Modification of alkoxo ligands of BINOL-Ti ladder: Isolation and X-ray crystallographic analysis

Article abstract of DOI:10.1016/j.ica.2005.11.052

The stable binaphthol-titanium ladder complexes have been successfully prepared by using bulky alkoxo ligands. From the secondary OR ligand (cyclohexyloxo, 2,4-dimethyl-3-pentyloxo or 2-adamantyloxo) and terially OR ligand (tert-butyloxo, 1-adamantyloxo), partial hydrolysis proceeded to give the μ³-oxo titanium complexes. The use of [Ti(BINOLato)(OEt)₂]_n made it possible to prepare the Ti(BINOLato)(OR)₂ complexes using alcohols (ROH) of high boiling point (R = cyclohexyl, 2-adamantyl, 1-adamantyl). X-ray analyses of [(R)-1,1′-bi-2-naphtholato]bis(O-2,4-dimethyl-3-pentyloxo)titanium and [(R)-3,3′-dimethyl-1,1′-bi-2-naphtholato]bis(2-adamantyloxo)titanium showed a good agreement with the estimated ladder complexes. The catalytic activity of BINOL-Ti catalyst analogues, obtained by partial hydrolysis of Ti(BINOLato)(OR)₂ with wet MS 4A was studied in asymmetric glyoxylate-ene reaction by two methods. Moderate to good chemical yields and enantioselectivities were obtained.

Full text of DOI:10.1016/j.ica.2005.11.052

Inorganica Chimica Acta 359 (2006) 4159–4167
www.elsevier.com/locate/ica
Modification of alkoxo ligands of BINOL–Ti ladder: Isolation and
X-ray crystallographic analysis
*
Koichi Mikami , Yousuke Matsumoto, Ling Xu
Department of Applied Chemistry, Tokyo Institute of Technology, Oookayama 2-12-1, Meguro-ku, Tokyo 152-8552, Japan
Received 22 August 2005; accepted 20 November 2005
Available online 4 August 2006
Abstract
The stable binaphthol–titanium ladder complexes have been successfully prepared by using bulky alkoxo ligands. From the secondary
OR ligand (cyclohexyloxo, 2,4-dimethyl-3-pentyloxo or 2-adamantyloxo) and terially OR ligand (tert-butyloxo, 1-adamantyloxo), par-
tial hydrolysis proceeded to give the l3-oxo titanium complexes. The use of [Ti(BINOLato)(OEt)2]n made it possible to prepare the
Ti(BINOLato)(OR)2 complexes using alcohols (ROH) of high boiling point (R = cyclohexyl, 2-adamantyl, 1-adamantyl). X-ray analyses
of [(R)-1,10-bi-2-naphtholato]bis(O-2,4-dimethyl-3-pentyloxo)titanium and [(R)-3,30-dimethyl-1,10-bi-2-naphtholato]bis(2-adamant-
yloxo)titanium showed a good agreement with the estimated ladder complexes. The catalytic activity of BINOL–Ti catalyst analogues,
obtained by partial hydrolysis of Ti(BINOLato)(OR)2 with wet MS 4A was studied in asymmetric glyoxylate-ene reaction by two meth-
ods. Moderate to good chemical yields and enantioselectivities were obtained.
Ó 2005 Elsevier B.V. All rights reserved.
Keywords: Alkoxo ligands; BINOL–Ti ladder; X-ray crystallographic analysis; Asymmetric glyoxylate-ene reaction
1. Introduction
which one of the oxygens of DMBINOLato ligand is coordi-
nated to the two titanium centers [13].
Binaphthol–titanium diisopropoxide complex, Ti(BINO-
Lato)(OPri)2, is the pre-catalyst for the BINOL–Ti catalyst
[1], which is one of the most important catalysts for a number
of highly enantioselective carbon–carbon bond forming pro-
cesses [2], including the cyanosilylation of aldehydes [12b],
Diels-Alder cycloadditions [3], hetero Diels-Alder cycload-
dition [4], carbonyl-ene reaction [5], Mukaiyama aldol co-
reaction [6], nitro-aldol reaction [7], asymmetric allylation
of aldehydes [8,11] and ketones [9], and asymmetric sulfide
oxidation [10]. Sharpless has already reported the X-ray
structure analysis of Ti(BINOLato)(OPri)2 (1), synthesized
via the reaction of BINOL with Ti(OPri)4 [12e]. Ti(BINO-
Lato)(OPri)2 (1) has been reported to be dimeric in solution,
though trimeric as a crystal. Heppert has also reported the
X-ray analysis of more stable 3,30-dimethyl-2-binaphthol–
titanium diisopropoxide, Ti(DMBINOLato)(OPri)2 (2), in
We have also estimated the structure of l3-oxo titanium
complex Ti4(BINOLato)4(OPri)4(l-O)4 (3), obtained dur-
ing the preparation of the BINOL–Ti catalyst via partial
hydrolysis of Ti(BINOLato)(OPri)2 (Scheme 1) [14,15].
This complex is unstable and hence, the single crystal is
not obtained yet. In an estimated structure of this complex
(3) (Fig. 1), the upper side of the ladder structure is steri-
cally less demanding. Water is assumed to attack the tita-
nium center from this less hindered side and cause
hydrolysis of l3-oxo titanium complex. We thus set up
the present work to stabilize this ladder complex by intro-
ducing bulky alkoxo ligands in order to isolate the ladder
complex for X-ray analysis.
2. Results and discussion
Ti(BINOLato)(OR)2 complexes were prepared by an
analogous method to that of Ti(BINOLato)(OPri)2. Prepa-
ration of other Ti(BINOLato)(OR)2 complexes via
*
Corresponding author. Tel.: +81 3 5734 2142; fax: +81 3 5734 2776.
E-mail address: kmikami@o.cc.titech.ac.jp (K. Mikami).
0020-1693/$ - see front matter Ó 2005 Elsevier B.V. All rights reserved.
doi:10.1016/j.ica.2005.11.052

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K. Mikami et al. / Inorganica Chimica Acta 359 (2006) 4159–4167
- EtOH
wet MS 4A
or H2O
Ti(OEt)4
ROH
Ti(OR)4
+
ROH
4
O
O
OPri
OPri
Ti4(BINOLato)4(OPri)4(μ-O)4
(3)
Ti
Product
Yield
2
quant. (80% after recrystallization)
quant.
Scheme 1.
4
HO
5
HO
Scheme 3.
[Ti(OR)4]
toluene
O
O
OR
OR
OH
OH
+
Ti
2ROH
n
Entry
R
Product
Yield
1
2
Et
Pri
But
6
1
complex mixture
quant.a
Fig. 1. Three-dimensional computer modeling structure of Ti4(BINO-
Lato)4(OPri)4(l3-O)4 (3).
3
4
7
8
quant.
[Ti(BINOLato)(OEt)2] was also examined. Partial hydroly-
sis of Ti(BINOLato)(OR)2 complex and X-ray structure
analysis of tetra-nuclear oxo complex were executed
(Scheme 2).
cyclohexyl
2,4-dimethyl-3-pentyloxo
quant.b
5
9
quant.c
a dimer reported by Sharpless12
;
b mixture with cyclohexanol; c oxo complex
Scheme 4.
3. Synthesis of Ti(BINOLato)(OR)2 complex from Ti(OR)4
nol proceeded quantitatively to give the corresponding
Ti(OR)4 complex.
The reaction of Ti(OR)4 (R = Et, t-Bu, cyclohexyl,
2,4-dimethyl-3-pentyl) and (R)-BINOL was examined.
Ti(OBut)4 and Ti(OEt)4 were commercially available.
Ti(O-cyclohexyl)4 (4) and Ti(2,4-dimethyl-3-pentyloxo)4
(5) were prepared from the reaction of Ti(OEt)4 with 4
equiv of cyclohexanol and 2,4-dimethyl-3-pentanol, respec-
tively (at room temperature for 1 h, without solvent), and
then EtOH was removed under reduced pressure (Scheme
The synthetic method for Ti(BINOLato)(OR)2 com-
plexes was similar to that of Ti(BINOLato)(OPri)2 (1)
(Scheme 4). Ti(OR)4 was added to BINOL in toluene at
room temperature, and then azeotropic removal of ROH
gave brown solid at 100 °C, 0.5 Torr.
Chart 1 showed 1H NMR data of the Ti(BINO-
Lato)(OR)2 complexes. In the case of R = t-Bu (Chart 1.
1
3). The H NMR analyses of the products suggested that
the reaction with cyclohexanol and 2,4-dimethyl-3-penta-
1
a) or cyclohexyl (Chart 1. b), the H NMR data of BINO-
O
O
OEt
OEt
Ti
2ROH
MS 4A
or
H2O
n
O
O
OR
OR
Ti
Ti4(BINOLato)4(OR)4(μ-O)4
Ti(OR)4
2
OH
OH
Scheme 2.

K. Mikami et al. / Inorganica Chimica Acta 359 (2006) 4159–4167
4161
evacuated at 170 °C, 0.5 Torr. Such a high temperature
treatment might promote epimerization of BINOLato
ligand, and this method turned out to be not effective for
the preparation of the Ti(BINOLato)(O-cyclohexyl)2 and
other complexes obtained from alcohols of high boiling
point.
4. Synthesis of Ti(BINOLato)(OR)2 complex from
[Ti(BINOLato)(OEt)2]n
For these reasons, Ti(BINOLato)(OR)2 analogues with
sterically bulky alcohols of high boiling point were desired
to be introduced. As a starting material, [Ti(BINO-
Lato)(OEt)2]n (6) was thus used (Scheme 5). The use of
low boiling point of EtOH made this method advanta-
geous. It is effective in the case of ROH with high boiling
point, and only 2 equiv of ROH are required.
Chart 1. (a) Ti(BINOLato)(O-t-Bu)2 (7); (b) Ti(BINOLato)(O-cyclo-
hexyl)2 (8); (c) Ti(BINOLato)(OPri)2 (1); (d) Ti(BINOLato)(O-2,4-
dimethyl-3-pentyl)2 (9).
Lato parts were analogous to those of Ti(BINO-
Lato)(OPri)2 (1) (Chart 1. c). The reaction of BINOL and
Ti(OEt)4 gave the complicated product unfortunately. Ster-
eochemically less demanding OEt moiety might cause olig-
omerization of Ti(BINOLato)(OEt)2 (6). The formation of
Ti(BINOLato)(2,4-dimethyl-3-pentyloxo)2 (9) was not
observed. However, the ladder complex, analogous to
Ti4(BINOLato)4(OPri)4(l-oxo)2, was observed. This com-
plex was supposed to be formed by partial hydrolysis of
Ti(BINOLato)(2,4-dimethyl-3-pentyloxo)2.
To the solution of BINOL and Ti(OEt)4 in toluene, 2
equiv of alcohols (cyclohexanol, 2-adamantanol, or 1-ada-
mantanol) were added at room temperature. Then EtOH
and toluene were evaporated under reduced pressure to
give brown solids.
In the case of R = cyclohexyl, 2-adamantyl, 1-adaman-
tyl, 1H NMR analysis (Chart 2) showed an analogous chart
to that of Ti(BINOLato)(OPri)2 (1) to suggest that the
reaction proceeded quantitatively. [Ti(BINOLato)(O-
cyclohexyl)2] (8) gave good agreement with the complex
obtained from the reaction of BINOL and Ti(O-cyclo-
hexyl)4 (4). However, the single crystal for X-ray analysis
However, in the preparation of Ti(BINOLato)(O-cyclo-
hexyl)2 (8), 2 equiv of cyclohexanol produced could not be
OH
OH
O
OEt
OEt
O
O
OR
OR
1) Ti(OEt)4
2) - 4EtOH
1) 2ROH
Ti
Ti
2) - 4EtOH
O
n
(6)
ROH
Product
Yield
quant.
quant.
quant.
HO
8
10
11
HO
HO
O
O
O
O
O
O
O
O
O
O
Ti
Ti
Ti
O
O
11
8
10
Scheme 5.

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K. Mikami et al. / Inorganica Chimica Acta 359 (2006) 4159–4167
Chart 2. (a) Ti(BINOLato)(O-cyclohexyl)2 (8); (b) Ti(BINOLato)(O-2-
adamantyl)2 (11); (c) Ti(BINOLato)(O-1-adamantyl)2 (10); (d) Ti(BINO-
Lato)(OPri)2 (1).
was not obtained in all cases. In order to obtain the X-ray
data for the complex prepared by this method, DMBINOL
was used. Similar to Heppert’s work [13c], Ti(DMBI-
NOLato)(OPri)2 (12) complex was more stable than
[Ti(BINOLato)(OPri)2] (1) and easy to be crystallized.
Ti(DMBINOLato)(O-2-adamantyl)2 (13) was thus synthe-
sized by the reaction of DMBINOL, Ti(OEt)4, and 2 equiv
of 2-adamantanol (Scheme 6).
The reaction proceeded quantitatively and the complex
was recrystallized from toluene. Crystal system was mono-
clinic and space group was C2. The structure was determined
by direct method (SIR92) and optimized by full-matrix least-
square method. R(I > 0.10r(I)) and Rw(I > 0.10r(I)) were
0.099 and 0.114, respectively. Two independent Ti(DMBI-
NOLato)(O-2-adamantyl)2 units were observed and each
unit was symmetrically expanded to give two dimeric
[Ti(DMBINOLato)(O-2-adamantyl)2]2. Fig. 2 shows the
ORTEP representation of one Ti(DMBINOLato)(O-2-ada-
mantyl)2 molecule, bond lengths and bond angles of major
atoms are listed in Table 1. The bond lengths and angles of
13 are quite similar to those of 12 [13c].
Fig. 2. ORTEP of [Ti(DMBINOLato)(O-2-adamantyl)2]2 [13]2.
of various Ti(BINOLato)(OR)2 complexes was carried out.
As secondary OR ligands, cyclohexyloxo and 2-adamant-
yloxo were used to generate Ti(BINOLato)(OR)2
(R = cyclohexyl, 2,4-dimethyl-3-pentyl and 2-adamantyl)
(0.05 mmol). After MS 4A (0.5 g containing 0.6 equiv. of
water) was added and stirred for 1 h, the suspension was fil-
1
trated and analyzed by H NMR.
Chart 3 showed the 1H NMR data of the product
derived from 2-adamantanol. In the case of R = cyclohexyl
or 2-adamantyl, partial hydrolysis of Ti(BINOLato)(OR)2
proceeded to give new complexes. These new complexes
1
gave the same pattern in H NMR peaks and were consid-
ered to be isostructural to l3-oxo titanium ladder complex
as compared with Ti(BINOLato)(OPri)2 reported by Hep-
pert [13a]. In the case of R = 2,4-dimethyl-3-pentyl, iso-
structural l3-oxo titanium complex was formed by the
reaction of BINOL and Ti(2,4-dimethyl-3-pentyloxo)4.
Adventitious water in solvent might cause this partial
hydrolysis. These complexes were more stable than the ori-
ginal ladder complex, Ti4(BINOLato)4(OPri)4(l3-O)2. The
single crystal of l3-oxo titanium ladder complex of 2,4-
dimethyl-3-pentyloxo was obtained by using (S)-BINOL
in diethyl ether. Then, X-ray analysis of l3-oxo titanium
complex of 2,4-dimethyl-3-pentyloxo analogue was carried
out. The single crystal, obtained at room temperature, was
5. Synthesis of l3-oxo titanium complex analogue
Ti4O2(BINOLato)4(2,4-dimethyl-3-pentyloxo)4
was
obtained by the reaction of BINOL and Ti(2,4-dimethyl-
3-pentyloxo)4. Other Ti4(BINOLato)4(OR)4(l-O)2 com-
plexes were thus synthesized (Scheme 7). Partial hydrolysis
Me
Me
1) Ti(OEt)4
OH
O
O
O
Ti
OH
O
( 2eq.)
2)
Me
Me
HO
(13)
-EtOH
Scheme 6.

K. Mikami et al. / Inorganica Chimica Acta 359 (2006) 4159–4167
4163
Table 1
Selected bond distance and bond angles
˚
˚
Bond
Distance (A)
Bond
Distance (A)
Angle
Degree
Angle
Degree
Ti(1)–O(1)
Ti(1)–O(3)
Ti(2)–O(6)
O(1)–C(2)
O(3)–C(24)
1.844(4)
1.768(3)
2.159(3)
1.353(6)
1.427(6)
Ti(1)–O(2)
Ti(1)–O(4)
Ti(2)–O(5)
O(2)–C(13)
O(4)–C(34)
2.181(3)
1.795(4)
1.832(4)
1.377(5)
1.426(7)
O(1)–Ti(1)–O(2)
O(1)–Ti(1)–O(4)
O(2)–Ti(1)–O(4)
C(2)–O(1)–Ti(1)
C(24)–O(3)–Ti(1)
85.4(1)
112.5(2)
87.4(2)
133.0(4)
150.0(4)
O(1)–Ti(1)–O(3)
O(2)–Ti(1)–O(3)
O(3)–Ti(1)–O(4)
C(13)–O(2)–Ti(1)
C(34)–O(4)–Ti(1)
99.5(2)
167.8(2)
100.9(2)
116.4(3)
132.6(3)
*
O'
O
*
Ti2
O'
O
O
O
OR
OR
Ti4
O
wet MS 4A
O
O'
Ti
Ti3
O
Ti1
O
2
*
O'
Oligomer
*
OH
ROH =
HO
HO
HO
HO
Scheme 7.
Chart 3. (a) Ti(BINOLato)(O-2-adamantyl)2 (11); (b) 1 h after treatment
of Ti(BINOLato)(O-2-adamantyl)2 with MS 4A; (c) 24 h after treatment
of Ti(BINOLato)(O-2-adamantyl)2 with MS 4A.
red plate shaped. The crystal was monoclinic system and
space group was C2. The positions of four titanium atoms
were fixed by direct method and optimized by Full-Matrix
least square (2h = 29.99, R = 0.1020, Rw = 0.1390)
(Fig. 3).
The ORTEP figure of 2,4-dimethyl-3-pentyloxo ana-
logue showed that the molecular equation of the complex
was Ti4(BINOLato)4(2,4-dimethyl-3-pentyloxo)4(l-O)2 of
which the structure was similar to Ti4(BINOLato)4(OPri)4
(l-O)2 proposed. Crystal system was monoclinic and space
group was C2. The skeleton of the complex was composed
of four titanium centers and four l3-oxo ligands. All BINO-
Lato ligands were bonded to two titanium centers. Two of
four BINOLato ligands coordinated to two titanium
Fig. 3. ORTEP of Ti4[(S)-(BINOLato)4(2,4-dimethyl-3-pentyloxo)4(l-
O)2] (9).
centers. All four 2,4-dimethyl-3-pentyloxo ligands were
bonded on the same side (see Table 2).
6. Catalytic activity of BINOL–Ti catalyst analogues
The catalytic activity of BINOL–Ti catalyst analogues
was examined. In the preparation of BINOL–Ti analogues,

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K. Mikami et al. / Inorganica Chimica Acta 359 (2006) 4159–4167
Table 2
Selected bond distance and bond angles
˚
˚
Bond
Distance (A)
Bond
Distance (A)
Angle
Degree
Angle
Degree
Ti(1)–O(1)
Ti(1)–O(3)
Ti(2)–O(6)
O(2)–C(2)
O(4)–C(41)
1.970(8)
2.122(9)
1.805(9)
1.380(2)
1.440(2)
Ti(1)–O(2)
Ti(1)–O(4)
Ti(2)–O(7)
O(3)–C(12)
O(5)–C(32)
1.846(9)
1.730(10)
1.768(10)
1.390(2)
1.290(2)
O(1)–Ti(1)–O(2)
O(1)–Ti(1)–O(4)
O(2)–Ti(1)–O(5)
C(2)–O(2)–Ti(1)
C(41)–O(4)–Ti(1)
132.7(4)
113.7(5)
96.3(5)
132.7(8)
164.0(1)
O(1)–Ti(1)–O(3)
O(1)–Ti(1)–O(5)
O(3)–Ti(1)–O(4)
C(12)–O(3)–Ti(1)
C(32)–O(5)–Ti(1)
71.0(4)
93.8(4)
95.6(5)
118.8(7)
175.0(1)
two methods were employed (Methods A and B). In the
method A, the mixture of (R)-BINOL (1.0 mmol) and
Ti(OR)2Cl2 (1.0 mmol) was treated with MS 4A (0.5 g) in
CH2Cl2 (4 mL) for 1 h. In the method B, Ti(BINO-
Lato)(OR)2 (1.0 mmol) was treated with MS 4A (0.5 g) in
CH2Cl2 (4 mL) for 1 h. The reaction of a-methylstyrene
(1.0 mmol) and n-butyl glyoxylate (1.2 mmol) in CH2Cl2
(4 mL) (for 1 h at ꢀ30 °C) was used as a probe reaction
(Table 3). Ti(O-cyclohexyl)2Cl2 was synthesized from the
reaction of Ti(O-cyclohexyl)4 and TiCl4 in hexane.
activity of the samples treated by MS 4A for 24 h (Method
B) was also low in the case of R = cyclohexyl, 2,4-dimethyl-
3-pentyl and 2-adamantyl. Increase in chemical yield was
observed only in the case of R = t-Bu. However, steric
bulkiness of alkoxo ligands was considered to interfere
the approach of substrate, and hence lower the catalytic
activity of the complexes.
7. Summary
The catalytic activity of all the complexes turned out to
be lower than that of the original BINOL–Ti catalyst
obtained by the method A and B (R = Pri). In the case
of R = cyclohexyl, the reaction gave the ene-product highly
enantioselectively, but chemical yield was moderate (73%,
98% ee). Such low catalytic activity of complex was due
to the stability of Ti(BINOLato)(OR)2 complex. Stabiliza-
tion by steric bulkiness of alkoxo ligands led to retardation
of the formation of the BINOL–Ti catalysts. The catalytic
The stabilization of the ladder complex has thus been
attained by using bulky alkoxo ligands. From the secondary
OR ligand (cyclohexyloxo, 2,4-dimethyl-3-pentyloxo or 2-
adamantyloxo) and tertially OR ligand (tert-butyloxo, 1-
adamantyloxo), partial hydrolysis proceeded to give the
l3-oxo titanium complexes. The X-ray analysis of
Ti4(BINOLato)4(2,4-dimethyl-3-pentyloxo)4(l-O)4 success-
fully showed the ORTEP figure of 2,4-dimethyl-3-pentyloxo
analogue, Ti4(BINOLato)4(2,4-dimethyl-3-pentyloxo)4(l-O)4.
Table 3
BINOL–Ti analogues catalyzed asymmetric glyoxylate-ene reaction
Method A
Method B
OH
OH
wet MS 4A
aging 1-24h
O
OR
OR
Ti
O
+
n
[Ti(OR)2Cl2]
O
OH
CO2Bun
(10monl% based on Ti)
+
Ph
H
CO2Bun
-30oC, 1 or 24h
CH2Cl2
Ph
Entry
ROH
Method
Aging time (h)
Yield (%)
Ee (%)
1
2
3
4
5
PriOH
A
B
B
B
A
A
B
B
B
B
1
1
1
24
1
24
1
24
1
24
97
97
38
63
73
16
2
1
17
10
98
98
94
91
98
97
93
42
93
85
PriOH
ButOH
ButOH
cyclohexanol
cyclohexanol
2,4-dimethyl-3-pentanol
2,4-dimethyl-3-pentanol
1-adamantanol
6
7a
8a
9
10
a
1-adamantanol
[Ti4(BINOLato)4(2,4-dimethyl-3-pentyloxo)4(l3-O)2] was used, in spite of Ti(BINOLato)(2,4-dimethyl-3-pentyloxo)2.

K. Mikami et al. / Inorganica Chimica Acta 359 (2006) 4159–4167
4165
The structure was similar to the estimated ladder complex,
8.1. Tetrakis(cyclohexyloxo)titanium (IV) (4)
Ti4(BINOLato)4(OPri)4(l-O)4. The pre-catalysts, Ti(BINO-
Lato)(OR)2, were prepared by the reaction of Ti(OR)4 and
(R)-BINOL (R = t-Bu, cyclohexyl). However, in the prepa-
ration of Ti(BINOLato)(O-cyclohexyl)2 (8), 2 equiv of cyclo-
hexanol produced could not be excluded even at high
temperature and low pressure. The use of [Ti(BINO-
Lato)(OEt)2]n made it possible to prepare the Ti(BINO-
Lato)(OR)2 complexes with alcohols of high boiling point
(R = cyclohexyl, 2-adamantyl, 1-adamantyl). [Ti(BINO-
Lato)(O-cyclohexyl)2]2 showed good agreement with the
complex synthesized from the reaction of BINOL and
Ti(O-cyclohexyl)4. The catalytic activity of BINOL–Ti cata-
lyst analogues, obtained by partial hydrolysis of Ti(BINO-
Lato)(OR)2 with wet MS 4A, turned out to be lower than
that of the original BINOL–Ti catalyst. In the case of
R = cyclohexyl, the reaction gave the ene-product with high
enantioselectivity, however, chemical yield was moderate
(73%, 98% ee).
A 20 mL schlenk tube equipped with a magnetic stirring
bar and argon inlet was charged with cyclohexanol (7.6 g,
76 mmol). To the solution was slowly added titanium eth-
oxide (3.2 mL, 15 mmol) at ambient temperature from a
syringe. After stirring for 1 min, the solution was allowed
to stand for 6 h at 70 °C. Non-reacted cyclohexanol was
removed under reduced pressure (140 °C, 10 mmHg) and
recrystallized from hexane to give tetrakis(O-cyclo-
hexyl)titanium (IV) (5.3 g, 12 mmol) as a white crystal.
1H NMR (300 MHz, CDCl3): d 1.13–1.58 (m, 24H),
1.65–1.81 (m, 8H), 1.83–2.10 (m, 8H), 4.07–4.17 (m, 4H).
8.2. Tetrakis(2,4-dimethyl-3-pentyloxo)titanium (IV) (5)
A 20 mL schlenk tube equipped with a magnetic stirring
bar and argon inlet was charged with 2,4-dimethyl-3-pro-
panol (13 g, 115 mmol). To the solution was added tita-
nium (IV) ethoxide (5.47 mL, 26 mmol) slowly at ambient
temperature from a syringe. After stirring for 10 min, the
solution was allowed to stand for 6 h at room temperature.
Non-reacted 2,4-dimethyl-3-propanol was removed under
reduced pressure to give tetrakis (2,4-dimethyl-3-pent-
yloxo)titanium (IV) (13 g, 26 mmol). The product was used
8. Experimental
General method: Melting points and boiling points were
1
uncorrected. H NMR and 13C NMR were measured on a
Varian Gemini 300 (300 Hz) spectrometers and 17O NMR
was measured on a GX-500 (500 Hz) spectrometers. Chem-
1
without any purification. H NMR (300 MHz, CDCl3): d
1
ical shifts of H NMR were expressed in parts per million
0.91 (d, J = 6.6 Hz, 24H), 0.96 (d, J = 6.6 Hz, 24H), 1.72
(m, 8H), 3.69 (sept, J = 6.0 Hz, 4H).
downfield from tetramethylsilane as an internal standard
(d = 0) in CDCl3. Chemical shifts of 13C NMR were
expressed in parts per million downfield from CDCl3 as
an internal standard (d = 77.0) in CDCl3. Chemical shifts
of 17O NMR were expressed in parts per million downfield
from H2O as an internal standard (d = 0) in C7D8. IR spec-
tra were measured on a JASCO FT/IR-5000 spectrometer.
Optical rotations were measured on a JASCO DIP-370.
Liquid chromatographic analyses (LC) were conducted
on a Shimadzu PU-980, LG-980-02, DG-980-50 and CO-
966 instrument equipped with model UV-975 spectrome-
ters as an ultra violet light. Peak areas were calculated by
Shimadzu C-R6A as an automatic integrator. Molecular
weight measurements were performed on Knauer vapor
pressure someter. Analytical thin layer chromatography
(TLC) was performed on a glass plates and/or aluminum
8.3. [(R)-1,10-Bi-2-naphtholato]bis(O-t-Bu)titanium (IV)
(7)
To a suspension of dried (R)-1,10-bi-2-naphthol (0.88 g,
3.1 mmol) in toluene (20 mL) was added dried Ti(O-t-Bu)4
(1.2 mL, 3.1 mmol) at room temperature. After stirring for
1 h at that temperature, the reaction mixture was azeotroped
until volume of the solution was reduced to 8 mL. Further
concentration was continued under reduced pressure to give
[(R)-1,10-bi-2-naptholato]bis(O-tert-butyloxo)titanium (IV)
1
(7) (1.5 g, 3.1 mmol, 99%) as an orange crystal. H NMR
(300 MHz, CDCl3): d 1.19 (s, 18H), 6.86 (d, J = 9.0 Hz,
2H), 7.12–7.24 (m, 4H), 7.34 (ddd, J = 8.4, 6.3, 1.8 Hz,
2H), 7.43 (d, J = 9.0 Hz, 2H), 7.86 (d, J = 8.1 Hz, 2H).
sheets pre-coated with silica gel (Merck Kieselgal 60 F254
,
layer thickness 0.25 and 0.2 mm). Visualization was accom-
plished by UV light (254 nm), anisaldehyde, KMnO4 and
phosphomolybdic acid. Column chromatography was per-
formed on Merck Kieselgel 60 and KANTO Silica Gel 60N
(spherical, neutral), employing hexane/ ethyl acetate mix-
ture as eluent unless otherwise noted. Molecular sieves
(MS 4A, activated powder and pelets) were purchased from
Aldrich Chemical Co. All experiments were carried out
under argon atmosphere unless noted. Diethyl ether (dehy-
drate), benzene (dehydrate), toluene (dehydrate), dichloro-
methane (dehydrate), chloroform-d3 and hexane
(dehydrate) were purchased from Kanto chemical Co.
Inc. and dried over molecular sieves (MS 4A, pelets).
8.4. [(R)-1,10-Bi-2-naphtholato]
bis(cyclohexyloxo)titanium (IV) (8)
To
a
suspension of dried (R)-1,10-bi-2-naphthol
(260 mg, 0.92 mmol) in toluene (10 mL) was added dried
Ti(OEt)4 (209 lL, 0.92 mmol) at room temperature. After
stirring for 1 h at that temperature, the reaction mixture
was added cyclohexanol (180 mg, 1.8 mmol) and stirred
for 1 h at that temperature. The reaction mixture was
azeotroped until volume of the solution was reduced to
1 mL. Further concentration was continued under reduced
pressure to give [(R)-1,10-bi-2-naptholato]bis(cyclo-
hexyloxo) titanium (IV) (8) (480 mg, 0.90 mmol) as an

4166
K. Mikami et al. / Inorganica Chimica Acta 359 (2006) 4159–4167
orange crystal. 1H NMR (300 MHz, CDCl3): d 1.0–1.8 (m,
20H), 4.24 (br, 2H), 6.76 (d, J = 8.7 Hz, 2H), 7.13–7.20 (m,
4H), 7.36 (m, 2H), 7.48 (d, J = 8.7 Hz, 2H), 7.88 (d,
J = 8.4 Hz, 2H).
for 1 h at that temperature. The reaction mixture was
azeotroped until volume of the solution was reduced to
1 mL. Further concentration was continued under reduced
pressure to give [(R)-1,10-bi-2-naptholato]bis(2-adamant-
yloxo)titanium (IV) (470 mg, 0.75 mmol, 82%) as an
1
8.5. [(R)-1,10-Bi-2-naphtholato]bis(2,4-dimethyl-3-
pentyloxo)titanium (IV) (9)
orange crystal. H NMR (300 MHz, CDCl3): d 1.21–2.16
(m, 30H), 4.54 (br, 2H), 6.79 (br, 2H), 7.81–7.19 (m, 4H),
7.35 (ddd, J = 7.5, 6.0, 1.2 Hz, 2H), 7.43 (br, 2H), 7.86
(d, J = 7.8 Hz, 2H).
To a suspension of dried (R)-1,10-bi-2-naphthol (1.1 g,
3.9 mmol) in toluene (30 mL) was added dried tita-
nium(2,4-dimethyl-3-pentyloxo)4 (2.2 mL, 3.9 mmol) at
room temperature. After stirring for 1 h at that tempera-
ture, the reaction mixture was azeotroped until volume of
the solution was reduced to 1 mL. Further concentration
was continued under reduced pressure. Orange solid was
recrystallized to give [(R)-1,10-bi-2-naptholato]bis(O-2,4-
8.8. [(R)-3,30-dimethyl-1,10-bi-2-naptholato]bis(2-
adamantyloxo)titanium (IV) (13)
To a suspension of dried (R)-3,30-dimethyl-1,10-bi-2-
naphthol (180 mg, 0.57 mmol) in toluene (10 mL) was
added dried Ti(OEt)4 (120 lL, 0.57 mmol) at room tem-
perature. After stirring for 1 h at that temperature, the
reaction mixture was added 2-adamantanol (170 mg,
1.1 mmol) and stirred for 1 h at that temperature. The
reaction mixture was azeotroped until volume of the solu-
tion was reduced to 1 mL. Further concentration was con-
tinued under reduced pressure and recrystallize in toluene
to give [(R)-3,30-dimethyl-1,10-Bi-2-naptholato]bis(2-ada-
mantyloxo) titanium (IV) (13) (160 mg, 0.25 mmol, 43%)
was obtained as X-ray grade yellow-orange crystal. 1H
NMR (300 MHz, CDCl3): d 0.90 (d, J = 12.6 Hz, 4H),
1.21–1.96 (m, 24H), 2.00 (s, 6H), 4.63 (br, 2H), 6.99 (d,
J = 7.8 Hz, 2H), 7.03 (dd, J = 8.1, 7.8 Hz, 2H), 7.21–
7.31 (m, 2H), 7.57 (s, 2H), 7.79 (d, J = 8.1 Hz, 2H).
dimethyl-3-pentyloxo)titanium
(IV)
(9)
(620 mg,
0.34 mmol, 35%) as an orange crystal. 1H NMR
(300 MHz, CDCl3): d 0.17 (d, J = 6.6 Hz, 6H), 0.44 (d,
J = 6.6 Hz, 6H), 0.60 (d, J = 6.9 Hz, 6H), 0.69 (d,
J = 6.6 Hz, 6H), 0.78 (d, J = 6.6 Hz, 6H), 0.93 (d,
J = 6.6 Hz, 6H), 1.01 (d, J = 7.2 Hz, 6H), 1.15 (d,
J = 6.6 Hz, 6H), 1.60–1.80 (m, 8H), 3.76 (m, 2H), 4.04
(m, 2H), 4.58 (d, J = 8.4 Hz, 2H), 4.74 (d, J = 8.7 Hz,
2H), 6.54 (d, J = 7.8 Hz, 2H), 6.65 (d, J = 5.7 Hz, 2H),
6.67 (s, 2H), 6.74 (d, J = 9.0 Hz, 2H), 6.82 (d, J = 9.0 Hz,
2H), 6.92 (t, J = 6.6 Hz, 2H), 6.97–7.04 (m, 6H), 7.12–
7.22 (m, 8H), 7.36–7.67 (m, 4H), 7.46 (d, J = 9.0 Hz,
2H), 7.60–7.70 (m, 4H), 7.70–7.77 (m, 4H), 7.79 (d,
J = 7.9 Hz, 2H), 7.71 (d, J = 8.4 Hz, 2H).
8.9. General procedure for preparation of ladder complex
8.6. [(R)-1,10-Bi-2-naphtholato]bis(1-adamantyloxo)-
titanium (IV) (10)
To a well-dried toluene (10 mL) was added 0.1 M ether
(0.5 mL) solution of H2O (0.05 mmol, 0.9 lL) at room tem-
perature and stirred for 1 min (the amount of H2O/Et2O
solution was optimized by try and error). Then,
[Ti(OR)2{(R)-l-BINOLato}] derivatives (1.0 mmol) was
added at room temperature under an argon atmosphere.
After stirring for 1 h, the solvent was removed under
reduced pressure to give [Ti4(OR)4{(R)-l-BINO-
Lato}4(l3-O)2] (>95%).
To a suspension of dried (R)-1,10-bi-2-naphthol (950 mg,
3.3 mmol) in toluene (10 mL) was added dried Ti(OEt)4
(700 lL, 3.3;mmol) at room temperature. After stirring for
1 h at room temperature, to the reaction mixture was added
2-adamantanol (280 mg, 1.8 mmol)and stirred for 1 hat that
temperature. The reaction mixture was azeotroped until
volume of the solution was reduced to 1 mL. Further concen-
tration was continued under reduced pressure to give [(R)-
1,10-bi-2-naptholato]bis(1-adamantyloxo)titanium
(IV)
8.10. Ladder complex
(2.0 g, 3.10 mmol, 94%) as an orange solid. 1H NMR
(300 MHz, CDCl3): d 1.42–1.55 (m, 8H), 1.71(br, 12H),
2.02(s, 6H), 2.15(s, 6H), 6.85 (d, J = 8.7 Hz, 2H),
7.11 ꢁ 7.19 (m, 4H), 7.34 (ddd, J = 8.1, 6.9, 1.2 Hz, 2H),
7.46 (d, J = 9.0, 2H), 7.81 (d, J = 8.1 Hz, 2H).
[Ti4{(R)-l-BINOLato}4(tert-butyloxo)4(l3-O)2]:
The
titled compound was prepared from (R)-[Ti{(R)-l-BINO-
Lato}(O-t-Bu)2] according to the general procedure (about
1
85% yield). H NMR (300 MHz, CDCl3): d1.40 (s, 36H),
4.73 (d, J = 8.4 Hz, 2H), 5.25 (d, J = 9.0 Hz, 2H), 6.03 (d,
J = 8.7 Hz, 2H), 6.18–6.33 (m, 2H), 6.67 (s, 2H), 6.71 (d,
J = 8.4 Hz, 2H), 6.95–6.30 (m, 20H), 7.48 (t, J = 6.6 Hz,
2H), 7.63 (d, J = 8.7, 2H), 7.66 ꢁ 7.84 (m, 12H).
8.7. [(R)-1,10-Bi-2-naptholato]bis(2-adamantyloxo)-
titanium (IV) (11)
To
a
suspension of dried (R)-1,10-bi-2-naphthol
(260 mg, 0.91 mmol) in toluene (20 mL) was added dried
Ti(OEt)4 (190 lL, 0.91 mmol) at room temperature. After
stirring for 1 h at that temperature, to the reaction mixture
was added 2-adamantanol (280 mg, 1.8 mmol) and stirred
9. Supplementary data
Crystallographic data (excluding structure factors) for
the structures reported in this paper have been deposited

K. Mikami et al. / Inorganica Chimica Acta 359 (2006) 4159–4167
4167
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in the Cambridge Crystallographic Data Center as supple-
mentary publication nos. CCDC-261195 and CCDC-
261196. Copies of this information can be obtained free
of charge from The Director, CCDC, 12, Union Road,
Cambridge CB2 1EZ, UK (fax: +44 1223 336033; e-mail:
deposit@ccdc.cam.ac.uk or http://www.ccdc.cam.ac.uk).
Acknowledgements
We are grateful to Prof. Masahiro Terada now in Toho-
ku University, Prof. Masahiro Yamanaka now in Rikkyo
University, and Dr. Kohsuke Aikawa in our group for
their useful discussions and suggestions.
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