3-Phenyl-5-(2-pyridyl)pyrazolato complexes of lithium, magnesium, calcium, and zinc

Article abstract of DOI:10.5560/ZNB.2012-0085

Metalation of 3-phenyl-5-(2-pyridyl)pyrazole (HPz, 1) with alkyllithium and -zinc compounds in tetrahydrofuran (thf) yields dinuclear products [(thf)Li(Pz)]2 (2) and [MeZn(Pz)]2 (3), respectively. Magnesiation of 1 with diethylmagnesium in tetrahydrofuran in the presence of 1,4-dioxane leads to cocrystallization of mononuclear [(thf)2Mg(Pz)2] (4a) and [(diox)2Mg(Pz)2] (4b). Metalation of 1 with KH followed by a metathesis reaction with CaI2 in tetrahydrofuran leads to the formation of dinuclear [{(thf)2Ca}(m-Pz)3Ca(Pz)] (5) with the calcium atoms in different coordination environments. The ligand precursor 1 crystallizes as a dimer with N-H...N bridges between the pyrazole fragments. The pyrazolate anions of the metal complexes 2 to 5 exhibit similar structural parameters regardless of a bridging or terminal coordination mode and the electronegativity of the coordinated metal.

Full text of DOI:10.5560/ZNB.2012-0085

3-Phenyl-5-(2-pyridyl)pyrazolato Complexes of Lithium, Magnesium,
Calcium, and Zinc
Tobias Kloubert, Helmar Go¨rls and Matthias Westerhausen
Institute of Inorganic and Analytical Chemistry, Friedrich Schiller University Jena,
Humboldtstrasse 8, D-07743 Jena, Germany
Reprint requests to Prof. M. Westerhausen. E-mail: m.we@uni-jena.de
Z. Naturforsch. 2012, 67b, 519 – 531 / DOI: 10.5560/ZNB.2012-0085
Received March 26, 2012
Dedicated to Professor Wolfgang Beck on the occasion of his 80th birthday
Metalation of 3-phenyl-5-(2-pyridyl)pyrazole (HPz, 1) with alkyllithium and -zinc compounds in
tetrahydrofuran (thf) yields dinuclear products [(thf)Li(Pz)]2 (2) and [MeZn(Pz)]2 (3), respectively.
Magnesiation of 1 with diethylmagnesium in tetrahydrofuran in the presence of 1,4-dioxane leads
to cocrystallization of mononuclear [(thf)2Mg(Pz)2] (4a) and [(diox)2Mg(Pz)2] (4b). Metalation of
1 with KH followed by a metathesis reaction with CaI2 in tetrahydrofuran leads to the formation of
dinuclear [{(thf)2Ca}(µ-Pz)3Ca(Pz)] (5) with the calcium atoms in different coordination environ-
ments. The ligand precursor 1 crystallizes as a dimer with N–H· · ·N bridges between the pyrazole
fragments. The pyrazolate anions of the metal complexes 2 to 5 exhibit similar structural parameters
regardless of a bridging or terminal coordination mode and the electronegativity of the coordinated
metal.
Key words: Calcium, Lithium, Magnesium, Metalation Reactions, Pyrazolates, Zinc
Introduction
strated restricting this concept to singly charged an-
ions with outer 2-pyridyl substituents. For many of
In dinuclear metal complexes with multidentate those anionic ligands diverse metal complexes have
aza ligands the non-bonding metal-metal distance been studied extensively, probably the most impor-
plays a significant role regarding the reactivity in tant group being the bis(2-pyridylmethyl)amidinates of
stoichiometric and catalytic reactions. In order to main group and transition metals [1]. Pyrazolates re-
vary the intramolecular metal-metal contact, slight present another class of ligands with extended appli-
variations within the ligand backbone can induce cations [2 – 8].
a large influence. In Scheme 1 the principle is demon-
A common problem in the chemistry of 3,5-bis(2-
pyridyl)pyrazolato complexes is their low solubility
in common organic solvents. Therefore, we investi-
gated selected coordination compounds with 3-phenyl-
5-(2-pyridyl)pyrazolato ligands (Pz) thus reducing the
denticity of this ligand. In principle, three mesomeric
forms can be formulated as shown in Scheme 2.
The degree of contribution of the third formula in-
fluences the rotation barrier around the C–C bond.
Computational investigations on a free 3-phenyl-5-(2-
pyridyl)pyrazolate anion have shown that the charge
is mainly localized on the pyrazolate moiety and that
the rotation barrier shows a value of approximately
42 kJ mol−1 slightly depending on the solvent. In ad-
dition, the trans conformer is slightly favored by 7
(in tetrahydrofuran) up to 21 kJ mol−1 (for the free
N
N
N
_
_
N
N
N
N
_
N
R
N
N
N
Scheme 1. Examples of singly charged aza ligands with
outer 2-pyridyl groups; bis(2-pyridylmethyl)amides (left),
N,N0-bis(2-pyridylmethyl)amidinates (middle), 3,5-bis(2-
pyridyl)pyrazolates (right).
c
ꢀ 2012 Verlag der Zeitschrift fu¨r Naturforschung, Tu¨bingen · http://znaturforsch.com

520
T. Kloubert et al. · 3-Phenyl-5-(2-pyridyl)pyrazolato Complexes of Lithium, Magnesium, Calcium, and Zinc
oxidation states with the main focus on late transi-
tion metals such as cobalt [11, 12], nickel [12, 13],
and copper [12, 14] as well as molybdenum [10],
ruthenium [15, 16], palladium [17 – 19], and plat-
inum [19, 20]. Recently, the coordination behavior
of the extended ligand 2,6-bis(5-phenyl-1H-pyrazol-
3-yl)pyridine towards d10 metal cations was also in-
vestigated [21]. The regioselective N-alkylation of the
pyrazole ring succeeded via metalation with NaH or
NaOEt with a subsequent metathesis reaction with
alkyl halides [9]. Results of computational studies sup-
port the formation of a sodium complex with a biden-
tate pyrazolato ligand enforcing regioselective alkyla-
_
N
N
N
N
N
N
_
_
N
N
N
Scheme 2. Mesomeric forms of the cis conformer of the
3-phenyl-5-(2-pyridyl)pyrazolate anion (Pz); the negative
charge can formally be located on any nitrogen atom.
molecule) compared to the cis isomer which is shown tion. Here, we add detailed studies of the coordina-
in Scheme 2 [9]. tion behavior of 3-phenyl-5-(2-pyridyl)pyrazolate an-
AM1 calculations on 3-phenyl-5-(2-pyridyl)py- ions towards the s-block metal ions of lithium, magne-
razole (HPz, 1), however, showed a preference of the sium, and calcium as well as methylzinc cations.
cis conformer by 13.6 kJ mol−1 due to the hydrogen
bridge between the pyridyl and the pyrazole frag- Results and Discussion
ments [10]. The formation of an N–H bond at the
pyridyl group is higher in energy by 57.4 kJ mol−1
Synthesis. 3-Phenyl-5-(2-pyridyl)pyrazole (HPz, 1)
supporting that the break-up of the aromaticity of the was prepared according to a well-known protocol
pyridyl moiety is strongly disfavored. For the 1,2- from 2-pyridinoyl-benzoylmethane and hydrazine hy-
migration of the proton from N1 to N2 at the pyrazole drate [22]. For comparison with related compounds, its
ring an energy of 13.4 kJ mol−1 has to be invested.
crystal structure was determined. The results verified
The interest in these 3-phenyl-5-(2-pyridyl)pyrazole the predicted molecular structure with an intramolec-
and -pyrazolato ligands is founded on their rich coor- ular N–H· · ·N hydrogen bond stabilizing the cis con-
dination chemistry with metals of different sizes and former. Molecular structure and numbering scheme of
Fig. 1. Molecular structure and number-
ing scheme of 3-phenyl-5-(2-pyridyl)py-
razole (HPz, 1). The ellipsoids represent
a probability of 40%, H atoms are drawn
with arbitrary radii. Selected bond lengths
(pm): N2–N3 135.1(2), N2–C6 135.3(2),
C6–C7 138.2(2), C7–C8 140.8(2), N3–
C8 134.4(2), C5–C6 146.6(2), C8–C9
147.4(2).

T. Kloubert et al. · 3-Phenyl-5-(2-pyridyl)pyrazolato Complexes of Lithium, Magnesium, Calcium, and Zinc
521
+2 KH
+ CaI2
THF
+2 PhLi
THF
N
N
N
N
N
N
1
2
2
- 2 H2
- 2 KI
- 2 C6H6
H
Ca2(thf)2
Li(thf)
N
N
N
4
2
5
1
2
+ MgEt2
- 2 C2H6
+ 2 ZnR2
- 2 RH
N
N
N
N
Mg(L)2
2
Zn-R
N
N
2
L = thf (4a), diox (4b)
R = Me (3a), N(SiMe3)2 (3b)
Scheme 3. Metalation of 3-phenyl-5-(2-pyridyl)pyrazole (1) with phenyllithium, dimethylzinc, bis[bis(trimethylsilyl)ami-
do]zinc, and diethylmagnesium yielding the corresponding complexes 2 to 4; metalation of 1 with potassium hydride and
subsequent metathesis reaction with calcium(II) iodide lead to the formation of dinuclear 5.
1 are displayed in Fig. 1. The numbering scheme of Phenyllithium, dimethylzinc (Scheme 3, coordinated
the ligand is identical throughout all structure presen- solvent is omitted), and diethylmagnesium were ap-
tations. All hydrogen atoms were refined isotropically plied to metalate 3-phenyl-5-(2-pyridyl)pyrazole (1)
and the pyrazole hydrogen atom shown to be bound at because the alkane by-products are easily removed.
N2 (N2–H 93(2) pm). Despite the localization of the Diethylmagnesium reacted with two equivalents of
N-bound hydrogen atom there exists a far-reaching de- the pyrazole in thf in the presence of 1,4-dioxane
localization of charge within the pyrazole ring. The (diox) according to Scheme 3 yielding mononu-
N2–C6 and N3–C8 bond lengths are very similar and clear [(thf)2Mg(Pz)2] (4a) and [(diox)2Mg(Pz)2]
the same is true for the C6–C7 and C7–C8 bonds. (4b) which co-crystallized in equimolar amounts.
This fact is understandable because the dimerization In contrast to diethylmagnesium, dimethylzinc and
via N2–H· · ·N3A hydrogen bridges decreases the dif- bis[bis(trimethylsilyl)amido]zinc reacted only with
ference between the chemical environments of N2 and equimolar amounts of 3-phenyl-5-(2-pyridyl)pyrazole
N3. Despite the planarity of the molecule, the C–C regardless of the applied stoichiometry. Lithium
bond lengths to the pyridyl (C5–C6 146.6(2) pm) and and zinc derivatives crystallized as the dinuclear
to the phenyl groups (C8–C9 147.4(2) pm) show no complexes [(thf)Li(Pz)]2 (2), [MeZn(Pz)]2 (3a) and
double bond character and represent values for single [(Me3Si)2NZn(Pz)]2 (3b).
bonds between formally sp2-hybridized carbon atoms.
Due to the fact that simple dialkylcalcium deriva-
In general, pyrazoles are quite acidic and, hence, tives are unknown or challenging to prepare we re-
easily deprotonated because pyrazolate anions are acted the pyrazole with potassium hydride and subse-
stabilized by five-membered aromatic ring systems. quently with calcium(II) iodide to give the dinuclear

522
T. Kloubert et al. · 3-Phenyl-5-(2-pyridyl)pyrazolato Complexes of Lithium, Magnesium, Calcium, and Zinc
[{(thf)2Ca}(µ-Pz)3Ca(Pz)] (5). The environments of lithium cation and also bridging two such cations. This
the calcium atoms are different, and a rather com- bridging leads to the formation of a six-membered
plex structure was suggested by the broadened NMR Li2N4 ring with a trans-annular cis arrangement of the
resonances which showed no temperature-dependent thf ligands. Whereas the Li–O bond lengths resem-
sharpening or splitting into several signals.
ble characteristic values (av. 195.3 pm), the Li–N bond
In summary, we synthesized two complexes with lengths vary within a large range. Due to electrostatic
a metal/pyrazolate ratio of 1 : 1 and two alkaline attraction the Li–N bond lengths to the pyrazolate an-
earth metal derivatives with a metal/pyrazolate ratio ion are much shorter (av. 200.2 pm) than the bonds
of 1 : 2. In order to obtain single crystals of good qual- to the pyridyl groups (av. 214.1 pm). A smaller value
ity, 1,4-dioxane was added to the tetrahydrofuran so- of 193.2(7) pm was observed for bis(thf)lithium 2,5-
lutions of the compounds. The magnesium complexes di(tert-butyl)pyrrolide with a three-coordinate lithium
4a,b precipitated as monomeric molecules with hexa- atom [23]. Lithium amides represent an extensively
coordinate metal centers; thf or 1,4-dioxane molecules investigated class of compounds due to their enor-
saturate the coordination sphere of this alkaline earth mous importance as nucleophiles in deprotonation
metal atom and are in trans position to each other. The and transamination reactions. Hence, several excel-
calcium derivative 5 crystallized as a dimer with two lent review articles deal with their structural proper-
ligands, however, the molecular structure proved to be ties [24 – 29]. The Li–N bonds to the pyridyl bases
rather complex containing alkaline earth metal atoms in 2 lie within the expected range as observed also
with different coordination numbers and chemical en- for picolylamido- and 8-quinolylamido-lithium com-
vironments.
plexes with five-membered LiN2C2 rings (see e. g.
In order to discuss the coordination chemistry to- refs. [30 – 35]).
ward s-block metal atoms and the methylzinc cation
Zinc pyrazolate complexes play an important
X-ray structure determinations were performed.
role in bioinorganic chemistry as models for zinc
enzymes [36 – 38]. In these complexes, the pyrazolato
ligand acts as a bridging ligand between two zinc
cations. The basic structure of the zinc derivative
Molecular structures
The molecular structure and numbering scheme [MeZn(Pz)]2 (3a) is very similar to that of complex
of (tetrahydrofuran)lithium 3-phenyl-5-(2-pyridyl)py- 2. The methyl groups also show a trans-annular
razolate ([(thf)Li(Pz)]2, 2) are displayed in Fig. 2. cis arrangement leading to molecular C2 symmetry
Molecular C2 symmetry is destroyed by the orienta- with bridging pyrazolate anions. The zinc atoms are
tion of the thf ligands. The ligands are chelating one embedded in a distorted tetrahedral environment with
Fig. 2. Molecular structure and numbering
scheme of dinuclear [(thf)Li(Pz)]2 (2). The
ellipsoids represent a probability of 40%, H
atoms are omitted for clarity. The asymmet-
ric unit contains two dimers but only one
of these molecules is shown. Selected bond
lengths (pm): Li1A–O1A 193.5(8), Li1A–
N3A 199.9(9), Li1A–N1B 213.4(10), Li1A–
N2B 202.1(10), Li1B–O1B 197.1(8), Li1B–
N3B 198.0(9), Li1B–N1A 214.7(9), Li1B–
N2A 200.8(8).

T. Kloubert et al. · 3-Phenyl-5-(2-pyridyl)pyrazolato Complexes of Lithium, Magnesium, Calcium, and Zinc
523
Fig. 3. Molecular structure and number-
ing scheme of [MeZn(Pz)]2 (3a). The el-
lipsoids represent a probability of 40%,
H atoms are neglected. Selected bond
lengths (pm): Zn1–C29 197.0(2), Zn1–
N1 211.9(2), Zn1–N2 205.2(2), Zn1–
N6 205.5(2), Zn2–C30 197.4(2), Zn2–
N3 208.2(2), Zn2–N4 215.7(2), Zn2–N5
204.8(2).
Fig. 4.
Molecular
structure
and numbering scheme of
[(Me3Si)2NZn(Pz)]2 (3b). The
ellipsoids represent a probability
of 40%, H atoms are omitted
for clarity. The asymmetric unit
contains two molecules A and
B; only molecule A is shown.
Selected bond lengths (pm) of
molecule A (molecule B in square
brackets): Zn1A–N7A 190.4(2)
[191.5(2)], Zn1A–N1A 214.1(2)
[212.8(2)], Zn1A–N2A 205.7(2)
[207.6(2)], Zn1A–N6A 204.3(2)
[203.6(2)], Zn2A–N8A 191.8(2)
[190.5(2)], Zn2A–N3A 203.1(2)
[203.9(2)], Zn2A–N4A 214.9(2)
[212.1(2)], Zn2A–N5A 206.5(2)
[206.3(2)].
the 3-phenyl-5-(2-pyridyl)pyrazolate anions acting as as observed for 3,5-di(2-pyridyl)pyrazolato-zinc
bidentate and bridging ligands. Molecular structure bis(trimethylsilyl)amide [40]. Again, the metal-
and numbering scheme of 3a are shown in Fig. 3. nitrogen distances to the pyrazolate anions are
The Zn–C bond lengths adopt values characteristic smaller than those to the pyridyl substitutents. Sim-
of tetra-coordinate zinc atoms [39]. Enhancement ilar observations were already discussed in detail
of steric strain by replacement of the zinc-bound for picolylamido- as well as 8-quinolylamido-zinc
methyl group by a bis(trimethylsilyl)amide anion derivatives (see for example refs. [41 – 47]).
(leading to structure 3b) only leads to minor changes
The molecular structures and numbering schemes
(Fig. 4). The structure is very similar, with trans- of [(thf)2Mg(Pz)2] (4a) and [(diox)2Mg(Pz)2] (4b)
annular cis-arranged bis(trimethylsilyl)amido ligands are represented in Fig. 5. In these mononuclear com-

524
T. Kloubert et al. · 3-Phenyl-5-(2-pyridyl)pyrazolato Complexes of Lithium, Magnesium, Calcium, and Zinc
Fig. 5. Molecular structure and numbering scheme of
mononuclear [(thf)2Mg(Pz)2] (4a, top, molecule A) and
[(diox)2Mg(Pz)2] (4b, at the bottom, molecule B). The asym-
metric units contain two half molecules that are completed
by the symmetry operations (−x, −y, −z) and (−x + 1, −y,
−z + 1) for molecules A and B, respectively. Selected bond
lengths (pm): Mg1A–N1A 219.5(2), Mg1A–N2A 208.2(2),
Mg1A–O1A 216.0(2), Mg1B–N1B 215.9(2), Mg1B–N2B
210.1(2), Mg1B–O1B 216.3(2).
to the pyrazolate moieties. A similar behavior was
also found for picolylamido- and 8-quinolylamido-
magnesium derivatives [45 – 47].
The larger size of calcium and the enhanced
ionic character lead to a unique dimerization in
[{(thf)2Ca}(µ-Pz)3Ca(Pz)] (5). The molecular struc-
ture and numbering scheme are shown in Fig. 6. The
coordination spheres of the calcium atoms differ sig-
nificantly. The six-coordinate atom Ca1 is in a distorted
octahedral environment of two thf molecules in a cis
arrangement and four nitrogen atoms of three pyra-
zolate anions and of one pyridyl group. The seven-
coordinate atom Ca2 is surrounded by three biden-
tate pyridylpyrazolato units and an additional pyrazo-
lato nitrogen atom. Thus, three pyrazolate anions act
as bridging ligands whereas one anion binds as a ter-
minal bidentate ligand to Ca2. The irregular coordi-
nation pattern leads to large variation of the Ca1–O
(238.5(3) and 245.3(3) pm) and Ca–N bond lengths
(238.7(3) to 264.6(3) pm). These restraints and the
three bridging pyrazolato units allow for a rather short
non-bonding Ca1· · ·Ca2 contact of 367.1(1) pm. In
tris(pyrazolyl)methanide complexes of calcium com-
parable Ca–N bond lengths were observed between
neutral pyrazolyl units and five- as well as six-
coordinate calcium centers [48]. Strong electrostatic
attraction between calcium cations and amide anions
leads to shorter Ca–N bond lengths [8, 49 – 55] sup-
porting the importance of electrostatic interactions in
mainly ionic amidocalcium complexes.
plexes the magnesium atoms are bound to two biden-
The 3-phenyl-5-(2-pyridyl)pyrazolate anions al-
tate 3-phenyl-5-(2-pyridyl)pyrazolate anions and to ways act as bidentate ligands forming five-membered
two ether ligands. The asymmetric unit contains two rings with the metal ions. Side-on coordination has al-
molecules which differ by their ether ligands: One ready been observed when oligomerization of the com-
complex contains two thf ligands, the other two 1,4- plexes occurred, but this coordination behavior was re-
dioxane molecules in trans positions. The complexes stricted to the heaviest alkaline earth metals [8]. Aggre-
have the metal atoms at the inversion centers. The Mg– gation with the lighter s-block metal atoms lithium and
N bonds to the pyridyl groups are longer than those calcium as well as zinc was always encountered with

T. Kloubert et al. · 3-Phenyl-5-(2-pyridyl)pyrazolato Complexes of Lithium, Magnesium, Calcium, and Zinc
525
Fig. 6. Molecular structure of dinu-
clear [{(thf)2Ca}(µ-Pz)3Ca(Pz)] (5).
The ellipsoids represent a probability
of 40%, H atoms are neglected for
clarity. The pyrazolate anions are
distinguished by the letters A, B, C,
and D. Selected bond lengths (pm):
Ca1–O1 245.3(3), Ca1–O2 238.5(3),
Ca1–N1A
248.9(3),
Ca1–N2A
245.1(3), Ca1–N3C 240.0(4), Ca1–
N3D 238.7(3), Ca2–N3A 242.8(3),
Ca2–N1B
263.2(3),
Ca2–N2B
247.5(4), Ca2–N1C 250.0(3), Ca2–
N2C 257.3(4), Ca2–N1D 264.6(3),
Ca2–N2D 256.5(3).
Table 1. Selected structural data of 3-phenyl-5-(2-pyridyl)pyrazole (HPz, 1) and the 3-phenyl-5-(2-pyridyl)pyrazolate anions
of the lithium (2), zinc (3a and 3b), magnesium (4), and calcium derivatives (5) (bond lengths in pm).
Compound
Ligand
N2–N3
N2–C6
N3–C8
C6–C7
C7–C8
C6–C5
C8–C9
HPz (1)
[(thf)Li(Pz)]2 (2)
135.1(2)
136.3(5)
136.5(7)
136.1(6)
135.5(5)
135.3(2)
135.3(2)
134.7(3)
135.4(3)
135.6(3)
136.0(3)
135.7(2)
135.6(3)
136.5(5)
135.8(5)
137.3(5)
136.3(5)
135.3(2)
135.4(5)
134.5(6)
135.1(6)
136.3(5)
134.3(2)
134.4(2)
135.3(3)
134.6(4)
134.9(4)
134.5(3)
136.1(3)
135.9(3)
136.3(5)
136.8(5)
135.8(5)
135.4(5)
134.4(2)
136.5(5)
135.5(6)
135.6(6)
135.4(5)
136.2(2)
135.3(2)
136.0(3)
135.5(4)
135.2(4)
136.0(3)
135.6(3)
135.1(3)
136.1(5)
134.8(5)
135.8(5)
136.0(5)
138.2(2)
139.3(6)
138.5(9)
139.4(7)
139.5(6)
139.4(2)
139.4(2)
139.9(4)
139.6(4)
139.2(4)
139.6(4)
139.7(3)
139.2(3)
138.9(6)
139.1(6)
139.1(6)
139.4(6)
140.8(2)
140.1(6)
140.8(9)
138.4(7)
139.9(6)
139.5(3)
140.0(3)
139.6(4)
139.6(4)
139.4(4)
139.7(4)
139.9(3)
140.2(3)
139.6(6)
138.7(6)
139.2(6)
138.9(6)
146.6(2)
147.1(6)
146.4(10) 144.8(9)
147.4(2)
145.2(7)
A
B
C
D
A
B
A
B
C
D
A
B
A
B
C
D
146.8(7)
146.7(6)
146.4(3)
146.6(2)
145.5(4)
146.3(4)
146.1(4)
145.8(4)
146.0(3)
146.1(3)
146.9(6)
145.4(6)
146.4(6)
146.1(6)
148.4(7)
147.5(6)
146.9(3)
147.1(2)
146.4(4)
148.3(4)
146.8(4)
147.0(4)
147.6(3)
147.7(3)
146.2(6)
147.2(6)
147.3(6)
146.5(6)
[MeZn(Pz)]2 (3a)
[(Me3Si)2NZn(Pz)]2 (3b)
[(thf)2Mg(Pz)2] (4a)
[(diox)2Mg(Pz)2] (4b)
[{(thf)2Ca}(µ-Pz)3Ca(Pz)] (5)
bridging pyrazolate fragment. Selected bond lengths of extended charge delocalization. Obviously, the phenyl
the pyrazolate anions are listed in Table 1. It is surpris- and pyridyl units express a similar electronic influence
ing that these parameters neither depend on the charge on the pyrazolate ring making the endocyclic N2–C6
and electronegativity of the metals nor on the termi- and N3–C8 bond lengths equal within the standard de-
nal or bridging coordination mode. The charge ap- viations. These observations suggest that the bonding
pears to be completely delocalized within the pyrazo- situation between the metal cations and the pyrazolate
late moiety. The bonds between the pyrazolate unit and anions is mainly based on electrostatic contributions.
the pyridyl (C5–C6) and phenyl substituents (C8–C9)
are rather short for C–C bonds between sp2-hybridized NMR studies
carbon atoms suggesting a slight charge delocalization
into the π systems of these groups. The planarity of the
For determining electronic effects, NMR spec-
3-phenyl-5-(2-pyridyl)pyrazolate anions supports the troscopy represents an excellent tool. However, due to

526
T. Kloubert et al. · 3-Phenyl-5-(2-pyridyl)pyrazolato Complexes of Lithium, Magnesium, Calcium, and Zinc
Table 2. Selected chemical shifts
δ (ppm) of 3-phenyl-5-(2-pyri-
dyl)pyrazole (HPz, 1) and the
3-phenyl-5-(2-pyridyl)pyrazolate
anions of the lithium (2), zinc
(3a and 3b), magnesium (4), and
calcium derivatives (5).
NMR
1
2
3a
3b
4
5
δ(H4)
δ(C31)
δ(C3)
δ(C4)
δ(C5)
δ(C51)
7.17
135.1
143.8
100.5
149.7
153.0
6.94
138.0
152.9
98.9
151.9
156.3
6.84
135.2
154.7
100.8
148.2
151.2
6.87
135.5
154.9
101.2
149.1
151.2
7.05
138.0
154.4
98.8
149.7
153.7
7.07
138.2
151.9
100.2
151.9
155.6
the poor solubility of compounds 2 – 5 strong Lewis repulsion. Therefore the large calcium atom gives rise
bases had to be added in order to obtain acceptable to large coordination numbers whereas lithium is gen-
signal-to-noise ratios. Therefore, the molecular struc- erally four-coordinate.
tures in the crystalline phase and in solution can be
different, allowing for deaggregation, dissociation and Experimental
exchange processes fast on the NMR time scale. This
dynamic behavior leads to chemically equivalent an-
General: All manipulations were carried out in an argon
or nitrogen atmosphere under anaerobic conditions. Prior to
ions and makes it impossible to distinguish between
use, all solvents were thoroughly dried and distilled in an in-
ert gas atmosphere. 1H NMR and 13C NMR spectra were
recorded at ambient temperature on Bruker AC 200 MHz,
AC 400 MHz or AC 600 MHz spectrometers. All spectra
were referenced to the deuterated solvent as an internal stan-
dard. EI-mass spectra were obtained on a Finnigan MAT
SSQ 710 system. Masses marked with an asterisk contain
the appropriate metal atom according to the isotopic pat-
tern. IR measurements were carried out on a Perkin Elmer
System 2000 FT-IR. The values of the elemental analyses
deviate from theoretical values because weighing of these
moisture sensitive compounds was challenging due to the
easy loss of co-crystallized thf and also due the carbon-
ate formation during combustion even though V2O5 was
added. Decomposition and melting points were measured
with a Reichert-Jung apparatus Type 302102. 3-Phenyl-5-(2-
pyridyl)pyrazole (HPz, 1) was prepared according to a liter-
ature procedure [22].
a terminal and a bridging coordination mode of the
pyrazolato ligands. The ionicity of the bonding situ-
ation becomes obvious from the chemical 1H and 13
NMR shifts.
C
Selected NMR parameters are summarized in Ta-
ble 2. The numbering scheme is shown in Scheme 4
and differs from the numbering used for the crystal
structures. Expectedly, the 13C{1H} NMR resonance
of C3 of 1 differs significantly from that of the deproto-
nated pyrazols. The chemical shifts of C4 and C5 show
only very small differences. However, despite the fact
that the influence of the metal on the chemical shifts is
rather small, characteristic trends can be observed. In-
creasingly ionic bonding (i. e. decreasing electronega-
tivity of the metal) leads to a low field shift of C5 and
the ipso-carbon atom C51 of the pyridyl group. The
NMR values of the lithium and the calcium deriva-
tives are very similar due to comparable electronega-
tivities even though the solid-state structures show no
similarities. This observation can easily be explained
assuming that planar anions and metal cations maxi-
mize electrostatic attraction and minimize inter-ligand
Synthesis of HPz (1)
1-Phenyl-3-(2-pyridyl)propane-1,3-dione (22.5 g, 99.4
mmol) was dissolved in 150 mL of ethanol and heated under
reflux. Hydrazine hydrate (10 g, 0.2 mol) was added drop-
wise. After 2 h the addition of hydrazine hydrate was re-
peated with the same amount, and reflux conditions were
maintained for additional two h. Removal of all volatiles
and recrystallization of the residue from toluene gave color-
less needles of 1. Yield: 17.3 g of crystalline 1 (78.2 mmol,
79%). M. p. 168 ◦C. – 1H NMR (400 MHz, 303 K, ([D8]thf):
δ = 12.7 (br. s, 1H, H1), 8.57 (d, 3J (H53,H54) = 4.8 Hz, 1H,
C55
C54
C53
C33
C32
C31
C56
C51
C34
C4
C3
C5
3
H53), 7.86–7.84 (m, 3H, H32,56), 7.75 (t, J (H55,H54,56) =
N52
7.6 Hz, 1H, H55), 7.37 (t, 3J (H33,H32,34) = 7.6 Hz, 2H,
H33), 7.25 (t, 3J (H34,H33) = 7.5 Hz, 1H, H34), 7.21–7.17
(m, 1H, H54), 7.17 (s, 1H, H4). – 13C NMR (600 MHz,
300 K, ([D8]thf): δ = 153.0 (C51), 150.1 (C53), 149.7 (C5),
143.8 (C3), 137.4 (C55), 135.1 (C31), 129.0 (C33), 127.9
N2 N1
1
Scheme 4. Numbering scheme for the assignment of the H
and 13C NMR spectra. The numbers of hydrogen atoms are
identical to those of the attached carbon atoms.

T. Kloubert et al. · 3-Phenyl-5-(2-pyridyl)pyrazolato Complexes of Lithium, Magnesium, Calcium, and Zinc
527
(C34), 126.0 (C32), 123.0 (C54), 120.3 (C56), 100.5 (C4). (C34), 122.5 (C54), 119.2 (C56), 100.8 (C4), –11.5 (CH3).
– MS (EI): m/z (%) = 221 (100) [M]+, 192 (85) [M– – MS (EI): m/z (%) = 587∗ (38) [2M–CH3]+, 299∗ (48)
N2]+, 165 (24), 115 (20), 78 (22) [C5H4N]+. – IR (cm−1): [M]+, 284∗ (44) [M–CH3]+, 192 (58) [M–ZnCH3,N2]+,
ν = 3237 br.s, 3061 w, 3006 vw, 1597 m, 1585 m, 1469 s, 94 (63), 79 (100) [C5H5N]+. – IR (cm−1): ν = 2937 w,
1449 vs, 1386 m, 1314 m, 1297 s, 1270 m, 1174 vs, 1148 m, 2895 w, 2826 w, 1699 vw, 1607 vs, 1567 w, 1538 w, 1470 vs,
1076 vs, 995 vs, 971 vs, 957 vs, 912 m, 802 m, 780 s, 756 vs, 1447 vw, 1432 m, 1393 m, 1341 vw, 1286 m, 1258 w,
733 s, 719 s, 690 s, 682 s, 658 s, 620 s, 516 m, 508 s, 485 s, 1235 m, 1204 m, 1152 m, 1125 m, 1083 m, 1064 m, 1016 s,
419 w. – Elemental analysis for C14H11N3, (221.26): calcd. 996 w, 968 w, 906 w, 884 m, 833 w, 798 s, 779 vs, 758 s,
C 76.00, H 5.01, N 18.99; found C 76.01, H 4.93, N 19.19.
727 m, 693 m, 638 vs, 522 vs, 492 m, 481 m, 463 m, 414 vs. –
Elemental analysis for C15H13N3Zn (300.66): calcd. C59.92,
H 4.36, N 13.98; found C 60.66, H 5.49, N 12.69.
Synthesis of [(thf)Li(Pz)]2 (2)
2-(3-Phenyl-1H-pyrazol-5-yl)pyridine (778 mg, 3.52
mmol) was dissolved in 15 mL of thf. Phenyllithium
(5.51 mL, c = 0.638 M, 3.52 mmol) was added drop-
Synthesis of [(Me3Si)2NZn(Pz)]2 (3b)
2-(3-Phenyl-1H-pyrazol-5-yl)pyridine (1) (577 mg, 2.61
wise, and a colorless precipitate of 2 formed quanti- mmol) was dissolved in 20 mL of thf and cooled to
tatively. In order to obtain single-crystalline material 0 ◦C. Bis[bis(trimethylsilyl)amino]zinc (1 g, 2.60 mmol) was
a small amount of the precipitate was dissolved in added dropwise and the reaction mixture stirred over night.
hot thf. Cooling led to the formation of colorless nee- The solvent was removed and the crude product recrys-
dles. M. p. 358 ◦C.
–
1H NMR (600 MHz, 300 K, tallized from toluene. Yield: 990 mg (2.22 mmol, 85%).
[D8]thf): δ = 8.59 (d, 3J (H53,H54) = 4.9 Hz, 1H, M. p. 295 ◦C. – 1H NMR (600 MHz, 300 K, [D8]thf):
H53), 7.95 (d, 3J (H32,H33) = 7.6 Hz, 2H, H32), 7.74 δ = 8.35 (d, 3J (H53,H53) = 5.3 Hz, 1H, H53), 7.98
(t, 3J (H55,H33) = 7.6 Hz, 4J (H55,H53) = 1.2 Hz, 1H, (t, 3J (H55,H56,54) = 7.9 Hz, 4J (H55,H53,) = 1.6 Hz, 1H,
H55), 7.66 (d, 3J (H56,H55) = 7.7 Hz, 1H, H56), 7.35 (t, H55), 7.81 (d, 3J (H56,H55) = 7.9 Hz, 1H, H56), 7.64 (d,
3J (H33,H32,34) = 7.7 Hz, 2H, H33), 7.14–7.12 (m, 2H, 3J (H32,H33) = 7.8 Hz, 2H, H32), 7.42–7.37 (m, 3H, H54,33),
H34,54), 6.94 (s, 1H, H4). – 13C NMR (600 MHz, 300 K, 7.35–7.34 (m, 1H, H34), 6.87 (s, 1H, H4), –0.04 (s, 18H,
[D8]thf): δ = 156.3 (C51), 152.9 (C3), 151.9 (C5), 149.2 SiMe3). – 13C NMR (600 MHz, 300 K, [D8]thf): δ = 154.9
(C53), 138.1 (C55), 138.0 (C31), 128.8 (C33), 125.7 (C34), (C3), 151.2 (C51), 149.1 (C5), 148.9 (C53), 141.2 (C55),
125.4 (C32), 120.9 (C54), 119.7 (C56), 98.9 (C4). – MS (EI): 135.5 (C31), 129.3 (C33), 128.5 (C34), 127.5 (C32), 124.0
m/z (%) = 234 (52), 227∗ (100) [M–thf]+. – IR (cm−1): (C54), 121.2 (C56), 101.2 (C4), 6.3 (SiMe3). – MS (EI):
ν = 3066 w, 3051 w, 3004 w, 2974 w, 2876 w, 1600 vs, m/z (%) = 505∗ (13) [M–N(SiMe3)2, 2 SiMe3, C5H5N]+,
1593 m, 1527 s, 1455 s, 1441 vs, 1390 vw, 1332 w, 1230 m, 221 (18) [ligand]+, 146 (10) [(N(SiMe3)2)2]+, 130 (22)
1178 m, 1152 m, 1106 m, 1075 s, 1051 s, 1006 m, 983 vs, [(N(SiMe3)2)2–MeH ]+. – IR (cm −1): ν = 3060 m, 2953 m,
964 m, 909 m, 842 vw, 807 w, 783 s, 755 vs, 723 s, 687 vs, 2892 w, 1603 vs, 1570 m, 1539 w, 1517 w, 1472 m, 1447 vs,
679 vs, 633 s, 525 m, 484 vs, 439 m, 422 vs, 408 vs.
1406 m, 1340 m, 1248 vs, 1181 m, 1151 m, 1124 m, 1083 w,
1050 w, 1012 s, 995 vs, 970 m, 927 vs, 884 m, 825 vs, 780 s,
755 vs, 727 vs, 694 vs, 634 m, 552 m, 494 m, 447 m, 432 w,
407 m. – Elemental analysis for C20H28N4Si2Zn (446.04 ):
calcd. C 53.86, H 6.33, N 12.56; (+1/3 toluene: C 55.10, H
6.41, N 12.14); found C 55.30, H 6.66, N 11.63.
Synthesis of [MeZn(Pz)]2 (3a)
2-(3-Phenyl-1H-pyrazol-5-yl)pyridine (1) (500 mg, 2.26
mmol) was dissolved in 30 mL of thf and cooled to –78 ◦C.
Dimethylzinc (1.9 mL, c = 1.2 M, 2.28 mmol) was added
dropwise. Then the reaction mixture was stirred over night
and warmed to r. t. A colorless precipitate formed and
was redissolved easily under heating. The product crystal-
Synthesis of [(thf)2Mg(Pz)2] (4a) and [(diox)2Mg(Pz)2] (4b)
2-(3-Phenyl-1H-pyrazol-5-yl)pyridine (304 mg, 1.37
lized as colorless cubes. Yield: 675 mg of 3 (2.24 mmol, mmol) was dissolved in 15 mL of thf. Diethylmagnesium-
99%). M. p. > 260 ◦C (dec.). – 1H NMR (600 MHz, 1,4-dioxane (117 mg, 0.68 mmol), dissoved in 5 mL of thf,
300 K, [D8]thf): δ = 7.81 (d, 3J (H32,H33) = 7.4 Hz, 2H, was added dropwise. Removal of 70% of the solvent, addi-
H32), 7.73 (d, 3J (H53,H54) = 4.3 Hz, 1H, H53), 7.55 (t, tion of 2 mL of 1,4-dioxane and storage at 4 ◦C produced
3J (H55,H56,54) = 7.4 Hz, 1H, H55), 7.47 (d, 3J (H56,H55) = colorless needles. Yield: 170 mg of a 1 : 1 mixture of 4a and
7.7 Hz, 1H, H56), 7.16–7.13 (m, 1H, H34), 7.10–7.08 (m, 4b (0.53 mmol, 37%). M. p. 228 ◦C. – 1H NMR (400 MHz,
2H, H33), 6.94–6.92 (m, 1H, H54), 6.84 (s, 1H, H4), –0.61 300 K, [D8]thf): δ = 8.23 (d, 3J (H53,H54) = 4.8 Hz,
(s, 1.5H, CH3). – 13C NMR (600 MHz, 300 K, [D8]thf): 1H, H53), 8.01 (d, 3J (H32,H300,33) = 7.5 Hz, 2H, H32),
δ = 154.7 (C3), 151.2 (C51), 148.6 (C53), 148.2 (C5), 7.69 (t, 3J (H55,H54,56) = 7.8 Hz, 4J (H55,H53,) = 1.6 Hz,
138.2 (C55), 135.2 (C31), 128.9 (C33), 127.7 (C32), 127.2 1H, H55), 7.62 (d, 3J (H56,H55) = 7.9 Hz, 1H, H56),

528
T. Kloubert et al. · 3-Phenyl-5-(2-pyridyl)pyrazolato Complexes of Lithium, Magnesium, Calcium, and Zinc

T. Kloubert et al. · 3-Phenyl-5-(2-pyridyl)pyrazolato Complexes of Lithium, Magnesium, Calcium, and Zinc
529
7.30 (t, 3J (H33,H32,34) = 7.6 Hz, 2H, H33), 7.11 (t, 221 (85) [ligand]+, 192 (76) [ligand–N2]+. – IR (cm−1):
3J (H34,H33) = 7.4 Hz, 1H, H34), 7.05 (s, 1H, H4), 6.98 (t, ν = 3062 w, 2973 w, 2956 w, 2882 vw, 2853 w, 1597 vs,
3J (H54,H53,55) = 5.9 Hz, 1H, H54). – 13C NMR (400 MHz, 1564 m, 1527 m, 1455 m, 1439 vs, 1381 w, 1330 w, 1277 w,
300 K, [D8]thf): δ = 154.4 (C3), 153.7 (C51), 149.7 (C5), 1253 w,1226 m, 1152 m, 1119 m, 1103 w, 1073 m, 1053 s,
148.8 (C53), 139.2 (C55), 138.0 (C31), 128.6 (C33), 125.8 1032 m, 1006 m, 982 vs, 910 m, 888 m, 873 s, 780 s, 755 vs,
(C34), 125.6 (C32), 121.2 (C54), 119.1 (C56), 98.8 (C4). – 721 vs, 697 vs, 684 vs, 631 s, 531 m, 521 w, 493 vw, 432 m,
MS (EI): m/z (%) = 488∗ (12) [M+Mg–2thf/diox]+, 464∗ 414 vs, 405 vs.
(2) [M–2thf/diox]+, 354 (16), 244∗ (20) [M–2thf/diox,
Structure determinations
ligand]+, 221 (48) [ligand]+, 192 (100) [ligand–N2]+. –
IR (cm−1): ν = 3076 vw, 3052 w, 2976 w, 2893 w, 2864 w,
1601 vs, 1560 s, 1527 s, 1457 s, 1441 vs, 1369 m, 1332 w,
1294 w, 1280 w, 1259 m, 1228 m, 1187 m, 1151 m, 1117 s,
1094 w, 1075 s, 1044 vs, 1017 m, 989 vs, 956 m, 916 m,
888 m, 873 vs, 802 s, 785 s, 765 vs, 753 s, 724 s, 698 s, 683 s,
644 s, 615 m, 527 w, 498 w, 465 s, 435 w, 417 s.
The intensity data for the compounds were collected
on a Nonius KappaCCD diffractometer, using graphite-
monochromatized MoKα radiation (λ = 0.71073 A). Data
˚
were corrected for Lorentz and polarization effects but not
for absorption [56, 57]. The structures were solved by Di-
rect Methods (SHELXS [58]) and refined by full-matrix least-
squares techniques against F2 (SHELXL-97 [58]). All hy-
drogen atoms of compound 1 were located by difference
Fourier techniques and refined isotropically. All other hy-
drogen atoms were included in calculated positions with
fixed thermal parameters. All non-disordered, non-hydrogen
atoms were refined anisotropically [58]. Crystallographic
data as well as structure solution and refinement details are
summarized in Table 3. XP (Siemens Analytical X-ray In-
struments, Inc.) was used for structure representations.
CCDC 871915 (1), 871916 (2), 871917 (3a), 872906 (3b),
871918 (4), and 871919 (5) contain the supplementary crys-
tallographic 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.
Synthesis of [{(thf)2Ca}(µ-Pz)3Ca(Pz)] (5)
2-(3-Phenyl-1H-pyrazol-5-yl)pyridine (500 mg, 2.26
mmol) was dissolved in 15 mL of thf. Potassium hydride
(200 mg, 4.99 mmol) was added and the mixture stirred for
20 min. Excessive KH was removed and calcium diiodide
(332 mg, 1.13 mmol) added. The reaction mixture was
stirred over night and precipitated potassium iodide removed
by filtration. 75% of the solvent was removed and the
solution stored at –20 ◦C. Colorless needles of the thf adduct
5 were obtained. Yield: 300 mg (1.15 mmol, 51%). M.
p. 342 ◦C. – 1H NMR (400 MHz, 300 K, [D8]thf/dmso):
δ = 8.56 (s, 1H, H53), 7.92 (d, 3J (H32,H33) = 6.9 Hz,
2H, H32), 7.86 (s, 1H, H56), 7.66 (s, 1H, H55), 7.29 (s, 2H,
H33), 7.09–7.05 (m, 2H, H4,34), 6.96 (s, 1H, H54). – 13C
NMR (400 MHz, 300 K, [D8]thf/dmso): δ = 155.6 (C51),
151.9 (C3,5), 150.2 (C53), 138.2 (C31), 137.7 (C55), 128.9
Acknowledgement
We thank the Deutsche Forschungsgemeinschaft (DFG,
(C33), 125.7 (C32,34), 120.4 (C54), 119.8 (C56), 100.2 (C4). Bonn/Germany; Project We 1561/12) and the Friedrich-
– MS (EI): m/z (%) = 479∗ (2) [M–thf, H]+, 402∗ (2) Schiller-Universita¨t in Jena/Germany for generous financial
[M–thf, PhH]+, 316 (36), 260∗ (100) [M–thf, ligand]+, support of this research project.
[1] F. T. Edelmann, Adv. Organomet. Chem. 2008, 57,
183 – 352.
[8] A. Torvisco, A. Y. O’Brien, K. Ruhlandt-Senge, Coord.
Chem. Rev. 2011, 255, 1268 – 1292.
[2] a) S. Trofimenko, Chem. Rev. 1972, 72, 497 – 509; b)
S. Trofimenko, Chem. Rev. 1993, 93, 943 – 980.
[9] V. Montoya, J. Pons, V. Branchadell, J. Ros, Tetrahe-
dron 2005, 61, 12377 – 12385.
[3] E. C. Constable, P. J. Steel, Coord. Chem. Rev. 1989, [10] W. R. Thiel, J. Eppinger, Chem. Eur. J. 1997, 3,
93, 205 – 223.
696 – 705. See also: W.-S. Yu, C.-C. Cheng, Y.-
M. Cheng, P.-C. Wu, Y.-H. Song, Y. Chi, P.-T. Chou, J.
Am. Chem. Soc. 2003, 125, 10800 – 10801.
[4] E. Bouwman, W. L. Driessen, J. Reedijk, Coord. Chem.
Rev. 1990, 104, 143 – 172.
[5] F. Mani, Coord. Chem. Rev. 1992, 120, 325 – 359.
[6] R. Mukherjee, Coord. Chem. Rev. 2000, 203, 151 – 218.
[7] a) C. Pettinari, R. Pettinari, Coord. Chem. Rev. 2005,
[11] A. Chadghan, J. Pons, A. Caubet, J. Casabo´, J. Ros,
A. Alvarez-Larena, J. F. Piniella, Polyhedron 2000, 19,
855 – 862.
249, 525 – 543; b) C. Pettinari, R. Pettinari, Coord. [12] J. Pons, A. Chadghan, A. Alvarez-Larena, J. F. Piniella,
Chem. Rev. 2005, 249, 663 – 691. J. Ros, Inorg. Chim. Acta 2001, 324, 342 – 346.

530
T. Kloubert et al. · 3-Phenyl-5-(2-pyridyl)pyrazolato Complexes of Lithium, Magnesium, Calcium, and Zinc
[13] J. Pons, A. Chadghan, J. Casabo´, A. Alvarez-Larena, [34] M. Westerhausen, A. N. Kneifel, P. Mayer, Z. Anorg.
J. F. Piniella, X. Solans, M. Font-Bardia, J. Ros, Poly-
hedron 2001, 20, 1029 – 1035.
Allg. Chem. 2006, 632, 634 – 638.
[35] C. Koch, H. Go¨rls, M. Westerhausen, Acta Crystallogr.
[14] J. Pons, A. Chadghan, J. Casabo´, A. Alvarez-Lare-
na, J. F. Piniella, J. Ros, Polyhedron 2001, 2531 –
2536.
2007, E63, m2633 – m2634.
[36] J. Weston, Chem. Rev. 2005, 105, 2151 – 2174.
[37] F. Meyer, Eur. J. Inorg. Chem. 2006, 3789 – 3800.
[15] J. Benet-Buchholz, P. Comba, A. Llobet, S. Roeser, [38] J. Klingele, S. Dechert, F. Meyer, Coord. Chem. Rev.
P. Vadivelu, S. Wiesner, Dalton Trans. 2010, 39,
3315 – 3320.
2009, 253, 2698 – 2741.
[39] M. Melnik, J. Skorsˇepa, K. Gyo¨ryova´, C. E. Holloway,
[16] Y. Kashiwame, M. Watanabe, K. Araki, S. Kuwata,
T. Ikariya, Bull. Chem. Soc. Jpn. 2011, 84, 251 –
258.
J. Organomet. Chem. 1995, 503, 1 – 9.
[40] T. Kloubert, H. Go¨rls, M. Westerhausen, Z. Anorg. Allg.
Chem. 2010, 636, 2405 – 2408.
[17] V. Montoya, J. Pons, J. Garc´ıa-Anto´n, X. Solans, [41] M. Westerhausen, T. Bollwein, N. Makropoulos, T. M.
M. Font-Bard´ıa, J. Ros, Organometallics 2007, 26,
Rotter, T. Habereder, M. Suter, H. No¨th, Eur. J. Inorg.
3183 – 3190.
Chem. 2001, 851 – 857.
[18] J. Pons, A. Chadghan, J. Casabo´, A. Alvarez-Larena, [42] C. Koch, H. Go¨rls, M. Westerhausen, Acta Crystallogr.
J. F. Piniella, J. Ros, Inorg. Chem. Commun. 2000, 3,
296 – 299.
[19] J. A. Perez, J. Pons, X. Solans, M. Font-Bard´ıa, J. Ros,
2007, E63, m2732.
[43] A. Malassa, C. Koch, B. Stein-Schaller, H. Go¨rls,
M. Friedrich, M. Westerhausen, Inorg. Chim. Acta
2008, 361, 1405 – 1414.
Inorg. Chim. Acta 2005, 358, 617 – 622.
[20] G. Gupta, C. Zheng, P. Wang, K. M. Rao, Z. Anorg. [44] C. Koch, H. Go¨rls, M. Westerhausen, Acta Crystallogr.
Allg. Chem. 2010, 636, 758 – 764. 2008, E64, m664.
[21] B. Zhao, H.-M. Shu, H.-M. Hu, T. Qin, X.-L. Chen, J. [45] L. M. Engelhardt, P. C. Junk, W. C. Patalinghug, R. E.
Coord. Chem. 2009, 62, 1025 – 1034.
Sue, C. L. Raston, B. W. Skelton, A. H. White, J. Chem.
[22] H. Hennig, J. Prakt. Chem. 1966, 34, 64 – 68.
Soc., Chem. Commun. 1991, 930 – 932.
[23] M. Westerhausen, M. Wieneke, H. No¨th, T. Seifert, [46] M. Westerhausen, T. Bollwein, N. Makropoulos, S.
A. Pfitzner, W. Schwarz, O. Schwarz, J. Weidlein, Eur.
J. Inorg. Chem. 1998, 1175 – 1182.
[24] M. F. Lappert, P. P. Power, A. R. Sanger, R. C. Srivas-
Schneiderbauer, M. Suter, H. No¨th, P. Mayer, H. Pi-
otrowski, K. Polborn, A. Pfitzner, Eur. J. Inorg. Chem.
2002, 389 – 404.
tava, Metal and Metaloid Amides: Syntheses, Struc- [47] C. Koch, A. Malassa, C. Agthe, H. Go¨rls, R. Bieder-
tures, and Physical and Chemical Properties, Ellis Hor-
wood, Chichester; 1980, chapter 2, p. 24 – 44.
mann, H. Krautscheid, M. Westerhausen, Z. Anorg.
Allg. Chem. 2007, 633, 375 – 382.
[25] W. N. Setzer, P. v. R. Schleyer, Adv. Organomet. Chem. [48] M. G. Cushion, J. Meyer, A. Heath, A. D. Schwarz,
1985, 24, 353 – 451.
I. Ferna´ndez, F. Breher, P. Mountford, Organometallics
[26] K. Gregory, P. v. R. Schleyer, R. Snaith, Adv. Inorg.
2010, 29, 1174 – 1190.
Chem. 1991, 37, 47 – 142.
[27] R. E. Mulvey, Chem. Soc. Rev. 1991, 20, 167 – 209.
[49] M. Westerhausen, Trends Organomet. Chem. 1997, 2,
89 – 105.
[28] F. Pauer, P. P. Power in Lithium Chemistry: A Theoret- [50] M. Westerhausen, Coord. Chem. Rev. 1998, 176,
ical and Experimental Overview, (Eds.: A. M. Sapsa, 157 – 210.
P. v. R. Schleyer); Wiley, New York; 1995, chapter 9, [51] M. Ga¨rtner, H. Go¨rls, M. Westerhausen, Inorg. Chem.
pp. 295 – 392. 2007, 46, 7678 – 7683.
[29] M. Lappert, A. Protchenko, P. Power, A. Seeber, Metal [52] M. Ga¨rtner, H. Go¨rls, M. Westerhausen, Dalton Trans.
Amide Chemistry, Wiley, Chichester; 2009, chapter 2,
pp. 7 – 38.
2008, 1574 – 1582.
[53] C. Glock, H. Go¨rls, M. Westerhausen, Inorg. Chem.
[30] L. M. Engelhardt, G. E. Jacobsen, P. C. Junk, C. L. Ras-
2009, 48, 394 – 399.
ton, B. W. Skelton, A. H. White, J. Chem. Soc., Dalton [54] C. Glock, H. Go¨rls, M. Westerhausen, Inorg. Chim.
Trans. 1988, 1011 – 1020. Acta 2011, 374, 429 – 434.
[31] C. Jones, P. C. Junk, N. A. Smithies, J. Organomet. [55] C. Glock, H. Go¨rls, M. Westerhausen, Dalton Trans.
Chem. 2000, 607, 105 – 111. 2011, 40, 8108 – 8113.
[32] M. Westerhausen, A. N. Kneifel, N. Makropoulos, In- [56] R. Hooft, COLLECT, Nonius KappaCCD Data Col-
org. Chem. Commun. 2004, 7, 990 – 993.
[33] M. Westerhausen, A. N. Kneifel, P. Mayer, H. No¨th, Z.
Anorg. Allg. Chem. 2004, 630, 2013 – 2021.
lection Software, Nonius BV, Delft (The Netherlands)
1998.

T. Kloubert et al. · 3-Phenyl-5-(2-pyridyl)pyrazolato Complexes of Lithium, Magnesium, Calcium, and Zinc
531
[57] Z. Otwinowski, W. Minor in Methods in Enzymology, [58] G. M. Sheldrick, SHELXS/L-97, Programs for Crys-
Vol. 276, Macromolecular Crystallography, Part A
(Eds.: C. W. Carter Jr, R. M. Sweet), Academic Press,
New York, 1997, pp. 307 – 326.
tal Structure Determination, University of Go¨ttingen,
Go¨ttingen (Germany) 1997. See also: G. M. Sheldrick,
Acta Crystallogr. 1990, A46, 467 – 473; ibid. 2008,
A64, 112 – 122.