α-Lithiated (R,R)-TMCDA as an efficient building block for the preparation of Chiral N,N,O ligands by asymmetric 1,2-addition

Article abstract of DOI:10.1002/ejic.201000631

The chiral diamine (1R,2R)-N,N,N′,N′-tetramethylcyclohexane-1, 2-diamine [(R,R)-TMCDA, 3] has been selectively deprotonated at one of its methyl groups by a series of alkyllithium bases. Although the enantiomerically pure compound formed a trimeric structure, direct lithiation of the racemic mixture of the amine (trans-TMCDA) yielded a tetrameric compound. With 2 equiv. of the deprotonation reagent a mixed aggregate of the lithiated amine and tert-butyllithium was formed. The lithiated amine was employed as a building block for the synthesis of novel nitrogen ligands. The asymmetric 1,2-addition of α-lithiated (R,R)-TMCDA onto different ketones and aldehydes yielded a series of novel N,N,O ligands with different substitution patterns. Depending on the carbonyl compound used, a new stereocentre and different substituents can be introduced. The coordination behaviour of these ligands is illustrated by the formation of metal salt complexes. (R,R)-TMCDA and its racemic mixture can be directly deprotonated at its methyl group. With 2 equiv. of the deprotonation reagent a mixed aggregate 8 of the lithiated amine 7 and tBuLi was formed. By addition of α-lithiated (R,R)-TMCDA onto carbonyl compounds a series of novel N,N,O ligands of type 4 with different substituents and a further stereocentre are accessible.

Full text of DOI:10.1002/ejic.201000631

FULL PAPER
DOI: 10.1002/ejic.201000631
α-Lithiated (R,R)-TMCDA as an Efficient Building Block for the Preparation
of Chiral N,N,O Ligands by Asymmetric 1,2-Addition
Viktoria H. Gessner,[a] Benjamin Fröhlich,[a] and Carsten Strohmann*[a]
Keywords: Lithium / Organolithium compounds / Structure elucidation / N ligands / Addition reactions
The chiral diamine (1R,2R)-N,N,NЈ,NЈ-tetramethylcyclohex- building block for the synthesis of novel nitrogen ligands.
ane-1,2-diamine [(R,R)-TMCDA, 3] has been selectively de-
The asymmetric 1,2-addition of α-lithiated (R,R)-TMCDA
protonated at one of its methyl groups by a series of alkyl-
onto different ketones and aldehydes yielded a series of
lithium bases. Although the enantiomerically pure com- novel N,N,O ligands with different substitution patterns. De-
pound formed a trimeric structure, direct lithiation of the ra- pending on the carbonyl compound used, a new stereocentre
cemic mixture of the amine (trans-TMCDA) yielded a tetra- and different substituents can be introduced. The coordina-
meric compound. With 2 equiv. of the deprotonation reagent
a mixed aggregate of the lithiated amine and tert-butyl-
lithium was formed. The lithiated amine was employed as a
tion behaviour of these ligands is illustrated by the formation
of metal salt complexes.
amine (PMDTA, 2)[3] and (1R,2R)-N,N,NЈ,NЈ-tetrameth-
ylcyclohexane-1,2-diamine [(R,R)-TMCDA, (R,R)-3; Fig-
ure 1].[4] The ready access to amino-functionalised building
blocks by direct lithiation prompted us to evaluate the po-
tential of these systems for the preparation of novel nitro-
gen ligands. In particular, the chiral (R,R)-TMCDA seemed
to be an attractive starting point due to its intrinsic stereo-
information. We were especially interested in the prepara-
tion of N,N,O ligands of type 4 with an additional hydroxy
function. This class of ligand has already found wide appli-
cation in many fields of chemistry, such as in transition-
metal-catalysed reactions, in coordination chemistry as
scorpionate ligands, and also in organolithium and metal–
organic chemistry.[10–12] In the latter case, several cyclohex-
anediamine-based ligands have already been employed in
the stereoselective reactions of the tetradentate derivatives
5 and 6 (Figure 2), which feature the same binding site
(NCH2CH2O) as the target molecules 4 based on lithiated
TMCDA. Ligands 5 and 6 were successfully employed by
Marson et al. in the asymmetric 1,2-addition of diethylzinc
to benzaldehyde with enantiomeric excesses of up to 92%.[12e]
Introduction
Nitrogen ligands have found wide application in many
fields of chemistry, such as coordination chemistry and ca-
talysis. In organolithium chemistry they are frequently ap-
plied to increase the reactivity of the deprotonation reagent
used, but also for a more controlled and selective reactivity
in, for example, asymmetric synthesis.[1] Access to novel,
especially chiral ligand systems is often synthetically chal-
lenging. Recently we reported on a series of direct depro-
tonation reactions of tertiary methylamines leading to α-
lithiated amines as intriguing building blocks.[2–5] The direct
deprotonation of tertiary amines is mainly limited to poly-
amines, which enables precoordination of the lithium base.
Alternative pathways include transmetallation,[6] reductive
C–S bond cleavage[7] or lithiation of the more readily depro-
tonated aminoboranes.[8]
The precoordination by polyamines is necessary for the
activation of the amines towards direct lithiation through
the proximity of reactive groups in the intermediate species.
Thus, the close proximity of reactive groups in this precoor-
dinated complex also enables selective deprotonation reac-
tions, for example, regioselective α- or β-lithiation reactions.
This phenomenon is known as the complex-induced prox-
imity effect (CIPE).[9] Amongst such amines that readily
undergo direct deprotonation are the commonly used
nitrogen ligands N,N,NЈ,NЈ-tetramethylethylenediamine
(TMEDA, 1),[2] N,N,NЈ,NЈЈ,NЈЈ-pentamethylethylenetri-
Figure 1. Tertiary amines that undergo direct deprotonation with
organolithium bases.
[a] Anorganische Chemie, Technische Universität Dortmund,
Otto-Hahn-Straße 6, 44227 Dortmund, Germany
Fax: +49-231-755-7062
E-mail: mail@carsten-strohmann.de
Supporting information for this article is available on the
WWW under http://dx.doi.org/10.1002/ejic.201000631.
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Eur. J. Inorg. Chem. 2010, 5640–5649

Preparation of Chiral N,N,O Ligands by Asymmetric 1,2-Addition
Figure 2. Tetradentate cyclohexanediamine-based ligands applied
to the asymmetric 1,2-addition of diethylzinc to benzaldehyde.
Scheme 1. Formation of lithiated (R,R)-TMCDA [(R,R)-7] and the
mixed aggregate [tBuLi·(R,R)-TMCDA–Li]2 [(R,R)-8] with excess
tert-butyllithium.
Encouraged by the wide application of such amine li-
gands with an additional hydroxy function we wanted to
evaluate the potential of lithiated TMCDA as a building
block for N,N,O ligands. We present herein a detailed inves-
tigation of the direct deprotonation of the diamine, also of
its racemic mixture and with an excess of the alkyllithium
reagent as a starting point for its following application. The
subsequent trapping reactions demonstrate the potential of
the lithiated amine by the preparation of N,N,O ligands of
type 4 with a series of different substituents. Preliminary
investigations of the coordination behaviour of the synthe-
sised ligands will give a first insight into their complexation
ability.
amine is only known for the cyclic amine N,NЈ,NЈЈ-tri-
methyl-1,4,7-triazacyclononan (Me3tacn).[5e] The formation
and thermodynamic stability of (R,R)-8 was confirmed by
computational studies at the B3LYP/6-31+G(d) level of
theory. Thus, [tBuLi·(R,R)-TMCDA-Li]2 shows a prefer-
ence of 12 kJmol–1 compared to trimeric lithiated (R,R)-
TMCDA [(R,R)-7] (2/3 of the aggregate) and tetrameric
(tBuLi)4, (1/2 of the tetramer), either of these oligomeric
structures having been detected in the crystal structures of
tBuLi and (R,R)-7.[4a,14g] Analogous structures of α-lithi-
ated (R,R)-TMCDA with further incorporated alkyllith-
iums have not been isolated so far, although even sBuLi,
nBuLi and iPrLi allow the direct deprotonation of 3.
Results and Discussion
Lithiation of (R,R)-TMCDA and trans-TMCDA
Recently we reported the direct deprotonation of the chi-
ral nitrogen ligand (R,R)-TMCDA with several organo-
lithium bases.[4a] The deprotonation of one methyl group of
the diamine proceeded easily by simple warming a solution
of 3 with an equivalent amount of the organolithium base
to room temperature. This facile lithiation prompted us to
investigate a possible deprotonation of a methyl group at
each nitrogen atom. However, these dilithiation attempts
were always unsuccessful, providing trapping products of
the monolithiated diamine (R,R)-7 and the excess alkyllith-
ium. Crystallisation of (R,R)-TMCDA with an excess of
tert-butyllithium resulted in the formation of a mixed aggre-
gate with incorporation of the second equivalent of organo-
lithium base into the lithiated amine. Storage of a mixture
of (R,R)-3 and tBuLi in a 1:2 ratio at –30 °C resulted in the
formation of colourless crystals of [tBuLi·(R,R)-TMCDA–
Li]2 [(R,R)-8]. The same crystals were obtained upon warm-
ing the solution to room temperature and subsequent cool-
ing to –78 °C (Scheme 1).
Figure 3. Molecular structure and numbering scheme of
[tBuLi·(R,R)-TMCDA–Li]2 [(R,R)-8] (hydrogen atoms of the lithi-
ated TMCDA omitted for clarity – except of those at the metalated
carbon atom). Selected bond lengths [Å] and angles [°]: Li1–C11
2.180(7), Li1–C7 2.247(6), Li2–C7 2.301(7), Li2–C11 2.198(7), Li2–
C25 2.151(7), Li3–C7 2.138(8), Li3–C15 2.188(8) Li3–C25 2.334(8)
Li4–C25 2.240(8), Li4–C15 2.177(8), Li1–N2 2.036(7), Li1–N1
1.975(7), Li4–N3 1.971(7), Li4–N4 2.004(7); Li3–C7–Li2 67.6(3),
Li1–C7–Li2 63.9(2), Li1–C11–Li2 66.7(2), Li2–C25–Li3 66.8(2),
Li2–C25–Li4 101.8(3), Li3–C25–Li4 63.6(3), Li3–C15–Li4 67.0(3).
For crystallographic details, see Table 2.
[tBuLi·(R,R)-TMCDA–Li]2 [(R,R)-8] crystallises in the
monoclinic crystal system, space group P21. The adduct
(Figure 3) consists of two molecules of tBuLi and two mole-
cules of the α-lithiated (R,R)-TMCDA. The central struc-
tural motif is formed by three Li–C–Li–C four-membered
rings connected by one common edge. The four-membered
rings exhibit a distorted arrangement with strongly varying
The formation of the mixed aggregate with tBuLi incor-
Li–C distances between 2.138(8) and 2.301(7) Å. The Li–N porated is also consistent with the non-observed dilithi-
distances range between 1.971(7) and 2.036(7) Å and are ation. Such a dilithiation has been observed for tetrameth-
thus in the range of known dimeric organolithium com- ylmethylenediamine.[5a] As is obvious from the crystal struc-
pounds.[13,14] Such a mixed aggregate of an α-lithiated ture, the distances between the carbanionic centre and the
Eur. J. Inorg. Chem. 2010, 5640–5649
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5641

V. H. Gessner, B. Fröhlich, C. Strohmann
FULL PAPER
α-carbon atoms are long such that in this rather rigid sys-
tem sufficient proximity between these groups can not be
realised.[15] In addition, starting from 8 as intermediate of
the deprotonation of the second NMe2 moiety, only a tran-
sition state is imaginable in which the aggregates open to
achieve the required spatial proximity. This leads to cleav-
age of the stabilising Li–C interactions and thus to an ener-
getic disadvantage of the direct deprotonation. Accordingly,
no reasonable transition states can be located for this lithi-
ation reaction.
Attempts to deprotonate the racemic mixture of (R,R)-
and (S,S)-TMCDA, trans-TMCDA (trans-3), gave results
comparable to the enantiomerically pure compound, that
is, selective lithiation of the methyl group of the diamine.
Warming of a previously cooled mixture of tBuLi and
trans-TMCDA to room temperature and subsequent cool-
ing to –30 °C resulted in the formation of colourless plates
of the tetrameric compound (trans-TMCDA–Li)4 (trans-7;
Scheme 2).
Figure 4. Molecular structure and numbering scheme of (trans-
TMCDA–Li)4 (trans-7; hydrogen atoms of the lithiated TMCDA
have been omitted for clarity except for those at the metallated
carbon atom). Selected bond lengths [Å] and angles [°] (symmetry
operations: y – 1, –x + 1, –z; –y + 1, x + 1, –z): C9–LiЈЈЈ 2.122(4),
C9–Li 2.163(5), Li–C9ЈЈ 2.122(4), Li–N2 2.021(4), Li–N1 2.102(5),
Li–LiЈЈ 3.043(6), Li–LiЈЈЈ 3.043(6); N2–C9–LiЈЈЈ 139.9(2), N2–C9–
Li 63.97(15), LiЈЈЈ–C9–Li 90.52(18), N2–Li–N1 86.42(15), N2–Li–
C9ЈЈ 148.2(2), N1–Li2–C9ЈЈ 109.3(2), N2–Li–C9 42.00(10) N1–Li–
C9 109.64(17), C9ЈЈ–Li–C9 140.4(2), C9–N2–Li 74.03(16), LiЈЈ–Li–
LiЈЈЈ 82.76(11). For crystallographic details, see Table 2.
Scheme 2. Direct deprotonation of trans-TMCDA with tert-butyl-
lithium to yield tetrameric, lithiated trans-TMCDA.
not be assigned due to the deficiency of a heavy atom. This
suggests that the use of trans-TMCDA results in the forma-
tion of a mixture of enantiomorphous crystals of the
enantiomers tBuLi·(R,R)-TMCDA and tBuLi·(S,S)-
TMCDA.
Racemic lithiated TMCDA (trans-7) crystallises in the te-
¯
tragonal crystal system in the space group P421/c. The
asymmetric unit contains one lithiated molecule which as-
sembles to the tetrameric structure shown in Figure 4 with
S4 symmetry. In the tetramer both enantiomers (R,R)- and Preparation of the N,N,O Ligands
(S,S)-TMCDA alternate. The central structural motif con-
For the preparation of the desired N,N,O ligands, (R,R)-
sists of a distorted Li–C eight-membered ring, the Li–C dis-
tances of which are 2.163(5) and 2.122(4) Å and the Li–N
distances are 2.102(5) and 2.021(4) Å and are thus compar-
able with monomeric and dimeric organolithium com-
pounds and lithiated (R,R)-TMCDA.[13] Most interestingly,
the change from the enantiomerically pure (R,R)-TMCDA
to the racemic mixture trans-TMCDA resulted in a struc-
tural change from the trimeric adduct, which we found for
(R,R)-7, to the highly symmetric tetramer. Analogous to
(R,R)-7, trans-TMCDA can also be deprotonated with sec-
butyl-, n-butyl and isopropyllithium as lithium bases.
The ready deprotonation of TMCDA to 7 presumably
proceeds by a two-step mechanism via the monomeric spe-
cies tBuLi·(R,R)-TMCDA. In this adduct the amine and
the deprotonation reagent are in proximity resulting in a
decrease in the reaction barrier thus enabling the lithiation
even under mild reaction conditions. This is confirmed by
computational studies showing a barrier of 98 kJ/mol for
the deprotonation with tert-butyllithium and of 94 kJ/mol
with sec-butyllithium. The monomeric adduct tBuLi·(R,R)-
TMCDA could also be isolated from a mixture of tBuLi
and racemic trans-TMCDA, crystallising in the same unit
cell. However, the absolute configuration of the amine can-
TMCDA [(R,R)-3] was treated with 1.2 equiv. of tert-butyl-
lithium for 4 h at room temperature to achieve quantitative
deprotonation. The lithiated amine (R,R)-5 was then
trapped with an aldehyde or ketone at low temperatures to
yield, after aqueous work-up and kugelrohr distillation, the
corresponding alcohol as colourless to slightly yellow oils
(see Scheme 3, Table 1). The yields of the thus-prepared
N,N,O ligands of type 4 varied only slightly between 61 and
70%. An increase in the yield could not be achieved even
by varying the amount of deprotonation reagent, which
may be related to a deprotonation of the aldehydes in a
side-reaction. The deprotonation of TMCDA itself occurs
almost quantitatively, which was shown by trapping the li-
thiated amine (R,R)-7 with tributyltin chloride to give the
α-stannylated amine (R,R)-9 in over 90% yield after work-
up and kugelrohr distillation.
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Preparation of Chiral N,N,O Ligands by Asymmetric 1,2-Addition
in dichloromethane resulted in the formation of colourless
plate-shaped crystals in 89% yield (Scheme 4, Figure 5).
The uniformity of the crystals was verified by CHN analy-
sis. Analogous compound 11 with the same structural fea-
tures is formed with copper(I) iodide, which is oxidised by
air-oxygen to copper(II) (Figure 6). The zinc complex is a
part of systematic studies on the catalysis of the ring-open-
ing polymerisation of lactide. Analogous complexes with
TMCDA-based diamine ligands have already been revealed
to be efficient initiators.
Scheme 3. Preparation of chiral N,N,O ligands 4 by a lithiation/
trapping sequence of (R,R)-TMCDA.
Table 1. Preparation of N,N,O ligands by trapping of lithiated
(R,R)-TMCDA with ketones and aldehydes.
Temp. Yield
Product
Carbonyl compd.
R
RЈ
dr[a]
Scheme 4. Formation of zinc complex 10.
[°C]
[%]
(R,R)-4a paraformaldehyde
(R,R)-4b benzophenone
(R,R)-4c benzaldehyde
(R,R)-4c benzaldehyde
(R,R)-4c benzaldehyde
(R,R)-4d isobutyraldehyde
(R,R)-4d isobutyraldehyde
(R,R)-4d isobutyraldehyde
(R,R)-4e isovaleraldehyde
(R,R)-4f pivaldehyde
H
Ph
Ph
Ph
Ph
iPr
iPr
iPr
iBu
tBu
tBu
H
Ph
H
H
H
H
H
H
H
H
H
–30
–30
–40
–90
–110
–40
68
65
68
64
68
60
70
65
61
61
62
65:35
80:20
82:18
65:35
79:21
82:18
78:22
55:45
80:20
–78
–110
–110
–40
(R,R)-4f pivaldehyde
–110
1
[a] Diastereomeric ratio determined by H NMR spectroscopy.
By using aldehydes or unsymmetrical ketones the asym-
Figure 5. Molecular structure and numbering scheme of the zinc
metric 1,2-addition of lithiated (R,R)-TMCDA according complex 10 with the ethanol derivative 4a of (R,R)-TMCDA in the
crystal. Selected bond lengths [Å] and angles [°]: Br1–Zn1
to Scheme 3 led to the introduction of further stereoinfor-
22.4080(16), Br2–Zn2 2.4250(15), N1–Zn1 2.150(8), N2–Zn1
mation into the molecule at the α position with respect to
2.277(7), N3–Zn2 2.207(8), N4–Zn2 2.212(8), O1–Zn1 1.983(7),
the hydroxy function. The facile variation of this introduced
O1–Zn2 2.010(7), O2A–Zn2 1.967(9), O2A–Zn1 2.069(10), O2B–
substituent is a great advantage of the preparation method
described herein. To evaluate the stereoselectivity of the in-
troduction of this additional stereocentre, the lithiated
amine was treated with benzaldehyde, isobutyraldehyde,
isovaleraldehyde and pivaldehyde. After aqueous work-up
Zn1 2.02(2), O2B–Zn2 2.16(2); Zn1–O1–Zn2 101.5(3), Zn2–O2A–
Zn1 100.0(4), Zn1–O2B–Zn2 95.6(10), O1–Zn1–O2B 80.5(7), O1–
Zn1–O2A 78.3(3), O1–Zn1–N1 126.9(3), O2B–Zn1–N1 77.2(7),
O2A–Zn1–N1 95.3(4), O1–Zn1–N2 84.0(3), O2B–Zn1–N2
136.3(8), O2A–Zn1–N2 154.0(4), N1–Zn1–N2 80.2(3), O2A–Zn2–
O1 80.1(4), O1–Zn2–O2B 76.5(7), O2A–Zn2–N3 126.6(4), O1–
the diastereomeric ratio of the crude product was deter- Zn2–N3 90.4(3), O2B–Zn2–N3 145.7(7), O2A–Zn2–N4 80.6(4),
O1–Zn2–N4 147.7(3), O2B–Zn2–N4 93.5(7), N3–Zn2–N4 80.8(3).
For crystallographic details, see Table 3.
mined by NMR spectroscopy. As can be seen from Table 1,
the ratio of the diastereomers is only moderate with ratios
of up to 82:18 for (R,R)-4c and (R,R)-4d with phenyl and
isopropyl substituents, respectively. The higher selectivities
The zinc compound 10 crystallises in the orthorhombic
observed at lower trapping temperatures are consistent with crystal system, space group P212121, the copper adduct 11
a kinetically controlled reaction process typical of such in the monoclinic crystal system, space group P21. The ste-
asymmetric addition reactions. Both diastereomers can be reogenic carbon atoms exhibit the R configuration, which
separated by column chromatography. Table 1 gives an confirms the retention of the absolute configuration during
overview of the reaction conditions and the selectivities and the lithiation/addition reaction sequence. The central struc-
yields obtained.
tural motif of both compounds is formed by a planar
Studies of the coordination behaviour of the N,N,O li- metal–oxygen four-membered ring [sum of angles: Zn com-
gands towards alkyllithiums resulted in no suitable crystals plex 10: 359.3(4)°; Cu complex 11: 360(3)°] with M–O bond
for structure analysis. This may be related to the higher sol- lengths between 1.982(8) and 2.027(8) Å for 10 and
ubility of the corresponding hydroxy adducts relative to the 1.914(10) and 1.977(10) for 11. The metal atoms exhibit a
non-hydroxy-functionalised TMCDA analogue ligands.[4] five-fold coordination with a distorted square-pyramidal ar-
However, crystallisation of the ethanol derivative 4a (trap- rangement of the ligand atoms. Thus, each metal atom pos-
ping product with paraformaldehyde) with zinc(II) bromide sesses two contacts with the oxygen and nitrogen atoms of
Eur. J. Inorg. Chem. 2010, 5640–5649
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5643

V. H. Gessner, B. Fröhlich, C. Strohmann
FULL PAPER
Conclusions
We have reported herein the direct deprotonation of en-
antiomerically pure (R,R)-TMCDA and its racemic mixture
trans-TMCDA with organolithium bases. Although the en-
antiomerically pure compound forms a trimeric structure,
direct lithiation of the racemic mixture of the amine (trans-
TMCDA) yields a tetrameric compound with both enantio-
meric forms in the crystal. With 2 equiv. of the deproton-
ation reagent, no dilithiation was observed but the forma-
tion of the mixed aggregate 8 consisting of the lithiated di-
amine and incorporated tert-butyllithium. On treatment of
lithiated TMCDA [(R,R)-7] with carbonyl compounds a
series of chiral N,N,O ligands can easily be synthesised by
varying the substituents at the α position with respect to
the hydroxy function. The employment of aldehydes also
led to the introduction of a further stereocentre. Prelimi-
nary crystallisation studies showed the formation of zinc
bromide and copper iodide complexes. We are currently fur-
ther investigating the coordination behaviour of the pre-
sented N,N,O ligands with special focus on the compounds
with a further stereocentre.
Figure 6. Molecular structure and numbering scheme of the copper
complex 11 with the ethanol derivative 4a of (R,R)-TMCDA in the
crystal. Selected bond lengths [Å)] and angles [°]: Cu1–O1 1.948(9),
Cu1–O2 1.977(10), Cu1–N2 2.036(11), Cu1–N1 2.054(12), Cu1–I1
2.884(2), Cu1–Cu2 2.959(2), Cu2–O1 1.914(10), Cu2–O2 1.968(9),
Cu2–N3 2.021(12), Cu2–N4 2.096(11), Cu2–I2 2.868(2), O1–C1–
N2 157.4(5), O2–Cu1–N2 96.5(4), O1–Cu1–N1 86.7(4), O2–Cu1–
N1 154.2(5), N2–Cu1–N1 86.8(5), O1–Cu2–O2 81.6(4), O1–Cu2–
N3 151.2(5), O2–Cu2–N3 83.0(4), O1–Cu2–N4 96.8(4), O2–Cu2–
N4 154.7(5), N3–Cu2–N4 87.0(5), Cu2–O1–Cu1 100.0(4), Cu2–
O2–Cu1 97.2(4), O1–Cu1–O2 80.5(4). For crystallographic details,
see Table 3.
the N,N,O ligand and one contact with the halide, which
occupies the vertex of the pyramid. Upon coordination of
the metal to the ligand the nitrogen atom of the ligand with
the ethanol side-arm becomes stereogenic. In the molecular
structures of 10 and 11, R and S configurations at the corre-
sponding nitrogen atoms are found in each molecule and
thus no configuration seems to be preferred in the crystalli-
sation process.
In the molecular structure of the zinc(II) complex 10 a
disorder of the ethoxy bridge is found in the crystal (not
depicted in Figure 5, see the Supporting Information).
Thus, the ethoxy bridge can also be detected at the nitrogen
atoms N1 and N3. Regarding the stereogenic nitrogen
atoms, only one isomer (with R as well as S configuration)
is present in the crystal, which packs differently in the crys-
tal. NMR studies also indicate the formation of both con-
Experimental Section
General: All experiments were carried out under dry, oxygen-free
argon using standard Schlenk techniques. Solvents were dried with
sodium and distilled prior to use. (R,R)- and trans-TMCDA were
prepared according to literature procedures by Eschweiler–Clarke
reaction of the corresponding amine and enantiomerically pure tar-
taric salt, respectively.[10c,17] “H2O” is distilled water. tert-Butyllith-
ium was titrated against diphenylacetic acid. 1H, 13C and 7Li NMR
spectra were recorded with DRX-300 and AMX-500 Bruker spec-
trometers at 22 °C. The signals were assigned on the basis of ad-
ditional DEPT-135 and C,H COSY experiments. All chemical
shifts (δ) are given in ppm. All spin–spin coupling constants (J)
are given in hertz (Hz). GC–MS analyses were performed with a
ThermoQuest TRIO-1000 apparatus (EI = 70 eV; column: Zebron;
figurations at the nitrogen atoms in solution, as found in
the crystal structure. The H NMR spectrum of the zinc with a Jasco P1030 polarimeter (cell path = 1.00 dm, temperature
capillary GC column: ZB-1. Optical rotations were determined
¯
1
= 20.0 °C, wavelength λ = 589 nm).
complex shows a splitting of the signals of the N(CH3)2 and
the N(CH3)CH2 moieties into four sharp signals of the
same and a fifth of double intensity (overlap of two signals;
see the Supporting Information). In the 13C NMR spec-
trum six signals for each of the six methyl groups are evi-
dent. This is expected for the coordination adduct of (R,R)-
4a in which the N(CH3)2 methyl groups become dia-
stereotopic upon coordination of the zinc bromide and ad-
ditionally differ in the configuration of the second nitrogen
atom. The same splitting is also evident in the H NMR
spectrum for the CH2OH units (see the Supporting Infor-
mation).
For the N,N,O ligands with a further stereocentre (4c–f),
no crystals of sufficient quality for X-ray diffraction analy-
sis could be obtained. Instead, with zinc(II) bromide, de-
composition reactions with the reformation of (R,R)-
TMCDA were observed. As such, TMCDA-coordinated
ZnBr2 could be isolated from a mixture of the methylbut-
anol derivative 4e and the metal salt in acetone.[16]
[tBuLi·(R,R)-TMCDA–Li]2 [(R,R)-8]: In a Schlenk vessel, (R,R)-
TMCDA [(R,R)-4; 170 mg, 1.00 mmol] was dissolved in n-pentane
(5 mL) and cooled to –78 °C. At this temperature tBuLi (1.6 m
solution in n-pentane, 1.3 mL, 2.08 mmol) was cautiously added
and kept at –30 °C for crystallisation. Colourless crystals of the
mixed aggregate formed after 3 d (175 mg, 0.73 mmol; 73%). NMR
studies were not possible due to lithiation of the solvent (benzene,
toluene) or insolubility (pentane). The same crystals were obtained
on warming to room temperature and subsequent cooling to
–78 °C.
1
(trans-TMCDA–Li)4 (7): In a Schlenk vessel, trans-TMCDA (trans-
3; 170 mg, 1.00 mmol) was dissolved in n-pentane (6 mL) and
cooled to –78 °C. At this temperature tBuLi (1.6 m solution in n-
pentane, 1 mL, 1.6 mmol) was cautiously added, the solid formed
was dissolved by warming to room temp. and then kept at room
temp. for an additional hour. Subsequent cooling to –78 °C gave
colourless crystals of the lithiated amine after 24 h
(137 mg,0.82 mmol; 82%). 1H NMR (500.1 MHz, [D8]Tol): δ =
0.99–1.04 (m, 5 H, 2 CH2, CH2Li), 1.38–1.40 (m, 1 H, CH2Li),
5644
www.eurjic.org
© 2010 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Eur. J. Inorg. Chem. 2010, 5640–5649

Preparation of Chiral N,N,O Ligands by Asymmetric 1,2-Addition
1.52–1.60 (m, 2 H, CH2), 1.66–1.70 (m, 3 H, LiCH2NCH3), 1.74–
1.79 (m, 2 H, CH2), 2.14 (br. s, 4 H, NCH3, NCH), 2.54 (br. s, 4
126.3, 127.3 (CHmeta), 127.0, 127.9 (CHortho), 148.0, 148.2
(Cipso) ppm. C23H32N2O (352.51): calcd. C 78.37, H 9.15, N 7.95;
H, NCH3, NCH) ppm. {1H}13C NMR (125.8 MHz, [D8]Tol): δ = found C 77.82, H 8.52, N 7.95. GC–MS (EI): tR = 12.41 min [80 °C
20.2 (CH2), 21.4, (CH2Li), 25.7 (2 CH2), 25.9 (CH2), 35.3 (2 min) – 10 °C/min – 280 °C (5 min)]: m/z (%) = 334 (5) [M –
(LiCH2NCH3), 43.4 (NCH3), 48.7 (NCH3), 64.8 (CHN), 66.0 H2O]+, 181 (25) [C6H10(NMe2)N(CH3)C2H2]+, 167 (40) [Ph2CH]+,
(CHN) ppm. 7Li NMR (194.4 MHz, [D8]Tol): δ = 1.9 ppm. VT
NMR studies showed no separation of the mainly broad signals
upon cooling to –80 °C.
124 (25) [C6H9N(CH3)CH2]+, 105 (80) [PhC2H4]+ 84 (55)
[C6H12]+, 77 (100) [C6H5]+.
Phenylethanol Derivative (R,R)-4c: By using the above general pro-
cedure, (R,R)-TMCDA [(R,R)-3; 5.00 g, 29.4 mmol] was treated
with benzaldehyde (1.3 equiv.) at low temperatures (see Table 1).
Work-up and bulb-to-bulb distillation (oven temperature 171 °C;
1ϫ10–2 mbar) gave the product as a colourless oil. NMR studies
showed the formation of both diastereomers in ratios that are de-
pendent upon the trapping temperatures. The two diastereomers
can be separated by column chromatography on silica gel (n-pen-
tane/2-propanol/triethylamine = 11:10:1). For yields and dia-
stereomeric ratios, see Table 1.
General Procedure for the Trapping of Lithiated TMCDA with Alde-
hydes and Ketones: (R,R)-TMCDA [(R,R)-3] was dissolved in n-
pentane and cooled to –50 °C. At this temperature a tert-butyllith-
ium (1.2 equiv.) solution in n-pentane was added, which resulted in
the formation of tBuLi·(R,R)-TMCDA as a colourless precipitate.
After warming to room temperature the mixture was stirred for
4 h, whereupon the solid dissolved. The mixture was then cooled
(temperature see below), trapped with an excess of the correspond-
ing aldehyde/ketone and stirred for further 2 h at room tempera-
ture. The alcoholate formed was hydrolysed by the addition of
2.5 m HCl (20 mL). After the addition of diethyl ether (30 mL) the
combined organic layers were extracted 2.5 m HCl (3ϫ20 mL). The
aqueous layers were afterwards basified to pH 12 with NaOH and
finally extracted with diethyl ether (3ϫ30 mL). The combined or-
ganic layers were dried with Na2SO4 and after removal of all vola-
tile compounds in vacuo, the crude product was purified through
bulb-to-bulb distillation to give the N,N,O ligands as colourless
oils. The diastereomeric ratios were determined by NMR spec-
troscopy.
Major diastereomer: 1H NMR (400.1 MHz, CDCl3): δ = 0.87–0.97
(m, 1 H, CH2 cyclohexyl), 1.08–1.15 (m, 3 H, CH2 cyclohexyl),
1.71–1.78 (m, 2 H, CH2 cyclohexyl), 1.87–1.95 (m, 2 H, CH2 cyclo-
2
hexyl), 2.23, 2.49 (AB system, JAB = 13.8 Hz, 2 H, CH2N), 2.29
[s, 6 H, N(CH3)2], 2.37–2.42 (m, 2 H, CHN), 2.50 [s, 3 H, N(CH3)
3
CH2], 4.64 (dd, JHH = 10.4 Hz, 1 H, CHOH), 7.17–7.22 (m, 1 H,
CHpara), 7.27–7.31 (m, 2 H, CHarom.), 7.34–7.37 (m, 2 H, CHarom.),
7.60–8.00 (br., 1 H, OH) ppm. {1H}13C NMR (100.6 MHz,
CDCl3):
δ = 21.3, 23.8, 25.3, 25.5 (CH2 cyclohexyl), 39.0
[N(CH3)2], 41.0 (NCH3), 58.7 (CH2N), 64.1, 64.2 (CHN), 70.9
[CH(Ph)OH], 125.9, 126.8, 128.1 (CHarom.), 144.0 (Cipso) ppm.
[α]2D0 = –145.2 (c = 0.493 g/100mL, cyclohexane). C17H28N2O
(276.42): calcd. C 73.87, H 10.21, N 10.13; found C 73.81, H 12.16,
N 10.86. GC–MS (EI): tR = 9.65 min [80 °C (2 min) – 10 °C/min –
280 °C (5 min)]: m/z (%) = 258 (32) [M – H2O]+, 170 (23) [C6H10-
(NMe2)2]+, 124 (60) [C6H9N(CH3)CH2]+, 84 (72) [C6H12]+, 71 (80)
[C4H10N]+, 58 (100) [N(CH3)2CH2]+. RF = 0.80 (n-pentane/2-pro-
panol/Et3N = 11:10:1).
Ethanol Derivative (R,R)-4a: By using the above general procedure,
(R,R)-TMCDA [(R,R)-3; 5.00 g, 29.4 mmol] was trapped with pa-
raformaldehyde (1.30 g, 42.9 mmol; suspension in ethyl ether) at
–35 °C. Bulb-to-bulb distillation (oven temperature 80 °C,
10–3 mbar) gave (R,R)-4a as a colourless oil (3.98 g, 19.9 mmol;
68%). 1H NMR (400.1 MHz, CDCl3): δ = 0.91–1.20 (m, 4 H, CH2
cyclohexyl), 1.66–1.75 (m, 2 H, CH2 cyclohexyl), 1.78–1.82 (m, 1
H, CH2 cyclohexyl), 1.88–1.94 (m, 1 H, CH2 cyclohexyl), 2.12–2.18
(m, 1 H, CH2N), 2.17 [s, 6 H, N(CH3)2], 2.23–2.29 (m, 2 H, CHN),
2.31 [s, 3 H, N(CH3)CH2], 2.63–2.73 (m, 1 H, CH2N), 3.30–3.36
Minor diastereomer: 1H NMR (400.1 MHz, CDCl3): δ = 1.08–1.16
(m, 4 H, CH2 cyclohexyl), 1.71–1.78 (m, 2 H, CH2 cyclohexyl),
1.84–1.89 (m, 2 H, CH2 cyclohexyl), 1.93 [s, 3 H, N(CH3)CH2],
2.27–2.33 (m, 1 H, CHN), 2.38 [s, 6 H, N(CH3)2], 2.38, 2.99 (AB
3
(m, 1 H, CH2OH), 3.53 (td, JHH = 10.7 Hz, 1 H, CH2OH), 6.20–
7.10 (br., 1 H, OH) ppm. {1H}13C NMR (100.6 MHz, CDCl3): δ
2
system, JAB = 13.5 Hz, 2 H, CH2N), 2.39–2.51 (m, 1 H, CHN),
=
21.3,
23.7,
25.4,
25.5
(CH2
cyclohexyl),
38.8
4.70 (br., 1 H, CHOH), 7.16–7.19 (m, 1 H, CHpara), 7.26–7.29 (m,
2 H, CHarom.), 7.33–7.35 (m, 2 H, CHarom.), 7.60–8.00 (br., 1 H,
OH) ppm. {1H}13C NMR (100.6 MHz, CDCl3): δ = 22.0, 24.1,
25.1, 25.5 (CH2 cyclohexyl), 39.1 [N(CH3)2], 40.0 (NCH3), 59.0
(CH2N), 63.4, 64.5 (CHN), 71.7 [CH(Ph)OH], 126.0, 126.3, 127.9
(CHarom.), 144.5 (Cipso) ppm. RF = 0.57 (n-pentane/2-propanol/
NEt3 = 11:10:1). [α]2D0 = 18.0 (c = 0.382 g/100mL, cyclohexane).
[N(CH3)2], 40.2 (NCH3), 51.2 (CH2N), 59.8 (CH2O), 64.14, 64.17
(CHN) ppm. [α]2D0 = –80.0 (c = 0.5538 g/100mL, cyclohexane).
C11H24N2O (200.32): calcd. C 65.95, H 12.08, N 13.98; found C
65.20, H 12.29, N 14.32. GC–MS (EI): tR = 6.85 min [80 °C
(2 min) – 10 °C/min – 280 °C (5 min)]: m/z (%) = 182 (32) [M –
H2O]+, 170 (23) [C6H10(NMe2)2]+, 124 (60) [C6H9N(CH3)CH2]+,
84 (72) [C6H12]+, 71 (80) [C4H10N]+, 58 (100) [N(CH3)2CH2]+.
Methylbutanol Derivative (R,R)-4d: By using the above general pro-
cedure, (R,R)-TMCDA [(R,R)-3; 5.00 g, 29.4 mmol] was treated
with isobutyraldehyde (1.3 equiv.) at low temperatures (Table 1).
Work-up and bulb-to-bulb distillation (oven temperature 125 °C;
1ϫ10–2 mbar) gave the product as a colourless oil. The two dia-
stereomers can be separated by column chromatography on silica
gel (n-pentane/2-propanol/triethylamine = 11:10:1). For yields and
diastereomeric ratios, see Table 1.
Diphenylethanol Derivative (R,R)-4b: By using the above general
procedure, (R,R)-TMCDA [(R,R)-2; 5.00 g, 29.4 mmol] was treated
with benzophenone (7.50 g, 41.2 mmol) at –40 °C. Work-up and
bulb-to-bulb distillation (oven temperature: 225 °C; 1ϫ10–2 mbar)
gave (R,R)-4b as a slightly yellow, highly viscous oil (6.72 g,
0.19 mmol; 65%). 1H NMR (400.1 MHz, CDCl3): δ = 1.02–1.14
(m, 4 H, CH2 cyclohexyl), 1.74 [s, 3 H, N(CH3)CH2], 1.75–1.79 (m,
2 H, CH2 cyclohexyl), 1,84–1.87 (m, 1 H, CH2 cyclohexyl), 1.92–
1.97 (m, 1 H, CH2 cyclohexyl), 2.22–2.29 (m, 1 H, CHN), 2.31 [s,
1
Major diastereomer: H NMR (500.1 MHz, CDCl3): δ = 0.89 (d,
3
6 H, N(CH3)2], 2.36–2.43 (m, 1 H, CHN), 3.06, 3.27 (AB system, 3JHH = 6.78 Hz, 3 H, CHCH3), 0.93 (d, JHH = 6.85 Hz, 3 H,
2JAB = 12.2 Hz, 2 H, CH2N), 7.13–7.15 (m, 2 H, CHpara), 7.16–
7.21 (m, 4 H, CHarom.), 7.23–7.27 (m, 2 H, CHarom.), 8.78 (br., 1
CHCH3), 0.98–1.16 (m, 4 H, CH2 cyclohexyl), 1.49–1.60 [m, 1 H,
CH(CH3)2], 1.71–1.75 (m, 2 H, CH2 cyclohexyl), 1,80–1.83 (m, 1
H, OH) ppm. {1H}13C NMR (100.6 MHz, CDCl3): δ = 21.3, 23.7, H, CH2 cyclohexyl), 1.91–1.95 (m, 1 H, CH2 cyclohexyl), 2.17 [s, 6
25.4, 25.5 (CH2 cyclohexyl), 38.9 [N(CH3)2], 42.2 (NCH3), 60.4
(CH2N), 63.7, 66.1 (CHN), 75.8 (COH), 125.7, 126.3 (CHpara),
H, N(CH3)2], 2.08, 2.31 (AB System, 2JAB = 12.1 Hz, 2 H, CH2N),
2.28–2.34 (m, 2 H, CHN), 2.35 (s, 3 H, NCH3), 3.28–3.31 (m, 1 H,
Eur. J. Inorg. Chem. 2010, 5640–5649
© 2010 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.eurjic.org
5645

V. H. Gessner, B. Fröhlich, C. Strohmann
FULL PAPER
CHOH), 8.78 (br., 1 H, OH) ppm. {1H}13C NMR (125.8 MHz, (100) [C6H9N(CH3)CH2]+, 84 (45) [C6H12]+, 58 (52) [N(CH3)2-
CDCl3): δ = 18.1, 18.8 [CH(CH3)2], 21.3, 23.7, 25.4, 25.6 (CH2
cyclohexyl), 32.0 [CH(CH3)2], 38.9 [N(CH3)2], 41.0 (NCH3), 53.0
CH2]+. RF = 0.39 (n-pentane/2-propanol/NEt3 = 11:10:1).
Dimethylbutanol Derivative (R,R)-4f: By using the above general
procedure, (R,R)-TMCDA [(R,R)-3; 5.09 g, 29.9 mmol] was treated
with pivaldehyde (1.3 equiv.) at low temperatures (Table 1). Work-
up and bulb-to-bulb distillation (oven temperature 125 °C;
1ϫ10–2 mbar) gave a mixture of two diastereomers of (R,R)-4f as
a colourless oil. For yields and diastereomeric ratios, see Table 1.
(NCH2),
64.0,
64.4
(CHN),
73.1
(CHOH) ppm.
[α]2D0 = –91.5 (c = 0.219 g/100mL, cyclohexane). C14H30N2O
(242.40): calcd. C 69.37, H 12.47, N 11.56; found C 69.41, H 12.46,
N 11.51. GC–MS (EI): tR = 7.10 min [80 °C (2 min) – 10 °C/min –
280 °C (5 min)]: m/z (%) = 224 (5) [M – H2O]+, 170 (40)
[C6H10(NMe2)2]+, 124 (100) [C6H9N(CH3)CH2]+, 84 (55) [C6H12]+,
77 (100) [C6H5]+, 58 (95) [N(CH3)2CH2]+. RF = 0.65 (n-pentane/2-
propanol/NEt3 = 11:10:1).
1
Major diastereomer: H NMR (500.1 MHz, CDCl3): δ = 0.88 [s, 9
H, C(CH3)3], 1.05–1.14 (m, 4 H, CH2 cyclohexyl), 1.71–1.75 (m, 2
H, CH2 cyclohexyl), 1,80–1.83 (m, 1 H, CH2 cyclohexyl), 1.93–1.96
(m, 1 H, CH2 cyclohexyl), 2.12, 2.32 (AB system, JAB = 11.8 Hz,
1 H, CH2N), 2.24 [s, 6 H, N(CH3)2], 2.28–2.37 (m, 2 H, CHN),
2.35 (s, 3 H, NCH3), 23.27 (dd, 3JHH = 11.0 Hz, 1 H, CHOH), 8.78
(br., 1 H, OH) ppm. {1H}13C NMR (125.8 MHz, CDCl3): δ = 23.3,
25.5, 25.8, 26.2 (CH2 cyclohexyl), 25.9 [C(CH3)3], 33.6 [C(CH3)3],
40.2 [N(CH3)2], 40.6 (NCH3), 56.8 (NCH2), 64.6, 65.2 (CHN), 74.0
1
Minor diastereomer: H NMR (500.1 MHz, CDCl3): δ = 0.86 (d,
3JHH = 6.80 Hz, 3 H, CHCH3), 0.96 (d, JHH = 6.70 Hz, 3 H,
CHCH3), 1.09–1.19 (m, 4 H, CH2 cyclohexyl), 1.56–1.62 [m, 1 H,
CH(CH3)2], 1.71–1.75 (m, 2 H, CH2 cyclohexyl), 1,80–1.83 (m, 1
H, CH2 cyclohexyl), 1.91–1.95 (m, 1 H, CH2 cyclohexyl), 2.22, 2.65
3
2
2
(AB system, JAB = 12.8 Hz, 2 H, CH2N), 2.26 [s, 6 H, N(CH3)2],
2.29 (s, 3 H, NCH3), 2.28–2.34 (m, 2 H, CHN), 3.21–3.25 (m, 1 H,
CHOH), 8.42 (br., 1 H, OH) ppm. {1H}13C NMR (125.8 MHz,
CDCl3): δ = 18.6, 19.1 [CH(CH3)2], 22.8, 25.4, 25.7 (CH2 cyclo-
hexyl), 32.3 [CH(CH3)2], 37.4 [N(CH3)2], 40.1 (NCH3), 57.7
(NCH2), 64.5, 65.4 (CHN), 72.9 (CHOH) ppm. RF = 0.45 (n-pen-
tane/2-propanol/NEt3 = 11:10:1) ppm. GC–MS (EI): analogous to
diastereomer 1 with a retention time of 7.18 min.
(CHOH) ppm. GC–MS (EI): tR
= 7.290 min [80 °C (2 min)
– 10 °C/min – 280 °C (5 min)]: m/z (%) = 257 (1) [MH]+, 199 (15)
[M – CCH3]+, 170 (50) [C6H10(NMe2)2]+, 124 (70) [C6H9N(CH3)-
CH2]+, 84 (45) [C6H12]+, 58 (100) [N(CH3)2CH2]+. RF = 0.67 (n-
pentane/2-propanol/Et3N = 11:10:1). C15H32N2O (256.43): calcd.
C 70.26, H 12.58, N 10.92; found C 69.55, H 12.62, N 11.88.
Methylpentanol Derivative (R,R)-4e: By using the above general
procedure, (R,R)-TMCDA [(R,R)-3; 5.00 g, 29.4 mmol] was treated
at –110 °C with isovaleraldehyde (1.3 equiv.) at low temperatures
(Table 1). Work-up and bulb-to-bulb distillation (oven temperature
171 °C; 2ϫ10–2 mbar) gave product (R,R)-4e as a 78:22 mixture of
two diastereomers as a colourless oil (4.64 g, 0.18 mmol; 61%).
Minor diastereomer: 1H NMR (500.1 MHz, CDCl3): δ = 0.86 [s, 9
H, C(CH3)3], 1.05–1.14 (m, 4 H, CH2 cyclohexyl), 1.71–1.75 (m, 2
H, CH2 cyclohexyl), 1,79–1.91 (m, 2 H, CH2 cyclohexyl), 2.19, 2.65
2
(AB system, JAB = 13.1 Hz, 1 H, CH2N), 2.17 [s, 6 H, N(CH3)2],
3
2.22 (s, 3 H, NCH3), 2.24–2.29 (m, 2 H, CHN), 3.19 (dd, JHH
=
10.5 Hz, 1 H, CHOH), 8.42 (br., 1 H, OH) ppm. {1H}13C NMR
(125.7 MHz, CDCl3): δ = 21.2, 23.7, 25.6, 25.7 (CH2 cyclohexyl),
25.8 [C(CH3)3], 33.3 [C(CH3)3], 35.4 (NCH3), 39.0 [N(CH3)2], 50.6
(NCH2), 63.9, 64.6 (CHN), 75.4 (CHOH) ppm. RF = 0.45 (n-pen-
tane/2-propanol/Et3N = 11:10:1). GC–MS (EI): analogous to dia-
stereomer 1 with a retention time of 7.167 min.
Major diastereomer: 1H NMR (500.1 MHz, CDCl3): δ = 0.87 [d,
3
3JHH = 6.62 Hz, 3 H, C(CH3)2], 0.87 [d, JHH = 6.63 Hz, 3 H,
C(CH3)2], 0.97, 1.27 [m, 2 H, CH2CH(CH3)2], 1.05–1.12 (m, 4 H,
CH2 cyclohexyl), 1.71–1.75 (m, 2 H, CH2 cyclohexyl), 1.74–1.81
[m, 1 H, CH(CH3)2], 1.80–1.83 (m, 1 H, CH2 cyclohexyl), 1.89–1.93
(m, 1 H, CH2 cyclohexyl), 2.03, 2.27 (AB system, 2JAB = 13.5 Hz, 2
H, CH2N), 2.18 [s, 6 H, N(CH3)2], 2.28–2.34 (m, 2 H, CHN), 2.36
(s, 3 H, NCH3), 3.57–3.62 (m, 1 H, CHOH), 6.75–7.05 (br., 1 H,
OH) ppm. {1H}13C NMR (125.8 MHz, CDCl3): δ = 21.1, 23.6,
25.4, 25.6 (CH2 cyclohexyl), 22.3, 23.6 [CH(CH3)2], 24.56
[CH(CH3)2], 38.9 [N(CH3)2], 41.2 (NCH3), 44.3 [CH2CH(CH3)2],
56.5 (NCH2), 63.9, 64.4 (CHN), 66.4 (CHOH) ppm. GC–MS (EI):
tR = 7.613 min [80 °C (2 min) – 10 °C/min – 280 °C (5 min)]: m/z
(%) = 257 (1) [MH]+, 170 (100) [C6H10(NMe2)2]+, 128 (40)
[C6H11NH(CH3)2]+, 110 (40) [C6H9NHCH2]+, 96 (35) [C6H9N]+.
C15H32N2O (256.43): calcd. C 70.26, H 12.58, N 10.92; found C
69.60, H 12.30, N 11.61. RF = 0.53 (n-pentane/2-propanol/Et3N =
11:10:1).
Preparation of α-Stannylated Amine (R,R)-9: By using the above
general procedure, (R,R)-TMCDA [(R,R)-3; 200 mg, 1.17 mmol]
was treated with tBuLi (1.2 equiv.) and trapped with tributyltin
chloride (1.3 equiv.) at –60 °C. Work-up and bulb-to-bulb distil-
lation (oven temperature 160 °C, 2ϫ10–2 mbar) gave the stan-
nylated compound (R,R)-7 as a colourless oil that solidifies upon
storage over weeks (491 mg, 1.07 mmol; 91%). 1H NMR
(500.1 MHz, CDCl3, CDCl3): δ = 0.77–0.95 (m, 6 H, SnCH2), 0.88
3
(t, JHH = 7.30 Hz, 9 H, SnCH2CH2CH2CH3), 1.07–1.21 [m, 4 H,
CH2 cyclohexyl], 1.30 (sext., 3JHH
=
7.26 Hz,
6
H,
SnCH2CH2CH2CH3), 1.37–1.52 (m, 6 H, SnCH2CH2CH2), 1.67–
1.72 (m, 2 H, CH2 cyclohexyl), 1.80–1.83 (m, 1 H, CH2 cyclohexyl),
1.85–1.87 (m, 1 H, CH2 cyclohexyl), 2.23 [s, 3 H, N(CH3)CH2Sn],
1
Minor diastereomer: H NMR (500.1 MHz, CDCl3): δ = 0.87 [d,
3
3JHH = 6.62 Hz, 3 H, C(CH3)2], 0.87 [d, JHH = 6.63 Hz, 3 H,
2.34 [s, 6 H, N(CH3)2], 2.34–2.38 (m, 2 H, CHN), 2.43, 2.63 (AB
3
system, JAB
=
11.9 Hz, NCH2Sn) ppm. {1H}13C NMR
C(CH3)2], 1.06, 1.38 [AB system, 2 H, CH2CH(CH3)2], 1.07–1.16
(m, 4 H, CH2 cyclohexyl), 1.71–1.75 (m, 2 H, CH2 cyclohexyl),
1.76–1.84 [m, 1 H, CH(CH3)2], 1,80–1.83 (m, 1 H, CH2 cyclohexyl),
(125.8 MHz, CDCl3, CDCl3): δ = 9.7 (1J117Sn–C = 146.9, J119Sn-C
1
= 153.6 Hz, SnCH2), 13.7 (CH3), 23.0, 25.5, 25.7, 26.5 (CH2 cyclo-
2
hexyl), 27.4 (3JSn-C = 27.0 Hz, SnCH2CH2CH2), 26.9 (2JSn-C
=
1.89–1.93 (m, 1 H, CH2 cyclohexyl), 2.14, 2.66 (AB system, JAB
10.1 Hz, SnCH2CH2), 40.1 (1J117Sn-C = 174.0, 1J119Sn-C = 180.6 Hz,
NCH2Sn), 40.7 [N(CH3)2], 41.2 [3JSn-C = 18.7 Hz, N(CH3)CH2Sn,
63.9 (CHNMe2), 66.6 [CHN(Me)CH2Sn] ppm. 119Sn NMR
(111.9 MHz, CDCl3, CDCl3): δ = –31.3 ppm.
= 13.1 Hz, 2 H, CH2N), 2.25 (s, 3 H, NCH3), 2.28 [s, 6 H,
N(CH3)2], 2.24–2.29 (m, 2 H, CHN), 3.21 (m, 1 H, CHOH), 6.75–
7.10 (br., 1 H, OH) ppm. {1H}13C NMR (125.7 MHz, CDCl3): δ
= 21.1, 22.5, 25.3, 25.6 (cyclohexyl), 22.3, 23.6 [CH(CH3)2], 24.7
[CH(CH3)2], 38.9 (NCH3), 40.1 [N(CH3)2], 44.5 (CH2CHOH), 56.5
(NCH2), 63.9, 64.6 (CHN), 65.4 (CHOH) ppm. GC–MS (EI): tR
=
Zinc(II) Bromide Adduct 10: Zinc(II) bromide (168 mg, 0.75 mmol)
and (R,R)-4a (150 mg, 0.75 mmol) were dissolved in dichlorometh-
7.669 min [80 °C (2 min) – 10 °C/min – 280 °C (5 min)]: m/z (%) =
257 (1) [MH]+, 238 (3) [M – H2O]+, 170 (20) [C6H10(NMe2)2]+, 124 ane (20 mL). After storage at room temp. and slow evaporation of
5646
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© 2010 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Eur. J. Inorg. Chem. 2010, 5640–5649

Preparation of Chiral N,N,O Ligands by Asymmetric 1,2-Addition
the solvent colourless plates of compound 10 (231 mg, 0.34 mmol;
89%) were formed. For crystallographic data, see Table 3. 1H
NMR (400.1 MHz, CDCl3, CDCl3): δ = 1.10–1.38 (m, 8 H, CH2,
The crystal structure determinations were effected at –100 °C (type
of radiation: Mo-Kα, α = 0.71073 Å). The structures were solved
by applying direct and Fourier methods using SHELXS-90[19] and
cyclohexyl), 1.78–1.82 (m, 4 H, CH2, cyclohexyl), 1.89–2.08 (m, 4 SHELXL-97.[20]
H, CH2, cyclohexyl), 2.10–2.14 (m, 1 H, CH2, cyclohexyl), 2.33,
Table 2 gives further details of the data collection and structure
2.35, 2.40, 2.44 [s, 3 H, N(CH3)2], 2.55 [br., 6 H, NCH3], 2.49–2.74
[m, 8 H, N(CH2)CH3, CHN], 3.52–3.57 (m, 1 H, CH2O), 3.60–3.66
(m, 1 H, CH2O), 3.84–3.89 (m, 1 H, CH2O), 3.91–3.95 (m, 1 H,
CH2O) ppm. {1H}13C NMR (100.6 MHz, CDCl3, CDCl3): δ =
21.8, 22.8, 23.5, 24.1, 24.6, 24.8, 25.0 (cyclohexyl), 37.9, 39.4, 40.6,
41.7 [N(CH3)2], 45.5, 46.8 (NCH3), 52.9, 56.9 (CH2N), 58.3, 60.3
(CH2O), 59.7, 62.9, 63.22, 63.25 (CHN) ppm. C22H46Br2N4O2Zn2
(689.21): calcd. C 38.34, H 6.73, N 8.13; found C 38.45, H 6.10, N
8.15.
refinement of compounds 7 and 8 and Table 3 the details for com-
plexes 10 and 11. Further information, including ORTEP diagrams
and atomic coordinates, are available in the Supporting Infor-
mation
Table 3. Data collection and structure refinement details for the
adducts of 4a with zinc bromide and copper iodide.
10[a]
11
Formula
C22H46Br2N4O2Zn2
689.19
173(2)
C22H46Cu2I2N4O2
779.51
173(2)
0.71073
monoclinic
P21 (4)
9.948(5)
8.405(4)
16.995(7)
95.299(11)
1414.9(11)
2
1.830
3.710
772
0.30ϫ0.30ϫ0.10
1.20–25.00
–11ՅhՅ11
–9ՅkՅ9
–20ՅlՅ20
15797
Copper Iodide Adduct 11: Copper(I) iodide (45 mg, 0.24 mmol) was
dissolved in acetonitrile (2.0 mL) and acetone (1.0 mL) and (R,R)-
4a (40 mg, 0.20 mmol) were added. After storage at room temp.
and slow evaporation of the solvent, green needles of the adduct
were formed (65 mg, 0.08 mmol; 69%).
Formula weight [g/mol]
Temperature [K]
Wavelength [Å]
Crystal system
Space group
a [Å]
0.71073
orthorhombic
P212121 (19)
8.3789(17)
10.015(2)
33.877(7)
90
2842.8(10)
4
1.610
Crystallographic Analysis: Data collection for (R,R)-8 and trans-7
was conducted with a Stoe IPDS diffractometer. Data collection:
expose in IPDS (Stoe & Cie, 1999); cell determination and refine-
ment: cell in IPDS (Stoe & Cie, 1999); integration: integrate in
IPDS (Stoe & Cie, 1999); numerical absorption correction: Faceit
in IPDS (Stoe & Cie, 1999). Data collection for 10 and 11 was
conducted with a Bruker APEX-CCD (D8 three-circle goniometer)
(Bruker AXS); cell determination and refinement: Smart version
5.622 (Bruker AXS, 2001); integration with SaintPlus version 6.02
(Bruker AXS, 1999); empirical absorption correction with SAD-
ABS version 2.01 (Bruker AXS, 1999). Crystals of compounds
trans-7 and (R,R)-8 were mounted in an inert oil (perfluoropolyal-
kyl ether) at –60 °C (N2 stream) using the X-TEMP 2 device.[18]
b [Å]
c [Å]
β [°]
Volume [Å3]
Z
Calcd. density [Mg/m3]
μ(Mo-Kα) [mm–1]
F(000)
4.523
1408
Crystal dimensions [mm]
θ range [°]
Index ranges
0.40ϫ0.20ϫ0.10
1.20–25.00
–9ՅhՅ9
–11ՅkՅ11
–40ՅlՅ40
58862
Reflections collected
Independent reflections
4994 [Rint = 0.1128] 4962 [Rint = 0.0706]
Data/restraints/parameters 4994/0/312
4962/1/295
1.063
R1 = 0.0613
wR2 = 0.1535
R1 = 0.0709,
wR2 = 0.1597
Table 2. Data collection and structure refinement details for the
lithiated compounds (R,R)-8 and trans-7.
Goodness-of-fit on F2
Final R indices
[IϾ2σ(I)]
1.089
R1 = 0.0629
wR2 = 0.1762
R1 = 0.0740
wR2 = 0.1857
[(R,R)-8]
(trans-7)
Indices (all data)
Formula
C28H60Li4N4
480.56
173(2)
0.71073
monoclinic
P21 (4)
8.483(3)
18.650(6)
10.622(4)
91.36(8)
1680.0(10)
Z = 2
C40H84Li4N8
702.91
173(2)
Formula weight [g/mol]
Temperature [K]
Wavelength [Å]
Crystal system
Space group
a [Å]
Absolute structure
parameter
0.09(3)
0.16(6)
0.71073
[a] For refinement of disordered 10 a splitting model was used for
the position of the ethoxy groups giving a 70:30 ratio of the two
isomers (the main isomer is shown in Figure 3).
tetragonal
¯
P421/c
12.2949(16)
12.2949(16)
15.025(4)
90
2271.3(8)
Z = 2
1.031
0.060
784
b [Å]
c [Å]
β [°]
CCDC-752093 [for (R,R)-8], -752094 (for trans-7), -752095 (for 10)
and -752096 (for 11) contain the supplementary 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.
Volume [Å3]
Z
Calcd. density [Mg/m3]
μ(Mo-Kα) [mm–1]
F(000)
0.950
0.053
536
Computational Details: All calculations were performed without
symmetry restrictions. Starting coordinates were obtained directly
from the crystal structures. Optimisation and additional harmonic
vibrational frequency analyses (to establish the nature of stationary
points on the potential energy surface) were performed with the
software package Gaussian 03[21] (Revision D.01 and Revision
E.01) using B3LYP [Becke’s three-parameter exchange functional
(B3) and the Lee–Yang–Parr correlation functional (LYP)] and the
6-31+G(d) basis set. The total (SCF) and zero-point energies (ZPE)
and the coordinates of all systems are available in the Supporting
Information. The vibrational frequency analyses showed imaginary
frequencies for the transition states representing the corresponding
vibration for the deprotonation. For the starting materials no imag-
Crystal dimensions [mm]
θ range [°]
Index ranges
0.40ϫ0.20ϫ0.20
2.21–24.99
–9ՅhՅ10
–22ϽkϽ16
–12ϽlϽ12
8793
0.40ϫ0.40ϫ0.30
2.14–26.00
–15ՅhՅ15
–15ϽkϽ13
–18ϽlϽ10
6740
Reflections collected
Independent reflections
4589 [Rint = 0.0430] 2109 [Rint = 0.0421]
Data/restraints/parameters 4589/1/353
2109/0/137
1.008
R1 = 0.0523
wR2 = 0.1278
R1 = 0.0688
wR2 = 0.1388
Goodness-of-fit on F2
Final R indices
[IϾ2σ(I)]
1.023
R1 = 0.0525
wR2 = 0.1083
R1 = 0.0921
wR2 = 0.1220
R indices (all data)
Eur. J. Inorg. Chem. 2010, 5640–5649
© 2010 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.eurjic.org
5647

V. H. Gessner, B. Fröhlich, C. Strohmann
FULL PAPER
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[7]
Supporting Information (see also the footnote on the first page of
this article): Computational details (coordinates and absolute ener-
gies), additional NMR spectra and ORTEP plots of the crystal
structures.
[8]
[9]
Acknowledgments
We are grateful to the Deutsche Forschungsgemeinschaft (DFG)
and the Fonds der Chemischen Industrie for financial support and
the award of a doctoral scholarship (to V. H. G.).
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Eur. J. Inorg. Chem. 2010, 5640–5649

Preparation of Chiral N,N,O Ligands by Asymmetric 1,2-Addition
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Received: June 6, 2010
Published Online: November 17, 2010
Eur. J. Inorg. Chem. 2010, 5640–5649
© 2010 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.eurjic.org
5649