Mechanistic studies on the alcoholysis and aminolysis of [(MeZn)2{μ-N(H)tBu}{μ-N(CH2Py)2}]

Article abstract of DOI:10.1016/j.jorganchem.2009.09.041

The reaction of bis(2-pyridylmethyl)amine (II) with t-butylamine and dimethylzinc gives the heteroleptic [(MeZn)₂{μ-N(H)tBu}{μ-N(CH₂Py)₂}] (1). Stoichiometric alcoholysis of 1 with methanol leads to the exchange of the μ-N(H)tBu moiety. Almost quantitatively the corresponding methoxide [(MeZn)₂(μ-OMe){μ-N(CH₂Py)₂}] (2) is formed. Alternatively bis(alkylzinc)methoxide-bis(2-pyridylmethyl)amides (Alkyl = methyl (2), bis(trimethylsilyl)methyl) (3)) are also accessible by direct zincation of bis(2-pyridylmethyl)amine (II) and methanol with dialkylzinc regardless of the bulkiness of the alkyl groups. Extensive DFT calculations on the alcoholysis mechanism reveal the preferential insertion of methanol into a zinc amide bond rather than the cleavage of zinc carbon bonds. An intermediate with a Zn[μ-(MeO?H?NHR)]Zn functionality is predicted. Aminolyis of 1 with t-butylamine leads to intermediates with Zn[μ-(RNH ? H ? NHR)]Zn functionalities, respectively. We were able to detect the latter by ¹H NMR spectroscopy. The aminolysis of 1 with an excess of phenylamine results in a partial decomposition of the complex leading to the hexanuclear amide [{Zn(μ-N(H)Ph)}{MeZn(μ-N(H)Ph)}₂{μ-N(CH₂Py)₂}]₂ (4). Compound 2 is able to cleave silicon grease when dissolved in t-butylamine yielding [(MeZn)₂{μ-N(CH₂Py)₂}₂Zn{μ-(OMe₂Si)₂O}] (5). The X-ray structures of complexes 1-5 are discussed.

Full text of DOI:10.1016/j.jorganchem.2009.09.041

Journal of Organometallic Chemistry 695 (2010) 280–290
Contents lists available at ScienceDirect
Journal of Organometallic Chemistry
journal homepage: www.elsevier.com/locate/jorganchem
Mechanistic studies on the alcoholysis and aminolysis
of [(MeZn)2{l-N(H)tBu}{l-N(CH2Py)2}]
Marcel Kahnes a, Julia Richthof a, Helmar Görls a, Daniel Escudero b, Leticia González b,
,
*
Matthias Westerhausen a,
*
a Institut für Anorganische und Analytische Chemie, August-Bebel-Str. 2, 07743 Jena, Germany
b Institut für Physikalische Chemie, Helmholtzweg 4, 07743 Jena, Germany
a r t i c l e i n f o
a b s t r a c t
Article history:
The reaction of bis(2-pyridylmethyl)amine (II) with t-butylamine and dimethylzinc gives the heteroleptic
[(MeZn)2{ -N(H)tBu}{ -N(CH2Py)2}] (1). Stoichiometric alcoholysis of 1 with methanol leads to the
exchange of the -N(H)tBu moiety. Almost quantitatively the corresponding methoxide [(MeZn)2(
OMe){ -N(CH2Py)2}] (2) is formed. Alternatively bis(alkylzinc)methoxide-bis(2-pyridylmethyl)amides
(Alkyl = methyl (2), bis(trimethylsilyl)methyl) (3)) are also accessible by direct zincation of bis(2-pyridyl-
methyl)amine (II) and methanol with dialkylzinc regardless of the bulkiness of the alkyl groups. Exten-
sive DFT calculations on the alcoholysis mechanism reveal the preferential insertion of methanol into a
Received 31 July 2009
Received in revised form 17 September
2009
Accepted 26 September 2009
Available online 9 October 2009
l
l
l
l-
l
Keywords:
Alkylzinc compounds
zinc amide bond rather than the cleavage of zinc carbon bonds. An intermediate with a Zn[l-
(MeOꢀ ꢀ ꢀHꢀ ꢀ ꢀNHR)]Zn functionality is predicted. Aminolyis of 1 with t-butylamine leads to intermediates
l-OMe, l-N(H)R functionalities
with Zn[
l
-(RNH ꢀ ꢀ ꢀ H ꢀ ꢀ ꢀ NHR)]Zn functionalities, respectively. We were able to detect the latter by 1H
Three-centered X–H–Y bonds
Mechanistic studies
NMR spectroscopy. The aminolysis of 1 with an excess of phenylamine results in a partial decomposition
DFT calculations
of the complex leading to the hexanuclear amide [{Zn(
(4). Compound 2 is able to cleave silicon grease when dissolved in t-butylamine yielding [(MeZn)2{
N(CH2Py)2}2Zn{ -(OMe2Si)2O}] (5). The X-ray structures of complexes 1–5 are discussed.
l-N(H)Ph)}{MeZn(l-N(H)Ph)}2{l-N(CH2Py)2}]2
l
-
l
Ó 2009 Elsevier B.V. All rights reserved.
1. Introduction
behavior towards dialkylzinc compounds in order to obtain multi-
nuclear zinc complexes. (2-Pyridylmethyl)amine reacts with
dialkylzinc to form the corresponding alkylzinc (2-pyridyl-
methyl)amide which, depending on the size of the zinc bound alkyl
substituent, crystallizes either as dimer or trimer [5]. Zincation of
N-silylated (2-pyridylmethyl)amine (I) with alkylzinc reagents
yields the dimeric silylamide (III). Addition of an excess of dimeth-
ylzinc to complex III results in an oxidative C–C coupling reaction
giving dinuclear IV. In the course of the reaction metallic zinc pre-
cipitates and methane is liberated [6,7] (Fig. 2). The reaction of dip-
icolylamine (II) with equimolar amounts of dialkylzinc leads to the
formation of dimeric alkylzinc dipicolylamide regardless of the ste-
ric bulk of the alkyl substituent. In the solid state only one pyridyl
group of each ligand coordinates to the zinc ion [8,9], however, in
solution both pyridyl groups are equivalent on the NMR time scale
due to exchange processes. In this case additional dimethylzinc
does not lead to oxidative C–C coupling reactions, but metallation
of one methylene group, resulting in complex VII, is observed.
Thermolysis of V at approximately 300 °C reveals a novel and
completely unexpected reaction behavior of the ambidentante
dipicolylamide. In a dehydrogenation reaction zinc bis[1,3-di(2-
pyridyl)-2-azapropenide] (VIII) is formed, which sublimates as
gold-shining crystals [10]. Although the reaction mechanism
remains unknown compound VII is considered as key intermediate
Playing an essential role in protein degradation as well as in
metabolic cycles binuclear zinc hydrolases are widely spread
among both eucaryotes and procaryotes. As a common feature they
display a Zn–OH–Zn bridge in the active site [1] and a bridging car-
boxylate ligand as backbone, keeping the zinc ions in fixed posi-
tions. Additional ligands which bind via a nitrogen or an oxygen
donor saturate the coordination sphere (Fig. 1).
Insight into the chemical processes taking place at the active
side of the metallo-enzyme can be obtained by investigating the
enzymatic system itself or by choosing a biomimetic model, which
can be studied kinetically or with quantum chemical methods [2].
A comprehensive summary in the field of synthetic enzyme ana-
logues was recently provided by Parkin [3].
As advantageous ligands in bioinorganic chemistry (2-pyridyl-
methyl)amine (2-picolylamine) and their substitution products
are a subject of great interest for the synthesis of biomimetic mod-
els [3,4]. In recent years our group has studied their reaction
* Corresponding authors. Tel.: +49 (0)3641 9 48360; fax: +49 (0)3641 9 4830 (L.
González); tel.: +49 (0)3641 9 48110; fax: +49 (0)3641 9 48102 (M. Westerhausen).
E-mail addresses: leticia.gonzalez@uni-jena.de (L. González), m.we@uni-jena.de
(M. Westerhausen).
0022-328X/$ - see front matter Ó 2009 Elsevier B.V. All rights reserved.
doi:10.1016/j.jorganchem.2009.09.041

M. Kahnes et al. / Journal of Organometallic Chemistry 695 (2010) 280–290
281
plex IX (Fig. 3), in which the dipicolylamide serves as tetradentate
backbone. Though being significantly more acidic, an amine is
eliminated in the course of hydrolysis, whereas the Zn–C bond re-
mains intact. Extensive DFT calculations at the B3LYP/lanl2dz level
of theory confirm the mode of action of hydrolysis reasoned by the
preferential formation of a relatively stable intermediate with a
R
O
O
(O/N)2,3 Zn
Zn (N/O)2,3
O
H
Zn[
l
-(HOꢀ ꢀ ꢀHꢀ ꢀ ꢀNR)]Zn moiety [9].
The existence of Zn[
l
-(HOꢀ ꢀ ꢀHꢀ ꢀ ꢀOH)]Zn fragments has already
Fig. 1. Common structural motif for the active side of many zinc hydrolases.
been shown experimentally by several solid-state structures of
biomimetic zinc complexes [12]. Kinetic investigations on binu-
clear zinc complexes show that such H3O2 species are intrinsically
on the way to complex VIII. A similar behavior is observed for the
dibenzylamido anion ((PhCH2)2Nꢁ) which, mediated by PMDETA
((Me2NCH2CH2)2NMe) solvated Li+, Na+ and K+ counterions, readily
converts to the corresponding 1,3-diphenyl-2-azapropenide. In
this case the azaallyl conversion can be explained as a two-step
process consisting of a b-elimination of a metal hydride followed
by hydride metallation of the produced imine PhCH2N = C(H)Ph
[11].
more reactive than l-OH units [12,13]. Therefore the formation of
H3O2 functionalities is discussed as an important step in the mode
of action of binuclear zinc hydrolases [14] also being demonstrated
by a recent DFT study [15].
In the course of this work we like to expand the concept of the
hydrolysis of alkylzinc dipicolylamides in order to obtain new
binuclear zinc complexes with a bridging
l-OR moiety. Further-
Exposure of a concentrated solution of VI to air leads to a slow
partial hydrolysis resulting in the formation of the hydroxide com-
more, we investigated the generality of the occurence of Zn[
(Xꢀ ꢀ ꢀHꢀ ꢀ ꢀY)]Zn (X = O, N; Y = N) according to biomimetic models.
l-
R' =SiR''3 ; R =Me (III)
2 ZnR2
N
N
- 2 RH
R' = CH2-py
R= Me (V) ; CH(SiMe3)2 (VI)
2
N
Zn
N
H
R'
R'
R
2
R' = SiR''3 (I); CH2-py (II);
+ ZnMe2
R' =SiR''3
T
+ ZnMe2
R' = CH2-py
- Zn
- MeH
- 2 CH4
R' = CH2-py
N
N
N
R
N
N
N
R'
N
N
N
N
Zn
N
Zn
N
N
R
R'
Zn
Zn
Zn
R
R
N
Zn
N
N
R
VIII
R= Me (VII)
R =Me (IV)
Fig. 2. Reactivity of N-substituted 2-pyridylmethylamines towards dialkylzinc reagents.
N
N
R
R
Zn
N
Zn
N
+ H2O
N
- II
N
N
Zn
N
O
Zn
N
R
H
R
R= CH(SiMe3)2 (VI)
IX
N
N
R
N
Zn
O
Zn
NR'2
R
H
H
R' = CH2-py
Fig. 3. Hydrolysis of VI.

282
M. Kahnes et al. / Journal of Organometallic Chemistry 695 (2010) 280–290
2. Results and discussion
2.1. Synthesis and characterization of bis(methylzinc)t-butylamide-
bis(2-pyridylmethyl)amide (1)
In order to gain the ability of a kinetically controlled hydrolysis
the heteroleptic zinc amide 1 was synthesized with a chelating
dipicolylamide as backbone and a bridging t-butylamide as the
reactive site. Direct metallation of stoichiometric amounts of
t-butylamine and dipicolylamine (II) with dimethylzinc in toluene
leads to the desired complex which crystallizes with tetra-coordi-
nated zinc atoms (see Fig. 4).
The molecular structure of 1 (Fig. 5) shows a Zn2N2 unit as cen-
tral structural element with different endocyclic Zn1/2–N2 and
Zn1/2–N4 bond lengths. The latter are slightly shorter (ꢂ5 pm)
than the Zn1/2–N2 bonds (209.9 and 208.8 pm) but still slightly
elongated compared to those reported for trimeric [EtZnNHtBu]3
(202.0 pm) [16]. This effect is a consequence of the enlarged coor-
dination sphere of zinc in compound 1. The exocycylic Zn–Npyridyl
bonds (216.3 and 219.0 pm) are somewhat larger than the Zn1/
2–N2 distances due to reduced electrostatic attraction. Neverthe-
less, those bond lengths are very similar to those of complex V
Fig. 5. Molecular structure and numbering of 1. The hydrogen atoms with
exception of the amido group are omitted for clarity. The ellipsoids of all non-
hydrogen atoms represent a probability of 40%. Selected structural data can be
found in Table 1.
ment with the Zn–O bond lengths found in [EtZn(py)(
(198.8 pm) [18] and [EtZn(py)( -OCH(CF3)2)]2 (210.4 pm) [19].
l
-OtBu)]2
(Zn–Npy = 217.6 pm; Zn–(l-N) = 210.3 pm) [9]. The Zn1–C13 bond
l
length in 1 (198.2 pm) is comparable to the one reported for V
(199.0 pm) but slightly elongated compared to dimethylzinc
(195.5 pm) with a metal atom of the coordination number of two
[17]. The Zn2N2 ring is significantly folded (ꢂ28.2°) and shows a
transannular non-bonding Zn1 ꢀ ꢀ ꢀ Zn2 distance of 285.8 pm.
Alkylzinc alkoxides have recently gained interest as excellent pre-
cursors for the preparation of ceramic materials, nano particles and
ZnO films (MOCVD) with semiconducting properties [18–20] (see
Fig. 7).
An interesting feature is the differing geometry around O1 in
the methoxides 2 and 3. In 2 a planar environment is observed en-
abling a strong out of the plane oscillation of O1. In 3 a pyramidal
geometry is realized which is caused by steric repulsion between
the methoxy substituent and the bis(trimethylsilyl)methyl groups.
The transannular Zn1ꢀ ꢀ ꢀZn2 contact is very similar in both com-
plexes but slightly longer than in the folded ring structure of 1.
2.2. Partial methanolysis of 1 and the synthesis of
bis(alkylzinc)methoxide-bis(2-pyridylmethyl)amides
The reaction of V with water, even diluted as toluene solution,
was reported to proceed quite violently and resulted in decompo-
sition of the complex into numerous products [9]. In order to slow
down the protonation reaction we treated amide 1 with one equiv-
alent of methanol under kinetically controlled conditions (slow
warming from ꢁ78 °C to r.t.). In the course of the reaction the
2.3. NMR-investigations on 1, 2 and 3
In the 1H NMR spectra (C6D6) of 1, 2 and 3 the pyridyl reso-
nances are very much alike. The major difference is observed for
the Pyr 1 signal in 1 which splits up in two separate resonances
due to the neighboring N4 carrying different substituents. For the
very same reason the proton resonances of the methylene groups
in 1 give two anisochronic signals. The Pyr 1 resonance in 3 is
slightly shifted downfield compared to the corresponding signal
of 2. The 1H NMR spectra of the latter shows very broad signals,
possibly indicating the dismutation of the complex into different
aggregates of [(MeZnOMe)n] and dimeric V. A detailed theoretical
investigation on the oligomerisation process of [MeZnOMe] mono-
mers was given by Steudel et al. [21]. In the 13C NMR spectrum a
slight difference is only observed for the zinc bound methyl groups
in 1 and 2 which are shifted upfield (3.5 ppm) when changing to
Zn–O coordination.
l-N(H)tBu moiety was substituted by a l-OMe substituent quanti-
tatively yielding complex 2. As observed previously the Zn–C bond
was not affected by the alcoholysis. Alternatively, bis(alkyl-
zinc)methoxide-bis(2-pyridylmethyl)amides (2, 3) were also
accessible by zincation of stoichiometric amounts of methanol
and dipicolylamine II with dialkylzinc at low temperatures (Fig. 6)
A comparison of the molecular structures of 2 and 3 shows very
similar Zn1–N1 and Zn1–N2 bond lengths (Table 1) which are
slightly shorter than in 1. This observation is a result of the reduced
steric demand of the
l-OMe moiety also being expressed by a
nearly planar Zn2NO ring. The Zn–C bond in 3 is slightly longer
due to the bulkiness of the CH(SiMe3)2 substituents at the metal
atoms. A slight (but not significant) difference with respect to the
Zn–OMe bond is observed in 3 in comparison to 2, being in agree-
N
N
+ 2 ZnMe2
- 2 MeH
N
N
+
Zn
Zn
HN
N
H
Me
N
Me
NH2
1
II
Fig. 4. Synthesis of bis(methylzinc)t-butylamide-bis(2-pyridylmethyl)amide 1.

M. Kahnes et al. / Journal of Organometallic Chemistry 695 (2010) 280–290
283
N
+ 2 ZnR2
MeOH
- 2 RH
N
H
N
N
N
R
N
N
R
N
+ MeOH
HN
N
Zn
Zn
Zn
Zn
t
- BuNH2
O
R
R
Me
R=Me (1)
R=Me (2), CH(SiMe3)2 (3)
Fig. 6. Synthesis of bis(alkylzinc)methoxide-bis(2-pyridylmethyl)amides (2/3).
II
2.4. Reactivity of 1 and 2
yielding the amide complex 4. Since the obtained crystals were
coated with dipicolylamine II a reliable determination of yield
and melting point was impossible. Mechanistically we still assume
an exchange of the bridging moiety as the initial reaction step. Sub-
sequent insertion of a second equivalent of phenylamine leads to
In order to evaluate the stability and reactivity of 1 towards
other bases containing acidic hydrogen atoms the heteroleptic
dimethylzinc amide 1 was exposed to an excess of phenylamine
(aniline). Immediate cooling upon addition of the amine led to
the deposition of a few crystals suitable for X-ray analysis. Quite
surprisingly the expected exchange of the t-butylamide moiety in
1 against an anilide similar to the methanolysis reaction proceeded
further under partial decomposition of the starting material (Fig. 8)
intermediate I4 which features a Zn[
l
-(Nꢀ ꢀ ꢀHꢀ ꢀ ꢀN)]Zn functional-
ity. The increased acidic nature of the bridging proton now enables
the partial protonation of Zn–C as well as Zn–N2 bonds.
The centrosymmetric structure of 4 is assembled of two six-
membered
rings which are interconnected via a central four-membered
Zn2( -N(H)Ph)2 unit. The ring expansion with the additional phe-
[{Zn(l-N(H)Ph)}{MeZn(l-N(H)Ph)}2{l-N(CH2Py)2}]
l
nylamide has no effect on the Zn–C bond lengths compared to 2
and 3 whereas the Zn1/2–N2 bonds experience a slight shortening.
The Zn1–N5 and Zn2–N6 bonds are almost identical and very sim-
ilar to the average Zn–N bond length observed in dimeric
[MeZn(NPh2)]2 (207.2(8) pm) [22]. Although being in a tetrahedral
coordination sphere the Zn3–N5/N6 bond lengths are significantly
shortened compared to [MeZn(NPh2)]2 arising from the increased
Table 1
Selected bond lengths (pm) and angles (°) of 1, 2 and 3.
1
2
3
Zn1–N1
Zn1–N2
Zn1–N4/O1
Zn1–CZn
Zn2–N2
216.3(2)
209.9(2)
204.7(2)
197.5(3)
208.8(2)
219.0(2)
203.8(2)
198.2(2)
285.8(4)
213.0(3)
206.8(2)
197.7(2)
197.0(3)
215.1(3)
205.8(3)
200.4(2)
200.7(3)
206.7(3)
211.9(3)
199.9(2)
200.3(2)
290.4(5)
ionic nature of Zn3. Within the Zn2(l-NHPh)2 ring the Zn–N bond
lengths resemble those in [MeZn(NPh2)]2 [22].
Zn2–N3
Zn2–N4/O1
Zn2–C14
Zn1ꢀ ꢀ ꢀZn1A/Zn2
Zn1–N2–Zn1A/Zn2
N2–Zn1–N4/O1
N1–Zn1–CZn
N2–Zn2–N4/O1
N3–Zn2–C14
Zn1–N4/O1–Zn1A/Zn2
Zn1–N4/O1–CO
Zn2–N4/O1–CO
C15–N4–H(1N4)
The methoxide 2 readily dissolves in t-butylamine. Expecting
the formation and eventually the crystallization of the intermedi-
ate M-I (Fig. 10) the solution was stored at 5 °C. After a period of
two weeks colorless crystals precipitated which could be charac-
terized by X-ray diffraction. To our surprise a trinuclear disiloxide
292.3(5)
86.1(1)
88.8(1)
124.4(1)
89.3(1)
110.7(1)
88.8(1)
125.8(2)
126.1(2)
106(2)
89.9(1)
87.4(1)
116.7(1)
89.5(1)
88.7(1)
124.4(1)
88.6(1)
125.4(1)
93.0(1)
121.0(2)
126.5(2)
complex [(MeZn)2{l-N(CH2Py)2}2Zn{l-(OMe2Si)2O}] (5) was
formed as a result of the accidental contact of the solution with sil-
icone grease (Wacker) sealed ground glass joints. The 1H NMR
spectra of the mixture shows several singlet signals in the range
0.1–0.4 ppm indicating the presence of various types of silicone
grease cleavage products. As demonstrated by Chang et al. the base
95.3(1)
132.3(1)
Fig. 7. Molecular structures and numbering schemes of 2 (to the left) and 3 (to the right). The hydrogen atoms are omitted for clarity. The ellipsoids represent a probability of
40%. Selected structural data can be found in Table 1.

284
M. Kahnes et al. / Journal of Organometallic Chemistry 695 (2010) 280–290
N
N
N
N
N
N
+ 6 PhNH2
- 3 tBuNH2; - 2 MeH; - II
Zn
Zn
Zn
Zn
3
H
Me
Me
Ph
NH
HN
N
Me
Me
Ph
Zn
Ph NH
1
4
2
N
- 2 MeH; - II
N
N
+ 3 PhNH2
3
Zn
Zn
H
Me
Me
N
Ph
+ 3 PhNH2
- 3 PhNH2
- 3 tBuNH2
N
N
N
N
N
N
Zn
Zn
Zn
Zn
3
3
Me
Me
Ph
Me
tBu
Me
Ph
NH
HN
NH
HN
Ph
H
H
I4
Fig. 8. Aminolysis of 1 with aniline and subsequent degradation to 4.
N
+ tBuNH2
- tBuNH2
N
N
N
N
N
Zn
O
Zn
Zn
Zn
Me
Me
Me
O
Me
tBu
Me
H
N
H
Me
2
M-I
+ 2
tBuNH2; (Me2SiO)x
- II; -ZnX; -Y
py
Zn
py
Me
N
N
Zn
py
Zn
O
Si
Me
O
py
Si
O
5
Fig. 10. Reaction of 1 with t-butylamine in the presence of adventitious silicone
grease.
Fig. 9. Molecular structure and numbering scheme of 4. The hydrogen atoms with
exception of the anilide groups are omitted for clarity. The ellipsoids of all non-
hydrogen atoms represent a probability of 40%. Symmetry related atoms (ꢁx + 1, y,
ꢁz) are marked with an ‘‘A”. Selected bond lengths (pm): Zn1–N1 218.6(3), Zn1–N2
204.9(2), Zn1–N5 208.4(3), Zn1–C32 197.5(3), Zn2–N2 204.4(2), Zn2–N3 213.0(3),
Zn2–N6 208.4(3), Zn2–C31 198.0(3), Zn3–N4 205.3(2), Zn3–N5 202.2(3), Zn3–N6
201.5(3), Zn3–N4A 207.7(2).
coordination sphere of Zn2 the Zn2–O1/Zn2–O2 bond lengths are
noticeably larger (210.3(2)/215.9(2) pm) when compared to the
Zn1–O1/Zn3–O3 bond lengths (199.9(2)/199.2(2) pm). A similar
lengthening is observed for the Zn2–N2/Zn2–N5 bonds (221.7(3)/
218.2(3) pm) whereas the Zn2–N3/Zn2–N4 bond distances
(218.3(3)/217.3(3) pm) are quite comparable to the Zn1–N1 bond
length in 1 (216.3(2) pm).
catalyzed aminolysis of poly(dimethylsiloxane) is a feasible route
leading to various oligo(dimethylsiloxan)amines and oligo(dime-
tylsiloxan)ols which may recondense in several side reactions
[23]. The formation of such polysiloxane cleavage products is
rather wide spread in the chemistry of highly polar organometallic
reagents, the anion O(SiMe2Oꢁ)2 being the most common one [24]
(see Fig. 9).
3. Mechanism of the methanolysis and aminolysis
3.1. Methanolysis of 1
The structure of complex 5 is a rare synthetic example for hav-
ing zinc ions in a tetrahedral and octahedral coordination sphere
within the same compound (Fig. 11). The basic dimeric skeleton
is comprised of two four-membered Zn2NO rings fused together
with the octahedral zinc ion as sharing corner. The zinc ions are al-
most aligned on an axis (Zn1–Zn2–Zn3 angle 170.4°) with an iden-
tical non-bonding contact of 302.3(5) pm to each other. The bond
lengths associated with Zn1 and Zn3 are very similar and in agree-
ment to those discussed for the complex 2. Due to the expanded
When treating 1 with methanol one would expect the elimina-
tion of methane on the basis of pKs values forming the correspond-
ing methanolate, but instead an exchange of the l-N(H)tBu moiety
is observed. Extensive DFT-calculations at the B3LYP/TZVP level of
theory were carried out in order to reveal the underlying mecha-
nism of this reaction, thus confirming and clarifying the experi-
mental findings.
Considering the expected protonation of the zinc bound methyl
group no stationary point on the hypersurface could be found

M. Kahnes et al. / Journal of Organometallic Chemistry 695 (2010) 280–290
285
Table 3
Gibb’s free energies of the methanolysis reaction, calculated at the B3LYP/TZVP and
the B2GP-PLYP/cc-PVTZ level of theory. The values are given relative to 1 and a free
methanol molecule.
B3LYP/TZVP
B2GP-PLYP/cc-pVTZ
1 + MeOH
M-E1
M-TS1
M-I
0.0
0.0
13.1
21.4
0.1
13.4
24.5
2.1
M-TS2
M-E2
5.6
7.5
ꢁ6.3
ꢁ6.4
2 + tBuNH2
ꢁ16.7
ꢁ16.7
PLYP predictions are in good agreement with deviations of less
than 3 kcal/mol to those obtained by the B3LYP functional.
3.2. Aminolysis of 1
Fig. 11. Molecular structure and numbering scheme of 5. The hydrogen atoms are
omitted for clarity. The ellipsoids represent a probability of 40%. Selected bond
lengths (pm): Zn1–N1 214.9(4), Zn1–N2 202.6(3), Zn1–O1 199.9(2), Zn1–C25
198.8(4), Zn2–O1 210.3(2), Zn2–O2 215.9(2), Zn2–N2 221.7(3), Zn2–N5 218.2(3),
Zn2–N3 218.3(3), Zn2–N4 217.3(3), Zn3–O2 199.2(2), Zn3–N5 203.9(3), Zn3–N6
214.6(3), Zn3–C26 198.4(3).
The synthesis of complex 2 through the conversion of 1 with
methanol proceeds very fast even at low temperature. Thus, it is
neither possible to find any spectroscopic evidence for the exis-
tence of the proposed pathway nor the corresponding intermedi-
ates. In order to follow up the calculated mechanism, compound
1 was reacted with an excess of t-butylamine (Fig. 13). This proce-
dure resulted in an exchange process of the t-butylamide moiety
involving the proposed intermediates (Iza/b). In this case z indi-
cates an integer (z = 1 ꢁ 3) standing for the three different path-
ways which lead to different stereo isomers.
Considering a comparable mechanism to the methanolysis, the
mechanism of the reaction path of 1 with t-butylamine follows
similar steps (see Fig. 14). Approaching the binuclear complex 1
the amine first comes in contact with either the proton in ortho
position of the pyridine ring (Eza) or the proton of the bridging
amide (Ezb), leading to the formation of a complex via a loose
hydrogen bond. From this position the insertion into one of the
N4–Zn bonds is enabled over TSza and TSzb, respectively (rate
favoring this reaction pathway. Instead the methanol molecule ap-
proaches the Zn1–N4 bond from the sterically less hindered side.
Thus the methanol first comes in contact with the pyridyl proton
in ortho-position to the aromatic nitrogen, leading to complex
M-E1. From this position methanol can attack the Zn1–N4 bond
via the transition structure M-TS1 (rate determining step;
D
G = +21.1 kcal/mol, see Table 3) in a [2+2] fashion leading to
the intermediate M-I. The latter intermediate features a Zn[
l
-
(Oꢀ ꢀ ꢀHꢀ ꢀ ꢀN)]Zn functionality, having the bridging proton already
closely bound to the amide. Then the oxygen atom in this three
center bond attacks the zinc atom to generate a
The former amino nitrogen is protonated in this step (M-TS2,
G = +5.6 kcal/mol) by the hydrogen atom originating from the
l-OMe group.
D
determining step;
ory, see Table 4). As a result, the intermediate structure (Iza;
Izb) is generated, featuring a Zn[
With a barrier of ca. 4 kcal/mol (cf. Table 4) the bridging proton is
able to migrate easily between the two amino groups (TSIzab).
The amine escapes from the six membered ring similar to the
way of insertion, yielding 1.
D
G ꢂ 30 kcal/mol at B3LYP/TZVP level of the-
methanol molecule. Complex M-E2 is then formed before the
t-butylamine molecule finally departs, yielding compound 2 (see
Fig. 12).
To assess the robustness of the obtained energies, single point
energy calculations on the optimized structures were carried out,
using the double hybrid B2GP-PLYP functional, which has been
claimed to deliver highly accurate thermochemistry values [25].
The parameters summerized in Table 3 support that the B2GP-
l
-(N ꢀ ꢀ ꢀ H ꢀ ꢀ ꢀ N)]Zn functionality.
The exchange progress can be followed by 1H NMR spectros-
copy. The 1H NMR spectra of 1 shows two different signals for
the py1 protons (8.22 ppm, 8.01 ppm, see Table 2) due to the
neighboring N4 atom which breaks the C2-symmetry of the mol-
ecule. When additional t-butylamine is added the magnetically
in-equivalent py1/10 signals merge to give one doublet with an
averaged shift at 8.10 ppm. This can be understood in terms of
an exchange of the t-butylamide which is fast on the NMR time
scale. Temperature-dependent NMR studies show that the chem-
ical shift is temperature-dependent and that the signal splits into
two resonances at low temperatures as shown in Fig. 15. Further-
more, three additional doublet resonances appear at 8.17, 8.23
and 8.31 ppm.
Table 2
NMR chemical shifts (ppm) at 30 °C for the compounds 1, 2 and 3.
d
1
2
3
1H
Pyr 1
Pyr 4
Pyr 3
Pyr 2
CH2N
ZnMe
OMe
8.22/8.01
6.66
6.88
8.04
6.63
6.84
6.39
4.07
ꢁ0.41
3.93
8.22
6.73
6.91
6.53
4.24
ꢁ1.24
3.79
6.47
4.28/4.21
ꢁ0.40
–
Consisting of two stereo centers the number of possible stereo
isomers of the intermediate structures Iza/b is, according to 2n
(with n = number of stereo centers), equal to four. Those include
two enantiomers (I2a; I2b), which can be easily converted into
each other via proton transfer (TSI2ab), and two diastereomers
(I1a; I3a), all shown in Fig. 16. Proton transfer in the latter via
the transition structures TSI1ab and TSI3ab leads to the intermedi-
ate structures I1b and I3b which are identical to I1a and I3a,
respectively.
13C
Pyr 1
Pyr 2
Pyr 3
Pyr 4
Pyr 5
CH2N
ZnMe/ZnCH
147.4/146.7
122.4
137.4
147.4
122.1
137.6
121.1
161.7
60.3
147.5
122.9
138.1
122.7
160.8
59.7
122.0
163.1/162.9
61.4/61.3
ꢁ15.2
ꢁ18.8
ꢁ3.0
(51.0)
54.6
55.2
OMe/(NCtBu)

286
M. Kahnes et al. / Journal of Organometallic Chemistry 695 (2010) 280–290
O
Zn1
N
ΔG [kcal/mol]
Zn2
N
M-TS1
(21.4)
20
O
Zn1
N
N
Zn2
N
15
10
5
N
Zn1
O
Zn2
M-E1
(13.1)
M-TS2
(5.6)
M-I
(0.1)
N
0
+ MeOH
(0.0)
1
Zn1
N
M-E2
(-6.3)
O
Zn2
N
-5
-10
-15
Zn1
O
Zn2
N
2+ tBuNH2
(-16.7)
reaction coordinate
Fig. 12. Energy diagram of the methanolysis pathway of compound 1, calculated at the B3LYP/TZVP level of theory. The values are given in kcal/mol relative to 1 and a free
methanol molecule. The optimized structures can be found in the Supplementary Material in Fig. S1.
[ tBuNH2]
N
H
N
N
N
N
N
N
py1
tBu
N
py1
py1'
py1'
H3C
Zn
Zn
Zn
Zn
H3C
CH3
CH3
tBu
H
1
1
t
+ tBuNH2
- BuNH2
N
N
N
Zn
Zn
H3C
CH3
tBu
H
H
*N
N*
H
tBu
Iza/b
Fig. 13. Reaction of 1 with t-butylamine.
The nuclear magnetic shielding constants of the intermediates
(Iza/b) and the involved transition structures (TSIzab) were calcu-
latedat the B3LYP/6-31++G(d,p)levelof theory. Calibratingtheaver-
age magnetic shielding constant of the py1/10 protons in I2a on the
experimental value of 8.23 ppm gives the chemical shifts for the
other structures which are listed in Table 5. Due to the proton behav-
ior only the average chemical shift of each triple (Iza ꢀ TSIzab ꢀ
Izb) was considered as observable value. As expected the two
enantiomeric structures I2a and I2b show the same chemical shift
predisposed to 8.23 ppm. The calculated chemical shift of the diaste-
reomeric intermediates I1a (8.34 ppm) and I3a (8.11 ppm) differ by
0.23 ppm and are in very good agreement to the observed experi-
mental values of 8.31 and 8.17 ppm, respectively.
b:I3a = 1:2:1 and indeed the signal at 8.23 ppm which corresponds
to I2a and I2b is the most prominent one. However, an exact match
of the intensity ratio was not obtained.
Despite of the slight incongruence in the signal intensity 1H
NMR spectroscopy in combination with quantum chemical calcu-
lations delivers a reasonable evidence for the existence of Zn[l-
(Xꢀ ꢀ ꢀHꢀ ꢀ ꢀY)]Zn (X = O, N; Y = N) functionalities in the mechanism
of alcoholysis and aminolyses of
conclusions.
1 and hence support the
4. Conclusions
Based on the calculated Gibb’s free energy of the transition
structures TSza/b, which are similar, presuming an error of
3 kcal/mol, each of the four intermediates Iza/b has the same
chance to be formed if the reaction is kinetically controlled. There-
fore the signal intensity ought to follow a ratio of I1a:I2a/
The DFT calculations propose a mechanism for the experi-
mentally observed exchange of the N(H)tBu moiety in 1 when
protolyzed with methanol. The importance of the intermediate
Zn[l
-(Xꢀ ꢀ ꢀHꢀ ꢀ ꢀY)]Zn (X = O/N, Y = N) functionalities could be
verified. Furthermore their existence was supported by 1H NMR

M. Kahnes et al. / Journal of Organometallic Chemistry 695 (2010) 280–290
287
N
Zn1
H
N
Zn1
N
R
Me
H
R
Me
X
H
Me
tBu
Me
N
N
X
H
Zn1
N
+ RXH
-RXH
Me
H
N
N
Zn2
N
Zn2
H
Me
Zn2
tBu
N
N
tBu
N
M- E1 X=O, R=Me
Eza X=NH, R=tBu
M-TS1 X=O, R=Me
TSza X=NH, R=tBu
1
+ RXH
- RXH
N
N
Zn1
N
Zn1
Zn1
Me
N
Me
Me
Me
Me
Me
N
N
R
X
Zn2
R
X
Zn2
R
X
Zn2
H
N
H
N
H
N
N
N
N
H
H
H
tBu
tBu
tBu
TSIzab X=NH, R=tBu
M- I X=O, R=Me
Izb X=NH, R=tBu
Iza X=NH, R=tBu
N
Zn1
N
N
Zn1
H
tBu
N
NH2
+ H2NtBu
Me
H
N
N
N
tBu
Zn1
Me
Me
Me
Me
Zn2
- H2NtBu
X
Zn2
X
R
X
Zn2
R
Me
R
N
N
N
M- E2 X=O, R=Me
Ezb X=NH, R=tBu
X=O, R=Me (2)
X=NH, R=tBu (1)
M-TS2 X=O, R=Me
TSzb X=NH, R=tBu
Fig. 14. Aminolysis and methanolysis pathway of compound 1. The optimized structures, calculated at the B3LYP/TZVP level of theory, can be found in the supplementary
material (Figs. S1–S4). The corresponding Gibb’s free energies are summerized in Tables 3 and 4.
Table 4
T =300 K
1
Gibb’s free energies of the aminolysis reaction, calculated at the B3LYP/TZVP level of
theory. They are given relative to 1 and a free t-butylamine molecule. The three
different pathways are indicated by the integer z (z = 1 ꢁ 3).
300 K
1+tBuNH
D
G (z = 1)
D
G (z = 2)
DG (z = 3)
2
1 + tBuNH2
Eza
TSza
Iza
TSIzab
Izb
TSzb
Ezb
1 + tBuNH2
0.0
7.2
0.0
7.8
0.0
8.9
273 K
253 K
243 K
233 K
29.6
14.5
18.7
14.5
29.6
7.2
31.6
14.5
20.6
16.3
26.8
10.2
0.0
29.4
14.6
18.0
14.6
29.4
8.9
0.0
0.0
8.3
8.2
8.1
8.0
7.9
7.8
[ppm]
spectroscopy. We are now exploring their use in catalysis in order
to evaluate their catalytic activity and the value of these complexes
as a biomimetic model for binuclear zinc hydrolases.
Fig. 15. D NMR studies of compound 1 (solvent: [D8]toluene). Only the 1H NMR
spectra of the resonances of the pyridyl protons in ortho position to the nitrogen
(py1; py10) are shown.
5. Computational details
based on the work of Schäfer et al. [28] was employed for the first
row atoms as implemented in Turbomole. For the zinc ions a Stutt-
gart relativistic pseudopotential (known as ECP 10 MDF) has been
employed [29]. All species found on the hypersurface were charac-
All geometry optimizations were performed with the gradient-
corrected hybrid B3LYP [26] density functional using the quantum
chemical program package Turbomole [27]. The TZVP basis set

288
M. Kahnes et al. / Journal of Organometallic Chemistry 695 (2010) 280–290
py1’
py1’
py1’
(8.21 ppm)
(8.16 ppm)
(8.04 ppm)
N
N
N
tBu
Me
But
Me
Me
Me
Me
Zn
N
H
Me
Zn
N
Zn
N
tBu
tBu
N
H
N
N
Zn
Zn
Zn
tBu
N
N
py1
(8.47 ppm)
H
N
py1
(8.17 ppm)
H
N
H
H
N
tBu
H
N
py1
(8.30 ppm)
H
H
I1a
I2a
I3a
py1’
py1’
py1’
(8.36 ppm)
(8.12 ppm)
N
N
(8.36 ppm) N
tBu
Me
Me
tBu
Me
N
Zn
N
Me
N
H
Zn
N
Me
N
py1’
(8.30 ppm)
Zn
N
tBu
Me
tBu
N
N
H
Zn
Zn
Zn
tBu
N
py1
(8.12 ppm)
H
H
N
H
N
H
H
N
tBu
py1
H
H
(8.11 ppm)
TSI1ab
TSI2ab
TSI3ab
py1’
py1’
py1’
(8.05 ppm)
(8.17 ppm)
N
N
N
(8.47 ppm)
Me
tBu
Me
Me
H
Me
H
Me
N
Zn
Zn
N
Zn
N
tBu
Me
H
N
N
H
N
Zn
Zn
Zn
tBu
tBu
H
N
py1
(8.04 ppm)
N
py1
(8.41 ppm)
H
N
N
N
tBu
H
H
N
tBu
py1
(8.21 ppm)
H
I1b (= I1a)
I2b
I3b (= I3a)
Fig. 16. Stereoisomeric intermediates created by the reaction of 1 with tBuNH2.
Table 5
ing constants was performed with the hybrid B3LYP functional
using the 6-31++G(d,p) basis as implemented in the GAUSSIAN pro-
gram package [30].
Calculated and experimental chemical shifts [ppm] for 1, Iza/b and TSIzab.
Calc. Chem. Shift [ppm] Exp. Chem. Shift [ppm]
py10
py1
Average
py10
8.01
py1
6. Experimental
1
7.99
8.21
8.36
8.47
8.20
8.47
8.30
8.21
8.11
8.34
8.33
8.34
8.22
I1a
8.34
TSI1ab
I1b
8.31
8.23
8.17
6.1. General remarks
I2a
TSI2ab
I2b
8.16
8.36
8.05
8.30
8.11
8.41
8.23
8.24
8.23
All reactions were performed in an argon atmosphere using
standard Schlenk techniques. All solvents were dried and thor-
oughly deoxygenated according to standard procedures prior to
use. IR spectra were recorded using Nujol suspensions between
KBr windows. The starting material Zn[CH(SiMe3)2]2 was prepared
by a known procedure [32].
8.23
8.11
I3a
TSI3ab
I3b
8.04
8.12
8.17
8.17
8.12
8.04
8.11
8.12
8.11
6.2. Synthesis of [(MeZn)2{l-N(H)t Bu}{l-N(CH2Py)2}] (1)
terized as energetic minima or transition structures via vibrational
analyses. Default convergence criteria were used and no symmetry
was employed in all the calculations. The relative stabilities are re-
ported as gas phase Gibbs free energies containing standard ther-
mochemical (298 K) and vibrational corrections. In order to
obtain more reliable energy data we have carried out single-point
energy calculations on the B3LYP/TZVP optimized geometries with
the GAUSSIAN03 [30] program package using the double hybrid B2GP-
PLYP functional which was implemented as described [25]. The
correlation consistent cc-pVTZ [31] basis set was applied to the
C, N, O and H atoms and the Stuttgart pseudopotential (ECP 10
MDF) to the zinc ions [29]. The calculation of the magnetic shield-
A mixture of bis(2-pyridylmethyl)amine (II) (0.60 g, 3.0 mmol)
and t-butylamine (0.22 g, 3.0 mmol) was dissolved in 10 ml of tol-
uene and cooled to ꢁ78 °C. To the stirred solution 5.0 ml
(6.0 mmol) of a 1.2 M solution of dimethylzinc in toluene were
added dropwise. The reaction mixture turned claret red whilst
methane was slowly liberated. After being warmed to r.t. the solu-
tion was stirred for additional 14 h. The volume of the solution was
reduced to a few milliliters. Cooling of this solution to 5 °C led to
the precipitation of colorless crystals of 1. Yield 1.02 g (79%).
M.p.: 85 °C (decomposition). NMR (C6D6, 300 K): 1H: d = 8.22 (s
(br), 1 H, Pyr1); 8.01 (s (br), 1H, Pyr10); 6.88 (dt, 3J(H,H) = 7.6 Hz,

M. Kahnes et al. / Journal of Organometallic Chemistry 695 (2010) 280–290
289
4J(H,H) = 1.6 Hz, 2H, Pyr3/30), 6.66 (d, 3J(H,H) = 7.6 Hz, 2H,0Pyr4/40);
6.47 (m, 2H, Pyr2/20); 4.28 (s, 2H, CH2N); 4.21 (s, 2H, CH2N); 1.28
(s, 9H, C(CH3)3); 0.00 (s, 1H, NH), and ꢁ0.40 (s, 6H, ZnCH3).
13C{1H}: d = 163.1 (Pyr5); 162.9 (Pyr50); 147.4 (Pyr1); 146.7 (Pyr10);
137.4 (Pyr3/30), 122.4 (Pyr2/20), 122.0 (Pyr4/40), 61.4 (CH2N), 61.3
(ZnCH3). IR (cmꢁ1): 2925 vs, 2854 vs, 2763 m, 2266 w, 2169 w,
1999 w, 1957 w, 1912 w, 1845 w, 1779 w, 1720 w, 1651 m,
1603 s, 1569 s, 1464 vs, 1379 s, 1343 s, 1285 s, 1235 s, 1213 m,
1150 s, 1096 s, 1048 s, 980 m, 957 m, 893 w, 811 m, 757 s, 728
s, 639 vs, 520 s. MS (EI, m/z): 372 ([M(64Zn/64Zn)-CH3]+, 2.2%);
342 ([C12H12N3O64Zn2]+, 0.9%); 262 ([C12H12N364Zn]+, 4.6%); 200
([C12H14N3]+, 6.9%) 198 ([C8H10N264Zn]+, 3.2%); 107 ([C6H7N2]+,
87%); 93 ([C6H7N]+, 100%). Anal. Calc. for C15H21N3Zn2 (390.13 g/
mol): C, 46.18; H, 5.43; N, 10.77. Found: C, 45.33; H, 5.51; N,
10.67%.
ðCH0 NÞ, 51.0 (C(CH3)3); 35.2 (C(CH3)3), and ꢁ15.2 (ZnCH3). IR
2
(cmꢁ1): 3271 w, 2925 vs, 2854 vs, 2761 m, 1990 w, 1913 w,
1841 w, 1645 m, 1602 s, 1568 s, 1462 vs, 1378 s, 1365 s, 1343 s,
1283 s, 1220 s, 1150 s, 1099 m, 1045 s, 1015 m, 959 m, 888 w,
812 w, 757 s, 729 s, 637 s, 560 m, 503 s. MS (EI, m/z) 413
([M(64Zn/64Zn)–CH3]+, 0.4%); 262 ([C12H12N364Zn]+, 1.7%); 198
([C8H10N264Zn]+, 1.2%); 107 ([C6H7N2]+, 21%); 93 ([C6H7N]+, 61%);
58 ([C3H8N]+, 100%). Anal. Calc. for C18H28N4Zn2 (431.18 g/mol):
C, 50.13; H, 6.54; N, 12.99. Found: C, 49.44; H, 6.38; N, 13.00%.
6.4. Synthesis of [{(Me3Si)2CHZn}2(l-OMe){l- N(CH2Py)2}] (3)
A mixture of bis(2-pyridylmethyl)amine (II) (0.60 g, 3.0 mmol)
and 3.0 ml of a 1.0 M solution of methanol in toluene (3.0 mmol)
was dissolved in 3 ml of toluene and cooled to ꢁ78 °C. To the stir-
6.3. Synthesis of [(MeZn)2(l-OMe){l-N(CH2Py)2}] (2)
red solution 12.0 ml of
a
0.5 M of bis[bis(trimethyl-
6.3.1. Procedure A
silyl)methyl]zinc in toluene (6.0 mmol) were added dropwise.
After being warmed to r.t. the solution was stirred for additional
14 h. The volume of the solution was reduced to a few milliliters.
Cooling of this solution to 5 °C led to the precipitation of colorless
crystals of 3. Yield 1.60 g (78%). M.p.: 98 °C. NMR (C6D6, 300 K): 1H:
d = 8.22 (d, 3J(H,H) = 4.8 Hz, 2H, Pyr1); 6.91 (dt 3J(H,H) = 7.6 Hz,
4J(H,H) = 1.6 Hz, 2H, Pyr3); 6.73 (d, 3J(H,H) = 7.6 Hz, 2H, Pyr4);
6.53 (m, 2H, Pyr2); 4.24 (s, 4H, CH2N); 3.79 (s, 3H, OCH3); 0.13
(s, 36H, CH(Si(CH3)3)2); ꢁ1.24 (s, 2H, ZnCH(SiMe3)2). 13C{1H}:
d = 160.8 (Pyr5); 147.5 (Pyr1); 138.1 (Pyr3); 122.9 (Pyr4); 122.7
(Pyr2); 59.7 (CH2N); 55.2 (OCH3); 4.7 (CH(Si(CH3)3)2); ꢁ3.0
(ZnCH(SiMe3)2). IR (cmꢁ1): 2924 vs, 2854 vs, 2742 m, 2677 w,
1984 w, 1950 w, 1912 w, 1840 w, 1640 w, 1606 s, 1571 m, 1456
vs, 1377 s, 1343 m, 1285 m, 1240 s, 1153 m, 1125 m, 1101 m,
1077 m, 1045 s, 1021 s, 980 m, 852 vs, 830 vs, 771 s, 755 s, 668
s, 642 m, 607 m, 488 s. MS (EI, m/z): 660 ([M(64Zn/64Zn)–CH3]+,
22%); 645 ([M(64Zn/64Zn)–2CH3]+, 20%); 520 ([M(64Zn/68Zn)–
Bis(methylzinc)t-butylamide-bis(2-pyridylmethyl)amide
(1)
(0.30 g, 0.7 mmol) was dissolved in 7 ml of toluene and cooled to
ꢁ78 °C. Then 0.7 ml of a 1.0 M solution of methanol in toluene
(0.7 mmol) were added. The reaction mixture was slowly warmed
to r.t. and afterwards concentrated under vacuum. At 5 °C colorless
crystals of 2 precipitated. Yield 0.25 g (90%).
6.3.2. Procedure B
A mixture of bis(2-pyridylmethyl)amine (II) (0.60 g, 3.0 mmol)
and 3.0 ml of a 1.0 M solution of methanol in toluene (3.0 mmol)
was dissolved in 15 ml of toluene and cooled to ꢁ78 °C. To the stir-
red solution 5.0 ml of a 1.2 M solution of dimethylzinc in toluene
(6.0 mmol) were added dropwise. The mixture was slowly warmed
to r.t. and concentrated under vacuo thereafter. Cooling of this
solution to 5 °C afforded the precipitation of colorless crystals of
2. Yield 0.96 g (82%). M.p.: 127 °C. NMR (C6D6, 300 K): 1H:
d = 8.04 (s (br), 2H, Pyr1); 6.84 (m, 2H, Pyr3); 6.63 (s (br), 2H,
Pyr4); 6.39 (m, 2H, Pyr2); 4.07 (s, 4H, CH2N); 3.93 (s, 3H, OCH3);
ꢁ0.41 (s, 6H, ZnCH3). 13C{1H}: d = 161.7 (Pyr5); 147.4 (Pyr1);
137.6 (Pyr3); 122.1 (Pyr2/4); 60.3 (CH2N); 54.6 (OCH3); ꢁ18.8
CH(SiMe3)2]+,
[M(66Zn/66Zn)–CH(SiMe3)2]+,
100%);
262
([C12H12N364Zn]+, 85%); 198 ([C12H12N3]+, 73%). Anal. Calc. for
C27H53N3OSi4Zn2 (678.85 g/mol): C, 47.77; H, 7.87; N, 6.19. Found:
C, 48.07; H, 7.94; N, 5.85%.
Table 6
Crystal data and refinement details for the X-ray structure determination.
Compound
1
2
3
4
5
Formula
Fw (g ꢀ molꢁ1
T (°C)
Crystal system
Spacegroup
C18H28N4Zn2
431.18
C15H21N3OZn2
390.09
C27H53N3OSi4Zn2
678.82
C64H72N12Zn6 ꢀ 2 C7H8
1585.82
C30H42N6O3Si2Zn3
786.99
)
ꢁ90(2)
ꢁ90(2)
ꢁ90(2)
ꢁ90(2)
ꢁ90(2)
Triclinic
Monoclinic
C2/c
Monoclinic
P21/n
Triclinic
Triclinic
P1
P1
P1
a (Å)
b (Å)
c (Å)
8.9787(4)
9.5358(4)
12.3484(6)
86.494(2)
82.775(2)
74.631(2)
1010.93(8)
2
16.1318(7)
11.1350(5)
9.5169(3)
90
101.420(3)
90
1675.65(12)
4
1.546
17.1250(6)
10.3814(2)
21.0288(9)
90
104.135(2)
90
3625.3(2)
4
1.244
11.9392(5)
13.3651(8)
13.4461(7)
117.482(2)
94.431(3)
93.689(3)
1885.60(17)
1
10.4652(5)
10.9809(7)
15.7968(6)
99.717(3)
94.430(3)
95.046(3)
1774.49(16)
2
a
(°)
b (°)
c
(°)
V (Å3)
Z
q
l
(g ꢀ cmꢁ3
)
1.417
23.79
1.397
19.28
1.473
21.17
(cmꢁ1
)
28.64
14.78
Measured data
7241
5734
24921
13367
12613
Measured data (I > 2
r(I))
3777
1597
5563
6188
4967
Unique data (Rint
)
4580/0.0270
0.0887
0.0330
1907/0.0690
0.0985
0.0377
8256/0.0718
0.1085
0.0457
8473/0.0284
0.0999
0.0417
8089/0.0396
0.1059
0.0457
wR2 (all data, on F2)a
R1 (I > 2
r
(I))a
sb
1.009
1.022
0.998
1.007
0.957
Residual density (eÅꢁ3
CCDC no.
)
0.612/ꢁ0.610
0.169/0.623/ꢁ0.741
0.641/ꢁ0.455
0.523/ꢁ0.466
0.477/ꢁ0.632
740264
740265
740266
740267
740268
qffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffi
P
P
P
P
2
2
2
½wðF2o ꢁ Fc2Þ ꢃ= ½wðF2o Þ ꢃ with wꢁ1
¼
r2ðF2o Þ þ ðaPÞ .
a
Definition of the R indices: R1 ¼ ð jjFoj ꢁ jFcjjÞ= jFoj. wR2
¼
qffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffi
P
2
½wðF2o ꢁ Fc2Þ ꢃ=ðNo ꢁ NpÞ.
b
s ¼

290
M. Kahnes et al. / Journal of Organometallic Chemistry 695 (2010) 280–290
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389.
6.5. Synthesis of [{Zn(l-N(H)Ph)}{MeZn(l-N(H)Ph)}2{l- N(CH2Py)2}]2
(4)
Phenylamine (aniline, 0.23 ml, 2.5 mmol) was added dropwise
solution of bis(methylzinc)t-butylamide-bis(2-pyridyl-
ˇ ´
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to
a
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duced to 1 ml. Cooling of this solution to 5 °C led to the precipita-
tion of colorless crystals of 4. Estimated yield: 20%. NMR (C6D6,
300 K): 1H: d = 7.60 (s (br), 2H, Pyr1); 7.10–7.00 (m, Ph); 6.88 (m,
Pyr3); 6.74–6.20 (m Ph/Pyr4); 6.39 (m, Pyr2); 4.17 (s, 4H, CH2N);
2.84 (s (br), NH); ꢁ0.29 (s, 6H, ZnCH3).
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Nonius Kappa CCD diffractometer using graphite-monochromated
Mo Ka radiation. Data were corrected for Lorentz and polarization
effects but not for absorption effects [33,34]. Crystallographic data
as well as structure solution and refinement details are summa-
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(
SHELXS [35]) and refined by full-matrix least squares techniques
against Fo2
(SHELXL-97 [36]). The hydrogen atoms were located by
difference Fourier synthesis and refined isotropically for the
methyl groups C13/C14 of compound 1 and 2 and for the amide
groups at N4, N5 and N6 of compound 1 and 4. The other hydrogen
atoms were included at calculated positions with fixed thermal
parameters. All non-hydrogen atoms were refined anisotropically
[36]. XP (SIEMENS Analytical X-ray Instruments, Inc.) was used
for structure representations.
Acknowledgements
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We thank the Deutsche Forschungsgemeinschaft (DFG, Bonn/
Germany) for generous financial support. M.K wishes to express
his gratitude to the Jena Graduate Academy for a Ph.D. grant. Furt-
ermore, D.E. is very grateful to the Carl-Zeiss-Schott-Förderstiftung
for a Ph.D. grant.
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Appendix A. Supplementary data
CCDC 740264,740265, 740266 and 740267 contains the supple-
mentary crystallographic data for 1, 2, 3 and 4. These data can be
obtained free of charge from The Cambridge Crystallographic Data
Centre via www.ccdc.cam.ac.uk/data_request/cif. Supplementary
data associated with this article can be found, in the online version,
at doi:10.1016/j.jorganchem.2009.09.041.
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