Enantiopure amidinate complexes of lutetium

Article abstract of DOI:10.1016/j.jorganchem.2017.03.041

Two new enantiomeric pure amidinates N,N’-bis-((R)-1-cyclohexylethyl)benzamidinate ((R)-CEBA)^- and N,N’-bis-((S)-1-phenylethyl)acetamidinate ((S)-PEAA)^- were synthesized by two different synthetic pathways. The chiral amidine (R)-HCE

Full text of DOI:10.1016/j.jorganchem.2017.03.041

Journal of Organometallic Chemistry xxx (2017) 1e7
Contents lists available at ScienceDirect
Journal of Organometallic Chemistry
journal homepage: www.elsevier.com/locate/jorganchem
*
Enantiopure amidinate complexes of lutetium
*
Tobias S. Brunner, Peter W. Roesky
Institute of Inorganic Chemistry, Karlsruhe Institute of Technology (KIT), Engesserstraße 15, 76131 Karlsruhe, Germany
a r t i c l e i n f o
a b s t r a c t
-
Article history:
Received 25 January 2017
Received in revised form
Two new enantiomeric pure amidinates N,N’-bis-((R)-1-cyclohexylethyl)benzamidinate ((R)-CEBA) and
-
N,N’-bis-((S)-1-phenylethyl)acetamidinate ((S)-PEAA) were synthesized by two different synthetic
pathways. The chiral amidine (R)-HCEBA was synthesized via the so-called imidoylchloride route. The
corresponding lithium derivative (R)-LiCEBA was best obtained by deprotonation of the amidinate hy-
drochloride (R)-HCEBA$HCl. In contrast (S)-LiPEAA was most efficiently accessed by reaction of meth-
16 March 2017
Accepted 21 March 2017
Available online xxx
yllithium with bis-((S)-1-phenylethyl)carbodiimide. Further reactions of these lithium salts with LuCl
a 2:1 ratio resulted in the enantiomeric pure bisamidinate lutetium complexes [{(R)-CEBA} Lu- -Cl] and
{(S)-PEAA} LuCl(thf)], which are either dimeric or monomeric in the solid state.
2017 Elsevier B.V. All rights reserved.
3
in
2
m
2
Keywords:
Amidinates
Chiral ligands
Lithium
[
2
©
Lutetium
1. Introduction
amidine N,N’-bis-(1-phenylethyl)benzamidine (HPEBA; Scheme 1)
38], which was reported for the first time about 35 years ago by H.
[
Recently, we introduced chiral amidinates into the coordination
Brunner et al. [15,18]. In 2011, we also reported the synthesis of the
chemistry of the rare earth elements and reported mono-, bis-, and
first rare earth metal complexes ligated by the corresponding chiral
amidinate (PEBA) . For catalytic applications chiral mono(-
amidinate) bisborohydride complexes were used as initator for the
ring opening polymerization of rac-lactide [39]. Moreover, bis(a-
midinate) amido complexes with yttrium and lutetium [{(S)-
-
tris(amidinate) complexes of these metals [1e3]. Whereas achiral
0
-
amidinates of the general formula [RC(NR )
2
]
and the closely
0
2 2
related guanidinates [R NC(NR ) ] are a well-established class of
-
N-chelating ligands, which form complexes with almost every
metal of the periodic table [4e10], chiral amidinates are far less
common. Besides our contribution in rare earth chemistry only a
few group 4 metal [11e14], molybdenum [15,16], rhodium [17,18],
and nickel [19] complexes with chiral amidinates are known. In rare
earth chemistry achiral amidinates, e.g. N,N'-bis-(trimethylsilyl)-
benzamidinate [20,21], have been found to stabilize lanthanide
compounds in all three common oxidation states (þII, þIII, þIV)
PEBA}
2
Ln{N(SiMe
3
)
2
}] (Ln ¼ Y, Lu) were used as catalysts in the
enantioselective hydroamination reaction [1,2]. Since the coordi-
nation chemistry of the lanthanides is strongly influenced by the
steric demand of the ligand, we started modifying the bite angle
and the substituents of the chiral amidinate ligands slightly. In a
-
recent approach we substituted the phenyl group in the (PEBA)
ligand backbone by the bulkier tBu group. This resulted in the chiral
amidine (S,S)-N,N'-bis-(1-phenylethyl)pivalamidine ((S)-HPETA)
(Scheme 1). Furthermore, a number of (S)-PETA rare-earth element
complexes including amides and alkyl compounds, which were
applied as catalysts in enantioselective intramolecular hydro-
amination reactions of non-activated terminal amino olefins were
reported [40]. It was shown by us that the substituent in the
backbone of the amidinate has an influence on the bite angle of the
ligand and thus also influences the catalytic activity [40].
[5,6,22e26]. The pioneering work has been performed by Edel-
mann et al. in the 1990s [22,27] followed by contributions from
Deacon and Junk et al. [28e33]. Selected amidinate complexes have
been used as homogeneous catalysts for the polymerization of
ethane [34] and isoprene [35,36], ring opening polymerization of
polar monomers (e.g. ε-caprolactone and trimethylene carbonate),
hydroboration, hydrosilylation and intramolecular hydro-
amination/cyclization [37] reactions [22,23,37].
We recently published an improved synthesis of the chiral
Also the naphthyl substituted ligand (S,S)-N,N'-bis-(1-(2-
naphthyl)ethyl)benzamidine ((S)-HNEBA) (Scheme 1) and a series
of the corresponding enantiomerically pure homoleptic rare earth
*
Dedicated to Prof. Richard D. Adams on the occasion of his 70th birthday.
Corresponding author.
E-mail address: roesky@kit.edu (P.W. Roesky).
metal complexes [Ln{(S)-NEBA}
known [41].
] (Ln ¼ Y, Sm, Tb, Dy, Er, Yb, Lu) are
3
*
http://dx.doi.org/10.1016/j.jorganchem.2017.03.041
022-328X/© 2017 Elsevier B.V. All rights reserved.
0
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T.S. Brunner, P.W. Roesky / Journal of Organometallic Chemistry xxx (2017) 1e7
Scheme 1. Chiral amidines which were recently used by us (S)-HPEBA, (S)-HPETA, and (S)-HNEBA for the synthesis of enantiomerically pure rare earth metal complexes [1e3],
40,41].
[
1
Herein, we now describe the synthesis of two other chiral
compound, the H NMR spectrum of (R)-HCEBA is rather complex
amidinates as well as their lithium and lutetium complexes. For the
design of the first ligand N,N’-bis-((R)-1-cyclohexylethyl)benzami-
dine ((R)-HCEBA) (Scheme 2), we used in comparison to HPEBA a
cyclohexyl group instead of a phenyl group on the side function of
the amidine. In the second ligand, N,N’-bis-((S)-1-phenylethyl)
acetamidine ((S)-HPEAA) (Scheme 2), we altered the group at the
ligand backbone by using a small methyl group instead of a phenyl
group in HPEBA or a tBu group in HPETA.
[10,44]. Mainly relatively broad peaks are observed. By using
DMSO-d as solvent the proton exchange is altered and better
6
resolved spectra were obtained. Due to the asymmetry, two signals
are seen for the NCH groups at 3.85 and 2.67 ppm. The signals of the
methyl groups are covered partly by the resonances of the cyclo-
1
hexyl rings. In contrast to the H NMR spectrum, the corresponding
13
1
C{ H}-NMR spectrum is much better resolved, e.g. four signals,
which can be assigned to the methyl and methine groups, are
observed at 57.9, 48.9, 21.2 and 16.7 ppm.
Since (R)-HCEBA is an oily compound, which is hard to transfer,
we decided to generate the corresponding lithium salt (R)-LiCEBA
directly from the hydrochloride (R)-HCEBA$HCl. Reaction of (R)-
HCEBA$HCl with two equiv of n-buthyllithium resulted directly in a
double deprotonation. As product the lithium salt was obtained in
2
. Results and discussion [42]
The new enantiomerically pure amidine (R)-HCEBA was syn-
thesized in a similar way as the previously described (S)-HPEBA
43] (Scheme 3). In the first step benzoylchloride was reacted with
enantiomerically pure (R)-1-cyclohexylethylamine to give (R)-N-
1-cyclohexylethyl)benzamide (I) in high yields. Treatment of I
with oxalylchloride and 2,6-lutidine in CH Cl resulted in the sec-
[
74% yield (Scheme 5). The desired compound was obtained as a
colorless solid, which includes one equivalent of lithium chloride.
Upon further reaction, the remaining lithium chloride was removed
at the next step. In contrast to (R)-HCEBA and in agreement with
(
2
2
ond step in (R)-N-(1-cyclohexylethyl)benzimidoylchloride (II),
which was further reacted without further purification and anal-
ysis. In the third step, compound II and (R)-1-cyclohexylethylamine
were heated in toluene. The resulting amidine hydrochloride ((R)-
HCEBA$HCl) precipitates from the hot reactions mixture. It was
recrystallized from toluene as analytically pure white crystals in an
overall yield of 63%.
(R)-HCEBA$HCl, the lithium salt shows a symmetric pattern in the
NMR spectra. Thus, the protons of the methine group show a well
3
resolved multiplett at 2.91 ppm ( JH,H ¼ 4.5 Hz). Also only one
13
1
resonance is seen in the C{ H} NMR spectrum for the methine
(56.8 ppm) and methyl groups (22.4 ppm), each. The characteristic
signal for the NCN unit is seen at 176.8 ppm, which corresponds to a
low field shift in comparison of the hydrochloride (166.1 ppm) of
Symmetrical patterns of the 1-cyclohexylethyl substituents
were observed in the NMR spectra. The signals of both N-H protons
20 ppm.
As second ligand system, we investigated N,N’-bis-((S)-1-
are seen at 10.46 ppm as a doublet, whereas all other signals are
multipletts. In the 13C{1H}-NMR spectrum, the peak of the NCN unit
phenylethyl)acetamidine ((S)-HPEAA). As mentioned in the intro-
duction, we intended to alter the bite angle of the ligand and to
draw a comparison to the previously used systems (S)-HPEBA and
shows a characteristic down field shift at 166.1 ppm whereas the
signals of the NCH and CH groups were detected in the expected
3
region at 56.7 ppm and 19.1 ppm. ESI-MS spectra and elemental
analysis support the proposed composition.
(S)-HPETA. To access the ligand, we chose a different strategy.
Similar to the synthesis of HPETA, we reacted methyllithium with
the corresponding chiral carbodiimide bis-((S)-1-phenylethyl)car-
bodiimide ((S)-PEC) [40,45e48] to obtain pure lithium-bis-((S)-1-
phenylethyl)acetamidinate ((S)-LiPEAA) in good yields (85%)
In contrast to the synthesis of (S)-HPEBA or (S)-HPETA, the
deprotonation of the hydrochloride (R)-HCEBA$HCl with NaHCO
3
or NaOH in aqueous alkaline solution did not lead to a clean
product. In contrast by using one equiv n-butyllithium as base in
toluene and subsequent workup, the desired product, the neutral
amidine (R)-HCEBA, was obtained in almost quantitative yield
(Scheme 6). In contrast, for the synthesis of (R)-HCEBA this simpler
reaction pathway resulted in low yields only [49]. The reaction of
carbodiimides with lithium alkyls to give lithium amidinates is a
well-established synthetic procedure [6,22,50,51]. As other alter-
native for the ligand synthesis, L. R. Sita described the reaction of
(
97%) (Scheme 4). The overall yield over all four steps thus is 61%.
As a result of the E/Z isomerization and the asymmetry of the
[
CpTiMe
carbodiimide into the Ti-Me bond the titanium complex [{(R)-
PEAA}CpTiMe ] was formed [13].
3
] with the carbodiimide(R)-PEC. Upon insertion of the
2
1
The H NMR spectrum of (S)-LiPEAA shows well resolved sig-
nals. As expected the methine proton is coupled to a quartet at
3
4
.41 ppm ( JH,H ¼ 6.6 Hz) and for the corresponding methyl group a
3
doublet at 1.21 ppm ( JH,H ¼ 6.6 Hz) is observed. In contrast, a sharp
singlet is seen for the methyl group bound to the NCN unit at
1
3
1
1
.58 ppm. In the C{ H} NMR spectrum the methine group and the
corresponding methyl group of the chiral side chain are observed at
7.5 ppm and 29.1 ppm. The signal of the NCN unit was detected at
5
Scheme 2. The chiral amidines ((R)-HCEBA and ((S)-HPEAA).
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T.S. Brunner, P.W. Roesky / Journal of Organometallic Chemistry xxx (2017) 1e7
3
Scheme 3. Synthesis of amidine hydrochloride ((R)-HCEBA$HCl).
Scheme 4. Synthesis of amidine (R)-HCEBA.
Scheme 5. Synthesis of (R)-LiCEBA.
Scheme 6. Synthesis of (S)-LiPEAA.
1
70.5 ppm.
Next, we reacted both lithium salts with LuCl
corresponding chiral lutetium complexes. First, (R)-LiCEBA was
reacted with LuCl at room temperature in a 2:1 stoichiometric
ratio. This results in the double substituted chloride complex [{(R)-
CEBA} Lu- -Cl] (1) (Scheme 7). Alternatively, the easy accessible
hydrochloride (R)-HCEBA$HCl can be deprotonated twice with
KN(SiMe . The resulting potassium salt was not isolated. Instead
R)-HCEBA$HCl, KN(SiMe and LuCl were heated in a one pot
reaction for two days in THF to give 1 (Scheme 7). Attempts to
generate the corresponding amido complex [{(R)-CEBA} Lu
{N(SiMe }] by using an excess of KN(SiMe were not successful.
Compound 1 was fully characterized by standard analytic/spec-
troscopic techniques and the solid state structure was established
by single crystal X-ray diffraction.
Single crystals of 1 were obtained from a hot and saturated
toluene solution. Compound 1 crystallizes in the tetragonal
1
Sohncke space group I4 22 with eight molecules of 1 and toluene in
3
to generate the
2
3
)
2
3 2
)
3
2
m
2
3 2
)
(
3
)
2
3
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4
T.S. Brunner, P.W. Roesky / Journal of Organometallic Chemistry xxx (2017) 1e7
Scheme 7. Two pathways for the synthesis of 1.
signals are seen in the aliphatic region. The 1H NMR spectrum is
13
1
thus not very conclusive. The C{ H} NMR spectrum points to an
asymmetric coordination of the amidinate ligands. Thus, two sets of
signals were observed for the amidinate ligands, e.g. the methyl
and methine group each shows two resonances at 59.5 ppm,
59.0 ppm, 22.3 ppm, 21.3 ppm. Since the amidinate ligands are
relatively large, we suggest steric reasons hamper a symmetric
coordination in solution. Unfortunately, the by-product LiCl from
salt metathesis could not be completely removed from the bulk
material.
In similar manner as for the synthesis of 1, we reacted (S)-
LiPEAA with LuCl
temperature to obtain [{(S)-PEAA}
. Single crystals of 2 were grown from THF/n-pentane.
Compound 2 crystallizes in the orthorhombic Sohncke space
group P2 with four molecules in the unit cell (Fig. 2). The
3
in a 2:1 stoichiometric ratio in THF at room
2
LuCl(thf)] (2) as product Scheme
8
1 1 1
2 2
lutetium atom is six-fold coordinated by two amidinate ligands,
one chlorine atom, and one additional molecule of THF. Compound
2
is the first monomeric lutetium bis amidinate chloro compound
with a chiral ligand. All other related lutetium complexes form
chloride bridged dimers e.g. 1, [{(S)-PETA} LuCl] [40] and [{(S)-
PEBA} LnCl] [1]. Obviously, in comparison to the other chiral
amidinates, the reduced steric demand of {(S)-PEAA} has a sig-
nificant influence on the complex geometry. The Lu-N (av. 2.291 Å)
bond distances in 2 are very similar to those observed in 1 (av.
Fig. 1. Molecular structure of 1 in the solid-state. Hydrogen atoms and solvent mol-
ecules are omitted for clarity. Selected bond lengths [Å] and angles [ ]: Lu1-Cl
ꢀ
2
2
2
.6405(13), Lu1-N1 2.267(5), Lu1-N2 2.351(5), Lu2-Cl 2.6640(13), Lu2-N3 2.255(5),
2
2
Lu2-N4 2.359(5), N1-C1 1.337(6), N2-C1 1.321(7),N3-C24 1.322(7), N4-C24 1.341(7);
N1-Lu1-N2 58.2(2), N3-Lu2-N4 58.1(2), Cl-Lu1-Cl‘ 80.38(5), Cl-Lu2-Cl‘ 79.52(5), Lu1-Cl-
Lu2 100.05(4), N1-C1-N2 115.3(5), N3-C24-N4 114.8(5).
-
2
.308 Å). On the other hand, the ligand is more symmetrically co-
the unit cell (Fig. 1). Only half of a molecule is localized in the
asymmetric unit. A crystallographic C2 axis is observed along Lu1
ordinated to the metal atom as observed in 1. Unfortunately, the
bite angles of the ligands (N1-Lu-N2 57.66(14) and N3-Lu-N4
ꢀ
and Lu2. Compound 1 is a di-m-chloro bridged dimeric compound.
ꢀ
59.18(15) ) differ significantly, precluding a detailed interpretation.
The central Lu-Cl-Lu-Cl four-membered ring is symmetrical with
1
In contrast to 1, the H NMR spectrum of 2 shows sharp peaks
ꢀ
ꢀ
angles of Cl-Lu1-Cl‘ 80.38(5) , Cl-Lu2-Cl‘ 79.52(5) , and Lu1-Cl-Lu2
and a symmetrical pattern. The characteristic signals of the methyl
groups are observed at 1.52 and 1.64 ppm. In the C{ H} NMR
spectrum, the signals of these groups were detected at 14.8 and
ꢀ
1
00.05(4) . The Lu-N-C-N planes formed by the amidinate ligands
are twisted to each other by about 99.8 (Lu1) and 104.8 (Lu2). The
13
1
ꢀ
amidinate ligands coordinate asymmetrically to the lutetium atoms
27.6 ppm. The characteristic signal of the NCN unit is seen at
(
Lu1-N1 2.267(5) Å, Lu1-N2 2.351(5) Å, Lu2-N3 2.255(5) Å, and Lu2-
178.8 ppm.
N4 2.359(5) Å). The deviation of the Lu-N bond distances of each
amidinate ligand is about 0.1 Å. The phenyl rings are almost rect-
angular localized to these planes. The bite angles in 1 (N1-Lu1-N2
3. Summary
ꢀ
ꢀ
5
(
8.2(2) , N3-Lu2-N4 58.1(2) ) are very similar to [Lu(PEBA)
2
(m-Cl)]
2
ꢀ
58.51(9) ) [1] but as expected larger than in the crowded PETA
In summary, we prepared two new chiral amidinates ((R)-
-
-
ꢀ
compound [{(S)-PETA}
2
LnCl]
2
(av. 57.6 ) [40].
CEBA) and ((S)-PEAA) by two different synthetic pathways. The
corresponding lithium salts (R)-LiCEBA and (S)-LiPEAA were ob-
tained by deprotonation of the amidine or by direct reaction of a
lithium alkyl reagent with the carbodiimide precursor. Further
1
13
1
The H and C{ H} NMR spectra of 1 show the expected signals.
However, as a result of the flexible cyclohexyl rings overlaid broad
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T.S. Brunner, P.W. Roesky / Journal of Organometallic Chemistry xxx (2017) 1e7
5
Scheme 8. Synthesis of 2.
4.1. (R)-N-(1-cyclohexylethyl)benzamide (I)
To a reaction mixture of 10.00 mL (8.66 g, 68.1 mmol) (R)-1-
cyclohexylethylamine in 55 mL of an aqueous sodium hydroxide
solution (10%), 8.30 mL (10.05 g, 71.5 mmol) benzoylchloride was
added dropwise under vigorous stirring. After 2 h of stirring at r.t.
the colorless precipitate formed was filtered off, washed several
times with water and then dried in vacuo. Yield: 14.0 g (60.5 mmol,
1
8
d
9%) of I as colorless solid. - H NMR (400 MHz, DMSO-d
6
, 298 K):
3
3
(ppm) ¼ 8.10 (d, J ¼ 8.4 Hz, 1 H, NH), 7.83 (d, J ¼ 7.2 Hz, 2 H, m-
3
3
Ph), 7.50 (t, J ¼ 7.2 Hz,1 H, p-Ph), 7.44 (t, J ¼ 7.2 Hz, 2 H, o-Ph), 3.84
3
(
1
m, J ¼ 7.2 Hz, 1 H, NCH), 1.76e1.69 (m, 4 H, cyclohexyl-H),
.61e1.59 (m, 1 H, cyclohexyl-H), 1.45e1.37 (m, 1 H, cyclohexyl-H),
1
.20e1.09 (m, 6 H, cyclohexyl-H und CH
3
), 0.99e0.90 (m, 2 H,
13
1
cyclohexyl-H). -
C{ H} NMR (101 MHz, DMSO-d , 298 K):
6
Fig. 2. Molecular structure of 2 in the solid-state. Hydrogen atoms are omitted for
clarity. Selected bond lengths [Å] and angles [ ]: Lu1-Cl 2.5590(11), Lu1-O1 2.311(4),
Lu1-N1 2.311(4), Lu1-N2 2.295(4), Lu1-N3 2.254(4), Lu1-N4 2.304(4), N1-C1 1.340(6),
N2-C1 1.339(7), N3-C19 1.342(6), N4-C19 1.332(7); N1-Lu-N2 57.66(14), N1-Lu-N3
ꢀ
d
(ppm) ¼ 165.6 (CO), 135.0 (i-Ph), 130.9 (Ph), 128.1 (Ph), 127.3 (Ph),
9.2 (NCH), 42.4 (cyclohexyl-CH), 29.3 (CH ), 29.0 (CH ), 26.1 (CH ),
), 17.7 (CH ).
4
2
2
2
25.8 (CH
2
3
114.0(2), N1-Lu-N4 159.6(2), N1-Lu-Cl 99.26(10), N1-Lu-O1 92.86(15), N2-Lu-N3
9
5
9
8.9(2), N2-Lu-N4 103(2), N2-Lu-Cl 156.80(11), N2-Lu-O1 88.80(15), N3-Lu-N4
9.18(15), N3-Lu-Cl 92.72(11), N3-Lu-O1 152.11(14), N4-Lu-Cl 100.21(12), N4-Lu-O1
3.01(14), Cl1-Lu-O1 90.24(10), N1-C1-N2 112.0(5), N3-C19-N4 114.7(4).
4.2. (R)-N-(1-cyclohexylethyl)benzimidoylchloride (II)
A mixture of I 14.0 g (60.5 mmol) and 7.75 mL (7.13 g,
6.6 mmol) of 2,6-lutidine was dissolved in 150 mL of dry CH Cl
6
2
2
reactions of these lithium salts with LuCl
dinate complexes [{(R)-CEBA} Lu- -Cl] and [{(S)-PEAA}
which are either dimeric or monomeric in the solid state. Further
3
resulted in the bisami-
and cooled in a water bath. 5.20 mL (7.68 g, 60.5 mmol) oxalyl-
chloride, dissolved in 50 mL dry CH Cl , was slowly added dropwise
2
m
2
2
LuCl(thf)],
2
2
to the reaction mixture within an hour. The color of the reaction
mixture turned to reddish-brown and the mixture was stirred at r.t.
for 2 h. The volatile components were removed in vacuo. Two times
reactions to amido or alkyl derivatives suitable for
metathesis failed, unfortunately.
s-bond
100 mL of dry n-pentane were added to the dark brown residue and
stirred for 1 h. The suspension was filtered and the volatile com-
ponents of the combined filtrates were removed under vacuum.
4
. Experimental [42]
General procedures: All manipulations of air-sensitive mate-
ꢀ
The resulting brown oil was distilled in vacuo at 125
C
ꢁ2
(3.4$10 mbar) to obtain 12.04 g (48.2 mmol, 80%) of light yellow
II.
rials were performed with the rigorous exclusion of oxygen and
moisture in Schlenk-type glassware, either on a dual-manifold
ꢁ
3
Schlenk line interfaced to a high-vacuum (10 mbar) line or in
an argon-filled MBraun glove box. THF was distilled under a ni-
trogen atmosphere from potassium benzophenone ketyl prior to
use. Hydrocarbon solvents (toluene, n-pentane and n-heptane)
were dried using an MBraun solvent purification system (SPS-800).
All solvents for vacuum-line manipulations were stored in vacuo
4.3. (R)-1-Cyclohexylethyl-benzimidamide-hydrochloride (R)-
HCEBA·HCl
The imidoylchloride II 12.04 g (48.2 mmol) was dissolved in
50 ml of dry toluene and 7.08 ml (6.13 g, 48.2 mmol) of (R)-1-
cyclohexylethylamine was added dropwise. The reaction mixture
was refluxed for 12 h. Upon cooling to room temperature, the
desired product precipitates as a colorless solid. The solid was
filtered off and recrystallized from hot toluene to obtain 16.23 g
4
over LiAlH in resealable flasks. Deuterated solvents were obtained
from Aldrich GmbH (99 atom% D) and were degassed, dried, and
stored in vacuo over Na/K alloy in resealable flasks. NMR spectra
were recorded on Bruker Avance II 300 MHz or Avance III 400 MHz
NMR spectrometers. Chemical shifts are referenced to internal
solvent resonances and are reported relative to tetramethylsilane.
IR spectra were obtained on a Bruker Tensor 37. Mass spectra were
recorded at 70 eV on a Finnigan MAT 8200. Elemental analysis was
1
(43.0 mmol, 89%) of colorless (R)-HCEBA$HCl. - H NMR (400 MHz,
3
CDCl
3
, 298 K):
d
(ppm) ¼ 10.46 (d, J ¼ 9.6 Hz, 2 H, NH), 7.64e7.56
(m, 3 H, Ph), 7.25 (s, 2 H, Ph), 2.86e2.77 (m, 2 H, NCH), 1.77e1.59 (m,
10 H, cyclohexyl-H), 1.39e1.34 (m, 2 H, cyclohexyl-H), 1.24e1.07 (m,
13
12 H, cyclohexyl-H and CH
3
), 0.99e0.84 (m, 4 H, cyclohexyl-H). -
, 298 K):
(ppm) ¼ 166.1 (NCN), 131.8 (i-
Ph), 129.8 (Ph), 127.1 (Ph), 126.9 (Ph), 56.7 (NCH), 43.4 (cyclohexyl-
CH), 29.4 (CH ), 29.0 (CH ), 26.1 (CH ), 26.1 (CH ), 19.1 (CH ). - HR
C
1
performed on an Elementar vario EL or microcube. LnCl
S)-PEC [40] were prepared according to literature procedures.
KN(SiMe was sublimed before use.
3
[52] and
{ H} NMR (101 MHz, CDCl
3
d
(
3
)
2
2
2
2
2
3
Please cite this article in press as: T.S. Brunner, P.W. Roesky, Journal of Organometallic Chemistry (2017), http://dx.doi.org/10.1016/
j.jorganchem.2017.03.041

6
T.S. Brunner, P.W. Roesky / Journal of Organometallic Chemistry xxx (2017) 1e7
þ
powder. Yield: 0.85 g (3.12 mmol, 85%). - 1H NMR (400 MHz, d
ESI-MS (toluene): m/z ¼ 717.57 ([(HCEBA)
2
$HCl] ), calc. for
8
-
ꢁ1
3
C
H
46 74
N
4
Cl: 717.56. - IR (ATR):
w), 3032 (m), 2969 (m), 2928 (vs), 2852 (vs), 2669 (w), 2019 (w),
939 (w), 1627 (vs), 1611 (w), 1572 (s), 1468 (w), 1448 (s), 1380 (m),
323 (w), 1315 (m), 1288 (w), 1265 (w), 1240 (w), 1191 (w), 1174 (w),
140 (m), 1080 (w), 1044 (w), 1015 (w), 1000 (w), 951 (w), 890 (w),
64 (w), 854 (w), 792 (s), 742 (m), 720 (s), 687 (w), 668 (w), 494
w), 443 (w), 429 (w), 410 (w), 384 (w), 362 (w). - elemental
analysis calc. (%) for C23 Cl (377.006 g/mol): C 73.27; H 9.89, N
n
(cm ) ¼ 3249 (w), 3154 (w), 3096
THF, 298 K):
d
(ppm) ¼ 7.30 (d, J ¼ 7.2 Hz, 4 H, Ph), 7.14 (t,
3
3
3
(
1
1
1
8
(
J ¼ 7.2 Hz, 4 H, Ph), 7.00 (t, J ¼ 7.2 Hz, 2 H, Ph), 4.41 (q, J ¼ 6.6 Hz,
3
13
4 H, CH), 1.58 (s, 3 H, CCH
3
), 1.21 (d, J ¼ 6.6 Hz, 6 H, CHCH
3
). -
C
1
{ H} NMR (75 MHz, d
8
-THF, 298 K):
d
(ppm) ¼ 170.5 (NCN), 153.8 (i-
3
Ph), 128.3 (Ph), 127.5 (Ph), 125.6 (Ph), 57.5 (CH), 29.1 (CHCH ), 12.1
ꢁ
1
(CCH
3
). - IR (ATR):
n
(cm ) ¼ 3428 (w), 3058 (w), 3023 (w), 2963
(m), 2922 (w), 2861 (w), 1947 (w), 1871 (w), 1808 (w), 1646 (m),
1621 (m), 1601 (w), 1583 (w), 1488 (s), 1446 (s), 1405 (w), 1363 (w),
1342 (w),1321 (m),1299 (w),1269 (w),1206 (w),1173 (w),1152 (w),
37 2
H N
7.43; found: C 72.19, H 8.71, N 7.42.
1091 (m), 1068 (w), 1024 (m), 1001 (w), 909 (w), 844 (w), 816 (w),
4.4. (R,R)-N,N’-bis-(1-cyclohexylethyl)benzamidine ((R)-HCEBA)
758 (s), 698 (vs), 614 (w), 585 (w), 496 (w), 439 (m), 356 (w).
1.0 ml (2.5 M in n-hexane, 2.50 mmol) n-butyl lithium was
2 2
4.7. [{(R)-CEBA} LuCl] (1)
added dropwise to a suspension of 0.80 g (2.12 mmol) (R)-HCE-
BA$HCl in 20 ml toluene. Upon reaction the suspension clears up
and was stirred at r.t. for 30 min. The clear solution is quenched
with 30 ml of a saturated sodium bicarbonate solution. After
vigorous stirring for 30 min, the phases were separated and the
organic layer was dried over magnesium sulfate. The solvent was
4.7.1. Route a
ꢀ
THF (ca. 10 ml) was condensed at ꢁ78 C onto a mixture of
228 mg (0.810 mmol) LuCl and 630 mg (1.620 mmol) (R)-LiCEBA
3
and the reaction mixture was stirred overnight at r.t. The solvent
was removed in vacuo and the residue was washed with 10 ml of n-
pentane and then extracted with 10 ml of hot toluene. The solvent
was removed in vacuo and the residue was washed with 10 ml n-
pentane. The product was crystallized from hot toluene to yield
375 mg (0.422 mmol, 52%) of 1.
removed in vacuo to obtain (R)-HCEBA as colorless oil. Yield: 0.70 g
1
(
2.06 mmol, 97%). - H NMR (300 MHz, DMSO-d
6
, 298 K):
d
(ppm) ¼ 7.42e7.32 (m, 3 H, Ph), 7.14e7.11 (m, 2 H, Ph), 5.48 (d,
3
3
J ¼ 6.9 Hz, 1 H, NH), 3.85 (br, 1 H, NCH), 2.67 (m, J ¼ 5.4 Hz, 1 H,
NHCH), 1.71e1.62 (m, 10 H, cyclohexyl-H), 1.14e0.77 (m, 18 H,
13
1
cyclohexyl-H and CH
3
). - C{ H} NMR (75 MHz, DMSO-d
(ppm) ¼ 155.9 (NCN), 136.9 (i-Ph), 128.1 (Ph), 127.9 (Ph), 127.4
Ph), 57.89 (NHCH), 48.9 (NCH), 45.1 (NHCH-cyclohexyl-CH), 41.4
NCH-cyclohexyl-CH), 30.0 (CH ), 29.7 (CH ), 28.4 (CH ), 28.0 (CH ),
), 21.2 (NCHCH ) 16.7 (NHCHCH ).
6
, 298 K):
4.7.2. Route b
ꢀ
d
THF (ca. 10 ml) was condensed at ꢁ78 C onto a mixture of
(
(
2
3
95 mg (0.337 mmol) LuCl , 254 mg (0.675 mmol) (R)-HCEBA$HCl
2
2
2
2
3 2
and 269 mg (1.349 mmol) KN(SiMe ) and the reaction mixture was
6.4 (CH
2
), 26.1 (CH
2
3
3
refluxed for two days. The reaction mixture was filtered and the
solvent was removed in vacuo from the clear pale yellow solution.
The residue was washed with 10 ml of n-pentane and the product
4.5. Lithium-N,N’-bis-((R)-1-cyclohexylethyl)benzamidinate ((R)-
LiCEBA)
was crystallized from hot toluene to yield 85 mg (0.096 mmol, 28%)
1
of 1. H NMR (400 MHz, d
8
-THF, 298 K):
d
(ppm) ¼ 7.42e7.06 (m,
3
3
3
.42 mL (2.5 M in n-hexane, 8.55 mmol) n-butyl lithium was
10 H, Ph), 2.86 (m, J ¼ 5.9 Hz, 1 H, NCH), 2.61 (m, J ¼ 7.0 Hz, 3 H,
NCH), 2.21 (br, 1 H, cyclohexyl-H), 1.99 (br, 1 H, cyclohexyl-H),
1.73e1.52 (m, 18 H, cyclohexyl-H), 1.44e1.33 (m, 4 H, cyclohexyl-H),
added dropwise to a solution of 1.50 g (3.98 mmol) (R)-HCEBA$HCl
in 50 mL toluene. The light yellow mixture was stirred for 3 h at r.t.
and the volatile components were removed in vacuo. The residue
was washed with 30 mL of n-pentane. After drying under vacuum,
the desired product is obtained as a colorless solid that includes one
3
1.27e1.21 (m, 8 H, cyclohexyl-H),1.17e1.13 (m,12 H, CH ),1.08e0.97
(m, 4 H, cyclohexyl-H), 0.92e0.85 (m, 2 H, cyclohexyl-H), 0.73e0.49
(m, 6 H, cyclohexyl-H). (The region between 2.9 and 0.49 shows
broad peaks, which overlap and shows small solvent signals. Per-
fect integration of these signals is not possible. Intensities are thus
equivalent of lithium chloride, which was not separated. Yield:
1
1.14 g (2.93 mmol, 74%) - H NMR (300 MHz, C
6
D
6
, 298 K):
13
1
d
(ppm) ¼ 7.26e7.20 (m, 4 H, Ph), 7.12e7.08 (m, 1 H, Ph), 2.91 (m,
8
partly estimated.) - C{ H} NMR (101 MHz, d -THF, 298 K):
3
J ¼ 4.5 Hz, 2 H, NCH), 1.95e1.70 (m, 11 H, cyclohexyl-H), 1.37e1.21
d
(ppm) ¼ 180.9 (NCN), 177.7 (NCN), 138.2 (i-Ph), 137.8 (i-Ph), 129.8
3
13
1
(
(
(
(
(
(
m,11 H, cyclohexyl-H), 1.06 (d, J ¼ 4.5 Hz, 6 H, CH
3
). - C{ H} NMR
(Ph), 128.9 (Ph), 128.5 (Ph), 128.3 (Ph), 128.0 (Ph), 127.9 (Ph), 59.5
75 MHz, C
6
D
6
, 298 K):
d
(ppm) ¼ 176.8 (NCN), 139.2 (i-Ph), 128.3
(NCH), 59.0 (NCH), 45.6 (cyclohexyl-CH), 45.1 (cyclohexyl-CH), 33.1
Ph), 127.9 (Ph), 127.1 (Ph), 56.8 (NCH), 47.1 (cyclohexyl-CH), 30.8
CH ), 30.5 (CH ), 27.5 (CH ), 27.3 (CH ), 27.2 (CH ), 22.4 (CH ). - IR
ATR):
(cm ) ¼ 3442 (w), 3080 (w), 3058 (w), 3025 (w), 2921
vs), 2850 (vs), 2665 (w), 1637 (vs), 1600 (m), 1578 (w), 1559 (w),
480 (s), 1447 (s), 1366 (m), 1333 (m), 1292 (m), 1260 (m), 1189 (w),
157 (w),1123 (w),1071 (w),1026 (s), 915 (w), 890 (m), 861 (w), 841
w), 798 (m), 768 (m), 701 (vs), 669 (w), 556 (w), 505 (w), 446 (m),
91 (w). elemental analysis calc. (%) for Li$LiCl
388.872 g/mol): C 71.04; H 9.07, N 7.20; found: C 72.05, H 9.18, N
(CH
(CH
2
), 32.8 (CH
), 27.3 (CH
2
), 31.2 (CH
), 22.3 (CH
2
), 29.6 (CH
), 21.3 (CH
2
), 28.1 (CH
). - IR (ATR): n
2
), 27.8 (CH
(cm ) ¼ 3442
2
), 27.4
ꢁ
1
2
2
2
2
2
3
2
2
3
3
ꢁ
1
n
(w), 3058 (w), 3024 (w), 2921 (vs), 2850 (s), 2665 (w), 1637 (vs),
1600 (w), 1577 (w), 1559 (w), 1540 (w), 1447 (vs), 1367 (m), 1339
(m),1294 (w), 1262 (w), 1240 (w), 1190 (w), 1153 (w), 1129 (w), 1104
(w), 1070 (w), 1028 (w), 988 (w), 968 (w), 915 (w), 890 (m), 841 (w),
773 (s), 740 (w), 726 (w), 701 (vs), 668 (w), 629 (w), 557 (w), 511
1
1
(
3
-
C
23
H
35
N
2
(w), 468 (w), 383 (w).
ClLuꢂLiCl (931.889 g/mol): C 59.29; H 7.57, N 6.01; found:
C 58.86, H 7.14, N 5.60.
- elemental analysis calc. (%) for
(
46 70 4
C H N
6
.89.
4.6. Lithium-N,N’-bis-((S)-1-phenylethyl)acetamidinate ((S)-
2
4.8. [{(S)-PEAA} LuCl(thf)] (2)
LiPEAA)
ꢀ
THF (ca. 10 ml) was condensed at ꢁ78 C onto a mixture of
152 mg (0.540 mmol) LuCl and 294 mg (1.081 mmol) (S)-LiPEAA
2
.3 ml (1.6 M in diethyl ether, 3.68 mmol) of methyl lithium was
3
added dropwise to a solution of 0.92 g (3.68 mmol) (S)-PEC [40] in
and the reaction mixture was stirred overnight at r.t. The solvent
was removed in vacuo and the residue was washed with 10 ml n-
pentane and then extracted with 10 ml of n-pentane. The solvent
was removed in vacuo and the product was crystallized from
ꢀ
2
0 ml of dry diethyl ether at ꢁ40 C. The mixture was stirred at r.t.
over night. All volatiles were removed in vacuo and the residue was
washed with 25 ml of n-pentane to obtain (S)-LiPEAA as orange
Please cite this article in press as: T.S. Brunner, P.W. Roesky, Journal of Organometallic Chemistry (2017), http://dx.doi.org/10.1016/
j.jorganchem.2017.03.041

T.S. Brunner, P.W. Roesky / Journal of Organometallic Chemistry xxx (2017) 1e7
7
saturated n-pentane/THF solution to yield 160 mg (0.197 mmol,
References
1
3
6%) of 2. - H NMR (300 MHz, d
8
-THF, 298 K):
d
(ppm) ¼ 7.39e7.36
3
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(
3
6
m, 8 H, Ph), 7.11e7.01 (m, 12 H, Ph), 4.48 (q, J ¼ 6.0 Hz, 4 H, CH),
1
2 2 2
.64e3.59 (m, 4 H, OCH ), 1.79e1.75 (m, 4 H, OCH CH ), 1.64 (br,
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13
1
H, CCH
3
), 1.52 (d, 3J ¼ 6.9 Hz, 12 H, CHCH
3
). - C{ H} NMR
2574e2576.
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(
(
2
(
1
75 MHz, d
8
-THF, 298 K):
d
(ppm) ¼ 178.8 (NCN), 150.2 (i-Ph), 128.9
Ph), 127.7 (Ph), 126.5 (Ph), 68.4 (OCH
6.5 (OCH CH ), 14.8 (CCH ). - IR (ATR):
w), 3025 (w), 2966 (m), 2926 (w), 2867 (w), 1950 (w), 1884 (w),
811 (w), 1643 (s), 1601 (w), 1583 (w), 1489 (s), 1447 (s), 1406 (w),
372 (w), 1317 (w), 1274 (w), 1214 (m), 1177 (w), 1148 (w), 1099 (m),
068 (w), 1024 (m), 987 (w), 910 (w), 864 (w), 820 (w), 761 (s), 699
2
), 57.8 (CH), 27.6 (CHCH
3
),
ꢁ
1
2
2
3
n
(cm ) ¼ 3429 (w), 3058
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[
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1
1
[10] M.P. Coles, Dalton Trans. (2006) 985e1001.
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32e36.
(
vs), 653 (w), 615 (w), 605 (w), 585 (w), 533 (m), 404 (w), 382 (w).
[
[
12] J. Li, S. Huang, L. Weng, D. Liu, J. Organomet. Chem. 691 (2006) 3003e3010.
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X-ray crystallographic studies of 1 and 2: Suitable crystals 1
and 2 were covered in mineral oil (Aldrich) and mounted onto a
glass fiber. The crystals were transferred directly into the cold
stream of a Stoe IPDS 2 or StadiVari diffractometer.
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[
[
15] H. Brunner, J. Lukassek, G. Agrifoglio, J. Organomet. Chem. 195 (1980) 63e76.
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(1980) 641e642.
All structures were solved by using the program SHELXS/T [53].
The remaining non-hydrogen atoms were located from successive
difference Fourier map calculations. The refinements were carried
[17] A. Bertogg, A. Togni, Organometallics 25 (2006) 622e630.
[
[
18] H. Brunner, G. Agrifoglio, Monatsh. Chem. 111 (1980) 275e287.
19] E. Nelkenbaum, M. Kapon, M.S. Eisen, J. Organomet. Chem. 690 (2005)
3154e3164.
2
out by using full-matrix least-squares techniques on F by using the
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[23] F. Edelmann, Struct. Bond. 137 (2010) 109e163.
program SHELXL [53]. The hydrogen atom contributions of all of the
compounds were calculated, but not refined. In each case, the lo-
cations of the largest peaks in the final difference Fourier map
calculations, as well as the magnitude of the residual electron
densities, were of no chemical significance.
[24] P.C. Junk, M.L. Cole, Chem. Commun. (2007) 1579e1590.
[
[
[
25] F.T. Edelmann, Angew. Chem. Int. Ed. 34 (1995) 2466e2488.
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27] M. Wedler, F. Kn o€ sel, U. Pieper, D. Stalke, F.T. Edelmann, H.-D. Amberger,
Crystal data for 1:
C
92
H
140Cl
2
Lu
2
N
8
$C
7
H
8
,
M
¼
1871.09,
Chem. Ber. 125 (1992) 2171e2181.
[28] M.L. Cole, G.B. Deacon, C.M. Forsyth, P.C. Junk, K. Konstas, J. Wang, H. Bittig,
3
a ¼ 19.8151(5) Å, c ¼ 49.3993(15) Å, V ¼ 19396.0(11) Å , T ¼ 190 K,
ꢁ1
D. Werner, Chem. Eur. J. 19 (2013) 1410e1420.
space group I4
1
22, Z ¼ 8,
m
(MoK
a
) ¼ 2.126 mm , 371232 re-
[
[
29] M.L. Cole, P.C. Junk, Chem. Commun. (2005) 2695e2697.
30] M.L. Cole, G.B. Deacon, P.C. Junk, K. Konstas, Chem. Commun. (2005)
1581e1583.
flections measured, 13638 independent reflections (Rint ¼ 0.0820).
2
1
The final R values were 0.0305 (I > 2s(I)). The final wR(F ) values
[31] M.L. Cole, G.B. Deacon, C.M. Forsyth, P.C. Junk, K. Konstas, J. Wang, Chem. Eur.
J. 13 (2007) 8092e8110.
were 0.0671 (I > 2 (I)). The final R values were 0.0537 (all data).
s
1
2
The final wR(F ) values were 0.0813 (all data). The goodness of fit on
[32] M.L. Cole, P.C. Junk, New J. Chem. 29 (2005) 135e140.
2
F was 1.091. Flack parameter ¼ ꢁ0.043(3).
[33] M.L. Cole, G.B. Deacon, C.M. Forsyth, K. Konstas, P.C. Junk, Dalton Trans. (2006)
360e3367.
3
Crystal data for 2: C40
H
50ClLuN
4
O, M ¼ 813.26, a ¼ 13.7119(2) Å,
[34] S. Bambirra, D. van Leusen, A. Meetsma, B. Hessen, J.H. Teuben, Chem. Com-
3
b ¼ 14.2659(3) Å, c ¼ 19.2517(3) Å, V ¼ 3765.88(11) Å , T ¼ 100 K,
mun. (2003) 522e523.
ꢁ1
space group P2
1
2
1
2
1
, Z ¼ 4,
m
(MoK
a
) ¼ 2.728 mm , 32388 re-
[35] L. Zhang, M. Nishiura, M. Yuki, Y. Luo, Z. Hou, Angew. Chem. Int. Ed. 47 (2008)
642e2645.
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150e1155.
2
flections measured, 9075 independent reflections (Rint ¼ 0.0358).
2
1
The final R values were 0.0247 (I > 2s(I)). The final wR(F ) values
(
were 0.0504 (I > 2 (I)). The final R values were 0.0277 (all data).
s
1
2
1
The final wR(F ) values were 0.0508 (all data). The goodness of fit
on F was 0.950. Flack parameter ¼ ꢁ0.011(5).
2
1
Crystallographic data (excluding structure factors) for the
structures reported in this paper have been deposited with the
Cambridge Crystallographic Data Centre as a supplementary pub-
lication no. 1529650e1529651. 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).
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[
[
T. S. B. thanks the Helmholtz Research School Energy-Related
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7
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(
190481) for support. Ms. S. Schneider and Dr. M. T. Gamer are
acknowledged for help in collecting and refining single crystal X-
ray diffraction data.
[
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7
[
Appendix A. Supplementary data
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[
Supplementary data related to this article can be found at http://
dx.doi.org/10.1016/j.jorganchem.2017.03.041.
Please cite this article in press as: T.S. Brunner, P.W. Roesky, Journal of Organometallic Chemistry (2017), http://dx.doi.org/10.1016/
j.jorganchem.2017.03.041