Multinuclear NMR solution studies on complexes of hexakis(pyrazol-1-yl)benzene (hpzb) with Ag(I)

Article abstract of DOI:10.1016/S0020-1693(02)01451-2

The reaction of the polydentate N-donor ligand hexakis(pyrazol-1-yl)benzene (hpzb) with AgSbF₆/PPh₃ or AgClO₄PPh₃ in a 1:1 ratio leads to the complexes [Ag(PPh₃)(hpzb)]SbF₆ (1) or [Ag(PPh₃)(hpzb)]ClO₄ (3). When two or three equivalents of the silver derivatives are used the species [Ag(PPh₃)₂]X are formed in addition to 1 or 3. In the case of SbF₆^- the remaining Ag⁺ competes with AgPPh₃⁺ for coordination to hpzb and the derivative [Ag(hpzb)]SbF₆ (2) is also obtained, while in the case of ClO₄^- the insoluble salt AgClO₄ is formed. The same reactions performed with hpzb-¹⁵N₁₂ confirmed the presence of the N-donor ligand in 1-3. At room temperature a Ag-P dissociation process is observed for all the derivatives containing Ag-PPh₃ fragments. Complexes 1-3 show in solution an intramolecular argentotropic shift that makes the six pyrazolyl rings of the hpzb ligand equivalent on the ¹H NMR time scale. When the amount of counteranion present in solution is sufficiently high, an intermediate of lower coordination number (stabilized with the anion) is observed for complexes 1 and 3 in the low temperature ³¹P NMR spectra in addition to the three-coordinated species. This intermediate is more stable in the case of ClO₄^- due to the higher coordinating ability of this anion.

Full text of DOI:10.1016/S0020-1693(02)01451-2

Inorganica Chimica Acta 347 (2003) 168ꢂ174
/
www.elsevier.com/locate/ica
Multinuclear NMR solution studies on complexes of
hexakis(pyrazol-1-yl)benzene (hpzb) with Ag(I)
Agust´ın Caballero a, Ana Guerrero a, Fe´lix A. Jalo´n a,*, Blanca R. Manzano a,
Rosa M. Claramunt b, M. Dolores Santa Mar´ıa b,
Consuelo Escola´stico b, Jose´ Elguero c
a Departamento de Qu´ımica Inorga´nica, Orga´nica y Bioqu´ımica, Facultad de Qu´ımicas, Universidad de Castilla-La Mancha, Avda. Camilo J. Cela, 10,
E-13071 Ciudad Real, Spain
b Departamento de Qu´ımica Orga´nica y Biolog´ıa, Facultad de Ciencias, UNED, Senda del Rey, 9, E-28040 Madrid, Spain
c Instituto de Qu´ımica Me´dica, CSIC, Juan de la Cierva, 3, E-28006 Madrid, Spain
Received 28 June 2002; accepted 23 September 2002
This paper is dedicated to Professor Uso´n for his outstanding contribution to organometallic chemistry
Abstract
The reaction of the polydentate N-donor ligand hexakis(pyrazol-1-yl)benzene (hpzb) with AgSbF6/PPh3 or AgClO4PPh3 in a 1:1
ratio leads to the complexes [Ag(PPh3)(hpzb)]SbF6 (1) or [Ag(PPh3)(hpzb)]ClO4 (3). When two or three equivalents of the silver
derivatives are used the species [Ag(PPh3)2]X are formed in addition to 1 or 3. In the case of SbF/ꢀ6 the remaining Agꢁ competes with
AgPPh/ꢁ3 for coordination to hpzb and the derivative [Ag(hpzb)]SbF6 (2) is also obtained, while in the case of ClO/ꢀ4 the insoluble salt
AgClO4 is formed. The same reactions performed with hpzbꢂ15
temperature a AgꢂP dissociation process is observed for all the derivatives containing Agꢂ
/
N12 confirmed the presence of the N-donor ligand in 1ꢂ
/
3. At room
3 show in
/
/
PPh3 fragments. Complexes 1ꢂ
/
solution an intramolecular argentotropic shift that makes the six pyrazolyl rings of the hpzb ligand equivalent on the 1H NMR time
scale. When the amount of counteranion present in solution is sufficiently high, an intermediate of lower coordination number
(stabilized with the anion) is observed for complexes 1 and 3 in the low temperature 31P NMR spectra in addition to the three-
coordinated species. This intermediate is more stable in the case of ClO/ꢀ4 due to the higher coordinating ability of this anion.
# 2002 Elsevier Science B.V. All rights reserved.
Keywords: Silver; N-donor ligands; Dynamic behaviour; Pyrazole; Phosphine
1. Introduction
B (‘coelenterands’) [3ꢂ
type C containing two [20ꢂ
/
19] and (pyrazol-1-yl)benzenes of
24], three [25] or four [26]
pyrazolyl rings have been studied as ligands (see Scheme
/
The coordination chemistry of N-donor ligands has
received a great deal of interest in recent decades [1]. The
use of ligands containing N-substituted pyrazoles is very
common [2], with the three main types of derivatives
being polypyrazolylborates (scorpionates), polypyrazo-
lylmethanes A (see Scheme 1) and polypyrazolylazines
(such as pyridines, pyrimidines and s-triazines). On the
other hand, polypyrazolylbenzenes have seldom been
used. Only the (pyrazol-1-yl-methyl) derivatives of type
1).
However, hexakis(pyrazol-1-yl)benzene (hpzb),
member of the ‘propellene’ class of ligands that we
have studied systematically [27ꢂ32], has very seldom
a
/
been used previously (see Scheme 2) [33].
In a previous work, we have described the coordina-
tion chemistry of hpzb with different metallic fragments
of Pd, Pt and Cu [33]. The use of these metals gives rise
to mono- or dinuclear derivatives. In only one case was
it possible to obtain a trinuclear complex. We decided to
explore the behaviour of this ligand in the reaction with
* Corresponding author. Tel.: ꢁ
/34-926-295-318.
E-mail address: felix.jalon@uclm.es (F.A. Jalo´n).
silver fragments. It is well known that silverꢂphosphine
/
0020-1693/02/$ - see front matter # 2002 Elsevier Science B.V. All rights reserved.
doi:10.1016/S0020-1693(02)01451-2

A. Caballero et al. / Inorganica Chimica Acta 347 (2003) 168ꢂ
/174
169
(91 K) was controlled by a standard unit calibrated
/
with a methanol reference. Mass spectra (position of the
peaks in Da) were recorded on a VG BIOTECH
Quattro spectrometer (University of La Coruna) using
˜
the FABꢁ technique and m-nitrobenzylic alcohol as
matrix.
Scheme 1.
2.2. Sample preparations
2.2.1. AgSbF6/PPh3/hpzb
A solution of [Ag(PPh3)](SbF6) (0.048 M, 2.0 ml) was
prepared in a Schlenk tube from AgSbF6 (32.87 mg,
95.9ꢃ
/
10ꢀ3 mmol) and PPh3 (25.18 mg, 96ꢃ10ꢀ3
mmol) in acetone-d6 and the solution was stirred for 1 h.
Three solutions were prepared in the corresponding
/
NMR tubes (tubes 1ꢂ
/
3) from hpzb (3.5 mg, 7.38ꢃ
10ꢂ3
mmol) and the corresponding volumes of the
/
[Ag(PPh3)](SbF6) solution (0.048 M): tube 1 (1:1),
0.154 ml, 7.36ꢃ
10ꢂ3 mmol; tube 2 (2:1), 0.307 ml,
/
Scheme 2.
14.71ꢃ
/
10ꢂ3 mmol and tube 3 (3:1), 0.461 ml, 22.13ꢃ
/
10ꢂ3 mmol). Additional quantities of acetone-d6 were
complexes [34ꢂ
/
51], not only homoleptic species but also
with other types of ligands, exhibit a rich dynamic
added to make up a volume of 0.5 ml in each tube. 19F
NMR (acetone-d6, 282 MHz, 193 K): tube 1, dꢄ ꢂ122.8
/
/
behaviour involving AgꢂP and/or AgꢂN bond rupture
/
/
121
(six broad lines, 6F, JFꢂ SbꢂFꢄ
/
1953 Hz) ppm; tube 3,
121
/
in intra- or intermolecular processes. Some of the
complexes reported contain pyrazolyl-derived ligands
[42,43,45,46]. On the basis of the information presented
above, the main goals of our work were as follows: (i) to
analyse the possibility of obtaining silver complexes with
different nuclearities, (ii) to study the fluxional beha-
viour of the new complexes obtained and (iii) to
compare the results with those previously obtained
with other metallic fragments.
dꢄ
/
ꢀ
/
123.1 (six broad lines, 6F, JFꢂ SbꢂFꢄ1977 Hz)
/
/
ppm. The significant broadening of the signals makes
the chemical shift and coupling constant values some-
what inaccurate. Partially overlapped signals corre-
sponding to the coupling with 123Sb were also observed.
2.2.2. AgClO4/PPh3/hpzb
The ligand hpzb (5.3 mg, 11.07ꢃ
introduced into three NMR tubes (4ꢂ
sponding amounts of [Ag(PPh3)]ClO4 were then added:
tube 4 (1:1), 5.2 mg, 11.07ꢃ
10ꢂ3 mmol; tube 5 (2:1),
10.4 mg, 22.15ꢃ
10ꢂ3 mmol; tube 6 (3:1), 15.6 mg,
33.22ꢃ
10ꢂ3 mmol. 0.5 ml of acetone-d6 was also added
/
10ꢂ3 mmol) was
6). The corre-
/
/
2. Experimental
/
/
2.1. General comments
to each tube.
Manipulations were carried out under an atmosphere
of dry oxygen-free nitrogen using standard Schlenk
techniques. Acetone-d6 was degassed before use.
AgSbF6 and PPh3 were used as purchased from Aldrich.
Other starting materials were prepared as reported in
the literature: AgClO4PPh3 [52],1 hpzb [30]. 1H,
13C{1H}, 31P{1H} and 19F NMR spectra were recorded
on a Varian Unity 300 spectrometer. 15N{1H} NMR
spectra were recorded on a Bruker DRX 400 spectro-
meter, Inverse Gated and gs-HMBC experiments were
carried out to assign the 15N signals. Chemical shifts
(ppm) are given relative to TMS (1H and 13C), H3PO4
(31P), CFCl3 (19F) and external CH3NO2 (15N). For
variable temperature spectra the probe temperature
3. Results and discussion
Schlenk techniques were used in the first reactions
carried out with hpzb and silver centres. After several
reactions, we realised that the product ratio depended to
a large extent on the experimental conditions and
manipulations of the product mixture. As a conse-
quence, we decided to carry out these reactions ‘in
situ’ in NMR tubes, using acetone-d6 as solvent, in order
to identify the resonances of the products in the absence
of any post-reaction manipulation.
The reactions carried out are indicated in the follow-
ing equations:
1AgSbF6 ꢁ1PPh3
1
Safety note: perchlorate salts of metal complexes with organic
ligands are potentially explosive.
ꢁ1hpzb 0[Ag(PPh3)(hpzb)]SbF6(1)
(1)

170
A. Caballero et al. / Inorganica Chimica Acta 347 (2003) 168ꢂ174
/
xAgSbF6 ꢁxPPh3 ꢁ1hpzb 01ꢁ[Ag(hpzb)]SbF6(2)
ꢁ[Ag(PPh3)2]SbF6
Table 2
1H NMR data for complexes 1ꢂ
/
3 in acetone-d6 at 233 K
(2)
1AgClO4PPh3 ꢁ1hpzb 0[Ag(PPh3)(hpzb)]ClO4(3) (3)
xAgClO4PPh3 ꢁ1hpzb 03ꢁAgClO4
Complex
H4
H3
H5
3
7.42 (t) J34
1
2
3
6.41 (pt)
6.57 (pt)
6.43 (bs)
ꢄ
ꢄ
/
2,2
7.82 a
8.03 (d) J45
ꢁ[Ag(PPh3)2]ClO4
(4)
3
7.82 (d) J34
3
/2,0
ꢄ/2,4
a
a
where xꢄ2, 3
/
Reactions made with a Agꢁ/hpzb ratio of 3:1. Ph signals appear in
the region 7.5ꢂ7.7 (1 and 2), 7.4ꢂ7.8 (3).
Overlapped.
/
/
3.1. Reactions of hpzb with AgSbF6/PPh3
a
For all the stoichiometries studied these reactions
gave products that were soluble in the NMR solvent.
ligand, which become identical on the NMR time scale.
The 19F NMR spectra show six broad lines correspond-
ing to the coupling of six equivalent F nuclei to 121Sb
121
The reaction products in Eqs. (1)ꢂ(4) show very broad
/
signals in the 31P NMR spectra at room temperature
and coupling between silver and phosphorus was not
observed in any case. This fact indicates a relatively fast
(Iꢄ
/
5/2), JFꢂ Sbꢄ1953 Hz. The lines corresponding to
/
the coupling with 123Sb (Iꢄ
/7/2) were partially over-
Agꢂ
/
PPh3 bond dissociation [34,35,37,41,42,45ꢂ
/
lapped and could not be observed clearly. From these
data we conclude that in solution the SbF6ꢀ anion does
not interact with the silver centre in a sufficiently strong
manner to allow differentiation between the F atoms.
When the reaction was performed using a 2:2:1 or
3:3:1 ratio of reactants (AgSbF6:PPh3:hpzb, Eq. (2)), the
P{1H} NMR (233 K) spectra showed the presence of a
new pair of doublets that was shown to correspond to
107
47,49,50] in solution in relation to the NMR time scale.
Consequently, in Eq. (2) a phosphine exchange process
is possible at this temperature and low temperature 31P
NMR spectra were therefore recorded to obtain further
structural information. The P{1H} NMR spectrum of
complex 1, obtained according to Eq. (1), clearly shows
at 233 K a pair of doublets due to a single PPh3 group
109
coupled to the two silver isotopes (1JPꢂ Agꢄ
/
745 Hz,
the complex [Ag(PPh3)2]SbF6 (1JPꢂ Agꢄ
/
493 Hz). The
resonance assigned to 1 was also present but this became
broader and gave larger AgꢂP coupling constants as the
1
107
JPꢂ Agꢄ
/
648 Hz) (see Table 1). The ratio
1J(109Agꢂ31
/
P)/1J(107Agꢂ31
/
P) is consistent with the
109Ag/107Ag gyromagnetic ratio. The same situation
was found for all the AgꢂP coupling constants in our
derivatives and, from now on, only the JPꢂ
/
amount of silver was increased. Importantly, a new set
1
of pyrazole resonances also appeared in the H NMR
/
1
107Ag
values
spectra, indicating the formation of a second complex
(2) bearing hpzb but not PPh3. In principle, complex 2
might be formulated as [Agx(hpzb)(SbF6)x]. A simple
mass balance based on the integration of the 31P and 1H
will be specified in the text. These results indicate that, at
this temperature, a PꢂAg bond dissociation process is
/
slow enough for coupling constants to be observed. The
1H NMR spectra (see Table 2) exhibit the three
resonances expected for only one type of pyrazole and
significant changes were not observed on lowering the
temperature down to 193 K. On the basis of these data it
is reasonable to propose that, with this reactant ratio, a
complex of stoichiometry [Ag(PPh3)(hpzb)]SbF6 (1) is
selectively formed and that this exhibits an argentotro-
pic shift [42] extended to the six pyrazole rings of the
NMR spectra concludes that xꢀ1 and, as a conse-
/
quence, 2 can be formulated as [Ag(hpzb)SbF6]. In a
similar way to 1, complex 2 exhibits the aforementioned
argentotropic behaviour that made the six pyrazole
rings of the ligand identical. The ratio of the pairs of
1
resonances, both in H (1 and 2) and 31P NMR (1 and
[Ag(PPh3)2]SbF6) spectra, varies with the two ratios of
Table 1
P{1H} NMR data for complexes 1ꢂ
/3 in acetone-d6
Reactant ratio (Agꢁ/hpzb)
Temperature (K)
d (ppm)
JP ꢂ
(Hz)
JP ꢂ
109
107
(Hz)
Ag
Complex
Ag
1
1:1
2:1
3:1
3:1
3:1
1:1
2:1
3:1
3:1
3:1
233
233
233
193
193
233
233
233
193
193
17.1 (2d)
17.2 (2bd)
16.8 (2bd)
17.2 (2bd)
15.3 (vb)
16.6 (vb)
16 (vb)
745
754
772
750
648
652
669
652
1
1
1a
1b
3
ca.850
724
ca.740
630
3
3
15.3 (vb)
16.0 (2d)
14.1 (2d)
3a
3b
750
767
650
667
2bdꢄ
/
two broad doublets, vbꢄvery broad.
/

A. Caballero et al. / Inorganica Chimica Acta 347 (2003) 168ꢂ
/174
171
reactants studied (Eq. (2), xꢄ
/
2 or 3), with an increasing
is bonded to two pyrazolato groups (565 or 590 Hz) [42]
amount of 2 and the diphosphine complex observed
when more silver is present in the solution. A pattern
similar to that found for the 1:1:1 reaction was obtained
or to phen (579 Hz) [50]. Consequently, in complex 1 the
fragment AgPPh3 will be bonded to two pyrazole
groups. One possible reason for the slightly higher value
found for 1 is the less basic character of the pyrazole
groups in hpzb compared with the reported ligands, a
in the 19F NMR spectrum at 193 K *
out the existence of strong Agꢂ
/
once again ruling
/SbF6 interactions.
The behaviour observed for the AgSbF6/PPh3/hpzb
system is consistent with the existence of the equilibrium
depicted in Eq. (5).
situation that could strengthen the AgꢂP bond. The
/
slight increase in the value of JPꢂAg observed for 1 when
the AgP:hpzb ratio is changed from 1:1 to 3:1 (see Table
1) could be explained in terms of the increasing
participation of a species of lower coordination number.
2[Ag(PPh3)]SbF6 XAgSbF6 ꢁ[Ag(PPh3)2]SbF6
(5)
In the reaction with the 1:1:1 reactant ratio the above
equilibrium does not take place to a great extent,
possibly because the Ag(PPh3)ꢁ group is coordinated
to the hpzb ligand and only complex 1 is formed.
The fact that dicoordinate ‘Nꢂ
/
AgꢂP’ species have been
/
reported [42a] must be taken into account in this
context. If we consider the possible mechanism for the
aforementioned intramolecular argentotropism process,
which would essentially involve an N,N metalotropic
shift (see Scheme 3), we find that this species could be an
intermediate of type b, formed after transient decoordi-
nation of one pyrazole group, which could in turn be
stabilised by an interaction with the counteranion. The
increase in the anion concentration when the
AgPPh3:hpzb ratio increases would imply a higher
participation of this intermediate in the process and,
consequently, in the weighed averaged JAgꢂP. In order
to ascertain whether the two species could be observed
separately, low temperature (193 K) P{1H} NMR
spectra were recorded in the tube with a metal:hpzb
ratio of 3:1. The resonances of 1 decoalesced and signals
corresponding to two species containing AgPPh3 groups
However, when a higher Agꢁ ꢂ
PPh3/hpzb ratio is used
/
the formation of dinuclear or trinuclear derivatives
seems to be less favoured, possibly because of the
repulsion between two cationic species. In this case,
equilibrium (5) operates and leads to the formation of
the diphosphino derivative [Ag(PPh3)2]SbF6 and Agꢁ
cations, which compete with Ag(PPh3)ꢁ for coordina-
tion of the hpzb ligand to form complex 2. Conse-
quently, it seems that the higher stability of the
[Ag(PPh3)2]SbF6 complex compared to that of the
expected dinuclear derivatives prevents the formation
of the dinuclear species under these conditions. The
1
observation of 1 and 2 as separate species in the H
NMR spectrum indicates that, although the intramole-
cular process of argentotropism is present, an inter-
molecular exchange between the two complexes
apparently does not take place on the NMR time scale.
Mass spectrometry (FABꢁ) provides some supple-
mentary information on these complexes. The solids
obtained by evaporation of the reaction solutions, for
both 1:1:1 and 3:3:1 reactant ratios, gave essentially the
same mass spectra and the following fragments were
were observed. The major component at 17.2 ppm
107Ag
1
(approximately 61%) had a JPꢂ
value of 652 Hz
and for the minor species (signals very broad and
partially overlapped), which appeared at higher field,
107Ag
1
the JPꢂ
was approximately 740 Hz. This observa-
tion supports the participation of ‘dicoordinated’ species
of type b, which exhibit higher JAgꢂP coupling con-
stants.
In order to confirm these results and to unambigu-
ously establish that the pyrazole rings are coordinated to
the silver centres in complexes 1 and 2, the reaction
depicted in Eq. (2) was carried out with hpzbꢂ15
N12 in a
2:2:1 ratio. The same results as for the non-labelled
ligand were obtained. At 233 K the P{1H} NMR
spectrum shows a complicated pattern of signals for 1
detected:
AgPPh3(hpzb)SbF6,
1080
Da;
AgPPh3(hpzb)ꢁ, 845 Da; AgPPh3ꢁ
,
369 Da;
Ag(hpzb)ꢁ, 581 Da; Ag(PPh3)2ꢁ, 631 Da. These data
indicate a facile interconversion between the species
shown in Eq. (5) under the conditions in the mass
spectrometer and also support the proposal that com-
plexes 1 and 2 are mononuclear in nature. The existence
of a fragment containing a SbF6 group possibly
indicates that a weak interaction with the silver centre
takes place.
/
The most informative data concerning the coordina-
tion mode of the silver centres is the Pꢂ
/
Ag coupling
107Ag
1
constant. According to bibliographic data the JPꢂ
coupling constants are inversely proportional to the
coordination number of the silver atom
[35,40,47,50,51,53] and increase with decreasing Agꢂ
/P
1
107
distances [38]. The value of JPꢂ Agꢄ
/648 Hz found
for complex 1 (obtained from Eq. (1)) is not very
different to that observed in species’ where the AgPPh3
Scheme 3.

172
A. Caballero et al. / Inorganica Chimica Acta 347 (2003) 168ꢂ174
/
due to coupling with 15N. The two doublets due to
[Ag(PPh3)2]SbF6 are not coupled with 15N according
In this case, the lack of solubility of AgClO4 prevents
competition between Agꢁ and Ag(PPh3)ꢁ for coordi-
nation of hpzb and a complex similar to 2 is not formed
in this reaction.
1
with the absence of hpzb in this complex. In the H
15N
NMR spectrum the corresponding JHꢂ
coupling
constants for the resonances of 1 and 2 could be
determined (see Table 3). Two signals at ꢀ70.8 (ꢀNꢂ
13.0 Hz) were
{1H} NMR spectrum of the free
hpzb (solvent, CDCl3). Complex 1 exhibits resonances
at ꢀ81.2 (br) and ꢀ 15Nꢄ12.2 Hz) while
184.6 (1J15Nꢂ
complex 2 shows signals at ꢀ93.4 (br) and ꢀ186.4 ppm
(1J15Nꢂ
15Nꢄ11.0 Hz). The signals at lower field are
The P{1H} NMR spectra of the products resulting
from the reactions with 2:1 or 3:1 reactant ratios were
registered at 233 K and very broad signals were
observed (besides [Ag(PPh3)2]ClO4). However, at 193
K two pairs of doublets were observed that were
broadened only slightly and these correspond to two
107
/
/
/)
1
and ꢂ
/
183.3 ppm (ꢁ
/
Nꢂ
/
, J15Nꢂ
/
15Nꢄ
/
observed in the 15Nꢂ
/
/
/
/
/
/
/
new derivatives: dꢄ
/
16.0 (1JPꢂ Agꢄ
/
650) and dꢄ/14.1
107
/
/
(1JPꢂ Agꢄ
/668) in a 43/57 ratio (for the 1:3 reaction)
broad in each case. This observation is understandable
when we consider that coordination has a greater
(see Fig. 1). The signals with larger coupling constants
can be assigned to the intermediate of type b. When
these intermediates were detected (reactions 3:1) and
both anions compared, it was noticeable that the
intermediate with ClO4 (i) exhibits a smaller JPꢂAg
(differences in JPꢂAg that depend on the distinct
coordinating ability of the anion have been described
[36,39]), (ii) is present in a higher ratio with respect to
the species of type a (see Scheme 3) and (iii) the
interchange process between the two species has a higher
activation energy. All these data can be explained in
terms of the greater coordinating ability of ClO4ꢀ with
respect to SbF6ꢀ, which results in stronger coordination
in the intermediate and, as a consequence, the stabilisa-
tion of this species.
influence on the chemical shift of the ꢀ
/
Nꢂ signal, and
/
that both resonances must correspond to the average of
the six pyrazoles.
3.2. Reactions of hpzb with AgClO4PPh3
These reactions evolved in a similar way to those with
AgSbF6/PPh3 but, in this case, AgClO4 is insoluble in
the NMR solvent (acetone-d6) and hence certain differ-
ences were observed. When the reaction was carried out
with
a
reactant
ratio
of
1:1,
complex
[Ag(PPh3)(hpzb)]ClO4 (3) was formed exclusively and
the six pyrazole groups were equivalent in the 1H NMR
spectrum (even at low temperature). Broad signals
appeared in the P{1H} NMR spectrum even at 193 K.
When x (Eq. (4)) was increased up to a value of 2 or 3,
signals corresponding to only one type of pyrazole ring
(3) were observed. In these reactions, precipitation of
AgClO4 was detected and the concomitant formation of
[Ag(PPh3)2]ClO4 occurred in solution. The precipitate
was identified as AgClO4 by redissolving the salt by
addition of PPh3. The formation of the complex
[Ag(PPh3)3]ClO4 [35,54] was observed and this product
was characterised by its P{1H} NMR spectrum.2
The formation of [Ag(PPh3)2]ClO4 in Eq. (4) indicates
that an equilibrium similar to that shown in Eq. (5) is
also operating (see Eq. (6)):
The results of the reactions of hpzbꢂ15
AgClO4PPh3 in different ratios led to the same conclu-
sions as deduced with the system Agꢁ/PPh3/SbF6ꢀ
The 13C{1H} NMR spectra of 1ꢂ
3 (see Table 4) are in
/
N12 with
.
/
agreement with the previous proposals.
4. Conclusions
Complexes
[Ag(PPh3)(hpzb)](SbF6)
(1)
and
[Ag(PPh3)(hpzb)](ClO4) (3) were synthesised as single
products in the reactions between hpzb and silver
centres with metal/PPh3/hpzb ratios of 1:1:1. Whereas
di- and trinuclear complexes have been prepared with
hpzb and other metallic fragments such as CuPPh3ꢁ, the
reactions performed with 2 or 3 silver centres per ligand
2AgClO4PPh3 XAgClO4 ꢁ[Ag(PPh3)2]ClO4
(6)
led only to mononuclear derivatives
because the disproportion reaction of the Ag(PPh3)ꢁ
fragment gives rise to the highly stable species
* probably
/
2
P{1H} NMR at 193 K in acetone-d6: dppm
ꢄ/
11.66, 1JP ꢂ 109Agꢄ
/366
1
Hz, JP ꢂ 107Agꢄ318.6 Hz.
/
Table 3
NMR spectra of compounds
15
N
ꢂ/
(1ꢂ
/
3) in acetone-d6 at r.t.
12
Complex
H4
H3
H5
15
a
N
N
N
ꢂ
ꢂ/
ꢂ/
/
1
2
3
6.27 (m)
6.54 (m)
6.37 (m)
7.45 (m)
7.98 (dd), JHN
12
12
12
15
15
2
7.76 (ddd), JHN
a
3
12.0, JHN
3
9.3, JH3H4
2
3
5.4, JH4H5
ꢄ/
ꢄ/
ꢄ/
2.2
ꢄ
ꢄ
/
ꢄ
ꢄ/
/
2.6
2
7.73 (dd), JHN
3
5.1, JH4H5
/
2.7
a
Overlapped signals.

A. Caballero et al. / Inorganica Chimica Acta 347 (2003) 168ꢂ
/174
173
Fig. 1. 31P NMR spectrum in acetone-d6 at 193 K corresponding to the result of the reaction of AgClO4PPh3 with hpzb in 3:1 ratio. For 3a and 3b,
see Scheme 3.
Table 4
13C{1H} NMR data of complexes 1ꢂ
3 in acetone-d6 at r.t.
/
Complex
hpzb
C4
PPh3
C3
C5
C (benzene)
Ortho
Meta
Para
2
134.1 (d), JCP
3
1
2
3
107.8
108.4
109.5
142.6
144.8
145.2
133.6
135.3
136.1
137.5
139.7
139.6
ꢄ
/
15.1
11.3
12.4
129.7 (d), JCP
129.6 (bs)
130.6 (bs)
ꢄ/
8.5
131.5
131.5
132.3
2
134.0 (d), JCP
ꢄ
/
2
135.2 (d), JCP
ꢄ/
Unless specified the signals are singlets.
[Ag(PPh3)2]ꢁ and Agꢁ. The Agꢁ cation is able to
compete with Ag(PPh3)ꢁ in the coordination of hpzb
when the counteranion does not precipitate as the
corresponding silver salt (SbF6ꢀ) and, as a result, the
derivative [Ag(hpzb)]SbF6 is formed. The reactions
Acknowledgements
Thanks are given to the DGI/MCyT of Spain for
financial support (project numbers BQU-2000-0252 and
BQU2002-00286.
performed with the hpzbꢂ15
presence in 1ꢂ3 of the N-donor ligand. At room
temperature an AgꢂP dissociation process is observed
for all the derivatives containing AgꢂPPh3 fragments. In
solution complexes 1ꢂ3 show an intramolecular argen-
/
N12 ligand confirmed the
/
/
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