Cl(1)–Pd–Cl(1i)
N(1)–Pd–N(3)
Cl(2)–Pd–N(3)
Cl(1)–Pd–N(1)
Cl(1)–Pd–N(3)
Cl(1i)–Pd–N(1)
N(2)–C(11)–N(4)
Pd···C(11)···C(12)···C(13)
Pd(1)–Cl(1)–Pd(1i)
2.3365(12)
3.42
2.017(4)
2.015(4)
1.466(7)
1.465(6)
2.032(3)
2.021(3)
1.441(4)
1.443(5)
90.00(3)
2.031(5)
2.027(5)
1.458(7)
1.457(7)
89.10(6)
2.046(7)
2.012(6)
1.451(9)
1.463(10)
90.29(8)
2.038(3)
2.018(3)
1.451(5)
1.454(5)
89.43(5)
86.16(5)
87.43(16)
86.13(11)
91.16(8)
92.56(8)
85.69(19)
91.87(15)
93.16(14)
86.3(3)
91.05(19)
92.2(2)
85.92(14)
92.34(10)
92.10(10)
92.95(12)
93.36(12)
109.2(4)
127.7
110.6(3)
91.9
109.6(4)
112.0
110.3(6)
115.6
108.9(3)
114.5
93.84(5)
[a] Symmetry i is –x + 1, –y + 2, –z + 1.
conformations in which the ester or benzyl group attached drimers[4] in this process has been followed by several stud-
to the methine carbon atom C(11) occupies an axial posi- ies on peripheral-[27–30] or core-metalated[31] dendrimers, as
tion, thereby avoiding the steric hindrance that would arise well as on composite materials obtained by anchoring the
in the equatorial positions with the adjacent methyl groups latter to inorganic or organic supports[32,33] or encapsulat-
at the 5-position of the pyrazolyl rings. This steric repulsion ing Pd nanoparticles inside dendrimers.[34]
confers rigidity on the metallacycle as no boat-to-boat con-
Complexes 3–16 were tested as catalysts in the Heck re-
formational exchange is observed in solution. The substitu- action between para-iodotoluene and methyl acrylate in the
ents on C(11) are oriented asymmetrically in relation to the presence of NEt3 as base under the conditions summarized
palladacycle, with the dihedral angle defined by the in Table 2. Methyl (E)-3-(4-methyphenyl)-2-propenoate
Pd···C(11) molecular axes and the C(12)–C(13) bonds (or (methyl 4-methylcinnamate) was the unique reaction prod-
axis for 3) being in the range of 112.0–115.6° for 4–6, some- uct, with neither the β-disubstituted nor the (Z) isomer be-
1
what wider (127.6°) for 17, and narrower (91.9°) for ester 3. ing detected by GC or H NMR analysis. It is important
The same asymmetrical arrangement of the benzyl group to note that the precipitation of varying amounts of Pd
observed for 4 is found in structures of tetrahedral nicke- black was observed in all cases. The conversions observed
l(II)[15] and octahedral molybdenum(0)[16] complexes con- after 23 h are summarized in Table 2 except for those for
taining ligand I, although their different coordination envi- the ester compounds 3 and 8, which showed the lowest con-
ronment yields broader or narrower N–M–N angles (ap- versions (62 and 83%, respectively). The conversions after
prox. 94 and 79°, respectively) than those found in the 2 h are also given for the G1 complexes. The performance
structures of the square-planar Pd complexes listed in of the remaining catalysts after 23 h is similar and indepen-
Table 1 (approx. 86°).
dent of the size or nature of the precursor.
The structure of 17 is centrosymmetric, consisting of a
dimetallic central cation, formed by two chlorido-bridged
subunits, and two [BArf4]– counterions (see Figure 2). The
most remarkable differences between this structure and
those of the neutral compounds 3–6 are the longer Pd–Cl
bonds (approx. 2.34 vs. 2.28 Å), the narrower Cl–Pd–Cl an-
gle (approx. 86° vs. 90°), and the above-mentioned dihedral
angle due to the asymmetric positioning of the benzyl
group.
Table 2. Heck coupling of methyl acrylate and 4-iodotoluene.[a]
Catalyst
Conversions (%) after 23 h[b]
G0
G1 (after 2 h) G1
G2
G3
4–7 ([PdCl2])
90
93
57
80
81
90
94
95
90
86
93
94
94
95
9–12 ([PdMeCl])
13–16 ([PdMe(NCMe)]+) 90
[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]% Determined by GC.
Evaluation of Dendronized Ligands in the Pd-Catalyzed
Heck Reaction
The Heck–Mizoroki reaction[24] is a fundamental palla-
The reaction profiles were determined by periodic GC
dium-catalyzed reaction for the olefination of aryl halides monitoring, and some of them are shown in Figure 3. The
that has found widespread use in organic synthesis.[25] The dashed line in Figure 3a represents the profile of a control
pioneering work by Reetz and co-workers[26] using Pd den- reaction obtained under the same conditions by using
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Fréchet-Type Pallado-Dendrimers Containing Bis(pyrazolyl)methane Ligands
PdCl2 in the absence of ligand as catalyst. The profiles dif- trile, which is a poor solvent for poly(aryl ether) dendrons
fer appreciably with the nature of the palladium precursor, and promotes the collapse of their structures, as has been
as illustrated by the G1 complexes 5, 10, and 14 in Fig- shown by PGSE diffusion NMR experiments (PGSE =
ure 3a. Thus, PdCl2 complexes 4–7 (and also 3 and PdCl2) pulse-gradient spin-echo) and fluorescence techniques.[36,37]
afforded slower rates at early reaction stages than the neu- Thus, studies carried out with pyrene-cored poly(aryl ether)
tral or cationic PdMeX complexes 9–16. For instance, the monodendrons have revealed that G3 and G4 poly(aryl
conversions reached after 2 h with the G1 complexes 10 and ether)s dissolved in acetonitrile are only partially permeable
14 were around 80% compared with 57% for 5 or 40% to the passage of small oxygen molecules. We therefore pro-
for PdCl2. In contrast, the generation of the dendron was pose that the initial reduction of PdII to Pd0 is accompanied
essentially irrelevant, as exemplified by the G0–G3 series 9– by decoordination of the bis(pyrazolyl)methane ligand from
12 in Figure 3b.
the palladium center to explain the similar behavior of all
the catalytic precursors. In the absence of good stabilizing
ligands, the observed formation of Pd0 aggregates and met-
allic Pd precipitates is easily explainable.
The mechanistic considerations made by Reetz and
de Vries for the Heck reaction under ligand-free conditions
are therefore applicable here.[38] A key point of their argu-
ment is the existence of equilibria between higher-order pal-
ladium species (i.e., palladium nanoparticles) of low reactiv-
ity and lower-order species (such as monomeric or dimeric
species) of high reactivity.[39] The effect of these equilibria
is that high concentrations of Pd are counterproductive and
result in decreased turnover frequencies because of a shift
of these equilibria towards the formation of aggregates and
Pd black.[40] The behavior of the above complexes at Pd
concentrations ranging from 1 to 0.01 mol-% is illustrated
with complex 14 in Figure 4. A reduction in metal loading
from 1 to 0.1 mol-% barely alters the reaction profile, and
the catalytic system is fairly active even at 0.01 mol-%. Of
more interest, however, is that the turnover frequencies in-
crease notably upon lowering the Pd concentrations. Thus,
for metal concentrations of 1, 0.5, 0.1, and 0.01 mol-%, the
respective TOF values are 80, 133, 667, and 1050 h–1,
respectively, at a fixed conversion of 20%, and 4.1, 8.3, 39.5,
and 244.8 h–1, respectively, after 23 h.
Figure 3. Effect of the nature of the palladium precursor and the
dendron generation on the conversion profiles exemplified by (a)
the G1 complexes 5, 10, and 14, and (b) the G0–G3 series 9–12,
respectively. The dashed line represents the profile obtained under
the same conditions for PdCl2.
The slower initial rates observed for the PdCl2 complexes
might be explained by their higher resistance to undergo
reduction to form the Pd0 active species involved in the Pd0/
PdII catalytic cycle.[35] The almost invariant reaction profile
with dendritic generation is, however, more intriguing. The
reactivity of core-substituted dendrimers should be affected,
at least after a critical size,[4] by the restricted accessibility
to the metal center imposed by the dendritic substituents.
Figure 4. Effect of the Pd concentration on the conversion by using
the cationic precursor 14.
We noted above the existence of slight differences in the
Indeed, we have shown in previous studies how [bis(pyrazol- reaction profiles in Figure 3 at early reaction stages de-
1-yl)methane]NiII or -PdII complexes are partially enclosed pending on the nature of the Pd precursor. For that reason,
in CDCl3 solution or the solid state by the dendritic arms of we performed a final experiment involving the repeated ad-
the poly(aryl ether) dendrons to which they are linked.[15,21] dition of fresh substrate to the reaction medium once the
Moreover, the Heck reactions were performed in acetoni- previous catalytic cycle was complete (48–72 h). These re-
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A. Sánchez-Méndez, E. de Jesús, J. C. Flores, P. Gómez-Sal
FULL PAPER
loading cycles were repeated up to six times, and the conver- dendrons of up to the third generation. These complexes
sions were measured by GC after 2 and 24 h after re-ad- have been studied as catalysts in the Heck reaction of para-
dition of substrates in each cycle. The results obtained with iodotoluene and methyl acrylate in acetonitrile. Several ob-
the G0–G3 series of cationic complexes 9–12 (Figure 5a) servations point to decoordination of the dendronized bi-
and plain PdCl2 (Figure 5b) are quite similar. Thus, the s(pyrazolyl) ligands at earlier stages of the catalytic reaction
conversions reached after 2 h tend to decrease from one to and to a “ligand-free” Heck mechanism involving the for-
the next cycle (for instance, average TOFs are 295, 175, 95, mation of Pd aggregates: (a) the reaction profiles are essen-
61, 75, and 33 h–1 for 12) but remain fairly constant after tially independent of the dendron size, (b) the precipitation
24 h, with somewhat higher values for the odd-generation of Pd black is observed in all cases, (c) the turnover fre-
dendrons G1 (10) and G3 (12). It is worth mentioning that, quencies increase at lower catalyst concentrations, and (d)
after storing the reaction vials for 1.5 months, the last run the conversions attained with these complexes and palla-
yielded comparable conversions for each generation of cata- dium dichloride are quite similar, except in the initial stages
lytic system derived from 9–12. These results show that the of the reaction, as shown in the consecutive cycles involving
influence of the precursor nature on the reaction kinetics is the addition of fresh substrate.
essentially limited to the first cycle, probably because de-
There is considerable evidence that phosphanes, N-
composition of the precursors after this initial cycle leads heterocyclic carbenes, and other ligands used in the Heck
to catalytic systems with a similar composition. The ligands and other Pd-catalyzed C–C coupling reactions form part
might nevertheless play some minor role in the equilibria of the truly active catalytic species under certain conditions,
between Pd species by interacting, to different degrees, with, especially at low temperatures. Nevertheless, many metal–
for instance, the Pd nanoparticles, thus explaining the small ligand complexes decompose to form Pd0 aggregates that
differences observed between dendron generations.
are precursors of the true molecular catalysts. This fact
complicates the design of, for instance, dendritic catalysts
that are recoverable by nanofiltration as these techniques
rely on stable ligand coordination.
Experimental Section
Reagents and General Techniques: All operations were performed
under argon by using Schlenk or dry-box techniques. Unless other-
wise stated, reagents were obtained from commercial sources and
used as received. Compounds Na[BArf4] [Arf = 3,5-(CF3)2C6H3],[41]
CH2(3,5-Me2pz)2,[10] and CH(3,5-Me2pz)2COOH,[42] dendrons Gn-
Br[22] and Gn-CH(3,5-Me2pz)2 (I–IV, n = 0–3),[15] and complexes
[PdCl2(cod)] (cod = η4-1,5-cyclooctadiene),[43] [PdClMe(cod)],[44]
and [PdCl2{Gn-CH(3,5-Me2pz)2}] (4–7)[21] were prepared accord-
ing to literature procedures. Solvents were dried prior to use and
distilled under argon as described elsewhere.[45] NMR spectra were
recorded with Varian Unity 500+, Varian Unity VR-300, or Varian
Unity 200 NMR spectrometers. Chemical shifts (δ) are reported in
ppm relative to SiMe4 and were measured relative to the 13C and
residual 1H resonances of the deuterated solvents. The following
abbreviations/notations are used: Ph refers to the aromatic ring of
terminal benzyl groups, Ar to internal rings of benzyl ethers, and
ipso refers to the first ring position on going from the didentate
pyrazolyl ligand. IR spectra were recorded with a Perkin–Elmer
FT-IR Spectrum-2000 spectrophotometer. Elemental analyses and
mass spectra were performed by the Microanalytical Laboratories
of the University of Alcalá (MLUAH) with a Heraeus CHN-O-
Rapid microanalyzer and a Thermoquest–Finningan Automass
Multi (APCI) or Agilent G3250AA LC/MSD TOF Multi (ESI)
mass spectrometer. The progress of the Heck reactions was deter-
mined with a Chrompack CP 9001 gas chromatograph by 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 detec-
tor temperatures: 250 and 260 °C, respectively; oven temperature
program: 100 °C/1 min, 10 °C/min ramp, 240 °C/10 min.
Figure 5. Catalytic conversions (%) after 2 and 24 h in successive
cycles after reloading the reaction media with fresh substrate. Cata-
lysts: (a) G0–G3 series of complexes 9–12 at 0.1 mol-% Pd and (b)
PdCl2 at 1 mol-% Pd.
Preparation of Benzyl Bis(3,5-dimethylpyrazol-2-yl)acetate [G0-
OC(O)CH(3,5-Me2pz)2] (1): A solution of CH(3,5-Me2pz)2COOH
(735 mg, 2.96 mmol) in thf (20 mL) was added to a suspension of
NaH (71 mg, 2.96 mmol) in the same solvent (15 mL) at 0 °C. After
Conclusions
We have reported the synthesis of a series of neutral and
cationic palladium coordination compounds with bis(pyr-
azol-1-yl)methane ligands embedded in poly(benzyl ether) stirring for 2 h, an excess of benzyl bromide was added from a
146 Eur. J. Inorg. Chem. 2010, 141–151
www.eurjic.org
© 2010 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim

Fréchet-Type Pallado-Dendrimers Containing Bis(pyrazolyl)methane Ligands
syringe (0.42 mL, 3.5 mmol) and the mixture maintained at reflux
for 2 d. The resulting solution was then cooled, the solvent removed
in vacuo, and the crude solid extracted with pentane (2ϫ25 mL).
Compound 1 precipitated as a white solid after concentration and
cooling of the solution, and was recrystallized from pentane to
eliminate the excess of BzBr. Compound 1 is soluble in alkanes,
ethers, and aromatic and chlorinated organic solvents. Yield:
502 mg (50%). C19H22N4O2 (338.41): calcd. C 67.44, H 6.55, N
16.56; found C 67.43, H 6.61, N 16.35. 1H NMR (CDCl3): δ = 2.07
(s, 6 H, pz-Me3), 2.18 (s, 6 H, pz-Me5), 5.31 (s, 2 H, CH2), 5.82 (s,
2 H, pz-H4), 6.94 (s, 1 H, CH), 7.25–7.40 (m, 5 H, Ph) ppm.
13C{1H} NMR (CDCl3): δ = 11.0 (pz-Me5), 13.6 (pz-Me3), 68.1
(CH), 73.3 (CH2), 107.5 (pz-C4), 128.3 and 128.4 (o-, m- and p-Ph),
134.8 (ipso-Ph), 141.1 (pz-C5), 148.3 (pz-C3), 164.7 (C=O) ppm. IR
Preparation of [PdClMe{G0-OC(O)CH(3,5-Me2pz)2}] (8): Diethyl
ether (30 mL) was added to [PdClMe(cod)] (50 mg, 0.19 mmol) and
ligand 1 (68 mg, 0.20 mmol) in a Schlenk tube at room temp. After
a few minutes, a solid started to precipitate from the solution. The
mixture was stirred overnight, then the solvent was removed under
vacuum, and the unreacted ligand and free cod were removed by
washing the residue with pentane (2ϫ15 mL). Compound 8 was
isolated as a white solid, which is insoluble in alkanes and slightly
and very soluble in diethyl ether and chlorinated solvents, respec-
tively. Yield: 86 mg (91%). C20H25ClN4O2Pd (495.32): calcd. C
1
48.50, H 5.09, N 11.31; found C 48.22, H 4.95, N 11.21. H NMR
(CDCl3): δ = 0.88 (s, 3 H, PdMe), 2.28 (s, 3 H, pz-Me3 adjacent to
PdMe) 2.36 (s, 3 H, pz-Me5), 2.37 (s, 3 H, pz-Me5), 2.45 (s, 3 H,
pz-Me3 adjacent to PdCl), 5.50 (s, 2 H, CH2), 5.84 (s, 2 H, pz-H4),
(KBr): ν = 1761 (vs, C=O), 1563 (s, C=N), 1456 (m, C=C) cm–1. 6.00 (s, 2 H, pz-H4), 6.35 (s, 1 H, CH), 7.3 (m, 3 H, Ph), 7.4 (m, 2
˜
MS (APCI in CH2Cl2 + MeOH/H2O, 3:1): m/z = 339 [M +
H, Ph) ppm. 13C{1H} NMR (CDCl3): δ = –6.0 (PdMe), 11.0, 11.5
(pz-Me5), 13.9, 14.8 (pz-Me3), 66.3 (CH), 70.2 (CH2), 107.5, 108.0
(pz-C4), 128.5, 128.6, 129.1 (o-, m-, p-Ph), 134.5 (ipso-Ph), 139.8,
H]+, 243 [M – Me2pz]+.
Preparation of G1-OC(O)CH(3,5-Me2pz)2 (2): Na[CH(3,5-Me2pz)2-
COO] (353 mg, 1.31 mmol), prepared as described above and iso-
lated as a white solid, and dendritic wedge G1-Br (500 mg,
1.30 mmol) were refluxed in acetone (30 mL) for 4 d. A white solid
precipitated during the course of the reaction. The solvent was then
removed in vacuo and the crude solid extracted with dichlorometh-
ane (2ϫ15 mL) to give an oily residue after removal of the solvent,
which was treated and washed with cold pentane (2ϫ15 mL) to
give compound 2 as a white solid. Compound 2 is partially soluble
in alkanes, and soluble in ether, acetone, and chlorinated organic
solvents. Persistent small amounts of CH(3,5-Me2pz)2COOH re-
mained after purification of 2. Yield: 151 mg (21%). 1H NMR
(CDCl3): δ = 2.08 (s, 6 H, pz-Me3), 2.16 (s, 6 H, pz-Me5), 4.97 (s,
4 H, PhCH2O), 5.26 (s, 2 H, ArCH2), 5.82 (s, 2 H, pz-H4), 6.53 (t,
141.2 (pz-C5), 152.7, 152.8 (pz-C3), 163.9 (C=O) ppm. IR (KBr): ν
˜
= 1749 (vs, C=O), 1620 (w, C=C), 1564 (s, C=N), 1465 (m, C=C),
1311, 1228 (s, C–O) cm–1. MS (APCI in CH2Cl2 + MeOH/H2O,
3:1): m/z = 512 [M – Me + MeOH]+, 477 [M – Me – Cl +
MeOH]+, 339 [M – PdClMe + H]+, 243 [M – PdClMe – Me2pz]+.
Preparation of [PdClMe{Gn-CH(3,5-Me2pz)2}] (9–12): These com-
pounds were synthesized as described above for 8, starting from the
amount of the corresponding chelating ligand Gn-CH(3,5-Me2pz)2
[n = 0 (I), 1 (II), 2 (III), 3 (IV)] indicated below and [PdClMe(cod)].
The reaction was very slow with ligand III, due to its limited solu-
bility, and the preparation of compound 12 was carried out simi-
larly but in warm (80 °C) toluene and in the dark. Purification of
11 and 12 also included washing with cold diethyl ether. Com-
pounds 9–12 were isolated as white solids, which are insoluble in
alkanes, methanol, and diethyl ether and soluble in toluene and
chlorinated solvents.
4
4JH,H = 2.0 Hz, 1 H, p-Ar), 6.57 (d, JH,H = 2.0 Hz, 2 H, o-Ar),
6.96 (s, 1 H, CH), 7.25–7.40 (m, 10 H, Ph) ppm. 13C{1H} NMR
(CDCl3): δ = 11.0 (pz-Me5), 13.5 (pz-Me3), 67.9 (CH), 70.1
(PhCH2O), 73.3 (CH2), 101.9 (p-Ar), 106.9 (o-Ar), 107.6 (pz-C4),
127.6, 128.0, 128.6 (o-, m-, p-Ph), 136.6 (ipso-Ph), 137.1 (ipso-Ar),
141.2 (pz-C5), 148.5 (pz-C3), 160.0 (m-Ar), 164.7 (C=O) ppm. IR
[PdClMe{G0-CH(3,5-Me2pz)2}] (9): G0-CH(3,5-Me2pz)2 (I; 70 mg,
0.24 mmol) and [PdClMe(cod)] (54 mg, 0.20 mmol). Yield: 85 mg
(94%). C19H25ClN4Pd (451.31): calcd. C 50.57, H 5.58, N 12.41;
(KBr): ν = 1767 (vs, C=O), 1563 (s, C=N), 1597, 1453 (vs, C=C),
˜
1
1164, 1060 (vs, C–O–C) cm–1. MS (ESI+-TOF in CH2Cl2/MeOH/
NH4HCOO 5 m): m/z = 573.25 [M + Na]+, 551.26 [M +
H]+.
found C 50.52, H 5.59, N 11.92. H NMR (CDCl3): δ = 1.03 (s, 3
H, PdMe), 1.95 (s, 3 H, pz-Me5) 2.03 (s, 3 H, pz-Me5), 2.38 (s, 3
H, pz-Me3 adjacent to PdMe), 2.50 (s, 3 H, pz-Me3 adjacent to
PdCl), 4.98 (dd, 2JH,H = 13.6, 3JH,H = 6.9 Hz, 1 H, CH2), 5.66 (dd,
Preparation of [PdCl2{G0-OC(O)CH(3,5-Me2pz)2}] (3): Ester 1
(68 mg, 0.2 mmol) and [PdCl2(cod)] (50 mg, 0.175 mmol) were
mixed in toluene (40 mL) and the mixture refluxed for 2 h. After
cooling the resulting orange solution to room temp., the solvent
was removed in vacuo and the residue washed with pentane
(2ϫ10 mL) to eliminate the cod by-product and the unreacted li-
gand. Compound 3 was isolated as a yellow-orange solid, which is
insoluble in alkanes and slightly and readily soluble in aromatic
and chlorinated solvents, respectively. Orange monocrystals were
obtained after recrystallization from CH2Cl2/pentane by the two-
layer diffusion technique. Yield: 82 mg (91%). C19H22Cl2N4O2Pd
(515.73): calcd. C 44.25, H 4.30, N 10.86; found C 44.02, H 4.30,
3
2JH,H = 13.6, JH,H = 8.6 Hz, 1 H, CH2), 5.74 (s, 1 H, pz-H4), 5.83
3
3
(s, 1 H, pz-H4), 6.04 (dd, JH,H = 6.9, JH,H = 8.6 Hz, 1 H, CH),
7.1 (m, 2 H, Ph), 7.2 (m, 3 H, Ph) ppm. 13C{1H} NMR (CDCl3):
δ = –6.7 (PdMe), 10.9, 11.2 (pz-Me5), 14.3, 15.3 (pz-Me3), 42.8
(CH2), 69.0 (CH), 106.9, 107.4 (pz-C4), 127.6, 128.8, 129.2 (o-,
m-, p-Ph), 134.6 (ipso-Ph), 138.7, 140.6 (pz-C5), 152.8 (pz-C3) ppm.
IR (KBr): ν = 1618 (m, C=C), 1561 (s, C=N), 1460 (s, C=C) cm–1.
˜
MS (APCI in CH2Cl2 + MeOH/H2O, 3:1): m/z = 468 [M – Me +
MeOH]+, 447 [M – Cl + MeOH]+, 433 [M – Cl – Me +
MeOH]+, 199 [M – PdClMe – Me2pz]+.
[PdClMe{G1-CH(3,5-Me2pz)2}] (10): G1-CH(3,5-Me2pz)2 (II;
229 mg, 0.45 mmol), [PdClMe(cod)] (120 mg, 0.45 mmol). Yield:
270 mg (90%). C33H37ClN4O2Pd (663.56): calcd. C 59.73, H 5.62,
1
N 10.74. H NMR (CDCl3): δ = 2.37 (s, 6 H, pz-Me5), 2.59 (s, 6
H, pz-Me3), 5.70 (s, 2 H, CH2), 5.96 (s, 2 H, pz-H4), 6.43 (s, 1 H,
CH), 7.3 (m, 3 H, Ph), 7.4 (m, 2 H, Ph) ppm. 13C{1H} NMR N 8.44; found C 59.43, H 5.77, N 8.21. 1H NMR (CDCl3): δ =
(CDCl3): δ = 11.6 (pz-Me5), 15.2 (pz-Me3), 66.6 (CH), 71.3 (CH2), 1.00 (s, 3 H, PdMe), 1.94 (s, 3 H, pz-Me5) 2.00 (s, 3 H, pz-Me5),
108.6 (pz-C4), 128.3, 128.6, 129.4 (o-, m-, p-Ph), 133.9 (ipso-Ph),
141.7 (pz-C5), 155.0 (pz-C3), 162.9 (C=O) ppm. IR (KBr): ν = 1755
2.35 (s, 3 H, pz-Me3 adjacent to PdMe), 2.46 (s, 3 H, pz-Me3 adja-
2
cent to PdCl), 4.88 (A part of an AB system, JH,H = 11.8 Hz, 2
˜
(vs, C=O), 1617 (m, C=C), 1567 (s, C=N), 1470 (m, C=C), 1315, H, PhCH2O), 4.95 (B part of an AB system, 2JH,H = 11.8 Hz, 2 H,
1234 (s, C–O) cm–1. MS (APCI in CH2Cl2 + MeOH/H2O, 3:1): m/z
PhCH2O), 5.06 (dd, JH,H = 13.6, JH,H = 7.3 Hz, 1 H, CH2), 5.38
2
3
= 995 [M2 – Cl]+, 512 [M – Cl + MeOH]+, 477 [M – Cl2
MeOH]+, 339 [M – PdCl2 + H]+, 243 [M – PdCl2 – Me2pz]+.
+
(dd, 2JH,H = 13.6, JH,H = 8.6 Hz, 1 H, CH2), 5.68 (s, 1 H, pz-H4),
3
5.81 (s, 1 H, pz-H4), 6.00 (dd, JH,H = 7.3, JH,H = 8.6 Hz, 1 H,
3
3
Eur. J. Inorg. Chem. 2010, 141–151
© 2010 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.eurjic.org
147

A. Sánchez-Méndez, E. de Jesús, J. C. Flores, P. Gómez-Sal
FULL PAPER
CH), 6.42 (d, JH,H = 2.0 Hz, 2 H, o-Ar), 6.48 (t, JH,H = 2.0 Hz,
Preparation of [PdMe(MeCN){Gn-CH(3,5-Me2pz)2}][BArf4] (13–
4
4
1 H, p-Ar), 7.25–7.45 (m, 10 H, Ph) ppm. 13C{1H} NMR (CDCl3): 16): The cationic compounds 13–16 were synthesized by using the
δ = –7.0 (PdMe), 10.8, 11.2 (pz-Me5), 14.1, 15.2 (pz-Me3), 42.7
(CH2), 68.6 (CH), 70.0 (PhCH2O), 102.0 (p-Ar), 106.9, 107.5 (pz-
following general procedure starting from the amounts indicated
below: 1 equiv. of Na[BArf4] was added to a solution of the corre-
C4), 108.1 (o-Ar), 127.4, 128.0, 128.6 (o-, m-, p-Ph), 136.8 (ipso-Ar, sponding precursor [PdClMe{Gn-CH(3,5-Me2pz)2}] (9–12) in
ipso-Ph), 139.0, 140.8 (pz-C5), 152.1, 152.2 (pz-C3), 160.0 (m-Ar) CH2Cl2 (25 mL) in the presence of an excess of CH3CN. The solu-
ppm. IR (KBr): ν = 1561 (s, C=N), 1595, 1450 (vs, C=C), 1154,
tion was stirred at room temp. for 1 h and the NaCl precipitate
removed by filtration. The solvent was evaporated under reduced
pressure and the crude solid washed with pentane (2ϫ15 mL).
Compounds 13–16 were isolated as orange solids, which are insolu-
ble in alkanes and diethyl ether, although the third-generation com-
pound is slightly soluble, and soluble in toluene and chlorinated
solvents. As corresponds to a noncoordinating anion, identical
spectroscopic data were obtained for the [BArf4]– ion for all four
compounds. These data are as follows and will not be reproduced
˜
1047 (vs, C–O–C) cm–1. MS (APCI in CH2Cl2 + MeOH/H2O, 3:1):
m/z = 680 [M – Me + MeOH]+, 507 [M – PdClMe + H]+, 411 [M –
PdClMe – Me2pz]+.
[PdClMe{G2-CH(3,5-Me2pz)2}] (11): G2-CH(3,5-Me2pz)2 (III;
171 mg, 0.18 mmol), [PdClMe(cod)] (49 mg, 0.18 mmol). Yield:
270 mg (90%). C61H61ClN4O6Pd (1088.05): calcd. C 67.34, H 5.65,
N 5.15; found C 66.84, H 5.50, N 5.17. 1H NMR (CDCl3): δ =
1.00 (s, 3 H, PdMe), 1.93 (s, 3 H, pz-Me5) 1.97 (s, 3 H, pz-Me5),
2.33 (s, 3 H, pz-Me3 adjacent to PdMe), 2.45 (s, 3 H, pz-Me3 adja-
1
later. H NMR (CDCl3): δ = 7.49 (br. s, 4 H, Arf-Hp), 7.68 (br. s,
Arf-Ho) ppm. 13C{1H} NMR (CDCl3): δ = 117.4 (Arf-Cp), 124.4
(q, JC,F = 272.1 Hz, CF3), 129.0 (q, 2JC,F = 29.0 Hz, Arf-Cm), 134.7
2
cent to PdCl), 4.82 (A part of an AB system, JH,H = 12.3 Hz, 2
H, ArCH2O), 4.90 (B part of an AB system, 2JH,H = 12.3 Hz, 2 H,
(Arf-Co), 161.6 (q, JC,B = 50.7 Hz, Arf-Cipso) ppm. IR (KBr): ν =
˜
2
3
ArCH2O), 5.01 (s, 8 H, PhCH2O), 5.08 (dd, JH,H = 13.4, JH,H
=
1357 (s), 1279 (vs), 1128 (vs, B–C, C–F) cm–1.
2
3
7.3 Hz, 1 H, CH2), 5.38 (dd, JH,H = 13.4, JH,H = 8.3 Hz, 1 H,
CH2), 5.67 (s, 1 H, pz-H4), 5.78 (s, 1 H, pz-H4), 5.99 (dd, JH,H
=
3
[PdMe(MeCN){G0-CH(3,5-Me2pz)2}][BArf4] (13): Compound
9
3
4
7.3, JH,H = 8.3 Hz, 1 H, CH), 6.40 (d, JH,H = 1.8 Hz, 2 H, G0-
o-Ar), 6.45 (t, JH,H = 1.8 Hz, 1 H, G0-p-Ar), 6.55 (t, JH,H
(51 mg, 0.11 mmol), Na[BArf4] (101 mg, 0.11 mmol), and CH3CN
(2 mL). Yield: 136 mg (94%). C53H40BF24N5Pd (1320.1): calcd. C
48.22, H 3.05, N 5.30; found C 47.84, H 2.97, N 5.12. 1H NMR
(CDCl3): δ = 1.08 (s, 3 H, PdMe), 1.89 (s, 3 H, pz-Me5) 1.98 (s, 3
H, pz-Me5), 2.18 (s, 3 H, pz-Me3 adjacent to Pd-NCMe), 2.28 (s,
3 H, MeCN), 2.30 (s, 3 H, pz-Me3 adjacent to PdMe), 4.50 (dd,
4
4
=
4
2.2 Hz, 2 H, G1-p-Ar), 6.62 (d, JH,H = 2.2 Hz, 4 H, G1-o-Ar),
7.25–7.45 (m, 20 H, Ph) ppm. 13C{1H} NMR (CDCl3): δ = –7.0
(PdMe), 10.7, 11.1 (pz-Me5), 14.1, 15.1 (pz-Me3), 42.7 (CH2), 68.6
(CH), 69.8 (ArCH2O), 70.0 (PhCH2O), 101.4 (G1-p-Ar), 101.9
(G0-p-Ar), 106.3 (G1-o-Ar), 106.9 (pz-C4), 107.4 (pz-C4), 108.1
(G0-o-Ar), 127.6, 128.0, 128.6 (o-, m-, p-Ph), 134.8 (G0-ipso-Ar),
136.7 (ipso-Ph), 139.3 (G1-ipso-Ar), 139.0, 140.8 (pz-C5), 152.1,
152.2 (pz-C3), 159.9 (G0-m-Ar), 160.2 (G1-m-Ar) ppm. IR (KBr):
3
2
2JH,H = 14.0, JH,H = 6.5 Hz, 1 H, CH2), 5.16 (dd, JH,H = 14.0,
3JH,H = 8.8 Hz, 1 H, CH2), 5.76 (s, 1 H, pz-H4), 5.86 (s, 1 H, pz-
3
3
H4), 6.04 (dd, JH,H = 6.5, JH,H = 8.8 Hz, 1 H, CH), 6.9 (m, 2 H,
Ph), 7.2 (m, 3 H, Ph) ppm. 13C{1H} NMR (CDCl3): δ = –3.6
(PdMe), 3.0 (CH3CN), 10.5, 10.9 (pz-Me5), 13.5, 15.1 (pz-Me3),
42.9 (CH2), 68.9 (CH), 107.3, 108.3 (pz-C4), 121.3 (MeCN), 128.5,
128.7, 129.3 (o-, m-, p-Ph), 133.3 (ipso-Ph), 140.9, 142.6 (pz-C5),
ν = 1560 (s, C=N), 1596, 1451 (vs, C=C), 1154, 1046 (vs, C–O–C)
˜
cm–1. MS (APCI in CH2Cl2 + MeOH/H2O, 3:1): m/z = 1104 [M –
Me + MeOH]+, 931 [M – PdClMe + H]+, 835 [M – PdClMe –
Me2pz]+.
151.1, 153.3 (pz-C3) ppm. IR (KBr): ν = 1611 (m, C=C), 1568 (m,
˜
C=N), 1465 (m, C=C) cm–1. MS (ESI+-TOF in CH2Cl2/MeOH/
NH4HCOO 5 m): m/z = 457.12 [M – BArf4]+, 446.09 [M – CH4 –
MeCN – BArf4 + HCOO]+, 416.11 [M – MeCN – BArf4]+, 400.08
[M – CH4 – MeCN – BArf4]+, 294.39 [M – PdMe(MeCN) –
BArf4]+, 199.28 [M – PdMe(MeCN) – BArf4 – Me2pz]+.
[PdClMe{G3-CH(3,5-Me2pz)2}] (12): G3-CH(3,5-Me2pz)2 (IV;
276 mg, 0.15 mmol) and [PdClMe(cod)] (41 mg, 0.15 mmol). Yield:
255 mg (88%). C117H109ClN4O14Pd (1937.04): calcd. C 72.55, H
1
5.67, N 2.89; found C 72.14, H 5.42, N 2.46. H NMR (CDCl3): δ
= 1.00 (s, 3 H, PdMe), 1.93 (s, 3 H, pz-Me5) 1.94 (s, 3 H, pz-Me5),
2.32 (s, 3 H, pz-Me3 adjacent to PdMe), 2.45 (s, 3 H, pz-Me3 adja-
2
cent to PdCl), 4.81 (A part of an AB system, JH,H = 12.2 Hz, 2 [PdMe(MeCN){G1-CH(3,5-Me2pz)2}][BArf4] (14): Compound 10
2
H, G1-ArCH2O), 4.88 (B part of an AB system, JH,H = 12.3 Hz,
2 H, G1-ArCH2O), 4.94 (s, 8 H, G2-ArCH2O), 5.00 (s, 16 H,
PhCH2O), 5.22 (br. m, 1 H, CH2), 5.65 (s, 1 H, pz-H4), 5.77 (s, 1
(91 mg, 0.14 mmol), Na[BArf4] (121 mg, 0.14 mmol), and CH3CN
(2 mL). Yield: 163 mg (76%). C67H52BF24N5O2Pd (1532.4): calcd.
1
C 52.52, H 3.42, N 4.57; found C 52.35, H 3.45, N 4.62. H NMR
H, pz-H4), 5.98 (br. t, JH,H ≈ 8.0 Hz, 1 H, CH), 6.41 (d, JH,H
=
(CDCl3): δ = 1.03 (s, 3 H, PdMe), 1.83 (s, 3 H, pz-Me5) 1.98 (s, 3
H, pz-Me5), 2.14 (s, 3 H, pz-Me3 adjacent to Pd-NCMe), 2.23 (s,
3 H, MeCN), 2.27 (s, 3 H, pz-Me3 adjacent to PdMe), 4.26 (dd,
3
4
2.0 Hz, 2 H, G0-o-Ar), 6.47 (t, 4JH,H = 2.0 Hz, 1 H, G0-p-Ar), 6.50
4
4
(t, JH,H = 2.0 Hz, 2 H, G1-p-Ar), 6.55 (t, JH,H = 2.2 Hz, 4 H,
4
3
G2-p-Ar), 6.60 (d, 4JH,H = 2.0 Hz, 4 H, G1-o-Ar), 6.65 (d, JH,H
=
2JH,H = 13.5, JH,H = 6.2 Hz, 1 H, CH2), 4.95 (s, 4 H, PhCH2O),
2.2 Hz, 8 H, G2-o-Ar), 7.25–7.40 (m, 40 H, Ph) ppm. 13C{1H} 5.16 (dd, 2JH,H = 13.5, 3JH,H = 9.1 Hz, 1 H, CH2), 5.75 (s, 1 H, pz-
3
3
NMR (CD Cl3): δ = –7.0 (PdMe), 10.7, 11.1 (pz-Me5), 14.1, 15.1
H4), 5.83 (s, 1 H, pz-H4), 5.96 (dd, JH,H = 6.2, JH,H = 9.1 Hz, 1
(pz-Me3), 42.6 (CH2), 68.5 (CH), 69.8 (G1-ArCH2O), 70.0 (G2-
H, CH), 6.17 (d, 4JH,H = 2.1 Hz, 2 H, o-Ar), 6.56 (t, 4JH,H = 2.1 Hz,
ArCH2O), 70.1 (PhCH2O), 101.3 (G1-p-Ar), 101.5, (G2-p-Ar), 1 H, p-Ar), 7.25–7.40 (m, 10 H, Ph) ppm. 13C{1H} NMR (CDCl3):
101.8 (G0-p-Ar), 106.3 (G1-o-Ar), 106.4 (G2-o-Ar), 106.8, 107.4
δ = –3.6 (PdMe), 2.9 (CH3CN), 10.6, 11.0 (pz-Me5), 13.5, 15.1 (pz-
(pz-C4), 108.0 (G0-o-Ar), 127.5, 128.0, 128.6 (o-, m-, p-Ph), 136.7 Me3), 43.1 (CH2), 68.6 (CH), 70.0 (PhCH2O), 101.6 (p-Ar), 107.3,
(G0-ipso-Ar, ipso-Ph), 139.1 (G2-ipso-Ar), 139.2 (G1-ipso-Ar),
108.2 (pz-C4), 108.1 (o-Ar), 121.3 (MeCN), 127.3, 128.2, 128.7
139.0, 140.8 (pz-C5), 152.0, 152.1 (pz-C3), 159.9 (G0-m-Ar), 160.0 (o-, m-, p-Ph), 135.5 (ipso-Ar), 136.3 (ipso-Ph), 140.7, 142.7 (pz-
(G1-m-Ar), 160.1 (G2-m-Ar) ppm. IR (KBr): ν = 1560 (m, C=N), C5), 151.1, 153.2 (pz-C3), 160.4 (m-Ar) ppm. IR (KBr): ν = 1609
˜
˜
1596, 1451 (vs, C=C), 1154, 1048 (vs, C–O–C) cm–1. MS (ESI+-
(m, C=C), 1564 (m, C=N), 1466 (m, C=C), 1154, 1048 (s, C–O–C)
TOF in CH2Cl2/MeOH): m/z = 1939.66 [M – Cl + K]+, 1917.70 cm–1. MS (ESI+-TOF in CH2Cl2/MeOH/NH4HCOO 5 m): m/z =
[M – Me – Cl + MeOH]+, 1900.70 [M –Cl]+, 1884.67 [M – Cl – 669.22 [M – BArf4]+, 627.28 [M – MeCN – BArf4]+, 612.17 [M –
CH4]+, 1802.77 [M – PdClMe + Na + H]+, 1762.74 [M – PdClMe –
CH4 – MeCN – BArf4]+, 411.21 [M – PdMe(MeCN) – BArf4
–
CH4]+.
Me2pz]+.
148
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© 2010 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Eur. J. Inorg. Chem. 2010, 141–151

Fréchet-Type Pallado-Dendrimers Containing Bis(pyrazolyl)methane Ligands
[PdMe(MeCN){G2-CH(3,5-Me2pz)2}][BArf4] (15): Compound 11
(91 mg, 0.08 mmol), Na[BArf4] (72 mg, 0.08 mmol), and CH3CN
(2 mL). Yield: 130 mg (83%). C95H76BF24N5O6Pd (1956.9): calcd.
4.91 (s, 8 H, G2-ArCH2O), 4.98 (s, 16 H, PhCH2O), 5.08 (over-
lapped m, CH2), 5.70 (s, 1 H, pz-H4), 5.78 (s, 1 H, pz-H4), 5.95 (br.
3
4
dd, JH,H ≈ 9, 7 Hz, 1 H, CH), 6.14 (br. d, JH,H ≈ 2 Hz, 2 H, G0-
1
4
C 58.31, H 3.91, N 3.58; found C 57.99, H 3.53, N 3.47. H NMR
o-Ar), 6.51 (br. t, JH,H ≈ 2 Hz, 1 H, G0-p-Ar), 6.55 (m, 6 H, G1-
(CDCl3): δ = 1.01 (s, 3 H, PdMe), 1.81 (s, 3 H, pz-Me5) 1.95 (s, 3
p-Ar, G2-p-Ar), 6.62 (br. resonance, 12 H, G1-o-Ar, G2-o-Ar),
H, pz-Me5), 2.10 (s, 3 H, pz-Me3 adjacent to Pd-NCMe), 2.18 (s,
7.25–7.40 (m, 40 H, Ph) ppm. 13C{1H} NMR (CDCl3): δ = –3.6
3 H, MeCN), 2.24 (s, 3 H, pz-Me3 adjacent to PdMe), 4.26 (dd, (PdMe), 2.7 (CH3CN), 10.6, 10.9 (pz-Me5), 13.5, 15.0 (pz-Me3),
3
2JH,H = 13.3, JH,H = 6.5 Hz, 1 H, CH2), 4.88 (s, 4 H, ArCH2O),
43.0 (CH2), 68.6 (CH), 69.7 (G1-ArCH2O), 70.0 (G2-ArCH2O),
70.1 (PhCH2O), 101.0 (G1-p-Ar), 101.3, (G2-p-Ar), 101.5 (G0-p-
2
3
4.99 (s, 8 H, PhCH2O), 5.10 (dd, JH,H = 13.3, JH,H = 8.8 Hz, 1
H, CH2), 5.70 (s, 1 H, pz-H4), 5.79 (s, 1 H, pz-H4), 5.95 (dd, JH,H Ar), 106.2 (G1-o-Ar), 106.4 (G2-o-Ar), 107.3, 108.2 (pz-C4), 108.1
3
= 6.5, JH,H = 8.8 Hz, 1 H, CH), 6.14 (d, 4JH,H = 2.2 Hz, 2 H, G0- (G0-o-Ar), 121.4 (MeCN), 127.5, 128.1, 128.6 (o-, m-, p-Ph), 135.6
3
4
o-Ar), 6.49 (t, JH,H = 2.2 Hz, 1 H, G0-p-Ar), 6.56 (br. s, 6 H,
(G0-ipso-Ar), 136.6 (ipso-Ph), 138.8 (G1-ipso-Ar), 138.9 (G2-ipso-
G1-p-Ar, G1-o-Ar), 7.25–7.40 (m, 20 H, Ph) ppm. 13C{1H} NMR Ar), 140.7, 142.7 (pz-C5), 151.1, 153.2 (pz-C3), 160.1 (G0-m-Ar,
(CDCl3): δ = –3.6 (PdMe), 2.9 (CH3CN), 10.5, 10.9 (pz-Me5), 13.5, G1-m-Ar overlapping), 160.2 (G2-m-Ar) ppm. IR (KBr): ν = 1595
˜
15.1 (pz-Me3), 43.1 (CH2), 68.6 (CH), 69.9 (ArCH2O), 70.2
(m, C=C), 1561 (w, C=N), 1452 (m, C=C), 1159, 1050 (s, C–O–C)
(PhCH2O), 101.0 (G1-p-Ar), 101.6 (G0-p-Ar), 106.2 (G1-o-Ar), cm–1. MS (ESI+-TOF in CH2Cl2/MeOH/NH4HCOO 5 m): m/z =
107.3, 108.3 (pz-C4), 108.0 (G0-o-Ar), 121.4 (MeCN), 127.5, 128.2,
128.7 (o-, m-, p-Ph), 135.5 (G0-ipso-Ar), 136.4 (ipso-Ph), 138.9 (G1-
ipso-Ar), 140.8, 142.7 (pz-C5), 152.1, 153.2 (pz-C3), 160.2 (G0-m-
1941.72 [M – BArf4]+, 1900.70 [M – MeCN – BArf4]+, 1884.67 [M –
CH4 – MeCN – BArf4]+.
X-ray Crystallographic Studies: Single crystals of 3–6 suitable for
X-ray diffraction studies were obtained by slow diffusion of pen-
tane or hexane into a dichloromethane solution of the palladium
complex at room temperature, whereas crystals of 17 incidentally
formed from a sample of 13 in CDCl3 upon standing in an NMR
tube for several weeks. A summary of crystal data, data collection,
and refinement parameters for the structural analysis of 3 and 17
is given in Table 3, whereas those corresponding to 4, 5, and 6 have
been reported previously.[21] Suitable crystals were covered with
mineral oil and mounted in the N2 stream of a Bruker-Nonius
Kappa-CCD diffractometer with area detector, and equipped with
an Oxford Cryostream 700 unit; data were collected by using
graphite-monochromated Mo-Kα radiation (λ = 0.71073 Å), at
200 K, with an exposure time of 20 s per frame (nine sets; 467
Ar), 160.3 (G1-m-Ar) ppm. IR (KBr): ν = 1596 (m, C=C), 1560
˜
(w, C=N), 1454 (m, C=C), 1160, 1051 (s, C–O–C) cm–1. MS (ESI+-
TOF in CH2Cl2/MeOH/NH4HCOO 5 m): m/z = 1093.39 [M –
BArf4]+, 1052.36 [M – MeCN – BArf4]+, 1036.33 [M – CH4
MeCN – BArf4]+, 931.44 [M – PdMe(MeCN) – BArf4 + H]+.
–
[PdMe(MeCN){G3-CH(3,5-Me2pz)2}][BArf4] (16): Compound 12
(86 mg, 0.04 mmol), Na[BArf4] (39 mg, 0.04 mmol), and CH3CN
(2 mL). Yield: 109 mg (97%). C151H124BF24N5O14Pd (2805.9):
1
calcd. C 64.64, H 4.45, N 2.50; found C 64.19, H 4.26, N 2.31. H
NMR (CDCl3): δ = 1.00 (s, 3 H, PdMe), 1.81 (s, 3 H, pz-Me5) 1.96
(s, 3 H, pz-Me5), 2.09 (s, 3 H, pz-Me3 adjacent to Pd-NCMe), 2.12
(s, 3 H, MeCN), 2.22 (s, 3 H, pz-Me3 adjacent to PdMe), 4.22 (br.
dd, 2JH,H ≈ 14, 3JH,H ≈ 6 Hz, 1 H, CH2), 4.86 (s, 4 H, G1-ArCH2O),
Table 3. Crystal data and structure refinement for compounds 3 and 17.
3
17
Empirical formula
Formula mass
Color
C19H22Cl2N4O2Pd
515.71
orange
C50H34BClF24N4Pd
1299.47
orange
Temperature
Wavelength
200(2) K
0.71073 Å
150(2) K
0.71073 Å
¯
Crystal system, space group
Unit cell dimensions
monoclinic, P21/n
a = 8.5493(8) Å
b = 15.0228(14) Å
c = 16.9694(7) Å
β = 90.608(7)°
triclinic, P1
a = 12.4379(12) Å
b = 13.0254(11) Å
c = 17.5787(12) Å
α = 82.859(7)
β = 88.324(7)
γ = 88.559(7)
2823.9(4) Å3
Volume
2179.3(3) Å3
4, 1.572 gcm–3
11.18 cm–1
Z, calculated density
Absorption coefficient
F(000)
2, 1.528 gcm–3
4.93 cm–1
1292
1040
Crystal size
θ range
0.8ϫ0.30ϫ0.2 mm
5.09–27.50°
0.35ϫ0.35ϫ0.25 mm
2.04–27.50°
Limiting indices
–11 Յ h Յ 10, –19 Յ k Յ 19, –22 Յ l Յ 21 –16 Յ h Յ 16, –16 Յ k Յ 16, –22 Յ l Յ 22
Reflections collected/unique
Reflections observed
Absorption correction
Max. and min. transmission
Refinement method
Data/restraints/parameters
Goodness of fit on F2
Final R[a] indices [I Ͼ 2s(I)]
R indices (all data)
Largest diff. peak and hole
17234/4955 [R(int) = 0.0886]
3562
semiempirical
96548/12938 [R(int) = 0.1534]
8918 [I Ͼ 2s(I)]
none
1.566 and 0.739
–
Full-matrix least squares on F2
4955/0/341
Full-matrix least squares on F2
12938/0/730
0.951
1.024
R1 = 0.0401, wR2 = 0.0816
R1 = 0.0711, wR2 = 0.0904
0.930 and –1.092 eÅ–3
R1 = 0.0694, wR2 = 0.1775
R1 = 0.1087, wR2 = 0.2080
1.673 and –1.058 eÅ–3
[a] R1 = Σ||Fo| – |Fc||/Σ|Fo|; wR2 = {[Σω(Fo – Fc )]/[Σω(Fo2)2]}1/2
.
2
2
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149

A. Sánchez-Méndez, E. de Jesús, J. C. Flores, P. Gómez-Sal
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GC. These reloading operations were repeated up to six consecutive
times.
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Acknowledgments
We gratefully acknowledge financial support from the DGI – Min-
isterio de Educación y Ciencia of Spain (project CTQ2008-02918/
BQU) and the Comunidad de Madrid (project S-0505/PPQ/0328-
03). A. S.-M. and P. G.-S. are also indebted to the Universidad de
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Received: September 2, 2009
Published Online: November 25, 2009
Eur. J. Inorg. Chem. 2010, 141–151
© 2010 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
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