Pyrazole complexes as anion receptors: Effects of changing the metal, the pyrazole substitution pattern, and the number of pyrazole ligands

Article abstract of DOI:10.1021/ic0700046

Compound cis,fac-[Mo(η³-allyl)(CO)₂(Hdmpz) ₃]BAr′₄ (1) (Hdmpz = 3,5-dimethylpyrazole, Ar′ = 3,5-bis(trifluoromethyl)-phenyl) undergoes rapid substitution of one of the pyrazole ligands by anions, including the low nucleophilic ReO₄ ^-, a reaction that afforded [Mo(OReO₃)(η³- allyl)(CO)₂(Hdmpz)₂] (2), structurally characterized by X-ray diffraction. The new compounds fac-[Mn(CO)₃(Hdmpz) ₃]BAr′₄ (4a) and fac-[Mn(CO)₃(H ^tBupz)₃]BAr′₄ (4b) (H^tBupz = 3(5)-tert-butylpyrazole) also undergo pyrazole substitution with most anions, and the product from the reaction with nitrate was crystallographically characterized. Compounds 4a,b were found to be substitutionally stable toward perrhenate, and the adducts [Mn(CO)₃(Hdmpz)₃] ·[ReO₄] (7a) and [Mn(CO)₃(H^tBupz) ₃]·[ReO₄]·[Bu₄N] ·[BAr′₄] (7b), crystallographically characterized, display hydrogen bonds between one of the perrhenate oxygens and the N-H groups of two of the pyrazole ligands. The structurally similar adduct [Re(CO) ₃(Hdmpz)₃]·[ReO₄] (8) was found to result from the interaction of [Re(CO)₃(Hdmpz)₃] BAr′₄ with perrhenate. The reaction of [Re(OTf)(CO) ₅] with 3,5-dimethylpyrazole (Hdmpz) afforded [Re(CO) ₅(Hdmpz)]OTf (9). The reaction of 9 with Hdmpz and NaBAr′₄ yielded [Re(CO)₄-(Hdmpz)₂] BAr′₄ (10), which was found to be unstable toward chloride anion. In contrast, the new compound fac,cis-[Re(CO)₃(CN ^tBu)(Hdmpz)₂]BAr′₄ (11) is stable in solution in the presence of different anions. Binding constants for 11 with chloride, bromide, and nitrate are 1-2 orders of magnitude lower than those found for these anions and rhenium tris(pyrazole) hosts, indicating that the presence of the third pyrazole ligand is crucial. Compounds fac-[Re(CO) ₃(HPhpz)₃]BAr′₄ (14) (HPhpz = 3(5)-phenylpyrazole) and fac-[Re(CO)₃(Hlndz)₃] BAr′₄ (15) (Hlndz = indazole) are, in terms of anion binding strength and selectivity, inferior to those with dimethylpyrazole or tert-butylpyrazole ligands.

Full text of DOI:10.1021/ic0700046

Inorg. Chem. 2007, 46, 3407−3418
Pyrazole Complexes as Anion Receptors: Effects of Changing the
Metal, the Pyrazole Substitution Pattern, and the Number of Pyrazole
Ligands
Sonia Nieto,† Julio Pe´rez,*,† Luc´ıa Riera,*,† V´ıctor Riera,† Daniel Miguel,‡ James A. Golen,§ and
Arnold L. Rheingold§
Departamento de Qu´ımica Orga´nica e Inorga´nica-IUQOEM, Facultad de Qu´ımica, UniVersidad
de OViedo-CSIC, 33006 OViedo, Spain, Departamento de Qu´ımica Inorga´nica, Facultad de
Ciencias, UniVersidad de Valladolid, 47005 Valladolid, Spain, and Department of Chemistry,
UniVersity of California, San Diego, 9500 Gilman DriVe, La Jolla, California 92093
Received January 2, 2007
Compound cis,fac-[Mo(
η
3-allyl)(CO)2(Hdmpz)3]BAr 4
′
(1) (Hdmpz
)
3,5-dimethylpyrazole, Ar′ ) 3,5-bis(trifluoromethyl)-
-
phenyl) undergoes rapid substitution of one of the pyrazole ligands by anions, including the low nucleophilic ReO4
a reaction that afforded [Mo(OReO3)(
new compounds fac-[Mn(CO)3(Hdmpz)3]BAr
,
η
3-allyl)(CO)2(Hdmpz)2] (2), structurally characterized by X-ray diffraction. The
(4a) and fac-[Mn(CO)3(HtBupz)3]BAr (4b) (HtBupz
3(5)-tert-
′
′
)
4
4
butylpyrazole) also undergo pyrazole substitution with most anions, and the product from the reaction with nitrate
was crystallographically characterized. Compounds 4a,b were found to be substitutionally stable toward perrhenate,
and the adducts [Mn(CO)3(Hdmpz)3]
graphically characterized, display hydrogen bonds between one of the perrhenate oxygens and the N
two of the pyrazole ligands. The structurally similar adduct [Re(CO)3(Hdmpz)3] [ReO4] (8) was found to result from
the interaction of [Re(CO)3(Hdmpz)3]BAr 4 with perrhenate. The reaction of [Re(OTf)(CO)5] with 3,5-dimethylpyrazole
(Hdmpz) afforded [Re(CO)5(Hdmpz)]OTf (9). The reaction of 9 with Hdmpz and NaBAr yielded [Re(CO)4-
‚
[ReO4] (7a) and [Mn(CO)3(HtBupz)3]
‚
[ReO4]
‚
[Bu4N]
‚
[BAr
′
4] (7b), crystallo-
−H groups of
‚
′
′
4
(Hdmpz)2]BAr′ (10), which was found to be unstable toward chloride anion. In contrast, the new compound fac,cis-
4
[Re(CO)3(CNtBu)(Hdmpz)2]BAr
′ (11) is stable in solution in the presence of different anions. Binding constants for
4
11 with chloride, bromide, and nitrate are 1
rhenium tris(pyrazole) hosts, indicating that the presence of the third pyrazole ligand is crucial. Compounds fac-
[Re(CO)3(HPhpz)3]BAr 4 (14) (HPhpz 3(5)-phenylpyrazole) and fac-[Re(CO)3(HIndz)3]BAr 4 (15) (HIndz indazole)
−2 orders of magnitude lower than those found for these anions and
′
)
′
)
are, in terms of anion binding strength and selectivity, inferior to those with dimethylpyrazole or tert-butylpyrazole
ligands.
Introduction
ligands featuring convergently arranged hydrogen-bond
donor groups have begun to be used as anion receptors.2
Parkin, Reger, and Halcrow have reported the structural
characterization of supramolecular adducts of the type
[LnM(Hpz′)3]‚‚‚Cl (Hpz′ ) generic pyrazole), featuring a
chloride anion hydrogen-bonded by the N-H groups of three
pyrazoles, the convergent geometry of which results from
their bonding to the metal- or metalloid-based LnM frag-
ment.3 Cationic metalloreceptors [LnM(Hpz′)3]+ could be
Metals have been incorporated into the structures of
supramolecular anion hosts for a variety of purposes.1
Recently, it has been found that metals can serve as the major
geometry-organizing element, thus allowing for a modular
synthesis of the hosts, and coordination compounds with
* To whom correspondence should be addressed. E-mail: japm@
uniovi.es (J.P.); lrm@fq.uniovi.es (L.R.). Fax: (34) 985103446 (J.P.).
† Universidad de Oviedo-CSIC.
‡ Universidad de Valladolid.
(2) (a) Bondy, C. R.; Gale, P. A.; Loeb, S. J. Chem. Commun. 2001, 729.
(b) Wallace, K. J.; Daari, R.; Belcher, W. J.; Abouderbala, L. O.;
Boutelle, M. G.; Steed, J. W. J. Organomet. Chem. 2003, 666, 63. (b)
Bondy, C. R.; Gale, P. A.; Loeb, S. J. J. Am. Chem. Soc. 2004, 126,
5030. (c) Rice, C. R. Coord. Chem. ReV. 2006, 250, 3190.
§ University of California.
(1) (a) Beer, P. D.; Gale, P. A. Angew. Chem., Int. Ed. 2001, 40, 486. (b)
Steed, J. W. Chem. Commun. 2006, 2637. (c) Filby, M. H.; Steed, J.
W. Coord. Chem. ReV. 2006, 250, 3200.
10.1021/ic0700046 CCC: $37.00
Published on Web 03/17/2007
© 2007 American Chemical Society
Inorganic Chemistry, Vol. 46, No. 8, 2007 3407

Nieto et al.
Scheme 1. Substitution of a Hdmpz Ligand for Chloride by Addtition of [Bu4N][Cl] to a Solution of cis,fac-[Mo(η3-C3H5)(CO)2(Hdmpz)3] (1)
thought of as the reverse of the tris(pyrazolyl)borates and
their analogues, a widely employed family of ligands.4
We have recently reported the synthesis of the octahedral
fac-[Re(CO)3(Hpz′)3]BAr′4 compounds and the study of their
behavior toward anions, both in solution and in the solid
state.5 These compounds constitute a new class of transition
metal-based supramolecular anion receptors where the geo-
metrical preferences of the metal are taken advantage of to
organize the ditopic pyrazole molecules such that their N-H
groups can converge toward an external anion. Distinctive
features of our receptors are the fac geometry of the pyrazoles
and the employment of the BAr′4- (Ar′ ) 3,5-bis(trifluoro-
methyl)phenyl) counteranion, with a high delocalization of
the negative charge. In the studies carried out so far,5 we
have found that, both in solution and in the solid state (for
the nitrate anion), two out of the three pyrazoles are the ones
that simultaneously form hydrogen bonds with anions, and
we have attributed this feature to the reluctance of our
complexes to distort the L-M-L angles. We set out to
complete these investigations, including structural studies of
adducts with other anions as well as the behavior of other
cationic octahedral fac-tris(pyrazole) transition metal com-
plexes. Our results in this area are the matter of the present
contribution.
behavior as an anion receptor because, in contrast to the
majority of Mo(II) carbonyl complexes,7 most pseudoocta-
hedral molybdenum allyl dicarbonyl complexes with two
coordination sites occupied by nitrogen-donor ligands are
structurally rigid in solution.8 Indeed, solution spectroscopic
studies showed that the structure of the cationic complex of
1 is rigid and that no fast pyrazole exchange was taking place.
In addition, complexes containing the {Mo(η3-allyl)(CO)2}
fragment do not need to be handled under strictly air- and
moisture-free conditions.9
The addition of the equimolar amount of tetrabutyl-
ammonium chloride to a CH2Cl2 solution of 1 led to the
almost instantaneous formation of a new species with IR
ν(CO) bands at 1939 and 1837 cm-1, significantly lower than
those found for 1 (1951 and 1863 cm-1) and closely similar
to those found for the neutral complex [MoBr(η3-allyl)(CO)2-
(Hdmpz)2], recently reported by Villafan˜e and co-workers
(1942 and 1843 cm-1).10 In fact, the new bands were found
to correspond to the complex [MoCl(η3-allyl)(CO)2(Hdmpz)2]
(2), independently prepared as depicted in Scheme 1 and
detailed in the Experimental Section. The 1H NMR spectrum
of the chloro complex indicates the presence of two non-
equivalent pyrazole ligands, consistent with the asymmetric
structure displayed in Scheme 1 and similar to the one
demonstrated by X-ray diffraction for [MoBr(η3-allyl)(CO)2-
(Hdmpz)2].10
Results and Discussion
Perrhenate, an anion much less nucleophilic than chloride,
also effects the substitution of one of the pyrazoles in 1.
The product, complex [Mo(OReO3)(η3-allyl)(CO)2(Hdmpz)2]
(3), was characterized by X-ray diffraction (see Figure 1).
Although of poor quality, the results of the crystallographic
analysis establish that its pseudooctahedral molecule consists
Metals Other Than Rhenium. Molybdenum and
Manganese Complexes. We have recently prepared the
compound cis,fac-[Mo(η3-allyl)(CO)2(Hdmpz)3]BAr′4 (1)
(Hdmpz ) 3,5-dimethylpyrazole), the structural characteriza-
tion of which confirmed the fac disposition of the three
pyrazole ligands.6 This compound was chosen to study its
-
of two Hdmpz ligands and a monodentate ReO4 ligand
(3) (a) Looney, A.; Parkin, G.; Rheingold, A. L. Inorg. Chem. 1991, 30,
3099. (b) Reger, D. L. Ding, Y.; Rheingold, A. L. Ostrander Inorg.
Chem. 1994, 33, 4226. (c) Liu, X.; Kilner, Colin A.; Halcrow, M. A.
Chem. Commun. 2002, 704. (d) Renard, S. L.; Kilner, C. A.; Fisher,
J.; Halcrow, M. A. Dalton Trans. 2002, 4206.
(6) Pe´rez, J.; Morales, D.; Nieto, S.; Riera, L.; Riera, V.; Miguel, D. Dalton
Trans. 2005, 884.
(7) Baker, P. K. AdV. Organomet. Chem. 1995, 40, 45.
(8) Pe´rez, J.; Riera, L.; Riera, V.; Garc´ıa-Granda, S.; Garc´ıa-Rodr´ıguez,
E. J. Am. Chem. Soc. 2001, 123, 7469.
(4) Trofimenko, S. Polyhedron 2004, 23, 193.
(5) (a) Nieto, S.; Pe´rez, J.; Riera, V.; Miguel, D.; Alvarez, C. Chem.
Commun. 2005, 546. (b) Nieto, S.; Pe´rez, J.; Riera, L.; Riera, V.;
Miguel, D. Chem.sEur. J. 2006, 12, 2244.
(9) Morales, D.; Navarro Clemente, M. E.; Pe´rez, J.; Riera, L.; Riera, V.;
Miguel, D. Organometallics 2002, 21, 4934.
(10) Paredes, P.; Miguel, D.; Villafan˜e, F. Eur. J. Inorg. Chem. 2003, 995.
3408 Inorganic Chemistry, Vol. 46, No. 8, 2007

Pyrazole Complexes as Anion Receptors
Figure 1. Thermal ellipsoid (30%) plot of cis,cis-[Mo(OReO3)(η3-
allyl)(CO)2(Hdmpz)2] (3).
Scheme 2. Synthesis of the Potential New Receptors
fac-[Mn(CO)3(Hdmpz)3]BAr′4 (4a) and fac-[Mn(CO)3(HtBupz)3]BAr′4
(4b)
coordinated to an unremarkable cis-{Mo(η3-allyl)(CO)2}
fragment. One of the pyrazole ligands is trans to the allyl
group, and the other is trans to one of the carbonyls, so that
the resulting asymmetric geometry is similar to that previ-
ously encountered for [MoBr(η3-allyl)(CO)2(Hdmpz)2].10 IR
Figure 2. (a) Thermal ellipsoid (30%) plot of fac-[Mn(CO)3(Hdmpz)3]-
BAr′4 (4a). (b) Thermal ellipsoid (30%) plot of fac-[Mn(CO)3(HtBupz)3]-
BAr′4 (4b).
1
and H NMR spectroscopies indicate that this structure is
maintained in solution.
As expected, like their rhenium congeners, the new
cationic complexes present in 4a,b have pseudooctahedral
geometry and a fac disposition of the three pyrazole ligands,
both in solution (as indicated by the fac-tricarbonyl pattern
of the ν(CO) bands in the IR spectra and by the presence of
a single set of pyrazole signals in the 1H NMR spectra) and
in the solid state.
The reactions of 4a,b with the equimolar amount of
tetrabutylammonium chloride in dichloromethane afforded
the products of the substitution of one of the pyrazole ligands
by chloride, namely, the neutral compounds fac-[MnCl(CO)3-
(Hdmpz)2] (5a) and fac-[MnCl(CO)3(HtBupz)2] (5b) (see
Scheme 3 and Experimental Section). These compounds are
closely similar to the manganese complexes recently reported
by Villafan˜e and co-workers.11 Most of the less nucleophilic
anions also led to pyrazole displacement, as judged by the
The results discussed above indicate that, due to the lability
of the pyrazole ligands in compound [Mo(η3-allyl)-
(CO)2(Hdmpz)3]BAr′4 (1), this cannot be used as an anion
receptor.
We next turned our attention to manganese compounds.
The structural chemistry of Mn(I) carbonyl complexes is
closely related to that of Re(I), the latter species being the
ones that we initially found to be stable anion receptors.5
Compounds fac-[Mn(CO)3(Hdmpz)3]BAr′4 (4a) and fac-
[Mn(CO)3(HtBupz)3]BAr′4 (4b) could be readily synthesized
by a method similar to the one previously employed for the
synthesis of the rhenium analogues (see Scheme 2 and
Experimental Section). These new compounds were char-
acterized in solution by spectroscopy (see Experimental
Section) and in the solid-state by X-ray diffraction (see Figure
2). Pyrazole complexes of Mn(I) carbonyl fragments are rare,
and in only a few examples X-ray structural data are
available.11
(11) Arroyo, M.; Lopez-Sanvicente, A.; Miguel, D.; Villafan˜e, F. Eur. J.
Inorg. Chem. 2005, 4430.
Inorganic Chemistry, Vol. 46, No. 8, 2007 3409

Nieto et al.
Scheme 3. Synthesis of fac-[MnCl(CO)3(Hpz′)2] (5a,b) Complexes: Straightforward or by Substitution of an Pyrazole Ligand for Chloride Anion
shift to significantly lower wavenumber values, typical of
neutral fac-[MnX(CO)3(Hdmpz)2] complexes, in the IR
ν(CO) bands. In particular, this was conclusively demon-
strated for the nitrate anion. Thus, the product of the reaction
of 4a with tetrabutylammonium nitrate was isolated and its
structure was determined by X-ray diffraction. The results
showed that the product is an adduct in which noncoordinated
3,5-dimethylpyrazole (resulting from its displacement by the
nitrate anion out of the first metal coordination sphere)
interacts only through hydrogen bonds with the new complex
fac,cis-[Mn(ONO2)(CO)3(Hdmpz)2] (6), featuring a mono-
dentate nitrato ligand (see Figure 3).
The main hydrogen bond interactions in the [6]‚[Hdmpz]
adduct are shown as dotted lines in Figure 3. The N-H group
of the second-sphere pyrazole acts as hydrogen bond donor
toward two of the oxygen atoms of the nitrato ligand
(O(5)‚‚‚N(8) ) 3.283(4) Å, H(8)‚‚‚O(5) ) 2.427 Å, N(8)‚‚‚
H(8)‚‚‚O(5) ) 174.9(3)°; O(4)‚‚‚N(8) ) 3.270(4) Å, H(8)‚‚‚
O(4) ) 2.695 Å, N(8)‚‚‚H(8)‚‚‚O(4) ) 125.6(3)°), and its
pyridine-type nitrogen acts as hydrogen bond acceptor toward
the N-H group of one of the pyrazole ligands (N(2)‚‚‚N(7)
) 2.904(4) Å, H(2)‚‚‚N(7) ) 1.947 Å, N(2)‚‚‚H(2)‚‚‚N(7)
) 163.3(3)°). In addition, there is an interligand nitrato-
pyrazole hydrogen bond (N(4)‚‚‚O(4) ) 2.871(4) Å,
H(4)‚‚‚O(4) ) 2.515 Å; N(4)‚‚‚H(4)‚‚‚O(4) ) 107.6(2)°).
Unlike the molybdenum compound 1, the manganese
compounds 4a,b are stable in solution (i.e., do not undergo
pyrazole substitution) in the presence of the poorly nucleo-
philic perrhenate anion, and the 1:1 binding constants in
acetonitrile were found to be 28(1) and 22(1) M-1, respec-
tively. Slow diffusion of hexane into a dichloromethane
solution of an equimolar mixture of compound 4a and [Bu4N]-
[ReO4] afforded two different types of crystals, and their 1H
NMR spectra showed them to have the fac-[Mn(CO)3-
(Hdmpz)3]‚[ReO4] (7a) and [Bu4N][BAr′4] compositions.
Such a segregation into two different phases has been
previously found by us when using cationic receptors
-
containing the BAr′4 counteranion together with tetra-
butylammonium salts. However, a similar crystallization of
an equimolar mixture of compound 4b and the salt [Bu4N]-
[ReO4] yielded crystals of a single phase 7b (see below)
containing the four ions [Mn(CO)3(HtBupz)3]+, [ReO4]-,
[Bu4N]+, and [BAr′4]-. Thus, changes that, at first sight, one
could expect to be of little significance in the exact
composition of the complexes exert a dramatic effect on the
composition of the crystalline phase. This is further illustrated
by the fact that the nitrate adduct of the complex fac-
[Re(CO)3(HtBupz)3]+, the rhenium analogue of the cation
present in 4b, was found to crystallize separately from
[Bu4N][BAr′4].5b
The structures of compounds 7a,b were determined by
single-crystal X-ray diffraction, and the results are displayed
in Figure 4. For comparison purposes, the structure of the
rhenium adduct [Re(CO)3(Hdmpz)3]‚[ReO4] (8), which crys-
tallized separately from the salt [Bu4N]‚[BAr′4], was also
determined, and the results are displayed in Figure 5.
Two features are common to the three structures (7a,b
and 8) and to that of fac-[Re(CO)3(HtBupz)3]‚[NO3], men-
tioned above and previously determined by us:5b (a) only
two out of the three pyrazole ligands of each cationic
complex are simultaneously forming hydrogen bonds with
a given oxoanion; (b) in these hydrogen bonds a single
oxygen atom of the oxoanion is acting as acceptor. Additional
hydrogen bonding between the third pyrazole ligand and
other oxygen atoms of the oxoanion contribute to the solid-
Figure 3. Thermal ellipsoid (30%) plot of the adduct fac,cis-[Mn(ONO2)-
(CO)3(Hdmpz)2] (6) with Hdmpz. Selected distances (Å) and angles (deg)
for 6: O(5)‚‚‚N(8) 3.283(4), H(8)‚‚‚O(5) 2.427; N(8)‚‚‚H(8)‚‚‚O(5) 174.9(3),
O(4)‚‚‚N(8) 3.270(4), H(8)‚‚‚O(4) 2.695, N(8)‚‚‚H(8)‚‚‚O(4) 125.6(3),
N(2)‚‚‚N(7) 2.904(4), H(2)‚‚‚N(7) 1.947, N(2)‚‚‚H(2)‚‚‚N(7) 163.3(3),
N(4)‚‚‚O(4) 2.871(4), H(4)‚‚‚O(4) 2.515, N(4)‚‚‚H(4)‚‚‚O(4) 107.6(2).
3410 Inorganic Chemistry, Vol. 46, No. 8, 2007

Pyrazole Complexes as Anion Receptors
Figure 4. (a) Thermal ellipsoid (30%) plot of the adduct [Mn(CO)3(Hdmpz)3]‚[ReO4] (7a). (b) Thermal ellipsoid (30%) plot of the [Mn(CO)3(HtBupz)3]‚
[ReO4] adduct present in 7b.
state network. Since these facts occur with cationic com-
plexes containing either Mn (7a,b) or (the substantially
larger) Re (8) as a central atom, and both in the presence
(7b) or absence (7a or 8) of the [Bu4N][BAr′4] salt in the
crystalline phase, it seems that they must be dictated by the
geometry of the fac-[M(CO)3(Hpz′)3] (Hpz′ ) generic
pyrazole) complexes rather than by the size or by packing
factors.
Compounds with Only Two Pyrazole Ligands. In our
previous studies with fac-[Re(CO)3(Hdmpz)3]BAr′4 and fac-
[Re(CO)3(HtBupz)3]BAr′4 receptors, we have shown that,
both in the solid state and in solution, the anionic guest forms
simultaneously hydrogen bonds with only two of the three
ligated pyrazoles.5b This is also the solid-state arrangement
found in the structures discussed above.
To complete these studies, and with the goal of evaluating
the effect of the presence of a third pyrazole ligand on the
strength of the host-guest interaction, we set out to prepare
Figure 5. Thermal ellipsoid (30%) plot of the adduct [Re(CO)3(Hdmpz)3]‚
[ReO4] (8).
Inorganic Chemistry, Vol. 46, No. 8, 2007 3411

Nieto et al.
Scheme 4. Synthesis of [Re(CO)4(Hdmpz)2]BAr′4 (10) via the Intermediate [Re(CO)5(Hdmpz)]OTf (9)
compounds of the kind fac,cis-[Re(CO)3(Hdmpz)2(L)]BAr′4
(L ) neutral, two-electron donor not able to act as a good
hydrogen bond donor) and compare the strength of their
anion binding with that displayed by the tris(pyrazole)
compounds. We first attempted to synthesize the compound
[Re(CO)3(Hdmpz)2(tmpz)]BAr′4 (tmpz ) 1,3,5-trimethylpyra-
zole), since the tmpz ligand would most closely mimic the
electronic and steric profile of 3,5-dimethylpyrazole, while
lacking its capability of engaging in strong hydrogen bonds.
However, we could not find a synthetic pathway that would
cleanly afford this compound. Similarly, attempts to prepare
the [Re(CO)3(Hdmpz)2(L)]BAr′4 (L ) N-methylimidazole)
led only to mixtures that could not be resolved.
5, was found to be stable toward anions in solution (see
below).
Besides its spectroscopic characterization in solution, the
solid-state structure of 11 was determined by means of X-ray
diffraction. The results are displayed in Figure 7.
The solution spectral data for compound 11 are consistent
with a structure in solution similar to that found in the solid
On the other hand, we could successfully prepare the
compound cis-[Re(CO)4(Hdmpz)2]BAr′4 (10) as shown in
Scheme 4. Compound 10 as well as the synthetic intermedi-
ate [Re(CO)5(Hdmpz)]OTf (9), both new compounds, were
1
characterized by IR, H NMR, and single-crystal X-ray
diffraction. Thermal ellipsoid representations and selected
distances and angles for compounds 9 and 10 are given in
Figure 6.
The preparation and spectroscopic characterization of the
pentacarbonyl pyrazole compound [Re(CO)5(Hpz)]BF4, closely
related to 9, has been previously reported by Beck and co-
workers.12
In the solid-state structure of 9, a hydrogen bond between
the pyrazole ligand and the triflate anion is characterized by
a N(2)‚‚‚O(11) ) 2.773(7) Å distance and a N(2)‚‚‚H‚‚‚O(11)
) 169(5)° angle, values that suggest a relatively strong
interaction. Treatment of 9 with the equimolar amount of
the salt NaBAr′4 in dichloromethane for a few minutes at
room temperature, followed by reaction with 3,5-dimethyl-
pyrazole in refluxing toluene, yielded cis-[Re(CO)4(Hdmpz)2]-
BAr′4 (10) (see Scheme 4 and Experimental Section).
However, the reaction is not clean, and 10 was obtained
contaminated with a second metal-carbonyl species, as
shown by the IR monitoring of the reaction. Fractional
crystallization afforded pure 10, although in a low yield.
Preliminary experiments revealed that 10 is not stable
toward chloride anion in solution; thus, further study of
its behavior was not pursued. Likewise, the compound
[Re(CO)3(Hdmpz)2(py)]BAr′4 (py ) pyridine) turned out to
be unstable toward substitution of the pyridine ligand by
anions.
Fortunately, the compound fac,cis-[Re(CO)3(CNtBu)-
(Hdmpz)2]BAr′4 (11), prepared as summarized in Scheme
Figure 6. (a) Molecular structure of complex [Re(CO)5(Hdmpz)]OTf (9).
Selected distances (Å) and angles (deg) for 9: N(2)‚‚‚O(11) 2.773(7);
N(2)‚‚‚H‚‚‚O(11) 169(5). (b) Molecular structure of the cation of cis-
[Re(CO)4(Hdmpz)2] BAr′4 (10).
(12) Appel, M.; Sacher, W.; Beck, W. J. Organomet. Chem. 1987, 333,
237.
3412 Inorganic Chemistry, Vol. 46, No. 8, 2007

Pyrazole Complexes as Anion Receptors
Scheme 5. Synthesis of Compound fac-[Re(CNtBu)(CO)3(Hdmpz)2]BAr′4 (11)
Scheme 6. Proposed Equilibria in Solution of Compounds
fac-[M(CO)3(Hpz′)3]BAr′4 in the Presence of an External Anion
state. Thus, the IR spectrum in dichloromethane featured
intense ν(CO) bands at 2038, 1960, and 1940 cm-1,
diagnostic of the fac-{Re(CO)3} fragment, and a medium
intensity ν(CN) band at 2186 cm-1, due to the isocyanide
ligand. As in the tris(pyrazole) complexes discussed above,
the presence of separate signals for the methyl groups in the
3 and 5 positions of the pyrazole ring indicates that the
pyrazole ligands are not labile.5a The presence of a mirror
plane in the molecule of 11 is reflected in the presence of
values of the ν(CO) bands corresponding to 11 undergo only
relatively minor changes to lower wavenumber values
attributed to the small increase in electron density resulting
from the anion hydrogen bonding. Thus, for instance, the
addition of 1 equiv of chloride shifts the higher frequency
ν(CO) band from 2040 to 2032 cm-1. This change is the
largest found for all the studied anions. The 1H NMR spectra
of the 11‚[Bu4NX] mixtures did not show evidence of free
3,5-dimethylpyrazole, and the changes were found to be
dependent on the amount of anion added and to be consistent
with the formation of hydrogen bonds between the pyrazole
N-H groups and the anion. Thus, the shift to lower field of
the pyrazole N-H signals as a response to the anion addition
was used to calculate the binding constants. These were
found to be 75(7), 174(7), and 133(11) M-1 (in CD3CN) for
chloride, bromide, and nitrate, respectively. These values are
1-2 orders of magnitude lower that those obtained for these
anions and the receptor fac-[Re(CO)3(Hdmpz)3]BAr′4.5 There-
1
only one set of pyrazole signals in the H NMR and 13C
NMR spectra and of two weak, low-field signals of different
intensity, due to the two types of carbonyl ligands, in the
13C NMR.
In the solid-state structure of 11, the Re-C(isocyanide)
distance, 2.078(7) Å, is only slightly longer than the Re-
C(carbonyl) distances (1.926(9), 1.962(8), and 1.968(8) Å),
reflecting that the isocyanide is a strong ligand, with
electronic properties similar to those of carbon monoxide.
The rigidity and linearity of the isocyanide ligand (Re-
C(4)-N(5) ) 176.8(6)° and C(4)-N(5)-C(41) ) 177.1(7)°)
keeps the bulky tert-butyl group far from the metal and from
the N-H groups of the pyrazole ligands, so that its presence
should not hinder the approach of the anionic guests.
Compound 11 was found to be substitutionally stable in
the presence of excess of tetrabutylammonium chloride,
bromide, and nitrate. Thus, in the IR spectra of such
solutions, the ν(CN) band of free tert-butyl isocyanide at
2140 cm-1 could not be observed, and the wavenumber
1
fore, in spite of the fact that the low-temperature H NMR
spectroscopy showed that the instantaneous solution struc-
tures are consistent with an interaction of the anionic guest
with only two of the three ligated pyrazoles5b and that it is
also the kind of interaction found in the solid state, the
presence of a third pyrazole ligand significantly enhances
the strength of the receptor-guest interaction. This cannot
be explained on the basis of the different electronic properties
of the pyrazole and the isocyanide as ligands. In fact, the
isocyanide is a stronger acceptor than the pyrazole, and
therefore, if there is any effect of the presence of either
pyrazole or isocyanide as the third ligand on the N-H groups
of the anion-binding pyrazoles, it should be to make stronger
those hydrogen-bond donors of the isocyanide-containing
complex. As mentioned above, since the bulky tBu group is
relatively away from the N-H groups, steric hindrance does
not seem an attractive explanation. Rather, we speculate that
the higher binding constants for the tris(pyrazole) compounds
can be attributed to the presence of three equivalent host-
guest interactions of sufficient strength and which intercon-
version should be kinetically facile (see Scheme 6). On the
other hand, we do not rule out the possibility that an
Figure 7. Thermal ellipsoid (30%) plot of the cation [Re(CNtBu)(CO)3-
(Hdmpz)2]+ of compound 11. Selected distances (Å) and angles (deg) for
11: Re(1)-C(4) 2.078(7); Re-C(4)-N(5) 176.8(6), C(4)-N(5)-C(41)
177.1(7).
Inorganic Chemistry, Vol. 46, No. 8, 2007 3413

Nieto et al.
Table 1. Binding Constant Values for Compound 15 in CD3CN
additional, weaker hydrogen bond between the anion and
the N-H group of the third pyrazole could account for the
difference in binding constants between complexes with two
or three pyrazoles.
anions
Ka (M-1
)
anions
Ka (M-1
)
Cl-
Br-
I-
320 ( 6
404 ( 2
100 ( 2
295 ( 2
HSO4
ReO4
ClO4
141 ( 6
48 ( 6
10.5 ( 0.2
-
-
-
Different Pyrazole Ligands. Since the geometry of the
interaction between the anionic guest and the cationic
[M(CO)3(Hpz’)3] (Hpz′ ) generic pyrazole) host is quali-
tatively the same for the complexes of either 3,5-dimethyl-
pyrazole or 3(5)-tert-butylpyrazole, we decided to investigate
how the choice of different pyrazole ligands could affect the
behavior of the tris(pyrazole) complexes toward anions.
Manganese and rhenium complexes of nonsubstituted
pyrazole were prepared using the same simple procedure that
allowed us to isolate the aforementioned derivatives of
substituted pyrazole. The new compounds fac-[Mn(CO)3-
(Hpz)3]BAr′4 (12) and fac-[Re(CO)3(Hpz)3]BAr′4 (13) were
spectroscopically characterized by IR and NMR. Like its
dimethyl- or tert-butyl-substituted congeners, the manganese
compound 12 was found to resist pyrazole substitution when
treated with perrhenate (a 1:1 binding constant of 28(1) M-1
was found for this anion in acetonitrile) but to undergo
pyrazole substitution in the presence of chloride, bromide,
and nitrate. Compound 13 was found to be substitutionally
stable toward bromide, nitrate, and perrhenate, and binding
constants of 540(27), 112(13), and 63(1) M-1, respectively,
were calculated for these anions (CD3CN). However, treat-
ment of 13 with tetrabutylammonium chloride led to
substitution of one of the pyrazole ligands by chloride. This
result contrasts with the stability showed by the 3,5-
dimethylpyrazole or the 3(5)-tert-butylpyrazole analogues.
The difference can be explained by the steric protection lent
by the substituents, previously noted when comparing the
behavior of fac-[Re(CO)3(Hdmpz)3]BAr′4 and fac-[Re(CO)3-
(HtBupz)3]BAr′4 receptors.5b
-
NO3
hydrogensulfate, perrhenate, and perchlorate. Binding con-
stants for these anions, displayed in Table 1, indicate an
interaction weaker than that found for the tris(pyrazole)
complexes and no selectivity. More basic anions such as
fluoride and dihydrogen phosphate were found to deprotonate
15 to afford a neutral complex, as indicated by the large
shift to lower wavenumber values in the IR ν(CO) bands, a
behavior also displayed by the previously reported tris-
(pyrazole) complexes derived from Hdmpz or HtBupz.5b The
solid-state structures of the 1:1 adducts fac-[Re(CO)3-
(HIndz)3]‚[ReO4] (16) and fac-[Re(CO)3(HIndz)3]‚[ClO4]
(17) were determined by X-ray diffraction, and the results
are shown in Figure 8.
The most revealing feature of these structures is that,
unlike in the adducts of the pyrazole compounds, now only
one of the N-H bonds of each cationic complex forms a
The presence of planar aromatic rings as substituents at
the pyrazole ligands can give rise to stronger hydrogen bond
donor N-H groups (due to the electron-withdrawing char-
acter of the aryl groups when compared with methyl or tert-
butyl groups) and perhaps to a more discriminating binding
cavity if the aryl groups are adequately disposed. Therefore,
we set out to prepare tris(pyrazole) receptors featuring
aromatic groups. Compound fac-[Re(CO)3(HPhpz)3]BAr′4
(14) (HPhpz ) 3(5)-phenylpyrazole) was prepared by the
method used for the derivatives mentioned above and
spectroscopically characterized (see Experimental Section).
Compound 14 was found to be stable toward chloride,
bromide, iodide, nitrate, hydrogensulfate, and perrhenate, and
1:1 binding constants of 2406(125), 1712(90), 80(1), 1592(1),
147(1), and 67(9) M-1, respectively, were calculated for these
anions in deuterated acetonitrile. Albeit comparable, these
values do not offer a clear advantage when compared with
the behavior of fac-[Re(CO)3(Hdmpz)3]BAr′4 and fac-
[Re(CO)3(HtBupz)3]BAr′4 receptors.
Indazole (HIndz) features a fused aromatic ring and thus
can be regarded as a rigid phenyl-substituted pyrazole.
Compound fac-[Re(CO)3(HIndz)3]BAr′4 (15) (see Experi-
mental Section for the synthesis and characterization) was
found to be stable toward chloride, bromide, iodide, nitrate,
Figure 8. (a) Thermal ellipsoid (30%) plot of the adduct fac-[Re(CO)3-
(HIndz)3]‚[ReO4] (16). (b) Thermal ellipsoid (50%) plot of the adduct fac-
[Re(CO)3(HIndz)3]‚[ClO4] (17).
3414 Inorganic Chemistry, Vol. 46, No. 8, 2007

Pyrazole Complexes as Anion Receptors
separately prepared and kept in a septum-stoppered vial during the
titration) were injected through the septum using Hamilton micro-
syringes (10-100 µL). The volume of each addition was 10 µL
before reaching the saturation zone (nearly horizontal line of the
titration profile) and 20 or 40 µL afterward. When the change in δ
is small (as for ReO4-), 20 µL of salt solution was added from the
beginning. Data were treated using the WinEQNMR program.15
Synthesis of [MoCl(η3-C3H5)(CO)2(Hdmpz)2] (2). A solution
of [Mo(CO)6] (0.100 g, 0.379 mmol) in thf (20 mL) was refluxed
until the IR spectrum showed the disappearance of the ν(CO) band
corresponding to the starting material (1981 cm-1, ca. 8 h). The
resulting solution was then allowed to reach room temperature, allyl
chloride (0.28 mL, 3.800 mmol) was added, and the mixture was
refluxed and stirred for 15 min. The solvent was evaporated under
reduced pressure to a volume of 2 mL, CH2Cl2 (20 mL) and Hdmpz
(0.073 g, 0.380 mmol) were added, and the reaction mixture was
stirred for 10 min. Then the resulting yellow solution was
concentrated under vacuum to a volume of 5 mL; addition of hexane
caused the precipitation of a yellow solid which was washed with
hexane (2 × 20 mL). Yield: 0.135 g, 84%. IR (CH2Cl2): ν 1939,
hydrogen bond to a given anion. Therefore, the main effect
of the fused ring, rather than providing an extra hydrogen
bond donor, seems to be hindering the anion approach. As
indicated by the comparison of the binding constants (that
reach higher values for the tris(phenylpyrazole) derivative),
this effect must be much more pronounced for the indazole
derivatives, where the benzene ring is rigidly linked to the
pyrazole ring, than for the phenylpyrazole derivatives, where
there must be free rotation around the phenyl-pyrazole bond.
Conclusion
Unlike previously reported rhenium compounds fac-
[Re(CO)3(Hpz*)3]BAr′4 (Hpz* ) Hdmpz or HtBupz),
molybdenum and manganese cationic tris(pyrazole) hosts
cis,fac-[Mo(η3-allyl)(CO)2(Hdmpz)3]BAr′4 (1) and fac-
[Mn(CO)3(Hpz*)3]BAr′4 (Hpz* ) Hdmpz (4a) or HtBupz
(4b)) are labile toward most anions. The geometry of the
adduct formed between the cationic complex and perrhenate
(the only anion for which no pyrazole substitution at the
manganese center takes place) is the same for manganese
and rhenium complexes.
Although the hydrogen bonding between these tris-
(pyrazole) compounds and anions occurs mainly through two
of the three N-H groups, the presence of the third pyrazole
ligand gives rise to a large enhancement of the binding
strength compared with the bis(pyrazole) compound fac,cis-
[Re(CO)3(CNtBu)(Hdmpz)2]BAr′4 (11).
1
1838 cm-1 (CO). H NMR (CD2Cl2): δ 11.41 [s, br, 1H, NH of
Hdmpz], 10.71 [s, br, 1H, NH of Hdmpz], 6.00 [s, 1H, CH of
Hdmpz], 5.83 [s, 1H, CH of Hdmpz], 3.98 [s, 1H, Hc of η3-C3H5],
3.76 [m, 1H, Hsyn of η3-C3H5], 3.09 [m, 1H, Hsyn of η3-C3H5], 2.96
[s, 3H, CH3 of Hdmpz], 2.26 [s, 3H, CH3 of Hdmpz], 2.15 [s, 3H,
CH3 of Hdmpz], 2.09 [s, 3H, CH3 of Hdmpz], 1.57 [d (3JHH) 11
Hz), 1H, Hanti of η3-C3H5], 1.25 [d (3JHH ) 11 Hz), 1H, Hanti of
η3-C3H5]. Anal. Calcd for C15H21ClMoN4O2: C, 42.82; H, 5.03;
N, 13.32. Found: C, 42.74; H, 5.11; N, 13.29.
Synthesis of [Mn(CO)3(Hdmpz)3]BAr′4 (4a). AgOTf (0.140 g,
0.546 mmol) was added to a solution of [MnBr(CO)5] (0.150 g,
0.546 mmol) in CH2Cl2 (20 mL), and the mixture was stirred in
the dark for 15 min. The resulting AgBr was filtered off and the
solvent evaporated under reduced pressure. The residue was
redissolved in toluene (30 mL), Hdmpz (0.158 g, 1.638 mmol) was
added, and the mixture was refluxed for 20 min. The yellow solution
was evaporated to dryness. The residue was dissolved in CH2Cl2
(20 mL), NaBAr′4 (0.484 g, 0.546 mmol) was added, and the
mixture was stirred at room temperature for 15 min. The solution
was filtered via canula, and the solvent was reduced under vacuum
to a volume of 5 mL. Addition of hexane (10 mL) caused the
precipitation of a yellow solid, which was washed with hexane (2
× 20 mL). Slow diffusion of hexane (15 mL) into a solution of 4a
in CH2Cl2 (5 mL) afforded yellow crystals, one of which was
employed for an X-ray structural determination. Yield: 0.599 g,
85%. IR (CH2Cl2): ν 2043, 1949 cm-1 (CO). 1H NMR (CD2Cl2):
δ 8.82 [s, br, 3H, NH of Hdmpz], 7.70 [m, 8H, Ho of BAr′4], 7.54
[m, 4H, Hp of BAr′4], 6.24 [s, 3H, CH of Hdmpz], 2.43 [s, 9H,
CH3 of Hdmpz], 2.19 [s, 9H, CH3 of Hdmpz]. 13C{1H} NMR
(CD2Cl2): δ 219.8 [CO], 162.2 [q (1JCB ) 49.9 Hz), Ci of BAr′4],
157.9, 145.9 [C3 and C5 of Hdmpz], 135.2 [Co of BAr′4], 129.3 [q
(2JCF ) 33.1 Hz), Cm of BAr′4], 125.0 [q (1JCF ) 271.7 Hz), CF3
of BAr′4], 117.9 [Cp of BAr′4], 110.6 [C4 of Hdmpz], 15.2 [CH3 of
Hdmpz], 11.2 [CH3 of Hdmpz]. Anal. Calcd for C50H36BF24-
MnN6O3: C, 46.53; H, 2.81; N, 6.51. Found: C, 46.68; H, 3.05;
N, 6.48.
Taking into account the stability of the receptors, the
strength of anion binding, and the difference in binding
strength as a response to the nature of the anion, the rhenium
receptors with 3,5-dimethylpyrazole or tert-butylpyrazole
perform better than complexes of Mo or Mn and than Re
complexes with nonsubstituted pyrazole, 3(5)-phenylpyrazole
or indazole.
Experimental Section
All manipulations were carried out under a nitrogen atmosphere
using Schlenk techniques. Compounds 1,6 [MnCl(CO)5],13 [MnBr-
(CO)5],13 and [ReBr(CO)5]14 were prepared as previously reported.
Tetrabutylammonium salts were purchased from Fluka or Aldrich.
Deuterated acetonitrile and dichloromethane (Cambridge Isotope
Laboratories, Inc.) were stored under nitrogen in Young tubes and
1
used without further purification. H NMR and 13C NMR spectra
were recorded on a Bruker Advance 300, DPX-300, or Advance
400 spectrometer. NMR spectra are referred to the internal residual
1
solvent peak for H and 13C{1H} NMR. IR solution spectra were
obtained in a Perkin-Elmer FT 1720-X spectrometer using 0.2 mm
CaF2 cells. NMR samples were prepared under nitrogen using
Kontes manifolds purchased from Aldrich. Oven-dried 5 mm NMR
tubes were subjected to several vacuum-nitrogen cycles, filled with
the solution of the receptor (prepared separately in a Schlenk tube,
typically in a 10-2 M concentration in CD3CN) by means of a 1
mL syringe, and stoppered with rubber septa. After the NMR
spectrum of the receptor was recorded, the successive aliquots of
the tetrabutylammonium salt (typically 4 × 10-2 M in CD3CN,
Synthesis of [Mn(CO)3(HtBupz)3]BAr′4 (4b). Compound 4b
was prepared as described above for 4a from [MnBr(CO)5] (0.150
g, 0.546 mmol), AgOTf (0.140 g, 0.546 mmol), HtBupz (0.203 g,
1.638 mmol), and NaBAr′4 (0.484 g, 0.546 mmol). Slow diffusion
of hexane into a concentrated solution of 4b in CH2Cl2 afforded
(13) Schmidt, S. P.; Trogler, W. C.; Basolo, F. Inorg. Synth. 1990, 28,
160.
(14) Reimer, K. J.; Shaver, A. Inorg. Synth. 1990, 28, 160.
(15) Hynes, M. J. J. Chem. Soc., Dalton Trans. 1993, 311.
Inorganic Chemistry, Vol. 46, No. 8, 2007 3415

Nieto et al.
crystals, one of which was employed for an X-ray determination.
The colorless solution was filtered and evaporated to dryness under
reduced pressure. The residue was extracted with toluene and
Hdmpz (0.011 g, 0.113 mmol) was added and refluxed for 30 min
affording a mixture of a tetracarbonylic and a tricarbonylic species.
The solvent was evaporated in vacuum and the white residue
redissolved in CH2Cl2 (5 mL); slow diffusion of hexane (20 mL)
at -20 °C afforded colorless crystals of the tetracarbonylic
compound 10, one of which was employed for an X-ray analysis.
Yield: 0.040 g, 26%. IR (CH2Cl2): ν 2017, 2014, 2011, 1972 cm-1
(CO). 1H NMR (CD2Cl2): δ 9.35 [s, br, 2H, NH of Hdmpz], 7.74
[m, 8H, Ho of BAr′4], 7.61 [m, 4H, Hp of BAr′4], 6.20 [s, 2H, CH
of Hdmpz], 2.34 [s, 6H, CH3 of Hdmpz], 2.21 [s, 6H, CH3 of
Hdmpz]. Anal. Calcd for C46H28BF24N4O4Re: C, 40.81; H, 2.08;
N, 4.14. Found: C, 40.78; H, 2.12; N, 4.19.
Synthesis of [Re(CNtBu)(CO)3(Hdmpz)2]BAr′4 (11). A mixture
of [ReBr(CO)5] (0.100 g, 0.246 mmol) and Hdmpz (0.047 g, 0.492
mmol) in toluene (20 mL) was refluxed for 30 min affording a
colorless solution that was evaporated to dryness under reduced
pressure. The residue was redissolved in CH2Cl2 (20 mL), AgOTf
(0.063 g, 0.246 mmol) was added, and the reaction mixture was
allowed to stir at room temperature for 1 h. The solution was then
filtered via canula, and CNtBu (0.027 mL, 0.246 mmol) was added.
After 15 min of stirring at room temperature, the solution was
concentrated to a volume of 10 mL and addition of hexane (20
mL) caused the precipitation of 11 as a white microcrystalline solid,
which was washed with hexane (2 × 15 mL). Slow diffusion of
hexane (20 mL) into a concentrated solution of compound 11 in
CH2Cl2 at -20 °C afforded colorless crystals, one of which was
employed for an X-ray analysis. Yield: 0.250 g, 72%. IR
(CH2Cl2): ν 2186 (CN); ν 2038, 1960, 1940 cm-1 (CO). 1H NMR
(CD2Cl2): δ 9.20 [s, br, 2H, NH of Hdmpz], 7.73 [m, 8H, Ho of
BAr′4], 7.58 [m, 4H, Hp of BAr′4], 6.07 [s, 2H, CH of Hdmpz],
2.26 [s, 6H, CH3 of Hdmpz], 2.16 [s, 6H, CH3 of Hdmpz], 1.53 [s,
9H, CNtBu]. 13C{1H} NMR (CD2Cl2): δ 191.6 [CO], 191.5 [2 ×
CO], 164.1 [q (1JCB ) 49.7 Hz), Ci of BAr′4], 158.1, 147.3, [C3
and C5 of Hdmpz], 137.2 [Co of BAr′4], 131.2 [q (2JCF) 31.3 Hz),
Cm of BAr′4], 127.0 [q (1JCF ) 272.3 Hz), CF3 of BAr′4], 119.9
[Cp of BAr′4], 110.2 [C4 of Hdmpz], 62.2 [C(CH3)3 of CNtBu],
32.2 [CH3 of CNtBu], 17.1 [CH3 of Hdmpz], 13.0 [CH3 of Hdmpz].
Anal. Calcd for C50H37BF24N5O3Re: C, 46.63; H, 2.65; N, 4.97.
Found: C, 46.81; H, 2.48; N, 5.21.
1
Yield: 0.608 g, 81%. IR (CH2Cl2): ν 2048, 1956 cm-1 (CO). H
NMR (CD2Cl2): δ 8.92 [s, br, 3H, NH of HtBupz], 7.74 [m, 8H,
Ho of BAr′4], 7.61 [s, br, 3H, CH of HtBupz], 7.58 [m, 4H, Hp of
BAr′4], 6.48 [s, br, 3H, CH of HtBupz], 1.23 [s, 27H, CH3 of
HtBupz]. 13C{1H} NMR (CD2Cl2): δ 218.0 [CO], 162.1 [q (1JCB
) 49.8 Hz), Ci of BAr′4], 159.7, 146.6 [C3 and C5 of HtBupz],
135.2 [Co of BAr′4], 129.3 [q (2JCF ) 30.0 Hz), Cm of BAr′4], 124.9
[q (1JCF ) 272.6 Hz), CF3 of BAr′4], 117.8 [Cp of BAr′4], 106.5
[C4 of HtBupz], 31.8 [C(CH3)3 of HtBupz], 29.7 [CH3 of HtBupz].
Anal. Calcd for C56H48BF24MnN6O3: C, 48.93; H, 3.52; N, 6.12.
Found: C, 49.25; H, 3.35; N, 5.90.
Synthesis of [MnCl(CO)3(Hdmpz)2] (5a). To a solution of
[MnCl(CO)5] (0.060 g, 0.260 mmol) in CH2Cl2 (15 mL) was added
Hdmpz (0.050 g, 0.520 mmol), and the reaction mixture was
refluxed for 2 h. The resulting yellow solution was concentrated
under vacuum to a volume of 5 mL; addition of hexane caused the
precipitation of a yellow solid which was washed with hexane (2
× 20 mL). Yield: 0.089 g, 93%. IR (CH2Cl2): ν 2033, 1940, 1911
cm-1 (CO). 1H NMR (CD2Cl2): δ 10.74 [s, br, 2H, NH of Hdmpz],
5.94 [s, br, 2H, CH of Hdmpz], 2.25 [s, br, 6H, 2 × CH3 of Hdmpz].
Anal. Calcd for C13H16ClMnN4O3: C, 42.85; H, 4.40; N, 15.28.
Found: C, 43.12; H, 4.54; N, 15.98.
Synthesis of [MnCl(CO)3(HtBupz)2] (5b). Compound 5b was
prepared as described above for 5a from [MnCl(CO)5] (0.060 g,
0.260 mmol) and HtBupz (0.065 g, 0. 520 mmol). Compound 5b
was obtained as a yellow powder. Yield: 0.099 g, 90%. IR
1
(CH2Cl2): ν 2136, 1944, 1914 cm-1 (CO). H NMR (CD2Cl2): δ
11.62 [s, br, 2H, NH of HtBupz], 7.60 [s, br, 2H, CH of HtBupz],
6.14 [s, br, 2H, CH of HtBupz], 1.28 [s, br, 18H, (CH3)3 of HtBupz].
Anal. Calcd for C17H24ClMnN4O3: C, 48.29; H, 5.72; N, 13.25.
Found: C, 47.98; H, 5.89; N, 12.88.
Synthesis of [Mn(ONO2)(CO)3(Hdmpz)2] (6). A mixture of
[MnBr(CO)5] (0.100 g, 0.364 mmol) and Hdmpz (0.070 g, 0.728
mmol) was refluxed in toluene (20 mL) for 30 min. The solution
was evaporated to dryness, the yellow residue redissolved in CH2Cl2
(20 mL), AgNO3 (0.062 g, 0.364 mmol) added, and the reaction
mixture stirred for 45 min. The resulting solution was filtered off
the white solid (AgBr) via canula and concentrated under reduced
pressure to a volume of 5 mL. Slow diffusion of hexane (15 mL)
at -20 °C afforded yellow crystals, one of which was employed
for an X-ray analysis. Yield: 0.102 g, 71%. IR (CH2Cl2): ν 2040,
Synthesis of [Mn(CO)3(Hpz)3]BAr′4 (12). Hpz (0.059 g, 0.872
mmol) was added to a solution of [Mn(OTf)(CO)5] (0.100 g, 0.291
mmol) in toluene (20 mL), and the mixture was refluxed for 1 h.
The solvent was then evaporated to dryness under reduced pressure,
the residue was redissolved in CH2Cl2 (20 mL), NaBAr′4 (0.256 g,
0.291 mmol) was added, and the reaction mixture was allowed to
stir at room temperature for 15 min. The solution was filtered off
(via canula) the white solid (NaOTf) and concentrated to a volume
of 5 mL; addition of hexane (20 mL) caused the precipitation of
12 as a yellow solid, which was washed with hexane (2 × 15 mL).
1
1947, 1923 cm-1 (CO). H NMR (CD2Cl2): δ 10.49 [s, br, 2H,
NH of Hdmpz], 5.96 [s, 2H, CH of Hdmpz], 2.21 [s, 6H, CH3 of
Hdmpz], 2.19 [s, 6H, CH3 of Hdmpz]. Anal. Calcd for C13H16-
MnN5O6: C, 39.71; H, 4.10; N, 17.81. Found: C, 39.68; H, 4.04;
N, 17.87.
Synthesis of [Re(CO)5(Hdmpz)]OTf (9). To a solution of
[Re(OTf)(CO)5] (0.050 g, 0.113 mmol) in CH2Cl2 (20 mL) was
added Hdmpz (0.011 g, 0.113 mmol), and the mixture was stirred
at room temperature for 30 min. The resulting colorless solution
was concentrated under reduced pressure to a volume of 5 mL.
Slow diffusion of hexane (15 mL) at -20 °C afforded colorless
crystals, one of which was employed for an X-ray analysis. Yield:
1
Yield: 0.281 g, 80%. IR (CH2Cl2): ν 2049, 1958 cm-1 (CO). H
NMR (CD2Cl2): δ 9.88 [s, br, 3H, NH of Hpz], 7.86 [d (3JHH
)
1.7 Hz), 3H, CH of Hpz], 7.72 [m, 8H, Ho of BAr′4], 7.60 [s, br,
3H, CH of Hpz], 7.57 [m, 4H, Hp of BAr′4], 6.67 [m, 3H, CH of
Hpz]. Anal. Calcd for C44H24BF24MnN6O3: C, 43.80; H, 2.00; N,
6.97. Found: C, 43.62; H, 2.17; N, 7.08.
1
0.059 g, 94%. IR (CH2Cl2): ν 2162, 2053, 2031 cm-1 (CO). H
NMR (CD2Cl2): δ 13.10 [s, br, 1H, NH of Hdmpz], 7.26 [s, 1H,
CH of Hdmpz], 2.40 [s, 3H, CH3 of Hdmpz], 2.34 [s, 3H, CH3 of
Hdmpz]. Anal. Calcd for C11H8F3N2O8ReS: C, 21.47; H, 1.44; N,
5.01. Found: C, 21.39; H, 1.51; N, 4.98.
Synthesis of [Re(CO)4(Hdmpz)2]BAr′4 (10). To a solution of
compound [Re(CO)5(Hdmpz)]OTf (9) (0.063 g, 0.113 mmol) in
CH2Cl2 (20 mL) was added NaBAr′4 (0.100 g, 0.113 mmol), and
the reaction mixture was stirred at room temperature for 15 min.
Synthesis of [Re(CO)3(Hpz)3]BAr′4 (13). Compound 13 was
prepared as described above for 12 from [Re(OTf)(CO)5] (0.100
g, 0.210 mmol), Hpz (0.043 g, 0.632 mmol), and NaBAr′4 (0.186
g, 0.210 mmol). Compound 13 was obtained as a yellow powder.
1
Yield: 0.228 g, 81%. IR (CH2Cl2): ν 2042, 1936 cm-1 (CO). H
NMR (CD2Cl2): δ 10.26 [s, br, 3H, NH of Hpz], 7.85 [m, 3H, CH
3416 Inorganic Chemistry, Vol. 46, No. 8, 2007

Pyrazole Complexes as Anion Receptors
Table 2. Selected Crystal, Measurement, and Refinement Data for Compounds 3, 4a,b, 6, 7a,b, 8-11, 16, and 17
param
3
4a
4b
6
7a
7b
formula
fw
cryst syst
space group
a, Å
C
15H21MoN4O6Re
C50H36BF24MnN6O3
1290.60
monoclinic
P21/n
14.775(3)
26.092(6)
15.489(3)
90
105.468(4)
90
5755(2)
4
C
56H48BF24MnN6O3
C
18H24MnN7O6
C
36H48Mn2N12O14Re2
C
72H84BF24MnN7O7Re
635.50
triclinic
P1h
1374.75
triclinic
P1h
10.814(7)
15.800(7)
19.850(9)
74.826(14)
76.374(15)
83.188(146)
3175(3)
489.38
monoclinic
P21/c
11.865(3)
14.837(4)
14.004(4)
90
110.941( 5)
90
1655.14
monoclinic
P21/c
13.887(6)
15.524(6)
23.611(10)
90
102.224(8)
90
4975(4)
4
1867.41
monoclinic
P21/c
18.566(3)
28.554(5)
18.475(3)
90
119.043(3)
90
8563(3)
9.907(10)
14.555(14)
16.175(16)
79.44(2)
75.718(16)
72.794(19)
2144(4)
4
b, Å
c, Å
R, deg
â, deg
γ, deg
V, Å3
Z
2302.6(1 1)
4
2
4
F(000)
D
1216
1.969
2592
1.490
1392
1.438
1016
1.412
2640
1.809
3768
1.449
calcd, g cm-3
radiatn (λ, Å)
Mo KR, 0.710 73
6.262
Mo KR, 0.710 73
0.353
Mo KR, 0.710 73
0.324
Mo KR, 0.710 73
0.621
Mo KR, 0.710 73
5.417
Mo KR, 0.710 73
1.663
µ, mm-1
cryst size, mm
temp, K
0.11 × 0.15 × 0.18 0.22 × 0.23 × 0.39
0.18 × 0.35 × 0.48
0.26 × 0.22 × 0.11 0.22 × 0.25 × 0.45
0.08 × 0.20 × 0.31
296(2)
293(2)
296(2)
293(2)
293(2)
296(2)
θ limits, deg
min/max h, k, l
1.31-23.41
-10/10, -14/16,
-14/17
9413
5976
SADABS
495/0
1.56-23.30
-16/16, -29/27,
-17/15
25 734
8295
SADABS
783/0
1.043
1.09-23.68
-11/12, -17/17,
-22/22
14 582
9319
SADABS
842/0
1.061
1.84-23.37
-2/13, -11/16,
-15/15
10 229
3334
SADABS
307/0
1.001
1.50-23.35
-14/15, -17/17,
-22/26
21 836
7155
SADABS
625/0
1.027
1.25-23.31
-20/19, -22/31,
-20/19
38 286
12 336
SADABS
1039/0
1.011
collcd reflcns
unique reflcns
abs
params/restraints
GOF on F2
1.056
R1 (on F, I > 2σ(I))
0.0925
0.0870
0.2888
0.859 and -0.450
0.0771
0.2442
1.073 and -0.599
0.0405
0.1118
0.529 and -0.300
0.0562
0.1436
5.434 and -1.917
0.0890
0.2639
1.828 and -0.709
wR2 (on F2, all data) 0.2672
max/min ∆F, e Å-3
3.874 and -5.102
param
8
9
10
11
16
17
formula
fw
cryst syst
space group
a, Å
C
36H48N12O14Re4
C
11H8F3N2O8ReS
C46H28BF24N4O4Re C50H37BF24N5O3Re C36H42N6O10Re2
C
24H18ClN6O7Re
1617.66
monoclinic
P21/c
13.926(3)
15.559(3)
23.677(5)
90
102.265(4)
90
5013.2(19)
4
571.45
monoclinic
P21/n
9.407(5)
18.291(10)
10.210(6)
90
92.686(11)
90
1353.73
triclinic
P1h
1408.86
monoclinic
P21/n
14.532(4)
23.467(6)
17.381(4)
90
1091.16
monoclinic
P21/n
11.790(7)
20.368(12)
17.485(10)
90
724.09
orthorhombic
P212121
10.7796(8)
12.6297(10)
19.6399(15)
90
90
90
2673.8(4)
4
10.6683(17)
12.405(2)
19.975(3)
95.593(4)
95.245(3)
99.650(3)
2578.0(7)
2
b, Å
c, Å
R, deg
â, deg
γ, deg
V, Å3
Z
103.523( 5)
90
93.392(12)
90
1754.9(17)
4
5763(2)
4
4192(4)
4
F(000)
D
3040
2.143
1080
2.163
1320
1.744
2768
1.624
2120
1.729
1408
1.799
calcd, g cm-3
radiatn (λ, Å)
Mo KR, 0.710 73
9.697
Mo KR, 0.710 73
7.116
Mo KR, 0.710 73
2.490
Mo KR, 0.710 73
2.231
Mo KR, 0.710 73
5.829
Mo KR, 0.710 73
4.699
µ, mm-1
cryst size, mm
temp, K
0.13 × 0.22 × 0.49 0.34 × 0.15 × 0.12 0.27 × 0.16 × 0.11
0.42 × 0.31 × 0.20
0.30 × 0.14 × 0.12 0.26 × 0.17 × 0.17
293(2)
296(2)
293(2)
296(2)
296(2)
100(2)
θ limits, deg
min/max h, k, l
1.50-23.28
-12/15, -14/17,
-26/26
21 799
7195
SADABS
625/0
2.23-23.28
-8/10, -20/19,
-11/10
7596
2518
SADABS
242/0
1.053
1.03-23.28
-11/11, -10/13,
-22/16
11 378
7263
SADABS
731/0
1.030
1.48-23.26
-16/14, -26/26,
-17/19
15 378
8273
SADABS
773/0
1.011
1.54-23.35
-13/12, -22/21,
-18/19
18 667
6066
SADABS
488/0
1.000
1.92-27.54
-13/13, -16/16, -24/25
collcd reflcns
unique reflcns
abs
params/restraints
GOF on F2
22 887
1032
SADABS
352/0
1.061
1.044
R1 (on F, I > 2σ(I))
0.0591
0.0282
0.0806
1.007 and -1.275
0.0433
0.1200
0.963 and -0.701
0.0464
0.1267
1.511 and -0.782
0.0326
0.0763
1.132 and -0.694
0.0232
0.0615
2.564 and -0.476
wR2 (on F2, all data) 0.1572
max/min ∆F, e Å-3
6.429 and -2.628
of Hpz], 7.72 [m, 8H, Ho of BAr′4], 7.56 [m, 4H, Hp of BAr′4],
7.35 [m, 3H, CH of Hpz], 6.60 [m, 3H, CH of Hpz]. 13C{1H} NMR
(CD2Cl2): δ 193.0 [CO], 162.1 [q (1JCB ) 49.9 Hz), Ci of BAr′4],
144.4, 134.0, [C3 and C5 of Hpz], 135.1 [Co of BAr′4], 129.2 [q
(2JCF ) 31.7 Hz), Cm of BAr′4], 125.0 [q (1JCF ) 272.5 Hz), CF3
of BAr′4], 117.8 [Cp of BAr′4], 109.5 [C4 of Hpz]. Anal. Calcd for
C44H24BF24N6O3Re: C, 39.51; H, 1.81; N, 6.28. Found: C, 39.73;
H, 1.89; N, 5.96.
Synthesis of [Re(CO)3(HPhpz)3]BAr′4 (14). Compound 14 was
prepared as described above for 13 from [Re(OTf)(CO)5] (0.100
g, 0.210 mmol), HPhpz (0.091 g, 0.631 mmol), and NaBAr′4 (0.186
g, 0.210 mmol). Yield: 0.254 g, 77%. IR (CH2Cl2): ν 2039, 1935,
1
1925 cm-1 (CO). H NMR (CD3CN): δ 11.85 [s, br, 3H, NH of
HPhpz], 7.71 [m, 21H, BAr′4 and Ph of HPhpz], 7.52 [m, 9H, Ph
and CH of HPhpz], 6.82 [s, br, 3H, CH of Hpz]. 13C{1H} NMR
(CD3CN): δ 193.6 [CO], 162.6 [q (1JCB ) 49.8 Hz), Ci of BAr′4],
Inorganic Chemistry, Vol. 46, No. 8, 2007 3417

Nieto et al.
147.3, 145.5, [C3 and C5 of HPhpz], 134.7 [Co of BAr′4], 129.1 [q
(2JCF ) 31.8 Hz), Cm of BAr′4], 124.5 [q (1JCF ) 271.7 Hz), CF3
of BAr′4], 130.0, 129.2, 127.1, 126.7 [Ph of HPhpz], 117.3 [Cp of
BAr′4], 105.5 [C4 of HPhpz]. Anal. Calcd for C62H36BF24N6O3Re:
C, 47.55; H, 2.32; N, 5.37. Found: C, 47.19; H, 2.68; N, 5.51.
Synthesis of [Re(CO)3(HIndz)3]BAr′4 (15). Compound 15 was
prepared as described above for 13 from [Re(OTf)(CO)5] (0.045
g, 0.102 mmol), HIndz (0.036 g, 0.306 mmol), and NaBAr′4 (0.090
g, 0.102 mmol). Yield: 0.132 g, 90%. IR (CH2Cl2): ν 2042, 1942
cm-1 (CO). 1H NMR (CD3CN): δ 11.91 [s, br, 3H, NH of HIndz],
8.06 [s, 3H, CH of HIndz], 7.81 [m, 3H, CH of HIndz], 7.72 [m,
11H, Ho of BAr′4 and CH of HIndz], 7.65 [m, 3H, CH of HIndz],
7.63 [m, 3H, CH of HIndz], 7.55 [m, 4H, Hp of BAr′4], 7.40 [m,
3H, CH of HIndz]. Anal. Calcd for C50H30BF24N6O3Re: C, 45.20;
H, 2.03; N, 5.65. Found: C, 45.02; H, 2.20; N, 5.51.
Crystal Structure Determination. General Description for
Compounds 3, 4a,b, 6, 7a,b, 8-11, and 16. A suitable crystal
was attached to a glass fiber and transferred to a Bruker AXS
SMART 1000 diffractometer with graphite-monochromatized Mo
KR X-radiation and a CCD area detector. One hemisphere of the
reciprocal space was collected in each case. Raw frame data were
integrated with the SAINT16 program. The structures were solved
by direct methods with SHELXTL.17 An empirical absorption
correction was applied with the program SADABS.18 All non-
hydrogen atoms were refined anisotropically. Hydrogen atoms were
set in calculated positions and refined as riding atoms. Drawings
and other calculations were made with SHELXTL. Crystal and
refinement details are collected in Table 2.
General Description for Compound 17. A crystal was mounted
on a CryoLoop with Paratone-N oil19 and cooled to 100 K. Data
were collected on a Bruker SMART APEX CCD diffractometer,
and the structure was solved by direct methods and refined as
indicated above. The Bruker suite of programs was used for data
collection, structure solution, refinement, and graphical presentation.
Crystal and refinement details are shown in Table 2.
Acknowledgment. We thank the Ministerio de Ciencia
y Tecnolog´ıa (Grants CTQ2006-08924 and CTQ2006-07036/
BQU) and European Union (ERG to L.R.) for support of
this work. L.R. thanks the Ministerio de Educacio´n y Ciencia
for a Ramo´n y Cajal contract.
Supporting Information Available: X-ray crystallographic data
1
for compounds 3, 4a,b, 6, 7a,b, 8-11, 16, and 17 as CIF and H
NMR titration profiles. This material is available free of charge
via the Internet at http://pubs.acs.org.
IC0700046
(16) SAINT+. SAXI area detector integration program, version 6.02; Bruker
AXS, Inc.: Madison, WI, 1999.
(17) Sheldrick, G. M. SHELXTL, An integrated system for solVing, refining,
and displaying crystal structures from diffraction data, version 5.1;
Bruker AXS, Inc.: Madison, WI, 1998.
(18) Sheldrick, G. M. SADABS, Empirical Absorption Correction Program;
University of Go¨ttingen: Go¨ttingen, Germany, 1997.
(19) Hamilton Research Laboratories.
3418 Inorganic Chemistry, Vol. 46, No. 8, 2007