Properties and separation method of enantiomers of the mono- and bis-substituted derivatives of 3,3′,4,4′-tetramethyl-1,1′-diphosphaferrocene: structural analysis using X-ray diffraction and circular dichroism

Article abstract of DOI:10.1016/j.tetasy.2016.11.003

This work expands on the recent separation of the enantiomers of the C₂-symmetrical bis-substituted derivatives of 1,1′-diphosphaferrocene. The effective separation of mono-substituted 1,1′-diphosphaferrocenes by the proposed method is demonstrated. The absolute configuration of the three separated components was established using X-ray diffraction. Circular dichroism spectra were collected for all of the separated compounds. The spectrum of each compound shows a characteristic curve, and the curves for the enantiomers are symmetrical. We also show that the correct absolute configuration for similar species can be assigned on the basis of the obtained data. We propose an explanation for the abnormal¹H NMR spectra of phospholyl protons in some derivatives of 1,1′-diphosphaferrocene. A density functional theory (DFT) study of the conformation, as well as circular dichroism and NMR spectra of the chosen species, is also presented.

Full text of DOI:10.1016/j.tetasy.2016.11.003

Tetrahedron: Asymmetry xxx (2016) xxx–xxx
Contents lists available at ScienceDirect
Tetrahedron: Asymmetry
journal homepage: www.elsevier.com/locate/tetasy
Properties and separation method of enantiomers of the
mono- and bis-substituted derivatives of 3,30,4,40-tetramethyl-1,10-
diphosphaferrocene: structural analysis using X-ray diffraction
and circular dichroism
c
b
Arkadiusz Kłys a, , Anna Makal , Anna Zdzienicka
⇑
a
´
´
´
University of Łódz, Laboratory of Molecular Spectroscopy, Department of Chemistry, 91-403 Łódz, Tamka 12, Poland
Medical University of Lódz, Bioorganic Chemistry Laboratory, Faculty of Pharmacy, 90-151-Lódz, Muszynskiego 1, Poland
University of Warsaw, Biological and Chemical Research Centre, Department of Chemistry, 02-089 Warszawa, Zwirki I Wigury 101, Poland
b
c
´
_
a r t i c l e i n f o
a b s t r a c t
Article history:
This work expands on the recent separation of the enantiomers of the C2-symmetrical bis-substituted
derivatives of 1,10-diphosphaferrocene. The effective separation of mono-substituted 1,10-diphosphafer-
rocenes by the proposed method is demonstrated. The absolute configuration of the three separated com-
ponents was established using X-ray diffraction. Circular dichroism spectra were collected for all of the
separated compounds. The spectrum of each compound shows a characteristic curve, and the curves for
the enantiomers are symmetrical. We also show that the correct absolute configuration for similar spe-
cies can be assigned on the basis of the obtained data. We propose an explanation for the abnormal 1H
NMR spectra of phospholyl protons in some derivatives of 1,10-diphosphaferrocene. A density functional
theory (DFT) study of the conformation, as well as circular dichroism and NMR spectra of the chosen spe-
cies, is also presented.
Received 13 October 2016
Accepted 7 November 2016
Available online xxxx
Ó 2016 Elsevier Ltd. All rights reserved.
1. Introduction
phine PPFA,18 many variants of this type of ligand have been
reported, including Josiphos,16,19 Taniphos,20 Walphos,21 and
Chiral phosphines play a key role in modern synthesis and have
been used as nucleophilic organocatalysts in many asymmetric
nucleophilic organocatalytic reactions.1 Kagan et al. developed
the ligands DIOP, the first ligands with C2-symmetry.2 Ligands with
a C2-axis are important because this symmetry reduces the num-
ber of possible competing diastereomeric transition states.3 Since
the development of these ligands, many chiral P,P-ligands have
been prepared and have played important roles in transition-
metal-catalysed asymmetric reactions. They are represented by
BINAP, CHIRAPHOS, DuPHOS, PHENEPHOS, and SEGPHOS.4–9
Metallocene-based phosphines10–13 offer exceptional possibilities
in transition-metal-catalysed asymmetric reactions, especially fer-
rocene derivatives,14 which exhibit a fascinating sandwich struc-
ture, because of their easily varied ligand bite angles15 and high
modularity.16 Enantiopure metallocenes containing phosphorus
ligands generally exhibit C1-symmetry combined with planar and
central chirality.17 Since 1974, when Hayashi et al. reported phos-
BPPFA.22 Ferrocene-based ligands with C2-symmetry are repre-
sented by FerroPhos23,24 or moieties such as Mandyphos (Fer-
riphos).25 In principle, the influence of the planar chirality should
be favourably expressed if the donor atom, such as phosphorus,
is embedded within the metallocene skeleton. Enantiopure phos-
phaferrocenes exhibit C1-symmetry,17,26–35 combining planar and
central chirality. In these compounds, C2-symmetry can be present
only in diphosphaferrocenes,36–38 whereas enantiopure mono-sub-
stituted diphosphaferrocenes display only C1-symmetry with pla-
nar elements39,40 or with planar and central symmetry
elements.41,42 Therefore, phosphaferrocenes have attracted consid-
erable attention as novel ligands for asymmetric catalysis.11,12
We were interested in devising a universal route to enantiopure
C2-symmetrical planar-chiral diphosphaferrocenes. Published
methods exist to obtain enantiopure diphosphaferrocenes by HPLC
resolution on a chiral stationary phase36 or by the enantioselective
synthesis of this discrete class of ligands.37,38 The first separation
was performed by Fu et al. via preparative HPLC using a DiacelChir-
acel OD column.36 Carmichael showed the possibility of separating
2,20-bis(tert-butyldimethylosilyl)-1,10-diphosphaferrocene via the
⇑
Corresponding author.
E-mail address: kareks@uni.lodz.pl (A. Kłys).
http://dx.doi.org/10.1016/j.tetasy.2016.11.003
0957-4166/Ó 2016 Elsevier Ltd. All rights reserved.
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2
A. Kłys et al. / Tetrahedron: Asymmetry xxx (2016) xxx–xxx
formation of a complex diastereo palladium.37 We demonstrated
the possibility of separating the enantiomers of 2,20-diacetyl-
3,30,4,40-tetramethyl-1,10-diphosphaferrocene38 by preparative
HPLC on a Sephadex Celulose-2 column, which can be adopted
for the separation at a scale of hundreds of milligrams. Herein,
we show that mono- and bis-substituted enantiomerically pure
derivatives of 1,10-diphosphaferrocenes can be easily separated
from a racemate using a chiral stationary phase. We also present
a method for predicting the absolute configuration of the deriva-
tives of 1,10-diphosphaferrocenes on the basis of their circular
dichroism spectra.
Table 1
HPLC chromatography conditions and assigned absolute configurations
rac-
Solvent
Solvent
ratio
Retention elution time and
configuration fraction
Compounds mixture
2
Methanol:
H2O
Hexane:IPA 20:1
Methanol:
H2O
Hexane:IPA 40:1
9:1
(Sp) 15.9: 17.6 (Rp)
3
4
(Rp)a5.7: 6.8 (Sp)a
9:1
(Sp,Sp)a 10.7: 13.2 (Rp,Rp)a
5
(Rp,Rp)a 6.1: 7.1 (Sp,Sp)a
a
Absolute configuration assigned by X-ray crystallography.
2. Results and discussion
20 to 50 mg of material per injection. All HPLC conditions are sum-
marized in Table 1.
The absolute configurations of the separated enantiomers for 3,
4, 5 were established by X-ray diffraction.
2.1. Synthesis and separation
The procedure for the preparation of compounds 2 and 3 is
summarized in Scheme 1. This procedure is a classical Friedel-Craft
acylation and has been previously described.43,44
2.2. Crystallographic characterization of compounds 3, 4, 5
These reactions generated a stereogenic centre at the 2-position
and gave a mixture of two enantiomers (Rp) and (Sp). Enantiomeric
pairs of the derivatives of metallocenes such as ferrocene,
ruthenocene, and osmocene, are known to be separated on chiral
All compounds analysed using X-ray diffraction were crystal-
lized as pure enantiomers in chiral space groups, as confirmed by
the low values of the Flack parameter (Table 2). In all cases, the
molecules of the compounds were located in general positions
and exhibited no exact internal symmetry. No solvent molecules
were present in the crystal structure of compound 3, 4 or 5.
In the case of the (Rp)-3 or (Sp)-3 isomers, the space group was
P21 and the compounds were isostructural apart from their respec-
tive right- or left-handedness. A single independent molecule was
present in the structures of (Rp)-3 or (Sp)-3. The ORTEP representa-
tions of both isomers are presented in Figure 1.
The diphosphaferrocene moiety in the structure of (Rp)-3 or
(Sp)-3 adopts an eclipsed conformation but with the phosphorus
atoms located far apart, above carbon atoms C16 and C2 for P1
and P2, respectively. The relative rotation of the two phospholyl
rings in the molecules of (Rp)-3 or (Sp)-3, as measured via the
P1–Ct1–Ct2–P2 dihedral angle, is approximately 155°, depending
on the enantiomer (Table 2). The unsubstituted phospholyl ring is,
in both cases, slightly farther from the Fe ion than the substituted
ring (Table 2). The carbonyl O1 oxygen atom is situated in a cis ori-
entation with respect to P1 and points below the plane of the phos-
pholyl ring (the P1–C1–C7–O1 dihedral angle is 48.5(5)° in the case
of (Sp)-3). Simultaneously, the carbonyl moiety is almost co-planar
with the phenyl ring (the corresponding dihedral angle is 21.5(6)°
in the case of (Sp)-3). This conformation is most likely the result of
crystal packing, which enables the formation of short intermolecu-
lar C–H. . .O and C–H. . .P contacts (C12–H12. . .O1: 2.468(6) Å, C14–
H14. . .O1: 2.636(6) Å and C11–H11. . .P1: 3.038(6) Å in the case of
(Sp)-3) involving H atoms from the phenyl ring.
stationary phases such as
a
cyclodextrin-bonded phase45 or
cellulose-based chiral stationary phases.46 Derivatives of
1,10-diphosphaferrocene have also been effectively separated on
cellulose-based chiral stationary phases36 or modified cellulose-
based chiral stationary phases.38 Here, the enantiomers were
separated on a Sephadex Celulose-2 HPLC column. The important
advantage of this column is its ability to operate in either the
normal or reversed phase depending on the requirements. All of
the separations were performed under isocratic conditions. The
procedures were optimized on an analytical 5
l
m, 150 ꢀ 4.6 mm2
column. Enantiomers of compound 2 were separated using a 9:1
mixture of methanol:water. By contrast, the enantiomers of com-
pound 3 were separated in a 40:1 mixture of hexane:isopropyl
alcohol (IPA). All HPLC conditions are summarized in Table 1.
The synthetic procedures for the preparation of compounds 4
and 5 are summarized in Scheme 2.
These reactions are also classical Friedel-Craft acylation reac-
tions but are performed in the presence of excess acylation agent
and aluminium chloride to give products with disubstitutions in
the 2- and 20-positions as a mixture of enantiomers (Rp,Rp), (Sp,
Sp) and optically inactive isomers, the meso-isomers of compound
4 or 5. The synthesis of 5 has been previously described;47 thus,
we present only the characterisation of compound 4.
Before separating the enantiomers, we preliminarily separated
the mixture of the rac- and meso-components by column chro-
matography on silica. The optimal solvent for the separation of
the enantiomer pairs of 4 was a methanol:water mixture (9:1);
for the enantiomer pairs of 5, it was hexane:IPA (40:1). For a
The compound (Rp,Rp)-5 crystallizes in the P1 space group, also
with a single independent molecule. The ORTEP representations of
this compound are presented in Figure 2.
The diphosphaferrocene moiety in this structure adopts a stag-
gered conformation, with the phosphorus atoms located very close
large-scale separation, a semi-preparative 5
HPLC column was used. On this column, it was possible to separate
l
m, 250 ꢀ 21.2 mm2
Me
Me
Me
Me
Me
Me
Me
Me
Me
Me
Me
Me
O
R
O
R
P
Fe
P
Fe
P
Fe
AlCl3/CH2Cl2
R-COCl
+
P
P
P
(Sp)-2 or (Sp)-3
(Rp)-2 or (Rp)-3
2
- R = Et
3- R = Ph
Scheme 1. Synthesis of compounds 2 and 3.
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A. Kłys et al. / Tetrahedron: Asymmetry xxx (2016) xxx–xxx
3
Me
Me
Me
Me
Me
Me
Me
Me
Me
Me
Me
Me
Me
Me
Me
Me
O
R
O
R
O
R
P
Fe
P
Fe
P
Fe
P
Fe
AlCl3/CH2Cl2
ex. R-COCl
+
+
O
R
O
R
O
R
P
P
P
P
4
5
4
5
(Rp,Rp)- or (Rp,Rp)-
(Sp,Sp)- or (Sp,Sp)-
meso-4 or meso-5
2
R = Et
3 R = Ph
Scheme 2. Synthesis of compounds 4 and 5.
Figure 1. Molecular structures of (Rp)-3 and (Sp)-3, with the numbering scheme in the ORTEP representation. The atomic displacement ellipsoids are drawn at the 50%
probability level.
Table 2
Selected geometrical parameters of the structures of compounds 3, 4 and 5, in Å and degrees
(Rp)-3
(Sp)-3
(Rp,Rp)-5
(Sp,Sp)-4
Distance/angle
mol 1
mol 2
mol 3
Fe1 P1
Fe1 P2
Fe Ct1
Fe Ct2
Average C. . .Fe
P. . .P
P1 C1
2.2670(4)
2.3016(4)
1.640(3)
1.652(3)
2.072(8)
n/a
1.7952(14)
1.7711(15)
1.7727(16)
1.7718(15)
1.2245(18)
n/a
2.2649(11)
2.3006(11)
1.643(5)
1.652(5)
2.072(8)
n/a
1.794(4)
1.766(4)
1.774(4)
1.773(4)
1.227(5)
n/a
2.2774(13)
2.2754(13)
1.647(6)
1.651(6)
2.079(21)
3.466(6)
1.797(5)
1.761(5)
1.787(5)
1.771(5)
1.228(5)
1.214(6)
1.495(6)
1.500(6)
1.515(7)
1.484(6)
178.3(2)
88.4(2)
2.2907(13)
2.2899(12)
1.656(6)
1.652(7)
2.080(15)
n/a
1.789(5)
1.765(5)
1.794(5)
1.757(5)
1.224(6)
1.214(6)
1.486(6)
1.505(6)
1.488(6)
1.513(6)
173.1(3)
89.1(2)
2.2867(13)
2.2825(13)
1.654(7)
1.655(7)
2.081(16)
3.450(7)
1.788(5)
1.767(5)
1.801(4)
1.762(5)
1.223(6)
1.216(5)
1.484(6)
1.500(7)
1.486(6)
1.505(7)
178.1(3)
88.7(2)
2.2853(12)
2.2886(13)
1.656(6)
1.656(7)
2.083(19)
3.464(7)
1.800(5)
1.769(5)
1.793(4)
1.776(5)
1.218(5)
1.216(6)
1.490(6)
1.511(6)
1.487(6)
1.505(6)
177.4(3)
88.6(2)
88.5(2)
17.7(7)
0.6(5)
0.7(5)
171.0(4)
4.7(7)
175.9(4)
0.1(7)
P1 C4
P2 C1A(C14)
P2 C4A(C17)
C7 O1
C7A O2
C7 C1
C7 C8
C7A C1A
C7A C8A
Ct1 Fe Ct2
C1 P1 C4
C1A P2 C4A (C14 P2 C17)
P1 Ct1 Ct2 P2
C1 C2 C3 C4
C1A C2A C3A C4A (C14 C15 C16 C17)
P1 C1 C7 O1
O1 C7 C8 C9
P2 C1A C7A O2
O2 C7A C8A C9A
1.493(2)
1.492(2)
n/a
1.487(5)
1.490(6)
n/a
n/a
n/a
178.64(8)
88.46(6)
88.54(6)
155.1(4)
ꢁ0.90(15)
ꢁ0.30(16)
ꢁ48.6(2)
ꢁ21.9(2)
n/a
178.58(3)
88.70(18)
88.37(18)
ꢁ155.1(7)
1.5(4)
88.1(2)
88.8(2)
116.4(6)
0.7(5)
0.3(5)
179.8(4)
6.4(6)
88.9(2)
19.2(7)
ꢁ29.6(8)
ꢁ0.2(6)
ꢁ0.4(6)
ꢁ0.4(6)
179.1(4)
0.1(7)
170.7(4)
3.1(6)
0.3(5)
ꢁ0.7(6)
48.5(5)
21.5(6)
n/a
150.7(4)
ꢁ24.7(7)
99.4(5)
179.5(4)
2.3(6)
n/a
n/a
ꢁ2.4(7)
together. The relative rotation of the two phospholyl rings, as mea-
sured via the P1–Ct1–Ct2–P2 dihedral angle, is ꢁ29.6(8)° (Table 2),
and the P1. . .P2 distance is 3.466(6) Å, which is notably shorter
than the sum of the van der Waals radii for the P atoms. Only a
slightly shorter (3.395 Å) P. . .P distance for racdiphosphaferroce-
nes has been reported to date.37 Our results are in agreement with
the postulated possibility of secondary bonding in this type of
molecule.48,49
The two carbonyl substituents adopt very different conforma-
tions relative to their respective phospholyl rings. The carbonyl
O1 oxygen atom is situated in the trans-orientation with respect
to P1 and points below the plane of the phospholyl ring (the
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A. Kłys et al. / Tetrahedron: Asymmetry xxx (2016) xxx–xxx
one above the other. In the case of molecules 2 and 3, the P atoms
are very close together, and the respective P–Ct1–Ct2–P dihedral
angles are only 19.2(7)° and 17.7(7)°. Similar to the case of
(Rp,Rp)-5, the P. . .P distances in molecules 2 and 3 are short, with
values of 3.450(7) Å and 3.464(7) Å, respectively. In these two
molecules, the carbonyl substituents are located far apart and the
molecules differ only in the detailed conformations of these
substituents. The ORTEP representations of the three molecules
are presented in Figure 3.
In all three molecules of (Sp,Sp)-4, all the carbonyl groups are
situated in the trans orientation with respect to the appropriate P
atoms and are almost exactly co-planar with the corresponding
phospholyl rings (the exact values of the dihedral angles are pre-
sented in Table 1). The further ethyl substituents also tend to be
co-planar with the phospholyl moieties to which they are attached.
All three (Sp,Sp)-4 molecules exhibit conformations with nearly C2
local symmetry.
The observed geometry differs substantially from that observed
for 2,20-diacetyl-3,30-4,40-tetramethyl-1,10-diphosphaferrocene,38
in which the P1–Ct1–Ct2–P2 dihedral angle is 101.3° and for which
no alternative conformations exist.
Figure 2. Molecular structure of (Rp,Rp)-5 with the numbering scheme in the ORTEP
representation. The chemically equivalent carbon atoms are labelled as, for
example, C1 or C1A, depending on the phospholyl ring to which they are attached.
P1–C1–C7–O1 dihedral angle is 150.7(4)°). Simultaneously, the
carbonyl moiety is nearly co-planar with the phenyl ring (the cor-
responding dihedral is ꢁ24.7(7)°), whereas the O2 carbonyl group
is almost perpendicular with respect to the P2 phospholyl ring,
(the P2–C1A–C7A–O2 dihedral angle is 99.4(5)°), with oxygen
pointing below the plane of the ring, and the phenyl ring, which
is exactly coplanar with the carbonyl moiety, directed above the
phospholyl ring. Similar to the structures of (Rp)-3 or (Sp)-3, many
short intermolecular C–H. . .O and C–H. . .P contacts involving
atoms from both phenyl rings are observed: (C9A–H9A. . .O1:
2.506(6) Å, C12A–H12A. . .O2: 2.447(6) Å, C10–H10. . .O2: 2.664
(6) Å, C13A–H13A. . .P1: 2.942(5) Å and C13–H13. . .P2: 3.024(6) Å).
Compound (Sp,Sp)-4 also crystallizes in the P1 space group.
However, three independent molecules of this compound, with dif-
ferent conformations, are present in a crystallographic asymmetric
unit. The molecules differ in the relative rotation of their respective
phospholyl rings. In the case of molecule 1, the conformation is
staggered, with the relative rotation of the rings, as measured via
the P1–Ct1–Ct2–P2 dihedral angle, which is equal to 116.4(6)°.
This finding indicates the significant separation of the two P atoms;
however, the carbonyl substituents in this molecule are located
In the current crystal structure of (Sp,Sp)-4, the presence of dif-
ferent conformers of the compound can be explained by the crystal
packing interactions. The crystal structure of (Sp,Sp)-4 is formed by
the layers of molecules parallel to the c-direction. Molecules 1, 2
and 3 occupy separate layers (Fig. 4). The only interlayer interac-
tions are steric contacts between the terminal methyl groups.
When (Sp,Sp)-4 is viewed along the c-direction, molecules 1, 2
and 3 are clearly observed to be located almost exactly one above
the other, forming a column. Their respective acetyl substituents
are distributed around the column’s axis so that the acetyl sub-
stituent from molecule 1 is not directly below the acetyl sub-
stituent of molecule 2. The location of substituents near the
edges of a pentagon forces one of the molecules to stack its sub-
stituents, but they are separated by the entire width of the diphos-
phaferrocene sandwich.
2.3. Circular dichroism
Unfortunately, all attempts to grow crystals of 2 with a quality
that was sufficient for X-ray diffraction analysis were unsuccessful.
Figure 3. Molecular structure of (Sp,Sp)-4: (a) molecule 1, (b) molecule 2 and (c) molecule 3, with the numbering scheme in the ORTEP representation. Within a single
molecule, chemically equivalent carbon atoms are labelled as, for example, C1 or C1A, depending on the phospholyl ring to which they belong (or are attached). The atoms
belonging to molecule 2 or 3 are numbered with 2 or 3, respectively, in the atomic label; for example, P21 in molecule 2 is analogous to P1 in molecule 1. The atomic
displacement ellipsoids are drawn at the 50% probability level.
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A. Kłys et al. / Tetrahedron: Asymmetry xxx (2016) xxx–xxx
5
Figure 4. Crystal packing of compound (Sp,Sp)-4. Molecules 1, 2 and 3 are represented in red, green and blue, respectively. Hydrogen atoms are omitted for clarity. (a) View
along the a crystallographic axis and (b) view along the c crystallographic axis.
In order to establish the absolute configuration of the enantiomers
of 2, we used experimental and theoretical calculated circular
dichroism spectra. Circular dichroism spectra can be a versatile
tool not only for predicting and establishing an absolute
configuration for organic molecules50 but also for the configura-
tional analysis of organometallic compounds such as ferrocene
derivatives.51–57 The experimental circular dichroism spectra of
the pairs of propionyl and benzoyl derivatives are shown in Figures
5 and 6, respectively.
locene d-d and charge-transfer transitions (350–600 nm)58 is in
accordance with the opposite planar metallocene chirality in all
series of separated compounds. An analysis of this region reveals
the possibility of establishing the absolute configuration of metal-
locenes of this type. In addition to using previous data,38 we can
expand the possibility of predicting the absolute configuration of
mono-substituted derivatives of 1,10-diphosphaferrocene. We saw
that when the circular dichroism spectra are observed from a lower
energy, the characteristic Cotton-effect values are initially negative
and then exhibit positive two-three values for (Sp) or (Sp,Sp) iso-
mers of the derivatives of 1,10-diphosphaferrocene. In contrast, cir-
cular dichroism spectra that initially show positive Cotton-effect
values and then show negative two-three values are characteristic
of isomers Rp or (Rp,Rp) in these types of molecules.
The region from 250 to 300 nm with a strong Cotton effect is
attributable to the
p–
p⁄ transition in acyls or other substituents.
The enantiomeric relationship observed in the region of metal-
On the basis of the aforementioned observations, the first frac-
tion of 2 that eluted was assigned the (Sp)-configuration while the
second was assigned the (Rp)-configuration.
We confirmed our prediction by calculating the theoretical cir-
cular dichroism spectra for the (Rp) and (Rp,Rp) isomers of 2–5. Geo-
metric optimization of the studied compounds without any
symmetry constraints was performed using the B3LYP60
exchange–correlation functional as implemented in the Gaussian
09 computational chemistry program.61 A basis set of 6-31G(d)
for C, O, P, Fe and H atoms was applied for the structure optimiza-
tions in the gas phase. A basis set of TZVP62,63 implemented in
Gaussian 09 package for C, O, P, Fe was used for the structure opti-
mization in a CHCl3 solution. We applied the integral equation for-
malism of the polarizable continuum model (IEFPCM) to study the
ground-state geometries in solution. Time-dependent density
functional (TD-DFT) calculations were performed at the B3LYP/
TZVP60,62,63 or B3LYP/aug-cc-VTZ64,65 level to determine the elec-
tronic transition energy, oscillator strength and rotatory strength.
The zero-point energies were compared for all calculated isomers
of 2–5; for the TD-DFT calculation, the preferred isomers were
investigated. The calculated energy values and a population analy-
sis for each possible conformer that represent local minima with
non-imaginary frequencies are shown in the Supplementary mate-
rial. A comparison of the calculated and experimental circular
dichroism spectra for (Rp)-2 is presented in Figure 7.
Figure 5. Experimental circular dichroism spectra of pure enantiomers of com-
pounds 2 and 4.
All theoretical spectra exhibit bands with the correct positive or
negative sign in the correct sequence (plus, minus, minus) for the
(Rp)-isomers. For calculations using the TZVP62,63 basis set, the
error in the position of the first two bands is 0.22 eV for the first
band and 0.33 eV for the second band. The accuracy for the last
two bands is better, and the bands are blue shifted by only
0.10 eV. Larger errors are observed for calculations performed in
the gas phase. Better accuracy was noted for calculations with
the aug-cc-pVTZ64,65 basis set. For the first two bands, the errors
Figure 6. Experimental circular dichroism spectra of pure enantiomers of com-
pounds 3 and 5.
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6
A. Kłys et al. / Tetrahedron: Asymmetry xxx (2016) xxx–xxx
Figure 7. Calculated and experimental circular dichroism spectra of (Rp)-2.
in the positions are 0.16 eV for the first band and 0.31 eV for the
second band.
The calculations shown in Figure 8 present the possibility of
changes; the position and sign depend on the value of the
P1–C2–C7–O1 torsion angles. A P–C–C–O torsion angle of 0° repre-
sents the trans-conformation, and a value of 180° represents the
cis-conformation.
The calculated circular dichroism spectra for all separated com-
pounds confirm that the chosen method for predicting these types
of spectra give the correct results, with similar errors. A compar-
ison of the calculated and experimental circular dichroism spectra
for (Rp)-3 and (Rp,Rp)-5 is present in Figure 8.
A comparison of the calculated and experimental circular
dichroism spectra for (Rp)-3. (Rp,Rp)-4 and (Rp,Rp)-5 is shown in
Figure 9. In all of these simulated spectra, much larger errors are
recorded for the excitation energy in the VIS region. In the UV
region, these errors are much smaller. The TD-DFT method used
for the calculations of metal organic compounds, such as ferrocene,
is known to yield data with some errors in the positions of the
absorption bands in UV–VIS spectra depending on the basis set
and the density functional used.66 Small errors in the prediction
of circular dichroism spectra are natural and were also observed
for much smaller organic molecules, such as Norcamphor or
Pinen.67 To simulate the circular dichroism spectra, we used the
Multiwfn software package68 with a velocity representation of
rotatory strength. The full-width at half-maximum was set to
0.2 eV, and the band was reproduced with Gaussian functions.
Figure 9. Calculated and experimental circular dichroism spectra of (Rp)-3. (Rp,Rp)-
4 and (Rp,Rp)-5.
reported for rac-2,20-dibenzoyl-3,30,4,40-tetramethyl-1,10-diphos-
phaferrocene,47 rac-2,20-bis(tert-butyldimethylsilyl)-1,10-diphos-
phaferrocene37 and rac-2,20-diacetyl-3,30,4,40-tetramethyl-1,10-
diphosphaferrocene.38 These phenomena were also present in the
1H NMR spectra of 1 and could be observed for the meso-isomers
of 4. By contrast, the ‘‘normal” proton doublet with JP-H ꢂ 36.0 Hz
for meso-5 was observed. This splitting pattern can also be
observed in the 31P NMR spectrum without 1H decoupling and in
the 13C{1H} NMR spectra. Carmichael et al. suggested that this phe-
nomenon arises from the magnetic nonequivalence of phosphorus
atoms and protons and proposed a description using a spin system
AA0XX0 for the characterization of the 31P and 1H-phospholyl
proton signal.37 In the described compounds, they also observed
2.4. Solution NMR studies of 4 and 5
0
a coupling constant of JH-P = 0.6 Hz. Figure 10 shows a comparison
of experimental and simulated 1H and 31P NMR spectra for the H5
The 1H NMR spectra of a racemic mixture and the pure enan-
tiomers of 4 and 5 show substantial differences in the splitting pat-
tern of the phospholyl protons (H-5 and H-50). This difference was
and P1 signals of rac-5. The simulation is in good agreement with
2
1
0
the experimental spectra for JP-P = 26.7 Hz, JH-P = 36.9 Hz,
0
0
JH-H = 0 Hz and JH-P = 0 Hz, and the spin system should be defined
as AA0XX0 for both phosphorus atoms.
We noted a more complicated situation in the 13C NMR spectra.
In this class of compounds, these 13C spectra constitute the X parts
of the AA0X or ABX spin system (A = B = 31P), depending on which
13C isotopomer is under study (Fig. 11). These phenomena in the
13C NMR spectra for this type of compound (1,10-diphosphaferroce-
nes) have not been previously reported.
The AA0X spin system, which is a special case of the ABX spin
system with (xA
ꢁ
x
B) ꢂ 0, occurs in symmetrical compounds con-
taining two chemically equivalent nuclei with a natural abundance
near 100% (e.g., 1H, 31P), which are bonded to a nucleus of low nat-
ural abundance (e.g., 13C or 15N).69 Many authors have noted that
diphosphines, transition-metal complexes with two phosphine
ligands,70 diphosphonates70,71 or phosphole dimers72 behave as
second-order ABX or AA0X spin systems. The 13C NMR spectrum
of rac-5 recorded under the conditions of proton noise decoupling
Figure 8. Calculated circular dichroism spectra of (Rp)-2 with different torsion
angles of P1-C2-C7-O1.
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A. Kłys et al. / Tetrahedron: Asymmetry xxx (2016) xxx–xxx
7
H5 - proton
4.05 4.00 3.95 3.90 3.85 3.80
ppm
-52.4
-52.6
-52.8
ppm
4.05 4.00 3.95 3.90 3.85 3.80
ppm
2
1
Figure 10. Simulated (upper parts) and experimental 1H NMR spectra of H5 protons in rac-5 data of coupling constant JP-P = 26.7 Hz, JH-P = 32.8 Hz, JH-H = 0 Hz and
0
0
JH-P = 0 Hz and 31P NMR spectra without proton decoupling of P1 in rac-5.
0
Me
Me
Me
Me
Me
Me
O
Me
Me
Me
O
O
C
C
C
C
C
C13
C
C
C
C
C
C13
C
C
C
P
P
P
R
R
R
Fe
Fe
Fe
Me
Me
Me
O
R
O
R
O
R
P
P
P
Me
Me
Me
O
Me
13C
Me
13C
C
C
Me
Me
O
O
C
C
C
C
C
C
C13
C
C
C
C
P
P
P
R
R
R
Fe
Fe
P
Fe
Me
Me
Me
Me
Me
O
O
R
O
P
P
R
R
Figure 11. Schematic representation of 12C and 13C isotopomers in 4 and 5.
consists of six multiplets corresponding to carbons C-2,C-3, C-4,
C-5, C–carbonyl, and C-ortho and five singlets corresponding to
the methyl carbons of the phospholyl ring and the remaining phe-
nyl carbons. In Figure 12 we show the experimental and simulated
proton-decoupled 13C NMR spectra of the C-2, C-4 and C-carbonyl
carbons.
NMR spectra of meso-5, the 31P–31P coupling constants are not
visible. By contrast, the 13C NMR spectrum of meso-4 displays a
second-order spin system for all carbons, except for two signals
of the methyl groups at the 3- and 4-positions, which are repre-
sented by a singlet. Some examples of experimental and simulated
13C NMR spectra of meso-4 are shown in Figure 13.
2
The designated value of 2JP-P = 26.7 Hz of the coupling constant
In this case, the value JP-P = 4.7 Hz is much smaller than that
0
0
used in the simulation can be easily extracted from the 1H NMR
spectra. For the simulations, we used the Daisy program, which
is part of the TopSpin 3.0 Bruker NMR software.73 The following
for the rac-isomers. These 13C spectra also show the X part of the
AA0X or ABX spin systems. In contrast to the 13C NMR spectra of
the racisomers, we observed 13C isotope effects on 31P for each of
the carbon signals from the phospholyl ring. The phosphorus
chemical shift, determined from the 31P and 13C spectra, indicates
that the 13C isotope effects on the 31P nuclear shielding range from
0.015 ppm in the case of carbons C3 and C4, which two bonds away
from phosphorus, to 0.062 ppm in the case of carbons C2 and C5,
which are directly bound to phosphorus. A similar value has been
observed for bis(diphenylphosphino)acetylene.74 The geometry of
the preferred conformers of meso-4 and meso-5 have been opti-
mized at the B3LYP level.59,60 The predicted conformation is shown
in Figure 14.
values were found for the 31P-13
C
coupling constant:
2JP-C@O = 19.4 Hz, JP-C4 = 6.8 Hz and JP-C2 = 61.0 Hz. In rac-4 and
rac-5, the C-2 and C-5 carbons represent the X parts of the ABX
spin system and display strong 13C isotope effects on
31P ꢂ 0.062 ppm. The remaining carbons in rac-4 and rac-5 are rep-
resented as the X component of the AA0X spin system or as singlets.
Due to the long distance to the phosphorus atom, these carbons do
not create isotope effects on the phosphorus atoms or these effects
are very small and are not visible. The 13C NMR spectra of meso-5
display ‘‘full symmetrical” compounds; all of the phospholyl
carbons and carbonyl carbons present the first-order spin system:
a doublet of the 31P–13C coupling constant. In the 1H, 31P and 13C
2
1
The torsion angle P1–Ct1–Ct2–P2 in the predicted conformer of
meso-4 was measured as 59.34°, and in meso-5, the value was
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8
A. Kłys et al. / Tetrahedron: Asymmetry xxx (2016) xxx–xxx
C-carbonyl
C5
C-CH2
C4
85.2
85.0
ppm
36.8
36.6
ppm
103.5
103.4
ppm
207.0
ppm
103.5
ppm
36.8
36.6
ppm
85.2
85.0
ppm
207.0
ppm
Figure 12. Simulated (upper parts) and experimental 13C{1H} NMR spectra of selected carbons of rac-5.
C-carbonyl
C5
C-CH2
C4
85.2
85.0
ppm
36.8
36.6
ppm
103.5
103.4
ppm
207.0
ppm
103.5
ppm
36.8
36.6
ppm
85.2
85.0
ppm
207.0
ppm
Figure 13. Simulated (upper parts) and experimental proton-decoupled 13C NMR spectra of C–carbonyl, C4, C5 and the carbon of the CH2 group in meso-4.
179.97°, thus revealing that the P1–P2 coupling constant can be
strongly dependent on the torsion angle of P1–Ct1–Ct2–P2 and
could display a similar relationship to the Karplus equation.75,76
can be effectively separated on a large scale by preparative HPLC
chromatography on chiral stationary phase. The absolute
a
configuration of the three separated derivatives was established
by X-ray diffraction. The absolute configuration of the separated
enantiomers of 2-propionyl-3,30,4,40-tetremathyl-1,10-diphospha-
ferrocene was established by circular dichroism spectral
analysis. We also demonstrated that circular dichroism spectra
can be used to establish the absolute configuration of planar chiral
3. Conclusion
The approach presented herein demonstrated that the enan-
tiomers of the mono- and bis-substituted 1,10-diphosphaferrocenes
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A. Kłys et al. / Tetrahedron: Asymmetry xxx (2016) xxx–xxx
9
then, 6.35 g (0.1 M) of FeCl3 were added. The obtained suspension
was sonicated for 30 min. The reaction mixture was then poured
into 500 ml of 3 M HCl and extracted by hexane. The organic phase
was dried and evaporated to dryness, and the obtained crude
product was purified by column chromatography with a hexane
eluent. One fraction was obtained containing 24.5 g (88%) of prod-
1
2
2
uct. H NMR (CDCl3): d3.73 (AA0XX0, JH-P = 36.7 Hz, JP-P = 6.2 Hz,
3
4
0
0
JP-H = 0 Hz, JP-H = 0.6 Hz 4H, 2 ꢀ H2 and 2 ꢀ H5), 2.14 (s, 12H,
4 ꢀ CH3).
4.3. 2-Propionyl-3,30,4,40-tetramethyl-1,10-diphosphaferrocene 2
This compound was prepared according to
a literature
2
procedure.43 1H NMR (CDCl3): d4.00 (d, JP-H = 36.4 Hz, 1H, H5),
Figure 14. Predicted conformation of the meso-isomers of 4 and 5; the centroids of
the phospholyl rings are marked in green.
2
4
3.69 (dd, JP-H = 36.2 Hz, JH-H = 1.6 Hz 1H, H20 or H50), 3.68 (dd,
2JP-H = 36.2 Hz, 4JH-H = 1.6 Hz 1H, H20 or H50), 2.66 (dq,
2JP-H = 16.9 Hz, JH-H = 7.4 Hz 1H, CH2), 2.62 (dq, JP-H = 16.9 Hz,
3
2
1,10-diphosphaferrocenes substituted at the 2- or 2,20-position. We
also observed that none of the conformational positions of C2v, C2, or
C2h were favoured in the described compounds, since the relative
differences in energy for the studied conformations were very
low. We have presented a new, faster and more efficient procedure
for the preparation of the starting material 3,30,4,40-tetramethyl-
1,10-diphosphaferrocene. When we used a two-step sonification
(the first step is the reaction of lithium with 1-phenyl-3,4-
dimethylphosphole, and the second step is the reaction of FeCl2
with the generated phospholyl anions) of the classical procedure
described by Lauzon,77 the duration of this procedure was reduced
to 3 h and the yield was increased to 88%. We expect that the results
of this study will introduce a new separation approach and will
simplify the identification of new enantiopure 1,10-diphosphafer-
rocenes. The potential of ligands, such as 4 and 5, to induce further
unusual coordination chemistry is currently under investigation.
3JH-H = 7.2 Hz 1H, CH2), 2.40 (s, Me), 2.11 (s, Me), 2.05 (s, Me),
3
3
1.99 (s, Me), 1.07 (dd, 2.66 JP-H = 7.4 Hz, JH-H = 7.2 Hz 1H, CH3)
ppm. 13C NMR (CHCl3): d 207.78 (d, JP-C = 21.2 Hz, CO), 102.41
2
2
2
(d, JP-C = 7.8 Hz, C3), 98.88 (d, JP-C = 6.7 Hz, C30 or C40), 98.86 (d,
2JP-C = 7.4 Hz, C30 or C40), 97.35 (d, JP-C = 5.4 Hz, C4), 89.36
2
1
1
(d, JP-C = 63.8 Hz, C2), 83.28 (d, JP-C = 60.8 Hz, C20 or C50), 83.18
1
1
(d, JP-C = 60.4 Hz, C20 or C50), 82.99 (d, JP-C = 58.4 Hz, C5), 36.38
1
(d, JP-C = 10.5 Hz, C–CH2), 15.58 (s, Me at C4), 14.49 (s, Me at C30
or C40), 14.14 (s, Me at C30 or C40), 14.01 (s, Me at C3), 8.72 (d,
1JP-C = 3.3 Hz, C-Me ethyl group) ppm. 31P NMR (CDCl3): d -53.22
2
2
2
(dd, JP-H = 36.4 Hz, JP-P = 12.3 Hz, P1), -68.39 (td, JP-H = 36.2 Hz,
2JP-P = 12.3 Hz, P10) ppm. Anal. Calcd for C15H20FeOP2: C, 53.92; H
6.03. Found for (Rp)-2 C, 54.16; H, 5.88; (Sp)-2 C, 53.75; H, 6.00;
(Rp)-2 [
a]
25 = ꢁ223; (c 0.20, CHCl3) ee > 99%.
D
4.4. 2-Benzoyl-3,30,4,40-tetramethyl-1,10-diphosphaferrocene 3
4. Experimental
4.1. General
A suspension of 0.230 g (1.5 mM) benzoyl chloride and 0.200 g
(1.50 mM) AlCl3 was mixed for 10 min in 10 ml of CH2Cl2 at 0 °C.
Next, 0.417 g (1.5 mM) of 1 were added slowly. The obtained mix-
ture was warmed to RT (room temperature) over 20 min and then
mixed for 4 h; the mixture was subsequently poured into 50 ml of
a 3 M solution of HCl. The organic phase was dried, evaporated to
dryness and purified by column chromatography (eluent CH2Cl2).
One fraction was obtained with 0.386 g (67%) of product. 1H
All reactions were conducted under an atmosphere of dry argon.
The solvents were freshly distilled over the appropriate drying
agents. Chromatographic separations were performed on silica
gel 60 (Merck, 230–400 mesh ASTM). 2,3-Dimethyl-1-phenylphos-
phole was obtained by a method described in the literature.78 All
other reagents were commercially available (Aldrich or Baker)
and were used as received. NMR spectra were recorded on a Bruker
Avance III 600 spectrometer operating at 600.26 MHz for 1H,
242.98 MHz for 31P and 150.95 MHz for 13C. Solvent peaks were
used as internal references for 1H and 13C chemical shifts (ppm).
31P peaks were referenced through the solvent lock (2H) signal
according to the IUPAC recommended secondary referencing
method and the manufacturer’s protocols. Circular dichroism spec-
tra were recorded on a Jasco J-815 circular dichroism spectropo-
larimeter. Elemental analyses were performed on a Vario Micro
Cube Elementarmicroanalyser.
3
3
NMR (CDCl3): d 7.78 (d, JH-H = 7.7 Hz, 2H, Ph ortho), 7.49 (t, JH-
3
H = 7.2 Hz, 1H, Ph para), 7.39 (t, JH-H = 7.2 Hz, 2H, Ph meta), 4.03
2
2
4
(d, JP-H = 36.5 Hz, 1H, H5), 3.72 (dd, JP-H = 36.0 Hz, JH-H = 1.9 Hz
2
4
1H, H20 or H50), 3.70 (dd, JP-H = 36.0 Hz, JH-H = 1.9 Hz 1H, H20 or
H50), 2.34 (s, Me), 2.18 (s, Me), 2.11 (s, Me), 2.05 (s, Me) ppm.
13C NMR (CHCl3): d 200.77 (d, 2JP-C = 20.3 Hz, CO), 140.84 (s, Ph ipso
4
C), 131.67 (s, Ph para C), 128.84 (d, JP-C = 6.5 Hz, Ph orthoC),
2
127.81 (s, Ph metaC), 100.99 (d, JP-C = 7.6 Hz, C3), 99.34 (d,
2JP-C = 7.2 Hz, C30 or C40), 99.08 (d, JP-C = 7.2 Hz, C30 or C40), 98.36
2
2
1
(d, JP-C = 4.8 Hz, C4), 91.61 (d, JP-C = 65.6 Hz, C2), 84.06
1
1
(d, JP-C = 60.9 Hz, C20 or C50), 83.89 (d, JP-C = 60.9 Hz, C20 or C50),
1
83.29 (d, JP-C = 60.1 Hz, C5), 15.86 (s, Me at C4), 14.76 (s, Me at
C30 or C40), 14.47 (s, Me at C30 or C40), 14.46 (s, Me at C3) ppm.
4.2. 3,30,4,40-Tetramethyl-1,10-diphosphaferrocene 1
31P NMR (CDCl3): d -47.62 (dd, JP-H = 36.5 Hz, JP-P = 10.6 Hz, P1),
2
2
2
2
-66.22 (td, JP-H = 36.0 Hz, JP-P = 10.6 Hz, P10) ppm. Anal. Calcd
for C19H20FeOP2: C, 59.72; H 5.28. Found for (Rp)-3 C, 59.58; H,
In a round-bottom flask, in a sonic bath with a mechanical stir-
rer, 3.5 g (0.5 M) of cut lithium wire and 2,3-dimethyl-1-pheny-
lophosphole (37.8 g, 0.2 M) were suspended in 500 ml of dry
THF. The obtained mixture was sonicated for 30 min (progress
was monitored by 31P NMR spectra). The solution was then trans-
ferred via a transfer tube under argon to a flask equipped with a
magnetic stirrer and placed in an ice bath. To the obtained mixture
was added AlCl3 (8.9 g, 0.066 M) in three portions over 30 min.
Next, the flask was placed in a sonic bath and mechanically stirred;
5.23; (Sp)-3 C, 59.53; H, 5.18. (Rp)-3 [
(Sp)-3 [
a
]
D
25 = ꢁ116 (c 0.19, CHCl3);
a]
D
25 = +116 (c 0.19, CHCl3) ee > 99%.
4.5. 2,20-Propionyl-3,30,4,40-tetramethyl-1,10-diphosphaferrocene
rac-4 and meso-4
A suspension of 0.252 g (2.72 mM) of propionyl chloride and
0.335 g (2.51 mM) of AlCl3 was mixed for 10 min in 10 ml CH2Cl2
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10
A. Kłys et al. / Tetrahedron: Asymmetry xxx (2016) xxx–xxx
2
at 0 °C. Later, 0.272 g (1.0 mM) of 1 was added slowly. The obtained
mixture was warmed to RT in 20 min and was refluxed for 4 h;
subsequently, the mixture was poured into 50 ml of a 3 M solution
of HCl. The organic phase was dried, evaporated to dryness and
purified by column chromatography (eluent CH2Cl2:hexane, 9:1).
Two fractions were obtained with rac-4 (0.152 g, 39%) and
(d, JP-C = 7.7 Hz, C4), 99.24 (d, 2JP-C = 4.9 Hz, C3), 95.33
1
1
(d, JP-C = 65.3 Hz, C2), 87.03 (d, JP-C = 60.9 Hz, C5), 16.07
3
3
(d, JP-C = 2.8 Hz Me at C4), 14.89 (d, JP-C = 2.4 Hz, Me at C3)
ppm. 31P NMR (CDCl3): d -38.04 (d, JP-H = 37.0 Hz, P1) ppm. Anal.
2
Calcd for C26H24FeO2P2: C, 64.22; H 4.97. Found for meso-5 C,
64.22; H, 5.17.
1
meso-4 (0.085 g, 22%). rac-4; H NMR (CDCl3): d 3.73 (AA0XX0,
3
4
2JH-P = 36.9 Hz, 2JP-P = 20.2 Hz,
JP-H = 0 Hz,
JP-H = 0 Hz 2H,
4.7. X-ray diffraction
0
0
2 ꢀ H5), 2.67 (dq, JH-H = 17.3 Hz,3JH-H = 7.3 Hz, 2H, 1H from CH2),
2
2
3
2.62 (dq, JH-H = 17.3 Hz, JH-H = 7.2 Hz, 2H, 1H from CH2), 2.28 (s,
Crystals suitable for X-ray analysis were obtained by evaporat-
ing a mixture of solvents (heptane:dichloromethane). Crystalliza-
tions were performed at 28 °C. The X-ray data for compounds 4
and 5 were collected on an Agilent Supernova Dual 4 circle diffrac-
tometer system equipped with both molybdenum and copper
microsources and an ATLAS CCD detector; a copper X-ray source
was used. The data were collected using the CrysAlis17179 soft-
ware and integrated with CrysAlisPRO80 software. Data were cor-
rected for absorption effects using the analytical absorption
correction based on crystal faces (SCALE3 ABSPACK79). The X-ray
data for compounds (Rp)-3 and (Sp)-3 were collected on a BRUKER
KAPPA APEX-II Ultra diffractometer equipped with a molybdenum
rotating anode as the X-ray source and multi-layer focusing mir-
rors. The data were collected using the Bruker APEX-II software,81
integrated with the Bruker SAINT software package82 using a nar-
row-frame algorithm, and corrected for absorption effects using
the multi-scan method (SADABS).83
2 ꢀ Me), 2.01 (s, 2 ꢀ Me), 1.07 (dd,3JH-H = 7.3 Hz, JH-H = 7.2 Hz,
3
6H, 2 ꢀ Me) ppm. 13C NMR (CHCl3):
d
207.15 (AA0X,
2
2
2
JP-C = 21.3 Hz, JP-P = 20.2 Hz, C = O), 104.65 (AA0X, JP-C = 7.6 Hz,
0
2
2
2
0
0
JP-P = 20.2 Hz, C4), 98.55 (ABX, JP-C = 4.5 Hz, JP-P = 20.2 Hz, C3),
89.31 (ABX, JP-C = 64.5 Hz, JP-P = 20.2 Hz,
1
2
0
D
D
m
m
= 0.061 ppm, C2),
= 0.061 ppm, C5),
1
2
0
84.06 (ABX, JP-C = 58.9 Hz, JP-P = 20.2 Hz,
3
2
36.39 (AA0X, JP-C = 11.9 Hz, JP-P = 20.2 Hz, CH2), 14.09 (s, Me at
0
C4), 12.93 (s, Me at C3), 8.56 (s, Me from ethyl) ppm. 31P NMR
2
2
3
(CDCl3): d -53.82 (AA0XX0, JP-H = 36.7 Hz, JP-P = 20.2 Hz, JP-H
=
0
4
0
0 Hz, JP-H = 0 Hz, P1) ppm. Anal. Calcd for C18H24FeO2P2: C,
55.41; H 6.20. Found for (Rp,Rp)-4 C, 55.16; H, 6.13; (SpSp)-4 C,
55.57; H, 6.04. (Rp,Rp)-4 [
a
]
D
25 = ꢁ73 (c 0.10, CHCl3); (SpSp)-4
[a
]
D
25 = 73 (c 0.10, CHCl3) ee > 99%. meso-4; 1H NMR(CDCl3): d
4.06 (AA0XX0, JP-H = 38.2 Hz, 2JP-P = 4.7 Hz, 3JP-H = 0 Hz, 4JP-H = 0 Hz,
2
0
0
3
2H, 2 ꢀ H5), 2.64 (dq,
2
JH-H = 17.3 Hz, JH-H = 7.3 Hz, 2H, 1H from
2
3
CH2), 2.55 (dq, JH-H = 17.3 Hz, JH-H = 7.3 Hz 2H, 1H from CH2),
2.25 (s, 2*Me), 2.05 (s, 2 ꢀ Me), 1.08 (dd,3JH-H = 7.3 Hz,
The structures were solved by direct methods using SXELXS84
and refined by the full-matrix least-squares procedure with
SHELXL84within the OLEX285 graphical interface. Figures were pro-
duced with the Ortep3v286 and the Mercury_3.587 software. The
Flack parameter was estimated using [(I+) ꢁ (Iꢁ)]/[(I+) + (Iꢁ)]
quotients.88
For all of the analysed compounds, all H atoms were visible in
the residual density map and were added geometrically and
refined in a riding approximation. No strong H-bonds requiring
more specific H atom treatment were present in the analysed crys-
tal structures.
3JH-H = 7.3 Hz 6H, 2 ꢀ Me). 13C NMR (CHCl3):
d
206.82
2
2
2
(AA0X, JP-C = 21.7 Hz, JP-P = 4.7 Hz, C = O), 103.45 (ABX, JP-C
=
0
2
0
7.4 Hz,
JP-P = 4.7 Hz,
D
m
= 0.019 ppm, C4), 98.43 (ABX,
= 0.014 ppm, C3), 90.95 (ABX,
= 0.062 ppm, C2), 85.02
= 0.062 ppm, C5), 36.58
2JP-C = 5.0 Hz, JP-P = 4.7 Hz,
Dm
2
1JP-C = 64.3 Hz,
2JP-P = 4.7 Hz,
Dm
1
2
(ABX, JP-C = 58.8 Hz, JP-P = 4.7 Hz,
D
m
3
2
(ABX, JP-C = 11.2 Hz, JP-P = 4.7 Hz, CH2), 15.09 (s, Me at C4),
4
2
13.08 (s, Me at C3), 8.44 (AA0X, JP-C = 3.5 Hz, JP-P = 4.7 Hz, CH3 of
ethyl group), ppm. 31P NMR (CDCl3): -50.36 (AA0XX0,
JP-H = 38.2 Hz, JP-P = 4.7 Hz, JP-H = 0 Hz, JP-H = 0 Hz, P1) ppm.
d
2
2
3
4
0
0
Anal. Calcd for C18H24FeO2P2: C, 55.41; H 6.20. Found for meso-4
C, 55.48; H, 6.53.
CCDC 1486761, 1486762, 1486763 and 1486764 contain the
supplementary crystallographic data for compounds (Sp)-3, (Rp)-
3, (Sp,Sp)-4 and (Rp,Rp)-5, respectively. These data can be obtained
free of charge from The Cambridge Crystallographic Data Centre
via https://summary.ccdc.cam.ac.uk/structure-summary-form.
4.6. 2,20-Dibenzoyl-3,30,4,40-tetramethyl-1,10-diphosphaferrocene
5
This compound was prepared according to a literature proce-
Acknowledgments
3
dure.47 rac-51H NMR(CDCl3d 7.74 (d, JH-H = 6.9 Hz, 4H, Ph ortho),
3
3
7.49 (t, JH-H = 7.9 Hz, 4H, Ph para), 7.37 (t, JH-H = 7.4 Hz, 4H, Ph
This study was financially supported by a research grant from
the Polish Ministry of Science and Higher Education: grant
N N204 331837. This research was supported in part by PL-Grid
Infrastructure.
2
2
3
meta), 3.91 (AA0XX0, JH-P = 36.7 Hz, JP-P = 26.7 Hz, JP-H = 0 Hz,
0
4
0
JP-H = 0 Hz, 2H, 2 ꢀ H5), 2.21 (s, 2 ꢀ Me), 2.16 (s, 2 ꢀ Me) ppm.
2
2
13C NMR (CHCl3): d 200.00 (AA0X, JP-C = 19.2 Hz, JP-P = 26.7 Hz,
C = O), 140.13 (s, Ph ipsoC), 132.06 (s, Ph paraC), 128.87 (AA0X,
4JP-C = 5.8 Hz, JP-P = 26.7 Hz, Ph orthoC), 127.95 (s, Ph metaC),
2
2
2
A. Supplementary data
103.36 (AA0X, JP-C = 8.5 Hz, JP-P = 26.7 Hz, C4), 99.80 (AA0X,
2JP-C = 4.3 Hz, JP-P = 26.7 Hz, C3), 91.83 (ABX, JP-C = 64.3 Hz,
2
1
1
2JP-P = 26.7 Hz,
D
m
= 0.063 ppm, C2), 85.03 (ABX, JP-C = 61.5 Hz,
Chromatogram of the racemic mixture of separated compounds.
Energy details and room temperature Boltzman populations3.
X-ray data processing and structure refinement 1H, 13C{1H}, 31P
NMR spectra of all study compounds. Crystallographic data for
3–5 (CIF). Supplementary data associated with this article can be
found, in the online version, at http://dx.doi.org/10.1016/j.tetasy.
2016.11.003.
2JP-P = 26.7 Hz,
Dm = 0.067 ppm, C5), 14.04 (s, Me at C4),
12.70 (d, JP-C = 2.4 Hz, Me at C3) ppm. 31P NMR (CDCl3): d -52.95
3
2
2
3
4
(AA0XX0, JH-P = 36.7 Hz, JP-P = 26.7 Hz, JP-H = 0 Hz, JP-H = 0 Hz,
P1) ppm. Anal. Calcd for C26H24FeO2P2: C, 64.22; H 4.97. Found
for (Rp,Rp)-5 C, 63.89; H, 5.05; (Sp,Sp)-5 C, 63.76; H, 5.19. (Rp,Rp)-4
0
0
[a
]
25 = ꢁ445 (c 0.20, CHCl3); (Sp,Sp)-4
[a]
25 = +445 ee > 99%.
D
D
meso-5; 1H NMR (CDCl3): d 7.71 (d, JH-H = 7.8 Hz, 4H, Ph ortho),
3
3
3
References
7.49 (t, JH-H = 7.4 Hz, 4H, Ph para), 7.37 (t, JH-H = 7.4 Hz, 4H, Ph
2
meta), 4.14 (d, JP-H = 37.0 Hz, 2H, 2 ꢀ H5), 2.31 (s, 2 ꢀ Me), 2.25
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