Synthesis of enantiomeric pure lithium and potassium benzamidinate complexes

Article abstract of DOI:10.1016/j.jorganchem.2010.07.020

A new synthesis leading to the chiral amidines (S,S)- and (R,R)-N,N-bis-(1-phenylethyl)benzamidine ((S)- and (R)-HPEBA) in good yields is presented. Further reaction of (S)-HPEBA with n-BuLi gave the chiral lithium salt (S)-LiPEBA. Treatment of KH with (S

Full text of DOI:10.1016/j.jorganchem.2010.07.020

Journal of Organometallic Chemistry 696 (2011) 1150e1155
Contents lists available at ScienceDirect
Journal of Organometallic Chemistry
journal homepage: www.elsevier.com/locate/jorganchem
Synthesis of enantiomeric pure lithium and potassium benzamidinate complexes
*
Paul Benndorf, Corinna Preuß, Peter W. Roesky
Institut für Anorganische Chemie, Karlsruher Institut für Technologie (KIT), Engesserstraße Geb. 30.45, 76131 Karlsruhe, Germany
a r t i c l e i n f o
a b s t r a c t
Article history:
A new synthesis leading to the chiral amidines (S,S)- and (R,R)-N,N-bis-(1-phenylethyl)benzamidine ((S)-
and (R)-HPEBA) in good yields is presented. Further reaction of (S)-HPEBA with n-BuLi gave the chiral
lithium salt (S)-LiPEBA. Treatment of KH with (S)-HPEBA in boiling THF afforded the corresponding
potassium salt (S)-KPEBA. In contrast by performing the reaction in boiling toluene a fast racemization
was observed. In the solid state racemic KPEBA formed a dimer, in which all four nitrogen atoms are in
Received 11 June 2010
Received in revised form
14 July 2010
Accepted 15 July 2010
a plane. To each potassium atom a toluene molecule is
h
6-coordinated.
Ó 2010 Elsevier B.V. All rights reserved.
Keywords:
Amidinate
Chelates
Chirality
Lithium
Potassium
X-ray structures
1. Introduction
Having all these in mind we were attracted by the chiral
compounds (S,S)- and (R,R)-N,N-bis-(1-phenylethyl)benzamidine
((S)- and (R)-HPEBA) (Typ I, Scheme 3), which were published
about 30 years ago by H. Brunner et al. [17,19]. Chiral complexes of
The use of non-cyclopentadienyl ligands in main group and
transition metal chemistry resulted some years ago in a renaissance
of amido metal complexes [1e6]. Within the broad series of N-
centered donor ligands the readily accessible amidinate and guani-
dinate anions play a major role. A number of recent comprehensive
reviews in this area cover the rapidly expanding chemistry [7e11].
Today amidinates and guanidinates complexes of the main group
and transition metals are used for various applications such as
catalysis and materials science [8]. The amidinate anions of the
general formula [RC(NR’)2]ꢀ (Scheme 1), which allows an effective
tuning of the steric and electronic requirements by varying the
substituents R and R0, can be considered as the nitrogen analogof the
carboxylate anions.
composition [(h
5-C5H5)(CO)2Mo(PEBA)] were synthesized and then
combined with rhodium complexes to form enantioselective cata-
lysts for the hydrogenation of prochiral olefins. Unfortunately, the
benzamidines (S)- and (R)-HPEBA, which were obtained via the
imidoylchloride route, were described as oily compounds and used
without any purification. The crystal structure of (S)-HPEBA was
established by I. Bernal et al. [21], but no new synthesis was
mentioned. In 2006 E. Yashima et al. published a new synthesis to
HPEBA based on the carbodiimide route. The disadvantage of this
new synthesis is a laborious purification of the products by column
chromatography [22].
Due to the large number of publications dealing with amidinates
a number of synthesis leading to these kinds of compounds
were established [12]. Most of them use either imidoylchlorides
(Scheme 2, A) or carbodiimides (Scheme 2, B) as intermediates [13].
Although a huge number of amidinate and guanidinate complexes
are known, the amount of reports dealing with chiral amidinates is
surprisingly small. Only relatively few complexes of group 4 metals
[14e16], molybdenum [17], nickel [17,18], and rhodium [19,20] with
chiral amidinate ligands were reported. In most of the published
work the chiral amidinates shown in Scheme 3 were used [14e20].
Herein we now report a new and convenient approach to (S)-
and (R)-HPEBA as well as the synthesis of the lithium and potas-
sium derivatives.
2. Results and discussion
2.1. Synthesis of (R)- and (S)-HPEBA
Based on the original synthesis by H. Brunner et al. we devel-
oped a significantly modified procedure to (R)- (1a) and (S)-HPEBA
(1b) (Scheme 4). In the first step benzoylchloride (2) was treated
with enantiomerically pure (R)- or (S)-1-phenylethylamine to give
(R)- or (S)-N-(1-phenylethyl)benzamide (3) in good yield. Further
* Corresponding author. Tel.: þ49 721 608 6117; fax: þ49 721 608 4858.
E-mail address: roesky@kit.edu (P.W. Roesky).
0022-328X/$ e see front matter Ó 2010 Elsevier B.V. All rights reserved.
doi:10.1016/j.jorganchem.2010.07.020

P. Benndorf et al. / Journal of Organometallic Chemistry 696 (2011) 1150e1155
1151
R
R'
R'
R
Fe
N
N
N
H
N
N
H
N
R= H, alkyl, aryl
Fe
PPh2 Ph2P
R'= H, alkyl, cycloalkyl, aryl, trimethylsilyl
I
II
Scheme 1. The amidinate anion.
reaction of 3 with oxalylchloride and lutidine in CH2Cl2 resulted in
(R)- or (S)-N-(1-phenylethyl)benzimidoylchloride (4). The second
step is based on a method published by R. F. Cunico et al. [23]. The
standard procedure chlorinating agents, which are either PCl5 or
thionylchloride, resulted in a significant amount of by-products,
which hampers purification of the final product [23,24]. In the third
step compound 4 was heated in toluene with (R)- or (S)-1-phen-
ylethylamine to give the adducts (R)- or (S)-HPEBA$HCl as an oily
compound, which was transformed to 1a,b by treatment with
NaHCO3. After crystallization from ethanol 1a,b were isolated as
analytical pure crystals. Both compounds were obtained as enan-
tiomeric pure products, which have been characterized by standard
analytical/spectroscopic techniques. The results are in agreement
with the data available from the literature [22].
As a result of the (Z)/(E) isomerism and tautomerism the NMR
spectra of compounds 1a,b are complex and strongly depend on the
nature of the solvent used and the measuring temperature. For 1a,b
only broad and non-characteristic signals were observed in the 1H
NMR spectrum by using CDCl3 as solvent (Fig. 1). In contrast, by
measuring 1a,b in d6-DMSO the proton exchange rate is slowed
down and the expected set of signals can be observed (Fig. 1) [25].
HN
NH
Si
N
N
R
R
H
N
R
N
R
III
IV
Scheme 3. Known chiral amidines.
heteroallylic NCN unit. As a result of the steric demand of the
phenyl rings a dimerization via hydrogen bonds is prevented [27].
2.2. Metal complexes
The reaction of 1b with a slight excess of n-butyl lithium in THF
resulted in the metallated compound lithium-N,N0-bis-((S)-1-phe-
nylethyl)benzamidinate ((S)-LiPEBA) (Scheme 5). (S)-LiPEBA was
isolated as an orange-red solid, which was characterized by
standard analytical/spectroscopic techniques. As a result of the
deprotonation, the symmetry of (S)-LiPEBA increases in compar-
ison to the starting material 1b in solution. Thus only one set of
signals is observed for the phenylethyl substituent. In compound
(S)-LiPEBA both methine protons are homotop giving only one
Two sets of signals are seen for the methyl (
d
(d6-DMSO) ¼ 5.16,
4.06 ppm) and the methine groups (
d
(d6-DMSO) ¼ 1.40, 1.20 ppm)
signal at
d
¼ 4.32 ppm in the 1H NMR spectrum. Consequently only
in the 1H NMR spectrum. The low field shifted set of signals can be
assigned to the substituent forming the Schiff-base function.
Consistent with these observations are the four signals observed in
one doublet is seen for the methyl groups at
d
¼ 1.41 ppm
(3J ¼ 6.5 Hz).
Treatment of 1b with potassium hydride in boiling THF afforded
the corresponding potassium salt (S)-KPEBA in high yields as an
orange solid (Scheme 6). In comparison with many other depro-
tonation reactions the appropriate reaction temperature for the
synthesis of (S)-KPEBA is essential. Running the reaction at room
temperature did not result in a complete conversion and afforded
a sticky product, which was a mixture of 1b and (S)-KPEBA. In
contrast by performing the reaction in boiling toluene a fast race-
mization was observed. This observation is not very surprising
because enantiomeric pure 1-phenyletyhlamine undergoes race-
mization in the presence of catalytic amounts of sodium amide or
sodium hydride within minutes in the temperature range of
70e150 ꢁC [28].
the 13C{1H} NMR spectrum for the aliphatic carbon atoms (
d(d6-
DMSO) ¼ 57.2, 50.1, 27.3, 23.6 ppm).
The solid state structure of compound 1a was also established
by single crystal X-ray diffraction (Fig. 2). Compound 1a crystallizes
in the orthorhombic space group P212121 having four molecules of
1a in the unit cell. The data is consistent with the earlier published
single crystal X-ray structure of the enantiomer 1b [21]. Therefore
only a brief structural discussion is given here. 1a crystallizes in
a E-syn configuration, which is typical for amidines in the solid state
[26,27]. The imine (C1eN1 1.276(2) Å) and the amine bond length
(C1eN2 1.374(2) Å) are in the expected range observed for amidines
[13]. The N1eC1eN2 bond angle (119.7(2)ꢁ) is almost ideal for an
sp2 hybridized carbon atom. The N2eC1eC2eC3 torsion angle
between the central phenyl group and the heteroallylic NCN unit is
66.7(2)ꢁ. This value, which is typical for benzamidines, shows that
there is not a conjugated system between the aromatic ring and the
(S)-KPEBA has been characterized by standard analytical/
spectroscopic techniques. The signals in the 1H NMR spectrum of
(S)-KPEBA are slightly broader at room temperature than those of
(S)-LiPEBA. The signals of the methyl (
methine group (
d
¼ 4.22 ppm) and the
d
¼ 1.30 ppm) of (S)-KPEBA are slightly upfield
O
Cl Cl
O
NH2
Ph
Ph
,
N
10 % NaOH sol.
r.t. , 1 h
O
Cl +
O
N
CH2Cl2, 0 °C, 3 h
H
2
3
NH2
1.
Ph
N
Ph
N
2. NaHCO3
N
Cl
toluene,
H
110 °C, 24 h
4
(S)-HPEBA
1b
(
)
Scheme 2. Imidoylchloride (A) and carbodiimide route (B) leading to amindines and
Scheme 4. Synthesis of (S)-HPEBA (1b).
amidinates.

1152
P. Benndorf et al. / Journal of Organometallic Chemistry 696 (2011) 1150e1155
Fig. 1. 1H NMR spectrum of HPEBA in CDCl3 (left) and d6-DMSO (right).
shifted in comparison to (S)-LiPEBA, whereas similar chemical
shifts are observed in the 13C{1H} NMR for both groups (CH:
value shows that there is not a conjugated system between the
aromatic ring and the heteroallylic NCN unit.
d
¼ 57.2 ppm; CH3:
d
¼ 22.3 ppm (KPEBA)).
Usually potassium amidinates and guanidinates either crystal-
lize with no coordinated solvent molecules or with donor solvents
such as THF coordinated to the metal atom [11,30e33]. In some
cases polymeric chains are formed [30]. Formamidinates were
Single crystals of racemic KPEBA ((rac)-KPEBA) could be obtained
from a toluene/n-pentane mixture (Fig. 3). The solid state structure
of (rac)-KPEBA was established by single crystal X-ray diffraction.
(rac)-KPEBA crystallizes in the monoclinic space group P21/n having
four molecules of (rac)-KPEBA and four molecules of toluene in the
unit cell. In the solid state (rac)-KPEBA forms a dimer, in which all
four nitrogen atoms form a plane. In the center of this plane a crys-
tallographic inversion center is observed. The potassium atoms,
reported to form N:
h
6-aryl-coordinated potassium compounds
6-coordinated to
[34,35]. In (rac)-KPEBA a toluene molecule is
h
each potassium atom. In this discussion we consider all CeK
interactions up to a value of 3.6 Å as bonds, which is a conservative
limit for KeC interactions [36,37]. The KeC distances range from
3.349(8)e3.554(7) Å. The difference in the bond distances are
a result of a slightly asymmetric coordination of the toluene ring.
which coordinate to both amidinate ligands in a me :h
h2 2 fashion, are
symmetrically localized above and below the plane having a KeK0
distance of 3.352(2) Å, which is twice the amount of the ion radius of
an eight fold coordinated potassium cation (1.65 Å) [29]. The KeN
bond distances of KeN1 2.831(4) Å and KeN2 2.830(4) Å show the
symmetric coordination of the potassium atoms. The observed bond
distances and angles of the amidinate ligand are in agreement with
published data [30e32]. The CeN bond distances within the ami-
dinate ligand are identical within the error range (C1eN11.334(5) Å
and C1eN21.336(5) Å). The N1eC1eN2 angle of 117.2(4)ꢁ is about 2ꢁ
smaller than in 1a. The N2eC1eC2eC3 torsion angle between the
central phenyl group and the heteroallylic NCN unit is 96.6(2)ꢁ. This
Moreover, the potassium atoms are also
p-coordinated by one
carbon atom (C19) of a phenyl ring of the phenylethyl substituents.
The KeC19 bond distance of 3.555(8) Å, which is not shown in
Fig. 3, indicates a h
1-coordination of the phenyl rings.
3. Summary
In summary we have developed a new synthesis, which gave the
chiral amidines (S,S)- and (R,R)-N,N-bis-(1-phenylethyl)benzami-
dine ((S)- and (R)-HPEBA) in good yields. Further reaction of (S)-
HPEBA with n-BuLi gave the chiral lithium salt (S)-LiPEBA. Treat-
ment of KH with (S)-HPEBA in boiling THF afforded the corre-
sponding potassium salt (S)-KPEBA. In contrast by performing the
reaction in boiling toluene a fast racemization was observed. In the
solid state (rac)-KPEBA forms a dimer, in which all four nitrogen
atoms are in a plane. To each potassium atom a toluene molecule is
h
6-coordinated.
4. Experimental section
4.1. General
All manipulations of air-sensitive materials were performed
with the rigorous exclusion of oxygen and moisture in flame-dried
THF, r.t. , 2 h
- n-BuH
+
n-BuLi
Fig. 2. Solid state structure of 1a. Selected bond lengths [Å] or angles [ꢁ]: N1eC1 1.276
(2), N1eC8 1.457(2), C1eN2 1.374(2), C1eC2 1.500(2), N2eC16 1.454(2), C8eC10 1.518
(3), C8eC9 1.528(3), C16eC17 1.517(3), C16eC18 1.521(3); C1eN1eC8 119.62(14),
N1eC1eN2 119.7(2), N1eC1eC2 127.3(2), N2eC1eC2 113.0(2), C1eN2eC16 120.9(2),
N1eC8eC10 110.29(14), N1eC8eC9 108.88(15), C10eC8eC9 110.5(2), N2eC16eC17
108.8(2), N2eC16eC18 112.95(14), C17eC16eC18 111.9(2); N2eC1eC2eC3 66.7(2).
N
N
N
H
N
Li
(S)-LiPEBA
Scheme 5. Synthesis of (S)-LiPEBA.

P. Benndorf et al. / Journal of Organometallic Chemistry 696 (2011) 1150e1155
1153
1 h of stirring at r.t. the colorless precipitate formed was filtered off,
washed several times with water and then dried in vacuo. 13.57 g
(60 mmol, 78%) of (R)- respectively (S)-N-(1-phenylethyl)benza-
mide (3) were obtained as colorless solid. e 1H NMR (400 MHz,
N
N
THF, 66 °C, 4 h
- H2
2
+
2 KH
K K
CDCl3, 23 ꢁC):
d
(ppm) ¼ 7.69e7.17 (m, 10 H, Ph), 6.47 (br s, 1 H, NH),
N
H
N
4.06 (q, 3J ¼ 6.8 Hz, 1H, CH), 1.49 (d, 3J ¼ 6.8 Hz, 3H, CH3). e 13C{1H}
N
N
NMR (101 MHz, CDCl3, 23 ꢁC):
d
(ppm) ¼ 166.6 (CO), 143.1 (i-Ph),
1b
134.5 (i-Ph), 131.4 (Ph), 128.7 (Ph), 128.5 (Ph), 127.3 (Ph), 126.9 (Ph),
126.2 (Ph), 49.2 (CH), 21.7 (CH3).
(S)-KPEBA
Scheme 6. Synthesis of (S)-KPEBA.
4.3. (R)- and (S)-N-(1-Phenylethyl) benzimidoylchloride (4)
A mixture of 3 and 11.65 mL (10.71 g, 100 mmol) of 2,6-luti-
dine was dissolved in 150 mL of dry CH2Cl2 and cooled to 0 ꢁC.
5.17 mL (7.65 g, 60 mmol) oxalylchloride, dissolved in 50 mL dry
CH2Cl2, was slowly added dropwise to the reaction mixture
within an hour. The color of the reaction mixture turned to
reddish-brown. The mixture was stirred for 30 min at 0 ꢁC and
after warming up to r.t. stirred for another 30 min. The volatile
components were removed in vacuo. 150 mL dry n-pentane was
added to the dark brown residue and stirred for 1 h. The
suspension was filtered and the volatile components of the
filtrate were removed under vacuum. The resulting brown oil was
distilled in vacuo at 130e140 ꢁC (2.1$10ꢀ1 mbar) to obtain 9.55 g
(39 mmol, 65%) of light yellow (R)- respectively (S)-N-(1-phe-
nylethyl) benzimidoylchloride (4). e 1H NMR (400 MHz, CDCl3,
Schlenk-type glassware either on a dual manifold Schlenk line,
interfaced to a high vacuum (10ꢀ3 torr) line, or in an argon-filled
MBraun glove box. THF was distilled under nitrogen from potas-
sium benzophenone ketyl prior to use. Hydrocarbon solvents
(toluene and n-pentane) were dried using an MBraun solvent
purification system (SPS-800). All solvents for vacuum line
manipulations were stored in vacuo over LiAlH4 in resealable flasks.
Deuterated solvents were obtained from Aldrich (99 atom % D).
NMR spectra were recorded on a Bruker Avance 400 MHz NMR
spectrometer. Chemical shifts are referenced to internal solvent
resonances and are reported relative to tetramethylsilane. IR
spectra were obtained on a Bruker Tensor 34. Mass spectra were
recorded at 70 eV on a Finnigan MAT 8200. Elemental analyses
were carried out with an Elementar vario EL. Optical rotation was
measured on a Jasco P2000.
23 ꢁC):
d
(ppm) ¼ 7.94e7.10 (m, 10 H, Ph), 6.99 (br s, 1 H, NH),
5.05 (q, 3J ¼ 6.6 Hz, 1 H, CH), 1.44 (d, 3J ¼ 6.6 Hz, 3 H, CH3). e 13C
{1H} NMR (101 MHz, CDCl3, 23 ꢁC):
(i-Ph), 136.0 (i-Ph), 131.5 (Ph), 129.3 (Ph), 128.6 (Ph), 128.3 (Ph),
127.2 (Ph), 126.8 (Ph), 63.2 (CH), 23.8 (CH3).
d
(ppm) ¼ 144.1 (CCl), 142.9
4.2. (R)- and (S)-N-(1-Phenylethyl)benzamide (3)
To a reaction mixture of 10.00 mL (9.40 g, 78 mmol) (R)-
respectively (S)-1- phenylethylamine in 80 mL of an aqueous
sodium hydroxide solution (10%), 9.46 mL (11.45 g, 81 mmol)
benzoylchloride was added dropwise under vigorous stirring. After
5. (R,R)- and (S,S)-N,N0-bis-(1-Phenylethyl)benzamidine ((R)-
and (S)-HPEBA) (1a,b)
The imidoylchloride (4) was dissolved in 40 mL dry toluene
and 5.05 ml (4.75 g, 39 mmol) of (R)- respectively (S)-1-phen-
ylethylamine was added dropwise. The reaction mixture was
refluxed for 12 h. After cooling to ꢀ30 ꢁC the solvent was dec-
anted from the highly viscous oil. The oily residue is dried in
vacuo, dissolved in 100 mL of CH2Cl2 and treated with 100 mL of
a saturated sodium bicarbonate solution. After 1 h of vigorous
stirring, the phases were separated and the water layer was
extracted twice with CH2Cl2. The combined organic layers were
dried over magnesium sulfate, filtered, and then the solvent was
removed in vacuo. After recrystallization from hot ethanol (R)-
respectively (S)-HPEBA (1a,b) were obtained as colorless crystals.
e Yield: 7.18 g, 22 mmol, 56% (overall yield: 28%). e 1H NMR
(300 MHz, d6-DMSO, 17 ꢁC):
d
(ppm) ¼ 7.42e6.67 (m, 15 H, Ph),
5.16 (br s, 1 H, NCH), 4.06 (br s, 1 H, NHCH), 1.40 (s, 3 H, NCHCH3),
1.20 (s, 3 H, NHCHCH3). e 13C{1H} NMR (75 MHz, d6-DMSO,
17 ꢁC):
d
(ppm) ¼ 156.4 (NCN), 148.7 (i-Ph), 147.5 (i-Ph), 136.2 (i-
Ph), 128.9e126.4 (m, Ph), 57.2 (NCH), 50.1 (NHCH), 27.3
(NCHCH3), 23.6 (NHCHCH3). e MS (EI, 70 eV): m/z (%) ¼ 328
([M]þ, 87), 313 ([M ꢀ CH3]þ, 15), 223 ([M ꢀ PhEt]þ, 94), 209
(M ꢀ PhEtN]þ, 27), 180 (42), 120 (PhEtN]þ, 100), 105 ([PhEt]þ,
100), 91 ([Bz]þ, 37), 77 ([Ph]þ, 92), 56 (68), 41 ([C2H3N]þ, 64). e
Fig. 3. Solid state structure of (rac)-KPEBA, omitting the hydrogen atoms. Selected
bond lengths [Å] or angles [ꢁ]: C1eN1 1.334(5), C1eN2 1.336(5), C8eN1 1.481(5),
C8eC9 1.527(7), C16eN2 1.465(5), C16eC17 1.516(7), KeN1 2.831(4), KeN2 2.830(4),
C19eK 3.555(8), C25eK 3.451(7), C26eK 3.349(8), C27eK 3.381(10), C28eK 3.436(10),
C29eK 3.530(9), C30eK 3.554(7), KeK0 3.352(2); N1eC1eN2 117.2(4), N1eC1eC2
121.7(4), N2eC1eC2 121.1(4), N1eC1eK 63.0(2), N2eC1eK 62.8(2), N1eC8eC9 107.8
(4), C10eC8eC9 110.9(4), N2eC16eC17 109.6(4), C1eN1eC8 119.4(4), C1eN1eK 90.0
(2), C8eN1eK 131.0(3), C1eN2eC16 120.1(4), C1eN2eK 92.4(2), C16eN2eK 133.4(3),
N2eKeN2 107.30(9), N1eKeN1 107.41(9).
IR (ATR):
n
(cmꢀ1) ¼ 3405 (w), 3058 (w), 2954 (w), 2917 (w),
1635 (m), 1484 (m), 1447 (m), 1303 (w), 1265 (w), 1141 (w), 1071
(m), 1027 (w), 762 (s), 699 (s), 543 (s). e C23H23N2 (328.45): Calc.:
C, 84.11; H, 7.37; N, 8.53; Found: C, 84.33; H, 7.40; N, 8.47. e ½a D28
ꢂ
58.9ꢁ (c 0.14, THF) for (S)-HPEBA; ½a 2D7
ꢂ
ꢀ53.2ꢁ (c 0.17, THF)
for (R)-HPEBA. The data is in agreement with the literature [22].
Mp: 98 ꢁC.

1154
P. Benndorf et al. / Journal of Organometallic Chemistry 696 (2011) 1150e1155
6. Lithium-N,N0-bis-((S)-1-phenylethyl)benzamidinate ((S)-
LiPEBA)
as the magnitude of the residual electron densities in each case
were of no chemical significance.
Crystal data for 1b: C23H24N2, M ¼ 328.44, orthorhombic,
3.14 mL (1.6 M in n-hexane, 5.02 mmol) n-butyl lithium was
added dropwise to a solution of 1.50 g (4.57 mmol) (S)-HPEBA in
20 mL THF. The mixture was stirred overnight at r.t. The solution
turns dark red. The volatile components were removed in vacuo.
After washing with 20 mL n-pentane and drying under vacuum, the
product is obtained as an orange solid. e Yield: 1.32 g, 3.96 mmol,
a ¼ 8.2244(9) Å, b ¼ 12.3838(11) Å, c ¼ 18.916(3) Å,
a
¼ 90.00ꢁ,
b
¼ 90.00ꢁ,
g
¼ 90.00ꢁ, V ¼ 1926.6(4) Å3, T ¼ 200(2) K, space group
P212121, Z ¼ 4,
m
(MoK
a
) ¼ 0.066 mmꢀ1, 5355 reflections measured,
3384 independent reflections (Rint ¼ 0.0298). The final R1 values
were 0.0387 (I > 2s
(I)). The final wR(F2) values were 0.0825 (all
data). The goodness of fit on F2 was 0.918. Flack parameter ¼ 0(3).
Crystal data for (rac)-KPEBA: C46H46K2N4$2(C7H8), M ¼ 917.34,
monoclinic, a ¼ 12.786(3) Å, b ¼ 13.424(3) Å, c ¼ 15.821(3) Å,
87%. e 1H NMR (400 MHz, C6D6, 25 ꢁC):
d
(ppm) ¼ 7.59e7.37 (m,
4 H, Ph), 7.34e6.98 (m, 11 H, Ph), 4.43e4.21 (m, 2 H, CH), 1.41 (d,
J ¼ 6.5 Hz, 6 H, CH3). e 13C{1H}-NMR (101 MHz, C6D6, 25 ꢁC):
a
¼ 90.00ꢁ,
b
¼ 105.36(3)ꢁ,
g
¼ 90.00ꢁ, V ¼ 2618.5(9) Å3, T ¼ 200(2)
d
(ppm) ¼ 176.2 (NCN), 151.4 (i-Ph), 139.6 (i-Ph), 129.5 (Ph), 128.7
K, space group P21/n, Z ¼ 2,
m
(MoK
a
) ¼ 0.222 mmꢀ1, 76916
(Ph), 128.3 (Ph), 128.1 (Ph), 127.6 (Ph), 126.8 (Ph), 57.7 (CH), 28.0
(CH3). e MS (EI, 70 eV): m/z (%) ¼ 341 ([M]þ, 100), 328 ([M ꢀ Li]þ,
95), 223 ([M-LiPhEt]þ, 86), 180 ([M-2Ph]þ, 35), 120 ([PhEtN]þ, 100),
105 ([PhEt]þ, 99), 77 ([Ph]þ, 86), 42 ([C2H4N]þ, 28), 27 ([CHN]þ, 9).
reflections measured, 7100 independent reflections (Rint ¼ 0.2436).
The final R1 values were 0.1304 (I > 2s
(I)). The final wR(F2) values
were 0.2366 (all data). The goodness of fit on F2 was 1.215.
e IR (ATR):
n
(cmꢀ1) ¼ 3058 (w), 2953 (w), 2919 (w), 2875 (w), 1635
Acknowledgement
(m), 1598 (w), 1484 (m), 1447 (m), 1355 (w), 1303 (w), 1265 (w),
1211 (w), 1141 (w), 1070 (w), 1025 (w), 1006 (w), 907 (w), 762 (m),
699 (s), 599 (w), 571 (w), 542 (w). e C23H23N2Li$2C4H8O (478.59):
Calc.: C, 77.80; H, 8.21; N, 5.85; Found: C, 78.12; H, 7.37; N, 5.93.
This work was supported by the Deutsche For-
schungsgemeinschaft (SPP 1166).
6.1. Potassium-N,N0-bis-((S)-1-phenylethyl)benzamidinate ((S)-
KPEBA)
Appendix. Supplementary material
Positional parameters, hydrogen atom parameters, thermal
parameters, bond distances and angles have been deposited as
supporting information. Crystallographic data (excluding structure
factors) for the structures reported in this paper have been
deposited with the Cambridge Crystallographic Data Centre as
a supplementary publication no. CCDC-779939 and CCDC-779940.
Copies of the data can be obtained free of charge on application to
CCDC, 12 Union Road, Cambridge CB21EZ, UK (fax: þ(44)1223-336-
033; email: deposit@ccdc.cam.ac.uk; website: www.ccdc.cam.ac.
uk/data_request/cif).
1.36 g (4.13 mmol) of (S)-HPEBA and 0.20 g (4.95 mmol) of KH
were suspended in 20 mL dry THF and refluxed for 3 h. The color of
the solution turned to pink. After cooling to r.t. the excess KH was
filtered off and the solvent was evaporated under vacuum. Washing
with 20 mL of n-pentane gave the orange product. The racemic
product was synthesized by carrying out the reaction in toluene.
Crystals were obtained by layering a toluene solution with n-
pentane. e Yield: 1.40 g, 3.82 mmol, 93%. e 1H NMR (300 MHz,
C6D6, 17 ꢁC):
d
(ppm) ¼ 7.51e6.82 (m, 15 H, Ph), 4.22 (br s, 2H, CH),
1.30 (d, 3J ¼ 6.3 Hz, 4 H, CH3). e 13C{1H} NMR (75 MHz, C6D6, 17 ꢁC):
d
(ppm) ¼ 171.8 (NCN), 152.0 (i-Ph), 141.7 (i-Ph), 128.2 (Ph), 127.8
References
(Ph), 127.6 (Ph), 126.6 (Ph), 126.1 (Ph), 125.1 (Ph), 57.2 (CH), 26.3
(CH3). e IR (ATR):
n
(cmꢀ1) ¼ 3057 (w), 3024 (w), 2974 (w), 2954
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