New binding modes of 1-acetyl- and 1-benzoyl-5-hydroxypyrazolines - Synthesis and characterization of O,O′-pyrazoline- and N,O-pyrazoline-zinc complexes

Article abstract of DOI:10.1002/ejic.201100248

The 1-acetyl- and 1-benzoyl-5-hydroxypyrazolines 1a [3,5-CF₃, 1-C(=O)CH₃], 1b [3,5-CH₃, 1-C(=O)CH₃] and 1c [3,5-CF₃, 1-C(=O)C₆H₅] have been synthesized in good yields and characterized by X-ray crystallography. The 1-acetyl- and 1-benzoyl-5-hydroxypyrazoline ligands were treated with dimethylzinc in a 1:1 molar ratio to form complexes 8 with a RO-Zn-Me motif. These complexes are accessible by simple Bronsted acid-base reactions generating methane as a side product. Characterization of complexes 8a and 8c by X-ray crystallography revealed a dimeric structure in the solid state. The two subunits generate a Zn₂O₂ square. The acetyl and benzoyl functionality of the ligands coordinate to the metal to span a six-membered ring. Moreover, the coordination mode of the ligand can be easily influenced by the addition of base. Here, N,N,N′,N′-tetramethylethylenediamine (tmeda) was applied to remove the acidic proton in the 4-position of the ligand and to cleave the hemiaminal functional group. The tmeda-H⁺ transfers the proton to the methyl group connected to the zinc and facilitates the removal of methane; the free tmeda coordinates to the zinc in a bidentate fashion. The positive charge at the zinc and the negative charge in the ligand recombine to form complex 9. Surprisingly, the characterization of complex 9c by X-ray crystallography showed the formation of the first zinc-based seven-membered system with covalent bonding (N¹,O⁶-coordination) in the solid state, whereas for other metals O⁶,N²,O⁷-coordination has been reported. The versatility of 5-hydroxypyrazoline ligands has been demonstrated. Various zinc complexes have been synthesized and characterized resulting in new coordination modes of pyrazoline ligands depending on the reaction conditions; zinc dimers havebeen observed with a O,O′-coordination mode, whereas addition of tmeda to the reaction mixture led to the formation of a zinc-containing seven-membered ring system with an O,N-mode. Copyright

Full text of DOI:10.1002/ejic.201100248

FULL PAPER
DOI: 10.1002/ejic.201100248
New Binding Modes of 1-Acetyl- and 1-Benzoyl-5-hydroxypyrazolines –
Synthesis and Characterization of O,OЈ-Pyrazoline- and N,O-Pyrazoline-Zinc
Complexes
Chika I. Someya,[a] Shigeyoshi Inoue,[b] Elisabeth Irran,[b] Sebastian Krackl,[a,b] and
Stephan Enthaler*[a]
Keywords: Zinc / N,O ligands / Coordination modes / Nitrogen heterocycles
The 1-acetyl- and 1-benzoyl-5-hydroxypyrazolines 1a [3,5-
CF3, 1-C(=O)CH3], 1b [3,5-CH3, 1-C(=O)CH3] and 1c [3,5-
CF3, 1-C(=O)C6H5] have been synthesized in good yields and
characterized by X-ray crystallography. The 1-acetyl- and 1-
benzoyl-5-hydroxypyrazoline ligands were treated with di-
methylzinc in a 1:1 molar ratio to form complexes 8 with a
RO–Zn–Me motif. These complexes are accessible by simple
Brønsted acid–base reactions generating methane as a side
product. Characterization of complexes 8a and 8c by X-ray
crystallography revealed a dimeric structure in the solid
state. The two subunits generate a Zn2O2 square. The acetyl
and benzoyl functionality of the ligands coordinate to the
metal to span a six-membered ring. Moreover, the coordina-
tion mode of the ligand can be easily influenced by the ad-
dition of base. Here, N,N,NЈ,NЈ-tetramethylethylenediamine
(tmeda) was applied to remove the acidic proton in the 4-
position of the ligand and to cleave the hemiaminal func-
tional group. The tmeda-H+ transfers the proton to the
methyl group connected to the zinc and facilitates the re-
moval of methane; the free tmeda coordinates to the zinc in
a bidentate fashion. The positive charge at the zinc and the
negative charge in the ligand recombine to form complex 9.
Surprisingly, the characterization of complex 9c by X-ray
crystallography showed the formation of the first zinc-based
seven-membered system with covalent bonding (N1,O6-coor-
dination) in the solid state, whereas for other metals
O6,N2,O7-coordination has been reported.
Introduction
of their coordination chemistry is an important research
goal.[4] With respect to these requirements, an interesting
motif is the 5-hydroxypyrazoline ligand (1), which has dif-
ferent coordination possibilities (Figure 1). Due to taut-
omerism, various forms have been discussed, for example,
the hydrazone and the corresponding enol, as well as ene-
hydrazine form.[5] Attempts to coordinate 1 to metals, such
as nickel, resulted in the formation of 2; complexes contain-
ing one six- and one five-membered ring with the O6,N2,O7-
coordination mode (Figure 1).[5c] Only this motif has been
structurally characterized by X-ray crystallography so far.
Due to the binding diversity of the 5-hydroxypyrazoline li-
gands, we wondered if other structural motifs, such as 3
and 4 (tautomer of 2), are feasible. As a metal that allows
flexible coordination geometries, zinc has been reported by
various research groups, but until now no pyrazoline–zinc
complexes have been studied.[6]
Based on our ongoing studies in zinc chemistry, we
herein report the synthesis and characterization of 5-hy-
droxypyrazoline zinc complexes by reacting cyclic 5-hy-
droxypyrazoline ligands with dimethylzinc.[7] Depending on
the reaction conditions, different coordination modes were
accessible. In the presence of N,N,NЈ,NЈ-tetramethylethyl-
enediamine (tmeda) as deprotonation reagent, a N1,O6-
binding mode was observed generating a seven-membered
The development of sustainable, more efficient, and se-
lective organic transformations remains a demanding task
central for chemical synthesis in academia as well as in in-
dustry. In this regard, catalysis is a key technology since
high atom efficiency, reduced amounts of waste and energy,
and, as a consequence, advantageous economics are feas-
ible.[1] In particular, molecular defined organometallic com-
pounds have proven to be an excellent tool box as illus-
trated by the huge number of applications in organic chem-
istry.[2] The abilities of the catalyst are influenced by the
selection of the central metal and by the design of sur-
rounding ligands.[3] In particular, the choice of ligands co-
ordinated to the transition metal center should be consid-
ered from chemical and economical points of view. Require-
ments for ligand technologies include cost efficiency, great
availability, easy synthesis, high tunability, high flexibility
and stability. Thus the design of new ligands and the study
[a] Technische Universität Berlin, Department of Chemistry,
Cluster of Excellence “Unifying Concepts in Catalysis”,
Straße des 17. Juni 135/C2, 10623 Berlin, Germany
Fax: +49-30314-29732
E-mail: stephan.enthaler@tu-berlin.de
[b] Institute of Chemistry, Metalorganics and Inorganic Materials,
Technische Universität Berlin,
Straße des 17. Juni 135, Sekr. C2, 10623 Berlin, Germany
Eur. J. Inorg. Chem. 2011, 2691–2697
© 2011 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
2691

C. Someya, S. Inoue, E. Irran, S. Krackl, S. Enthaler
FULL PAPER
was observed.[5c,5d] The bond length between the hydrogen
atom of the hydroxy group [HO(2)] and the oxygen atom of
acetyl group [O(1)] indicates that 1a has an intramolecular
hydrogen-bonding interaction with a distance of 2.381 Å
(Figure 2, a); the same was observed in 1c for which the
intramolecular hydrogen-bonding distance was 2.158 Å
(Figure 2, c). In case of 1b, a dimeric structure was ob-
served, in which an intermolecular hydrogen-bonding inter-
action is seen between the hydroxy group and the acetyl
group of the neighboring molecule with a distance of
2.861 Å (Figure 2, b).
Figure 1. Coordination modes of 5-hydroxypyrazoline.
ring (4; Figure 1), whereas, in the absence of additional
base, coordination to the 5-hydroxy functionality was ob-
served (3; Figure 1).
Results and Discussion
Ligand Synthesis and Characterization
The ligands were prepared as outlined in Scheme 1. Aceto-
hydrazide 6a and benzohydrazide 6b were synthesized by
reacting equimolar amounts of hydrazine monohydrate
with ethyl acetate or methyl benzoate, respectively, in etha-
nol under refluxing conditions.[5a] Both hydrazides were iso-
lated in good yields as colorless solids. The hydrazides were
treated with acetyl acetone 7a or hexafluoroacetyl acetone
7b under refluxing conditions to obtain pyrazolines 1a–c in
good yields (69–87%). The pyrazolines were purified either
by crystallization from n-hexane or by high-vacuum subli-
mation. Surprisingly, the pyrazolines are quite stable since
no elimination of water to form pyrazole derivatives was
detected. In the case of compounds 1a–c, crystals suitable
for X-ray measurements were grown by the slow cooling of
a saturated n-hexane solution. The reaction of 6b and 7a
did not result in the desired product.
The solid-state structures of compounds 1a–c have been
characterized by single-crystal X-ray diffraction analysis.
Thermal ellipsoid plots for the ligands are displayed in Fig-
ure 2 and selected bond lengths and angles are listed in
Figure 2. Molecular structure of 1a (a), 1b (b), and 1c (c). Thermal
Table 1. In agreement with earlier reports, the cyclic form ellipsoids are drawn at the 50% probability level.
Scheme 1. Synthesis of 1-acetyl- and 1-benzoyl-5-hydroxypyrazoline ligands 1.
2692
www.eurjic.org
© 2011 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Eur. J. Inorg. Chem. 2011, 2691–2697

New Binding Modes of Substituted Hydroxypyrazolines
Table 1. Selected bond lengths [Å] of 1a, 1b, and 1c.
tion of the acetyl and benzoyl functionality was investigated
by IR spectroscopic measurements. A shift of 43 cm–1 was
observed for 8a [ν(C=O) 1655 cm–1] compared with the free
ligand 1a [ν(C=O) 1698 cm–1]. The complexes 8 were also
1a
1b
1c
N1–N2
N1–C3
N2–C1
C2–C3
C1–C2
C1–C4
C3–C5
N1–C6
C6–O1
C3–O2
1.396(4)
1.496(4)
1.263(4)
1.531(4)
1.487(4)
1.481(5)
1.536(4)
1.365(4)
1.221(4)
1.387(3)
1.418(3)
1.493(4)
1.284(4)
1.487(4)
1.532(3)
1.521(3)
1.499(3)
1.367(3)
1.231(3)
1.420(3)
1.396(2)
1.486(3)
1.271(3)
1.536(3)
1.487(3)
1.494(3)
1.540(3)
1.382(3)
1.224(2)
1.379(2)
1
characterized by H NMR spectroscopy, which showed sig-
nals for Zn-CH3 at δ = –0.44 (8a), –0.34 (8b) and –0.29 (8c)
ppm. Furthermore, as expected the 1H NMR signals for the
hydroxy group disappeared on complexation. Experiments
to confirm the presence of monomeric or dimeric species in
solution or an equilibrium between these two forms have
so far been unsuccessful, however, due to the use of non-
coordinating solvents, such as C6D6, we assume a dimeric
structure in solution.
With these suitable ligands in hand, we turned our atten-
tion to their coordination abilities towards zinc.
Synthesis and Characterization of the Zinc Complexes
In Scheme 2, the synthetic protocol to access pyrazoline–
zinc complexes is given. The reaction of ligands 1a–c with
ZnMe2 in a 1:1 ratio was carried out at low temperature
(–78 °C) in toluene. After the evolution of methane, the re-
action mixture was slowly warmed to room temperature
and all volatiles were removed under vacuum to generate a
powder, which was purified by crystallization giving color-
less crystals.
Scheme 2. Synthesis of pyrazoline-zinc complexes 8a–c.
For complexes 8a and 8c suitable crystals were obtained
for single-crystal X-ray diffraction analysis. As shown in
Figure 3, the zinc complexes exist in a dimeric form span-
ning a square planar Zn2O2 core with one pyrazoline above
the plane and the other one underneath (trans positioned
to each other). A similar structural motif has been recently
reported in complexes of the type [ArOZnMe]2 in which
sterically hindered phenols are utilized as ligands.[7c] The
selected bond lengths and angles around the zinc atoms in
complexes 8a and 8c are listed in Table 2. These bond
lengths are within the expected range based on previously
reported four-membered Zn2O2 ring-containing com-
plexes.[8] The acetyl and benzoyl functionality coordinates
to the zinc atom (tetrahedral environment) from the top or
bottom of the Zn2O2 plane, respectively. Interestingly, this
motif can probably be seen as a potential intermediate (co-
ordination and activation of the substrate) in the zinc-cata-
lyzed reduction of amides or ketones.[7,9,10] The coordina-
Figure 3. Molecular structure of 8a (a) and 8c (b). Thermal ellip-
soids are drawn at the 50% probability level.
Table 2. Selected bond lengths [Å] for 8a and 8c.
8a
8c
N1–N2
N1–C3
N2–C1
C2–C3
C1–C2
C1–C4
C3–C5
N1–C6
C6–O2
C3–O1
1.391(3)
1.513(3)
1.273(3)
1.549(3)
1.491(3)
1.498(3)
1.542(3)
1.357(3)
1.238(3)
1.355(3)
1.399(3)
1.524(3)
1.274(3)
1.547(3)
1.489(3)
1.491(3)
1.530(3)
1.364(3)
1.247(3)
1.355(3)
Eur. J. Inorg. Chem. 2011, 2691–2697
© 2011 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.eurjic.org
2693

C. Someya, S. Inoue, E. Irran, S. Krackl, S. Enthaler
FULL PAPER
These complexes are the first examples in which 1-acetyl- covalent bonds between the oxygen, nitrogen and the zinc
and 1-benzoyl-5-hydroxypyrazolines coordinate in the atom forming the first zinc-containing seven-membered
O6,O7-fashion without the opening of the pyrazoline ring. ring system (Figure 4).
Thus, we were interested in changing the coordination motif
Interestingly, the seven-membered ring is arranged in a
by opening the pyrazoline ring, which has been demon- plane and the tmeda ligand coordinates horizontally to this
strated for nickel complexes in the presence of base.[5c] plane; the zinc atom has a tetrahedral coordination mode.
Furthermore, labeling studies of the ligand in CD3OD The Zn1–O2 bond length (1.946 Å) bond is comparable to
showed an exchange of one proton of the CH2 group and, the distance observed for 8c (Zn1–O1: 2.057 Å). The dis-
as a consequence, provided proof of the acidity of this func- tance from the oxygen of the benzoyl group to the zinc
tionality.
atom is significantly longer (Zn1–O1: 2.611 Å) than that
Complexes 8 were dissolved in toluene and cooled to seen in 8c (Zn1–O4: 2.078 Å). 19F NMR spectroscopy was
0 °C (Scheme 3). After the slow addition of 1 equiv. of used as a probe to study the differences between compound
tmeda all volatiles were removed under vacuum and the 1c and 9c (Table 3); a significant shift to lower field was
white residues were purified by crystallization. The reaction observed for one signal, which probably corresponds to the
1
was followed by H NMR spectroscopy and reached com- CF3 group attached to the enolate motif. In the IR spec-
1
pletion within one hour. During the reaction, the H NMR trum, differences in the position of the ν(C=O) peak, rela-
signal for the Zn-CH3 disappeared and the former CH2 sig- tive to that of 1c, of 81 cm–1 for 8c and 58 cm–1 for 9c were
nal significantly shifted to lower field [δ = 2.87 (br., 8a) observed.
compared with 5.79 (s; 9a) ppm]; the integral area also re-
duced to only account for one proton. This corresponds to
Table 3. Comparison of selected properties of 1c, 8c, and 9c.
1c
8c
9c
the deprotonation of the acidic CH2 group by tmeda and
transfer of the proton to the Zn-CH3 to eliminate methane.
The tmeda coordinates to the zinc ion, evidenced by shifts
in the 1H NMR signals compared with uncoordinated
tmeda. Nevertheless, it is difficult to distinguish between
the possible coordination modes of the ligand, such as
O6,N1,O7 as reported for nickel,[5c] by NMR spectroscopy.
Fortunately, crystals suitable for single-crystal X-ray dif-
fraction analysis were obtained for complex 9c. The solid-
state structure of 9c revealed a new coordination mode of
1-acetyl- and 1-benzoyl-5-hydroxypyrazoline ligands with
1H NMR 4-CH(H) [ppm] 3.00–3.66
2.94–3.15
–68.0; –82.1
1599
5.79
–67.2; –71.6
1622
19F NMR [ppm]
–67.4; –80.5
1680
IR ν(C=O) [cm–1
C=N (Å)
]
1.271
1.277
1.287
C–C–O (Å)
1.536
1.547
1.345
N–C(=O) (Å)
1.382
1.363
1.355
Although the reaction mechanism for the formation of
9c is unknown, a reasonable reaction mechanism is de-
scribed in Scheme 4. The ring opening of the cyclic pyraz-
oline ligand 7 is initiated by the deprotonation of the acidic
CH2 functionality by tmeda to give the ring-opened inter-
mediate 10. The nine-membered ring-containing intermedi-
ate 10 undergoes intramolecular ligand substitution
through nitrogen coordination to the zinc atom with the
concomitant departure of the amide oxygen. The formation
of compound 9 is completed by the elimination of methane
gas and coordination of tmeda to the zinc center. This reac-
tion mechanism was supported by theoretical calculations.
DFT calculations were performed at B3LYP level using 6-
Scheme 3. Reaction of complexes 8 with tmeda to form 9.
Figure 4. Molecular structure of 9c. Thermal ellipsoids are drawn
at the 50% probability level. Zn1–O2: 1.9462(15) Å; Zn1–N1:
1.9615(17) Å; Zn1–N3: 2.0710(17) Å; Zn1–N4: 2.0931(18) Å.
Scheme 4. Potential reaction pathway for the synthesis of 9.
2694
www.eurjic.org
© 2011 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Eur. J. Inorg. Chem. 2011, 2691–2697

New Binding Modes of Substituted Hydroxypyrazolines
3020 (m), 3202 (m), 2879 (m), 1662 (m), 1616 (s), 1567 (m), 1350
(s), 1121 (m), 987 (m), 885 (m), 685 (s) cm–1.
31G(d) basis set for C, N, O, F, and H atoms and
LANL2DZ for the Zn atom with the GAUSSIAN-03 pro-
gram package.[11] These calculation show that the formation
of compound 9c (and 2 equiv of methane) from compound
8c with 2 equiv of tmeda is exothermal by 17.8 kcalmol–1.
1-Acetyl-5-hydroxy-3,5-bis(trifluoromethyl)pyrazoline (1a): A solu-
tion of acetohydrazide (55.8 mmol) in ethanol (60 mL) was added
to
a
solution of 1,1,1,5,5,5-hexafluoropeta-2,4-dione (7b,
55.8 mmol) in ethanol (60 mL). After refluxing the mixture for 5 h
the solvent was removed under vacuum. The colorless residue was
purified by recrystallization from n-hexane or by sublimation under
high vacuum; yield 12.2 g (83%, colorless crystals). 1H NMR
(200 MHz, CDCl3, 25 °C): δ = 5.98 (br. s, 1 H, OH), 3.30–3.80 (m,
2 H, CH2), 2.29 [s, 3 H, C(=O)CH3] ppm. 13C NMR (50 MHz,
CDCl3, 25 °C): δ = 173.3, 143.6 (m), 120.6 (m), 92.5 (m), 41.4
(CH2), 22.4 (H3CC=O) ppm. 19F NMR (50 MHz, CDCl3, 25 °C):
Conclusion
We have synthesized and characterized the first 5-hy-
droxypyrazoline zinc complexes with new coordination
modes of pyrazolines, which demonstrate the modularity
of pyrazoline ligands. The Brønsted acid–base reactions of
dimethylzinc with 1-acetyl- and 1-benzoyl-5-hydroxypyraz-
oline resulted in the formation of [RO-Zn-Me]2 complexes
with a central Zn2O2 unit, which is stabilized by coordina-
tion of acetyl or benzoyl oxygens. Noteworthy, the pyraz-
oline ring is untouched. The addition of tmeda as base and
ligand forces the opening of the pyrazoline ring at the hemi-
aminale position to form complexes with the O6,N1 coordi-
nation mode of the pyrazoline ligand. Here the first zinc-
based seven-membered system with covalent bonding in the
solid state has been observed. Future work will focus on
the application of these complexes in catalysis.
δ = –67.8, –81.3 ppm. IR (KBr): ν = 2961 (w), 2933 (w), 2851 (w),
˜
1655 (m), 1626 (s), 1466 (m), 1373 (m), 1344 (m), 1321 (m), 1282
(m), 1234 (m), 1166 (s), 1204 (m), 1193 (m), 1152 (m), 1101 (w),
1070 (w), 1039 (w), 993 (w), 932 (w), 866 (w), 842 (w), 762 (w), 734
(w), 664 (w) cm–1. HRMS calcd. for C7H6F6N2O2 + H: 265.04117;
found 265.04031.
1-Acetyl-5-hydroxy-3,5-dimethylpyrazoline (1b):[5] A solution of
acetohydrazide (55.8 mmol) in ethanol (60 mL) was added to a
solution of 2,4-pentadione (7a, 55.8 mmol) in ethanol (60 mL). Af-
ter refluxing the mixture for 5 h the solvent was removed under
vacuum. The colorless residue was purified by recrystallization
from n-hexane; yield 6.0 g (69%, colorless crystals). 1H NMR
(200 MHz, CDCl3, 25 °C): δ = 4.78 (br. s, 1 H, OH), 2.64–3.20 (m,
2 H, CH2), 2.20 (m, 3 H), 1.96 (m, 3 H), 1.78 (m, 3 H) ppm. IR
(KBr): ν = 3412 (m), 2982 (w), 2934 (w), 1648 (s), 1632 (s), 1421
˜
Experimental Section
(s), 1377 (s), 1320 (m), 1221 (m), 1117 (m), 964 (m), 940 (w), 866
(w), 742 (w), 638 (w), 560 (w) cm–1. HRMS calcd. for C7H12N2O2
+ H: 157.09715; found 157.09666.
General: All manipulations with oxygen- and moisture-sensitive
compounds were performed under N2 using standard Schlenk tech-
niques. Toluene and n-hexane were distilled from sodium/benzo-
phenone ketyl under N2. Dimethylzinc solution (1.2 m in toluene
purchased from Aldrich) was used without further manipulation.
1H, 19F and 13C NMR spectra were recorded on a Bruker AFM
200 spectrometer (1H: 200.13 MHz; 13C: 50.32 MHz; 19F:
188.31 MHz) using the proton signals of the deuterated solvents
as reference. Single crystal X-ray diffraction measurements were
recorded on an Oxford Diffraction Xcalibur S Saphire spectrome-
ter. IR spectra were recorded on either a Nicolet Series II Magna-
IR-System 750 FTR-IR or on a Perkin–Elmer Spectrum 100 FT-
IR.
1-Benzoyl-5-hydroxy-3,5-bis(trifluoromethyl)pyrazoline (1c): A solu-
tion of benzohydrazide (55.8 mmol) in ethanol (60 mL) was added
to
a
solution of 1,1,1,5,5,5-hexafluoropeta-2,4-dione (7b,
55.8 mmol) in ethanol (60 mL). After refluxing the mixture for 5 h
the solvent was removed under vacuum. The colorless residue was
purified by recrystallization from ethanol/n-hexane (9:1); yield
15.9 g (87%, colorless crystals). 1H NMR (200 MHz, CDCl3,
25 °C): δ = 7.84–7.92 (m, 2 H, Ar), 7.40–7.65 (m, 3 H, Ar), 6.40
(br. s, 1 H, OH), 3.00–3.66 (m, 2 H, CH2) ppm. 13C NMR
(50 MHz, CDCl3, 25 °C): δ = 171.6, 144.1, 143.7, 133.3, 131.6,
130.5, 128.3, 94.2, 93.8, 41.4 (CH2) ppm. 19F NMR (50 MHz,
Acetohydrazide (6a):[12] Hydrazine monohydrate (0.20 mol) was
added to a solution of ethyl acetate (0.19 mol) in ethanol (50 mL)
at room temperature. After refluxing the mixture for 6 h the solvent
was removed under vacuum and the colorless residue was dried
under high vacuum; yield 10.3 g (87%, colorless crystals). 1H NMR
(200 MHz, CDCl3, 25 °C): δ = 8.07 (br., 1 H, NH), 3.80 (br., 2 H,
NH2), 1.88 (s, 3 H, CH3) ppm. 13C NMR (50 MHz, CDCl3, 25 °C):
CDCl , 25 °C): δ = –67.4, –80.5 ppm. IR (KBr): ν = 3390 (m), 3324
˜
3
(m), 1680 (s), 1637 (m), 1451 (m), 1434 (m), 1333 (m), 1305 (m),
1275 (s), 1176 (s), 1152 (s), 1078 (m), 1028 (w), 1009 (m), 1009 (m),
905 (w), 792 (w), 757 (w), 715 (w), 672 (w), 631 (w) cm–1. HRMS
calcd. for C12H8F6N2O2 + H: 327.05627; found 327.05569.
8a: A solution of dimethylzinc (4.6 mmol, 1.2 m in toluene) was
added to a solution of 1a (4.6 mmol) in toluene (10 mL) at –78 °C.
The solution was warmed to room temperature overnight. After
removing all volatiles under vacuum a colorless solid was obtained.
The residue was crystallized either from n-hexane or toluene. Crys-
tals suitable for X-ray diffraction analysis were obtained from a
concentrated C6D6 solution at room temperature; yield 0.87 g
(55%, first harvest, colorless crystals). 1H NMR (200 MHz, C6D6,
25 °C): δ = 2.80 (m, 2 H, CH2), 1.73 [s, 3 H, C(=O)CH3], –0.38 (s,
3 H, ZnCH3) ppm. 13C NMR (50 MHz, C6D6, 25 °C): δ = 177.4,
δ = 171.0, 20.6 ppm. IR (KBr): ν = 3292 (m), 1667 (s), 1528 (w),
˜
1376 (w), 1311 (w), 1244 (m), 1157 (w), 993 (w) cm–1.
Benzohydrazide (6b):[13] Hydrazine monohydrate (0.22 mol) was
added to a solution of methyl benzoate (0.22 mol) in ethanol
(50 mL) at room temperature. After refluxing the mixture for 6 h
the solvent was reduced by half under vacuum. The colorless pre-
cipitate was filtered off, recrystallized from ethanol/n-hexane and
dried under vacuum; yield 12.8 g (43%, colorless crystals). 1H
NMR (200 MHz, CDCl3, 25 °C): δ = 7.90 (br., 1 H, NH-NH2),
7.72–7.81 (m, 3 H, C6H5), 7.37–7.56 (m, 2 H, C6H5), 4.13 (br., 2
148.4 (m), 120.6 (m), 98.4 (m), 43.1, 22.5, –16.7 (ZnCH3) ppm. 19
NMR (50 MHz, C D , 25 °C): δ = –68.4, –82.9 ppm. IR (KBr): ν
F
˜
6
6
H, NH-NH2) ppm. 13C NMR (50 MHz, CDCl3, 25 °C): δ = 168.7 = 3384 (m), 2962 (w), 2994 (w), 1698 (s), 1645 (s), 1459 (m), 1378
(C=O), 132.6, 131.8, 128.6, 126.8 ppm. IR (KBr): ν = 3300 (m), (m), 1275 (m), 1198 (s), 1027 (m), 996 (m), 876 (m), 876 (m), 760
˜
Eur. J. Inorg. Chem. 2011, 2691–2697
© 2011 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.eurjic.org
2695

C. Someya, S. Inoue, E. Irran, S. Krackl, S. Enthaler
FULL PAPER
(m), 734 (w), 658 (m), 581 (m), 501 (m), 474 (w) cm–1. HRMS
calcd. for C8H8F6N2O2Zn + H: 342.98542; found 342.98542.
9a: N,N,NЈ,NЈ-Tetramethylethylenediamine (0.61 mmol) was added
dropwise to a solution of 8a (0.61 mmol) in toluene (10 mL) at
room temperature. After stirring for 12 h all volatiles were removed
under vacuum to obtain a solid. The colorless residue was purified
by recrystallization from n-hexane; yield 0.25 g (91%, colorless
crystals). 1H NMR (200 MHz, C6D6, 25 °C): δ = 5.79 (s, 1 H,C-
H), 2.36 (s, 3 H, C-CH3), 1.74 (s, 12 H, N-CH3), 1.50 (br., 4 H,
CH2-CH2) ppm. 13C NMR (50 MHz, C6D6, 25 °C): δ = 182.6,
156.0, 157.7, 134.7, 134.4, 129.0, 128.7, 124.6, 123.8, 121.9, 121.0,
84.7, 50.0, 46.1, 18.4 ppm. 19F NMR (50 MHz, C6D6, 25 °C): δ =
8b: A solution of dimethylzinc (12.6 mmol, 1.2 m in toluene) was
added to a solution of 1b (12.6 mmol) in toluene (10 mL) at –78 °C.
The solution was warmed to room temperature overnight. After
removing all volatiles under vacuum a colorless solid was obtained;
yield 0.62 g (21%, first harvest, colorless crystals). 1H NMR
(200 MHz, C6D6, 25 °C): δ = 2.87 (br., 1 H, CH2), 2.77 (br., 1 H,
CH2), 2.07 [s, 3 H, C(=O)CH3], 1.51 (s, 3 H, CH3), 1.44 (s, 3 H,
CH3), –0.34 (s, 3 H, ZnCH3) ppm. 13C NMR (50 MHz, C6D6,
25 °C): δ = 171.9, 158.7, 97.1, 54.4, 28.7, 22.4, 16.2, –16.0 (ZnCH3)
–67.6, –71.7 ppm. IR (KBr): ν = 2961 (w), 2933 (w), 1619 (m), 1563
˜
(m), 1468 (m), 1404 (w), 1294 (m), 1271 (s), 1181 (s), 1166 (s), 1122
(m), 1105 (m), 1040 (m), 949 (w), 886 (w), 693 (m) cm–1. HRMS
calcd. for C13H20F6N4O2Zn: 443.08547; found 443.08606.
ppm. IR (KBr): ν = 2983 (w), 2939 (w), 2901 (w), 2829 (w), 1635
˜
(w), 1584 (s), 1488 (m), 1418 (m), 1383 (w), 1371 (w), 1321 (m),
1237 (s), 1158 (w), 1111 (m), 1004 (w), 976 (w), 939 (m), 862 (m),
732 (m), 575 (w), 555 (w), 530 (w), 496 (w), 466 (w) cm–1. HRMS
calcd. for C8H14N2O2Zn + H: 235.04195; found 235.04234.
9b: N,N,NЈ,NЈ-Tetramethylethylenediamine (1.5 mmol) was added
dropwise to a solution of 8b (1.3 mmol) in toluene (10 mL) at 0 °C.
After stirring for 12 h at room temperature all volatiles were re-
moved under vacuum to obtain a colorless solid; yield 0.33 g
8c: A solution of dimethylzinc (6.01 mmol, 1.2 m in toluene) was
added to a solution of 1c (6.01 mmol) in toluene (10 mL) at –78 °C.
The solution was warmed to room temperature overnight. After
removing all volatiles under vacuum a colorless solid was obtained;
yield 1.7 g (72%, colorless crystals from toluene). 1H NMR
(200 MHz, C6D6, 25 °C): δ = 7.57–7.69 (m, 2 H, Ar), 6.80–7.00 (m,
3 H, Ar), 2.94–3.15 (m, 2 H, CH2), –0.29 (s, 3 H, ZnCH3) ppm.
13C NMR: not detected owing to poor solubility. 19F NMR
1
(76%). H NMR (200 MHz, C6D6, 25 °C): δ = 4.85 (s, 1 H, C-H),
2.47 (s, 3 H), 2.31 (s, 3 H), 2.04 (s, 3 H), 1.96 (s, 12 H, N-CH3),
1.79 (br., 4 H, CH2-CH2) ppm. 13C NMR (50 MHz, C6D6, 25 °C):
δ = 175.7, 168.4, 161.4, 94.5, 56.5, 46.4, 28.0, 23.0, 20.2 ppm. IR
(KBr): ν = 2967 (w), 2913 (m), 1602 (m), 1533 (s), 1510 (s), 1464
˜
(m), 1418 (s), 1406 (s), 1329 (w), 1273 (m), 1216 (w), 1127 (w), 1029
(m), 1012 (m), 952 (m), 927 (w), 797 (m), 743 (w), 645 (w) cm–1.
HRMS calcd. for C13H26N4O2Zn: 334.14200; found 334.14273.
(50 MHz, C D , 25 °C): δ = –68.0, –82.1 ppm. IR (KBr): ν = 2983
˜
6
6
(w), 2950 (w), 2917 (w), 2846 (w), 1599 (s), 1572 (s), 1457 (m), 1350
(m), 1279 (m), 1237 (m), 1176 (s), 1075 (m), 1048 (w), 859 (w),
9c: N,N,NЈ,NЈ-Tetramethylethylenediamine (3.1 mmol) was added
722 (w), 680 (m) cm–1. HRMS calcd. for C13H10F6N2O2Zn + H: dropwise to a solution of 8c (3.0 mmol) in toluene (10 mL) at 0 °C.
405.00107; found 405.00153.
After stirring for 12 h at room temperature all volatiles were re-
Table 4. Data collection and refinement parameters for 1a, 1b, 1c, 8a, 8c and 9c.
1a
1b
1c
8a
8c
9c
Empirical formula
Formula weight [g/mol]
Temperature [K]
Space group
a [Å]
b [Å]
c [Å]
α [°]
C7H6F6N2O2
264.14
150(2)
C7H12N2O2
156.19
150(2)
C12H8F6N2O2
326.20
150(2)
C16H16F12N4O4Zn2 C26H20F12N4O4Zn2 C18H22F6N4O2Zn1
687.07
811.24
505.77
150(2)
150(2)
150(2)
P21/c
P21/n
P21/c
P21/n
P21/c
Pbca
11.8393(6)
9.0842(4)
8.5465(9)
90
8.7490(6)
9.2277(7)
21.1708(18)
90
13.289(2)
9.6993(15)
10.412(2)
90
7.2494(2)
17.0254(4)
9.3704(2)
90
13.6470(6)
9.6084(3)
12.9663(6)
90
17.4838(4)
12.1420(3)
20.2310(6)
90
β [°]
γ [°]
100.378(5)
90
1962.05(16)
8
1.788
1056
95.103(7)
90
1702.4(2)
8
1.219
672
100.776(18)
90
1318.4(4)
4
1.643
656
90.787(2)
90
1156.42(5)
2
1.973
680
115.308(6)
90
1537.03(11)
2
1.753
808.0
90
90
Volume [Å3]
Z
4294.80(19)
8
1.564
Dcalcd. [g/cm3]
F(000)
2064
Crystal size [mm]
θ range [°]
Index ranges
0.27ϫ0.21ϫ0.09
2.94 to 25.00
–14 Յ h Յ 14
–10 Յ k Յ 10
–22 Յ l Յ 20
9805
0.42ϫ0.40ϫ0.09
3.56 to 25.00
–10 Յ h Յ 10
–10 Յ k Յ 10
–9 Յ l Յ 25
5619
0.49ϫ0.42ϫ0.36
3.46 to 25.00
–15 Յ h Յ 15
–11 Յ k Յ 10
–9 Յ l Յ 12
4899
0.32ϫ0.31 ϫ0.28
3.53 to 25.00
–8 Յ h Յ 4
–20 Յ k Յ 19
–11 Յ l Յ 10
4354
0.35ϫ0.23ϫ0.14
3.30 to 25.00
–16 Յ h Յ 16
–7 Յ k Յ 11
–15 Յ l Յ 15
5552
0.57ϫ0.25ϫ0.23
3.36 to 25.00
–19 Յ h Յ 20
–14 Յ k Յ 6
–14 Յ l Յ 24
14049
Refl. collected
Independent refl.
[R(int)]
3461
[0.0771]
2993
[0.0714]
2317
[0.0279]
1989
[0.0190]
2698
[0.0278]
3779
[0.0355]
Completeness to
θ = 25.00° [%]
Rel. transm. factors
Parameters
99.8
0.950 and 0.982
311
99.7
0.963 and 0.992
207
99.8
0.942 and 0.922
200
97.8
0.539 and 0.577
174
99.8
0.584 and 0.799
218
99.8
0.544 and 0.767
284
GOF
0.858
0.834
0.970
1.010
0.925
0.925
R1 [IϾ2σ(I)][a]
wR2 [IϾ2σ(I)][b]
R1 (all data)[a]
wR2 (all data)[b]
0.0515
0.0572
0.0572
0.0691
0.0592
0.0683
0.1664
0.0858
0.0429
0.0978
0.0681
0.1061
0.0255
0.0587
0.0322
0.0601
0.0299
0.0587
0.0429
0.0606
0.0290
0.0545
0.0492
0.0577
[a] R1 = Σ||Fo| – |Fc||/ΣFo. [b] wR2 = {Σ[w(Fo – Fc ) ]/Σ[w(Fo2)2]}1/2
.
2
2 2
2696
www.eurjic.org
© 2011 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Eur. J. Inorg. Chem. 2011, 2691–2697

New Binding Modes of Substituted Hydroxypyrazolines
[4] For a selection, see: a) A. L. Gavrilova, B. Bosnich, Chem. Rev.
2004, 104, 349–383; b) P. J. Steel, Acc. Chem. Res. 2005, 38,
243–250; c) R. D. Hancock, A. E. Martell, Chem. Rev. 1989,
89, 1875–1914; d) M. Miura, Angew. Chem. 2004, 116, 2251–
2253; Angew. Chem. Int. Ed. 2004, 43, 2201–2203; e) A. S.
Borovik, Acc. Chem. Res. 2005, 38, 54–61.
moved under vacuum. The obtained orange solid was crystallized
from n-hexane/toluene (5:1) to give colorless crystals. The crystals
were filtered off and dried under vacuum. Crystals suitable for X-
ray diffraction analysis were obtained from a concentrated C6D6
solution at room temperature overnight; yield 1.3 g (84%, colorless
1
crystals). H NMR (200 MHz, C6D6, 25 °C): δ = 8.30–8.38 (m, 2
[5] a) L. Sacconi, Z. Anorg. Allg. Chem. 1954, 275, 249–256; b) L.
Sacconi, P. Paoletti, F. Maggio, J. Am. Chem. Soc. 1957, 79,
4067–4069; c) K. C. Joshi, R. Bohra, B. S. Joshi, Inorg. Chem.
1992, 31, 598–603; d) A. Mukhopadhyay, S. Pal, Polyhedron
2004, 23, 1997–2004; e) K. N. Zelenin, M. Y. Malov, I. V.
Zerova, P. B. Terent’ev, A. G. Kalandarishvili, Khim. Geterot-
sikl. Soedin. 1987, 1210–1218; f) K. N. Zelenin, M. Y. Malov,
I. P. Bezhan, V. A. Khrustalev, S. I. Yakimovich, Khim. Geter-
otsikl. Soedin. 1985, 1000–1001; g) M. Y. Malov, K. N. Zelenin,
S. I. Yakimovich, Khim. Geterotsikl. Soedin. 1988, 1358–1361;
h) A. Y. Ershov, Zh. Org. Khim. 1995, 31, 1057–1059; i) S. I.
Yakimovich, I. V. Zerova, Zh. Org. Khim. 1987, 23, 1433–1440;
j) V. G. Yusupov, S. I. Yakimovich, S. D. Nasirdinov, N. A. Par-
piev, Zh. Org. Khim. 1980, 16, 415–420.
H, C6H5), 7.07–7.25 (m, 3 H, C6H5), 5.79 (s, 1 H, =CH), 1.82 [s,
12 H, N(CH3)2], 1.63 (br., 4 H, CH2-CH2) ppm. 13C NMR
(50 MHz, C6D6, 25 °C): δ = 177.7, 156.9, 156.4, 137.0, 136.4, 134.1,
131.7, 131.0, 85.0, 56.5, 46.5 ppm. 19F NMR (50 MHz, C6D6,
25 °C): δ = –67.2, –71.6 ppm. IR (KBr): ν = 2928 (w), 1622 (s),
˜
1468 (m), 1400 (m), 1304 (m), 1275 (m), 1192 (s), 1124 (s),
1024 (m), 952 (w), 846 (m), 804 (w), 786 (w), 731 (w), 689 (w)
cm–1. HRMS calcd. for C18H22F6N4O2Zn: 505.10112; found
505.10239.
Single-Crystal X-ray Structure Determination: Crystals were
mounted on a glass capillary in perfluorinated oil and measured in
a cold N2 flow. The data were collected using an Oxford Diffraction
Xcalibur S Sapphire at 150(2) K (Mo-Kα radiation, λ = 0.71073 Å).
The structures were solved by direct methods and refined on F2
with the SHELX-97 software package.[14] The positions of the hy-
drogen atoms were calculated and considered isotropically accord-
ing to a riding model (Table 4).
[6] a) G. Parkin, Chem. Rev. 2004, 104, 699–767; b) J. Weston,
Chem. Rev. 2005, 105, 2151–2174.
[7] a) N. A. Marinos, S. Enthaler, M. Driess, ChemCatChem 2010,
2, 846–853; b) S. Enthaler, K. Schröder, S. Inoue, B. Eckhardt,
K. Junge, M. Beller, M. Driess, Eur. J. Org. Chem. 2010, 4893–
4901; c) S. Enthaler, B. Eckhardt, S. Inoue, E. Irran, M. Driess,
Chem. Asian J. 2010, 5, 2027–2035; d) S. Enthaler, Catal. Lett.
2011, 141, 55–61; e) S. Enthaler, Catal. Sci. Technol. 2011, 1,
104–110.
CCDC-816673 (for 1a), -816674 (for 1b), -816675 (for 1c), -816676
(for 8a), -816678 (for 8c) and -816677 (for 9c) 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.
[8] M. Parvez, G. L. Bergstresser, H. G. Richey Jr., Acta Crys-
tallogr., Sect. C 1992, 48, 641–644.
[9] S. Das, D. Addis, S. Zhou, K. Junge, M. Beller, J. Am. Chem.
Soc. 2010, 132, 1770–1771.
[10] R. Noyori, S. Suga, H. Oka, M. Kitamura, Chem. Rec. 2001,
1, 85–100.
Acknowledgments
[11] a) M. J. Frisch, G. W. Trucks, H. B. Schlegel, G. E. Scuseria,
M. A. Robb, J. R. Cheeseman, J. A. Montgomery Jr., T.
Vreven, K. N. Kudin, J. C. Burant, J. M. Millam, S. S. Iyengar,
J. Tomasi, V. Barone, B. Mennucci, M. Cossi, G. Scalmani, N.
Rega, G. A. Petersson, H. Nakatsuji, M. Hada, M. Ehara, K.
Toyota, R. Fukuda, J. Hasegawa, M. Ishida, T. Nakajima, Y.
Honda, O. Kitao, H. Nakai, M. Klene, X. Li, J. E. Knox, H. P.
Hratchian, J. B. Cross, V. Bakken, C. Adamo, J. Jaramillo, R.
Gomperts, R. E. Stratmann, O. Yazyev, A. J. Austin, R.
Cammi, C. Pomelli, J. W. Ochterski, P. Y. Ayala, K. Morok-
uma, G. A. Voth, P. Salvador, J. J. Dannenberg, V. G. Zakrzew-
ski, S. Dapprich, A. D. Daniels, M. C. Strain, O. Farkas, D. K.
Malick, A. D. Rabuck, K. Raghavachari, J. B. Foresman, J. V.
Ortiz, Q. Cui, A. G. Baboul, S. Clifford, J. Cioslowski, B. B.
Stefanov, G. Liu, A. Liashenko, P. Piskorz, I. Komaromi, R. L.
Martin, D. J. Fox, T. Keith, M. A. Al-Laham, C. Y. Peng, A.
Nanayakkara, M. Challacombe, P. M. W. Gill, B. Johnson, W.
Chen, M. W. Wong, C. Gonzalez, J. A. Pople, Gaussian 03,
rev. E.01, Gaussian, Inc., Wallingford CT, 2004; b) A. D.
Becke, J. Chem. Phys. 1993, 98, 5648–5652; c) C. Lee, W. Yang,
R. G. Parr, Phys. Rev. B 1988, 37, 785–789; d) B. Miehlich, A.
Savin, H. Stoll, H. Preuss, Chem. Phys. Lett. 1989, 157, 200–
206.
Financial support by the Deutsche Forschungsgemeinschaft
(DFG) and the Technische Universität Berlin (Cluster of Excel-
lence, “Unifying Concepts in Catalysis”, EXC 314/1) is gratefully
acknowledged. C. I. S. thanks the Berlin International Graduate
School of Natural Sciences and Engineering (BIG-NSE). S. I.
thanks the Japan Society for the Promotion of Science (JSPS) for
financial support of his work. S. K. thanks the Fonds der Chem-
ischen Industrie for a Kekulé scholarship and the Berlin Inter-
national Graduate School of Natural Sciences and Engineering
(BIG-NSE) for ideational support.
[1] a) P. T. Anastas, M. M. Kirchhoff, Acc. Chem. Res. 2002, 35,
686–694; b) P. T. Anastas, M. M. Kirchhoff, T. C. Williamson,
Appl. Catal. A 2001, 221, 3–13; c) P. T. Anastas, ChemSusChem
2009, 2, 391–392.
[2] a) M. Beller, C. Bolm, Transition Metals for Organic Synthesis,
2nd ed., Wiley-VCH, Weinheim, Germany, 2004; b) B. Cornils,
W. A. Herrmann, Applied Homogeneous Catalysis with Organo-
metallic Compounds, Wiley-VCH, Weinheim, Germany, 1996;
c) A. Behr, Angewandte homogene Katalyse, Wiley-VCH,
Weinheim, Germany, 2008; d) B. Cornils, W. A. Herrmann,
I. T. Horvath, Multiphase Homogenous Catalysis, Wiley-VCH,
Weinheim, Germany, 2005.
[12] M. H. Klingele, S. Brooker, Eur. J. Org. Chem. 2004, 3422–
3434.
[13] B. H. Zhou, Acta Crystallogr., Sect. E 2009, 65, o2821.
[14] G. M. Sheldrick, SHELXL93, Program for the Refinement of
Crystal Structures, University of Göttingen, Göttingen, Ger-
many, 1997.
[3] a) Phosphorus Ligands in Asymmetric Catalysis: Synthesis and
Applications (Ed.: A. Börner), Wiley-VCH, Weinheim, Ger-
many, 2008; b) Privileged Chiral Ligands and Catalysts (Ed.:
Q.-L. Zhou), Wiley-VCH, Weinheim, Germany, 2011.
Received: March 11, 2011
Published Online: May 4, 2011
Eur. J. Inorg. Chem. 2011, 2691–2697
© 2011 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.eurjic.org
2697