More than steric effects: Unlocking the coordination chemistry of barium pyrazolates

Article abstract of DOI:10.1002/ejic.200701020

To further our understanding of the coordination chemistry of the heavy alkaline earth metals, we here report on a family of barium pyrazolates bearing various substitution patterns that illustrate the delicate balance between ligand bulk, donor size, sto

Full text of DOI:10.1002/ejic.200701020

FULL PAPER
DOI: 10.1002/ejic.200701020
More than Steric Effects: Unlocking the Coordination Chemistry of Barium
Pyrazolates
[a]
[a,b]
[a]
[b]
Anna Y. O’Brien, Julia Hitzbleck,
Ana Torvisco, Glen B. Deacon, and
[a,b]
Karin Ruhlandt-Senge*
Keywords: Pyrazolates / Barium / N ligands / Coordination modes / Structure elucidation / CVD precursors / Synthetic
methods
To further our understanding of the coordination chemistry
of the heavy alkaline earth metals, we here report on a family
of barium pyrazolates bearing various substitution patterns
that illustrate the delicate balance between ligand bulk, do-
nor size, stoichiometry, and hapticity, while emphasizing the
importance of secondary interactions including π-bonding,
agostic interactions, and hydrogen bonding to stabilize these
pz)
(pmdta)}
(tmeda)}
and the monomer [Ba(Ph
prepared using a variety of synthetic methods and were char-
acterized spectroscopically and structurally.
(© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim,
Germany, 2008)
2
(pmdta)}
] (3), [{Ba(MePhpz)
]·TMEDA (6), the polymer [{Ba(tBupz)
pz) (tmeda) ]·TMEDA (7), were
2
] (1), [{Ba(Phpz)
2
(pmdta)}
2
] (2), [{Ba(tBupz)
] (5), [{Ba(Ph pz)
(NH
2
-
2
2
(tmeda)}
2
2
2
-
2
2
3 2 n
) } ] (4),
2
2
2
2
heavy-metal complexes. The dimeric compounds [{Ba(Me -
Introduction
In the quest for volatile, thermally robust CVD precur-
sors of the heavy alkaline earth metals, metal-organic bar-
ium reagents remain a priority.[1–4] For large metals such
as barium, the prediction of the coordination chemistry is
difficult due to weak metal–ligand and metal–donor inter-
actions and tendency towards aggregation. Thus, a better
understanding and control of factors governing the steric
saturation of the metal center is critically needed. With
many competing factors, such as solvation vs. ligation and
possible secondary interactions, systematic studies compar-
ing such influences are beneficial.
Solvation by a sterically demanding neutral donor is
common practice for reducing aggregation in metal-organic
compounds of larger metals, such as barium. With a range
of possible substitution patterns, and thus control over ste-
ric demand, as well as solubility, the pyrazolate ligand sys-
tem has been of interest as an alternative to oxygen-con-
taining β-diketonates. In this paper, we report a systematic
study of barium pyrazolate compounds with varied substi-
tution patterns (see Figure 1) in the presence of various
neutral donors.
Figure 1. Pyrazolate substitution patterns and neutral donors with
abbreviations.
[
a] Department of Chemistry, 1-014 Center for Science and Tech-
nology, Syracuse University,
Through the course of this and previous work, it has
become apparent that secondary interactions play an
equally important role as steric saturation in heavy alkaline
Syracuse, NY 13244-4100, USA
Fax: +1-315-443-4070
E-mail: kruhland@syr.edu
[b] School of Chemistry, Monash University,
Clayton, Victoria 3168, Australia
[
4]
earth metal pyrazolates. These secondary interactions in-
clude π-bonding, hydrogen bonding, and agostic interac-
tions, as observed in the crystal structures of a number of
Fax: +61-3-9905-4597
E-mail: Glen.Deacon@sci.monash.edu.au
Supporting information for this article is available on the
WWW under http://www.eurjic.org or from the author.
[
4c]
pyrazolates such as [Ba (tBu pz) ],
[Sr(Me pz) (Me -
6
2
12
2 2 2
172
© 2008 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Eur. J. Inorg. Chem. 2008, 172–182

Unlocking the Coordination Chemistry of Barium Pyrazolates
pzH)4],[4d] and [{Sr(tBu pz) (thf) } ], respectively. Others over, direct metallation at elevated temperatures is done in
[4b]
2
2
2 2
have reported the significance of secondary interactions of the absence of organic solvents or transmetallating agents
the related barium tetrazolate compounds, Ba[CN (NMe )] - (i.e. HgR ) (Scheme 1).
4
2
2
2
[5]
(
18-crown-6) and Ba[CN (NiPr )] (18-crown-6),
where
4
2 2
weak C–H···N interactions between donors and tetrazolate
ligands are believed to influence the tetrazolate coordina-
tion modes.
These data also show that the understanding of the coor-
dination chemistry of the heavy alkaline earth metals lags
far behind that for magnesium, prompting us to initiate a
detailed study into the coordination chemistry of barium
pyrazolates. By focusing on one metal, we can better evalu-
ate the effects of the steric demand of the pyrazolate ligand
and the nature and stoichiometry of the donor, as well as
the influence of secondary interactions. In this report, we
discuss these effects in a comprehensive and systematic
fashion by analyzing a family of new barium pyrazolate
compounds: five dimeric complexes [{Ba(Me pz) -
Scheme 1. Synthetic routes.
2
2
(
(
pmdta)} ] (1), [{Ba(Phpz) (pmdta)} ] (2), [{Ba(tBupz) -
2
2
2
2
The dimeric compounds [{Ba(Me pz) (pmdta)} ] (1),
2
2
2
pmdta)}2]
(3), [{Ba(MePhpz) (tmeda)} ] (5), and
2 2
[{Ba(Phpz) (pmdta)} ] (2), and [{Ba(tBupz) (pmdta)} ] (3)
2 2 2 2
[
[
[
{Ba(Ph pz) (tmeda)} ]·TMEDA (6), one monomer
Ba(Ph pz) (tmeda) ]·TMEDA (7), and one polymer
{Ba(tBupz) (NH ) } ] (4), along with previously reported
2 2 2
(Figures 2, 3, and 4) were synthesized according to method
B, introducing stoichiometric amounts of PMDTA to the
initial reaction mixtures. In addition, 1 was also obtained
by method A with a stoichiometric amount of PMDTA,
and 3 was also obtained by method C after extraction with
a hexane/PMDTA solution.
2
2
2
2
3 2 n
compounds.
In the absence of a secondary donor, synthesis by
method B resulted in the formation of a polymeric barium
complex [{Ba(tBupz) (NH ) } ] (4) (Figure 5), with ammo-
Results and Discussion
2
3 2 n
(i) Preparation of Barium Pyrazolates
nia as the coordinated neutral donor. The dimeric com-
Transamination (method A) and salt metathesis (method pounds [{Ba(MePhpz) (tmeda)} ] (5) and [{Ba(Ph pz) -
2
2
2
2
D) have been well established, but require the preparation (tmeda)} ]·TMEDA (6) (Figures 6 and 7) were also pre-
2
of air-sensitive starting materials.[
4d,6]
We here show direct pared by method B through the addition of stoichiometric
metallation either at elevated temperatures (method C) or amounts of TMEDA to the initial reaction mixtures. Use
in anhydrous liquid ammonia (method B) to be facile, inex- of TMEDA in excess quantities resulted in the formation
pensive, one-step routes. Workup of the reaction products of the monomeric [Ba(Ph pz) (tmeda) ]·TMEDA, 7 (Fig-
2
2
2
is simple due to the gaseous hydrogen byproduct.[ More- ure 8).
4d]
Figure 2. [{Ba(Me
removed for clarity.
2 2 2
pz) (pmdta)} ] (1) with anisotropic displacement parameters depicting 50% probability. Hydrogen atoms have been
Eur. J. Inorg. Chem. 2008, 172–182
© 2008 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
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173

A. Y. O’Brien, J. Hitzbleck, A. Torvisco, G. B. Deacon, K. Ruhlandt-Senge
FULL PAPER
2 2
Figure 4. [{Ba(tBupz) (pmdta)} ] (3) with anisotropic displacement
parameters depicting 50% probability. Hydrogen atoms and
PMDTA methyl groups have been removed for clarity.
2 2
Figure 3. [{Ba(Phpz) (pmdta)} ] (2) with anisotropic displacement
parameters depicting 50% probability. Hydrogen atoms have been
removed for clarity.
ported 1:1 stoichiometry of donor/metal which was em-
ployed for the formation of [Ba(tBu pz) (tetraglyme)] and
2
2
3a]
[
Attempts to reduce the nuclearity through the use of ex- [Ba(tBu pz) (triglyme)] by Winter et al.
Conversely, our
2
2
cess PMDTA during the synthetic procedures for 1–3 re- group has reported a group of heavy alkaline earth metal
sulted in intractable product mixtures, in line with the re- pyrazolates which were reduced in nuclearity from the
Figure 5. Fragment of [{Ba(tBupz)
have been removed from pyrazolate ligands for clarity.
2 3 2 n
(NH ) } ] (4) with anisotropic displacement parameters depicting 50% probability. Hydrogen atoms
2 2
Figure 6. Molecular representation of [{Ba(MePhpz) (tmeda)} ] (5). Disordered components have been removed for clarity.
174
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Unlocking the Coordination Chemistry of Barium Pyrazolates
Figure 7. [{Ba(Ph
2 2 2
pz) (tmeda)} ]·TMEDA (6) with anisotropic displacement parameters depicting 50% probability. The solvent of
crystallization TMEDA, hydrogen atoms and TMEDA methyl groups have been removed for clarity.
In most cases, the geometry of the barium atom can be
2
described by approximating σ-η -bonding of the pyrazolate
ligands as connected through the center of the N–N bond
[(cen)N–N, see Figure 9a], on the basis of the narrow bite
angle (N–Ba–N), and the symmetry of the Ba–N bond
2
lengths (∆Ba–N). For terminal σ-η -bonded pyrazolates, this
approximation is also justified by the near co-planarity of
the terminal pyrazolate ring with the Ba–N–N plane. For
bridging pyrazolates which include π-bonded ligands (η3
)
–5
a similar approximation can be made, based on the distance
from the barium atom to the centroid of the pyrazolate ring
[
(cen)pz].
The extent of the π-character of a pyrazolate–metal in-
teraction is discussed in terms of Ba–C distances as well
as the following geometric details: the angle between the
Figure 8. [Ba(Ph
2
pz)
2
(tmeda)
2
]·TMEDA (7) with anisotropic dis- plane of a pyrazolate and a vector connecting the centroid
placement parameters depicting 50% probability. The solvent of of the pyrazolate ring to the metal atom (Ba/pz angle)
crystallization TMEDA, hydrogen atoms, TMEDA methyl groups,
and the minor disordered components have been removed for clar-
gives an indication of π-interactions; the optimum orienta-
tion for π-interactions is a 90° Ba/pz angle (see Figure 9b).
ity.
Additionally, for bridging pyrazolates, the angle between
the barium–barium axis and the plane of the bridging pyr-
azolate (tilt angle) gives an indication of the extent of the
oligomeric [{M(tBu pz) } ] (M = Ca, n = 3; M = Sr, n = 4;
2
2 n
inclination and π-interactions. For example, a pyrazolate
plane perpendicular to the barium–barium axis (tilt angle
M = Ba, n = 6) to the dimeric [{M(tBu pz) (thf) } ] (x =
2
2
x 2
1
, M = Ca, Sr; x = 2, M = Ba) by dissolving the oligomeric
2
2
[4b,4c]
90°) indicates perfectly symmetrical µ-η :η -bridging (see
Figure 9c).
compounds in tetrahydrofuran (thf).
Thus, the use of
reaction stoichiometry to control the product nuclearity
may be limited by the ease with which the product can be
isolated from the excess of neutral donor.
Thecomplexes [{Ba(Me pz) (pmdta)} ](1), [{Ba(Phpz) -
2
2
2
2
(
pmdta)} ] (2), and [{Ba(tBupz) (pmdta)} ] (3) are all cen-
2 2 2
trosymmetric dimers, with two barium atoms bridged by
two pyrazolates. Each barium atom is further coordinated
2
by a terminal η -pyrazolate and a tridentate PMDTA do-
(ii) Structure Descriptions
nor. This results in a formal coordination number of 9;
Low-temperature single-crystal X-ray structure determi- however, if the pyrazolate binding is approximated as
nations have been carried out for the compounds 1–7. Se- monodentate, as described above, each barium atom can
vere disorder in 5 prevented a quality-data refinement, but be assigned a distorted octahedral environment (see
we present an illustration of 5 (Figure 6) to show the con- Table 1).
nectivity. A structural description of compounds 1–4 and
–7 follows. Descriptive data are given in Table 1, while ad- ium atom between the bridging and terminal pyrazolates
ditional bond lengths and angles are given in the Support- [(cen)N–N–Ba–(cen)N–N 114.96° (1), 110.38° (2), (cen)N–N
A coordinatively unsaturated area on the face of the bar-
6
–
ing Information.
Ba–(cen)pz 105.5° (3)] arises from the restricted bite of the
Eur. J. Inorg. Chem. 2008, 172–182
© 2008 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
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175

A. Y. O’Brien, J. Hitzbleck, A. Torvisco, G. B. Deacon, K. Ruhlandt-Senge
FULL PAPER
Table 1. Structural description data for 1–4, 6–7.
1
2
3
4
6
7
µ-η :η2
2
µ-η :η
2
2
µ-η :η
4
2
µ-η :η
5
2
µ-η :η
5
2
NA
Bridging mode
and
µ-η :η
2
1
CN of Ba
Axial
9
10
11
12
11
8
η2-bound
η2-bound
η4-bound
η5-bound
η5-bound
η2-bound
N–Ba–N [°]
Ba–(cen)N–N [Å]
Ba–(cen)pz [Å]
Ba–N [Å]
27.2(1)
2.846
NA
26.77(8)
2.904
NA
2.935(3)
2.966(3)
0.099
27.24(6)
NA
3.048
2.928(2)
2.955(2)
0.027
26.71(6)
NA
2.982
2.965(2)
3.048(2)
0.083
3.202(3)-
3.439
26.52(10)
NA
2.890
2.910(4)
3.053(4)
0.143
3.058(5)-
3.281(5)
81.4
29.10(4)
2.639
NA
2.684(1)
2.768(2)
0.084
2.807(3)
3.048(3)
∆Ba–N [Å]
0.214
NA
Ba–C [Å]
NA
3.346(3)
NA
3.396(2)
Ba/pz angle [°]
Tilt angle [°]
NA
90.0
61.4
64.6
69.5
58.3
77.5
47.3
NA
NA
43.5
Axial
N
PMDTA
N
PMDTA
N
PMDTA
η2-bound
N
TMEDA
η2-bound
N–Ba–N [°]
Ba–(cen)N–N [Å]
Ba–N [Å]
NA
NA
2.965(4)
NA
NA
3.070(3)
NA
NA
3.039(2)
27.47(6)
2.831
2.942(2)
NA
NA
2.890(4)
29.10(4)
2.639
2.684(1)
2.768(2)
0.084
2.886(2)
∆Ba–N [Å]
NA
NA
NA
0.056
NA
Equatorial
Ba–N [Å]
Equatorial
Ba–N [Å]
Equatorial
N
PMDTA
N
PMDTA
N
PMDTA
N
NH3
N
TMEDA
N
TMEDA
2.933(5)
2.966(3)
2.957(2)
2.897(3)
2.880(4)
NA
2.906(2)
N
PMDTA
N
PMDTA
N
PMDTA
N
NH3
N
TMEDA
2.965(4)
η2-bound
2.910(3)
η2-bound
2.983(2)
η2-bound
2.928(3)
η2-bound
NA
η2-bound
2.995(2)
N
TMEDA
N–Ba–N [°]
Ba–(cen)N–N [Å]
Ba–N [Å]
27.2(1)
2.846
2.807(3)
28.54(8)
2.722
2.801(3)
2.817(3)
0.016
23.84(6)
3.014
2.799(2)
3.360(2)
0.561
28.76(7)
2.712
2.775(2)
2.825(2)
0.050
28.62(11)
2.695
2.775(4)
2.788(4)
0.013
NA
NA
2.906(2)
3.048(3)
∆Ba–N [Å]
0.214
NA
Equatorial
η2-bound
η2-bound
η2-bound
η1-bound
η2-bound
N
TMEDA
N–Ba–N [°]
Ba–(cen)N–N [Å]
Ba–N [Å]
29.7(1)
2.609
2.699(3
29.02(8)
2.722
2.712(3)
29.44(6)
2.626
2.711(2)
2.720(2)
0.09
10.2
NA
NA
NA
2.842(2)
29.26(11)
2.613
2.678(4)
2.723(4)
0.045
1.5
NA
NA
NA
2.995(2)
2.776(3)
∆Ba–N [Å]
0.00
1.4
NA
0.064
10.2
NA
NA
NA
84.4
NA
NA
NA
Deviation from planarity [°]
Tilt angle [°]
equatorial PMDTA nitrogen atoms [N–Ba–N 61.96° (1), (3.056–3.39 Å),[3b,4,8,9] and beyond the weakly bonding Ba–
[4b]
5
9.70° (2), 61.7° (3)]. Each dimer “fills” this exposed area C distance [3.499(2) Å] found in [{Ba(tBu pz) (thf) } ].
2 2 2 2
in a unique way. In 1, the bridging pyrazolates bind asym- Accordingly, the bridging pyrazolates are considered to
2
2
metrically (∆M–N 0.241 Å). Steric repulsion between the have µ-η :η -bonding interactions, with a tilt angle of 90°.
PMDTA and the methyl substituents of the pyrazolate re- In compound 2, this void is filled by an agostic interac-
sults in a longer Ba–N distance on the pyrazolate nitrogen tion from a methyl group of the PMDTA [Ba–C(312)
atom closest to the PMDTA [Ba(1)–N(21) 3.048(3) Å], cre- 3.277(4) Å], in contrast to the twisting of the bridging pyr-
ating an unsaturated area that causes the pyrazolate to azolate observed in 1. The coordination of the bridging pyr-
2
2
twist. This leads to a shorter Ba–N distance [Ba(1)–N(21) azolates in 2 is described as µ-η :η because the Ba–C dis-
3 2.807 Å] and a Ba–C bond length [Ba(1)–C(23)#3 tances (3.508–3.952 Å) lie outside of the values reported for
.829 Å] just within the sum (3.90–3.97 Å) of the π-bonded pyrazolates (vide supra). However, the tilt angle
van der Waals radius of a barium atom [2.17(CN = 8) to (64.6°) deviates significantly from the ideal 90° and other
#
3
2
2
2
.24 (CN = 12) Å] and the van der Waals radius of a π- known values for µ-η :η -bonding {90.0° (1) and 87.8(9)°
[7]
[4c]
bonded carbon atom of a phenyl ring (1.73 Å). The Ba···C [Ba (tBu pz) ] }, consistent with weak π-interactions.
6
2
12
separation lies outside of established values for π-bonding Yet, the tilt angle in 2 is not small enough to imply signifi-
between a substituted pyrazolate ring and a barium atom cant π-bonding when compared to values reported for µ-
176
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Unlocking the Coordination Chemistry of Barium Pyrazolates
azolates, compound 5 is isostructural with the lighter alka-
line earth and rare-earth congeners, [{M(MePhpz)2-
[
8b]
(
tmeda)} ] (M = Ca, Yb, Sr, Eu).
2
[
{Ba(Ph pz) (tmeda)} ]·TMEDA (6) crystallizes as a di-
2 2 2
[
4a]
mer similar to 1–3, 5 and [{Ba(iPr pz) (py) } ].
Again,
2
2
3 2
2
5
approximating the η - and η -coordination of the bridging
pyrazolates as monodentate, 6 exhibits a distorted trigonal-
bipyramidal metal coordination environment (see Tabl-
η :η -bound, based on the close Ba–C contacts [3.058(5)–
.281(5) Å] which lie well within the accepted range for Ba–
5
2
3
C bonding, the small tilt angle (43.5°), and nearly perpen-
dicular Ba/pz angle (81.4°).
In the monomeric (TMEDA)barium compound
[
Ba(Ph pz) (tmeda) ]·TMEDA 7, the metal atom is located
2 2 2
on a center of symmetry, as such only one ligand and one
TMEDA ligand are symmetry-independent, with pairs of
ligands and donors arranged in a transoid orientation. The
formally eight-coordinate metal center exhibits a severely
distorted octahedral geometry when the pyrazolates are ap-
proximated as monodentate (see Table 1).
Figure 9. Angles used in structural analysis (a) location of
centroids, (b) Ba–cen/pz angle (c) tilt angle.
5
2
(iii) Structural Discussion
η :η -bridging pyrazolates in [(thf) Ba (Me pz) {(OSi-
6
6
2
8
[9]
[4c]
Me ) O} ] (45.8°, 54.1°), [Ba (tBu pz) ] (45.6°, 47.2°)
and the µ-η :η -bridging pyrazolates in [{Ba(tBu pz) -
thf) } ] (48.7°)
Thus, the bridging is considered to be µ-η :η .
2
2
2
6
2
12
The barium pyrazolate complexes presented here join a
growing family of reported heavy alkaline earth and rare
earth metal pyrazolate complexes that have been structur-
4
2
2
2
[4c]
[
4b]
(
and [Ba (tBu pz) ] (44.8°, 44.7°).
2
2
6 2 12
2
2
[
3,4,6,8–10]
ally characterized.
A comprehensive examination
The vacancy in the coordination sphere in 3 is filled by
of the structures of these complexes lends insight into the
different means by which these large metal ions achieve co-
ordinative saturation. Specifically, we look at the effects of
pyrazolate substitution and the neutral donor type, with an
emphasis on the role of secondary interactions such as π-
bonding, agostic interactions, and hydrogen bonding. A
comprehensive list of tilt and Ba/pz angles for the barium
pyrazolate compounds that contain bridging pyrazolates is
found in Table 2.
4
donation of π-pyrazolate electrons in an η -interaction, be-
cause the Ba–C distances for the 3,5-positions [C(23)
.396(2), C(25) 3.346(3) Å] fall within established π-bond-
ing values (vide supra), while the carbon atom in the 4-
3
position [Ba(1)–C(24) 3.640 Å] does not (vide supra).
The polymeric barium complex, [{Ba(tBupz) (NH ) } ]
2
3 2 n
(
4), has ten-coordinate barium atoms, each bridged by two
µ-η :η - and two µ-η :η -pyrazolates, in addition to having
two terminal neutral ammonia molecules.
5
2
2
1
5
Ligand Effects: Pyrazolate Substitution
The η -bonding mode is justified by the Ba–C distances
[
C(23) 3.335(3), C(25) 3.202(3) Å] falling within the re-
To compare the effects of the pyrazolate ligand substitu-
ported values for barium–pyrazolate π-bonding (vide su- tion, it is useful to examine complexes that have the same
pra). The third Ba–C distance [C(24) 3.439(3) Å] lies just metal and neutral donor type, but vary in the ligand substi-
outside this range, but it is nonetheless shorter than one tution pattern. The only reported example of such a set for
reported value that is considered a weak π-interaction (vide the heavy alkaline earth metals includes complexes 1–3 (En-
5
supra). Accordingly, this interaction is considered to be η - tries 2, 5, 7; Table 2). In all three compounds, the metal is
bonding.
barium, and PMDTA is used as a donor, with bite angles
2
1
The unusual µ-η :η -bridging mode in 4 is the result of restricted by the carbon backbone, resulting in a sterically
hydrogen bonding between a hydrogen atom of the ammo- unsaturated area of the barium atom coordination sphere.
1
2+
nia donor and the η -bound nitrogen atom [N(32)–H(32B)··· However, each of the Ba ions in each of the three com-
N(12)#2: N(32)–H(32B) 0.95(4) Å, H(32B)···N(12)#2 plexes adopt a different strategy to achieve steric saturation.
2
1
2
2
2
.46(4) Å]. Examples of unassisted µ-η :η -bridging include In 1, the µ-η :η -bridging pyrazolate twists due to the pres-
[
10a]
[
[10b]
[
Sc (Ph pz) ],
[Li(Ph pz)(OEt )] ,
and [Li(tBu2- ence of a methyl group in the 5-position of the pyrazolate
2
2
6
2
2 2
10c]
pz)(tBu pzH) ] .
ring. In 2, because of the lack of a substituent in the 5-
2
2 2
The
(TMEDA)barium
complex
[{Ba(MePhpz)2- position, agostic interactions arising from a PMDTA
(
tmeda)} ] (5) shows a similar geometrical arrangement to methyl group fill this area. In compound 3, π-bonding by
2
1
–4, but more pronounced pyrazolate tilting resulting in a the bridging pyrazolate fills the exposed area.
2
5
µ-η :η -pyrazolate bridging mode. Due to significant disor-
These differences illustrate the delicate balance between
der, we present only this general structural trend. Except stabilization by σ- and π-donation and destabilization origi-
for slight variations in the inclination of the bridging pyr- nating from the steric repulsion between ligands and do-
Eur. J. Inorg. Chem. 2008, 172–182
© 2008 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.eurjic.org
177

A. Y. O’Brien, J. Hitzbleck, A. Torvisco, G. B. Deacon, K. Ruhlandt-Senge
FULL PAPER
Table 2. Tilt angles and Ba/pz angles for selected complexes.
Entry
Formula
Binding mode
Tilt angle [°]
Ba/pz [°]
Ref.
2
1
2
2
2
2
2
2
2
2
2
2
2
2
84.4[a]
90.0
87.8
72.8
64.6
63.4
58.3
48.7
44.8, 44.7
47.3
1
2
3
4
5
6
7
8
9
1
1
1
1
[{Ba(tBupz)
2
(NH
(pmdta)}
pz)12
(Me
(pmdta)}
pz) (py)
[{Ba(tBupz) (pmdta)}
[{Ba(tBu pz) (thf)
[Ba (tBu pz)12
[{Ba(tBupz)
3
)
2
}
n
] (4)
2
µ-η :η
2
[{Ba(Me
[Ba (tBu
[(thf) Ba
2
2
6
pz)
2
] (1)
µ-η :η
2
[4c]
[9]
6
]
2
µ-η :η
2
6
pz)
8
{(OSiMe
] (2)
2
)
2
O}
2
]
µ-η :η
2
[{Ba(Phpz)
[{Ba(iPr
2
2
µ-η :η
61.4
61.1
2
[4a]
2
2
3
}
2
]
µ-η :η
4
2
2
] (3)
µ-η :η
69.5
74.5
86, 87
77.5
70, 78
80–84
81.4
4
[4b]
[4c]
2
2
2
}
2
]
µ-η :η
4
6
2
]
µ-η :η
5
0
1
2
3
2
(NH
3
)
2
}
n
] (4)
µ-η :η
5
[9]
[(thf)
[Ba (tBu
[{Ba(Ph
6
Ba
6
(Me
pz)12
(tmeda)}
2
pz)
8
{(OSiMe
2
)
2
O}
2
]
µ-η :η
45.8, 54.1
45.6, 47.2
43.5
5
[4c]
6
2
pz)
]
µ-η :η
5
2
2
2
]·TMEDA (6)
µ-η :η
1
[
a] Involves hydrogen bonding to η -nitrogen atom.
nors. In 1, the steric repulsion between the methyl groups of (ii) the steric repulsion between the terminal methyl groups
the bridging and terminal pyrazolates prevents subsequent of the PMDTA and the three-dimensional tert-butyl groups
tilting and a significant π-contribution from the bridging of the bridging pyrazolate in 3. This might prevent the
ligand. The steric repulsion results from the symmetrical proximity required for agostic interactions to occur or sim-
arrangement of the terminal pyrazolate with respect to the ply provide more coverage of the metal atom than the two-
PMDTA semi-circular arrangement, dictated by its sym- dimensional phenyl ring in 2.
metrical 3,5-dimethyl substitution pattern. The symmetrical
arrangement might be quantified by the difference in the
Donor Effects
two smallest Nterminalpz–Ba–N(exo)PMDTA angles [N(11)–
The effects of different donors on molecular structure
Ba(1)–N(31) 78.35(10)°; symmetry required ∆(N–M–N) 0°]. can be analyzed by comparing compounds with the same
2
2
Therefore, the µ-η :η -bridging pyrazolate twists (∆
metal atom and pyrazolate ligand, but different donor
M–N
0.241 Å), rather than tilts (tilt angle 90°), to fill the steri- types. Several sets of such examples are available.
cally unsaturated area of the barium atom.
One set of pyrazolates, which illustrate the effect of dif-
[4c]
It is instructive to compare the molecular geometry in ferent donors, comprises: the hexameric [Ba (tBu pz) ],
6
2
12
[
4a]
[4b]
1
with [{Ba(iPr pz) (py) } ],
(Entry 6, Table 2) where a the dimeric [{Ba(tBu pz) (thf) } ] (Entries 3, 9, 12 and 8,
2
2
3 2
2 2 2 2
2
2
similar twisting is seen in the µ-η :η -bridging pyrazolate respectively; Table 2), and the monomeric [Ba(tBu pz) (tet-
2
2
[
3a]
(∆M–N 0.185, 0.176 Å) due to the steric repulsion between raglyme)] and [Ba(tBu pz) (triglyme)].
All contain bar-
2
2
the diisopropyl substituents on the terminal and bridging ium and the tBu pz ligand. In this series, a reduction in
2
pyrazolates, an effect possibly enhanced by the increased nuclearity along this list can be attributed to the corre-
steric demand of three pyridine donors as compared to one sponding increase in donor hapticity and size.
tridentate PMDTA. However, [{Ba(iPr pz) (py) } ] exhibits
A second set of compounds illustrates another effect.
2
2
3 2
a more pronounced tilt (63.4°) than 1, possibly due to the The dimeric 3 and polymeric 4 both employ barium and
improved electron-donating ability of the isopropyl than the the asymmetrically substituted tBupz ligand (Entries 1, 7,
methyl groups, enhancing the tendency of the bridging pyr- and 10; Table 2). The arrangement of the ligands and do-
azolate in [{Ba(iPr pz) (py) } ] towards π-bonding.
nors about the barium atom in 4 is very similar to that
2
2
3 2
π-Coordination appears to be favored if asymmetrically observed in 3, except that the smaller coordinative and ste-
substituted pyrazolates are employed, as observed in com- ric requirement of two ammonia donors, as compared to
pounds 2 and 3. Here, the terminally bound pyrazolates are the tridentate PMDTA, results in (i) the increased π-bond-
4
5
2
no longer symmetrical with respect to the PMDTA semi- ing from η to η , (ii) the conversion of the terminal η -
2
1
circular arrangement, but arranged to reduce steric repul- pyrazolate in 3 to a bridging µ-η :η -arrangement in 4, and
sion from their asymmetrically located substituents, 3- (iii) stabilization through hydrogen bonding of an ammonia
phenyl in 2 [N(11)–Ba(1)–N(37) 73.37(9)°, N(12)–Ba(1)– hydrogen atom to the uncoordinated nitrogen atom of the
1
N(31) 90.63(9)°; ∆(N–M–N) 17.26°], and 3-tert-butyl in 3 η -bound pyrazolate.
[
8
N(11)–Ba(1)–N(31)
6.47(6)°; ∆(N–M–N) 10.68°]. The reduction of steric re- bonding usually affects the resulting structure. Other exam-
pulsion between the substituents of the bridging and ter- ples of such hydrogen bonding are found in the monomeric
75.79(6)°,
N(12)–Ba(1)–N(37)
The ability of the neutral donor to engage in hydrogen
[
4d]
minal pyrazolates allows the bridging pyrazolate to tilt [M(Me pz) (Me pzH) ] (M = Ca, Sr),
towards the metal atom [tilt angle 64.6° (2), 58.3° (3)].
[Mg(tBu pz) -
2
2
2
4
2 2
[
11]
2
1
(tBu pzH) ],
and [Nd(η -Me pz) (η -Me pz)(Me pzH)-
2
2
2 2 2 2
The cause of stabilization through agostic interactions, py][10a] and the dimeric [{M(iPr pz) (iPr pzH) } ] (M =
2
2
2
2 2
[
4a]
rather than π-coordination in 2 is not obvious, but may be Mg, Ca, Eu).
In these complexes, as in 4, a nitrogen-
related to (i) the weaker electron-donating ability of the bound hydrogen atom on the neutral donor (Me pzH,
2
phenyl compared to the tert-butyl substituent in 3, or rather tBu pzH, or iPr pzH vs. NH ) is donated to a nitrogen
2
2
3
178
www.eurjic.org
© 2008 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Eur. J. Inorg. Chem. 2008, 172–182

Unlocking the Coordination Chemistry of Barium Pyrazolates
atom of the pyrazolate ring. This hydrogen-bonded em- cooling to 194 K affords two cleanly separated peaks. Anal-
2
1
brace reduces pyrazolate hapticity (from η to η in the mo- ogous observations are made for the C4 and C5(pz)–H,
[
4d,10a,11]
nomeric compounds
and [{Mg(iPr pz) (iPr - peaks with broadening at 233 K, and splitting at 194 K.
2 2 2
[
4a]
2
2
2
1
pzH) } ],
from µ-η :η to µ-η :η in [{Ca(iPr pz) (iPr - The dynamic behavior of 3 was analyzed using the Gutow-
2
2
2 2 2
[
4a]
5
2
5
1
[12]
pzH) } ]
and 4, and from µ-η :η to µ-η :η in sky–Holm and Eyring equations, with the free energy of
2
2
[4a]
activation ∆Gc‡ for the dynamic exchange of the tBupz li-
[
{Eu(iPr pz) (iPr pzH) } ]).
2
2
2
2 2
–1
A third set of compounds, 2, 5, and 6 (Entries 5, 13; gands in solution estimated to be 11.15 kcalmol . Recent
Table 2), vary in both ligand substitution and donor type, variable-temperature H NMR studies in [D ]toluene of a
1
8
but nicely illustrate the tendency towards π-bonding and/or series of heavy alkaline earth metal pyrazolate dimers
aggregation, upon reduction of the size and/or hapticity of [{M(tBu pz) (thf) } ] and homoleptic linear oligomers
2
2
x 2
[
4b,4c]
the neutral donor. The reduced coordination number and [{M(tBu pz) } ] (M = Ca, Sr, Ba),
also indicated dy-
2
2 n
‡
steric requirements of the bidentate TMEDA in compounds namic behavior, but did not allow the computation of ∆Gc
5
and 6, as compared to the tridentate PMDTA in 2, allow due to incomplete peak splitting in both cases. ∆Gc‡ ob-
for µ-η :η -bridging in 5 and 6 despite the increased steric tained for 3 agrees well with data from previous dynamic
demand of the ligands by means of an additional phenyl or studies by Westerhausen et al. focusing on the heavy alka-
methyl substituent. Similarly, coordination of only two thf line earth metal bis[bis(trimethylsilyl)amide] dimers,
5
2
[
4b]
[13]
donors in [{Ba(tBu pz) (thf) } ]
(Entry 8, Table 2) com- {M[N(SiMe ) ] } (M = Mg, Ca, Sr, Ba).
For the Ca
2
2
2 2
3 2 2 2
[
4a]
‡
pared to three pyridine donors in [{Ba(iPr pz) (py) } ]
and Sr compounds, ∆Gc was computed to be 17.20 and
Entry 6, Table 2) allows for µ-η :η -bridging in the former. 12.67 kcalmol respectively. The smaller value for the heav-
2
2
3 2
4
2
–1
(
Since pyridine and thf have the same steric coordination ier analogue is indicative of the reduced metal–ligand bond
number values, these dimers vividly illustrate the effect of strength observed in the heavier analogues.
reduction in bulk from tBu pz to iPr pz. In the extreme
2
2
case of the donor-free dimer of trinuclear units [Ba -
6
[
4c]
(
tBu pz) ], the dominant π-bonding of the bridging pyr-
2 12
Conclusions
azolates allows the formation of a highly unusual linear ar-
rangement.
The analysis of factors influencing the coordination
chemistry of the target barium pyrazolates include (i) ligand
bulk, (ii) donor size and hapticity, (iii) the capability for
secondary interactions (π-bonding, agostic interactions, hy-
drogen bonding), and (iv) stoichiometry. When steric satu-
ration is not achieved by the steric demand of the ligands
and neutral donors, secondary interactions compensate.
Their degree and type depend on the pyrazolate substitu-
tion pattern, as documented in 1–3. In the absence of a
sterically demanding donor, as seen in 4, oligomerization
takes place. Showing the importance of donor size and hap-
ticity, the comparison of compounds 2 and 6 indicates that
the nature of the donor seems to play a more structurally
determining role than the steric bulk of the pyrazolate.
Agostic interactions provide an alternative for achieving
steric saturation when the metal atom is too small to allow
further donor coordination. For example, close M–H con-
tacts were observed in the dimeric compounds [{M(tBu pz) -
2
2
(
thf)} ] (M = Sr, Eu) between the metal atom and a tert-
2
butyl group of a bridging pyrazolate as well as between the
metal atom and a hydrogen atom on an α-position in a thf
molecule. Upon increasing the metal size to Ba, the dimeric
[
{Ba(tBu pz) (thf) } ] was isolated in which agostic interac-
2 2 2 2
tions were not needed due to the presence of a second thf
[
4b]
donor.
(iv) Solution Behavior
1H NMR spectra of the dimeric compounds 1–3, 5, and Experimental Section
6
collected at room temperature do not distinguish between
General: All manipulations were carried out under strict exclusion
of air and moisture using Schlenk techniques and purified nitrogen
or argon. All reagents were stored in a glove box. All solvents were
distilled from Na/K alloy and degassed by two freeze-pump-thaw
terminal and bridging pyrazolates. For example, compound
exhibits a single peak observed at δ = 1.54 ppm corre-
sponding to the tBu substituent (see Exp. Sect.), caused by
3
either rapid terminal bridging ligand fluxionality on the cycles prior to use. The barium metal (ingots, 99.7%, Cerac) was
NMR time scale or loss of the dimeric structure upon dis- rinsed with hexane before use. Me pzH (Lancaster) was dried un-
solution in the NMR solvent. Similarly, all bridging pyraz- der vacuum and recrystallized from hexane. PhpzH, tBupzH,
2
[
14]
pzH,[ and Ba[N(SiMe
15]
)
2
]
2
(thf)
[16]
were prepared according
tBu
2
3
2
olates in 4 displayed the same chemical shifts at room tem-
perature.
to literature methods. MePhpzH was synthesized by a modified
literature procedure by refluxing the diketone with hydrazine hy-
drate in ethanol for 24 h.[ PMDTA and TMEDA were distilled
As a representative of the dimeric compounds, the solu-
17]
tion behavior of 3 was further analyzed by low-temperature
2
from CaH . Ammonia gas was made anhydrous by being con-
1
H NMR studies in [D ]toluene. Indeed, upon cooling,
8
densed over Na before condensation in a reaction flask. NMR
spectroscopic data were obtained with a Bruker Avance spectrome-
ter (300 MHz, 25 °C). The chemical shifts were referenced to the
splitting of the tBu signal, as well as those of the C4– and
C5(pz)–H peaks is observed. From a single peak at 298 K
at δ = 1.39 ppm, the tBu signal broadens, and at 238 K residual solvent signals ([D ]benzene: δH = 7.16 ppm, δC
=
6
begins to split into two broad but distinct peaks. Further 128.38 ppm; [D
8
]thf: δ
H
= 3.58, 1.73 ppm; δ
C
= 67.5, 25.3 ppm).
Eur. J. Inorg. Chem. 2008, 172–182
© 2008 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.eurjic.org 179

A. Y. O’Brien, J. Hitzbleck, A. Torvisco, G. B. Deacon, K. Ruhlandt-Senge
1.0 mmol). Yield: 0.42 g (70%); m.p. 320 °C (dec.) to brown solid;
FULL PAPER
Melting points were collected with a MelTemp apparatus in capil-
laries sealed under nitrogen and are uncalibrated. IR spectra were
collected as Nujol mulls using KBr plates with a Perkin–Elmer FT-
IR spectrometer. Due to limited quantities, only a representative
set of compounds (2, 3) were sent for elemental analysis. However,
the correlation between purity of the sample and correctly inte-
1
H NMR ([D
6
]benzene): δ = 8.18 [s, 8 H, o-H(Ph)], 8.12 [s, 4 H,
C5(pz)-H], 7.35 [t, 8 H, m-H(Ph)], 7.16 [s, p-H(Ph)] (integration not
possible due to C
1.99 (s, 16 H, CH
([D
129.1 [o-C(Ph)], 126.6 [m-, p-C(Ph)], 104.5 [C4(pz)], 57.5 (CH
55.7 (CH ), 45.3 [N(CH ], 42.6 (NCH ) ppm. IR (Nujol): ν˜ =
6
H
6
), 6.95 [s, 4 H, C4(pz)-H], 2.11 (s, 6 H, NCH
3
),
1
3
2
CH
2
), 1.70 [s, 24 H, N(CH
3
)
2
] ppm. C NMR
6
]benzene): δ = 152.29 [C3(pz)], 139.8 [C5(pz)], 137.2 [i-C(Ph)],
),
1
grated, clean H NMR spectra for these types of compounds has
been demonstrated extensively by our group. X-ray crystallo-
graphic data were collected with a Bruker SMART system, with
2
[4]
2
3
)
2
3
2672 (w), 1601 (s), 1514 (m), 1335 (w), 1286 (m), 1107 (w), 1078
(w), 1053 (m), 1024 (m), 976 (w), 941 (w), 924 (m), 887 (w), 862
α
monochromatic Mo-K radiation (λ = 0.71073 Å), a 3-circle goni-
–
1
ometer and APEX CCD detector. Suitable crystals for single-crys-
tal X-ray analysis were removed from a Schlenk tube under a flow
of nitrogen gas, immediately covered with viscous hydrocarbon oil
Infineum), and subsequently mounted on a glass fiber with the aid
of a microscope. The mounted crystal remained under a nitrogen
(w) cm . C54
16.4; found C 54.4, H 6.1, Ba 22.6, N 16.1. C54
(1193.95), colorless plates, 0.22ϫ0.22ϫ0.02 mm, monoclinic,
space group P2 /c (no. 14), a = 12.4638.7(7), b = 13.1822(8), c =
16.9058(1) Å, β = 93.9630(1)°, V = 2771.0(3) Å , Z = 2, Dcalcd.
H
74Ba
2
N
14 (1193.9): calcd. C 54.3, H 6.2, Ba 23.0, N
2 14
H74Ba N
(
1
[
18]
3
=
3
flow at low temperature using a custom-built device by H. Hope. 1.43 g/cm , F(000) = 1216, T = 90(2) K, 2θmax = 58.98°; 13437 re-
For data collection and integration, the Bruker SMART and
SAINT software was employed. Empirical adsorption corrections
were calculated using the program SADABS.[ Solution and re-
finement with the program SHELXTL-Plus used a total of N
flections collected, 5499 unique (Rint = 0.0592). Final GooF =
0.805, R = 0.0396, wR = 0.0535, R indices based on 5499 reflec-
tions with IϾ2σ(I) (refinement on F ), 316 parameters, 0 restraints.
1
2
19]
2
–
1
Lp and absorption corrections applied, µ = 1.461 mm .
{Ba(tBupz) (pmdta)} ] (3). Method B: The general procedure was
applied for 3-tert-butylpyrazole (0.25 g, 2.0 mmol) and PMDTA
0
unique reflections {N [IϾ2σ(I)] observed} in least-squares refine-
[
2
2
[
20]
ment. All non-hydrogen atoms were refined anisotropically. Hy-
drogen atoms were placed in calculated positions. CCDC-649496,
(
(
0.21 mL, 1.0 mmol). Yield: 0.22 g (40%). Method C: Barium
5 mmol, 0.69 g) and 3-tert-butylpyrazole (0.29 g, 2.0 mmol) were
-649497, -649498, -649499, -649500, -649501 contain the supple-
mentary crystallographic data for this paper. These data can be
obtained free of charge from The Cambridge Crystallographic
Data Centre via www.ccdc.cam.ac.uk/data_request/cif. Syntheses
of compounds 1–7 are as follows (see Scheme 1). Unless otherwise
noted, for method B anhydrous ammonia (10 mL) was condensed
in a mixture of barium (0.14 g, 1.0 mmol), the appropriate pyr-
azole, toluene (50 mL) and, if required, neutral donor. Upon com-
plete consumption of the metal, the reaction mixture was warmed
slowly to room temperature. If necessary, the solution was passed
through a sintered glas frit. The solvent volume was reduced, and
the solution was stored at –23 °C to yield colorless X-ray quality
crystals.
heated at 200 °C in vacuo for 48 h, after which a white powder
coated the barium pieces. The white powder was extracted with
hexane in which it was slightly soluble. Solubility was increased
upon the addition of excess PMDTA. Crystals suitable for X-ray
study were formed from this solution after storage at –23 °C over-
night. Yield: 0.33 g (30%), decomposes over temperature range
7
0 °C (wet) Ǟ 100 (dry) Ǟ 170 (wet) Ǟ 210 (dry) Ǟ 350 (wet,
1
brown) Ǟ 374 °C (melted). H NMR ([D
H, C5(pz)-H], 6.52 [s, 4 H, C4(pz)-H], 2.11 (s, 6 H, NCH
6 H, CH CH N), 1.90 [s, 24 H, N(CH ], 1.54 [s, 36 H, C(CH
ppm. C NMR ([D ]benzene): δ = 162.4 [C3(pz)], 138.8 [C5(pz)],
04.07 [C4(pz)], 57.8 (CH ), 56.4 (CH ), 45.6 [N(CH ], 42.7
(NCH ), 32.8 [C(CH ], 32.5 [C(CH ] ppm. IR (Nujol): ν˜ = 3063
(w), 1364 (w), 1288 (w), 1204 (w), 1110 (w), 1026 (m), 980 (w), 926
6
]benzene): δ = 7.87 [s, 4
3
), 2.08 (b,
1
2
2
3
)
2
3 3
) ]
13
6
1
2
2
3 2
)
[
{Ba(Me
applied for 3,5-dimethylpyrazole (0.38 g, 4.0 mmol) and PMDTA
0.21 mL, 1.0 mmol). Yield: 0.20 g (40%); m.p. (dec.) over tempera-
ture range 70 °C (wet) Ǟ 100 (dry) Ǟ 170 °C (wet) suggesting loss
2
pz)
2
(pmdta)}
2
] (1). Method B: The general procedure was
3
3
)
3
3 3
)
–
1
(
(w), 780 (w), 755 (w), 724 (w) cm . C46
C 49.6, H 8.1, Ba 24.7, N 17.6; found C 49.3, H 8.4, Ba 25.0, N
17.4. (1114.00), colorless plates,
N), 2.11 [s, 24 0.26ϫ0.18ϫ0.16 mm, triclinic, space group P1 (no. 2), a =
) ppm. 13C NMR ([D
]benzene): 9.8835(5), b = 11.7007(5), c = 12.8989(6) Å, α = 72.246(1), β =
δ = 144.5 [C(3)5(pz)], 104.5 [C4(pz)], 58.5 (CH ), 57.3 (CH
N(CH ], 30.6 (NCH ), 12.7 [CH (pz)] ppm. IR (Nujol): ν˜ = 3206 1.36 g/cm , F(000) = 576, T = 90(2) K, 2θmax = 58.00°; 14998 reflec-
w), 3132 (w), 3086 (w), 1578 (w), 1560 (w), 1508 (m), 1406 (m), tions collected, 7158 unique (Rint = 0.0308). Final GooF = 1.012,
= 0.0326, wR = 0.0678, R indices based on 7158 reflections
with IϾ2σ(I) (refinement on F ), 280 parameters, 0 restraints. Lp
2
H90Ba N14 (1114.0): calcd.
1
of donor. H NMR ([D
m, 24 H, N(CH ], 2.29–2.27 (m, 16 H, CH
H, CH (pz)], 1.97 (s, 6 H, NCH
6
]benzene): δ = 5.76 [s, 4 H, C4(pz)-H], 2.41
46 2 14
C H90Ba N ,
¯
[
3
)
2
2
CH
2
3
3
6
3
2
2
), 46.4
74.780(1), γ = 80.011(1)°, V = 1363.71(11) Å , Z = 1, Dcalcd. =
3
[
(
1
(
3
)
2
3
3
–1
290 (w), 1107 (w), 1029 (m), 979 (w), 765 (w) cm . C38
H74Ba
2
N
14
R
1
2
2
1001.79), colorless plates, 0.12ϫ0.10ϫ0.03 mm, orthorhombic,
–
1
space group Cmca (no. 64), a = 18.6285(10), b = 15.4487(8), c =
and absorption corrections applied, µ = 1.478 mm .
3
3
1
=
3
wR
6.6879(9) Å, V = 4802.5(4) Å , Z = 4, Dcalcd. = 1.39 g/cm , F(000)
2048, T = 90(2) K, 2θmax = 60.00°, 24472 reflections collected,
597 unique (Rint = 0.0903). Final GooF = 0.939, R = 0.0449,
= 0.0817, R indices based on 3597 reflections with IϾ2σ(I)
[
{Ba(tBupz) (NH ] (4). Method B: The general procedure was
2
3 2 n
) }
applied for 3-tert-butylpyrazole (0.25 g, 2.0 mmol). Colorless nee-
dle-like crystals suitable for X-ray studies were obtained overnight
at –13 °C. Removal of solvent for further characterization resulted
in loss of the coordinated ammonia, limiting the characterization
of this compound due to reduced solubility. Yield: 0.12 g (30%) for
1
2
2
(
refinement on F ), 159 parameters, 6 restraints. Lp and absorption
–1
corrections applied (ψ scan), µ = 1.671 mm .
{Ba(Phpz) (pmdta)} ] (2). Method A: A thf solution (50 mL) of BaN
Ba{N(SiMe (thf) (0.30 g, 0.50 mmol), phenylpyrazole Ǟ 200 °C (dry) Ǟ 261 °C (melt), suggesting loss of donor.
1.0 mmol, 0.14 g), and PMDTA (0.10 mL, 0.50 mmol) was re- NMR ([D
H], 1.266 [s, 18 H, C(CH
[
2
2
4 14
C H22 unit; decomposes over temperature range 135 °C (wet)
1
3
)
2
}
2
2
H
(
8
]thf): δ = 7.339 [s, 2 H, C5(pz)-H], 5.971 [s, 2 H, C4(pz)-
1
3
fluxed for 12 h. The thf was removed in vacuo and the resulting
white precipitate dissolved in toluene. Storage of the solution at
3
)
3
] ppm. C NMR ([D
8
]thf): δ = 160.24
[C3(pz)], 136.21 [C5(pz)], 101.10 [C4(pz)], 32.74 [C(CH
[C(CH ] ppm. IR (Nujol): ν˜ = 3348.7 (s), 2728.9 (w), 1567.0 (m),
1225.2 (w), 1093.1 (s), 1020.2 (s), 929.0 (w), 860.7 (m), 783.2 (m)
3 3
) ], 32.19
–23 °C yielded colorless crystals suitable for X-ray studies. Yield:
3 3
)
0.09 g (30%). Method B: The general procedure was applied for
–
1
phenylpyrazole (0.28 g, 2.0 mmol) and PMDTA (0.21 mL,
cm .
C
14
H28BaN
6
(417.76),
colorless
needles,
180
www.eurjic.org
© 2008 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Eur. J. Inorg. Chem. 2008, 172–182

Unlocking the Coordination Chemistry of Barium Pyrazolates
¯
0
8
8
.50ϫ0.06ϫ0.06 mm, triclinic, space group P1 (no. 2), a =
(w), 1743 (w), 1665 (w), 1601 (s), 1526 (m), 1511 (m), 1359 (m),
1337 (m), 1292 (m), 1264 (m), 1218 (m), 1180 (w), 1161 (m), 1133
.4996(8), b = 9.7276(9), c = 11.6162(11) Å, α = 89.138(2), β =
9.316(2), γ = 84.284(2)°, V = 955.50(16) Å , Z = 2, Dcalcd. = 1.45 g/
cm , F(000) = 420, T = 90(2) K, 2θmax = 60.00°; 10952 reflections (m), 836 (m), 808 (m), 784 (s), 756 (s), 730 (w), 695 (s) cm .
3
(m), 1098 (w), 1076 (m), 1052 (s), 1031 (s), 965 (s), 945 (m), 909
3
–1
collected, 5458 unique (Rint = 0.0205). Final GooF = 1.082, R
.0299, wR = 0.0767, R indices based on 5458 reflections with
IϾ2σ(I) (refinement on F ), 209 parameters, 6 restraints. Lp and
1
=
C
48
H
70BaN10 (924.46), colorless blocks, 0.30ϫ0.22ϫ0.18 mm,
0
2
monoclinic, space group C2/c, a = 26.023(2), b = 11.970(1), c =
17.170(1) Å, β = 114.084(1)°, V = 4882.67 Å , Z = 4, Dcalcd.
1.100 g/cm , F(000) = 1672, T = 123(2) K, 2θmax = 55.00°; 23882
reflections collected, 5609 unique (Rint = 0.0281). Final GooF =
2
3
=
–1
3
absorption corrections applied, µ = 2.082 mm .
[
{Ba(MePhpz) (tmeda)} ] (5). Method B: The general procedure was
2
2
1 2
1.117, R = 0.0251, wR = 0.0645, R indices based on 5609 reflec-
applied for barium (0.27 g, 2.0 mmol), 3-methyl-5-phenylpyrazole
0.63 g, 4.0 mmol), toluene (40 mL) and TMEDA (1.5 mL) with
2
tions with IϾ2σ(I) (refinement on F ), 294 parameters, 84 re-
straints. Lp and absorption corrections applied, µ = 0.846 mm .
Compound 7 contains a lattice TMEDA molecule, which was
highly disordered, non-resolvable, and therefore removed from the
crystal structure refinement using the “squeeze” function in the
(
–1
dry ammonia (10 mL). The solvent was evaporated to 20 mL, and
layered with hexane to yield small yellow blocks upon cooling to
1
0
°C. Yield: 0.68 g (69%); m.p. 135–140 °C. H NMR ([D
6
]ben-
3
zene): δ = 8.12 [s, 8 H, o-H(Ph)], 7.36 [t, J(H,H) = 7.2 Hz, 8 H,
m-H(Ph)], 7.23 [s, 4 H, p-H(Ph)], 6.65 [s, 4 H, C4(pz)-H], 2.36, 2.11
[21]
program package PLATON.
s, 12 H, Me), 1.78 (s, 32 H, TMEDA) ppm. 1 C NMR ([D
3
Supporting Information (see footnote on the first page of this arti-
cle): Additional structure descriptions, selected bond lengths and
angles for compounds 1–4, 6, and 7.
(
6
]ben-
zene): δ = 152.4 [C(pz)-Ph], 150.3 [C(pz)-Me], 136.1 [i-C(Ph)], 129.3
o-C(Ph)], 126.9 [p-C(Ph)], 126.1 [m-C(Ph)], 105.7 [CH(pz)], 57.6
NCH ), 45.3 (CH N), 14.1 (Me) ppm. IR (Nujol): ν˜ = 3051 (m),
949 (w), 1889 (w), 1811 (w), 1762 (w), 1674 (w), 1599 (s), 1568
[
(
1
2
3
Acknowledgments
(
(
(
s), 1505 (s), 1411 (s), 1292 (m), 1253 (m), 1198 (m), 1161 (m), 1131
m), 1098 (m), 1071 (m), 1020 (s), 995 (m), 962 (m), 916 (m), 949
m), 916 (m), 834 (m), 783 (s), 762 (s), 695 (s), 671 (m) cm .
We gratefully acknowledge support from the National Science
Foundation (CHE-0108098 and CHE-0505863), and the Australian
Research Council. Purchase of the X-ray diffraction equipment was
made possible with grants from the National Science Foundation
–
1
[
{Ba(Ph
2
pz) (tmeda)} ]·TMEDA (6). Method B: The general pro-
2
2
cedure was applied for barium (0.27 g, 2.0 mmol), 3,5-diphenylpyr-
azole (0.88 g, 4.0 mmol), toluene (10 mL) and TMEDA (15 mL)
with condensed anhydrous ammonia (10 mL). Yield: 0.78 g (52%);
(
CHE-9527858 and CHE-0234912), Syracuse University and the
W. M. Keck Foundation.
dec. Ͼ350 °C; 1H NMR ([D
8
7
]benzene): δ = 8.03, [d, J(H,H) =
3
6
3
.3 Hz, 16 H, o-H(Ph)], 7.36 [t, J(H,H) = 8.3 Hz, 16 H, m-H(Ph)],
.17 [m, 8 H, p-H(Ph)], 7.02 [d, 4 H, C4(pz)-H], 2.22 (s, 12 H,
), 2.08 (s, 36 H, NCH ]benzene): δ =
) ppm. 13C NMR ([D
29.3 [o-C(Ph)], 126.9 [p-C(Ph)], 126.0 [m-C(Ph)], 102.2 [C4(pz)],
8.6 (NCH ), 46.3 (NCH ) ppm; C(pz)-Ph and i-C(Ph) unresolved.
[
1] L. G. Hubert-Pfalzgraf, J. Mater. Chem. 2004, 14, 3113–3123.
[2] G. A. Battiston, R. Gerbasi, G. Carta, F. Marchetti, C. Pettin-
ari, A. Rodriguez, D. Barreca, C. Maragno, E. Tondello, J.
Electrochem. Soc. 2006, 153, F35–F38.
NCH
2
3
6
1
5
[
3] a) H. M. El-Kaderi, M. J. Heeg, C. H. Winter, Polyhedron
2
3
2
005, 24, 645–653; b) H. M. El-Kaderi, M. J. Heeg, C. H. Win-
IR (Nujol): ν˜ = 3059 (m), 3032 (m), 1946 (w), 1883 (w), 1820 (w),
751 (w), 1668 (w), 1597 (s), 1522 (m), 1338 (m), 1290 (m), 1260
m), 1216 (m), 1175 (m), 1155 (m), 1038 (s), 966 (s), 909 (m), 886
ter, Eur. J. Inorg. Chem. 2005, 2081–2088.
1
[
4] a) J. Hitzbleck, G. B. Deacon, K. Ruhlandt-Senge, Eur. J. Inorg.
Chem. 2007, 592–601; b) J. Hitzbleck, A. Y. O’Brien, G. B.
Deacon, K. Ruhlandt-Senge, Inorg. Chem. 2006, 45, 10329–
(
(
–
1
2
s), 842 (w), 799 (m), 755 (s), 695 (s) cm . C78H92Ba N14 (1500.29),
¯
colorless needles, 0.28ϫ0.08ϫ0.05 mm, triclinic, space group P1
no. 2), a = 12.821(3), b = 13.055(3), c = 13.758(3) Å, α = 94.26(3),
1
0337; c) J. Hitzbleck, G. B. Deacon, K. Ruhlandt-Senge, An-
(
gew. Chem. Int. Ed. 2004, 43, 5218–5220; d) J. Hitzbleck, A. Y.
O’Brien, C. M. Forsyth, G. B. Deacon, K. Ruhlandt-Senge,
Chem. Eur. J. 2004, 10, 3315–3323.
3
β = 110.74(3), γ = 111.74(3)°, V = 1943.6(11) Å , Z = 1, Dcalcd.
3
=
1.183 g/cm , F(000) = 704, T = 94(2) K, 2θmax = 50.00°; 15865
reflections collected, 6835 unique (Rint = 0.0326). Final GooF =
.029, R = 0.0461, wR = 0.1187, R indices based on 6835 reflec-
tions with IϾ2σ(I) (refinement on F ), 371 parameters, 108 re-
[5] I. Kobrsi, J. E. Knox, M. J. Heeg, H. B. Schlegel, C. H. Winter,
Inorg. Chem. 2005, 44, 4894–4896.
1
1
2
2
[6] D. Pfeiffer, M. J. Heeg, C. H. Winter, Inorg. Chem. 2000, 39,
377–2384.
2
–
1
straints. Lp and absorption corrections applied, µ = 1.050 mm .
Heavy disorder of lattice TMEDA could not be handled by refining
split positions and required treatment with the “squeeze” function
in the PLATON program package.[
[
7] a) A. F. Wells, Structural Inorganic Chemistry, 5th ed., Oxford,
Clarendon, 1984; b) L. Pauling, The Nature of the Chemical
Bond, 3rd ed., Cornell University Press, Ithaca, NY, 1960.
21]
[8] a) A. Y. O’Brien, Doctoral Thesis, Syracuse University, Syra-
cuse, NY, 2005; b) J. Hitzbleck, Doctoral Thesis, Syracuse Uni-
versity, Syracuse, NY, 2004.
2 2 2
[Ba(Ph pz) (tmeda) ]·TMEDA (7). Method B: The general pro-
cedure was applied for barium (0.27 g, 2.0 mmol), 3,5-diphenylpyr-
azole (0.88 g, 4.0 mmol), toluene (20 mL) and TMEDA (30 mL),
with condensed anhydrous ammonia (10 mL). The solvent was re-
[9] A. Steiner, G. T. Lawson, B. Walfort, D. Leusser, D. Stalke, J.
Chem. Soc. Dalton Trans. 2001, 219–221.
[10] a) G. B. Deacon, C. M. Forsyth, A. Gitlits, R. Harika, P. C.
Junk, B. W. Skelton, A. H. White, Angew. Chem. Int. Ed. 2002,
41, 3249–3251; b) S. Beaini, G. B. Deacon, A. P. Erven, P. C.
Junk, D. R. Turner, Chem. Asian J. 2007, 2, 539–550; c) S.-Á.
Cortés-Llamas, R. Hernández-Lamoneda, M.-Á. Velázquez-
Carmona, M.-A. Muñoz-Hernández, R. A. Toscano, Inorg.
Chem. 2006, 45, 286–294; d) G. B. Deacon, B. M. Gatehouse,
S. Nickel, S. N. Platts, Aust. J. Chem. 1991, 44, 613–621; e)
J. E. Cosgriff, G. B. Deacon, B. M. Gatehouse, H. Hemling, H.
Schumann, Angew. Chem. Int. Ed. Engl. 1993, 32, 871–875; f)
J. E. Cosgriff, G. B. Deacon, B. M. Gatehouse, Aust. J. Chem.
duced to 20 mL and cooling to –20 °C yielded colorless prisms.
1
Yield: 0.47 g (51%); m.p. Ͼ350 °C; H NMR ([D
6
]benzene): δ =
3
3
8
8
4
.10 [d, J(H,H) = 7.5 Hz, 8 H, o-H(Ph)], 7.41 [t, J(H,H) = 7.6 Hz,
H, m-H(Ph)], 7.32 [s, 2 H, C4(pz)-H], 7.21 [t, J(H,H) = 7.3 Hz,
3
H, p-H(Ph)], 2.14, 1.98 (br. d, 32 H, TMEDA) ppm, indicating
1
3
loss of the lattice TMEDA molecule. C NMR ([D
52.2 [C(pz)-Ph], 136.6 [ipso-C(Ph)], 129.6 [o-C(Ph)], 126.7 [p-
C(Ph)], 125.9 [m-C(Ph)], 103.1 [C4(pz)], 58.1 (NCH ), 46.1 (NCH
ppm. IR (Nujol): ν˜ = 3062 (m), 3031 (m), 1945 (w), 1874 (w), 1800
6
]benzene): δ =
1
2
3
)
Eur. J. Inorg. Chem. 2008, 172–182
© 2008 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.eurjic.org
181

A. Y. O’Brien, J. Hitzbleck, A. Torvisco, G. B. Deacon, K. Ruhlandt-Senge
FULL PAPER
1
993, 46, 1881–1896; g) J. E. Cosgriff, G. B. Deacon, B. M.
Beaini, G. B. Deacon, M. Hilder, P. C. Junk, D. R. Turner, Eur.
J. Inorg. Chem. 2006, 3434–3441.
[11] N. C. Mösch-Zanetti, M. Ferbinteanu, J. Magull, Eur. J. Inorg.
Chem. 2002, 950–956.
[12] a) A. R. Katritzky, I. Ghiviriga, P. J. Steel, D. C. Oniciu, J.
Chem. Soc. Perkin Trans. 2 1996, 443; b) P. Fischer, A. Fettig,
Magn. Reson. Chem. 1997, 35, 839; c) B. K. Shull, D. E. Spiel-
vogel, R. Gopalaswamy, S. Sankar, P. D. Boyle, G. Head, K.
Devito, J. Chem. Soc. Perkin Trans. 2 2000, 557; d) H. S. Gu-
towsky, C. H. Holm, J. Chem. Phys. 1956, 25, 1228; e) J. B.
Lambert, L. Lin, Magn. Reson. Chem. 2001, 39, 714; f)
Sandström, J. Dynamic NMR Spectroscopy, Academic Press,
New York, 1982, p. 93.
[13] M. Westerhausen, Inorg. Chem. 1991, 30, 96.
[14] S. Trofimenko, J. C. Calabrese, J. S. Thompson, Inorg. Chem.
1987, 26, 1507–1514.
[15] J. Elguero, E. Gonzalez, R. Jacquier, Bull. Soc. Chim. Fr. 1968,
707–713.
[16] M. Westerhausen, Trends Organomet. Chem. 1997, 2, 89–105.
[17] J. Elguero, E. Gonzalez, R. Jacquier, Bull. Soc. Chim. Fr. 1966,
2832.
Gatehouse, H. Hemling, H. Schumann, Aust. J. Chem. 1994,
4
7, 1223–1235; h) J. E. Cosgriff, G. B. Deacon, B. M. Gate-
house, P. R. Lee, H. Schumann, Z. Anorg. Allg. Chem. 1996,
22, 1399–1403; i) J. E. Cosgriff, G. B. Deacon, G. D. Fallon,
B. M. Gatehouse, H. Schumann, R. Weiman, Chem. Ber. 1996,
29, 953–958; j) J. E. Cosgriff, G. B. Deacon, Angew. Chem.
6
1
Int. Ed. 1998, 37, 286–287; k) G. B. Deacon, E. E. Delbridge,
B. W. Skelton, A. H. White, Eur. J. Inorg. Chem. 1998, 543–545;
l) G. B. Deacon, E. E. Delbridge, B. W. Skelton, A. H. White,
Angew. Chem. Int. Ed. 1998, 37, 2251–2252; m) J. E. Cosgriff,
G. B. Deacon, E. E. Delbridge, C. Jones, B. W. Skelton, A. H.
White, Mater. Sci. Forum 1999, 315–317, 136–143; n) G. B.
Deacon, E. E. Delbridge, B. W. Skelton, A. H. White, Eur. J.
Inorg. Chem. 1999, 751–761; o) G. B. Deacon, E. E. Delbridge,
C. M. Forsyth, Angew. Chem. Int. Ed. 1999, 38, 1766–1767; p)
G. B. Deacon, A. Gitlis, B. W. Skelton, A. H. White, Chem.
Commun. 1999, 1213–1214; q) G. B. Deacon, E. E. Delbridge,
C. M. Forsyth, P. C. Junk, B. W. Skelton, A. H. White, Aust. J.
Chem. 1999, 52, 733–739; r) G. B. Deacon, E. E. Delbridge,
C. M. Forsyth, B. W. Skelton, A. H. White, J. Chem. Soc. Dal-
ton Trans. 2000, 745–751; s) G. B. Deacon, E. E. Delbridge,
G. D. Fallon, C. Jones, D. E. Hibbs, M. B. Hursthouse, B. W.
Skelton, A. H. White, Organometallics 2000, 19, 1713–1721; t)
G. B. Deacon, A. Gitlits, P. W. Roesky, M. K. Burgstein, K. C.
[18] H. Hope, Prog. Inorg. Chem. 1994, 41, 1.
[19] G. M. Sheldrick, University of Göttingen, Göttingen, Ger-
many, 1996.
[20] G. M. Sheldrick, Siemens, Madison, WI, USA, 1999.
Lim, B. W. Skelton, A. H. White, Chem. Eur. J. 2001, 7, 127– [21] a) A. L. Spek, Acta Crystallogr., Sect. A 1990, 46, C34; b)
1
38; u) G. B. Deacon, E. E. Delbridge, D. J. Evans, R. Harika,
P. C. Junk, B. W. Skelton, A. H. White, Chem. Eur. J. 2004, 10,
193–1204; v) G. B. Deacon, C. M. Forsyth, A. Gitlits, B. W.
PLATON – A Multipurpose Crystallographic Tool, Utrecht
University, Utrecht, The Netherlands, 2005.
Received: September 20, 2007
1
Skelton, A. H. White, Dalton Trans. 2004, 1239–1247; w) S.
Published Online: November 15, 2007
182
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Eur. J. Inorg. Chem. 2008, 172–182