Silver(I) Pyrazolates. Synthesis and X-ray and 31P-NMR Characterization of Triphenylphosphine Complexes and Their Reactivity toward Heterocumulenes

Article abstract of DOI:10.1021/ic960908j

Silver(I) pyrazolate was reacted with triphenylphosphine, leading to the dinuclear [Ag₂(pz)₂(PPh₃)₂] and [Ag₂(pz)₂ (PPh₃)₃] complexes (Hpz = pyrazole), which were exte

Full text of DOI:10.1021/ic960908j

Inorg. Chem. 1997, 36, 2321-2328
2321
31
Silver(I) Pyrazolates. Synthesis and X-ray and P-NMR Characterization of
Triphenylphosphine Complexes and Their Reactivity toward Heterocumulenes
G. Attilio Ardizzoia,*,1 Girolamo La Monica,1 Angelo Maspero,1 Massimo Moret,2 and
Norberto Masciocchi*,2
Dipartimento di Chimica Inorganica, Metallorganica e Analitica, Centro CNR, and Dipartimento di
Chimica Strutturale e Stereochimica Inorganica, Universita` di Milano, via Venezian 21,
I 20133 Milano, Italy
ReceiVed August 1, 1996X
Silver(I) pyrazolate was reacted with triphenylphosphine, leading to the dinuclear [Ag2(pz)2(PPh3)2] and [Ag2(pz)2
(PPh3)3] complexes (Hpz ) pyrazole), which were extensively characterized by 31P-NMR methods and single-
crystal X-ray analyses. Crystals of [Ag2(pz)2(PPh3)2] are triclinic, space group P1h, with a ) 9.567(2) Å, b )
11.440(2) Å, c ) 10.073(2) Å, R ) 93.59(2)°, â ) 64.01(2)°, γ ) 107.24(2)°, Z ) 1, and Dcalc ) 1.539 g‚cm-3
;
final R ) 0.028 for 2532 independent reflections having F > 4σ(F). They contain centrosymmetric dimers with
trigonally coordinated silver atoms, which are 3.870(1) Å apart. Crystals of [Ag2(pz)2 (PPh3)3] are triclinic,
space group P1h, with a ) 9.752(2) Å, b ) 14.163(2) Å, c ) 20.450(2) Å, R ) 101.84(1)°, â ) 99.83(2)°, γ )
100.68(2)°, Z ) 2, and Dcalc ) 1.424 g‚cm-3; final R ) 0.025 for 7075 independent reflections having F >
4σ(F). Each molecule contains two inequivalent silver ions, bearing one and two phosphines, respectively, and
a Ag(µ-pz)2Ag ring with a rare twisted conformation. Both complexes readily react with heterocumulenes such
as CS2, COS, CO2, and RNCO, affording new derivatives, the nature of which is dependent on the experimental
conditions. Single-crystal X-ray analysis of [Ag(pz-CS2)(PPh3)2] has shown the unexpected S,S coordination of
the pyrazolecarbodithioate fragment. Its crystals are triclinic, space group P1h, with a ) 10.329(4) Å, b ) 13.082(2)
Å, c ) 14.284(3) Å, R ) 86.71(2)°, â ) 75.14(2)°, γ ) 74.79(2)°, Z ) 2, and Dcalc ) 1.431 g‚cm-3; final R )
0.028 for 5179 independent reflections having F > 4σ(F).
Introduction
(PPh3)2], obtained by reacting [Ag2(pz)2(PPh3)3] with CS2, is
also reported.
We have been actively working in the field of metal
pyrazolates and have extensively reported on Cu(I) and Cu(II)
species, demonstrating the structural versatility caused by the
pyrazolate ligands and the catalytic activity of some of its
derivatives.3 As early as 1889, Bu¨chner reported the synthesis
of the insoluble “silver salt” [Ag(pz)]n (Hpz ) pyrazole).4 Since
then, this derivative has always been claimed to be polymeric,
but its molecular structure has never been clearly identified.
As a part of a systematic study of the chemistry of group 11
metal pyrazolates, we recently reported the ab-initio crystal
structure determination from powder diffraction data of, among
others, [Ag(pz)]n, confirming its polymeric nature.5
Despite the fact that [Ag(pz)]n was first synthesized over a
century ago, its chemical reactivity has never been fully
explored, probably because of its poor solubility. In this paper,
we report the synthesis of the dinuclear [Ag(pz)(PPh3)]2 and
[Ag2(pz)2(PPh3)3] species derived from reaction of [Ag(pz)]n
with triphenylphosphine, their structural characterization, and
their reactivity with heterocumulenes. The full structural
characterization of the monomeric derivative [Ag(pz-CS2)-
Results and Discussion
The reaction of [Ag(pz)]n with PPh3 in dichloromethane leads
to the isolation of two distinct products depending on the PPh3:
Ag ratio employed. The dimeric complex [Ag(pz)(PPh3)]2, 1,
is isolated in the presence of a PPh3:Ag ratio of 1.5:1. When
the reaction is carried out with excess triphenylphosphine (PPh3:
Ag > 5:1), the reaction product is the dinuclear species
[Ag2(pz)2(PPh3)3], 2.
In both cases it has proved essential, in order to isolate
analytically pure products, to operate in the presence of a slight
excess of PPh3 with respect to the stoichiometric amount
required; in fact, only an excess of PPh3 ensures complete
depolymerization of the starting [Ag(pz)]n phase and, on the
other hand, represses dissociation of the coordinated phosphine.
Complex 2 can also be obtained by reaction of 1 with PPh3,
suggesting the intermediacy of 1 in the formation of 2.
Moreover, as revealed by 31P-NMR spectroscopy (see later),
complex 1 is generated when 2 is dissolved in CH2Cl2, and as
expected, when 2 is suspended in diethyl ether, an easy
dissociation of one triphenylphosphine ligand takes place,
restoring [Ag(pz)(PPh3)]2, 1:
X Abstract published in AdVance ACS Abstracts, March 1, 1997.
(1) Dipartimento di Chimica Inorganica, Metallorganica e Analitica and
Centro CNR.
(2) Dipartimento di Chimica Strutturale e Stereochimica Inorganica.
(3) (a) Ardizzoia, G. A.; Angaroni, M.; La Monica, G.; Cariati, F.; Cenini,
S.; Moret, M.; Masciocchi, N. Inorg. Chem. 1991, 30, 4347. (b)
Angaroni, M.; Ardizzoia, G. A.; La Monica, G.; Beccalli, E. M.;
Masciocchi, N.; Moret, M. J. Chem. Soc., Dalton Trans. 1992, 2715.
(c) Ardizzoia, G. A.; Cenini, S.; La Monica, G.; Masciocchi, N.; Moret,
M. Inorg. Chem. 1994, 33, 1458.
2PPh3
PPh3
(2/n)[Ag(pz)]n
8 [Ag(pz)(PPh3)]2 y
z
-PPh3
[Ag2(pz)2(PPh3)3] (1)
(4) Bu¨chner, E. Ber. Dtsch. Chem. Ges. 1889, 22, 842.
(5) Masciocchi, N.; Moret, M.; Cairati, P.; Sironi, A.; Ardizzoia, G. A.;
La Monica, G. J. Am. Chem. Soc. 1994, 116, 7668.
Complexes 1 and 2 exhibit, in the 4000-900 cm-1 region,
similar IR spectra. This similarity is attributable to the (roughly)
S0020-1669(96)00908-1 CCC: $14.00 © 1997 American Chemical Society

2322 Inorganic Chemistry, Vol. 36, No. 11, 1997
Ardizzoia et al.
Table 1. Selected Bond Lengths (Å) and Angles (deg) for
Complexes 1 and 2a
Complex 1
Ag‚‚‚Ag′
Ag-N1
3.870(1)
2.204(3)
Ag-N2′
Ag-P
2.213(3)
2.376(1)
N1-Ag-N2'
N1-Ag-P
110.68(10)
125.24(8)
N2′-Ag-P
124.04(8)
Complex 2
Ag1‚‚‚Ag2
Ag1-N1
Ag1-N3
Ag1-P1
3.706(1)
2.295(2)
2.323(2)
2.461(1)
Ag1-P2
Ag2-N2
Ag2-N4
Ag2-P3
2.484(1)
2.235(2)
2.176(2)
2.370(1)
N1-Ag1-N3
N1-Ag1-P1
N1-Ag1-P2
100.67(8)
112.03(6)
108.98(6)
N3-Ag1-P1
N3-Ag1-P2
P1-Ag1-P2
99.38(5)
111.70(6)
121.73(3)
N2-Ag2-N4
N2-Ag2-P3
110.39(8)
117.28(6)
N4-Ag2-P3
132.24(6)
Figure 2. ORTEP drawing of the [Ag2(pz)2(PPh3)3] molecule, 2, with
partial labeling scheme. Thermal ellipsoids are drawn at the 30%
probability level. Hydrogen atoms are omitted for clarity.
a Primed atoms are generated by the -x, -1 - y, 1 - z symmetry
operation.
The influence of different coordinations around a silver atom
on the Ag-N distances is also visible ([N,P]Ag-N ca. 2.20 Å
and [N,P,P]Ag-N ca. 2.30 Å); moreover, the central ring
conformation is markedly different: 1 (which possesses crys-
tallographically imposed inversion symmetry) contains a planar
six-membered metallacycle (maximum deviation 0.033(2) Å),
while in 2 a flattened chair is observed, with the presence of a
rare case of a “twisted” Ag-N-N-Ag conformation, where
the two silver atoms lie on opposite sides of one pyrazolate
ligand (Ag1-N1-N2-Ag2 -31.6(2)°). Such an unfavorable
twist is rare but is present, for example, in the [Cu(dppz)-
7
(RNC)]26 (Hdppz ) 3,5-diphenylpyrazole) and [(Cp)2Ti(pz)]2
(Cp ) η5-cyclopentadienyl) dimers, where the [M-N-N-M-
N-N-] rings possess a chair conformation. This geometry,
which is unexpected on the basis of the structural model put
forward in ref 8 for dimeric Cu(I) pyrazolates, has been
attributed to the steric demand of the bulky ligands on the
metals, which is probably the source of the observed distortion
also in 2. Accordingly, we failed to isolate the hypothetical
[(PPh3)2Ag(µ-pz)2Ag(PPh3)2] species even by operating in the
presence of a large excess of triphenylphosphine; instead,
formation of monomeric silver complexes was observed.
31P{1H}-NMR Spectra. It is well-known that the solution
and solid state structures of transition-metal complexes are not
necessarily the same. This is particularly true for substitutionally
labile complexes such as (PR3)nAgX, where it is possible for
several species to exist in solution through fast ligand-exchange
equilibria.9,10
Figure 1. ORTEP drawing of the [Ag2(pz)2(PPh3)2] molecule, 1, with
partial labeling scheme. Thermal ellipsoids are drawn at the 30%
probability level. Hydrogen atoms are omitted for clarity.
similar coordination modes of the pyrazolate ligands in the two
species. Differences are evident in the 900-600 region of the
spectra, where the absorptions of the phenyl rings of the PPh3
ligands appear. In this region, complex 1 shows two bands at
748 and 694 cm-1. In contrast, complex 2 shows a more
complex pattern, with three bands at 764, 735, and 691 cm-1
,
revealing the presence of (at least) two inequivalent PPh3
ligands, which were confirmed by single-crystal X-ray structural
analyses.
Crystal and Molecular Structures of 1 and 2. Crystals of
1 and 2 contain discrete molecules, packed by normal van der
Waals interactions. Relevant bond distances and angles are
collected in Table 1.
In order to establish the real nature of complexes 1 and 2
also in solution, we decided to carry out a 31P-NMR study on
these complexes. Due to (107Ag, 109Ag)-P coupling, the
solution 31P-NMR spectra for silver(I) phosphine complexes are
typically characterized by a diagnostic pair of doublets for each
phosphorus environment. The high kinetic lability of mono-
dentate phosphines generally leads to a rapid ligand exchange
on the NMR time scale and necessitates low temperatures for
resolution of the silver-phosphorus coupling.11
Molecules of 1 and 2 are based on a central Ag(µ-pz)2Ag
core (Ag‚‚‚Ag 3.870(1) and 3.706(1) Å, for 1 and 2, respec-
tively), surrounded by two and three phosphines, respectively
(see Figures 1 and 2). Therefore, while in 1 the crystallo-
graphically unique silver atom is trigonally coordinated, in 2
Ag(2) is tri-coordinated and Ag(1), bearing two phosphines, has
a pseudotetrahedral geometry. Consistently, the Ag-P bond
distances show shorter (2.376(1) Å in 1 and 2.370(1) Å in 2)
and longer (2.461(1) and 2.484(1) Å in 2) interactions, in
agreement with the different coordination geometries about the
metal atoms, for trigonal and tetrahedral silver atoms, respec-
tively. Surprisingly, a search in the Cambridge Structural
Database revealed that the Ag-P bond distances for tri- and
tetracoordinated silver atoms are almost equal [mean Ag-P
values: 2.433 Å (33 cases) and 2.454 Å (109 cases), respec-
tively], possibly reflecting the wide variety of ligands and
lacking, therefore, internal consistency.
(6) Ardizzoia, G. A.; Cenini, S.; La Monica, G.; Masciocchi, N.; Moret,
M.; Inorg. Chem. 1994, 33, 1458.
(7) Fieselman, B. F.; Stucky, G. D. Inorg. Chem. 1978, 17, 2074.
(8) Ardizzoia, G. A.; Beccalli, E. M.; La Monica, G.; Masciocchi, N.;
Moret, M. Inorg. Chem. 1992, 31, 2706.
(9) Attar, S.; Alcock, N. W.; Bowmaker, G. A.; Frye, J. S.; Bearden, W.
H.; Nelson, J. H. Inorg. Chem. 1991, 30, 4166.
(10) Alyea, C.; Malito, J.; Nelson, J. H. Inorg. Chem. 1987, 26, 4294.
(11) Muetterties, E. L; Alegranti, C. W. J. Am. Chem. Soc. 1972, 94, 6386.

Silver(I) Pyrazolates
Inorganic Chemistry, Vol. 36, No. 11, 1997 2323
Figure 3. 31P{1H}-NMR of complex 2 (CD2Cl2/CDCl3, 158 K).
Figure 4. 31P{1H}-NMR of complex 2 obtained in the presence of
free PPh3 (CD2Cl2, 173 K).
(a) [Ag(pz)(PPh3)]2, 1. The 31P{1H }-NMR spectrum of 1
at room temperature shows a single sharp signal at 9.87 ppm.
When the temperature is lowered, the signal broadens, and at
223 K, it begins to split into two broad resonances. A further
lowering of the temperature causes the resolution of the signals
into two sharp doublets centered at 10.96 ppm, and the splitting
due to the coupling to the silver centers can be accurately
measured, giving J(107Ag-31P) ) 513 Hz and J(109Ag-31P)
) 592 Hz (Figure S1 in the Supporting Information). The
measured coupling constants are higher than those reported in
the literature for sp2-hybridized silver(I) complexes of the
L2Ag-X (L ) monodentate arylphosphine) type11 but are
comparable with those reported for similar pyrazolate complexes
containing a silver(I) center in a trigonal planar geometry, i.e.
[η5-Cp*Ir(pz)(µ-pz)2Ag(PPh3)] (1J(107Ag-31P) ) 565 Hz),12 [η5-
Cp*Ir(pz)3{Ag(PPh3)}2]+ (1J(107Ag-31P) ) 573 Hz)12 and [η5-
Cp*(PPh3)Ir(pz)2Ag(PPh3)]+ (1J(107Ag-31P) ) 590 Hz).13 There-
fore, the spectral data indicate that, at 173 K, only one type of
PPh3 ligand is present, bound to a sp2 -hybridized silver center
and that complex 1 maintains its dimeric structure also when
in solution.
1.15). Figure 3 shows the 31P-NMR spectrum of 2 recorded at
-115 °C (CD2Cl2/CDCl3, 2:1 mixture).
The set of signals labeled with A is the same as in the limiting
spectrum of 1 and is therefore attributable to the [Ag(pz)(PPh3)]2
species, generated from 2 by dissociation of one PPh3 ligand.
This agrees with our observations that, when complex 2 is
suspended in diethyl ether at room temperature, dissociation of
one triphenylphosphine rapidly occurs, affording complex 1 in
an analytically pure form.
1
1
The set of signals labeled with C, centered at 4.85 ppm, shows
a 1J(107Ag-P) of 223 Hz. Coupling constants of this order are
found in ionic species of the type [AgL4]X (L ) arylphosphines;
X ) Cl-, Br-, PF6-, NO3-, CF3COO-). The value of J for
this class of compounds is practically independent of the nature
of the (uncoordinated) counteranion.11 On the basis of these
considerations, the observed coupling constants and chemical
shifts for 2 suggest the presence, in solution, of the ionic species
[Ag(PPh3)4]+(pz)- containing a pyrazolate anion in a non-
coordinating fashion. As further support of the above inter-
pretation, we observed that, when the 31P-NMR spectrum of 2
is registered in acetone-d6 (instead of CD2Cl2), the spectrum
dramatically simplifies. In this solvent, at 183 K only two well-
resolved sets of signals are detected. The first one presents a
1J(107Ag-P) of 223 Hz and is assignable to the ionic [Ag(PPh3)4]-
(pz) species, whose formation is favored by the presence of a
solvent of higher dielectric constant. The second set of signals
presents coupling constant values (1J(107Ag-P ) 253 Hz,
1J(109Ag-P) ) 292 Hz) agreeing with a silver(I) center in a
tetrahedral arrangement of the L3AgX (sp3-hybridized) type.11,14
These peaks can therefore be associated with the [Ag(PPh3)3-
(pz)] species, containing a monodentate pyrazolate group.
Similar behavior is observed when the 31P-NMR spectrum of 2
is recorded in CD2Cl2 in the presence of free PPh3 (Figure 4).
In fact, also in this case, only two sets of signals were detected
(in addition to that due to free phosphine itself at -7.8 ppm)
(b) [Ag2(pz)2(PPh3)3], 2. The solution behavior of 2 is much
more complex. From the 31P{1H}-NMR spectrum of a solution
of 2 in CH2Cl2 at room temperature, only one sharp signal,
centered at 6.13 ppm, is observed, suggesting a fluxional process
equalizing all PPh3 ligands. When the temperature is lowered,
the signal broadens and splits: At -90 °C the spectrum contains
two sharp doublets and three broad resonances. At -115 °C
eleven sharp and two broad peaks can be observed.
As a matter of fact, at this limiting temperature, at least five
different PPh3 environments exist: for four of them, the coupling
constant 1J(Ag-P) can be accurately measured (the assignment
of each set of signals is based on their relative intensities and
on the calculation of the 1J(109Ag-P)/1J(107Ag-P) ratio, which
should approach the theoretical value of γ(109Ag)/γ(107Ag) )
(12) Carmona, D.; Lahoz, F. J.; Oro, L. A.; Lamata, M. P.; Buzarra, S.
Organometallics 1991, 10, 3123.
(13) Carmona, D.; Oro, L. A.; Lamata, M. P.; Jimeno, M. L.; Elguero, J.;
Belguise, A.; Lux, P. Inorg. Chem. 1994, 33, 2196.
(14) Barron, P. F.; Dyason, J. C.; Healy, P. C.; Englehardt, L. M.; Skeleton,
B. W.; White, A. H. J. Chem. Soc., Dalton Trans. 1986, 1965.

2324 Inorganic Chemistry, Vol. 36, No. 11, 1997
Ardizzoia et al.
Scheme 1
Figure 5. Molar conductivity vs the Ag:PPh3 ratio for complex 2
(CH2Cl2).
and are assigned to the [Ag(PPh3)4](pz) (set D, Figure 4) and
[Ag(PPh3)3(pz)] (set E, Figure 4) species, their relative ratio
depending on the amount of PPh3 added.
Moreover, conductance measurements carried out on CH2Cl2
solutions of 2 in the presence of free PPh3 shows a clear
dependence of Λmol on the amount of added PPh3 in the range
PPh3:Ag ) 1-20. For PPh3:Ag ratios higher than 20, the molar
conductivity of the solution remains practically constant,
indicating complete conversion of the silver(I) existing in
solution to the ionic [Ag(PPh3)4](pz) species (Figure 5).
Returning to the discussion of the 31P-NMR spectrum of 2,
the remaining set of clear signals labeled with B, centered at
formation of a new silver-pyrazolate phase, different from the
starting polymeric [Ag(pz)]n was observed.
H2O2
3[Ag(pz)(PPh3)]2
3[Ag2(pz)2(PPh3)3]
8 2[Ag(pz)]3 + 6OdPPh3 (2)
H2O2
8 2[Ag(pz)]3 + 9OdPPh3 (3)
1
7.24 ppm, presents a J(107Ag-P) of 409 Hz (1J(109Ag-P )
472 Hz)). This value can tentatively be attributed to the PPh3
ligands bound to a tetracoordinated silver(I) center such as
X2Ag(PPh3)2. i.e. to the tetrahedral silver center of the undis-
sociated dinuclear species [Ag2(pz)2(PPh3)3], 2. The related set
of signals corresponding to the trigonal silver(I) center probably
coincides with those of 1 (set A, Figure 3).
The solution behavior of complex 2 in CH2Cl2 is obviously
quite complicated, and some aspects are still obscure. Moreover,
the presence of unresolved sets of signals causes a lack of
precious spectral information. The above results show that
complex 2 dissociates, upon dissolution, forming a variety of
complexes of very different stoichiometries. This behavior is
not surprising, as it has previously been reported for dimeric
silver(I) complexes containing 1-phenyl-3,4-dimethylphosphole
(DMPP) or 1-phenyldibenzophosphole (DBP).9 In these cases
halide derivatives such as [(DBP)2AgX]2 or [(DMPP)2AgCl]2
were shown to dissociate to give ionic species such as
[Ag(DMPP)4]X and [Ag(DBP)4]X and mononuclear covalent
derivatives, i.e. [Ag(DMPP)3X] or [Ag(DBP)3X].9
Several attempts to isolate [Ag(PPh3)4](pz) or [Ag(PPh3)3-
(pz)] from solutions of 2 in the presence of excess PPh3 failed,
[Ag2(pz)2(PPh3)3] being always restored in pure form. It thus
appears that steric considerations result in the formation of the
dinuclear species in the solid state. The fact that steric effects
play a determining role on the nature of the solid state species
is confirmed by the observation that, when [Ag(pz)]n is reacted
with a bulky phosphine such as P(Cy)3, a unique product, the
dimeric [Ag(pz)(PCy3)]2 species, 3, was isolated, also in the
presence of a large excess of ligand, with no evidence for the
formation of the more crowded dinuclear [Ag2(pz)2(PCy3)3]
species.
The full structural characterization of the [Ag(pz)]3 phase has
been already reported.5
Despite the substantial structural differences, the reactivity
of [Ag(pz)]3 toward PPh3 parallels that of the polymeric phase
[Ag(pz)]n. Evidently, the first step of the reaction with PPh3,
in both cases, is the formation of mononuclear species such as
[Ag(PPh3)x(pz)], which, depending on the experimental condi-
tions, later evolve to the final products. Scheme 1 summarizes
the solution behavior of 2.
Reactions with Heterocumulenes. Complexes 1 and 2
readily react with heterocumulenes such as CS2, COS, CO2, and
RNCO (R ) cyclohexyl and p-tolyl) giving rise to new
derivatives, the nature of which is dependent on the experimental
conditions.
(a) Reaction with Carbon Disulfide. Carbon disulfide reacts
with complexes 1 and 2 in a variety of solvents in the presence
of PPh3, affording a pale-pink product, formulated on the basis
of elemental analysis as [Ag(PPh3)2(pz-CS2)], 4, containing a
pyrazolecarbodithioate anion derived from the formal nucleo-
philic addition of the pyrazolate anion to the carbon atom of
the CS2 molecule.
The pyrazolecarbodithioate anion can, in principle, coordinate
to a metal center in a (chelating) N,S or S,S fashion. The
It is worth mentioning here that, when coordinated PPh3 is
removed from complexes 1 and 2 by using H2O2, selective

Silver(I) Pyrazolates
Inorganic Chemistry, Vol. 36, No. 11, 1997 2325
Table 2. Selected Bond Lengths (Å) and Angles (deg) for
Complex 4
synthesis of a series of metal(II) pyrazolecarbodithioates (Mn,
Fe, Co, Ni, Cu, Zn) was reported by Trofimenko,15 who
suggested that the coordination properties of the polydentate
Ag-P1
Ag-P2
2.474(1)
2.441(1)
Ag-S1
Ag-S2
2.630(1)
2.710(1)
-
pzCS2 ligand produce MN2S2 instead of MS4 coordination
environments. In the case of copper(II) centers, the N2S2
coordination was confirmed in 1978 by Bereman et al.16 on the
basis of spectroscopic evidence. Recently, we reported the
crystal structure of the product derived by reacting CS2 with
[Cu(dmpz)(RNC)]2 (Hdmpz ) 3,5-dimethylpyrazole, RNC )
cyclohexyl isocyanide), showing the N,S coordination mode also
for a rather soft metal center like copper(I).17
The IR spectrum of 4 does not show any band assignable to
the CdS stretching (in the 1300-1350 cm-1 region) expected
for a N,S coordination mode. Instead, strong absorptions are
present in the 1150-1250 cm-1 region, which we attribute to
ν(CS2-) vibration modes,18 indicating a S,S coordination of the
pyrazolecarbodithioate ligand. However, overlap with other
ligand modes precluded an unambiguous assignment. The S,S
coordination mode has been confirmed by an X-ray crystal
structure analysis.
C1-S1
C1-S2
C1-N1
1.672(3)
1.678(3)
1.414(3)
N1-N2
N1-C2
1.362(4)
1.360(4)
P1-Ag-P2
P1-Ag-S1
P1-Ag-P2
123.96(3)
108.96(3)
104.53(3)
P2-Ag-S1
P2-Ag-S2
S1-Ag-S2
124.73(3)
109.57(3)
67.20(3)
N1-C1-S1
N1-C1-S2
118.8(2)
117.3(2)
S1-C1-S2
124.9(2)
When complex 4 is dissolved in CH2Cl2, a rapid dissociation
of PPh3 takes place, affording an insoluble orange compound
analyzing as [Ag(PPh3)(pz-CS2)], 5. Formation of the latter
species takes place also upon suspending 4 in diethyl ether. The
dissociation is reversible, and complex 4 is easily restored by
treating 5 in diethyl ether with PPh3:
[(PPh3)2Ag(pz-CS2)] h 5 + PPh3
Complex 5 can also be obtained by reacting [Ag(pz)(PPh3)]2,
1, or [(Ag2(pz)2(PPh3)3], 2, with CS2 in the absence of PPh3.
The IR spectrum of complex 5 is similar to that of the parent
[(PPh3)2Ag(pz-CS2)] species, suggesting that the S,S coordina-
tion mode is maintained also after the dissociation of a PPh3
molecule. The formulation of 5 as a monomeric species
conflicts with its marked insolubility in common, noncoordi-
nating solvents. Most probably, 5 possesses a more complex
structure, oligomeric or maybe polymeric, where the pyrazole-
carbodithioate group behaves as a tridentate ligand, in a S,S,N
fashion, with two sulfur atoms chelating to a silver(I) center
and the free nitrogen atom of the pyrazole group bridging a
second metal, giving rise to a sequence of tetracoordinated
silver(I) centers.
Figure 6. ORTEP drawing of the [Ag2(pz-CS2)(PPh3)2] molecule, 4,
with partial labeling scheme. Thermal ellipsoids are drawn at the 30%
probability level. Hydrogen atoms are omitted for clarity.
analogies between 4 and 4a (IR spectra and color) seem to
indicate the S,S coordination mode of the pyrazolecarbodithioate
group also in the latter species.
When complex 4 is suspended in refluxing acetone, complete
abstraction of the phosphine ligands occurs, leaving a (highly
insoluble) brown residue, analyzing as [Ag(pz-CS2)], 6. It is
worthy of note that, in contrast to complex 5, [Ag(pz-CS2)], in
the presence of excess triphenylphosphine, does not restore the
parent compound 4, thus suggesting a different coordination
mode of the pyrazolecarbodithioate ligand. Studies are in
progress to assess its complete crystal structure by ab-initio
powder diffraction techniques.
(b) Crystal and Molecular Structure of 4. Crystals of 4
contain discrete molecules, packed by normal van der Waals
interactions. Relevant bond distances and angles are collected
in Table 2. Compound 4, which is monomeric and contains a
pseudotetrahedral silver atom (Ag-P1 2.441(1) Å and Ag-P2
2.474(1) Å; P1-Ag-P2 123.96(3)°), bears a chelating R-CS2
ligand, bonded through the two sulfur atoms (Ag-S1 2.630(1)
Å and Ag-S2 2.710(1) Å; see Figure 6). The molecule, which
has no imposed crystallographic symmetry, shows, however,
an idealized mirror plane passing through the silver and
phosphorus atoms, bisecting the CS2 and pyrazolato ring (once
disordered C and N atoms for the azaaromatic moiety are
assumed; see Experimental Section).
Interestingly, complex 5 reacts with 1,2-bis(diphenylphos-
phino)ethane (dppe) giving a derivative formulated as [(dppe)-
Ag(pz-CS2)], 4a. Complex 4a, which is pink, has been verified
to be stable in solution due the chelating effect of dppe. The
Interestingly, this compound shows the first structurally
characterized S,S coordination of a pyrazolecarbodithioate
(bearing a nucleophilic N atom), contrasting with previous
observations and the structural hypothesis put forward by
Trofimenko back in 1968.15 Although no evidence for a N,S
coordinated moiety, leading to a rather stable five-membered
(15) Trofimenko, S. J. Org. Chem. 1968, 33, 890.
(16) Bereman, R. D.; Shields, G. D.; Nalawajek, D. Inorg. Chem. 1978,
17, 3713.
(17) Ardizzoia, G. A.; Angaroni, M.; La Monica, G.; Moret, M.; Mascio-
cchi, N. Inorg. Chim. Acta 1991, 185, 63.
(18) Light, R. W.; Hutchins, L. D.; Paine, R. T.; Campana, C. F. Inorg.
Chem. 1980, 19, 3597.

2326 Inorganic Chemistry, Vol. 36, No. 11, 1997
Ardizzoia et al.
ring similar to those found for [Cu(dmpz-CS2)(RNC)2]17 and
[Pd(dmpz-COS)2]19 was found, and in spite of the soft character
of the Ag(I) ion (favoring the S, rather than the N, coordination),
we could expect possible interconversion of 4 into [Ag(pz-CS2-
N,S)(PPh3)2] if suitable conditions are found. This would agree
with our recent observation of the coexistence, in the solid state,
of the two coordination modes for the [Pd(dmpz-CS2)]2
complex,20 showing that both linkage isomers can exist, despite
their different steric interactions and bonding patterns.
Scheme 2
(c) Reactions with COS, CO2, and Isocyanates. When
COS is bubbled at room temperature through a solution of
complex 1 or 2 containing free PPh3, a rapid color change of
the solution, from colorless to pale yellow and finally to deep
brown, takes place. The (brown) solid isolated after workup
of the solution shows an IR absorption at 1619 cm-1, indicating
that a reaction has occurred. However, it has been verified that
under these experimental conditions, extraction of sulfur from
COS easily takes place and that the final product is always
contaminated by variable amounts of Ag2S. Indeed, it has been
shown that the weakening of the CdS bond of COS upon
coordination to a metal, due to dπ-π* back-donation, is
sufficient to promote elimination of sulfur, if a suitable sulfur
acceptor is present.21,22
When the reaction is carried out at -80 °C in the absence of
solvent, it is possible to isolate a white product, 7, showing a
strong IR band at 1612 cm-1. This species is quite stable at
low temperatures, also under vacuum, but when the temperature
is raised above -10 °C, rapid sulfur extraction once again takes
place even in the solid state. A full characterization of this
derivative was hampered by its low stability; nevertheless, if
complex 1 or 2 is reacted with COS at -80 °C in the presence
of dppe, a rather stable (also at room temperature) derivative,
7a, is isolated. The IR spectrum of the latter shows a strong
IR band at 1621 cm-1, attributable to the ν(CdO) of the
pyrazolecarbothioate anion, pz-COS-, derived from nucleophilic
addition of the pyrazolate group to the COS molecule. Ac-
cording to the elemental analysis, complex 7a was formulated
as [Ag(dppe)(pz-COS)]. On the basis of the IR spectrum of
7a, and taking into account the scarce affinity of the soft silver(I)
centers for hard oxygen-donor ligands, we assign to the ligand
pyrazolecarbothioate a N,S coordination mode, analogous to that
of the known [Cu(dmpz-COS)(RNC)2]23 (1670 cm-1) and
[Pd(dmpz-COS)2]19 (1658 cm-1) derivatives.
The extreme lability of CO2 in the pyrazolecarboxylate
derivatives, i.e. the reversibility of the insertion process, can
be ascribed to the low stability of Ag-O bonds, which is easily
avoided in the COS or RNCO derivatives. Thus, the extremely
soft nature of the silver center seems to play again a determinant
role.24
In contrast, the reactions of complexes 1 and 2 with RNCO
give well-characterized derivatives of the general formula
[Ag(pz-N(CO)R)(PPh3)2] (R ) cyclohexyl, 9; R ) p-tolyl, 10):
PPh3
[Ag2(pz)2(PPh3)3] + 2RNCO
8 2[Ag(pz-N(CO)R)(PPh3)2]
(4)
Complexes 9 and 10 exhibit in their IR spectra strong absorp-
tions at 1653 and 1667 cm-1, respectively, attributable to the
ν(CO) mode of the pz-N(CO)R ligand coordinated in a N,N
fashion. These values compare well with those previously
reported for the copper(I) [Cu(dmpz-N(CO)R)(RNC)2] (1670
cm-1) derivative23 and for the copper(II) species containing the
chelating dmpz-N(CO)H- ligand, derived by nucleophilic attack
of 3,5-dimethylpyrazole on NCO- (about 1690 cm-1).25
Complexes 9 and 10 are quite stable, also in solution, but
the two PPh3 ligands can be easily displaced by dppe, giving
the substituted derivatives [Ag(pz-N(CO)R)(dppe)] (R ) cy-
clohexyl, 9a; R ) p-tolyl, 10a) showing ν(CdO) shifts to 1637
and 1649 cm-1 respectively.
If a PPh3-containing diethyl ether suspension of complex 1
or 2 is saturated with CO2, the formation of a white product,
showing a strong IR absorption at 1740 cm-1, occurs. On the
basis of the IR spectrum and in analogy to the reaction with
COS previously described, the new species is formulated as
[Ag(pz-CO2)(PPh3)2], 8. Complex 8 shows a very fast loss of
CO2 if suspended or dissolved in any solvent, and even in the
solid state it rapidly extrudes carbon dioxide, giving the starting
[Ag2(pz)2(PPh3)3] complex and free PPh3. If 8 is reacted with
dppe (under a CO2 atmosphere), a product formulated as [Ag(pz-
CO2)(dppe)], 8a, is obtained. Complex 8a exhibits a strong IR
band centered at 1713 cm-1. However, although 8a is appar-
ently more stable than complex 8, also in this case any further
characterization is hampered by the easy loss of carbon dioxide.
Reactions of complexes 1 and 2 with COS, CO2, and RNCO
(R ) cyclohexyl or p-tolyl) give a series of products which
have similar structures (as inferred on the basis of IR spectra)
but present different stabilities, depending on the nature of the
heterocumulene employed. The common reaction pathway can
be exemplified by Scheme 2. In all cases, the presence of free
PPh3 in the reaction medium was proved to be necessary to
obtain high yields (>90%) of analytically pure products.
Probably, in order to favor the reactions between complex 1
or 2 and heterocumulenes, the (incipient) opening of the Ag(µ-
pz)2Ag bridge is necessary. The presence of free PPh3
transforms 1 into 2 and then promotes the formation of
monomeric species, such as [(PPh3)3Ag(pz)] and [(PPh3)4Ag]-
(19) Masciocchi, N.; Moret, M.; Sironi, A.; Ardizzoia, G. A.; Cenini, S.;
La Monica, G. J. Chem. Soc., Chem. Commun. 1995, 1955.
(20) Ardizzoia, G. A.; Maspero, A.; La Monica, G.; Moret, M.; Masciocchi,
N. To be published.
(21) Pandey, K. K. Coord. Chem. ReV. 1995, 140, 37.
(22) Brehnan, G. J.; Anderson, R. A.; Zalkin, A. Inorg. Chem. 1986, 25,
1761.
(24) However, the formation of a labile Ag(I)-{CO2} species, i.e. [L2Ag-
(pz)(CO2)], cannot be ruled out. For comparison, [Ni(PCy3)2(CO2)],
which contains a side-on CO2 bound to the nickel atom, has been
reported to exhibit a ν(CO2) at 1740 cm-1, exactly at the same
frequency evidenced by complex 8. See: Aresta, M.; Nobile, C. F.;
Albano, V. G.; Forni, E.; Manassero, M. J. Chem. Soc., Chem.
Commun. 1975, 637.
(23) Ardizzoia, G. A.; Angaroni, M.; La Monica, G.; Masciocchi, N.; Moret,
M. J. Chem. Soc., Dalton Trans. 1990, 2277.
(25) Valach, F.; Kohout, J.; Dunaj-Jurco, M.; Hvastijova´, M.; Gazo, J. J.
Chem. Soc., Dalton Trans. 1979, 1867.

Silver(I) Pyrazolates
Inorganic Chemistry, Vol. 36, No. 11, 1997 2327
(pz) (detected by 31P-NMR spectra), where nucleophilic attack
of uncoordinated nitrogen atoms on the heterocumulenes can
occur.
mmol). The suspension was stirred for 2 h at -78 °C, and then COS
was removed under vacuum. A 20 mL portion of diethyl ether
(maintained at -78 °C) was then added, and the suspension was stirred
for an additional 1/2 h. The diethyl ether (containing excess PPh3) was
carefully decanted, and the procedure was repeated twice. Finally, the
white residue was vacuum-pumped to remove residual Et2O. Complex
7 shows a strong IR absorption at 1612 cm-1, and is quite stable at
-78 °C, but rapidly turns brown when the temperature is raised above
-10 °C, thus preventing any further characterization.
[Ag(pz-COS)(dppe), 7a. When the aforementioned procedure was
carried out in the presence of dppe (in place of PPh3), after workup of
the residue (employing acetone instead of diethyl ether) it was possible
to isolate complex 7a, which was sufficiently stable to allow an
analytical characterization. Anal. Calcd for C30H27AgN2P2OS: C,
56.87; H, 4.27; N, 4.42. Found: C, 56.90; H, 3.95; N, 4.44.
[Ag(pz-CO2)(PPh3)2], 8. CO2 was bubbled through a suspension
of 2 (250 mg, 0.22 mmol) in diethyl ether containing PPh3 (120 mg,
0.46 mmol). The suspension was stirred for 2 h in a CO2 atmosphere,
and then the solid was isolated by filtration (under CO2) and dried in
a flow of carbon dioxide. The extreme lability of the functionalized
CO2 molecule in complex 8 hampered any further characterization of
the species.
Experimental Section
All reactions were carried out under an atmosphere of dry nitrogen
to avoid moisture. All chemicals (Aldrich Chemical Co.) were used
as supplied except 1,2-bis(diphenylphosphino)ethane (dppe), which was
recrystallized from methanol. Solvents were purified and dried by
standard methods. [Ag(pz)]n was prepared according to the Bu¨chner
method.4 Infrared spectra were recorded on a Bio-Rad FTIR 7
instrument, 31P-NMR spectra were acquired on a Varian XL-200
spectrometer operating at 81 MHz, and conductivity measurements were
performed on an Orion Research Type 101-A instrument. Elemental
analyses were carried out at the microanalytical laboratory of this
university.
[Ag(pz)(PPh3)]2, 1. To a suspension of [Ag(pz)]n (2.78 g, 15.9
mmol) in CH2Cl2 (40 mL) was added solid PPh3 (6.20 g, 23.7 mmol).
The suspension was stirred overnight and then filtered, and the white
solid was washed with diethyl ether (50 mL) and dried under vacuum
(82% yield). Anal. Calcd for C21H18AgN2P: C, 57.66; H, 4.12; N,
6.41. Found: C, 57,42; H, 4.35; N, 6.35. Crystals suitable for X-ray
analysis were obtained by slow diffusion of diethyl ether into a
dichloromethane solution of 1.
[Ag2(pz)2(PPh3)3], 2. To a suspension of [Ag(pz)]n (2.74 g, 15.7
mmol) in 150 mL of CH2Cl2 was added PPh3 (20.4 g, 78.5 mmol)
with stirring. In a few minutes, [Ag(pz)]n dissolved, giving a clear
solution. The solution was stirred for an additional 1 h and then
evaporated to dryness. The oily residue was treated with diethyl ether,
giving a white solid, which was filtered off, washed with diethyl ether,
and dried under vacuum (92% yield). Anal. Calcd for C60H51-
Ag2N4P3: C, 63.38; H, 4.49; N, 4.93. Found: C, 63.56; H, 4.28; N,
5.01. Crystals suitable for X-ray analysis were obtained by slow
diffusion of diethyl ether into a dichloromethane solution of 2 containing
PPh3.
[Ag(pz-CO2)(dppe)], 8a. This derivative was obtained by reacting
2 with CO2 in the presence of dppe in acetone under the experimental
conditions used for 8. Also in this case, the rapid loss of CO2 from
complex 8a prevented characterization.
[Ag(pz-N(CO)R)(PPh3)2] (R ) Cyclohexyl, 9; R ) p-Tolyl, 10).
To a diethyl ether suspension (10 mL) of 2 (250 mg, 0.22 mmol) were
added under stirring 120 mg of PPh3 (0.46 mmol) and the appropriate
isocyanate (200 µL). After 30 min, the white solid was filtered off,
washed with diethyl ether, and dried under vacuum (yields >90%).
Anal. Calcd for C46H44AgN3P2O (9): C, 66.99; H, 5.34; N, 3.40.
Found: C, 66.95; H, 5.30; N, 3.42. Calcd for C47H40AgN3P2O (10):
C, 67.79; H, 4.81; N, 5.05. Found: C, 67.81; H, 4.79; N, 5.10.
[Ag(pz-N(CO)R)(dppe)] (R ) Cyclohexyl, 9a; R ) p-Tolyl, 10a).
Complex 9 or 10 was dissolved in the minimum amount of dichlo-
romethane, and solid dppe (Ag:dppe molar ratio of 1:1.2) was added.
The solution was stirred for 2 h and then concentrated to a small volume.
The white solid that formed was isolated by filtration, washed with
acetone, and dried under vacuum. Anal. Calcd for C36H38AgN3P2O
(9a): C, 61.89; H, 5.44; N, 6.02. Found: C, 61.93; H, 5.43; N, 6.05.
Calcd for C37H34AgN3P2O (10a): C, 62.89; H, 4.82; N, 5.95. Found:
C, 62.67; H, 4.68; N, 5.88.
Crystallography. Crystal data and experimental conditions are
summarized in Table 3. A least-squares fit of 25 randomly oriented
intense reflections in the 10-14° (θ) range provided the unit cell
parameters. Intensities were collected, at room temperature, on a four-
circle automated CAD4 diffractometer, using graphite-monochromatized
Mo KR radiation (λ ) 0.701 73 Å) and a variable scan range with a
25% extension at each end for background evaluation. Three standard
reflections, measured at regular intervals, showed stability of the crystals
over the data collection period. All data were corrected for Lorentz
and polarization effects. An empirical absorption correction,26 based
on ψ scans of three reflections having ø near 90°, was applied (ψ
0-360°, every 10°).
[Ag(pz)(PCy3)]2, 3. The preparation of 3 was similar to that of
complex 1 (87% yield). Employing a large PCy3:Ag molar ratio, we
isolated only the 1:1 adduct. Anal. Calcd for C21H36AgPN2: C, 55.39;
H, 7.91; N, 6.15. Found: C, 55.43; H, 7.84; N, 6.21. 31P-NMR (223
1
K, CD2Cl2): two doublets centered at 37.9 ppm; J(107Ag-P) ) 583
1
Hz, J(109Ag-P) ) 672 Hz.
[Ag(pz-CS2)(PPh3)2], 4. To a solution of complex 1 or 2 (about
100 mg) in CH2Cl2 (6 mL) containing PPh3 (1:2 Ag:PPh3 ratio) was
added CS2 (0.5 mL). The solution rapidly turned red. After 30 min,
the volume was reduced to ca. 1 mL, and diethyl ether (10 mL) was
added. The pink precipitate was filtered off, washed with diethyl ether
(2 mL), and dried under vacuum (78% yield). The reaction can also
be carried out in pure CS2 or in diethyl ether, complex 4 being always
recovered in an analytically pure form. Anal. Calcd for C40H33-
AgN2P2S2: C, 61.94; H, 4.26; N, 3.61. Found: C, 62.01; H, 4.20; N,
3.53. Crystals suitable for X-ray analysis were obtained by slow
evaporation of a CS2 solution of 4.
[Ag(pz-CS2)(dppe)], 4a. Complex 4 was suspended in acetone, and
solid dppe (Ag:dppe molar ratio of 1:1.2) was added. The solution
was stirred for 2 h, and then the pink solid was filtered off, washed
with acetone, and dried under vacuum (84% yield). Anal. Calcd for
C30H27AgN2P2S2: C, 55.47; H, 4.16; N, 4.31. Found: C, 55.51; H,
4.27; N, 4.42.
[Ag(pz-CS2)(PPh3)], 5. Complex 5 was simply obtained by
suspending 4 in diethyl ether. The initially pink suspension became
orange within a few minutes. After 2 h of stirring, the orange solid
was filtered off, washed with diethyl ether, and dried under vacuum.
Anal. Calcd for C22H18AgN2P2S2: C, 51.46; H, 3.51; N, 5.46.
Found: C, 51.59; H, 3.47; N, 5.48.
[Ag(pz-CS2)]n, 6. Complex 4 or 5 was suspended in acetone, and
the suspension was stirred at 50 °C for 2 h, affording a brown solid,
which was recovered by filtration, washed with acetone and diethyl
ether, and dried under vacuum. Anal. Calcd for C4H3AgN2S2: C,
19.12; H, 1.19; N, 11.16. Found: C, 19.17; H, 1.18; N, 11.08.
[Ag(pz-COS)(PPh3)2], 7. At -78 °C, 3 mL of COS was condensed
onto 300 mg (0.26 mmol) of complex 2 and 140 mg of PPh3 (0.53
The structures were solved by direct methods (SIR 9227 ) and
difference Fourier methods and refined by full-matrix least-squares
procedures using the SHELX 93 suite of programs,28 locally adapted
on a Silicon Graphics Indigo computer running IRIX 4.01. Scattering
factors, corrected for the real and imaginary anomalous dispersion terms,
were taken from the internal library of SHELX 93. Anisotropic thermal
parameters were assigned to all non-hydrogen atoms. Phenyl rings
were treated as rigid bodies, with C-C bond distances of 1.390 Å and
internal angles of 120°; the contribution of the hydrogen atoms to the
scattering factors was included in the last stages of the refinement,
setting the H atoms in ideal positions with isotropic thermal parameters
(26) North, A. C. T.; Phillips, D. C.; Mathews, F. S. Acta Crystallogr.,
Sect. A 1968, 24, 351.
(27) Altomare, A.; Cascarano, G.; Giacovazzo, C.; Guagliardi, A.; Burla,
M. C.; Polidori, G.; Camalli, M. J. Appl. Crystallogr. 1994, 27, 435.
(28) Sheldrick, G. M. SHELXL 93: Program for the refinement of crystal
structures. University of Go¨ttingen, 1993.

2328 Inorganic Chemistry, Vol. 36, No. 11, 1997
Ardizzoia et al.
Table 3. Crystal Data and Data Collection Parameters for Compounds 1, 2, and 4
1
2
4
formula
fw
crystal system
space group
a, Å
b, Å
c, Å
R, deg
â, deg
γ, deg
V, Å3
C42H36Ag2N4P2
874.42
triclinic
P1h
9.567(2)
11.440(2)
10.073(2)
93.59(2)
64.01(2)
107.24(2)
943.5(3)
1
C60H51Ag2N4P3
1136.70
triclinic
P1h
9.752(2)
14.163(2)
20.450(2)
101.84(1)
99.83(2)
100.68(2)
2651.8(7)
C40H33AgN2P2S2
775.61
triclinic
P1h
10.329(4)
13.082(2)
14.284(3)
86.71(2)
75.14(2)
74.79(2)
1800.1(8)
2
Z
D
2
calc g‚cm-3
1.539
1.16
22
1.424
0.87
22
1.431
0.80
22
µ, mm-1
T, °C
radiation
graphite-monochromatized Mo KR, λ ) 0.710 73 Å
crystal size, µm
60 × 60 × 80
0.92
0.028, 0.065
70 × 120 × 200
30 × 200 × 250
0.64
0.028, 0.070
min transm factor
0.81
0.025, 0.064
b
R,a Rw
2
4
a R ) Σ||Fo| -|Fc||/Σ|Fo|. b Rw ) [Σw(Fo - Fc2)2/ΣwFo ]1/2
.
riding on those of the carbon atoms to which they are attached. For
complex 4, the X-ray data did not allow discrimination among the two
possible orientations of the pyrazolato ring; therefore, we arbitrarily
attributed the N and C labels to the atoms adjacent to the ipso nitrogen
atom, bearing in mind that, as evidenced also from the molecular
features (see Results and Discussion), they are probably disordered over
the two sites. The peaks in the final difference Fourier maps were
randomly located. Final fractional atomic coordinates and bond
distances and angles are supplied as Supporting Information.
silver metals might be accessible. In principle, fine tuning of
such properties could be achieved by varying the electronic,
and steric, properties of the phosphine ligands, as well as by
employing suitably substituted pyrazoles. Studies are in
progress to verify these hypotheses.
Acknowledgment. We thank the Consiglio Nazionale delle
Ricerche (CNR) and the Ministero dell’Universita` e della
Ricerca Scientifica e Tecnologica (MURST) for financial
support. We gratefully acknowledge the reviewers for thorough
revisions and suggestions. The technical support of Mr. Gianni
Mezza is also acknowledged.
Supporting Information Available: The 31P-NMR spectrum of
complex 1 (CD2Cl2, 173 K) (1 page). X-ray crystallographic files, in
CIF format, for compounds 1, 2, and 4 are available on the Internet
only. Ordering and access information is given on any current masthead
page.
Conclusions
The synthesis, the structural properties, and the reactivity
toward heterocumulenes of the dinuclear triphenylphosphine/
pyrazolate derivatives of silver(I) [Ag(pz)(PPh3)]2 and
[Ag2(pz)2(PPh3)3] have been described. The lability of the
triphenylphosphine ligands, evidenced, in solution, by the
presence of several (complex) equilibria processes, suggests that
a rich chemistry involving substitution (and insertion) at the
IC960908J