The synthesis of [Ti(O-i-Pr)Cl2(PhCHO)(μ-Cl)]2 and its reactions with oxygen-containing ligands L (L = DMF, DMSO, i-PrOH). The crystal structure of Ti(O-i-Pr)Cl3(PhCHO)(i-PrOH) and the 1H variable-temperature NMR studies of solution structures of [Ti(O-i-Pr)Cl2(PhCHO)(μ-Cl)]2 and Ti(O-i-Pr)Cl3(PhCHO)L

Article abstract of DOI:10.1016/S0020-1693(00)00033-5

Ti(O-i-Pr)Cl₃ reacted with 1 molar equiv. of benzaldehyde to give the dimeric complex [Ti(O-i-Pr)Cl₂(PhCHO)(μ-Cl)]₂ (2) which reacted further with 2 molar equiv. of N,N-dimethylformamide (DMF), dimethyl sulfoxide (DMSO), or 2-propanol (i-PrOH) to give the six-coordinate monomeric complexes Ti(O-i-Pr)Cl₃(PhCHO)L (L = DMF (3), DMSO (4), or i-PrOH (5)). In the reaction of 2 with i-PrOH, the formation of the simple adduct 5 demonstrates the preferred nature of the monomeric six-coordinate species to the chloride-bridged or the alkoxide-bridged dimeric complex. The complexes 2-5 are highly dynamic in solution and the ¹H variable-temperature NMR studies show 17 observable -CHO signals for the chloride-bridged dimeric complex 2, indicating the presence of more than 10 isomeric species in solution. For the monomeric complexes 3 and 4, all four geometric isomers are observed. For the complex 5, however, the observation of 11 benzaldehyde -CHO signals indicates the presence of hydrogen-bonded dimeric species in solution in addition to the four expected monomeric isomers. The solution structures of complexes 2-5 are discussed. For the complex 5, the dynamic process for the exchange of the hydroxy hydrogen between the O-i-Pr and the i-PrOH ligands is observed. Despite the presence of several isomeric speices in solution, the lowest-enegy species 5-A crystallizes in the triclinic P 1? space group with a = 8.976(2), b = 10.412(2), c = 11.744(2) A?, α = 67.49(1), β = 69.18(1), γ = 71.68(1)°, z = 2, R = 0.043, R_W = 0.064, and Gof = 1.57. The solid state structure of 5-A exhibits the trans position of the benzaldehyde ligand relative to the 2-propoxide ligand, suggesting a relative bonding order of ^-O-i-Pr > Cl^- > i-PrOH > PhCHO. (C) 2000 Elsevier Science S.A.

Full text of DOI:10.1016/S0020-1693(00)00033-5

www.elsevier.nl/locate/ica
Inorganica Chimica Acta 303 (2000) 190–198
The synthesis of [Ti(O-i-Pr)Cl2(PhCHO)(m-Cl)]2 and its reactions
with oxygen-containing ligands L (L=DMF, DMSO, i-PrOH).
1
The crystal structure of Ti(O-i-Pr)Cl3(PhCHO)(i-PrOH) and the H
variable-temperature NMR studies of solution structures of
[Ti(O-i-Pr)Cl2(PhCHO)(m-Cl)]2 and Ti(O-i-Pr)Cl3(PhCHO)L
Tyng-Yuh Hwang, Jian-Yang Cho, Ming-Ke Jiang, Han-Mou Gau *
Department of Chemistry, National Chung-Hsing Uni6ersity, Taichung 402, Taiwan, ROC
Received 29 June 1999; accepted 6 December 1999
Abstract
Ti(O-i-Pr)Cl3 reacted with 1 molar equiv. of benzaldehyde to give the dimeric complex [Ti(O-i-Pr)Cl2(PhCHO)(m-Cl)]2 (2) which
reacted further with 2 molar equiv. of N,N-dimethylformamide (DMF), dimethyl sulfoxide (DMSO), or 2-propanol (i-PrOH) to
give the six-coordinate monomeric complexes Ti(O-i-Pr)Cl3(PhCHO)L (L=DMF (3), DMSO (4), or i-PrOH (5)). In the reaction
of 2 with i-PrOH, the formation of the simple adduct 5 demonstrates the preferred nature of the monomeric six-coordinate species
1
to the chloride-bridged or the alkoxide-bridged dimeric complex. The complexes 2–5 are highly dynamic in solution and the H
variable-temperature NMR studies show 17 observable ꢀCHO signals for the chloride-bridged dimeric complex 2, indicating the
presence of more than 10 isomeric species in solution. For the monomeric complexes 3 and 4, all four geometric isomers are
observed. For the complex 5, however, the observation of 11 benzaldehyde ꢀCHO signals indicates the presence of hydrogen-
bonded dimeric species in solution in addition to the four expected monomeric isomers. The solution structures of complexes 2–5
are discussed. For the complex 5, the dynamic process for the exchange of the hydroxy hydrogen between the O-i-Pr and the
i-PrOH ligands is observed. Despite the presence of several isomeric speices in solution, the lowest-enegy species 5-A crystallizes
(
,
in the triclinic P1 space group with a=8.976(2), b=10.412(2), c=11.744(2) A, h=67.49(1), i=69.18(1), k=71.68(1)°, z=2,
R=0.043, Rw=0.064, and Gof=1.57. The solid state structure of 5-A exhibits the trans position of the benzaldehyde ligand
relative to the 2-propoxide ligand, suggesting a relative bonding order of −O-i-Pr\Cl−\i-PrOH\PhCHO. © 2000 Elsevier
Science S.A. All rights reserved.
Keywords: Crystal structures; Titanium complexes; Alkoxide complexes; Aldehyde complexes
1. Introduction
which are capable of coordinating to the titanium metal
center, are the most extensively used substrates in
asymmetric synthesis. Due to the activation by the
metal center and the stereo-environment provided by
the chiral ligand, high enantioselectivities have been
achieved. Despite extensive studies of the titanium com-
plex systems in asymmetric catalysis, the mechanistic
details remain to be the subject of extensive discussions
[4–8]. The difficulties encountered in these studies in-
clude the characteristic features of aggregation [9–11]
and fluxionality [12,13] in solution. Previous studies
have shown that the six-coordinate octahedral is the
major geometry for titanium complexes containing lig-
The alkoxides are one of the most important ligands
found in numerous titanium complexes which were
extensively used as starting material for the synthesis of
new complexes and as reagents to mediate many types
of organic reactions. For titanium alkoxides containing
the chiral diolate ligand, they were effective catalysts in
various asymmetric syntheses of organic compounds
[1–3]. In these applications, the organic carbonyls,
* Corresponding author. Tel.: +886-4-286 2547; fax: +886-4-284
0729.
0020-1693/00/$ - see front matter © 2000 Elsevier Science S.A. All rights reserved.
PII: S0020-1693(00)00033-5

T.-Y. Hwang et al. / Inorganica Chimica Acta 303 (2000) 190–198
191
ands of small to medium in size and dynamic processes
were usually observed in solution [14–16].
2.3. Synthesis of (benzaldehyde)trichloro(N,N-
dimethylformamide)(2-propoxo)titanium(IV) (3)
In order to probe the bonding abilities of organic
carbonyls with titanium(IV) metal and to investigate
the structural variations in solution of titanium(IV)-car-
bonyl complexes in various solvents, we report here the
N,N-Dimethylformamide (0.23 ml, 3.00 mmol) was
added to a colorless solution of 2 (0.94 g, 1.50 mmol) in
25 ml of CH2Cl2 at r.t. The solution changed color to
orange and was stirred for 30 min. The solvent was
then removed in vacuo to afford a quantitative yield of
synthesis
of
the
dimeric
complex
[Ti(O-i-
Pr)Cl2(PhCHO)(m-Cl)]2 (2) which reacts further with 2
molar equiv. of oxygen-containing ligands, such as
N,N-dimethylformamide (DMF), dimethyl sulfoxide
(DMSO), or 2-propanol (i-PrOH), to give the
monomeric complex Ti(O-i-Pr)Cl3(PhCHO)L (L=
DMF (3), DMSO (4), or i-PrOH (5)). All these com-
plexes are highly dynamic in solution due to the lability
of the relatively weak coordination of the benzaldehyde
ligand.
1
orange oil. H NMR (CDCl3): l 10.13 (s, 1H), 8.55 (br,
1H), 8.05–7.50 (m, 5H), 5.30 (br, 1H), 3.20 (s, 3H),
3
3.12 (s, 3H), 1.54 (d, JHH=8.7 Hz, 6H) ppm. 13C{1H}
NMR (CDCl3): l 198.3, 167.8 (CHO), 136.5, 134.9,
131.6, 129.4 (Ph), 92.5 (CH), 38.7, 34.0, 23.5 (CH3)
ppm. IR (Nujol): 1637 (s, br), 1597 (s), 1579 (s), 1491
(m), 1315 (m), 1293 (w), 1219 (s), 1203 (sh), 1169 (m),
1107 (s), 1073 (w), 1059 (w), 1009 (s), 925 (w), 863 (m),
837 (s), 753 (s), 689 (s), 661 (m), 625 (m), 451 (m)
cm−1. Anal. Calc. for C13H20NO3Cl3Ti: C, 39.78; N,
3.57; H, 5.14. Found: C, 39.10; N, 3.56; H, 5.16%.
2. Experimental
2.4. Synthesis of (benzaldehyde)trichloro(dimethyl
sulfoxide)(2-propoxo)titanium(IV) (4)
2.1. Reagents and general techniques
All syntheses and manipulations were carried out
under a dry dinitrogen atmosphere. Ti(O-i-Pr)Cl3 was
prepared according to the literature procedures [17].
Dimethyl sulfoxide (0.20 ml, 3.00 mmol) was added
to a colorless solution of 2 (0.94 g, 1.50 mmol) in 25 ml
of CH2Cl2 at r.t. The solution changed to orange in
color and was stirred for 30 min. The mixture was dried
Benzaldehyde
(Aldrich),
N,N-dimethylformamide
(Aldrich), and dimethyl sulfoxide (Aldrich) were dis-
tilled and stored over molecular sieves. 2-Propanol
(Aldrich) was refluxed over CaH2 (Aldrich), distilled,
1
in vacuo to give a quantitative yield of orange oil. H
NMR (CDCl3): l 10.10 (s, 1H), 8.05–7.50 (m, 5H),
3
5.26 (br, 1H), 2.96 (s, 6H), 1.46 (d, JHH=8.7 Hz, 6H)
,
and stored over 4 A molecular sieves. Solvents were
ppm. 13C{1H} NMR (CDCl3): l 198.7 (CHO), 136.8,
134.4, 131.6, 129.4 (Ph), 91.9 (CH), 37.2 (SCH3), 23.3
(CH3) ppm. IR (Nujol): 1682 (s), 1658 (s), 1596 (s),
1580 (s), 1494 (w), 1316 (m), 1297 (w), 1265 (w), 1220
(m), 1206 (sh), 1169 (m), 1104 (s), 1018 (s), 955 (s), 865
(m), 840 (m), 810 (m), 755 (m), 702 (w), 686 (m), 662
dried by refluxing for at least 24 h over P2O5
(dichloromethane) or sodium–benzophenone (n-hex-
ane) and were freshly distilled prior to use. Deuterated
solvents (CDCl3, CD2Cl2) were dried over molecular
sieves.
(m), 627 (m), 455 (s) cm−1
. Anal. Calc. for
2.2. Synthesis of bis[(benzaldehyde)(v-chloro)-
dichloro(2-propoxo)titanium(IV)] (2)
C12H19O3SCl2Ti: C, 36.25; H, 4.82. Found: C, 35.66; H,
4.74%.
Benzaldehyde (0.12 ml, 3.42 mmol) was added to a
solution of Ti(O-i-Pr)Cl3 (0.73 g, 3.42 mmol) in 25 ml
of CH2Cl2 at room temperature (r.t.). The solution
changed color from yellow to orange–yellow and was
stirred for 15 min. The solvent was removed in vacuo to
give a quantitative yield of white powder, m.p. 102.5–
104.1°C (dec.). 1H NMR (CDCl3): l 10.17 (s, 2H),
8.10–7.55 (m, 10H), 5.30 (sept, 3JHH=9.3 Hz, 2H),
1.59 (d, 3JHH=9.3 Hz, 12H) ppm. 13C{1H} NMR
(CDCl3): l 201.6 (CHO), 138.2, 133.8, 133.0, 129.7
(Ph), 94.7 (CH), 23.8 (CH3) ppm. IR (Nujol): 1683 (m),
1632 (s), 1594 (s), 1565 (s), 1315 (m), 1218 (m), 1165
(m), 1100 (s), 1013 (s), 983 (sh), 838 (m), 756 (m), 667
2.5. Synthesis of (benzaldehyde)trichloro(2-propanol)-
(2-propoxo)titanium(IV) (5)
To a colorless solution of 2 (0.94 g, 1.50 mmol) in 25
ml of CH2Cl2, 2-propanol (0.23 ml, 3.00 mmol) was
added at r.t. The solution changed color to yellow and
was stirred for 30 min. The solution was concentrated
to about 15 ml and then 20 ml of n-hexane was added
slowly to make two layers. The solution was allowed to
stand for 3 days to afford pale yellow crystals (0.65 g,
1
57.1%), m.p. 87.4–89.0°C. H NMR (CDCl3): l 10.13
(s, 1H), 8.10–7.55 (m, 5H), 4.85 (br, 2H), 1.49 (d,
3JHH=8.7 Hz, 12H) ppm. 13C{1H} NMR (CDCl3): l
199.9 (CHO), 137.4, 134.4, 132.3, 129.6 (Ph), 93.5
(CH), 23.8 (CH3) ppm. IR (Nujol): 3329 (br), 1684 (m),
1642 (s), 1595 (m), 1577 (m), 1315 (m), 1285 (m), 1261
(m), 496 (m), 460 (m) cm−1
. Anal. Calc. for
C20H26O4Cl6Ti2: C, 37.60; H, 4.10. Found: C, 37.36; H,
4.10%.

192
T.-Y. Hwang et al. / Inorganica Chimica Acta 303 (2000) 190–198
(w), 1219 (m), 1171 (m), 1105 (s), 1093 (s), 1015 (s), 917
(m), 869 (w), 835 (m), 811 (m), 753 (m), 681 (m), 659
(m), 481 (m), 465 (m), 451 (m) cm−1. Anal. Calc. for
C13H21O3Cl3Ti: C, 41.14; H, 5.58. Found: C, 41.29; H,
5.64%.
ment. The analysis values for complexes 3 and 4 are off
slightly from the requirement due to the oily nature of
these two complexes which prevent us from further
purifications.
2.7. Crystal structure determinations
2.6. Physical measurements
A pale yellow crystal of 5 of size 0.15×0.60×0.80
mm in a sealed capillary under dinitrogen atmosphere
was used for X-ray diffraction study. The diffraction
intensities were collected on a Siemens P4 diffractome-
ter equipped with graphite-monochromated Mo Ka
1H NMR spectra were obtained with a Varian Gem-
ini-200 (200 MHz) or a Varian VXR-300 (300 MHz)
spectrometer and 13C NMR spectra were recorded with
the Varian VXR-300 (75.43 MHz) spectrometer. The
1H and 13C chemical shifts were measured relative to
,
radiation (u=0.71073 A). Semi-empirical absorption
1
tetramethylsilane as the internal reference. The H vari-
correction was performed on this sample. All refine-
ments and calculations were carried out with the
Siemens SHELXTL PLUS [18] software package on an
SGI Indigo computer. The positions of heavy atoms for
the structure were determined by direct methods and
the remaining non-hydrogen atoms were located from
successive difference Fourier map calculations. The
refinements were carried out using full-matrix least-
squares techniques. All non-hydrogen atoms were
refined as individual anisotropic atoms. The hydrogen
atoms, except the hydroxy hydrogen which was also
located from the successive Fourier difference map
calculations, were considered as the riding atom on the
able-temperature (VT) NMR spectra in CD2Cl2 were
obtained with the Varian VXR-300 spectrometer and
the temperatures were calibrated with the methanol
resonances. Infrared spectra were recorded on a Hitachi
270-30 spectrometer in the region 4000–400 cm−1; the
peak positions were calibrated with the 1601.4 cm−1
peak of polystyrene. Melting points were measured
with a Bu¨chi 535 instrument and the temperatures were
not calibrated. Elemental analyses of complexes were
performed using a Heraeus CHN-O-RAPID instru-
,
carbon atom with a CꢀH bond length of 0.96 A and the
hydrogen atom temperature factors were fixed at 0.08
,
A. The hydrogen atoms were included for refinements
Table 1
in the final cycles. Two disordered 2-propyl groups with
an equal population of 0.5 were determined for the
2-propoxide ligand. The crystallographic data of the
complex 5 are summarized in Table 1.
Crystallographic data of complex 5
Formula
TiCl3O3C13H21
379.5
triclinic
Formula weight
Crystal system
Space group
(
P1
Unit cell dimensions
,
a (A)
8.976(2)
10.412(2)
11.744(2)
67.49(1)
69.18(1)
71.68(1)
927.3(3)
2
1.359
0.71073
0.896
4.0–45.0
q/2q
2534
3. Results and discussion
,
b (A)
,
c (A)
3.1. Synthesis and characterizations
h (°)
i (°)
k (°)
The synthesis of [Ti(O-i-Pr)Cl2(PhCHO)(m-Cl)]2 (2)
and its reactions with DMF, DMSO, or i -PrOH are
outlined in Scheme 1. Complex 2 can be obtained by
removing Et2O from Ti(O-i-Pr)Cl3(PhCHO)(OEt2) (1)
[14] in vacuo or synthesized directly from the reaction
of Ti(O-i-Pr)Cl3 with 1 molar equiv. of benzaldehyde.
Complex 2 reacted further with 2 molar equiv. of
various ligands, such as DMF, DMSO, or i-PrOH, to
give six-coordinate monomeric complexes 3–5, respec-
tively. Complexes 3 and 4 were obtained as orange oil
in quantitative yield and no further purifications were
performed. Complex 5 can be obtained as pale yellow
crystals. For the reaction of the complex 2 with 2-
propanol, two reaction routes leading to two different
products are possible: (1) the formation of the chloride-
or alkoxide-bridged dimeric di-alkoxide complex with
the evolution of 2 molar equiv. of HCl gas or (2) the
3
,
V (A )
Z
Dcalc (g cm−3
)
,
u(Mo Ka) (A)
Absorption coefficient (mm−1
Range (°)
)
Scan type
Reflections collected
Independent reflections
Observed reflections
Weighting scheme
2358 (Rint=1.84%)
2010 (I\2.0|(I))
w
−1=|2(F)+0.0010F2
Refined parameters
208
a
R
for significant reflections
0.043
0.064
1.57
b
Rw for significant reflections
Goodness-of-fit c
a R=[ꢀ(Fo−Fc)/ꢀFo].
b Rw=[ꢀw(Fo−Fc)2/ꢀwFo2]1/2
.
c The goodness of fit equals [ꢀw(Fo−Fc)2/(Nrflns−Nparams)]1/2
.

T.-Y. Hwang et al. / Inorganica Chimica Acta 303 (2000) 190–198
193
formation of the monomeric complex 5 via the simple
addition of 2-propanol to 2. In the reaction, the forma-
tion of 5 via the latter pathway suggests the preference
of the monomeric complex to the chloride- or the
alkoxide-bridged dimeric complex and this preference
can be attributed mainly to the better donation ability
of the alcohol than the bridging chloride or the bridg-
1
ing alkoxide ligand [14–16]. The H chemical shifts of
the carbonyl hydrogen and the 2-propoxide methyl
groups for complexes 3–5 appear upfield slightly rela-
tive to the chemical shifts for complex 2 and the 13C
chemical shifts reveal a similar trend. The upfield shifts
may reflect the better bonding of DMF, DMSO, and
i-PrOH than m-Cl− [14]. Structurally, the better donat-
ing ability of the ligand L would weaken the other
ligand X attached to the metal center by lengthening
the TiꢀX distance. Spectroscopically, the weakening
effect results in the upfield shift of the 1H and 13C
resonances. Therefore, for the DMSO complex 4, the
upfield shift of the 1H resonances relative to that for the
DMF complex 3 suggests a better donating ability of
the DMSO ligand than that of the DMF ligand. This
observation is further supported by the relative basicity
of DMSO\DMF [19]. For complex 5, an averaging
set of signals was observed for the 2-propoxide and
2-propanol ligands, indicating fast exchange of the hy-
droxy hydrogen between these two ligands [15,16].
Scheme 1.
3.2. Molecular structure of 5
The molecular structure of 5 is shown in Fig. 1 and
the selected bond distances and bond angles are listed
in Table 2. The structure of 5 shows a very short
,
TiꢀO(i-Pr) distance at 1.713(2) A (TiꢀO(1)) which is a
general feature for six-coordinate titanium complexes
containing only one alkoxide group [15,16,20–23]. Due
to the strong bonding of 2-propoxide ligand, all
O(1)ꢀTiꢀL(cis) angles bend away from the 2-propoxide
with angles ranging from 94.7(1) to 97.4(1)°. The 2-
propanol ligand is in the cis position to the 2-propoxide
,
group with a TiꢀO(2) distance of 2.105(4) A. The
Table 2
,
Selected bond lengths (A) and bond angles (°) of 5
TiꢀO(1)
TiꢀO(3)
TiꢀCl(2)
O(1)ꢀC(1)
O(2)ꢀC(4)
H···Cl(1a)
1.713(2)
2.170(2)
2.292(2)
1.470(17)
1.454(5)
2.280
TiꢀO(2)
2.105(4)
2.376(1)
2.301(1)
1.416(21)
1.221(5)
TiꢀCl(1)
TiꢀCl(3)
O(1)ꢀC(1%)
O(3)ꢀC(7)
TiꢀO(1)ꢀC(1)
TiꢀO(2)ꢀC(4)
O(1)ꢀTiꢀCl(1)
O(1)ꢀTiꢀCl(3)
O(1)ꢀTiꢀO(3)
154.2(7)
131.8(3)
94.7(1)
96.6(1)
174.6(2)
TiꢀO(1)ꢀC(1%)
TiꢀO(3)ꢀC(7)
O(1)ꢀTiꢀCl(2)
O(1)ꢀTiꢀO(2)
O(2)ꢀH···Cl(1a)
176.6(14)
134.3(3)
97.4(1)
95.1(1)
163.2
Fig. 1. Molecular structure of Ti(O-i-Pr)Cl3(PhCHO)(HO-i-Pr) (5).
Hydrogen atoms except for the hydroxy hydrogen are omitted for
clarity.

194
T.-Y. Hwang et al. / Inorganica Chimica Acta 303 (2000) 190–198
shown in Fig. 2. Only one set of rather sharp signals is
observed at 20.0°C. At 0.0°C, an upfield shoulder at l
1.47 ppm appears for the 2-propoxide methyl resonance
besides the doublet at l 1.55 ppm. This shoulder devel-
ops into a doublet at l 1.43 ppm at −20.0°C with a
relative intensity of 22%. However, the downfield
methyl doublet sharpens at this temperature with a
relative intensity of 78%. The peak corresponding to
the carbonyl hydrogens broadens slightly for tempera-
tures down to −20.0°C. At −40.0°C, in addition to
the major broad carbonyl hydrogen resonance, two
trace peaks are also seen. Similarly, small doublets of
the 2-propoxide methyls, which are barely seen on the
spectrum, suggest additional species presented in solu-
tion. At −60.0°C, the major carbonyl hydrogen reso-
nances develop into a very broad peak with shoulders
and, in the 2-propoxide methyl region, another methyl
doublet is seen at the upfield side from the major
resonances. At temperatures below −80.0°C, six dou-
blets and several small humps are seen in the 2-propox-
ide methyl region. To our surprise, 17 carbonyl
hydrogen peaks with intensities ]1% are clearly ob-
served at −90.0°C with the chemical shifts at l 10.49
(1%), 10.34 (1%), 10.30 (1%), 10.24 (2%), 10.22 (17%),
10.17 (3%), 10.14 (2%), 10.09 (9%), 10.06 (23%), 10.00
(6%), 9.98 (2%), 9.96 (3%), 9.95 (3%), 9.91 (2%), 9.88
(11%), 9.80 (14%), 9.70 (2%) ppm. In a close examina-
tion of the geometrical isomers of complex 2 with
formulae [Ti(O-i-Pr)Cl2(PhCHO)(m-Cl)]2, more than 20
geometrical isomers are possible and some of the iso-
meric species possess inequivalent PhCHO ligands
which would give two ꢀCHO signals. Taking into ac-
count the species containing two inequivalent PhCHO
ligands, the observation of 17 ꢀCHO resonances at low
temperatures suggests the presence of more than 10
geometric isomeric species in solution and these iso-
meric species undergo facile rearrangements at room
temperature.
Two mechanistic processes may account for the inter-
conversion among these isomers (Fig. 3). Mechanism
(a) involves the simultaneous breaking two of the
TiꢀCl(bridging) bonds and moving of the two axial
terminal chlorides into bridging positions. Mechanism
(b) involves the breaking of one TiꢀCl(bridging) bond
to make one metal center five-coordination followed by
the attachment of one chloride ligand on the second Ti
metal center to the five-coordinate metal center. How-
ever, the first mechanism seems unlikely due to the
limited number of isomers resulting from the lowest-en-
ergy isomer I. For example, isomer I can rearrange only
into the much higher-energy isomer II which converts
back to isomer I solely. The second mechanism is more
likely owing to the seemingly lower-energy process of
breaking only one TiꢀCl(m) bond which is trans to the
the strong 2-propoxide ligand. Furthermore, the second
process operating on both metal centers would convert
isomer I into all other isomers.
Fig. 2. 1H NMR spectra of [Ti(O-i-Pr)Cl2(PhCHO)(m-Cl)]2 (2) in
CD2Cl2 at −90.0°C at 300 MHz in (a) the ꢀCHO hydrogen region
and (b) the 2-propoxide methyl region.
benzaldehyde ligand is in the trans position to the
2-propoxide ligand with a relatively long TiꢀO(3) bond
,
distance of 2.170(2) A [24,25] and the trans position of
the benzaldehyde to the 2-propoxide ligand suggests a
relative bonding order of i-PrOH\PhCHO. The Cl(2)
atom is trans to the 2-propanol with the TiꢀCl(2)
,
distance at 2.292(2) A which is shorter as expected than
the other two TiꢀCl distances which are trans to each
other. In the solid state, complex 5 is found to be a
weakly associated dimeric species via the hydrogen
bonding from the hydroxy hydrogen to the Cl(1) of
another molecule. Due to the formation of hydrogen
bonding, the TiꢀCl(1) bond is long with a distance of
,
2.376(1) A.
1
3.3. H VT NMR study of 2
1
Complex 2 was subjected to the H VT NMR study
in CD2Cl2 and the expanded spectra at −90.0°C are

T.-Y. Hwang et al. / Inorganica Chimica Acta 303 (2000) 190–198
195
Fig. 3. Possible rearrangements of complex 2: (a) simultaneous breaking of two TiꢀCl(m) bonds and moving of TiꢀCl(t) bonds into bridging
positions; (b) bond rupture of one TiꢀCl(m) to make one metal center five-coordinate followed with the attachment of one terminal chloride on
another metal.
3.4. VT NMR studies of 3–5
nances. At −40.0°C, four sets of peaks for the 2-pro-
poxide methyls are observed at l 1.54 (17%), 1.48
(56%), 1.42 (18%), and 1.38 (9%) ppm. However, only
three slightly broad resonances are observed for the
DMF-CH3 groups at l 3.19 and 3.08 (9%), 3.16 and
3.06 (59%), and 3.11 and 3.01 (32%) ppm. The peak
with intensity 32% corresponds to two isomers of over-
lapped chemical shifts and these overlapped peaks be-
Complexes 3–5 in CD2Cl2 were also subjected to the
1H VT NMR studies for temperatures down to −
90.0°C. The expanded spectra at −80.0 or −90.0°C
are shown in Figs. 4–6. One set of resonances for 3 is
observed at RT and, at −20.0°C, a shoulder appears
for both the DMF and the 2-propoxide methyl reso-

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T.-Y. Hwang et al. / Inorganica Chimica Acta 303 (2000) 190–198
9.90 (9%) ppm are clearly observed. Due to the simplic-
ity of the benzaldehyde ꢀCHO signals, the relative
Fig. 4. 1H NMR spectra of Ti(O-i-Pr)Cl3(PhCHO)(DMF) (3) in
CD2Cl2 at −80.0°C at 300 MHz in (a) the ꢀCHO region of PhCHO
ligand; (b) the methyl region of DMF ligand, and (c) the 2-propoxide
methyl region.
come well-resolved with the relative intensities of
roughly 18% (l 3.11, 3.01 ppm) and 17% (l 3.09, 2.98
ppm) at −60.0°C. The 1H resonance of the ꢀCHO
group of the benzaldehyde ligand broadens slightly and
remains a single peak from r.t. to temperatures down to
Fig. 5. 1H NMR spectra of Ti(O-i-Pr)Cl3(PhCHO)(DMSO) (4) in
CD2Cl2 at −80.0°C at 300 MHz in (a) the ꢀCHO region; (b) the
DMSO methyl region, and (c) the 2-propoxide methyl region.
1
−60.0°C. At −80.0°C, four H signals with chemical
shifts at l 10.22 (14%), 10.18 (54%), 10.06 (24%), and

T.-Y. Hwang et al. / Inorganica Chimica Acta 303 (2000) 190–198
197
A single set of resonances is also observed for com-
plex 4 at r.t. and at 0.0°C, the DMSO methyl resonance
splits into two inequivalent peaks at l 3.03 and 2.97
ppm with intensities of 18 and 82%. However, the
2-propoxide methyl resonance remains a single doublet
down to 0.0°C and, at −20.0°C, this peak develops
into a broad resonance with an upfield shoulder.
At −40.0°C or below, three resonances for both
the 2-propoxide and the DMSO methyls are observed.
The carbonyl hydrogen peak broadens at low tempera-
tures, but it still remains a single peak down to −
60.0°C. At −80.0°C, four peaks at l 10.22 (10%),
10.17 (36%), 10.06 (16%), and 9.97 (36%) ppm are
observed. The observation of four major species is
similar to that of complex 3 with slightly different
abundances in solution. Similarly, minor peaks are also
observed.
For complex 5, the observation of a single 2-propox-
ide methyl resonance at r.t. indicates fast transfer of
the hydroxy hydrogen between the 2-propoxide and
the 2-propanol ligands. The transfer process slows
down at lower temperatures and at 0.0°C, the methyl
resonances corresponding to the 2-propoxide and the
2-propanol ligands are well resolved. These two reso-
nances remains as doublets at temperatures down to
−60.0°C and at −90.0°C, these two signals split into
several overlapped resonances. For the carbonyl hydro-
gen, a broadened peak is observed at temperatures
down to −60.0°C. At −90.0°C, besides the five
major resonances at l 10.21 (13%), 10.06 (13%),
10.01 (36%), 9.93 (br, 10%) and 9.78 (10%) ppm, six
additional resonances with intensities ranged from 2 to
5% are observed. The observation of more species than
the expected four geometric isomers is due to the
presence of the hydrogen-bonded dimeric species at low
temperatures [16]. The hydrogen-bonded dimeric spe-
cies is confirmed by the solid state structure of 5. It
should be noted that some of the minor peaks are also
likely due to other unknown species, similar to the
observations for the complexes 3 and 4 at low tempera-
tures.
Fig. 6. 1H NMR spectra of Ti(O-i-Pr)Cl3(PhCHO)(HO-i-Pr) (5) in
CD2Cl2 at −90.0°C at 300 MHz in (a) the ꢀCHO region and (b) the
2-propyl methyl region.
intensities are more reliable based on this set of reso-
nances. For the complex with formula Ti(O-i-
Pr)Cl3(PhCHO)(L), a total of four geometrical isomers
(isomers L-A, L-B, L-C, and L-D) is possible and the
observation of four major species matches the possible
number of isomers for the complex 3. Considering the
relative bonding order of −O-i-Pr\Cl−\L\Ph-
CHO, the relative energies of these isomers are in the
order of E(L-A)BE(L-B)BE(L-C)BE(L-D) with the
relative abundances of 54, 23, 14, and 9% for L=DMF
(complex 3) at −80.0°C. Due to the observation of
four major isomeric species in solution, the energy
difference between the lowest-energy isomer 3-A and
the highest-energy isomer 3-D is expected to be very
small. For complex 3, a minor peak at lꢀ10.01 ppm is
also observed. However, it is hard to justify whether
this peak is due to an unknown species in solution or
due to an impure species.

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T.-Y. Hwang et al. / Inorganica Chimica Acta 303 (2000) 190–198
[2] W.A. Nugent, R.L. Harlow, J. Am. Chem. Soc. 116 (1994) 6142.
4. Conclusions
[3] K.V. Gothelf, I. Thomsen, K.A. Jørgensen, J. Am. Chem. Soc.
118 (1996) 59.
Complexes of [Ti(O-i-Pr)Cl2(PhCHO)(m-Cl)]2 (2) and
Ti(O-i-Pr)Cl3(PhCHO)L (L=DMF (3), DMSO (4), or
i-PrOH (5)) are prepared in high yield. Though only the
lowest-energy isomer is isolated in the solid state for
[4] K. Narasaka, N. Iwasawa, M. Inoue, T. Yamada, M.
Nakashima, J. Sugimori, J. Am. Chem. Soc. 111 (1989) 5340.
[5] E.J. Corey, Y. Matsumura, Tetrahedron Lett. 32 (1991) 6289.
[6] C. Haase, C.R. Sarko, M. DiMare, J. Org. Chem. 60 (1995)
1777.
[7] K.V. Gothelf, R.G. Hazell, K.A. Jørgensen, J. Am. Chem. Soc.
117 (1995) 4435.
[8] D. Seebach, R.E. Marti, T. Hintermann, Helv. Chim. Acta 79
(1996) 1710.
[9] C.N. Caughlan, H.S. Smith, W. Katz, W. Hodgson, R.W.
Crowe, J. Am. Chem. Soc. 73 (1951) 5652.
[10] D.C. Bradley, C.E. Holloway, Inorg. Chem. 3 (1964) 1163.
[11] S.F. Pederson, J.C. Dewan, R.R. Eckmann, K.B. Sharpless, J.
Am. Chem. Soc. 109 (1987) 1279.
[12] N. Bagget, D.S.P. Poolton, W.B. Jennings, J. Chem. Soc., Dal-
ton Trans. (1979) 1128.
[13] R.C. Fay, A.F. Lindmark, J. Am. Chem. Soc. 105 (1983) 2118.
[14] H.-M. Gau, C.-S. Lee, C.-C. Lin, M.-K. Jiang, Y.-C. Ho, C.-N.
Kuo, J. Am. Chem. Soc. 118 (1996) 2936.
1
complex 5, the H VT NMR studies of the complexes
2–5 reveal that these complexes are highly dynamic in
solution with the observation of several isomeric species
in solution at low temperatures. The dynamic behavior
is a general feature for titanium alkoxides containing a
relatively weak-coordinated ligand like organic car-
bonyl or bridging chloride. For titanium complexes
containing a diolate ligand, they are also dynamic in
solution. Furthermore, the presence of several isomers
in solution for complexes 2–5 suggests small energy
differences among the geometric isomers. For complex
5, in addition to the four major monomeric geometrical
isomers, seven other species, which are the hydrogen-
bonded dimeric species or some unknown species, are
observed in solution. The solid state structure of 5
suggests a relative bonding of −O-i-Pr\Cl−\HO-i-
Pr\PhCHO.
[15] Y.-T. Wu, Y.-C. Ho, C.-C. Lin, H.-M. Gau, Inorg. Chem. 35
(1996) 5948.
[16] C.-S. Lee, C.-N. Kuo, M.-Y. Shao, H.-M. Gau, Inorg. Chim.
Acta 285 (1999) 254.
[17] D.C. Bradley, D.C. Hancock, W. Wardlaw, J. Chem. Soc. (1952)
2773.
[18] G.M. Sheldrick, In Crystallographic Computing 3: Data Collec-
tion, Structure Determination, Proteins, and Databases, Claren-
don Press, New York, 1985, p. 175.
Acknowledgements
[19] W.B. Jensen, Chem. Rev. 78 (1978) 1.
[20] D.A. Wright, D.A. Williams, Acta Crystallogr., Sect. B 24 (1968)
1107.
[21] A.R. Siedle, J.C. Huffman, Inorg. Chem. 29 (1990) 3131.
[22] B. Bachand, F. Be´langer-Garie´py, J.D. Wuest, Organometallics
9 (1990) 2860.
The authors would like to thank the National Science
Council of the Republic of China for financial support
(Grant no. NSC 88-2113-M-005-021).
[23] T.J. Boyle, R.W. Schwartz, R.J. Doedens, J.W. Ziller, Inorg.
Chem. 34 (1995) 1110.
References
[24] G. Meier, U. Seipp, R. Boses, Tetrahedron Lett. 28 (1987) 4515.
[25] B. Bachand, J.D. Wuest, Organometallics 10 (1991) 2015.
[1] A. Hafner, R.O. Duthaler, R. Marti, G. Rihs, P. Rothe-Streit, F.
Scharsenbach, J. Am. Chem. Soc. 114 (1992) 2321.
.
.