Nickel scorpionate complexes containing poly(aryl ether) dendritic substituents

Article abstract of DOI:10.1016/j.jorganchem.2016.07.004

Novel dinitratonickel(II) complexes with bis(pyrazolyl)methane ligands at the focal point of poly(aryl ether) Fréchet dendrons of up to the third generation are reported. The complexes are accessible by direct reaction of the corresponding scorpionate ligand with Ni(NO₃)₂, or by treatment of the dibromidonickel derivatives with AgNO₃, although they reversibly convert to the dibromidos in the presence of KBr. The paramagnetic compounds could be characterized by¹H NMR in solution. The molecular structure of metallodendrimers G0 and G1 [Ni(NO₃)₂{(Gn-dend)CH(3,5-Me₂pz)₂}] have been determined by X-ray diffraction methods. Both structures show an almost identical three-dimensional organization of the –ArCH₂CH(3,5-Me₂pz)₂Ni(NO₃)₂moieties, with the nickel atoms exhibiting a distorted octahedral structure with a scorpionate-κ²and two bidentate nitrato ligands.

Full text of DOI:10.1016/j.jorganchem.2016.07.004

Journal of Organometallic Chemistry 819 (2016) 201e208
Contents lists available at ScienceDirect
Journal of Organometallic Chemistry
journal homepage: www.elsevier.com/locate/jorganchem
Nickel scorpionate complexes containing poly(aryl ether) dendritic
substituents
*
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Alberto Sanchez-Mendez, Juan C. Flores , Pilar Gomez-Sal
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Departamento de Química Organica y Química Inorganica, Universidad de Alcala Campus Universitario, 28871 Alcala de Henares, Madrid, Spain
a r t i c l e i n f o
a b s t r a c t
Article history:
Novel dinitratonickel(II) complexes with bis(pyrazolyl)methane ligands at the focal point of poly(aryl
Received 21 March 2016
Received in revised form
11 July 2016
Accepted 14 July 2016
Available online 16 July 2016
ꢀ
ether) Frechet dendrons of up to the third generation are reported. The complexes are accessible by
direct reaction of the corresponding scorpionate ligand with Ni(NO3)2, or by treatment of the dibro-
midonickel derivatives with AgNO3, although they reversibly convert to the dibromidos in the presence
of KBr. The paramagnetic compounds could be characterized by 1H NMR in solution. The molecular
structure of metallodendrimers G0 and G1 [Ni(NO3)2{(Gn-dend)CH(3,5-Me2pz)2}] have been determined
by X-ray diffraction methods. Both structures show an almost identical three-dimensional organization
of the eArCH2CH(3,5-Me2pz)2Ni(NO3)2 moieties, with the nickel atoms exhibiting a distorted octahedral
structure with a scorpionate-k2 and two bidentate nitrato ligands.
Keywords:
N-ligands
Scorpionates
Bispyrazolylmethane
Dendrimers
Nickel
© 2016 Elsevier B.V. All rights reserved.
1. Introduction
described carbosilane dendritic cores grafting tris- or bis(pyrazolyl)
methane complexes of molybdenum [8a] or palladium at their
The fruitful chemistry of scorpionates was initiated with the
introduction of poly(pyrazol-1-yl)borates by Trofimenko half a
century ago [1]. Subsequent widespread research in the area raised
these versatile di- or tridentate N-donors to the major league of
useful ligands in coordination and organometallic chemistry,
resulting in a plethora of reported complexes of most metals, which
were found suitable for a wide range of applications [2]. More
recently, significant advances in the synthesis of poly(pyrazol-1-yl)
alkanes [3] have decisively facilitated numerous advances with this
new generation of isoelectronic and isosteric, but neutral, scorpi-
onate ligands [4].
We have contributed to the field with studies on dendrimers of
different topologies decorated with scorpionate complexes. The
preparation strategy for the ligands was based on the well known
facile substitution of the respective reactive proton in the methine
[5] or methylene [6] group of tri- or bis-(pyrazolyl)methanes, and
consisted in the functionalization of the bridging carbon atom with
a dendritic scaffold. Other different approaches have been reported
to synthesize carbosilane dendrimers anchoring peripheral bis- or
tris(pyrazolyl)borate complexes of rhodium [7]. Thus, we have also
periphery, respectively, and evaluated the latter as polymetallic
catalysts for the Mizoroki-Heck coupling [8b]. We have also re-
ported monometallic dendrimers based on poly(aryl ether) den-
ꢀ
drons (Frechet dendrons) functionalized at the focal point with
dibromido[bis(pyrazolyl)methane]nickel complexes [9], neutral
and cationic derivatives of palladium(II) [10], and with bis- and
tris(pyrazolyl)methane scorpionates of molybdenum in low and
high oxidation state [11]. The Pd(II) compounds were explored as
catalysts for the Heck reaction [10b], the Ni(II) complexes for
ethylene polymerization [9], and the Mo(VI) metallodendrimers for
catalytic olefin epoxidation [11]. Additionally, the single-crystal
structures of a series of Pd(II) complexes from zeroth (G0) to the
second (G2) generation, showed a similar 3D organization, layer by
layer, on going from the G0 to the G2 structure, with the dendritic
wedges progressively engulfing the metal center [10a]. Similarly, 1H
NMR studies performed with nickel(II) dibromido complexes in
CDCl3 solution, and using the nickel center as a paramagnetic probe
to gather structural information, also led to the conclusion that the
dendrons tend to wrap up the metal center in this solvent [9].
Herein we report on the synthesis and characterization, including
1H NMR data, of the paramagnetic complexes [Ni(NO3)2{(Gn-dend)
CH(3,5-Me2pz)2}] (Gn ¼ G0eG3; pz ¼ pyrazol-1-yl).
* Corresponding author.
E-mail address: juanc.flores@uah.es (J.C. Flores).
http://dx.doi.org/10.1016/j.jorganchem.2016.07.004
0022-328X/© 2016 Elsevier B.V. All rights reserved.

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A. Sanchez-Mendez et al. / Journal of Organometallic Chemistry 819 (2016) 201e208
202
2. Results and discussion
reactions between nickel nitrate and ligands 1e4 (i.e., CH2Cl2,
reflux, 4 h). Nevertheless, the reactions proceed to completion in
acetone at room temperature after 6 h, with a striking color change
of the solution from the deep blue of the dibromidos to a green
solution for the nitrates, and with simultaneous precipitation of
AgBr. The reaction is also quite straightforward in this solvent and
the products are isolated in high yields (ca. 90%), although it is
obvious that a direct synthesis of the nitrates from 1e4 is more
convenient than the two steps procedure. The formation of com-
pounds 9e12 from the dibromidos 5e8 is fully reversible by simply
stirring the acetone solutions of the nitrates in the presence of an
excess of KBr (Scheme 1), in a transformation that is evident to the
naked eye by the corresponding drastic color change. Whilst the
conversion between the two series of complexes is driven by the
precipitation of AgBr on going to the nitrates, the shift back to
dibromidos 5e8 is in agreement with the relatively labile coordi-
nation of the nitrato ligand described for compounds of same type
[12,13]. This lability involves a flexible denticity through the oxygen
2.1. Synthesis and characterization of nickel complexes
The nitrato complexes 9e12 can be readily prepared using the
procedure reported by Baho and Zargarian for the synthesis of a
related compound with interesting chromic properties in solution
[12] (i.e., [Ni(NO3)2{(Ph2C(pz)2}]). Accordingly, addition of 1 equiv
of Ni(NO3)2$6H2O to a dichloromethane solution of chelates 1e4
[9], followed by reflux (Scheme 1), resulted in the steady disap-
pearance of the insoluble nickel precursor with concomitant for-
mation of
a vivid lime-green solution. After workup (see
Experimental Section), complexes 9e12 were isolated as dark green
solids (yields ca. 90%), they are stable to air in the solid and in so-
lution, and are insoluble in alkanes but soluble in chlorinated and
aromatic solvents or in acetone, and slightly soluble in diethyl
ether.
The complexes 9e12 can alternatively be synthesized from the
corresponding nickel dibromido complexes 5e8 by reaction with
two equivalents of AgNO3 (Scheme 1). Interestingly, no progress of
the reaction was observed using the conditions applied in direct
atoms of the nitrate ion (-k k k
2, - 1, or - 0), as has been observed for
related Ni(II) [12,14] and Cu(II) [15] compounds. In fact, we have
founddeither at preparative or at NMR-tube scaledthat the
Scheme 1. Synthesis of dendronized dinitratonickel scorpionate complexes.

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203
reaction of 1 with Ni(NO3)2 in molar ratio 2:1, or the addition of a
second equivalent of 1 to complex 9, both resulted in irresoluble
complex mixtures, most likely involving similar species to those
identified by Zargarian with the NOꢀ3 ligand displaying different
denticities [12].
The C, H, and N elemental analyses, and the IR, UVevis, 1H NMR,
and mass spectrometry spectra are all consistent with the proposed
structures in Scheme 1 for the new complexes. In addition, the
molecular structures of compounds 9 and 10 have been analyzed by
single-crystal X-ray diffraction studies.
A C¼Nasym absorption due to the pz-rings is observed at around
1562 cmꢀ1 in the IR spectra of compounds 9e12. Intense bands
assigned to the vibrations of the aromatic CeC bonds are also
clearly visible, together with absorptions at normal wavenumbers
corresponding to CeOeC ether groups in 10e12. Of more interest,
however, are the NO stretching bands observed at ca. 1035
Fig. 2. UVevis spectra for solutions of 5 and 8 in CH2Cl2 (0.2 mM).
[
nsym(NO2)], at around 1280 [nasym(NO2)], and above 1465 [n(N]O)]
cmꢀ1. The large separation of the two highest-frequency bands
(>185 cmꢀ1) points to a chelating bidentate coordination of the
nitrato ligands in the solid state, as this gap is expected to be
smaller (<120 cmꢀ1) in the unidentate mode [12e16]. Even so, the
KBr pellets prepared for recording the IR spectra of 9e12 turned
from greenish to bluish within a couple of hours, in agreement with
a facile ligand substitution of NOꢀ3 by Brꢀ also in the solid state.
Moreover, the IR spectra of solutions of these complexes in CHCl3
show an additional band at 1380-1350 cmꢀ1, which can be assigned
to nitrate ligands in a monodentate mode of coordination [12,14],
thus supporting the flexible denticity of this ligand in solution. The
isolated complexes gave accurate elemental analyses, and their
ESI(þ) mass spectra also prove the facile removal of the nitrato li-
gands from the nickel coordination sphere, since the most char-
acteristic peak observed for 9e11 corresponds to their elimination
and recombination of the resulting fragment with another biden-
tate ligand and a formate anion from the ionizing agent (i.e.,
[M ꢀ 2(NO3) þ L þ HCOO]þ; L ¼ 1e3). Although ESI MS has not
been informative for complex 12, the MALDI-TOF mass spectrum
recorded in dithranol shows the peak matching for cation
[M þ H2O]þ.
(9e12). Very intense charge transfer transitions are observed at 310
and 355 nm for the dibromido complexes 5e8, whereas the nitrato
compounds display a strong absorption with maximum below
300 nm, which is assigned to a typical
p* ) p aromatic phenyl
group band because it intensifies on going from 9 to 12 (i.e., with
the size of the dendron). As for ded transitions, Tables 1 and 2
collect the band maxima, assignations, and the crystal field pa-
rameters derived from these data. Complexes 9e12 show the ex-
pected three bands for octahedral Ni(II) complexes [17,18], at
around 1065, 680 and 400 nmdthe regions observed for closely
related nitrate compounds [12]dwith the band at 680 nm
featuring a weak shoulder at ca. 790 nm (Fig. 1 and Table 1). The
three main absorptions (l1, l2, and l3, respectively) are due to spin-
allowed ded transitions from the ground state (3A2g) to the excited
3
states (3T2g
,
3T1g(F), and T1g(P), respectively), and the shoulder
corresponds to the spin-forbidden 1Eg ) 3A2g transition, all bands
commonly observed for Ni(II) octahedral coordination environ-
ments [12,17,18]. Although the interpretation of the spectra of
tetrahedral Ni(II) complexes uses to be more challenging because of
the splitting of the ground term (3T1(F)) due to Jahn-Teller distor-
tion, it is quite straightforward in the case of dibromidos 5e8. Their
spectra depict two higher energy bands, at around 535 and 570 nm
(Fig. 2 and Table 2), which has been ordinarily associated to the
same excited term (3T1(P)), split by spin-orbit coupling and the low
symmetry component of the ligand field related with the Jahn-
Teller distortion [17]. In addition, the transition assigned to the to
the second excited state (3A2 at low Dt/B) appears at ca. 1025 nm,
and that of the first band (3T2 ) 3T1(F)) is supposed to occur at too
The contrast in color of the new compounds compared with
their dibromido counterparts suggests differences in the electronic
transitions of the two families of d8 complexes. In fact, their UVevis
spectra display patterns that can be allocated to octahedral and
tetrahedral Ni(II) complexes [17], respectively (Figs. 1 and 2 show
the spectra for the corresponding G0 and G3 compounds). As ex-
pected taking into consideration the Laporte selection rule, the
absorption spectra for solutions in dry CH2Cl2 show more intense
bands for the tetrahedral (5e8) than for the octahedral compounds
low energy to be observed [17]. Crystal field parameters (
D, B, and
b) can be calculated using empirical relationships in the case of the
data for complexes 9e12 [12,18], or estimated from the Tana-
beeSugano diagrams in the case of d8 tetrahedral complexes 5e8
[17]. Accordingly, the obtained values (Table 1) for the octahedral
ligand field splitting (Do
¼
l1), Racah (15B ¼ l2
þ
l3 e 3l1) and
nephelauxetic parameters
(b
¼
Bcomplex/Bfree
,
considering
ion
B(Ni2þ
)
¼ 1042 cmꢀ1 [17]) for complexes 9e12 (Table 1), are
free ion
comparable to those reported for related octahedral complexes
[12,18]. As expected, the ligand field splitting for the tetrahedral
complexes (Dt) is quite smaller. No evidence is observed in the
spectra, for instance, suggesting changes in the coordination
environment with the generation within each series of complexes.
However, the mathematical determination of B for complexes
9e12, appears to indicate a small decrease in interelectronic
repulsion (up to 60 cmꢀ1) with increasing generation of the com-
plex compared to the free ion, which results in slightly more co-
valent metal-ligand bonding on going form 9 to 12, as indicated by
the
b parameter. Such as differences could not be established for
Fig. 1. UVevis spectra for solutions of 8 and 12 in CH2Cl2 (1 mM).

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204
Table 1
Absorption spectral data for octahedral complexes 9e12.a
Complex
Assignment of d-d transitions,
l
(nm)
Crystal field Parametersb
1Eg
)
3A2g
l2
l3
Do(cmꢀ1
)
B(cmꢀ1
)
b
c
l1
)
3T2g
3A2g
3T1g(F) ) 3A2g
3T1g(P) ) 3A2g
9
1065
1064
1063
1063
792
792
790
789
678
678
673
677
397
404
408
411
9390
9398
9407
9407
785
758
743
725
0.75
0.73
0.71
0.70
10
11
12
a
At r.t., 1 ꢁ 10ꢀ3
M
in CH2Cl2.
b
Calculated using empirical relations [12,18].
Spin-forbidden transition.
c
Table 2
Absorption spectral data for tetrahedral complexes 5e8.a
Complex
Assignment of d-d transitions,
3A2 3T1(F)
l
(nm)
Crystal field Parametersb
)
3T1(P) ) 3T1(F)
Dt(cmꢀ1
)
B(cmꢀ1
)
b
9
1024
1027
1028
1025
533 þ 567
537 þ 570
535 þ 569
536 þ 567
10
11
12
5350
930
0.89
a
At r.t., 2 ꢁ 10ꢀ4
M in CH2Cl2.
b
Calculated using Tanabe-Sugano diagram for d8 tetrahedral complexes (C/B ¼ 4.42) at Dt/B ¼ 5.75, and taking the center of the dicomponent band as the transition to
3T1(P) [17].
compounds 5e8 because of the lack of precision in the graphical
estimation of Dt and B. Nevertheless, a lower degree of covalency is
verified with a
NMR spectroscopy can be useful for the characterization of
paramagnetic compounds if the unpaired electron/s has/ve a rela-
tively minor effect on the longitudinal relaxation of the observed
nuclei. This often happens for first-row transition metal complexes
with triply degenerate (T) electronic ground states, for which the
spectra show “fairly sharp” resonances spread over a “reasonably
appear together at the most broadened (Dn1/2 ¼ 350e280 Hz) and
most upfield signal in the spectra (ꢀ3 ppm). The rest of resonances
show narrower linewidths (Dn1/2 < 130 Hz), being all spread in less
than 60 ppm due to hyperfine shift, with that appearing to lowest
field (52 ppm) corresponding to the pz-protons in 4-position, or
that for pz-Me5 shifted upfield (0.5 ppm), relative to their chemical
shift in the diamagnetic free ligands (3.8, 6.1, 5.7, and 2.2 ppm for
CH2, CH, pz-H4, and pz-Me5, respectively [9]; pz-ring numbering in
Scheme 1). Nevertheless, the resonance for the protons of the pz-
Me3 groups was never detected, probably because of an extreme
broadening of the signal caused by the close proximity of the
paramagnetic metal center. At this point it is worth mentioning
that, in agreement with the general behavior commented above,
the protons of the hexacoordinated nickel complexes 9e12 appear
with larger linewidths than those of 5e8 with a tetrahedral metal
environment, although their observation is most likely facilitated
by changes in the coordination mode from nitrato-k2 to nitrato-k1
in solutiondas also suggested by the IR spectra in chlor-
oformdreducing the coordination number around the Ni(II)-spe-
cies. Thus, the most affected resonances, which are due to the
nearest protons to the metal (i.e., eCH2CH(3,5-Me2pz)2 moiety and
ortho protons of the adjacent aryl group), show Dn1/2 values of
110e85 (o-Ar), 350e280 (CH2 and CH overlapping), 35-25 (pz-
Me5), 105-95 Hz (pz-H4), and with pz-Me3 not observed for the
nitrates 9e12, whereas they were 25e20 (o-Ar), 110e70 (CH2), 25-
20 (CH), 7-4 (pz-Me5), 25-20 Hz (pz-H4), and 105-85 Hz (pz-Me3)
for the dibromidos 5e8 [9]. As observed for the dihalides, the
resonances for the remaining protons of the dendrons in 9e12
show chemical shifts and linewidths that gradually approach to the
values found for the free ligands, or related diamagnetic metal
complexes [10,11], as the distance from the paramagnetic center
increases.
b
¼ 0.89 for the tetrahedral compounds (Table 2).
narrow” spectral window [19]. That is the case for many nickel(II
)
complexes with tetrahedral, pseudo-tetrahedral, such as 5e8 [9], or
high-spin (S ¼ 1) pentacoordinate geometries, whereas broader
resonances are expected for octahedral Ni(II) complexes, although
they can also sharpen due to zero-field splitting [20].
Gratifyingly, the 1H NMR spectra of complexes 9e12 showed
well-resolved resonances, which provided useful structural infor-
mation (Fig. 3 depicts the spectrum of 9 as an example). The
assignment of signals has been based on their integrated in-
tensities, on their position in the full series of spectra, and in our
previous experience with dibromidos 5e8. These data confirm the
chemical equivalence of the pz-groups and the presence of a plane
of symmetry bisecting the scorpionate ligand. The CH2CH protons
2.2. X-ray diffraction studies of 9 and 10
Complexes 9 and 10 were analyzed by single-crystal X-ray
diffraction. Figs. 4 and 5 show an ORTEP representation and rele-
Fig. 3. NMR spectrum of 9 in CDCl3 (*H2O from the deuterated solvent).
vant structural data of the molecular structure of the (OC-6-210-
D)-

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A. Sanchez-Mendez et al. / Journal of Organometallic Chemistry 819 (2016) 201e208
205
enantiomers found in the unit cells of trischelates 9 and 10,
respectively.
pz-ring, with dihedral angles defined by the C(12)eC(13) bond and
the Ni(1)$$$C(11) molecular axes and the C(12)eC(13) bonds of
123e124ꢂ.
It is remarkable that the dendritic wedge of the G1 compound
10 is fairly extended, with an average dihedral angle at the ether
linkages (AreOeCePh) of ca. 175ꢂ. In contrast, the PdCl2-analog
showed a much more back-folded orientation of the PhCH2O-arms
to the dendritic core (average AreOeCePh of ca. 75ꢂ), reflecting
conformational flexibility of the dendron [10a].
As in previous findings in the solid state for Pd(II) complexes
containing these ligands [10a], the structural parameters of the
ArCH2CH(3,5-Me2pz)2Ni(NO3)2 unit (Ar ¼ Ph (9), G0-Ar (10)) are
fairly similar for the G0 and G1 nitrates. The structure of both
consists of a discrete molecule with the central nickel atom dis-
playing a quite distorted octahedral geometry owing to the coor-
dination of 4 oxygen and 2 nitrogen atoms from two nitrato-
k
2 and
one scorpionate-
k
2 ligands, respectively. The distortion is caused by
the small bite angle of the bidentate nitrato ligand, thus imposing
an acute OeNieO angle within each of these chelates (ca. 61ꢂ),
whereas the N-donor renders an almost right angle (ca. 91ꢂ). The
cis-OeNieO angle between the two nitrato ligands is smaller when
both oxygen are trans to nitrogen atoms (i.e., O1eNieO5; ca. 84ꢂ),
compared with those formed with one of the oxygen atoms
mutually trans (i.e., with O2 or with O4; 97-91ꢂ), whilst trans-
OeNieO and trans-NeNieO angles are also separated from a
straight angle (ca. 148ꢂ and 161ꢂ, respectively). Nevertheless, the
structures can also be seen as pseudo tetrahedral arrangements of
the four nitrogen atoms around the metal center with
3. Conclusions
The reaction of Ni(NO3)2 with bis(pyrazolyl)methane ligands
dendronized with Frechet-type wedges at the bridging carbon
ꢀ
atom, straightforwardly leads to the corresponding metal-
lodendrimer [Ni(NO3)2{(Gn-dend)CH(3,5-Me2pz)2}] of up to the
third generation (n ¼ 0e3). The compounds are characterized by a
chelating mode of coordination of the nitrato ligands and the
scorpionate N-donor, giving rise to paramagnetic Ni(II) complexes
with a rather distorted octahedral geometry in the solid state. The
nitrato-k2O,O0 bonding appears to be labile, as demonstrated by
facile substitution to form the respective tetrahedral dibromido
Ni(II) complexes in the presence of Brꢀdalthough the trans-
formation can be fully reversed by subsequent treatment with
AgNO3. Despite their octahedral geometry in the solid state, and in
solution as evidenced by UVevis, 1H NMR spectroscopy was suit-
able for the characterization of these paramagnetic complexes,
most likely because Ni(II) species of lower coordination number are
NpzeNi$$$Nnitrate and Nnitrate$$$Ni$$$Nnitrate angles in the range of
133e97ꢂ and 108-105ꢂ, respectively. The average NieNpz (ca.
2.05 Å) and NieO (ca. 2.15 and 2.10 Å) bond distances are similar to
those found in the structure reported for [Ni(NO3)2{(Ph2C(pz)2}],
with two average NieO bond lengths slightly different due to the
somewhat superior trans influence of the pyrazolyl over the nitrato
ligand [12].
The arrangement of the ArCH2CH(3,5-Me2pz)2Ni moiety in 9
and 10 resembles that shown by the Pd(II) complexes mentioned
above [10a], by related complexes of Pd(II) [10b] or Mo(0) [11] with
ligand 1, and even by that found in the structure of the tetrahedral
nickel complex 5 [9]. Thus, the Ni(1)(NN)2C(11) nickellacycle
adopts a boat conformation in which the ArCH2 group attached to
the methine carbon C(11) occupies an axial position, thereby
minimizing steric repulsion with the adjacent pz-Me5 groups. The
boat conformation is also more pronounced on the side of the
methine bridge than on that of the metal center, and the ArCH2
groups are orientated asymmetrically in relation with the nickel-
lacycle, and towards the hemi-space that contains the N(3)eN(4)
involved in solution through changes in denticity from nitrato-
k
2 to
nitrato-
k
1. In addition, the single-crystal structure of the G1 com-
plex shows an arrangement that seems to be assembled taking the
structure of the G0 compound as starting building block at the core.
This study introduce for the first time synthetic and characteriza-
tion aspects of metallodendrimers attaching octahedral scorpio-
nato complexes of nickel(II).
4. Experimental section
4.1. Reagents and general techniques
All operations were performed under an argon atmosphere
using standard Schlenk techniques. Solvents were dried using an
MBraun-Solvent Purification System and deoxygenated prior to
use. Alternatively, solvents and other chemicals were dried and
purified as described elsewhere [21]. Unless otherwise stated,
chemicals were obtained from commercial suppliers and used as
received. The dendronized ligands (Gn-dend)CH(3,5-Me2pz)2
(G0eG3) 1e4 and their respective nickel dibromido complexes
5e8, were prepared according to literature procedures [9]. NMR
spectra were recorded at room temperature (20 ꢂC) using Varian
Mercury 300 or Unity 300 spectrometers. Chemical shifts (d, parts
per million) are quoted relative to SiMe4. Coupling constants (J) are
given in Hertz. The following abbreviations are used: pz refers to
pyrazolic heterocycle, Ph to phenyl moiety of terminal benzyl
groups, Ar to internal rings of benzyl ethers, ipso refers to the first
ring-position on going from the bidentate pyrazolyl ligand
(numbering for the pyrazolyl ring-positions in Scheme 1). IR
spectra were recorded on a PerkineElmer FT-IR Spectrum-2000
spectrophotometer. The UVevis spectra were recorded between
1100 and 300 nm in 1 cm quartz cells on a PerkineElmer Lambda 35
UV/Vis Spectrophotometer. The Analytical Services of the Uni-
Fig. 4. Crystal structure of 9 showing 50% probability thermal ellipsoids. Hydrogen
atoms omitted for clarity. Selected bond [Å] and angles [ꢂ]: Ni(1)eN(3), 2.043(3); Ni(1)
eN(1), 2.076(3); Ni(1)eO(2), 2.089(4); Ni(1)eO(1), 2.105(4); Ni(1)eO(4), 2.113(3);
Ni(1)eO(5), 2.204(4); Ni(1)$$$N(5), 2.475(8); Ni(1)$$$N(6), 2.556(6); N(2)eC(11),
1.470(4); N(4)eC(11) 1.459(4); N(5)eO(3), 1.224(6); N(6)eO(6), 1.233(6); N(3)-Ni(1)-
N(1), 91.8(1); N(3)-Ni(1)-O(1), 160.0(2); N(1)-Ni(1)-O(1), 100.8(2); O(2)-Ni(1)-O(1),
63.0(2); N(3)-Ni(1)-O(4), 102.3(1); O(2)-Ni(1)-O(4), 148.0(2); O(1)-Ni(1)-O(4),
90.7(2); O(1)-Ni(1)-O(5), 82.7(2); N(1)-Ni(1)-O(5), 160.0(1); O(4)-Ni(1)-O(5), 59.2(1);
O(6)-N(6)-O(4), 123.2(4); O(5)-N(6)-O(4), 115.0(4); N(4)-C(11)-N(2), 111.0(3).
ꢀ
versidad de Alcala performed the C, H, and N analyses using a LECO
CHNS-932 microanalyzer, and recorded the high-resolution mass
spectra using an Agilent G3250AA LC/MSD TOF Multi (MALDI and
ESI) spectrometer.

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A. Sanchez-Mendez et al. / Journal of Organometallic Chemistry 819 (2016) 201e208
206
Fig. 5. Crystal structure of 10 showing 50% probability thermal ellipsoids. Hydrogen atoms omitted for clarity. Selected bond [Å] and angles [ꢂ]: Ni(1)eN(3), 2.035(5); Ni(1)eN(1),
2.056(4); Ni(1)eO(2), 2.098(4); Ni(1)eO(1), 2.110(4); Ni(1)eO(4), 2.095(4); Ni(1)eO(5), 2.176(4); Ni(1)$$$N(5), 2.496(5); Ni(1)$$$N(6), 2.521(6); N(2)eC(11), 1.462(6); N(4)eC(11)
1.453(6); N(5)eO(3), 1.219(5); N(6)eO(6), 1.235(6); N(3)-Ni(1)-N(1), 91.0(2); N(3)-Ni(1)-O(1), 160.7(2); N(1)-Ni(1)-O(1), 98.9(2); O(2)-Ni(1)-O(1), 62.0(2); N(3)-Ni(1)-O(4), 102.3(2);
O(2)-Ni(1)-O(4), 148.8(2); O(1)-Ni(1)-O(4), 91.8(2); O(1)-Ni(1)-O(5), 84.7(2); N(1)-Ni(1)-O(5), 163.6(2); O(4)-Ni(1)-O(5), 61.2(2); O(6)-N(6)-O(4), 121.2(6); O(5)-N(6)-O(4), 115.8(5);
N(4)-C(11)-N(2), 110.9(4).
4.2. General procedure for the synthesis and characterization data
for nickel complexes (9e12)
[M ꢀ 2(NO3) þ 2 þ HCOO]þ 1115.4694, found 1115.4681; calcd for
[2 þ H]þ 507.2760, found 507.2763.
The corresponding (Gn-dend)CH(3,5-Me2pz)2 1e4 ligand and
NiNO3$6H2O were combined in a molar ratio 1:1 (quantities of
reagents specified below individually), together with CH2Cl2
(20 mL), and the reaction mixture was stirred and heated to reflux
for 4 h. Back to room temperature, the resulting lime green solution
was evaporated to dryness under vacuum, and the crude residue
washed with hexane and diethyl ether (2 ꢁ 10 mL). The nickel
complexes were isolated as green solids, which can be recrystal-
lized by diffusion of hexane into concentrated CH2Cl2 solutions.
Alternatively, 9e12 can be prepared less straightforwardly by the
reaction of the corresponding nickel dibromido complex 5e8 with
AgNO3 (molar ratio 1:2), in acetone at room temperature during
6 h, followed by the same workup.
4.2.3. [Ni(NO3)2{(G2-dend)CH(3,5-Me2pz)2}] (11)
Ni(NO3)2 (94 mg, 0.32 mmol) and 3 (0.30 g, 0.32 mmol). Yield:
320 mg (90%). Anal. Calcd for C60H58N6NiO12 (1113.83): C, 64.70; H,
5.55; N, 7.55. Found: C, 64.46; H, 5.26; N, 7.34%. 1H NMR (CDCl3):
d
ꢀ3.0 (vbr. s, Dn1/2 ¼ 341 Hz, 3H, CH and CH2 overlapping), 0.6 (br.
s, Dn1/2 ¼ 29 Hz, 6H, pz-Me5), 4.99 (s, 4H, G1-CH2O), 5.06 (s, 4H,
PhCH2O), 6.1 (br. s, Dn1/2 ¼ 106 Hz, 2H, G0-o-Ar), 6.51 (s, 1H, G0-p-
Ar), 6.63 (s, 2H, G1-p-Ar), 6.73 (s, 4H, G1-o-Ar), 7.2e7.8 (m, 20H,
Ph), 51.9 (br. s, Dn1/2 ¼ 103 Hz, 2H, pz-H4), pz-Me3 not observed. IR
(KBr pellet): 1595 (vs, C-Carom), 1562 (s, C]N), 1450 (s, C-Carom),
1523 (s, N]O), 1291 (m, CeO-Casym and NO2asym), 1155 and 1054
(vs, CeO-Csym), and 1027 (s, NO2sym) cmꢀ1. ESI-MS (CH2Cl2/MeOH/
NH4HCOO 5 m
M
): m/z calcd for [M ꢀ 2(NO3) þ 3 þ HCOO]þ
1963.8043, found 1963.8036; calcd for [3 þ H]þ 931.4435, found
931.4431.
4.2.1. [Ni(NO3)2{(G0-dend)CH(3,5-Me2pz)2}] (9)
Ni(NO3)2 (297 mg, 1.02 mmol) and 1 (0.300 g, 1.02 mmol). Yield:
448 mg (92%). Anal. Calcd for C88H22BN6NiO6 (477.10): C, 45.31; H,
4.65; N, 17.61. Found: C, 45.11; H, 4.46; N, 17.98%. 1H NMR (CDCl3):
4.2.4. [Ni(NO3)2{(G3-dend)CH(3,5-Me2pz)2}] (12)
Ni(NO3)2 (59 mg, 0.20 mmol) and 4 (363 mg, 0.20 mmol). Yield:
341 mg (87%). Anal. Calcd for C116H106N6NiO20 (1962.80): C, 70.98;
H, 5.44; N, 4.28. Found: C, 70.95; H, 5.64; N, 4.75%. 1H NMR (CDCl3):
d
ꢀ3.0 (vbr. s, Dn1/2 ¼ 282 Hz, 3H, CH and CH2 overlapping), 0.6 (br.
s, Dn1/2 ¼ 23 Hz, 6H, pz-Me5), 6.9 (br. s, Dn1/2 ¼ 83 Hz, 2H, o-Ph),
7.2e7.5 (m, 3H, m- and p-Ph), 51.9 (br. s, Dn1/2 ¼ 98 Hz, 2H, pz-H4),
pz-Me3 not observed. IR (KBr pellet): 1606 (m, C-Carom), 1562 (s, C]
N), 1467 (vs, C-Carom and N]O ovelapping), 1278 (s, NO2asym), and
d
ꢀ3.0 (vbr. s, Dn1/2 ¼ 353 Hz, 3H, CH and CH2 overlapping), 0.5 (br.
s, Dn1/2 ¼ 35 Hz, 6H, pz-Me5), 5.00 (s, 28H, G1-CH2O, G2-CH2O and
PhCH2O overlapping), 6.1 (br. s, Dn1/2 ¼ 102 Hz, 2H, G0-o-Ar), 6.52
(s, 1H, G0-p-Ar), 6.56 (s, 4H, G2-p-Ar), 6.63 (s, 2H, G1-p-Ar), 6.69 (s,
12H, G1-o-Ar and G2-o-Ar overlapping), 7.2e7.8 (m, 40H, Ph), 51.6
(br. s, Dn1/2 ¼ 95 Hz, 2H, pz-H4), pz-Me3 not observed. IR (KBr
pellet): 1595 (vs, C-Carom), 1562 (s, C]N), 1497 (s, C-Carom and N]
O), 1294 (m, CeO-Casym) 1271 (s, NO2asym), 1155 and 1047 (vs, CeO-
1022 (s, NO2sym) cmꢀ1. ESI-MS (CH2Cl2/MeOH/NH4HCOO 5 m
M): m/
z calcd for [M ꢀ 2(NO3) þ 1 þ HCOO]þ 691.3019, found 691.3011;
calcd for [M ꢀ 2(NO3) þ COOH]þ 397.1174, found 397.1181.
4.2.2. [Ni(NO3)2{(G1-dend)CH(3,5-Me2pz)2}] (10)
Csym and NO2sym) cmꢀ1. ESI-MS (CH2Cl2/MeOH/NH4HCOO 5 m
M)
Ni(NO3)2 (229 mg, 0.788 mmol) and 2 (403 mg, 0.795 mmol).
Yield: 511 mg (94%). Anal. Calcd for C32H34N6NiO8 (689.34): C,
55.76; H, 4.97; N, 12.19. Found: C, 55.50; H, 5.10; N, 11.97%. 1H NMR
was not informative; MALDI-TOF-MS (dithranol): m/z calcd. for
[M þ H2O]þ 1978.6921, found 1978.8170; calcd. for [M þ 3H]þ
1963.7050, found 1963.8016; calcd. for [4 þ H]þ 1779.79, found
1779.90.
(CDCl3):
d
ꢀ3.0 (vbr. s, Dn1/2 ¼ 309 Hz, 3H, CH and CH2 overlapping),
0.6 (br. s, Dn1/2 ¼ 27 Hz, 6H, pz-Me5), 5.1 (br. s, Dn1/2 ¼ 25 Hz, 4H,
PhCH2O), 6.1 (br. s, Dn1/2 ¼ 100 Hz, 2H, o-Ar), 6.58 (s, 1H, p-Ar),
7.2e7.8 (m, 10H, Ph), 51.9 (br. s, Dn1/2 ¼ 97 Hz, 2H, pz-H4), pz-Me3
not observed. IR (KBr pellet): 1607 (m, C-Carom), 1563 (s, C]N),1465
(m, C-Carom and N]O ovelapping), 1279 (m, CeO-Casym and NO2asym
4.3. X-ray crystallographic studies
Single crystals of 9 and 10 suitable for X-ray diffraction studies
were obtained by recrystallization from a mixture CH2Cl2/hexane
(1:1) solutions at room temperature. A summary of crystal data,
overlapping), 1151 and 1060 (s, CeO-Csym), and 1040 (s, NO2sym
)
cmꢀ1. ESI-MS (CH2Cl2/MeOH/NH4HCOO 5 m
M
): m/z calcd for

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A. Sanchez-Mendez et al. / Journal of Organometallic Chemistry 819 (2016) 201e208
207
Table 3
Crystallographic data for compounds 9 and 10.
9
10
Empirical formula
Formula weight
Crystal size [mm]
Color
C18H22O6N6Ni
477.10
C32H34N6O8Ni
689.35
0.5 ꢁ 0.35 ꢁ 0.3
0.5 ꢁ 0.22 ꢁ 0.12
green
green
Temperature [K]
Wavelength [Å]
Crystal system, space group
a [Å]
b [Å]
c [Å]
200(2)
0.71073
triclinic, P-1
9.894(5)
10.717(5)
11.618(5)
113.816(5)
93.390(5)
102.200(5)
1087.1(9)
2
1.458
0.939
200(2)
0.71073
monoclinic, P21/n
14.193(4)
9.569(3)
25.211(10)
90
103.62(4)
90
3327.7(19)
4
a
b
g
[ꢂ]
[ꢂ]
[ꢂ]
Volume [Å3]
Z
Calcd. density [g/cm3]
1.376
0.642
m
[mmꢀ1
]
F(000)
range [ꢂ]
Limiting indices (h, k, l)
Completeness to [%]
496
3.11 to 27.49
1440
3.03 to 25. 04
q
ꢀ12 ꢃ h ꢃ 12, ꢀ13 ꢃ k ꢃ 13, ꢀ15 ꢃ l ꢃ 14
ꢀ16 ꢃ h ꢃ 16, ꢀ11 ꢃ k ꢃ 11, ꢀ29 ꢃ l ꢃ 29
q
98.6
99.4
Reflections collected
Unique reflections (Rint
Absorption correction
9341
4924 (0.0332)
multi-scan
19857
5863 (0.1514)
multi-scan
)
Max. and Min. transmission
Refinement method
0.743, 0.660
full-matrix least-squares on F2
4924/0/280
0.905, 0.799
full-matrix least-squares on F2
5863/0/424
Data/restraints/parameters
Goodness of fit on F2
0.998
0.782
R1/wR2 [I > 2
s
(I)]
0.0708/0.1845
0.0900/0.1974
1.434 and ꢀ0.985
0.0569/0.1154
0.1486/0.1507
0.450 and ꢀ0.546
R1/wR2 (all data)
Largest diff. peak - hole [e/Å3]
data collection, and refinement parameters for the structural ana-
lyses is given in Table 3. Suitable crystals were glued to a glass fiber
using an inert polyfluorinated oil and mounted in the low tem-
supplementary crystallographic data for this paper. These data can
be obtained free of charge from The Cambridge Crystallographic
Data Center via www.ccdc.cam.ac.uk/data_request/cif.
perature N2 stream (200 K) of
a Bruker-Nonius Kappa-CCD
diffractometer equipped with an area detector and an Oxford
Cryostream 700 unit.
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