Alkylzinc complexes with achiral and chiral monoanionic N,N,O heteroscorpionate ligands

Article abstract of DOI:10.1002/ejic.200390046

The synthesis of the new chiral ligand (3,5-di-tertbutylpyrazol-1-yl) (3′,5′-dimethylpyrazol-1-yl) acetic acid (bpaH^tBu2,Me2) (4) has been achieved. Two different synthetic routes to its precursor 3,5-di-tert-butyl-1-[(3,5-dimethyl-1H-pyrazol-1-yl)methyl]-1H-pyrazole (bpm^tBu2,Me2) (3) are reported. Deprotonation at the methylene group, followed by reaction with carbon dioxide, yielded a racemic mixture of 4. The chemical behaviour of bis(3,5-di-tert-butylpyrazol-1-yl)acetic acid (bdtbpzaH) (2) and the new chiral N,N,O scorpionate ligand 4 involving their coordination to zinc ions was studied. [Zn(bpa^tBu2,Me2)Cl] (5) was formed from a mixture of ZnCl₂, 4 and base. Reaction of bis(3,5-di-tert-butylpyrazol-1-yl)acetic acid (bdtbpzaH) (2) with Zn(CH₃)₂ or Zn(CH₂CH₃)₂ gave the alkylzinc complexes Zn(bdtbpza)(CH₃)] (6) and [Zn(bdtbpza)(CH₂CH₃)] (7). [Zn(bpat^Bu2,Me2)(CH₃)] (8) was obtained from a synthesis analogous to that of 6 with 4. The further reactions of 6 and 8 with acetic acid resulted in the acetato complexes [Zn(OAc)(bdtbpza)] (9) and [Zn(OAc)(bpa^tBu2,Me2)] (10). The chiral methyl complex 8 may serve as a precursor for structural model complexes of the active sites of zinc enzymes, such as thermolysin or carboxypeptidase A. [Zn(bpa^tBu2,Me2)₂] (11) was formed from a side reaction. Crystal structures of 4, 5, 8 and 11 were obtained; 5 crystallised as the dimer [Zn(bpa^tBu2,Me2) Cl]₂; 11 presents an unusual zinc binding geometry. Wiley-VCH Verlag GmbH & Co KGaA, 69451 Weinheim, Germany, 2003.

Full text of DOI:10.1002/ejic.200390046

FULL PAPER
Alkylzinc Complexes with Achiral and Chiral Monoanionic N,N,O
Heteroscorpionate Ligands
Ina Hegelmann,[a] Alexander Beck,[a] Christian Eichhorn,[b] Bernhard Weibert,[a] and
Nicolai Burzlaff*[a]
Keywords: Scorpionate ligands / Zinc / Bioinorganic chemistry / Tripodal ligands / N ligands
The synthesis of the new chiral ligand (3,5-di-tert-
butylpyrazol-1-yl)(3Ј,5Ј-dimethylpyrazol-1-yl)acetic acid
(bpaHtBu2,Me2) (4) has been achieved. Two different synthetic
[Zn(bdtbpza)(CH2CH3)] (7). [Zn(bpatBu2,Me2)(CH3)] (8) was
obtained from a synthesis analogous to that of 6 with 4.
The further reactions of 6 and 8 with acetic acid resulted
routes to its precursor 3,5-di-tert-butyl-1-[(3,5-dimethyl-1H- in the acetato complexes [Zn(OAc)(bdtbpza)] (9) and
pyrazol-1-yl)methyl]-1H-pyrazole (bpmtBu2,Me2) (3) are re- [Zn(OAc)(bpatBu2,Me2)] (10). The chiral methyl complex 8 may
ported. Deprotonation at the methylene group, followed by
reaction with carbon dioxide, yielded a racemic mixture of
4. The chemical behaviour of bis(3,5-di-tert-butylpyrazol-1-
yl)acetic acid (bdtbpzaH) (2) and the new chiral N,N,O scor-
pionate ligand 4 involving their coordination to zinc ions was
studied. [Zn(bpatBu2,Me2)Cl] (5) was formed from a mixture of
ZnCl2, 4 and base. Reaction of bis(3,5-di-tert-butylpyrazol-1-
yl)acetic acid (bdtbpzaH) (2) with Zn(CH3)2 or Zn(CH2CH3)2
gave the alkylzinc complexes [Zn(bdtbpza)(CH3)] (6) and
serve as a precursor for structural model complexes of the
active sites of zinc enzymes, such as thermolysin or carboxy-
peptidase A. [Zn(bpatBu2,Me2)2] (11) was formed from a side
reaction. Crystal structures of 4, 5, 8 and 11 were obtained;
5 crystallised as the dimer [Zn(bpatBu2,Me2)Cl]2; 11 presents
an unusual zinc binding geometry.
( Wiley-VCH Verlag GmbH & Co KGaA, 69451 Weinheim,
Germany, 2003)
Introduction
Zinc complexes with N,N,O ligands can serve as models
for the active site of zinc-containing enzymes that bind the
metal ion with two histidine groups and one aspartate or
glutamate group. Examples are carboxypeptidase A,
thermolysin (Figure 1) and other proteases.[1Ϫ5]
There are only a few examples of N,N,O tripod ligands
that mimic this motif. Carrano et al. used the scorpionate
ligand (3-tert-butyl-2-hydroxy-5-methylphenyl)bis(3,5-di-
methylpyrazol-1-yl)methane to generate model complexes
of zinc-containing enzymes.[6] However, instead of a carb-
oxylate O-donor, this ligand contained a phenolate O-
donor. By insertion of formaldehyde or carbon dioxide into
a BϪH bond of zinc bis(pyrazol-1-yl)hydroborate com-
plexes, Parkin et al. also formed N,N,O model complexes.[7]
Recently, we reported on the synthesis of structural models
for this class of enzymes by using bis(3,5-di-tert-butylpyra-
zol-1-yl)acetic acid.[8]
Figure 1. Active site of thermolysin with inhibitor (2S)-2-benzyl-3-
carboxypropionic acid bound to a zinc ion (PDB-Code: 1HYT)[5]
Since enzymes are chiral compounds there has been a
major effort in bioinorganic chemistry to supply chiral
[a]
Fachbereich Chemie der Universität Konstanz,
models for the active sites of metalloenzymes. Alsfasser et
al.[9] and Vahrenkamp et al.[10] achieved this by including
amino acids in the ligand systems. Modification of hydro-
tris(pyrazol-1-yl)borate (Tp) ligands by chiral pyrazoles de-
Universitätsstraße 10, Fach M728, 78457 Konstanz, Germany
Fax: (internat.) ϩ 49-(0)7531/88-3136
E-mail: nicolai@chemie.uni-konstanz.de
[b]
Institut für Anorganische Chemie der Universität Würzburg,
Am Hubland, 97074 Würzburg, Germany
Eur. J. Inorg. Chem. 2003, 339Ϫ347  2003 WILEY-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim 1434Ϫ1948/03/0102Ϫ0339 $ 20.00ϩ.50/0
339

I. Hegelmann, A. Beck, C. Eichhorn, B. Weibert, N. Burzlaff
FULL PAPER
rived from the chiral pool is another way to form chiral
Deprotonation of a methylene group in 3 followed
N,N,N tripod ligands. This was the method used by Tolman by reaction with carbon dioxide and acidic workup
et al.[11]
yielded a racemic mixture of (3,5-di-tert-butylpyrazol-1-
In recent years some of these zinc model complexes have yl)(3Ј,5Ј-dimethylpyrazol-1-yl)acetic acid (bpaHtBu2,Me2) (4)
been tested as catalysts for CO2 activation.[12] Major pro- (Scheme 1). As in 3 two sets of signals are found in the IR,
gress has been made by using ZnII-based catalysts for the 1H and 13C NMR spectra. A strong IR band at 1758 cmϪ1
1
copolymerisation of carbon dioxide and epoxides with the and a H NMR signal at δ ϭ 11.09 ppm are an indication
focus being on the tacticity of the polycarbonates.[13,14]
of the carboxylate group. Crystals of 4 suitable for X-ray
structure determination were obtained by crystallisation
from acetone (Figure 2). Bond lengths and bond angles
in 4 (Table 1) are in good agreement with those reported
earlier for bdtbpzaH (2).[8]
Results and Discussion
Based on the ligand synthesis of bdmpza published by
Otero et al.,[15] we recently developed a simple synthesis for
the sterically hindered bdtbpzaH (2) suitable for use in for-
ming the model complexes [Zn(bdtbpza)Cl].[8] This route
was also applied in the synthesis of a racemic mixture of a
new chiral N,N,O scorpionate ligand. The unsymmetrical
3,5-di-tert-butyl-1-[(3,5-dimethyl-1H-pyrazol-1-yl)methyl]-
1H-pyrazole (bpmtBu2,Me2) (3) served as the starting mat-
erial.[16] It was obtained by a phase-transfer-catalysed reac-
tion of 1-chloromethyl-3,5-dimethylpyrazole hydrochloride
with 3,5-di-tert-butylpyrazole under basic conditions
(Scheme 1). However, the one-step phase-transfer-catalysed
reaction of 3,5-dimethylpyrazole with 3,5-di-tert-butylpyra-
zole, dichloromethane and base was more convenient
(Scheme 1).
Figure 2. Molecular structure of bpaHtBu2,Me2 (4); thermal ellips-
oids are drawn at the 50% probability level
Table 1. Selected bond lengths and angles of 4
˚
Distance [A]
4
Angle [°]
4
C(1)ϪC(2)
C(2)ϪO(1)
C(2)ϪO(2)
C(1)ϪN(12)
C(1)ϪN(22)
1.540(3)
1.318(3)
1.205(3)
1.463(3)
1.454(3)
O(1)ϪC(2)ϪO(2)
C(2)ϪC(1)ϪN(12)
C(2)ϪC(1)ϪN(22)
N(12)ϪC(1)ϪN(22)
125.2(2)
113.17(17)
111.26(17)
113.88(17)
The proton of the carboxylate group was located. It
forms an intermolecular hydrogen bond to a pyrazole nitro-
˚
gen atom of another molecule [d(H10ϪN11) ϭ 1.576(3) A].
Reaction of 4 with base and water-free ZnCl2 yielded
[Zn(bpatBu2,Me2)Cl] (5) [Equation (1)]. Suitable crystals of 5
were obtained from dichloromethane. Complex 5 crys-
tallised as a cross-linked dimer [Zn(bpatBu2,Me2)Cl]2 (Fig-
ure 3). Selected bond lengths and bond angles of 5 are
summarised in Table 2.
Scheme 1
After separation by column chromatography on silica, 3
was isolated in a yield of up to 17% from the reaction mix-
ture of the three possible products. Since the other two
products bis(3,5-dimethylpyrazol-1-yl)methane and espe-
cially bis(3,5-di-tert-butylpyrazol-1-yl)methane (1) can also
be isolated in pure form and used for further syntheses, the
second synthetic route is currently preferred. Two sets of
signals are detected for the two different pyrazolyl rings in
(1)
1
the H and 13C NMR spectra. Two medium-intensive IR
bands at 1559 and 1541 cmϪ1 are also found for these two
pyrazolyl rings.
340
Eur. J. Inorg. Chem. 2003, 339Ϫ347

Alkylzinc Complexes with N,N,O Heteroscorpionate Ligands
FULL PAPER
Thus, reaction of bis(3,5-di-tert-butylpyrazol-1-yl)acetic
acid (2) with dialkylzinc ZnR2 (R ϭ CH3, CH2CH3) gener-
ates alkylzinc complexes [Zn(bdtbpza)(CH3)] (6) and
[Zn(bdtbpza)(CH2CH3)] (7) [Equation (2)] with the elimina-
tion of alkane.
(2)
Figure 3. Molecular structure of [Zn(bpatBu2,Me2)Cl]2 (5); thermal
ellipsoids are drawn at the 50% probability level
Earlier studies by H. Vahrenkamp et al.[18] and G. Parkin
et al.[19] have already shown that four-coordinated alkyl[hy-
drotris(pyrazol-1-yl)borato]zinc complexes can be obtained
by metathesis of ZnR2 with potassium or thallium salts of
sterically demanding hydrotris(pyrazol-1-yl)borate ligands.
Since bis(pyrazol-1-yl)acetic acid, and not an alkali carb-
oxylate ligand salt, was used for this synthesis, the workup
procedure was simple and 6 and 7 were obtained in high
yield and purity; [Zn(bdtbpza)(CH3)] (6) is characterised by
resonances attributed to the ZnϪMe group at δ ϭ
Ϫ0.35 ppm (1H NMR) and δ ϭ Ϫ10.1 ppm (13C NMR).
For the ZnϪEt group of [Zn(bdtbpza)(CH2CH3)] (7) sig-
Table 2. Selected bond lengths and angles of complex 5
˚
Distance [A]
5
Angle [°]
5
Zn(1)ϪN(11)
Zn(1)ϪN(21)
Zn(1)ϪO(1A)
Zn(1)ϪCl(1)
2.031(3)
2.095(2)
1.942(2)
2.233(2)
N(11)ϪZn(1)ϪN(21)
O(1A)ϪZn(1)ϪN(11)
O(1A)ϪZn(1)ϪN(21)
N(11)ϪZn(1)ϪCl(1)
N(21)ϪZn(1)ϪCl(1)
O(1A)ϪZn(1)ϪCl(1)
95.17(10)
112.43(9)
103.95(9)
109.77(8)
115.91(6)
117.42(9)
1
nals are found in the H NMR spectrum at δ ϭ 0.52 ppm
3
3
The coordination sphere around the zinc atom is almost (q, JH,H ϭ 8.0 Hz, CH2) and δ ϭ 1.29 ppm (t, JH,H
ϭ
tetrahedral, although the angle N(11)ϪZnϪN(21) 8.0 Hz, CH3) and in the 13C NMR spectrum at δ ϭ 3.3 ppm
[95.17(10)°] is smaller than the ideal tetrahedral one would (CH2) and δ ϭ 11.9 ppm (CH3). The remaining resonances
be. Nevertheless, this tetrahedron is less flattened compared of 6 and 7 can be assigned to the bis(3,5-di-tert-butylpyra-
to that previously observed in the structure of the monomer zol-1-yl)acetato ligand. The analogous reaction of (3,5-
[Zn(bdtbpza)Cl].[8] The coordination of the carboxylate di-tert-butylpyrazol-1-yl)(3Ј,5Ј-dimethylpyrazol-1-yl)acetic
group to the zinc atom is less of an anti- and more of a syn- acid (bpaHtBu2,Me2) (4) with dimethylzinc gave the chiral
type compared with the structure of [Zn(bdtbpza)Cl].[8] The methylzinc complex [Zn(bpatBu2,Me2)(CH3)] (8) [Equa-
better donor properties of this syn-type coordination may tion (2)]. The resonances attributed to the ZnϪMe group
explain the high νas(CO2Ϫ) absorption around 1696 cmϪ1 are observed at δ ϭ Ϫ0.42 ppm (1H NMR) and δ ϭ
(KBr pellet). This νas(CO2Ϫ) absorption is rather broad in Ϫ14.1 ppm (13C NMR). In the infrared spectrum the
solution and is found at 1687 cmϪ1. An IR signal at 1468 νas(CO2Ϫ) absorption is assigned to a band at 1669 cmϪ1
cmϪ1 is assigned to νs(CO2Ϫ). The proposal of a syn-type and νs(CO2Ϫ) is assigned to a band at 1466 cmϪ1. Two sets
coordination is also supported by a significantly shorter of NMR and IR signals are found for the two different
˚
ZnϪO(1) distance [1.942(2) A] and a longer ZnϪCl dis- pyrazolyl groups of the (3,5-di-tert-butylpyrazol-1-yl)(3Ј,5Ј-
˚
tance [2.233(2) A] compared to those in [Zn(bdtbpza)Cl] dimethylpyrazol-1-yl)acetato ligand. Complex 8 was ob-
[8]
˚
[1.990(2) and 2.170(2) A]. Again, two sets of signals are tained as a racemic mixture of a chiral complex. Crystals
observed in the NMR spectra due to the two different pyra- of 8 suitable for X-ray structure determination were ob-
zolyl groups. Not all of the quaternary signals are detected tained from a racemic solution of 8 in CH2Cl2. The struc-
in the 13C NMR spectrum that might be caused by a mono- ture of complex 8 represents one of the rare examples of
mer/dimer equilibrium.
monomeric four-coordinated alkylzinc complexes and is the
In the presence of Lewis base type ligands such as pyri- first with a carboxylate O-donor ligand. Monomers of both
dine (py) an equimolar amount of acetic acid selectively enantiomers crystallised in the cell as a result of the centro-
cleaves one of the ZnϪC bonds of dimethylzinc to form symmetric space group (Figure 4). Selected bond lengths
methane and the dimer [Zn(OAc)(CH3)(py)]2.[17] We have and bond angles of 8 are summarised in Table 3.
˚
observed, that with sterically demanding bis(pyrazol-1-yl)-
The ZnϪCH3 bond length in complex 8 [1.962(8) A] is
acetic acids, monomeric four-coordinated alkyl[bis(pyrazol- similar to that in [Zn(CH3)TpMe2] [1.981(8) A].[19] The most
˚
1-yl)acetato]zinc complexes are obtained in a similar way. striking features of the molecular structure of 8 are
Eur. J. Inorg. Chem. 2003, 339Ϫ347
341

I. Hegelmann, A. Beck, C. Eichhorn, B. Weibert, N. Burzlaff
FULL PAPER
of the recently published [Zn(bdtbpza)Cl] complex. These
broad resonances may indicate an η1/η2 equilibrium of the
acetato ligand. Two additional IR signals at 1633 cmϪ1 and
1602 cmϪ1 are therefore assigned to νas(CO2Ϫ) of η1- and
η2-bound acetato ligands. The IR signals at 1681 cmϪ1 and
1467 cmϪ1 are assigned to νas(CO2Ϫ) and νs(CO2Ϫ) of the
bdtbpza ligand. This is proof of the monomeric structure
of 9, since the monomer [Zn(bdtbpza)Cl] shows a similar
νas(CO2Ϫ) signal at 1681 cmϪ1 [8]
The value of ∆νas-s indic-
.
ates the binding mode of the carboxylate ligand. Values of
∆νas-s Ն 200 cmϪ1 are typical for a unidentate binding
mode of acetates which is in good agreement with the ∆νas-s
values of the bis(pyrazol-1-yl)acetato ligands in the com-
plexes 5Ϫ9.[20]
The NMR spectra of the complex [Zn(OAc)(bpatBu2,Me2)]
(10) formed in benzene are similar to those of 9 although
two sets of signals for the two different pyrazolyl groups are
visible. Three 1H NMR signals at δ ϭ 2.10 ppm, δ ϭ
2.36 ppm and δ ϭ 2.49 ppm are ascribed to two methyl
groups of the bpatBu2,Me2 ligand and one of the acetato li-
gand. A resonance at δ ϭ 22.1 ppm in the 13C NMR spec-
trum is assigned to the methyl group of the acetato ligand.
The carboxylate signal of the acetato ligand was found at
δ ϭ 181.2 ppm in the 13C NMR spectrum of 10. Most of
the NMR signals of 10 are broader than those of 9. Qua-
ternary carbon atoms are difficult to detect in the 13C NMR
Figure 4. Molecular structure of [Zn(bpatBu2,Me2)(CH3)] (8); ther-
mal ellipsoids are drawn at the 50% probability level
Table 3. Selected bond lengths and angles of complex 8
˚
Distance [A]
8
Angle [°]
8
Zn(1)ϪN(11)
Zn(1)ϪN(21)
Zn(1)ϪO(1)
Zn(1)ϪC(3)
2.085(7)
2.104(6)
2.054(6)
1.962(8)
N(11)ϪZn(1)ϪN(21)
O(1)ϪZn(1)ϪN(11)
O(1)ϪZn(1)ϪN(21)
C(3)ϪZn(1)ϪN(11)
C(3)ϪZn(1)ϪN(21)
C(3)ϪZn(1)ϪO(1)
88.3(3)
88.5(2)
87.0(2)
119.8(3)
133.1(3)
126.8(3)
1
spectrum due to the signals being broad. A H NMR spec-
trum at Ϫ70 °C shows two sets of signals, again indicating
an η1/η2 equilibrium of the acetato ligand. These slight dif-
ferences compared with 9 might be explained by the fact
that complex 10 is sterically less hindered. In addition to
two acetato νas(CO2Ϫ) absorptions at 1624 cmϪ1 and 1601
cmϪ1, weak IR signals are visible at 1442 cmϪ1 and 1427
cmϪ1 which might be assigned to νs(CO2Ϫ). The resulting
∆νas-s values of 159 cmϪ1 and 197 cmϪ1 also verify an η1/
η2 equilibrium.
the two different angles C(3)ϪZnϪN(11) [119.8(3)°] and
C(3)ϪZnϪN(21) [133.1(3)°]. Obviously, the methyl group
C(3) is avoiding the bulky tert-butyl group. This implies a
possible stereoselective induction for future alkyl-transfer
reactions.
The reactivity of 6 and 8 towards acetic acid has been
examined to provide acetato complexes as useful precursors
to enzyme models. A slight excess of acetic acid cleaves the
ZnϪCH3 bond with the elimination of methane and yields
[Zn(OAc)(bdtbpza)] (9) and [Zn(OAc)(bpatBu2,Me2)] (10)
[Equation (3)].
[Zn(OAc)(bdtbpza)] (9) and [Zn(OAc)(bpatBu2,Me2)] (10)
may also be prepared by reaction of bdtbpzaH (2) or
(bpaHtBu2,Me2) (4) with Zn(OAc)2 or from the reaction of
(3)
Therefore, 6 and 8 exhibit a reactivity similar to that of
[Zn(CH3)(TpPh)] and [Zn(CH3)(TptBu)].[18,19] Signals at δ ϭ
1
2.12 ppm in the H NMR and δ ϭ 21.1 ppm in the 13C
NMR spectra of 9 are assigned to the methyl group of the
acetato ligand. The carboxylate signal of the acetato ligand
was found at δ ϭ 178.2 ppm in the 13C NMR spectrum.
Figure 5. Molecular structure of [Zn(bpatBu2,Me2)2] (11); thermal
ellipsoids are drawn at the 50% probability level; only one of the
Most of the NMR signals of 9 are broad compared to those zinc positions is shown
342
Eur. J. Inorg. Chem. 2003, 339Ϫ347

Alkylzinc Complexes with N,N,O Heteroscorpionate Ligands
FULL PAPER
the chloro complexes [Zn(bdtbpza)Cl] or [Zn(bpatBu2,Me2)- but its coordination properties are similar to those of 2. The
Cl] (5) with silver acetate. Due to a more complicated reaction of 2 or 4 with dialkylzinc yields the new alkylzinc
workup in these routes along with the formation of by- complexes [Zn(bdtbpza)(CH3)] (6), [Zn(bdtbpza)(CH2-
products we prefer the alkylzinc route.
CH3)] (7) and [Zn(bpatBu2,Me2)(CH3)] (8). Complex 8 is an
During the synthesis of 10 in an acetonitrile solution a example of rare monomeric alkylzinc complexes and is the
sandwich complex [Zn(bpatBu2,Me2)2] (11) was formed as a first one with a carboxylate O-donor ligand. Acetato com-
by-product. The facile formation of the related six-coordi- plexes [Zn(OAc)(bdtbpza)] (9) and [Zn(OAc)(bpatBu2,Me2)]
nated complexes [Zn(TpR)2] in the reactions of [Zn(TpR)X] (10), that serve as models for the active sites of the zinc-
(X ϭ OH, CH3, Cl) has already been reported by H. Vah- containing enzymes carboxypeptidase A or thermolysin,
renkamp et al.,[18] G. Parkin et al.[19] and Kläui et al.[21] were obtained by reaction of 6 and 8 with acetic acid. Fu-
with either octahedral[19] or tetrahedral[21] structures of the ture work has to define a synthetic way to obtain enantio-
complexes [Zn(TpR)2]. This redistribution seems to be fa- merically pure bis(pyrazol-1-yl)acetic acids and has to prove
voured by polar solvents and sterically less demanding li- whether the configuration of these is stable. This might be
gands, since the synthesis of [Zn(OAc)(bdtbpza)] (9) is less useful for structural model complexes of metalloenzymes
problematic. Crystals of compound 11 suitable for X-ray as well as for organometallic complexes with bis(pyrazol-1-
analysis were obtained from a solution in CHCl3 (Figure 5). yl)acetate ligands. The first examples of manganese, rhe-
Bond lengths and bond angles of 11 are summarised in nium and ruthenium complexes with non-chiral bis(pyra-
Table 4.
zol-1-yl)acetate ligands have already been published.[23]
Table 4. Selected bond lengths and angles of complex 11
Experimental Section
˚
Distance [A]
11
Angle [°]
11
General: All experiments were carried out in Schlenk tubes using
suitable purified solvents. Microcrystalline precipitates were separ-
ated by centrifugation with a Hettich Rotina 46 R Schlenk tube
Zn(1)ϪN(11)
Zn(1)ϪN(21)
Zn(1)ϪN(21A)
Zn(1)ϪO(1)
2.156(3)
N(11)ϪZn(1)ϪN(21)
O(1)ϪZn(1)ϪN(11)
O(1)ϪZn(1)ϪN(21)
83.99(9)
86.66(10)
89.62(8)
2.3456(17)
2.7319(18)
2.006(3)
1
centrifuge. IR: Biorad FTS 60, CaF2 cuvets (0.5 mm). H and 13C
Zn(1)ϪZn(1A)
0.405(2)
NMR: Bruker WM 250, Bruker AC 250, JEOL GX 400, δ values
relative to TMS; in some cases the 13C NMR signals of quaternary
carbon atoms were too weak to be detected. EI-MS and FAB MS:
modified Finnigan MAT 312. Elemental analyses: Analytical
Laboratory of the Fachbereich Chemie, Universität Konstanz. A
modified Siemens P4 diffractometer was used for X-ray structure
determinations. 3,5-Dimethylpyrazole, 2,2,6,6-tetramethyl-3,5-hep-
tanedione, Zn(CH3)2 solution, Zn(CH2CH3)2 solution and ZnCl2
were used as purchased. 1-Chloromethyl-3,5-dimethylpyrazole hy-
drochloride was synthesised according to the literature.[24] 3,5-Di-
tert-butylpyrazole was obtained by a standard literature method
from 2,2,6,6-tetramethyl-3,5-heptanedione and hydrazine hy-
drate.[25] The synthesis of bis(3,5-di-tert-butylpyrazol-1-yl)acetic
acid (bdtbpzaH) (2) via bis(3,5-di-tert-butylpyrazol-1-yl)methane
(1) was reported recently.[8]
A structural model with the zinc atom in the centre of
the symmetry resembled that of [Zn(bdmpza)2], which we
reported recently.[8] The main differences were the extraor-
dinary long bonds of the Zn atom to each of the nitrogen
atoms of the two 3,5-di-tert-butylpyrazol-1-yl rings. This
˚
distance ZnϪN(21) [2.5369(14) A] was in between that of
[Zn(bdmpza)2] [2.180(3) A] and the sum of the van der
˚
˚
˚
Waals radii [N 1.55 A; Zn 1.40 A]. Until now examples of
octahedral zinc complexes with a longer ZnϪN distance
were rare, and in most cases were caused by a disorder.[22]
In addition to the long bond the thermal ellipsoid of the
zinc atom is rather elongated towards the two 3,5-di-tert-
butylpyrazol-1-yl rings. Therefore, the zinc atom in 11 is
disordered with two equally occupied positions slightly off
the centre of symmetry; 11 exhibits a distorted square-pyr-
amidal coordination with the 3,5-di-tert-butylpyrazol-1-yl
group slightly bent away from the ZnϪN(21) axis and the
other 3,5-di-tert-butylpyrazol-1-yl group has a weak inter-
Ligand Syntheses
Synthesis of 3,5-Di-tert-butyl-1-[(3,5-dimethyl-1H-pyrazol-1-yl)me-
thyl]-1H-pyrazole (bpmtBu2,Me2) (3): 3,5-Dimethylpyrazole (6.93 g,
72.1 mmol), 3,5-di-tert-butylpyrazole (13.0 g, 72.1 mmol), KOH
(8.42 g, 150 mmol), K2CO3 (20.7 g, 150 mmol) and benzyltriethyl-
ammonium chloride (2.00 g) were dissolved in dichloromethane
action with the zinc ion from the base direction of the pyr- (300 mL) and heated under reflux for 12 h. Salts were removed by
filtration and the filtrate was concentrated in vacuo to dryness. The
white residue was dissolved in water and extracted with pentane (4
ϫ 200 mL). The organic layer was dried (Na2SO4) and the solvent
removed in vacuo yielding a crude mixture of bis(3,5-dimethylpyra-
zol-1-yl)methane (bdmpzm), bis(3,5-di-tert-butylpyrazol-1-yl)me-
thane (bdtbpzm) (1) and 3,5-di-tert-butyl-1-[(3,5-dimethyl-1H-pyr-
azol-1-yl)methyl]-1H-pyrazole (bpmtBu2,Me2) (3). Column chroma-
tography with pentane on silica (20 cm) yielded a fraction of
bdtbpzm (1) and with pentane/ethyl acetate (14:1) a pure fraction
of bpmtBu2,Me2 (3). The solutions were dried (Na2SO4) and solvents
were evaporated; bdtbpzm (yield 8.52 g, 63%) was used as de-
amid.
Conclusions
A synthetic route to a racemic mixture of the new chiral
scorpionate ligand (3,5-di-tert-butylpyrazol-1-yl)(3Ј,5Ј-
dimethylpyrazol-1-yl)acetic acid (4) was found via 3,5-di-
tert-butyl-1-[(3,5-dimethyl-1H-pyrazol-1-yl)methyl]-1H-
pyrazole (3). It is sterically less hindered than the recently
published bis(3,5-di-tert-butylpyrazol-1-yl)acetic acid (2), scribed earlier to synthesise bdtbpza (3).[8] The white residue of
Eur. J. Inorg. Chem. 2003, 339Ϫ347 343

I. Hegelmann, A. Beck, C. Eichhorn, B. Weibert, N. Burzlaff
FULL PAPER
bpmtBu2,Me2 (3) was recrystallised from acetone to give 3 as colour-
less crystals, which were dried in vacuo. Rf (pentane/ethyl acetate,
14:1, v/v, silica 60 plate, ammonium vanadate stain) ϭ 0.78
CH3), 6.00 (s, 1 H, Hpz), 6.09 (s, 1 H, Hpz), 6.82 (s, 1 H, CH) ppm.
13C NMR (CDCl3, 62.5 MHz): δ ϭ 11.5 (CH3), 13.6 (CH3), 30.1
(CH3), 30.4 (CH3), 31.6 (C-tBu), 32.5 (C-tBu), 70.0 (CH), 103.1
[bdtbpzm (1)], 0.30 [bpmtBu2,Me2 (3)]; yield (3) 3.52 g (17%); m.p. (Cpz), 107.8 (Cpz), four Cpz signals not detected, 164.6 (CO2Ϫ) ppm.
1
75 °C. H NMR (CDCl3, 250 MHz): δ ϭ 1.25 (s, 9 H, CH3), 1.37
EI MS (70 eV, 270 °C): m/z (%) ϭ 430 (2) [Mϩ], 386 (48) [Mϩ
Ϫ
(s, 9 H, CH3), 2.18 (s, 3 H, CH3), 2.32 (s, 3 H, CH3), 5.78 (s, 1 H, CO2], 329 (100) [Mϩ Ϫ CO2 Ϫ C4H9], 290 (22) [Mϩ Ϫ C5H8N2 Ϫ
Hpz), 5.86 (s, 1 H, Hpz), 6.27 (s, 2 H, CH2) ppm. 13C NMR (CDCl3, CO2], 108 (39) [C6H8N2]. IR (CH2Cl2): ν˜ ϭ 1687 br (as-CO2Ϫ),
62.5 MHz): δ ϭ 11.4 (CH3), 13.4 (CH3), 30.3 (CH3), 30.4 (CH3), 1561 (CϭN), 1548 (CϭN), 1468 (s-CO2Ϫ) cmϪ1. IR (KBr): ν˜ ϭ
31.6 (C-tBu), 31.9 (C-tBu), 63.1 (CH2), 101.0 (Cpz), 106.5 (Cpz), 1696 (as-CO2Ϫ), 1558 (CϭN), 1547 (CϭN), 1467 (s-CO2Ϫ) cmϪ1
.
141.2 (Cpz), 147.6 (Cpz), 152.6 (Cpz), 160.1 (Cpz) ppm. EI MS
C18H27ClN4O2Zn (432.27): calcd. C 50.01, H 6.30, N 12.96; found
(70 eV): m/z (%) ϭ 288 (26) [Mϩ], 193 (30) [Mϩ Ϫ C5H7N2], 108 C 49.86, H 6.51, N 12.68.
(100) [Mϩ Ϫ C11H19N2]. IR (THF): ν˜ ϭ 1559 (CϭN), 1541 (CϭN)
Method A. General Procedure for Bis(pyrazol-1-yl)acetato(alkyl)-
zinc Complexes: A solution of a sterically demanding bis(pyrazol-
1-yl)acetic acid in diethyl ether was added to a slight excess of dial-
kylzinc in diethyl ether. Gas evolution was observed. The solution
was stirred at ambient temperature for 1 h. After this time, gas
evolution had ceased and the solvent was evaporated. The white
residue was dissolved in CH2Cl2 or benzene and filtered through
Celite. The solvent was again removed in vacuo to yield the product
as a white residue.
cmϪ1. C17H28N4 (288.44): calcd. C 70.79, H 9.78, N 19.42; found C
70.99, H 9.88, N 19.17. Reaction of 1-chloromethyl-3,5-dimethyl-
pyrazole hydrochloride with 1 equiv. of 3,5-di-tert-butylpyrazole,
traces of benzyltriethylammonium chloride and excess of KOH and
K2CO3 in THF yielded an identical sample of 3.
Synthesis of (3,5-Di-tert-butylpyrazol-1-yl)(3Ј,5Ј-dimethylpyrazol-1-
yl)acetic Acid (bpaHtBu2,Me2) (4): A solution of 3,5-di-tert-butyl-1-
[(3,5-dimethyl-1H-pyrazol-1-yl)methyl]-1H-pyrazole (bpmtBu2,Me2
)
(3) (6.50 g, 22.5 mmol) in THF (100 mL) was treated with nBuLi
(ca. 1.6  solution in hexane, 15.0 mL, 24.0 mmol) at Ϫ70 °C. The
solution was heated to Ϫ45 °C over a period of 2 h and finally
flushed with a flow of carbon dioxide. At ambient temperature, the
solvent was removed in vacuo and the white residue dissolved in
water (100 mL). The aqueous solution was acidified with concen-
trated HCl to a pH value of 1 and extracted with diethyl ether (4
ϫ 200 mL). The combined organic layers were dried (Na2SO4) and
concentrated in vacuo to give a white residue. The residue was
Synthesis of [Zn(bdtbpza)(CH3)] (6): Reaction of bis(3,5-di-tert-bu-
tylpyrazol-1-yl)acetic acid (bdtbpzaH) (2) (500 mg, 1.20 mmol) in
diethyl ether (10 mL) with Zn(CH3)2 (0.620 mL of a 2  solution
in toluene, 1.24 mmol) in diethyl ether (10 mL) according to
Method A and subsequent workup with CH2Cl2 (20 mL) yielded
product 6 as a white residue. Yield 550 mg (92%); m.p. 229 °C
(dec.). 1H NMR (CDCl3, 250 MHz): δ ϭ Ϫ0.35 (s, 3 H, CH3), 1.36
(s, 18 H, CH3), 1.53 (s, 18 H, CH3), 6.08 (s, 2 H, Hpz), 7.32 (s, 1
H, CH) ppm. 13C NMR (CDCl3, 62.5 MHz): δ ϭ Ϫ10.1 (CH3-Zn),
30.2 (CH3), 31.2 (CH3), 32.0 (C-tBu), 32.3 (C-tBu), 72.1 (CH),
103.1 (Cpz), 155.1 (Cpz), 163.1 (Cpz), 166.3 (CO2Ϫ) ppm. EI MS
washed with pentane (2
ϫ 200 mL) to remove unchanged
bpmtBu2,Me2 (3) and dried in vacuo to yield (3,5-di-tert-butylpyra-
zol-1-yl)(3Ј,5Ј-dimethylpyrazol-1-yl)acetic acid (bpaHtBu2,Me2) (4)
as a colourless powder. Yield 4.00 g (53%); m.p. 172 °C (dec.). H
(70 eV, 180 °C): m/z (%) ϭ 481 (18) [Mϩ Ϫ CH3], 452 (8) [Mϩ
Ϫ
1
CO2], 435 (100) [Mϩ Ϫ C4H9], 393 (83) [Mϩ Ϫ CO2 Ϫ C4H9], 371
(71) [Mϩ Ϫ Zn Ϫ CH3 Ϫ CO2], 321 (12) [Mϩ Ϫ Zn Ϫ CH3 Ϫ CO2
Ϫ 2 C4H9], 57 (62) [C4H9]. IR (CH2Cl2): ν˜ ϭ 1673 (as-CO2Ϫ), 1543
(CϭN), 1465 (s-CO2Ϫ) cmϪ1. C25H42N4O2Zn (496.01): calcd. C
60.54, H 8.53, N 11.30; found C 60.50, H 8.72, N 11.30.
NMR (CDCl3, 250 MHz): δ ϭ 1.25 (s, 9 H, CH3), 1.28 (s, 9 H,
CH3), 2.11 (s, 3 H, CH3), 2.19 (s, 3 H, CH3), 5.82 (s, 1 H, Hpz),
5.98 (s, 1 H, Hpz), 7.14 (s, 1 H, CH), 11.09 (br. s, 1 H, CO2H) ppm.
13C NMR (CDCl3, 62.5 MHz): δ ϭ 11.5 (CH3), 13.1 (CH3), 30.1
(CH3), 30.3 (CH3), 31.6 (C-tBu), 32.1 (C-tBu), 72.6 (CH), 102.0
(Cpz), 108.1 (Cpz), 141.3 (Cpz), 148.6 (Cpz), 154.7 (Cpz), 160.3 (Cpz),
166.1 (CO2H) ppm. EI MS (70 eV, 160 °C): m/z (%) ϭ 332 (7)
[Mϩ], 288 (20) [Mϩ Ϫ CO2], 193 (100) [Mϩ Ϫ C5H7N2 Ϫ CO2],
109 (58) [Mϩ Ϫ C11H19N2 Ϫ CO2], 57 (20) [C4H9]. IR (THF):
ν˜ ϭ 1758 (CO2H), 1560 (CϭN), 1546 (CϭN) cmϪ1. C18H28N4O2
(332.45): calcd. C 65.03, H 8.49, N 16.85; found C 64.79, H 8.76,
N 16.31.
Synthesis of [Zn(bdtbpza)(CH2CH3)] (7): Reaction of bis(3,5-di-
tert-butylpyrazol-1-yl)acetic acid (bdtbpzaH) (2) (500 mg,
1.20 mmol) in diethyl ether (20 mL) with Zn(CH2CH3)2 (1.30 mL
of a 1  solution in hexane, 1.30 mmol) in diethyl ether (10 mL)
according to Method A and subsequent workup with CH2Cl2
(20 mL) yielded product 7 as a white residue. Yield 502 mg (82%);
m.p. 168Ϫ170 °C. 1H NMR (CDCl3, 250 MHz): δ ϭ 0.52 (q,
3
3JH,H ϭ 8.0 Hz, 2 H, CH2), 1.29 (t, JH,H ϭ 8.0 Hz, 3 H, CH3),
Synthesis of Model Compounds
1.35 (s, 18 H, CH3), 1.52 (s, 18 H, CH3), 6.06 (s, 2 H, Hpz), 7.30
(s, 1 H, CH) ppm. 13C NMR (CDCl3, 62.5 MHz): δ ϭ 3.3 (CH2),
11.9 (CH3), 30.2 (CH3), 31.2 (CH3), 32.0 (C-tBu), 32.3 (C-tBu),
72.1 (CH), 103.1 (Cpz), 155.1 (Cpz), 163.0 (Cpz), 166.6 (CO2Ϫ) ppm.
EI MS (70 eV, 240 °C): m/z (%) ϭ 479 (40) [Mϩ Ϫ CH2CH3], 435
(96) [Mϩ Ϫ CH2CH3 Ϫ CO2], 407 (56) [Mϩ Ϫ CO2 Ϫ C4H9], 371
(100) [Mϩ Ϫ CH2CH3 Ϫ CO2 Ϫ Zn], 321 (14) [Mϩ Ϫ CH2CH3 Ϫ
CO2 Ϫ Zn Ϫ 2 C4H9], 193 (53) [C12H21N2], 57 (43) [C4H9]. IR
Synthesis of [Zn(bpatBu2,Me2)Cl]2 (5): ZnCl2 (200 mg, 1.47 mmol)
was added to a solution of (3,5-di-tert-butylpyrazol-1-yl)(3,5-di-
methylpyrazol-1-yl)acetic acid (bpaHtBu2,Me2
)
(4) (400 mg,
1.20 mmol) in acetonitrile (30 mL), and the solution was stirred
vigorously at ambient temperature. After 5 min, potassium tert-bu-
toxide (135 mg, 1.20 mmol) was added. Within 1 min, a white pre-
cipitate formed. After 2 h, the solvent was removed in vacuo. The
residue was dissolved in dichloromethane (15 mL) and salts were
separated by centrifugation or filtration through Celite. Dichloro-
methane was removed in vacuo, the residue washed with diethyl
ether (2 ϫ 10 mL) and dried in vacuo to afford [Zn(bpatBu2,Me2)Cl]2
(5) as a white crystal powder. An air-exposed solution in dichloro-
methane at room temperature yielded, within 1 d, prism-like col-
(CH2Cl2): ν˜ ϭ 1671 (as-CO2Ϫ), 1544 (CϭN), 1465 (s-CO2Ϫ) cmϪ1
.
C26H44N4O2Zn (510.04): calcd. C 61.23, H 8.70, N 10.98; found C
60.75, H 8.82, N 10.43.
Synthesis of [Zn(bpatBu2,Me2)(CH3)] (8): Reaction of (3,5-di-tert-bu-
tylpyrazol-1-yl)(3,5-dimethylpyrazol-1-yl)acetic acid (bpaHtBu2,Me2
)
ourless crystals suitable for X-ray structure determination. Yield (4) (0.970 g, 2.92 mmol) in diethyl ether (20 mL) with Zn(CH3)2
390 mg (75%); m.p. 259 °C. 1H NMR (CDCl3, 250 MHz): δ ϭ 1.37 (1.65 mL of a 2  solution in toluene, 3.30 mmol) in diethyl ether
(s, 9 H, CH3), 1.48 (s, 9 H, CH3), 2.47 (s, 3 H, CH3), 2.50 (s, 3 H, (20 mL) according to Method A and subsequent workup with
344
Eur. J. Inorg. Chem. 2003, 339Ϫ347

Alkylzinc Complexes with N,N,O Heteroscorpionate Ligands
FULL PAPER
CH2Cl2 (20 mL) yielded product 8 as a white residue. Yield 1.12 g
(93%); m.p. 187 °C. H NMR (CDCl3, 250 MHz): δ ϭ Ϫ0.42 (s, 3 [ZnOAc(bdtbpza)] (9) as a white crystalline powder. A similar re-
acid (100%, 70.0 µL, 1.22 mmol) according to Method B afforded
1
H, CH3), 1.38 (s, 9 H, CH3), 1.52 (s, 9 H, CH3), 2.30 (s, 3 H, CH3), sult in yield and purity was obtained from an acetonitrile solution.
2.50 (s, 3 H, CH3), 5.99 (s, 1 H, Hpz), 6.01 (s, 1 H, Hpz), 6.89 (s, 1
Yield 400 mg (77%); m.p. 109Ϫ111 °C. 1H NMR (CDCl3,
H, CH) ppm. 13C NMR (CDCl3, 62.5 MHz): δ ϭ Ϫ14.1 (CH3- 250 MHz): δ ϭ 1.37 (s, 18 H, CH3), 1.53 (s, 18 H, CH3), 2.12 (s, 3
1
Zn), 11.5 (CH3), 12.9 (CH3), 30.3 (CH3), 30.5 (CH3), 31.5 (C-tBu), H, CH3ϪAc), 6.12 (s, 2 H, Hpz), 7.36 (s, 1 H, CH) ppm. H NMR
32.1 (C-tBu), 70.2 (CH), 102.1 (Cpz), 107.3 (Cpz), 141.6 (Cpz), 150.7 (C6D6, 250 MHz): δ ϭ 1.21 (s, 18 H, CH3), 1.43 (s, 18 H, CH3),
(Cpz), 154.1 (Cpz), 162.7 (Cpz), 165.4 (CO2Ϫ) ppm. FAB MS 1.93 (s, 3 H, CH3ϪAc), 6.01 (s, 2 H, Hpz), 7.55 (s, 1 H, CH) ppm.
(NBOH matrix): m/z (%) ϭ 809 (21) [M2Hϩ Ϫ CH3], 763 (10) 13C NMR (CDCl3, 62.5 MHz): δ ϭ 21.1 (CH3-Ac), 29.9 (CH3),
[M2Hϩ Ϫ CH3 Ϫ CO2], 411 (100) [MHϩ], 395 (9) [Mϩ Ϫ CH3], 31.0 (CH3), 32.0 (C-tBu), 32.3 (C-tBu), 72.6 (CH), 103.4 (Cpz),
365 (31) [Mϩ Ϫ CO2H], 351 (78) [Mϩ Ϫ CH3 Ϫ CO2], 287 (86) 155.7 (Cpz), 163.2 (Cpz), 166.0 (CO2Ϫ), 178.2 (CO2Ϫ) ppm. 13C
[Mϩ Ϫ CH3 Ϫ CO2 Ϫ Zn]. IR (CH2Cl2): ν˜ ϭ 1669 (as-CO2Ϫ), NMR (C6D6, 62.5 MHz): δ ϭ 21.9 (CH3-Ac), 30.5 (CH3), 30.8
1559 (CϭN), 1539 (CϭN), 1466 (s-CO2Ϫ) cmϪ1. C19H30N4O2Zn
(411.85): calcd. C 55.41, H 7.34, N 13.60; found C 55.02, H 7.21,
N 13.62.
(CH3), 32.2 (C-tBu), 32.4 (C-tBu), 75.0 (CH), 103.0 (Cpz), 154.7
(Cpz), 161.8 (Cpz), 168.5 (CO2Ϫ), 179.8 (CO2Ϫ) ppm. EI MS (70 eV,
200 °C): m/z (%) ϭ 494 (55) [Mϩ Ϫ CO2], 479 (43) [Mϩ
Ϫ
CO2CH3], 437 (85) [Mϩ Ϫ CO2 Ϫ C4H9], 371 (61) [Mϩ Ϫ CO2CH3
Ϫ CO2 Ϫ Zn], 193 (100) [C12H21N2], 179 (66) [C11H19N2]. IR
(CH2Cl2): ν˜ ϭ 1681 (as-CO2Ϫ), 1633 (as-CO2Ϫ), 1602 (as-CO2Ϫ),
1546 (CϭN), 1467 (s-CO2Ϫ) cmϪ1. C26H42N4O4Zn (540.02): calcd.
C 57.83, H 7.84, N 10.37; found C 58.00, H 8.20, N 10.98.
Method B. General Procedure for Acetato[bis(pyrazol-1-yl)acetato]-
zinc Complexes: An excess of acetic acid was added to a solution
of a methyl[bis(pyrazol-1-yl)acetato]zinc complex in benzene. Gas
evolution was observed. The solution was stirred at ambient tem-
perature for 30 min. After this time, gas evolution had ceased, the
solution was filtered through Celite and the volume of the solution
was reduced in vacuo to 1 mL. The product was precipitated with
hexane and dried in vacuo to yield the product as a white solid.
Synthesis of [Zn(OAc)(bpatBu2,Me2)] (10): Reaction of [Zn-
(bpatBu2,Me2)(CH3)] (8) (400 mg, 0.971 mmol) in benzene (5 mL) with
acetic acid (100%, 57.0 µL, 1.00 mmol) according to Method B but
without filtration through Celite afforded [Zn(OAc)(bpatBu2,Me2)]
(10) as a white crystalline powder. Yield 401 mg (91%); m.p.
Synthesis of [Zn(OAc)(bdtbpza)] (9): Reaction of [Zn(bdtbpza)-
(CH3)] (6) (480 mg, 0.968 mmol) in benzene (10 mL) with acetic
Table 5. Structure determination details of compounds 4, 5, 8 and 11
4
5
8
11
Empirical formula
C18H28N4O2
ϫ 1/3 C3H6O
351.80
colourless plate
rhombohedral
R-3
17.691(3)
17.691(3)
17.691(3)
115.061(12)
115.061(12)
115.061(12)
3081.4(22)
2.32Ϫ27.00
Ϫ19 to 22
Ϫ22 to 22
Ϫ22 to 22
1144
C18H27ClN4O2Zn
ϫ 1.5 CH2Cl2
559.65
colourless column
monoclinic C
C2/c
14.008(14)
20.489(15)
19.101(19)
90.00
104.15(4)
90.00
C19H30N4O2Zn
ϫ CH2Cl2
496.77
colourless plate
monoclinic P
P21/c
11.599(14)
21.658(17)
11.130(8)
90.00
116.35(8)
90.00
2505(4)
2.17Ϫ24.01
Ϫ13 to 12
Ϫ1 to 24
Ϫ1 to 12
1040
C18H27N4O2Zn0.5
ϫ CHCl3
483.49
colourless block
monoclinic P
P21/n
9.8566(4)
22.2125(9)
11.3820(5)
90.000(1)
112.300(1)
90.000(1)
2305.60(17)
1.83Ϫ28.20
Ϫ12 to 12
Ϫ29 to 28
Ϫ15 to 15
1008
Formula mass
Crystal colour/habit
Crystal system
Space group
˚
a [A]
˚
b [A]
˚
c [A]
α [°]
β [°]
γ [°]
3
˚
V [A ]
5316(8)
θ [°]
h
k
l
2.20Ϫ27.01
Ϫ17 to 17
Ϫ26 to 26
Ϫ24 to 24
2312
F(000)
Z
6
8
4
4
µ(Mo-Kα) [mmϪ1
]
0.076
1.348
1.215
0.927
Crystal size [mm]
0.5 ϫ 0.3 ϫ 0.15
1.138
188(2)
0.5 ϫ 0.3 ϫ 0.3
1.399
231(2)
0.2 ϫ 0.15 ϫ 0.1
1.317
258(2)
0.3 ϫ 0.2 ϫ 0.2
1.393
143(2)
Dcalcd. [gcmϪ1
T [K]
]
Reflections collected
Independent reflections
Obsd. refl. (Ͼ 2σI)
Parameter
Weight parameter a
Weight parameter b
R1 (obsd.)
9037
4371
3396
242
0.1050
2.1776
0.0700
11494
5797
4321
307
0.0465
3.8902
0.0412
4869
3926
1787
262
0.0411
0.2667
0.0748
36682
5423
4866
262
0.0527
1.1558
0.0377
R1 (overall)
wR2 (obsd.)
0.0868
0.1875
0.0635
0.0954
0.1887
0.1155
0.0421
0.1011
wR2 (overall)
Diff. peak/hole [e/A ]
0.2035
0.812/Ϫ0.617
0.1055
0.497/Ϫ0.609
0.1512
0.316/Ϫ0.387
0.1035
0.681/Ϫ0.631
3
˚
Eur. J. Inorg. Chem. 2003, 339Ϫ347
345

I. Hegelmann, A. Beck, C. Eichhorn, B. Weibert, N. Burzlaff
FULL PAPER
196 °C (dec.). 1H NMR (CDCl3, 250 MHz): δ ϭ 1.33 (s, 9 H, CH3), in Table 5. The structure pictures were prepared with the program
1.51 (s, 9 H, CH3), 2.10 (s, 3 H, CH3), 2.36 (s, 3 H, CH3), 2.49 (s, Diamond 2.1c.[27] CCDC-184127 [Zn(bpatBu2,Me2)Cl]2 (5), -184128
3 H, CH3ϪOAc), 6.00 (s, 1 H, Hpz), 6.07 (s, 1 H, Hpz), 6.88 (s, 1 [Zn(bpatBu2,Me2)(CH3)] (8) and -184129 [Zn(bpatBu2,Me2)2] (11) con-
1
H, CH) ppm. H NMR (C6D6, 250 MHz): δ ϭ 1.24 (s, 9 H, CH3), tain the supplementary crystallographic data for this paper. These
1.36 (s, 9 H, CH3), 1.92 (s, 3 H, CH3), 1.97 (s, 3 H, CH3), 2.31 (s, data can be obtained free of charge at www.ccdc.cam.ac.uk/conts/
3 H, CH3-OAc), 5.39 (s, 1 H, Hpz), 5.96 (s, 1 H, Hpz), 6.97 (s, 1 H,
retrieving.html or from the Cambridge Crystallographic Data
CH) ppm. 13C NMR (CDCl3, 62.5 MHz): δ ϭ 11.8 (CH3), 13.1 Centre, 12, Union Road, Cambridge CB2 1EZ, UK [Fax: (in-
(CH3), 22.1 (CH3-OAc), 30.1 (CH3), 30.7 (CH3), 31.8 (C-tBu), 32.3
(C-tBu), 70.5 (CH), 102.9 (Cpz), 108.0 (Cpz), 142.6 (Cpz), 152.3
(Cpz), 156.0 (Cpz), 164.3 (Cpz), 165.1 (CO2Ϫ), 181.2 (CO2Ϫ) ppm.
EI MS (70 eV, 230 °C): m/z (%) ϭ 410 (18) [Mϩ Ϫ CO2], 353 (58)
[Mϩ Ϫ CO2 Ϫ C4H9], 288 (100) [Mϩ Ϫ CO2 Ϫ O2CCH3 Ϫ Zn],
ternat.) ϩ 44-1223/336-033; E-mail: deposit@ccdc.cam.ac.uk].
Acknowledgments
193 (30) [C12H21N2], 109 (44) [C6H9N2]. IR (CH2Cl2): ν˜ ϭ 1677 Generous financial support by the Fonds der Chemischen Industrie
(as-CO2Ϫ), 1624 (as-CO2Ϫ), 1601 (as-CO2Ϫ), 1562 (CϭN), 1544 (Liebig-Stipendium to N. B.) and the European Commission
(CϭN), 1467 (s-CO2Ϫ), 1442 (s-CO2Ϫ), 1427 (s-CO2Ϫ) cmϪ1
C20H30N4O4Zn (455.86): calcd. C 52.70, H 6.63, N 12.29; found C
52.55, H 6.51, N 11.74.
.
(Copernicus 2 Program, Contract no. ICA2-CT-2000Ϫ10002) is
gratefully acknowledged. Special thanks to Prof. Dr. H. Fischer for
support and discussion and also to Prof. Dr. W. A. Schenk for giving
us access to a Bruker Smart Apex in Würzburg. We are indebted to
Mr. Hägele and Mr. Galetskiy for recording mass spectra.
Synthesis of [Zn(OAc)(bpatBu2,Me2)] (10) in Acetonitrile: Reaction
of [Zn(bpatBu2,Me2)(CH3)] (8) (310 mg, 0.753 mmol) in acetonitrile
(5 mL) with acetic acid (100%, 80.0 µL, 1.40 mmol) according to
Method B afforded [Zn(OAc)(bpatBu2,Me2)] (10) as a white crystal-
line powder. The spectroscopic data are identical to those of 10
that was obtained in benzene solution. Yield (10) 162 mg (47%).
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1
80.0 mg (29%); m.p. 207 °C (dec.). H NMR (CDCl3, 400 MHz):
δ ϭ 1.08 (s, 9 H, CH3), 1.53 (s, 9 H, CH3), 1.92 (s, 3 H, CH3) 2.42
(s, 3 H, CH3), 5.86 (s, 1 H, Hpz), 5.96 (s, 1 H, Hpz), 6.90 (s, 1 H,
CH) ppm. 13C NMR (CDCl3, 62.5 MHz): δ ϭ 11.8 (CH3), 13.1
(CH3), 30.1 (CH3), 30.8 (CH3), 31.6 (C-tBu), 32.3 (C-tBu), 70.5
(CH), 102.6 (Cpz), 107.6 (Cpz), 140.8 (Cpz), 150.8 (Cpz), 153.0 (Cpz),
163.0 (Cpz), 166.4 (CO2Ϫ) ppm. EI MS (70 eV, 250 °C): m/z (%) ϭ
684 (0.5) [Mϩ Ϫ CO2], 353 (2) [C17H28N4 ϩ Zn], 288 (5.5)
[C17H28N4], 192 (26) [C12H20N2], 177 (100) [C11H17N2]. IR
(CH2Cl2): ν˜ ϭ 1664 (as-CO2Ϫ), 1562 (CϭN), 1540 (CϭN), 1466
(s-CO2Ϫ) cmϪ1. C36H54N8O4Zn·2 CHCl3 (967.01): calcd. C 47.39,
H 5.87, N 11.64; found C 47.08, H 6.02, N 11.41.
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346
Eur. J. Inorg. Chem. 2003, 339Ϫ347

Alkylzinc Complexes with N,N,O Heteroscorpionate Ligands
FULL PAPER
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