Achiral and planar chiral ferrocene diols: Preparation and complexation with titanium(IV)

Article abstract of DOI:10.1016/S0022-328X(98)00930-9

Achiral ferrocene diol, 1,1′-bis(diphenylhydroxymethyl)ferrocene 5, was prepared by the direct dilithiation of ferrocene with n-butyllithium in the presence of TMEDA followed by treatment with benzophenone, while the first chiral C₂-symmetric ferrocene diol possessing only the planar chirality, (+)-(R,R)-1,1′-bis(diphenylhydroxymethyl)-2,2′-dimethylferrocene 6, was prepared from (+)-(R,R)-1,1′-bis(oxazolinyl)-2,2′-dimethylferrocene 1b by the transformation of the oxazoline moieties. It was shown that diols 5 and 6 can form 1:1 complexes with tetraisopropyl titanate with ease. The X-ray crystal structure analysis of 5 with an intramolecular hydrogen-bonding showed that the phenyl groups in the molecule occupy quasi-axial and quasi-equatorial positions and these structures can be taken as the models of the titanium complexes of ferrocene diols. As a preliminary experiment, the titanium-catalyzed hydrosilylation of a ketone with 6 has also been carried out.

Full text of DOI:10.1016/S0022-328X(98)00930-9

Journal of Organometallic Chemistry 574 (1999) 19–23
Achiral and planar chiral ferrocene diols: preparation and
complexation with titanium(IV)ꢀ
Wanbin Zhang, Yoh-ichi Yoneda, Toshiyuki Kida, Yohji Nakatsuji, Isao Ikeda *
Department of Applied Chemistry, Faculty of Engineering, Osaka Uni6ersity, Suita, Osaka 565-0871, Japan
Received 28 April 1998
Abstract
Achiral ferrocene diol, 1,1%-bis(diphenylhydroxymethyl)ferrocene 5, was prepared by the direct dilithiation of ferrocene with
n-butyllithium in the presence of TMEDA followed by treatment with benzophenone, while the first chiral C2-symmetric ferrocene
diol possessing only the planar chirality, (+)-(R,R)-1,1%-bis(diphenylhydroxymethyl)-2,2%-dimethylferrocene 6, was prepared from
(+)-(R,R)-1,1%-bis(oxazolinyl)-2,2%-dimethylferrocene 1b by the transformation of the oxazoline moieties. It was shown that diols
5 and 6 can form 1:1 complexes with tetraisopropyl titanate with ease. The X-ray crystal structure analysis of 5 with an
intramolecular hydrogen-bonding showed that the phenyl groups in the molecule occupy quasi-axial and quasi-equatorial
positions and these structures can be taken as the models of the titanium complexes of ferrocene diols. As a preliminary
experiment, the titanium-catalyzed hydrosilylation of a ketone with 6 has also been carried out. © 1999 Elsevier Science S.A. All
rights reserved.
Keywords: Ferrocene; Diol; Titanium; Oxazoline; Planar chirality; Crystal structure
1. Introduction
The authors’ recent attention has been focused on the
development of C2-symmetric ligands possessing the
planar chirality of ferrocene for asymmetric catalytic
reactions [1]. In the preceding papers, they described
the preparation of C2-symmetric 1,1%,2,2%-tetrasubsti-
tuted ferrocene compounds 1 via the highly diastereose-
lective dilithiation of 1,1%-bis(oxazolinyl)ferrocene [1a].
Compound 1a can be directly used as a P,N-chelating
chiral ligand [1b]; furthermore, it can also be trans-
formed to novel C2-symmetric P,P-chelating ligand 2
[1c], which is the first C2-symmetric ligand with only the
planar chirality of ferrocene. With these novel C2-sym-
metric ligands 1a and 2, excellent enantiomeric excesses
have been attained for the palladium-catalyzed asym-
metric allylic alkylation [1b,c]. Meanwhile, in recent
years, chiral titanium reagents derived from C1- and
ꢀ Dedicated to the memory of the late Professor Rokuro Okawara.
* Corresponding author. E-mail: ikeda@ap.chem.eng.osaka-u.ac.jp.
C2-symmetric chiral h,h,h%,h%-tetraphenyl diol, such as
TADDOLs 3 and chiral binaphthol 4, have received
0022-328X/99/$ - see front matter © 1999 Elsevier Science S.A. All rights reserved.
PII: S0022-328X(98)00930-9

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W. Zhang et al. / Journal of Organometallic Chemistry 574 (1999) 19–23
n-butyllithium in the presence of 2.6 equivalents of
tetramethylethylenediamine (TMEDA) at r.t. for 1 day,
and then the dilithiated species was treated with 2.7
equivalents of benzophenone. After the reaction mix-
ture was stirred at r.t. overnight, 5 was isolated in 93%
yield with silica gel column chromatography.
Then the complexation of 5 with titanium(IV) was
examined. Compound 5 was reacted with one equiva-
lent of tetraisopropyl titanate in toluene under argon at
r.t. for 4 h. After the solvent and the liberated iso-
propanol were evaporated in vacuo, a 1:1 titanium
complex 7 was formed as expected. The structure of 7
Scheme 1.
1
was determined by H-NMR and fast atom bombard-
ment mass spectroscopy (FAB MS) analysis (Scheme
1). Attempts to determine the X-ray crystal structure of
this complex failed, because it is very sensitive to mois-
ture in air.
much attention as chiral Lewis acid catalysts in asym-
metric synthesis [2,3]. However, the chiral titanium
reagents derived from other types of diols are rarely
reported [4]. Based on a preceding study, therefore, the
authors prepared achiral and planar chiral C2-symmet-
ric h,h,h%,h%-tetraphenyl diol 5 and 6, respectively, with
a ferrocene backbone and examined their complexation
behavior with titanium(IV) and their probability as
Lewis acid catalysts [5].
However, a stable crystal of diol 5 was obtained from
its ethyl acetate solution in the presence of a trace
amount of piperidine. From the X-ray crystal analysis,
it was found that two kinds of structures (A and B)
existed in one crystal, and in both the two OH groups
formed an intramolecular hydrogen bond (Fig. 1). The
˚
OꢀO distances in these diol structures (2.84 A in A and
˚
˚
2.68 A in B) are similar to those of diol 3 (ca. 2.6 A)
˚
and its corresponding Ti complex (ca. 2.8 A) [3g].
2. Results and discussion
Similar to diol 3 and its corresponding Ti complex, the
phenyl groups in both A and B also occupy quasi-axial
and quasi-equatorial positions. Therefore, these struc-
tures of diol 5 can be taken as the models of its
titanium complex [3g].
Then, the C2-symmetric chiral diol 6 was prepared
with only the planar chirality of ferrocene and its
complexation property with tetraisopropyl titanate was
examined. Diol 6 can be prepared with ease from 1b
Before the preparation of the chiral diol 6, the achiral
ferrocene diol 5 was first prepared and its complexation
property with titanium(IV) and its crystal structure
were examined.
Diol 5 can be prepared from ferrocene with ease in
high yield in a one-pot synthesis (Scheme 1). Thus,
ferrocene was first dilithiated with 2.6 equivalents of
Fig. 1. Two crystal structures (A and B) of 5 (ORTEP, ellipsoids at the 20% probability level, R=0.073, Rw=0.046).

W. Zhang et al. / Journal of Organometallic Chemistry 574 (1999) 19–23
21
Scheme 2.
3. Experimental
[1a] by the transformation of the oxazoline moieties
(Scheme 2). Thus, treatment of 1b with trifluoroacetic
acid in aqueous THF caused ring opening of the oxazo-
line moiety, to give an unstable ammonium salt. The
salt was successively acetylated, without isolation, with
acetic anhydride in the presence of pyridine to provide
the ester amide 8 in 57% yield. The hydrolysis of 8 in a
methanol–water solution in the presence of sodium
hydroxide gave quantitatively 2,2%-dimethyl-1,1%-fer-
rocenedicarboxylic acid 9, which is a novel C2-symmet-
ric chiral dicarboxylic acid, with only the planar
chirality of ferrocene, and may have great potential in
molecular recognition and asymmetric synthesis. Trans-
esterification of 8 using methanolic sodium methoxide
at r.t. for 1 day gave the corresponding dimethyl ester
10 in 91% yield. Compound 10 was then treated with
7.5 equivalents of PhMgBr in THF at r.t. for 3 h to
give 6 in 65% yield.
Compound 6 was then treated with 1.1 equivalents of
tetraisopropyl titanate in dry toluene at r.t. under argon
for 6 h. The isopropanol liberated by ligand exchange
was removed thoroughly, along with the solvent, under
high vacuum to give titanate 11, the structure of which
was determined by 1H-NMR and FAB MS analysis
(Scheme 2).
Recently, Nakai et al. reported a successful titanium-
catalyzed asymmetric hydrosilylation of prochiral ke-
tone with inexpensive triethoxysilane [6]. With the
present new kind of diol 6 as a ligand, the current
authors also carried out this reaction as a preliminary
experiment. They found that the catalytic hydrosilyla-
tion of acetophenone with triethoxysilane proceeded
cleanly at 50°C for 6 h to give 1-phenylethanol in 94%
yield. No significant level of enantioselectivity has been
observed for this reaction so far, and work on further
modification of the ligand and the examination on
other titanium-catalyzed asymmetric reactions is in
progress.
Melting points were measured on a Yanagimoto
micromelting point apparatus and have not been cor-
rected. Optical rotations were measured on a JASCO
DIP-181 digital polarimeter. 1H-NMR spectra were
recorded on a JEOL GSX-400 spectrometer, and the
chemical shifts were referenced to CHCl3 (l 7.27 in
CDCl3). IR spectra were obtained on a HORIBA FT-
710 IR spectrophotometer. The FAB MS spectra were
obtained on a JEOL JMS-DX303HF spectrometer. Ele-
mental analyses were performed on a Yanagimoto
CHN-Corder. The X-ray crystallography was per-
formed on a Rigaku AFC5R diffractometer. Ether was
freshly distilled from sodium, and toluene and TMEDA
from CaH2 before use. Merck 70–230 mesh silica gel
was used for column chromatography. All other chemi-
cals used in the synthetic procedures were of reagent
grade.
3.1. 1,1%-Bis(diphenylhydroxymethyl)ferrocene, 5
To a mixture of TMEDA (11.1 ml, 73.7 mmol) and
1.6 M n-butyllithium (46.1 ml, 73.7 mmol) a solution of
ferrocene (5.00 g, 26.9 mmol) was added dropwise in
dry ether (60 ml) at 0°C and the reaction mixture was
stirred at r.t. for 24 h. A solution of benzophenone
(13.50 g, 74.0 mmol) in dry ether (60 ml) was added to
the above reaction mixture at −10°C and the reaction
mixture was stirred at r.t. overnight. HCl (1 N, 100 ml)
was added to the reaction mixture. After separation,
the organic layer was washed with water (100 ml), brine
(100 ml) and dried over MgSO4. After the solvent was
evaporated, the residue was purified by silica gel
column chromatography, eluted with a mixture of ben-
zene and ethyl acetate (1:1, v/v) to give 5 (14.1 g, 93%
yield).
A yellow solid, m.p. 166–168°C. Rf=0.14 (benzene).
1H-NMR (400 MHz, CDCl3): l=3.97 (t, 4H, J=1.8

22
W. Zhang et al. / Journal of Organometallic Chemistry 574 (1999) 19–23
overnight. HCl (1 N) was added to this solution until
pH 2 and then the resulting solid was filtered and
purified by silica gel column chromatography with ethyl
acetate to give 9 (0.075 g, 100%).
Hz, FcH), 4.03 (s, 2H, OH), 4.18 (t, 4H, J=1.8 Hz,
FcH), 7.21–7.31 (m, 20H, ArH). IR (KBr): w=3340,
3060, 1490, 1444, 1014, 752, 700 cm−1; FAB MS: m/z:
550 (M+). Anal. calc. for C36H30O2Fe: C, 78.55; H,
5.49. Found: C, 78.28, H, 5.49.
An orange solid, m.p. 219–221°C (decomp.). Rf=
1
0.24 (ethyl acetate). [h]2D7= +290 (c 0.5, CHCl3). H-
3.2. Preparation of titanium complex 7
NMR (400 MHz, CD3OD): l=2.13 (s, 6H, CH3), 4.27
(m, 4H, FcH), 4.67 (t, 2H, =1.3 Hz, FcH). IR (KBr):
J
w=3415, 2960, 1709, 1261, 1030, 800 cm−1
.
To a solution of 5 (0.50 g, 0.91 mmol) in dry toluene
(12 ml) under argon, tetraisopropyl titanate (0.26 g,
0.91 mmol) was added. The resulting yellow solution
was stirred for 3 h at r.t. The isopropanol liberated by
ligand exchange was removed thoroughly, along with
the solvent, under high vacuum at 40°C. The residue
thus obtained was dried under these conditions for 2 h
to give the titanium complex 7.
3.5. (+)-(R,R)-2,2%-Dimethyl-1,1%-ferrocenedicar-
boxylic acid dimethyl ester, 10
To a solution of 8 (1.44 g, 2.59 mmol) in THF (10
ml), a sodium methoxide solution prepared by the
dissolution of sodium (2.55 g, 111 mmol) in methanol
(140 ml) was added. After stirring at r.t. for 24 h, the
mixture was neutralized with methanolic acetic acid and
the solvent was removed by rotary evaporation. The
residue was dissolved in dichloromethane (100 ml) and
the solution was washed with water (50 ml) and brine
(50 ml) successively, and then dried over MgSO4. After
removal of the solvent, the residue was purified by silica
gel chromatography with ethyl acetate to afford 10
(0.78 g, 91% yield).
A yellow solid, m.p. 198°C (decomp.). Rf=0.61
(ethyl acetate). [h]2D4= +120.3 (c 0.61, CHCl3). 1H-
NMR (400 MHz, CDCl3): l=2.25 (s, 6H, FcCH3),
3.95 (s, 6H, OCH3), 4.22 (t, 2H, J=2.6 Hz, FcH), 4.25
(t, 2H, J=1.7 Hz, FcH), 4.68 (t, 2H, J=1.7, 2.6 Hz,
FcH). IR (KBr): w=2952, 1712, 1440, 1278, 1214, 1093
cm−1. FAB MS: m/z: 330 (M+).
1H-NMR (400 MHz, CDCl3): l=1.14 (d, 12H, J=
6.1 Hz, CH3), 3.92 (brs, 4H, FcH), 4.26 (brs, 4H, FcH),
4.45 (m, 2H, CHMe2), 7.19–7.41 (m, 20H, ArH). FAB
MS: m/z: 715 (M+H+).
3.3. Preparation of ester amide 8 (Scheme 2)
To a solution of 1b (2.32 g, 5.31 mmol) in THF (130
ml), water (7.2 ml), trifluoroacetic acid (12.3 ml, 160
mmol) and Na2SO4 (60.0 g) were added, and the result-
ing suspension was stirred overnight at r.t. After re-
moval of solid material by filtration and the solvent in
vacuo below r.t., an unstable ester ammonium salt was
obtained as a brown solid, which was used in the next
step without purification. To a solution of this ester
ammonium salt in dichloromethane (120 ml), pyridine
(20 ml, 241 mmol) and acetic anhydride (33 ml, 340
mmol) were added, and the mixture was stirred at r.t.
overnight. The mixture was washed with HCl (1N, 50
ml) three times, water (50 ml), and brine (50 ml) and
dried over Na2SO4. After the removal of solid material
by filtration and of the solvent in vacuo, a red residue
was obtained. The residue was purified by silica gel
chromatography, with ethyl acetate to afford pure ester
amide 8 (1.69 g, 57% overall yield from compound 1b).
A yellow solid, m.p. 102–104°C. Rf=0.11 (ethyl
acetate). 1H-NMR (400 MHz, CDCl3): l=1.02 (t,
12H, J=6.5 Hz, CH3), 1.95 (m, 2H, Me2CH), 2.07 (s,
6H, FcCH3), 2.19 (s, 6H, COCH3), 4.20 (m, 4H, NCH
and FcH), 4.28 (m, 4H, OCH2), 4.32 (t, 2H, J=1.7 Hz,
FcH), 4.57 (t, 2H, J=1.7 Hz, FcH), 6.36 (d, 2H,
J=8.1 Hz, NH). FAB MS: m/z: 556 (M+).
3.6. (+)-(R,R)-1,1%-Bis(diphenylhydroxy-
methyl)-2,2%-dimethylferrocene, 6
To a solution of PhMgBr in ether (3.0 ml) prepared
from Mg (0.16 g, 6.50 mmol) and bromobenzene (1.02
g, 6.50 mmol), a solution of 10 (0.30 g, 0.92 mmol) in
ether (4.0 ml) was added at 0°C, and then the reaction
solution was stirred at r.t. overnight. The resulting dark
oil was dissolved in benzene (50 ml) and washed with
saturated NH4Cl aqueous solution. The organic layer
was dried over MgSO4. After removal of the solvent,
the residue was purified by silica gel chromatography
with benzene to afford 6 (0.34 g, 65% yield).
A yellow solid, m.p. 47–49°C. Rf=0.39 (benzene).
1
[h]2D3= +337.0 (c 5.14, CHCl3). H-NMR (400 MHz,
CDCl3): l=1.74 (s, 6H, CH3), 3.44 (s, 2H, OH), 3.55
(brs, 2H, FcH), 4.03 (brs, 2H, FcH), 4.35 (brs, 2H,
FcH), 7.16–7.39 (m, 20H, ArH). IR (KBr): w=3535,
3057, 2916, 1446, 1018, 750 cm−1. FAB MS: m/z: 578
(M+). Anal. calc. for C38H34O2Fe: C, 78.90; H, 5.92.
Found: C, 78.53, H, 6.05.
3.4. (+)-(R,R)-2,2%-Dimethyl-1,1%ferrocenedi-
carboxylic acid, 9
To
a solution of 8 (0.14 g, 0.25 mmol) in
methanol:water (1:1, 12 ml) sodium hydroxide (0.40 g,
10 mmol) was added and the solution was stirred

W. Zhang et al. / Journal of Organometallic Chemistry 574 (1999) 19–23
23
3.7. Preparation of chiral titanium complex 11
served reflections (I\3.00|(I)) and 361 variable
parameters. R=0.073, Rw=0.046. Tables of atomic
co-ordinates, bond lengths, angles and thermal parame-
ters are available from the authors.
To a solution of 6 (0.178 g, 0.308 mmol) in dry
toluene (3 ml) under argon, tetraisopropyl titanate
(0.096 g, 0.338 mmol) was added. The reaction mixture
was stirred at r.t. for 6 h. The isopropanol liberated by
ligand exchange was removed thoroughly, along with
the solvent, under high vacuum at 40°C. The residue
thus obtained was dried under these conditions for 2 h
to give titanium complex 11.
Acknowledgements
The authors are grateful to Professor Yasushi Kai
and Dr Nobuko Kanehisa, Osaka University, for their
help in X-ray crystallographic determination. Financial
support from the Ministry of Education, Science and
Culture, Japan, is gratefully acknowledged.
1H-NMR (400 MHz, CDCl3): l=1.15 (d, 6H, J=
6.2 Hz, OCCH3), 1.27 (m, 12H, OCCH3 and FcCH3),
3.64 (dd, 2H, J=1.8, 2.2 Hz, FcH), 4.07 (dd, 2H,
J=1.8, 2.2 Hz, FcH), 4.51 (m, 2H, CHMe2), 4.68 (dd,
2H, J=1.8, 2.2 Hz, FcH), 7.15–7.40 (m, 20H, ArH).
FAB MS: m/z: 743 (M+H+).
References
3.8. Procedure for the titanium-catalyzed asymmetric
hydrosilylation of acetophenone
[1] (a) W. Zhang, Y. Adachi, T. Hirao, I. Ikeda, Tetrahedron
Asymm. 7 (1996) 451. (b) W. Zhang, T. Hirao, I. Ikeda, Tetrahe-
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I. Ikeda, Tetrahedron Lett. 37 (1996) 7795. The related work was
also reported independently by Park and Ahn’s group: (d) J.
Park, S. Lee, K.H. Ahn, C.-W. Cho, Tetrahedron Lett. 37 (1996)
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To a solution of titanium complex 11 prepared from
6 (0.190 g, 0.33 mmol) and (i-PrO)4Ti (0.085 g, 0.30
mmol) in toluene (5 ml), acetophenone (0.360 g, 3.0
mmol) and HSi(OEt)3 (2.96 g, 18.0 mmol) were added.
The reaction solution was stirred at 50°C until the
acetophenone disappeared by TLC analysis (5 h), then
it was quenched by adding slowly methanol (5 ml),
water (5 ml) and then NaOH (1N, 50 ml). The resulting
mixture was stirred at r.t. for 2.5 h, then neutralized by
4 N HCl. After removal of insoluble material and the
solvent by filtration and evaporation respectively, the
residue was purified by silica gel column chromatogra-
phy to give 1-phenylethanol (0.344 g, 94%).
3.9. X-ray crystal structure determination of 5
An orange crystal of 5 (C36H30O2Fe) with approxi-
mate dimensions of 0.20×0.20×0.20 mm3 was
mounted on a glass fiber. The measurement was made
on a Rigaku AFC5R diffractometer with graphite
monochromated Mo–Kh radiation and a 12 kW ro-
tating anode generator. Cell constants and an orienta-
tion matrix for data collection were obtained from
least-squares refinement using the setting angles of 23
carefully centered reflections in the range 26.97°B2qB
27.49° corresponding to a monoclinic cell with dimen-
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H.W. David, L.L. Martin, J.W. Patrick, Tetrahedron Lett. 38
(1997) 3867. (c) F. Almqvist, L. Torstensson, A. Gudmundsson,
T. Frejd, Angew. Chem. Int. Ed. Engl. 36 (1997) 376.
[5] Reported as a poster presentation at the 44th Symposium on
Organometallic Chemistry, Kansai University, Japan, 20–21
September, 1997, Abstracts, 106.
˚
sions: a=13.267(5), b=23.229(8), c=18.760(3) A;
3
˚
V=5571(2) A . The data were collected at 2391°C
using the ꢀ–2q scan technique to a maximum 2q value
of 55.1°. A total of 6888 reflections was collected. The
structure was solved by direct methods and expanded
using Fourier techniques. The non-hydrogen atoms
were refined anisotropically. The final cycle of full-ma-
trix least-squares refinement was based on 2653 ob-
[6] H. Imma, T. Nakai, Synlett (1996) 1229.
.