Synthesis of epimer of Taniaphos ligand

Article abstract of DOI:10.1016/j.jorganchem.2016.01.004

The spatial arrangement of groups within a chiral ligand is essential for its catalytic performance. This work describes convenient synthesis of (R,S_p)-1-(2-(diphenylphosphano)ferrocenyl)-1-(2-diphenylphosphanophenyl)-N,N-dimethylmethanamine, a

Full text of DOI:10.1016/j.jorganchem.2016.01.004

Journal of Organometallic Chemistry 805 (2016) 130e138
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Journal of Organometallic Chemistry
journal homepage: www.elsevier.com/locate/jorganchem
Synthesis of epimer of Taniaphos ligand
a
b
a
a
Ambroz Alm aꢀ ssy , Erik Rakovský , Andrea Malastov aꢀ , Zuzana Sor aꢀ dov aꢀ ,
Radovan Sebesta
a
ꢁ
a, *
Department of Organic Chemistry, Faculty of Natural Sciences, Comenius University in Bratislava, Mlynsk aꢀ dolina, Ilkovi ꢁc ova 6, 842 15 Bratislava, Slovakia
Department of Inorganic Chemistry, Faculty of Natural Sciences, Comenius University in Bratislava, Mlynsk aꢀ dolina, Ilkovi ꢁc ova 6, 842 15 Bratislava,
b
Slovakia
a r t i c l e i n f o
a b s t r a c t
Article history:
Received 14 July 2015
Received in revised form
The spatial arrangement of groups within a chiral ligand is essential for its catalytic performance. This
work
describes
convenient
synthesis
of
(R,S
p
)-1-(2-(diphenylphosphano)ferrocenyl)-1-(2-
diastereomer of the well known (R,R )-
diphenylphosphanophenyl)-N,N-dimethylmethanamine,
a
p
1
December 2015
Taniaphos ligand. The compound was prepared from the same homochiral amine as Taniaphos by
sequential twofold lithiation followed by trapping with diphenyphosphane chloride. Sequential twofold
lithiation, in contrast to simultaneous dilithiation, leads to the opposite configuration of the stereogenic
Accepted 8 January 2016
Available online 15 January 2016
p
plane. The structure and configuration of the (R,S )-diastereomer along with its CuBr-complex were
confirmed by X-ray structural analysis. DFT calculations elucidated underlying effects controlling the
stereochemical outcome of the lithiation.
Keywords:
Ferrocene
Directed ortho-metalation
Diastereoselective lithiation
Chiral ligand
© 2016 Elsevier B.V. All rights reserved.
Asymmetric catalysis
1. Introduction
control of the lithiation leads predominantly to (R*,S*
p
)- relative
configuration of the product (Scheme 1) [27,28].
Ferrocene is one of the prominent structural elements for
building chiral ligands for asymmetric catalysis [1e6]. In particular,
ferrocenyl phosphanes possessing elements of central and planar
chirality represent an important group of ligands used in homo-
geneous asymmetric catalysis with transition metals [7,8]. Ferro-
cenyl phosphane, Taniaphos, introduced by Knochel and co-
workers, is the highly useful type of chiral ligand [9]. Taniaphos
proved helpful in the copper-catalyzed conjugate additions of
organometallic reagents [10e18], copper-catalyzed allylic sub-
stitutions [19e22], or rhodium catalyzed hydrogenations [23e25].
Introduction and manipulation of stereogenic units during
synthesis of chiral ferrocene ligands is an important topic [26].
Many chiral ferrocene ligands can be synthesized from suitable
In this transition state model, the hydrogen atom on a-carbon
occupies the space between the planes of ferrocenyl Cp rings
relieving the steric interaction of bulkier groups with the ferrocenyl
fragment. These substituents on stereogenic center are located
above the plane of the substituted Cp ring, and the introduction of
lithium atom is directed by the nitrogen of the amino group. This
model of the lithiation applies even in such constrained systems as
0
N,N-dimethyl-[5]ferrocenophan-1 -amine [29].
On the other hand, dilithiation of compound (R)-1 and subse-
quent reaction with PPh Cl leads to diphosphane (R,R )-3 (Tania-
2 p
phos). The formation of a quasi-dimeric arrangement of lithium
atoms in the transition state explains the configuration of the chiral
plane (Scheme 1). Another factor, which further stabilizes this
pathway may be an interaction of Li with Fe [30].
chiral amines. These homochiral a-amino derivatives often result
from the resolution of corresponding racemic amines (Ugi's reso-
lution) or stereoselective reduction of carbonyl compounds fol-
lowed by a nucleophilic substitution with retention of the
configuration. Stereoselective induction of the planar chirality is
The presence of two lithium atoms in the transition state is
essential to achieving the observed stereochemical result of the
lithiation. Separating the lithiations in two distinct steps should,
therefore, lead to the opposite configuration of the chiral plane
similarly to other mono-lithiations.
allowed by the ortho-directing amino group on
a-carbon. Steric
Alternatively, Taniaphos-type ligands can also be synthesized by
stereoselective ortho-lithiation of chiral ferrocenyl sulfoxides.
Electrophilic quenching of the resulting Li-intermediate with 2-
*
Corresponding author.
E-mail address: radovan.sebesta@fns.uniba.sk (R. Sebesta).
ꢁ
(diphenylphosphano)benzaldehyde
provided
two
http://dx.doi.org/10.1016/j.jorganchem.2016.01.004
022-328X/© 2016 Elsevier B.V. All rights reserved.
0

A. Alm aꢀ ssy et al. / Journal of Organometallic Chemistry 805 (2016) 130e138
131
Scheme 1. Schematic representation of different course of double and step-wise lithiation.
diastereoisomeric alcohols with a different configuration of the
chiral center on -carbon formed in approximately equal amounts
31e34]. These alcohols were separated by chromatography and
the sulfoxide group substituted with phosphano group. However,
a
[
p
this method was not employed for the synthesis of (R,S )-config-
ured diphosphane-amines [32].
In another approach, Fukuzawa and coworkers protected (pro-S)
ortho-position of 1-ferrocenyl-N,N-dimethyl-1-
phenylmethanamine with a trimethylsilyl group. Ensuing lith-
iation of the second ortho-position of Cp ring and phenyl ring helps
to introduce two diphenylphosphano groups. After deprotection,
they obtained (R,R
In this context, we decided to investigate step-wise twofold
lithiation for the synthesis of (R,S )-epimer of Taniaphos, com-
pound (R,S )-3. To the best of our knowledge, the synthesis of
p
)-Taniaphos [35,36].
Scheme 2. Synthesis of phosphane 2.
p
p
diastereomer 3 was not accomplished, despite several attempts. We
show that a careful control of reaction parameters enables one to
perform the desired step-wise dilithiation and thus obtain epimer
of Taniaphos.
2
. Results and discussion
2.1. Synthesis
Enantioselective CBS-reduction of (2-bromobenzoyl)ferrocene
p
Scheme 3. Synthesis of (R,S )-3.
afforded the starting amine (R)-1. Crystallization of alcohol from
heptane provided the corresponding product in 99% enantiomeric
excess. The resulting alcohol was acetylated, and acetoxy group
subsequently substituted for dimethylamino group following the
procedure of Knochel and coworkers [9]. The nucleophilic substi-
tution in the a-position to ferrocenyl moiety proceeds with com-
plete retention of the configuration on the stereogenic center as
was well documented in many ferrocenyl compounds.
slowly decomposes in chloroform solution forming the para-
1
13
31
magnetic particles. Satisfactory H, C, and P NMR spectra were
recorded in d -acetone solution. The chemical shift of the phos-
phorus, a singlet at ꢀ17.2 ppm, is similar to that of the phenyl
attached phosphorus in (R,R
6
p
)-Taniaphos (doublet ꢀ16.7 ppm).
The subsequent lithiation of compound (R)-2 proceeded slowly
Exposure of compound (R)-1 to t-BuLi resulted in an exchange of
the bromine atom in ortho-position of the phenyl ring. This BreLi
exchange proceeded quickly even at low temperatures. Complete
conversion of starting bromoamine 1 was achieved within one hour
(
Scheme 3). It required elevated reaction temperature and longer
time. Lithium was stereoselectively directed to the preferred ortho-
position of the substituted Cp ring by coordination to the nitrogen
atom of the amino group (see Scheme 1). Trapping of the corre-
ꢁ
in THF at ꢀ50 C. Lithiated intermediate Int-1 is moisture sensitive
sponding lithiated intermediate Int-2 with PPh
2
Cl afforded the
)-3. The P chemical shifts of phosphorus atoms in
)-3 (
¼ ꢀ18.1 ppm for Ph-P and ꢀ27.0 ppm for Cp-
at 242.8 MHz) are similar to that of the
phosphorus signals of diphosphane (R,R )-3
ꢀ16.7
and ꢀ23.2 ppm, J(P,P) ¼ 19.1 Hz in CDCl at 81 MHz). Coupling with
and decomposes by protolysis to the corresponding debrominated
31
compound (R,S
compound (R,S
p
amine. To minimize this side reaction, the starting material (R)-1
p
d
should be dried carefully by heating above its melting point (m.p.
P, J(P,P) ¼ 39.6 Hz in CDCl
3
ꢁ
7
3 C) under vacuum [23]. Quenching of the reaction with PPh
2
Cl
p
(d
¼
afforded aminophosphane (R)-2 in 75% yield (Scheme 2).
The compound (R)-2 is an orange crystalline compound, which
3

132
A. Alm aꢀ ssy et al. / Journal of Organometallic Chemistry 805 (2016) 130e138
both phosphorus atoms was observed on hydrogen H-C
a
structurally characterized. The appropriate X-ray crystallographic
sample was obtained by crystallization from CHCl /hexane. The
complex [Cu(R,S -3)Br] is a stable yellow crystalline compound.
Chiu and coworkers described the structure of the corresponding
diastereomeric complex [Cu(R,R -3)Br] [43]. Both ligands coordi-
nate the central copper atom by both phosphorus atoms forming an
(
J(H,P) ¼ 7.4; 4.7 Hz in CDCl
3
at 600 MHz). Crystallization of the
/heptane mixture afforded the sample suitable
3
material from CHCl
3
p
for X-ray crystallographic analysis.
Zheng et al. reported preparation of Taniaphos ligand from
a
-
p
ferrocenylbenzyl-N,N-dimethylamine [37]. The reported synthesis
consisted of two distinct lithiation steps each followed by reaction
eight-membered metallacycle. In the [Cu(R,S
127.7 is wider in comparison with Cu-complex of Taniaphos 114.7 .
p
-3)Br], bite angle
ꢁ
ꢁ
with PPh
2
Cl. In that case, however, the first diphenylphosphanyl
group was introduced stereoselectively on the substituted Cp ring
by the directed ortho-lithiation resulting in phosphano-amine as
described by Yamamoto and co-workers [38]. The absolute
configuration of the product was determined by comparing of CD
spectra with related compounds and later was confirmed in our
laboratory by X-ray crystallographic analysis. While the absolute
configuration of this compound remains the same during the next
ortho-lithiation of the phenyl ring, the formation of diphosphane
p
The CueBr bond in complex [Cu(R,S -3)Br] (2.34 Å) is perpendic-
ular to the axis of the ferrocenyl fragment and is directed in the
plane of the ring. On the other hand, the metallacycle is more bend
in the Taniaphos complex, and the CueBr bond (2.32 Å) is almost
parallel to the axis of ferrocene fragment. Compound [Cu(R,S
crystallizes in P2 (Supporting information, Figs. S3 and S4).
The molecule has (R)-configuration on C6 and (S )-configuration of
p
-3)Br]
1 1 1
2 2
p
the stereogenic plane. The intermolecular interactions are pre-
(
R,S
diphospane (R,R
We attempted the lithiation of the compound with n-BuLi, s-BuLi or
p
)-3 should be expected. However, we could not obtain neither
dominantly based on weak CeH … N and CeH … Br interactions
(Table 1) with some contribution of CeH … p interactions [44]. The
p
)-3, nor diphosphane (R,S )-3 by this procedure.
p
structure contained solvent-accessible voids with the total volume
3
t-BuLi,
respectively,
and
subsequent
reaction
with
of 223.4 Å (5.9% of the cell volume). By using solvent masking
chlorophosphane.
technique, we revealed that these voids are empty (electron pop-
ulation 0.0) [45].
The dihedral angle between Cp rings is 6.5(3) . Fe to Cp distance
is 1.64 Å from C1eC5 ring and 1.66 Å from C1AeC5A ring.
ꢁ
2.2. Structural characterization
The absolute structure was determined from anomalous
dispersion effects by post-refinement Flack x factor calculation
using Parson's quotients [46]. Hooft y parameter obtained with x
set to 0 is 0.008(6). Based on both parameters, the compound
Compound (R,S )-3 crystallizes in space group P2
p
1
2
1
2
1
(Sup-
porting information, Figs. S1 and S2). The molecule has the (R)-
configuration on C15 and (S )-configuration of the stereogenic
plane. Intermolecular interaction are based on dispersive forces,
predominantly CeH … interactions; however, based on X-ray
p
p
[Cu(R,S -3)Br] is also enantiopure, and the absolute structure is
p
determined with correct handedness (Fig. 2).
data, there are no interactions shorter than the sum of VdW radii
found.
p
We have also measured CD spectra of both diastereomers (R,R )
p
and (R,S )-3. These spectra suggest that the planar stereogenic unit
ꢁ
The dihedral angle of the Cp rings is 2.9 . Fe to Cp distances are
is a dominant element of chirality (Fig. 3).
1
.65 Å and 1.66 Å for C1eC5 and C6eC10 rings, respectively.
The absolute structure was determined from anomalous
dispersion effects using Friedel difference restraints for obtaining
better convergence of Flack x parameter [39,40]. Hooft y parameter
obtained with x set to 0 is ꢀ0.016(6). Both x and y values indicate
correct handedness and enantiopurity (Fig. 1) [41].
2
.3. DFT calculations
Quantum chemical calculations helped elucidate underlying
reasons for the observed stereoselectivity of the lithiation. Steric
interactions govern the stereochemical course of the lithium atom
introduction to the Cp-ring.
Taniaphos type ligands can coordinate on the transition metals
by two phosphorus and one nitrogen atom [42,43]. For the
The double lithiation, which is employed in the synthesis of
demonstration of coordination ability of the ligand (R,S
p
)-3 com-
p p
Taniaphos ligand ((R,R )-3), proceeds preferentially to the pro-S
plex of CuBr with homochiral (R,S )-3 was prepared and
p
position due to the formation of dilithium arrangement in the
transition state. Another reason helping reverse the course of the
lithiation may be an interaction of Fe with one of the lithium atoms
[30]. Fig. 4 depicts the reaction coordinate for the lithiation of
phosphane (R)-2. The reaction starts with complex formation be-
tween ferrocene derivative (R)-2 and the base t-BuLi. There are two
conformers of the starting complex. These conformers lead to two
p p
transition states (pro-R ) and (pro-S ). The t-BuLi coordinated by
lithium to both nitrogen and phosphorus attacks the acidic
hydrogen of the ferrocene. The presence of bulky diphenylphos-
phano group at the benzyl moiety and the fact that lithium is co-
ordinated to phosphorus brings the benzene groups closer to the
reaction center. These factors make the transition states rather
p
sterically hindered. In the (pro-S ) transition state, the phenyl
Table 1
p
Selected intermolecular interactions in the crystal structure of [Cu(R,S -3)Br].
ꢁ
d(CeH) [Å]
d(H … A) [Å]
d(D … A) [Å]
DeH...A [ ]
i
C5AeH5A … N1
0.93
0.93
0.93
2.85
3.03
3.07
3.724(9)
3.850(8)
3.781(8)
157.1
148.0
134.4
ii
C15eH15/Br1
ii
C29eH29/Br1
Fig. 1. X-ray crystallographic structure of (R,S
0% probability level.
p
)-3. Thermal ellipsoids were drawn at
3
Symmetry operations: i ¼ (½ þ x, ½ e y, 1 e z), ii ¼ (e ½ þ x, 3/2 e y, 1 e z).

A. Alm aꢀ ssy et al. / Journal of Organometallic Chemistry 805 (2016) 130e138
133
intermediates. The solvent stabilizes the lithium of intermediates
that results in more stable structures.
2.4. Catalytic activity
p
The catalytic activity of ligand (R,S )-3 in transition metal ho-
mogeneous catalysis was demonstrated on stereoselective Rh-
catalyzed hydrogenation of dimethyl itaconate. These preliminary
results were compared with those obtained using Rh complex of
Taniaphos ligand (R,R
complete after 24 h in both cases. The ligand (R,R
corresponding hydrogenation product, (S)-2-methylsuccinate
dimethyl ester (5) with 91% ee. The epimeric ligand (R,S )-3 affor-
p
)-3. Conversion of the starting material 4 was
p
)-3 provided the
p
ded this product with opposite (R)-configuration but only in 21% ee.
These experiments show that the configuration of the ligands chiral
plane has a major influence on the stereoselective outcome of the
reduction (see Scheme 4).
p
Fig. 2. X-ray crystallographic structure of [Cu(R,S -3)Br]. Thermal ellipsoids were
drawn at 30% probability level.
We have also tested both epimers of diphosphane 3 in the Cu-
p p
Fig. 3. CD spectra of compounds (R,S ) and (R,R )-3.
groups of the PPh
these phenyls lies parallel with the Cp-ring of the ferrocene moiety.
While in (pro-R ) transition state, two phenyl groups are oriented
towards the ferrocene skeleton that disfavors the formation of the
pro-R ) transition state. NCI visualization demonstrates these re-
pulsions (Fig. 5). The lithiation reaction results in the formation of
stable intermediates Int-2. Energies of these intermediates are very
similar.
2
group are located over the Cp-ring. In fact, one of
catalyzed enantioselective conjugate addition of ethylmagnesium
bromide to enones (Scheme 5). A similar trend to the Rh-catalyzed
hydrogenation was observed. Copper complexes with both epimers
promoted the reaction with full conversion. However, the ligand
p
(
p
(R,S
meric purities, and with opposite absolute configuration than
(R,R )-3 (Taniaphos). The results of Cu-catalyzed conjugate addi-
p
)-3 afforded the corresponding adducts 7a-c in low enantio-
p
tions are summarized in Table 3.
Calculated energies for the lithiation of (R)-2 with t-BuLi are
To elucidate the difference in catalytic performance between
summarized in Table 2. The energy difference between (pro-S
and (pro-R )-TS is 10 kJ/mol. This energy difference would corre-
spond to Boltzmann distribution of products about 98:2. The in-
clusion of the solvation effect of Et O leads to higher activation
barrier of the reaction, but the energy difference between diaste-
reomeric transition states remains the same. The positive influence
of solvation effect can be observed in energies of formed
p
)-TS
(R,R
p
)-3 and (R,S
p
)-3 in the Rh-catalyzed hydrogenation, we also
-3)COD.BF ] was
p
prepared its Rh-complex. The complex [Rh(R,S
p
4
1
13
31
characterized by H, C, and P NMR, however, we were not able
to characterize it by X-ray crystallography. Therefore, its 3-D
structure was obtained by DFT calculations. This structure was
then compared with X-ray structure of Rh-Taniaphos obtained by
Knochel [9]. Rhodium atom in Taniaphos complex is more tightly
2

134
A. Alm aꢀ ssy et al. / Journal of Organometallic Chemistry 805 (2016) 130e138
Fig. 4. Reaction coordinate for the lithiation of (R)-2.
Fig. 5. NCI plot of the transition states.
Table 2
Calculated energies for lithiation of (R)-2.
Compound
DE (kJ/mol)
D
Ea(kJ/mol)
Conf1-(R)-2$t-BuLi
Conf2-(R)-2$t-BuLi
0.0
10.9
40.0
50.1
0.0
7.6
47.7
58.6
(
(
(
(
pro-S
pro-R
p
)-TS
p
)-TS
pro-S
pro-R
p
)-Int-2
ꢀ11.2
ꢀ22.9
p
)-Int-2
ꢀ16.3
ꢀ24.1
a
2
The solvent (Et O) is included.
p p
Scheme 4. Rh-catalyzed hydrogenation of 4 using (R,R ) and (R,S )-3.
surrounded by neighboring groups (ferrocene moiety, phenyl
groups on the phosphorus and NMe ). On the other hand in the epi-
Taniaphos complex, these groups seem to be further away (Fig. 6).
2

A. Alm aꢀ ssy et al. / Journal of Organometallic Chemistry 805 (2016) 130e138
135
4. Experimental section
4.1. Synthesis of phosphane (R)-2
To the solution of amine (R)-1 (375 mg, 0.94 mmol) in dry
degassed Et
2
O (10 mL) was added 1.6 M solution of t-BuLi in
ꢁ
pentane (890 uL, 1.41 mmol) dropwise at ꢀ60 C. Mixture was
ꢁ
stirred at ꢀ50 C for 45 min. Neat distilled PPh
2
Cl (290 uL,
ꢁ
Scheme 5. Cu-catalyzed conjugate addition of EtMgBr to enones using (R,R
R,S )-3.
p
) and
1.6 mmol) was added dropwise at ꢀ50 C. Mixture was stirred at RT
(
p
for 16 h. 5% NaHCO
3
aq. soln. (3 mL) was added and layers were
separated. Aqueous layer was extracted with Et
2
O (3 ꢂ 8 mL).
Combined organic layers were washed with water (2 ꢂ 8 mL) and
Table 3
a
brine (8 mL). The product was isolated by flash chromatography
Cu-Catalyzed conjugate addition of EtMgBr to enones.
(
SiO
2
, hexanes/EtOAc 3:1 þ 1% Et
3
N) as 356 mg (75%) of orange oil.
Enone
Ligand
(R,R )-3
Conversion (%)b
ee of 7a-c (%)c
20
Product was recrystallized from MeOH. [
BuOMe). H NMR (d
a
]
D
¼ ꢀ27.9 (c ¼ 0.615, t-
1
ꢁ
6a
6b
6c
p
100
100
100
95
100
100
82 (R)
6 (S)
4 (R)
2 (S)
12(R)
4 (S)
6
-acetone, 600 MHz, 20 C, TMS):
d
¼ 7.78 (ddd,
(
R,S )-3
(R,R
R,S
(R,R
R,S
p
Ph
J ¼ 7.8 Hz, J ¼ 4.4 Hz, J ¼ 1.2 Hz, 1H, H-C ), 7.33e7.48 (m, 11H, H-
p
)-3
)-3
Ph
Ph
C
), 7.24 (ddd, J ¼ 7.5 Hz, J ¼ 7.5 Hz, J ¼ 1.3 Hz,1H, H-C ), 7.11 (ddd,
(
p
Ph
p
)-3
)-3
J ¼ 7.7 Hz, J ¼ 3.8 Hz, J ¼ 1.2 Hz, 1H, H-C ), 5.05 (d, JH,P ¼ 8.0 Hz, 1H,
a Fc Fc
(
p
H-C ), 4.25e4.28 (m, 1H, H-C ), 4.16e4.18 (m, 1H, H-C ), 4.12e4.15
Fc
13
a
b
c
(m, 2H, H-C ), 3.79 (s, 5H, Cp),1.77 (s, 6H, NMe
acetone, 150.8 MHz, 20 C, TMS):
) ppm. C NMR (d
-
Reaction was performed with CuCl (5 mol%), Ligand (6 mol%), EtMgBr (140 mol%).
Determined by GC.
Determined by chiral GC.
2
6
ꢁ
d
¼ 149.5 (JC,P ¼ 22.4 Hz), 138.0
p p
Fig. 6. Structures of Rh-complexes with (R,S ) and (R,R )-3.
This fact likely means that the chiral environment around the Rh is
less well defined. During the catalytic reaction, a few orientations of
the substrate are probably possible, thus leading to lower
enantioselectivity.
(JC,P ¼ 13.3 Hz), 137.4 (JC,P ¼ 10.3 Hz), 136.1 (JC,P ¼ 13.8 Hz), 134.0,
133.9, 133.8, 133.7, 128.9 (JC,P ¼ 4.8 Hz), 128.7, 128.6, 128.5, 128.4
(JC,P ¼ 7.3 Hz), 126.7, 90.8, 70.1, 68.7, 67.7, 67.3, 66.4 (JC,P ¼ 23.0 Hz),
31
ꢁ
65.8, 42.7 ppm.
P NMR (d
6
-acetone, 242.8 MHz, 20 C):
þ
d
¼ ꢀ17.2 ppm. MS (m/z): 459.0 [M e NMe
2
] .
3
. Conclusions
4.2. Synthesis of diphosphane (R,Sp)-3
Step-wise di-lithiation of amine 1 proceeds with the different
stereochemical course than simultaneous dilithiation. The presence
of lithium atom on phenyl ring participates in the formation of Li-
dimeric species and also interacts with iron, and this is only
To the solution of phosphane (R)-2 (155 mg, 0.31 mmol) in dry
degassed Et
2
O (4 mL) was added 1.6 M solution of t-BuLi in pentane
ꢁ
(670 uL, 0.79 mmol) dropwise at ꢀ50 C. The mixture was stirred
ꢁ
possible in the ortho-lithiation to (pro-R
On the other hand, sequential dilithiation is controlled only steri-
cally by introducing the lithium into (pro-S ) position on the Cp-
ring. This feature enables synthesis of (R,S )-epimer of Taniaphos
ligand, which was not accessible easily so far. X-ray crystallography
confirmed the absolute configuration of the ligand (R,S )-3 and its
p
)-position of the Cp-ring.
for 2.5 h while the temperature rose to 0 C. The solution was
ꢁ
ꢁ
stirred at 0 C for another 2 h then cooled to ꢀ30 C and neat PPh
(95 ul, 0.53 mmol) was added. After heating to RT, the reaction was
quenched with 5% NaHCO aq. soln. (1.5 mL). Layers were sepa-
rated, and the aqueous layer was extracted with 1% solution of Et
in DCM (3 ꢂ 3 mL). Combined organic parts were dried over Na SO
and evaporated. The product was isolated by flash chromatography
2
Cl
p
p
3
3
N
p
2
4
coordination to copper. DFT calculations helped elucidate the ste-
reochemical course of the lithiation. In the Rh-catalyzed hydroge-
nation, diastereomers of 3 afforded product with the opposite
configuration, which means that the planar stereogenic unit of the
ligand controlled stereochemical outcome of the hydrogenation.
(SiO
solid.
2
, hexanes/EtOAc 8:1 þ 1% Et
3
N) as 50.2 mg (24%) of orange
2
0
). 1H NMR (CDCl
, 600 MHz,
3
[
a
]
D
¼ ꢀ230.1 (c ¼ 0.900, CHCl
3
ꢁ
Ph
Ph
20 C, TMS):
d
¼ 7.83e7.88 (m, 1H, H-C ), 7.63e7.69 (m, 2H, H-C ),

136
A. Alm aꢀ ssy et al. / Journal of Organometallic Chemistry 805 (2016) 130e138
Table 4
p p
Experimental data for (R,S )-3 and [Cu(R,S -3)Br].
Empirical formula
CCDC No.
C
43
H
39FeNP
2
((R,S
p
)-3)
43 2 p
C H39BrCuFeNP ([Cu(R,S -3)Br])
951497
687.58
1003402
830.99
M
r
Crystal system, space group
Orthorombic, P212121
determined from 23972 reflections
10.7370(2), 90
15.1527(3), 90
21.5290(4), 90
Orthorombic, P212121
determined from 11739 reflections
10.2549(4), 90
16.7919(7), 90
Unit cell dimensions
ꢁ
a [Å],
b [Å],
c [Å],
a
b
g
[ ]
ꢁ
[ ]
ꢁ
[ ]
21.9178(9), 90
V [Å3]
3502.64(12)
4, 1
0.554, 1.304
3774.2(3)
4, 1
2.123, 1.462
0
Z, Z
[mm 1],
ꢀ
r
(calcd.) [g cm
ꢀ3
]
m
F(000)
1440
1696
Absorption correction, Tmin, Tmax
Crystal size [mm]
Analytical, 0.574, 0.893
1.38 ꢂ 0.37 ꢂ 0.31
Prism, yellow
Gaussian integration with beam profile correction, 0.498, 0.686
0.48 ꢂ 0.36 ꢂ 0.24
Crystal habit, color
Block, orange
ꢁ
q
range for data collection [ ]
2.998e26.371
2.506e26.372
Limiting indices
h ¼ ꢀ13 / 13
h ¼ ꢀ12 / 11
k ¼ ꢀ18 / 18
k ¼ ꢀ17 / 20
l ¼ ꢀ26 / 26
l ¼ ꢀ27 / 26
Reflections collected/unique/observed
68302/7149/6750
[Rint ¼ 0.035, Friedel opposites not merged]
19545/7671/6038
[Rint ¼ 0.061, Friedel opposites not merged]
[
I > 2
s(I)]
ꢁ
ꢁ
ꢁ
Completeness to
q
[ ]
99.8%e26.371
99.8%e26.372
Data/restraints/parameters
Final weighting scheme
7149/2160/425
7671/544/444
2
2
2
2
2
2
w ¼ 1/[
s
(F
o
) þ (0.04P) þ 0.99P]
w ¼ 1/[
s
(F
o
) þ (0.0571P) þ 0.2505P]
2
2
2
2
where P ¼ [max(F
o
, 0) þ 2F
c
]/3
where P ¼ (F
o
þ 2F
c
)/3
Absolute structure determination
From anomalous dispersion effects
453 Friedel pairs using 2161 difference restraints
From anomalous dispersion effects
3370 Friedel pairs using 2258 quotients
Flack x factor ꢀ0.008(7)
1.030/1.033 (restrained)
R ¼ 4.36%, wR ¼ 9.98%
3
Flack x factor ꢀ0.0036(18)
S (goodness-of-fit)
1.0134
Final R indices [I > 2
s(I)]
R ¼ 2.96%, wR ¼ 7.37%
R ¼ 3.22%, wR ¼ 7.61%
0.53/e0.36
Final R indices (all data)
R ¼ 6.28%, wR ¼ 10.91%
0.598/e0.445
Largest difference peak/hole [e Åꢀ3]
7
6
4
1
.46e7.57 (m, 4H, H-CPh), 7.29e7.46 (m, 11 H, H-CPh), 7.16e7.28 (m,
131.4, 130.8 (JC,P ¼ 15.4 Hz), 130.4, 130.0, 129.8 (JC,P ¼ 9.2 Hz), 129.0
(JC,P ¼ 9.4 Hz), 128.9 (JC,P ¼ 5.2 Hz), 128.8 (JC,P ¼ 8.8 Hz), 128.4
(JC,P ¼ 6.9 Hz), 128.4 (JC,P ¼ 6.0 Hz), 127.3 (JC,P ¼ 5.0 Hz), 98.7
Ph
a
H, H-C ), 5.39e5.47 (dd, JH,P ¼ 7.4 Hz, JH,P ¼ 4.7 Hz, 1H, H-C ),
Fc
Fc
.62e4.72 (m, 1H, H-C ), 4.36e4.41 (m, 1H, H-C ), 4.08e4.11 (m,
Fc
13
H, H-C ), 3.36 (s, 5H, Cp), 1.53 (s, 6H, NMe
2
) ppm. C NMR (CDCl
3
,
(JC,P ¼ 20.3 Hz), 71.3, 71.2, 70.7 (JC,P ¼ 4.0 Hz), 70.3 (C
5
H
5
), 63.8, 44.8
ꢁ
31
ꢁ
150.8 MHz, 20 C, TMS):
d
¼ 149.8 (JC,P ¼ 24.8 Hz), 140.5
(N-(CH
J
3
)
2
) ppm. P NMR (CDCl
3
, 242.8 MHz, 20 C):
d
¼ ꢀ12.2 (d,
(J
C,P ¼ 10.6 Hz), 139.7 (JC,P ¼ 12.0 Hz), 137.7 (JC,P ¼ 14.4 Hz), 136.6
C,P ¼ 16.9 Hz), 135.3 (JC,P ¼ 22.0 Hz), 134.7 (JC,P ¼ 20.0 Hz), 134.2,
P,P ¼ 150 Hz); ꢀ18.8 (d, JP,P ¼ 150 Hz) ppm.
(J
1
34.1 (JC,P ¼ 19.1 Hz), 132.9 (JC,P ¼ 18.9 Hz), 128.7, 127.1
p 4
4.4. Synthesis of complex [Rh(R,S -3)cod.BF ]
(J
C,P ¼ 64.7 Hz), 132.6 (JC,P ¼ 18.0 Hz), 128.7, 128.5 (JC,P ¼ 6.5 Hz),
1
28.4 (JC,P ¼ 39.6 Hz), 128.3 (JC,P ¼ 14.0 Hz), 127.8 (JC,P ¼ 7.9 Hz),
To the solution of ligand (R,S
p
-3) (12.3 mg, 0.18 mmol) in dry
].BF (7.3 mg, 0.18 mmol). The
127.6 (JC,P ¼ 5.9 Hz), 127.4 (JC,P ¼ 64.6 Hz), 70.6 (br s), 70.1, 69.9, 69.5
CH
2
Cl (1.5 mL) was added [Rh(cod)
2
2
4
31
ꢁ
(
br s), 64.7 (br s), 44.0 ppm. P NMR (CDCl , 242.8 MHz, 20 C):
3
mixture was stirred for 2 h at RT. Product was precipitated by
addition of hexane. Orange crystals were filtered off and washed
d
6
¼ ꢀ18.1 (d, JP,P ¼ 39.6 Hz), ꢀ27.0 (d, JP,P ¼ 39.6 Hz) ppm. MS (m/z):
þ
43.3 [M - NMe
2
] .
with hexane. Product was recrystallized from CH
2
Cl
¼ 8.19e8.27 (m, 1H),
.90e8.02 (m, 2H), 7.64e7.77 (m, 4H), 6.88e7.49 (m, 17H),
2
/hexane.
1
ꢁ
3
H NMR (CDCl , 600 MHz, 20 C, TMS): d
7
4.3. Synthesis of complex [Cu(R,Sp-3)Br]
6.26e6.41 (m, 2H), 5.82e5.92 (m, 1H), 5.23e5.29 (m, 1H),
3
NMe
.82e3.69 (m, 2H), 3.45 (s, 5H, Cp), 1.90e2.90 (m, 8H), 2.63 (s, 6H,
A mixture of ligand (R,S
2.0 mg, 0.01 mmol) and dry CH
through the short basic alumina pad), was stirred for 1 h at RT until
the white cuprous salt dissolved. The solvent was evaporated under
vacuum, and the yellow precipitate was recrystallized from CH
p
)-3 (6.7 mg, 0.01 mmol), CuBr.Me
2
S
13
ꢁ
2
) ppm. C NMR (CDCl
3
, 150.8 MHz, 20 C, TMS):
d
¼ 155.6,
(
2
2
Cl (1.5 mL, neutralized by passing
1
1
1
55.4, 138.0, 137.2, 136.6, 133.9, 133.5, 133.3, 132.4, 132.1, 131.2,
30.8, 130.0, 129.9, 129.5, 129.3, 129.1, 128.9, 128.9, 128.7, 128.2,
28.1, 127.4, 127.3, 126.8, 126.7, 105.1, 104.9, 74.4, 73.8, 73.3, 71.9,
2 2
Cl /
31
71.3, 70.8, 70.6, 70.3, 70.2, 69.1, 69.0, 46.6, 31.9, 30.4 ppm. P NMR
hexane to yield 6.2 mg (81%) of yellow crystals. The crystallographic
sample was obtained by recrystallization from CHCl
ꢁ
(CDCl
3
, 242.8 MHz, 20 C):
d
¼ 13.0 (dd, JRh,P ¼ 136.9 Hz,
3
/hexane.
1
ꢁ
JP,P ¼ 18.6 Hz), 10.6 (dd, JRh,P ¼ 138.8 Hz, JP,P ¼ 18.6 Hz) ppm.
H NMR (CDCl
3
, 600 MHz, 20 C, TMS):
d
¼ 8.03e7.88 (m, 3H, H-
CPh); 8.01e7.97 (m, 1H, H-C ); 7.95e7.89 (m, 2H, H-C ); 7.86e7.81
Ph
Ph
Ph
Ph
(
C
(
4
1
d
1
m, 2H, H-C ); 7.81e7.76 (m, 2H, H-C ); 7.58e7.52 (m, 10H, H-
4.5. X-ray structure determination
Ph
Ph
Ph
); 7.42e7.37 (m, 1H, H-C ); 7.37e7.31 (m, 5H, H-C ); 7.14e7.09
Ph
Fc
m, 1H, H-C ); 5.27e5.21 (m, 1H, HCN); 4.83e4.77 (m, 1H, H-C );
.47e4.44 (m, 1H, H-C ); 4.04e4.00 (m, 1H, H-C ); 3.51 (s, 5H, Cp);
The intensity data for (R,S
on a Kuma KM-4 CCD -axis diffractometer using graphite-
monochromated MoK radiation (0.71073 Å) at room tempera-
ture (293 K). The diffraction intensities were corrected for Lorentz,
polarization and absorption effects. Data collection, cell refinement,
p p
)-3 and [Cu(R,S -3)Br] were collected
Fc
Fc
k
13
ꢁ
.28 (s, 6H, NMe
2
) ppm. C NMR (CDCl
¼ 151.1 (JC,P ¼ 14.8 Hz), 135.6 (JC,P ¼ 15.3 Hz), 135.3 (JC,P ¼ 15.6 Hz),
34.0 (JC,P ¼ 14.0 Hz), 133.8, 133.6 (JC,P ¼ 14.7 Hz), 131.8, 131.6, 131.5,
3
, 150.8 MHz, 20 C, TMS):
a

A. Alm aꢀ ssy et al. / Journal of Organometallic Chemistry 805 (2016) 130e138
137
data reduction and finalization including all corrections mentioned
above were carried by CrysAlis Pro software [47].
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The structures were solved by charge flipping using olex2.solve
[
(
[
Olex2 ver. 1.2.5) [48].
The structure of (R,S )-3 were refined by CRYSTALS (ver. 14.40)
p
49]. All non-H atoms were refined anisotropically with free co-
a
metal catalyzed asymmetric hydrogenation of functionalized double bonds,
Angew. Chem. Int. Ed. 38 (1999) 3212e3215.
[
[
[
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ordinates. The H atoms were localized in difference density map
and refined using soft restraints on bond length and angles
(
d(CeH) ¼ 0.93e0.98 Å) to regularize geometry; in the final cycles
of the refinement, riding constraints were used [50]. Uiso(H) were
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12] R. Sebesta, F. Bilcík, P. Fodran, Enantioselective one-pot conjugate addition of
Grignard reagents followed by a Mannich reaction, Eur. J. Org. Chem. (2010)
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U
eq
of the parent atoms with
U
iso(H) ¼ 1.2Ueq(Csp2) and Uiso(H) ¼ 1.5Ueq(Csp3).
5666e5671.
The structure of [Cu(R,S
p
-3)Br] was refined by SHELXL-2014
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atoms mentioned; rigid bond (RIGU) restraints for whole molecule
to improve data-to-parameter ratio were also applied. All aromatic
H atoms were placed into idealised positions with riding co-
ordinates and Uiso ¼ 1.2Ueq(Csp2) [for disordered H1AeH5A atoms,
ꢁ
[
[
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SM-130686 based on the development of asymmetric Cu(I)F catalysis to ac-
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[
U
iso ¼ 1.5Ueq(Csp2) were used]. Methyl groups were refined as freely
rotating group with Uiso(H) ¼ 1.5Ueq(Csp3).
Hooft y parameter was calculated by CRYSTALS ((R,S
p
)-3) and
p
Olex2 ([Cu(R,S -3)Br]) using Gaussian distribution. The geometrical
analysis was performed using SHELXL-2014 and Olex2; Olex2 was
also used for structural drawings. Crystal data and conditions of the
data collection and refinement are reported in Table 4.
[
(2009) 6946e6948.
[
[
19] F. Lopez, A.W. van Zijl, A.J. Minnaard, B.L. Feringa, Highly enantioselective Cu-
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Notes
4
09e411.
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or -Alkyl-substituted alcohols through copper-catalyzed asymmetric
allylic alkylation with organolithium reagents, J. Org. Chem. 78 (2013)
274e8280.
The deposition number CCDC 951497 ((R,S
p
)-3) and CCDC
b-
g
1003402 ([Cu(R,S -3)Br]) contains the supplementary crystallo-
p
8
graphic data for this paper (including structure factors). These data
can be obtained free of charge via www.ccdc.cam.ac.uk/data_
request/cif or Cambridge Crystallographic Data Centre, 12 Union
Road, Cambridge CB2 1EZ, UK; fax: þ44 1223 336033.
[
21] T. den Hartog, B. Maci ꢀa , A.J. Minnaard, B.L. Feringa, Copper-catalyzed asym-
metric allylic alkylation of halocrotonates: efficient synthesis of versatile
chiral multifunctional building blocks, Adv. Synth. Catal. 352 (2010)
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22] M. P eꢀ rez, M. Fa n~ an aꢀ s-Mastral, P.H. Bos, A. Rudolph, S.R. Harutyunyan,
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Acknowledgments
[
For financial support, we thank the Slovak Research and
Development Agency, grant no. APVV-0321-12, and Slovak Grant
Agency VEGA, grant no. 1/0623/12 and 1/0336/13. This publication
is the result of the project implementation: 26240120025 sup-
ported by the Research & Development Operational Programme
funded by the European Regional Development Fund.
[24] N. Yoshikawa, L. Tan, J.C. McWilliams, D. Ramasamy, R. Sheppard, Catalytic
enantioselective hydrogenation of N-alkoxycarbonyl hydrazones: a practical
synthesis of chiral hydrazines, Org. Lett. 12 (2010) 276e279.
[
25] L.-B. Luo, D.-Y. Wang, X.-M. Zhou, Z. Zheng, X.-P. Hu, Asymmetric synthesis of
2-alkyl-3-phosphonopropanoic acid derivatives via Rh-catalyzed asymmetric
hydrogenation, Tetrahedron Asymmetry 22 (2011) 2117e2123.
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Organometallics 32 (2013) 5668e5704.
[
Appendix A. Supplementary data
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thesis. VIII. Absolute configuration of a 1,2-disubstituted ferrocene derivative
with planar and central elements of chirality and the mechanism of the
optically active.alpha.-ferrocenyl tertiary amines, J. Am. Chem. Soc. 95 (1973)
482e486.
Supplementary data related to this article can be found at http://
dx.doi.org/10.1016/j.jorganchem.2016.01.004.
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