Synthesis, structure, and catalytic activity of titanium complexes with chiral biaryl Schiff-base ligands

Article abstract of DOI:10.1016/j.ica.2013.04.008

A series of chiral organo-titanium complexes have been prepared from the reaction between Ti(OⁱPr)₄ and chiral biaryl Schiff-base ligands 1H₂-12H. The steric demand of the ligand plays an important role in the formation of

Full text of DOI:10.1016/j.ica.2013.04.008

Inorganica Chimica Acta 402 (2013) 140–155
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Inorganica Chimica Acta
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Synthesis, structure, and catalytic activity of titanium complexes
with chiral biaryl Schiff-base ligands
Liang Chen a, Ning Zhao a, Qiuwen Wang a, Guohua Hou a, Haibin Song b, Guofu Zi a,
⇑
a Department of Chemistry, Beijing Normal University, Beijing 100875, China
b State Key Laboratory of Elemento-Organic Chemistry, Nankai University, Tianjin 300071, China
a r t i c l e i n f o
a b s t r a c t
A series of chiral organo-titanium complexes have been prepared from the reaction between Ti(OiPr)4 and
chiral biaryl Schiff-base ligands 1H2–12H. The steric demand of the ligand plays an important role in the
formation of the titanium complexes. For example, treatment of ligand 1H2 with 1 equiv of Ti(OiPr)4 in
toluene at room temperature gives, after recrystallization from a toluene solution, the chiral bis-ligated
titanium complex (L1)2Ti (14). While under similar reaction conditions, the more bulky ligands 2H2, 4H2,
and 6H2 form the mono-ligated titanium complexes (L2)Ti(OiPr)2 (15), (L4)Ti(OiPr)2 (19), and (L6)Ti(Oi-
Pr)2 (22), respectively, in good yields. The mono-ligated titanium alkoxides can be converted to bis-
ligated complex via ligand redistribution reaction. For one instance, treatment of mono-ligated complex
(L2)Ti(OiPr)2 (15) in benzene at 60 °C results in the isolation of the bis-ligated complex (L2)2Ti (16) in 92%
yield. All titanium complexes have been characterized by various spectroscopic techniques and elemental
analyses. The solid-state structures of complexes 14–21, 23, 24 and 29 have further been confirmed by
X-ray diffraction analyses. The titanium complexes are active catalysts for the asymmetric hydrophos-
phonylation of aromatic aldehydes with moderate enantioselectivities.
Article history:
Received 22 February 2013
Received in revised form 1 April 2013
Accepted 2 April 2013
Available online 18 April 2013
Keywords:
Chiral Schiff-base ligand
Titanium complex
Synthesis
Crystal structure
Asymmetric hydrophosphonylation
Ó 2013 Elsevier B.V. All rights reserved.
1. Introduction
and lanthanide complexes that are useful catalysts for a wide range
of transformations [36–62]. Furthermore we demonstrated that the
Hydrophosphonylation is an economical process in which a
dialkyl phosphite is added to carbonyl or imine compounds
biaryl-based bis-ligated lanthanide amides [(S)-2-Me2N-C20H12-20-
(NCHC4H3N)]2LnN(SiMe3)2 with C1-symmetric N3-ligand are more
effective chiral catalysts for the enantioselective hydroamination/
cyclization reaction than those [(R)-C20H12(NCHC4H3N)2]-
LnN(SiMe3)2(thf) (Ln = Sm, Y, Yb) with C2-symmetric N4-ligands
[39,41]. In our ongoing research, we are now focusing on the prep-
aration of the type of bis-ligated catalysts coordinated by chiral
C1-symmetric tridentate ligands. In our endeavor to further explore
the biaryl-backbones, we have recently extended our work to chiral
C1-symmetric ligands, 1H2–6H2 and 7H (Fig. 1), in which can bind in
tridentate fashion. In the literatures, binaphthyl-based salicyaldi-
mine NOO-type titanium complexes have been shown that they
are efficient chiral cataysts for the asymmetric aldol additions
[63–66] and hetero-Diels–Alder reactions [67,68], in which
excellent enantioselectivities have been obtained. In this paper,
we report on some observations concerning the coordination
chemistry of the ligands 1H2–6H2 and 7H (Fig. 1), which are derived
from (R)-2-amino-20-hydroxy-1,10-binaphthyl or (R)-2-amino-20-
hydroxy-6,60-dimethyl-1,10-biphenyl, with titanium isopropoxide,
and the use of the resulting complexes as catalysts in asymmetric
hydrophosphonylation. For comparison, the C2-symmetric ligands
8H2–11H2 and C1-symmetric ligand 12H (Fig. 1), which are
derived from (R)-2,20-diamino-6,60-dimethyl-1,10-biphenyl or
(Pudovik reaction), leading to the formation of the
a-hydroxy or
a-amino phosphonates that are found in numerous biologically
and pharmacologically active compounds [1–5]. Therefore, it is
not surprising that recent efforts have focused on the development
of chiral catalysts for the asymmetric hydrophosphonylation of
aldehydes [6–10]. Since the pioneering work of Shibuya and co-
workers in 1993 [11,12], many chiral catalysts based on lanthanide
[12–17], aluminum [18–26], titanium [11,15,16,27–33] and late
transition metals [34,35] have extensively been studied. Among
these, the chiral titanium catalysts have been identified as very
promising candidates for this transformation [11,15,16,27–33].
However, even within this class, successful catalysts affording
significant stereoselectivity are rare [31]. Thus, the development
of new chiral titanium catalysts for the enantioselective
hydrophosphonylation is still
goal.
a desirable and challenging
Recently, we have developed a series of chiral biaryl-based mul-
ti-dentate ligands, and their Zr(IV), V(IV), Ta(V), Rh(III), Ir(III), Ni(II)
⇑
Corresponding author. Tel.: +86 10 5880 6051; fax: +86 10 5880 2075.
E-mail address: gzi@bnu.edu.cn (G. Zi).
0020-1693/$ - see front matter Ó 2013 Elsevier B.V. All rights reserved.
http://dx.doi.org/10.1016/j.ica.2013.04.008

L. Chen et al. / Inorganica Chimica Acta 402 (2013) 140–155
141
N
N
N
OH
OH
HO
OH
HO
HO
CMe3
1H2
2H2
3H2
CMe3
CMe3
N
N
N
OH
OH
HO
OH
HO
HO
CMe3
CMe3
4H2
5H2
6H2
Me3C
HO
HO
N
N
N
N
N
N
OH
HO
HO
Me3C
9H2
8H2
7H
Me3C
HO
Me3C
Me3C
HO
HO
CMe3
CMe3
N
N
N
N
N
NH2
CMe3
HO
HO
12H
Me3C
Me3C
10H2
11H2
Fig. 1. Chiral Schiff-base ligands.
(R)-2,20-diamino-1,10-binaphthyl, respectively, will also be in-
cluded in this contribution.
recorded on a Bruker AV 400 spectrometer. All chemical shifts are re-
ported in d units with reference to the residual protons of the deuter-
ated solvents. HPLC analyses were conducted on a Shimadzu Series
SPD-20A with UV–Vis detector using a Chiralcel AS-H or AD-H or
OD-H column (length: 25 cm, inner diameter: 4.6 mm, particle size:
2. Experimental
5 lm). Retention time was given in minutes. Melting points were
2.1. General methods
measured on an X-6 melting point apparatus and were uncorrected.
Elemental analyses were performed on a Vario EL elemental
analyzer.
Titanium complexes and catalytic reactions were performed un-
der an atmosphere of dry dinitrogen with rigorous exclusion of air
and moisture using standard Schlenk or cannula techniques, or in
a glovebox. All organic solvents were freshly distilled from sodium
benzophenone ketyl immediately prior to use. (R)-2-amino-20-hy-
droxy-1,10-binaphthyl [40], (R)-5,50,6,60,7,70,8,80-octahydro-2-ami-
no-20-hydroxy-1,10-binaphthyl [40], (R)-2-amino-20-hydroxy-6,
60-dimethyl-1,10-biphenyl [40], (R)-2,20-diamino-6,60-dimethyl-
1,10-biphenyl [56], (R)-2,20-diamino-1,10-binaphthyl [56], 9H2 [56],
10H2 [56] and 11H2 [56] were prepared according to the literature
methods. All chemicals were purchased from Aldrich Chemical Co.
and Beijing Chemical Co., and were used as received unless other-
wise noted. Infrared spectra were obtained from KBr pellets on an
Avatar 360 Fourier transform spectrometer. 1H NMR spectra were
2.2. Preparation of 1H2
Modified method [69]. Salicylaldehyde (1.22 g, 10.0 mmol) was
mixed with (R)-2-amino-20-hydroxy-1,10-binaphthyl (2.85 g,
10.0 mmol) in dry toluene (50 mL). A few 4 Å molecular sieves
were added, and the solution was warmed up to 70 °C and kept
for two days at this temperature. The solution was filtered, and
the filtrate was concentrated to 10 mL. Yellow microcrystals 1H2
were isolated when this solution was kept at ꢀ20 °C for two days.
Yield: 3.31 g (85%). M.p.: 120–122 °C. 1H NMR (C6D6): d 12.45
(s, 1H, OH), 8.23 (s, 1H, CH@N), 7.83 (m, 2H, aryl), 7.74 (m, 2H,
aryl), 7.57 (d, J = 8.4 Hz, 1H, aryl), 7.36 (m, 1H, aryl), 7.28

142
L. Chen et al. / Inorganica Chimica Acta 402 (2013) 140–155
(m, 2H, aryl), 7.17 (m, 2H, aryl), 7.11 (m, 2H, aryl), 6.96–6.83 (m,
3H, aryl), 6.62 (t, J = 7.2 Hz, 1H, aryl), 4.73 (s, 1H OH). These spec-
troscopic data were in agreement with those reported in the liter-
ature [69].
2.66 g (84%). M.p.: 120–122 °C. 1H NMR (C6D6): d 12.67 (s, 1H, OH),
8.21 (s, 1H, CH@N), 7.17 (m, 2H, aryl), 7.09 (d, J = 7.5 Hz, 1H, aryl),
7.01 (m, 3H, aryl), 6.92 (d, J = 7.6 Hz, 1H, aryl), 6.86 (d, J = 8.1 Hz,
1H, aryl), 6.81 (d, J = 7.9 Hz, 1H, aryl), 6.69 (m, 1H, aryl), 4.32 (s,
1H, OH), 2.07 (s, 3H, CH3), 2.03 (s, 3H, CH3). These spectroscopic
data were in agreement with those reported in the literature [70].
2.3. Preparation of 2H2
Modified method [67]. 3-tert-Butylsalicylaldehyde (1.78 g,
10.0 mmol) was mixed with (R)-2-amino-20-hydroxy-1,10-binaph-
thyl (2.85 g, 10.0 mmol) in dry toluene (50 mL). A few 4 Å molecu-
lar sieves were added, and the solution was warmed up to 70 °C
and kept for two days at this temperature. The solution was filtered
and the solvent was removed under reduced pressure. The residue
was purified by column chromatography (n-hexane/ethyl ace-
tate = 5:1) to give 2H2 as a yellow solid. Yield: 4.09 g (92%). M.p.:
86–88 °C. 1H NMR (C6D6): d 13.28 (s, 1H, OH), 8.31 (s, 1H, CH@N),
7.80 (m, 4H, aryl), 7.62 (d, J = 8.4 Hz, 1H, aryl), 7.38 (d, J = 8.9 Hz,
1H, aryl), 7.22 (m, 5H, aryl), 7.12 (m, 2H, aryl), 6.87 (d, J = 7.5 Hz,
1H, aryl), 6.71 (t, J = 7.6 Hz, 1H, aryl), 4.52 (br s, 1H, OH), 1.45 (s,
9H, CH3). These spectroscopic data were in agreement with those
reported in the literature [67].
2.7. Preparation of 6H2
This compound was prepared as an orange solid from the
reaction of 3,5-di-tert-butylsalicylaldehyde (2.34 g, 10.0 mmol)
with (R)-2-amino-20-hydroxy-6,60-dimethyl-1,10-biphenyl (2.13 g,
10.0 mmol) in dry toluene (50 mL) in the presence of 4 Å molecular
sieves at 70 °C and purified by flash column chromatography
(n-hexane/ethyl acetate = 5:1) using a similar procedure as in the
synthesis of 2H2. Yield: 3.65 g (85%). M.p.: 75–77 °C. 1H NMR
(C6D6): d 13.29 (s, 1H, OH), 8.28 (s, 1H, CH@N), 7.62 (d, J = 1.9 Hz,
1H, aryl), 7.21 (t, J = 7.7 Hz, 2H, aryl), 7.10 (d, J = 8.4 Hz, 2H, aryl),
6.92 (d, J = 7.4 Hz, 1H, aryl), 6.86 (t, J = 7.0 Hz, 2H, aryl), 4.54 (br
s, 1H, OH), 2.09 (s, 3H, CH3), 2.03 (s, 3H, CH3), 1.62 (s, 9H, CH3),
1.40 (s, 9H, CH3). These spectroscopic data were in agreement with
those reported in the literature [70].
2.4. Preparation of 3H2
2.8. Preparation of 7H
This compound was prepared as a yellow solid from the reac-
tion of salicylaldehyde (1.22 g, 10.0 mmol) with (R)-
5,50,6,60,7,70,8,80-octahydro-2-amino-20-hydroxy-1,10-binaphthyl
(2.93 g, 10.0 mmol) in dry toluene (50 mL) in the presence of 4 Å
molecular sieves at 70 °C and recrystallization from a solvent mix-
ture of toluene and n-hexane (1:4) by a similar procedure as in the
synthesis of 1H2. Yield: 3.38 g (85%). M.p.: 162–164 °C. 1H NMR
(C6D6): d 12.72 (s, 1H, OH), 8.32 (s, 1H, CH@N), 7.07 (t, J = 8.4 Hz,
2H, aryl), 7.01 (m, 2H, aryl), 6.93 (d, J = 8.2 Hz, 1H, aryl), 6.88 (d,
J = 8.2 Hz, 1H, aryl), 6.70 (m, 2H, aryl), 4.26 (br s, 1H, OH), 2.80
(m, 4H, CH2), 2.64 (m, 2H, CH2), 2.40 (m, 2H, CH2), 1.77–1.59 (m,
This compound was prepared as a yellow solid from the
reaction of pyridine-2-carboxaldehyde (1.07 g, 10.0 mmol) with
(R)-2-amino-20-hydroxy-1,10-binaphthyl (2.85 g, 10.0 mmol) in
dry toluene (50 mL) in the presence of 4 Å molecular sieves at
70 °C and recrystallization from a toluene solution by a similar
procedure as in the synthesis of 1H2. Yield: 2.99 g (80%). M.p.:
180–182 °C. 1H NMR (C6D6): d 8.62 (s, 1H, CH@N), 7.88 (s, 1H, aryl),
7.61 (m, 2H, aryl), 7.52 (m, 5H, aryl), 7.24 (d, J = 8.0 Hz, 1H, aryl),
7.10–6.95 (m, 5H, aryl), 6.56 (t, J = 6.8 Hz, 1H, aryl), 6.24 (m, 1H,
aryl); the proton of the OH group was not observed. These spectro-
scopic data were in agreement with those reported in the literature
[69].
8H, CH2). IR (KBr, cmꢀ1):
m 3412 (m), 2929 (s), 1617 (s), 1590 (s),
1493 (s), 1469 (s), 1453 (s), 1277 (s), 1205 (s), 1152 (s), 936 (s),
807 (s), 757 (s). Anal. Calc. for C27H27NO2: C, 81.58; H, 6.85; N,
3.52. Found: C, 81.61; H, 6.82; N, 3.56%.
2.9. Preparation of 8H2
2.5. Preparation of 4H2
This compound was prepared as an orange solid from the reac-
tion of salicylaldehyde (2,44 g, 20.0 mmol) with (R)-2,20-diamino-
6,60-dimethyl-1,1-biphenyl (2.12 g, 10 mmol) in dry toluene
(50 mL) in the presence of 4 Å molecular sieves at 70 °C and puri-
fied by flash column chromatography (n-hexane/ethyl ace-
tate = 5:1) using a similar procedure as in the synthesis of 2H2.
Yield: 3.36 g (80%). M.p.: 185–187 °C. 1H NMR (C6D6): d 12.65 (s,
2H, OH), 8.17 (s, 2H, N@CH), 7.18 (m, 4H, aryl), 6.87 (m, 4H, aryl),
6.78 (m, 4H, aryl), 6.54 (m, 2H, aryl), 2.00 (s, 6H, CH3). These spec-
troscopic data were in agreement with those reported in the liter-
ature [71].
This compound was prepared as a yellow solid from the reac-
tion of 3,5-di-tert-butylsalicylaldehyde (2.34 g, 10.0 mmol) with
(R)-5,50,6,60,7,70,8,80-octahydro-2-amino-20-hydroxy-1,10-binaph-
thyl (2.93 g, 10.0 mmol) in dry toluene (50 mL) in the presence of
4 Å molecular sieves at 70 °C and purified by flash column chroma-
tography (n-hexane/ethyl acetate = 5:1) using a similar procedure
as in the synthesis of 2H2. Yield: 4.13 g (81%). M.p.: 92–94 °C. 1H
NMR (C6D6): d 13.46 (s, 1H, OH), 8.37 (s, 1H, CH@N), 7.62 (d,
J = 1.8 Hz, 1H, aryl), 7.11 (m, 3H, aryl), 6.95 (m, 2H, aryl), 4.26 (s,
1H, OH), 2.87 (m, 2H, CH2), 2.75 (m, 2H, CH2), 2.63 (m, 2H, CH2),
2.44 (m, 2H, CH2), 1.84 (m, 4H, CH2), 1.64 (s, 9H, CH3), 1.62 (m,
2.10. Preparation of 12H
4H, CH2), 1.41 (s, 9H, CH3). IR (KBr, cmꢀ1):
m 3435 (m), 2955 (s),
2930 (s), 2859 (s), 1617 (s), 1594 (s), 1473 (s), 1438 (s), 1249 (s),
1171 (s), 1025 (s), 806 (s). Anal. Calc. for C35H43NO2: C, 82.47; H,
8.50; N, 2.75. Found: C, 82.51; H, 8.52; N, 2.76%.
A drop of H2O was added to a toluene (5 mL) solution of 10H2
(0.65 g, 1 mmol). The solution was warmed up to 65 °C and kept
for one hour at this temperature. Solvent was removed, and the
residue was purified by flash column chromatography (n-hexane/
ethyl acetate = 5:1) to give 12H as a bright yellow solid. Yeild:
0.41 g (95%). M.p.: 93–95 °C. 1H NMR (C6D6): d 13.40 (s, 1H, OH),
8.24 (s, 1H, N@CH), 7.46 (s, 1H, aryl), 7.13 (m, 4H, aryl), 6.75 (m,
2H, aryl), 6.37 (s, 1H, aryl), 2.96 (s, 2H, NH), 2.03 (s, 3H, CH3),
1.99 (s, 3H, CH3), 1.53 (s, 9H, CH3), 1.25 (s, 9H, CH3). IR (KBr,
2.6. Preparation of 5H2
This compound was prepared as an orange solid from the reac-
tion of salicylaldehyde (1.22 g, 10.0 mmol) with (R)-2-amino-20-
hydroxy-6,60-dimethyl-1,10-biphenyl (2.13 g, 10.0 mmol) in dry
toluene (50 mL) in the presence of 4 Å molecular sieves at 70 °C
and recrystallization from a solvent mixture of toluene and n-hex-
ane (10:1) by a similar procedure as in the synthesis of 1H2. Yield:
cmꢀ1):
m 3439 (s), 3420 (s), 3346 (s), 2957 (s), 2905 (s), 2867 (s),
1618 (s), 1568 (s), 1460 (s), 1441 (s), 1360 (s), 1250 (s), 1175 (s),
945 (s), 790 (s). Anal. Calc. for C29H36N2O: C, 81.27; H, 8.47; N,

L. Chen et al. / Inorganica Chimica Acta 402 (2013) 140–155
143
6.54. Found: C, 81.24; H, 8.46; N, 6.44%. This compound could also
be prepared in 40% yield by condensation of 3,5-di-tert-butylsali-
cylaldehyde with 1 equiv of (R)-2,20-diamino-6,60-dimethylbi-
phenyl in the presence of 4 Å molecular sieves in dry toluene at
70 °C, and purification by flash column chromatography (n-hex-
ane/ethyl acetate = 5:1) by a similar procedure as in the synthesis
of 2H2.
with stirring at room temperature. The resulting yellow solution
was stirred at room temperature for one day. The solution was fil-
tered, and the filtrate was concentrated to about 2 mL. Yellow crys-
tals, which were identified as 17ꢁ18 by X-ray diffraction analysis,
were isolated after this solution was kept at room temperature
for three days. Yield: 0.28 g (60%). M.p: 170–172 °C (dec.). 17: 1H
NMR (C6D6): 8.01 (s, 1H, N@CH), 7.08–5.80 (m, 8H, aryl), 5.24 (m,
1H, OCH), 4.75 (m, 1H, OCH), 2.69–1.25 (m, 28H, CH2 and CH3).
18: 1H NMR (C6D6): 8.15 (s, 2H, N = CH), 7.08–5.80 (m, 16H, aryl),
2.11. Preparation of (L1)2Ti (14)
2.69–1.25 (m, 32H, CH2). IR (KBr, cmꢀ1):
m 2962 (s), 1606 (s),
A toluene solution (10 mL) of 1H2 (0.39 g, 1.0 mmol) was slowly
added to a toluene solution (10 mL) of Ti(OiPr)4 (0.28 g, 1.0 mmol)
with stirring at room temperature. The resulting yellow solution
was stirred at room temperature for one day. The solution was fil-
tered, and the filtrate was concentrated to about 2 mL. Yellow
microcrystals 14 were isolated when this solution was kept at
room temperature for three days. Yield: 0.29 g (70%). M.p.:
120–122 °C (dec.). 1H NMR (C6D6): d 7.77 (s, 2H, N@CH), 7.68 (m,
2H, aryl), 7.56 (m, 4H, aryl), 7.35 (m, 6H, aryl), 6.99 (m, 10H, aryl),
6.66 (m, 2H, aryl), 6.32 (m, 6H, aryl), 5.74 (m, 2H, aryl); these spec-
troscopic data were in agreement with those reported in the liter-
1542 (m), 1439 (s), 1260 (s), 1092 (s), 1018 (s), 799 (s). Anal. Calc.
for C87H89N3O8Ti2: C, 74.62; H, 6.41; N, 3.00. Found: C, 74.65; H,
6.46; N, 2.96%. The 1H NMR spectrum of the mixture 17ꢁ18 could
not be assigned unambiguously, but on the basis of the analogous
complexes 15 and 16, their CH = N groups were assigned, which
showed that the ratio of 17/18 is 1:1.
2.15. Preparation of (L4)Ti(OiPr)2 (19)
This compound was prepared as yellow crystals from the reac-
tion of 4H2 (0.51 g, 1.0 mmol) with Ti(OiPr)4 (0.28 g, 1.0 mmol) in
toluene (20 mL) and recrystallization from a toluene solution by
a similar procedure as in the synthesis of 14. Yield: 0.55 g (82%).
M.p.: 182–184 °C (dec.). 1H NMR (C6D6): d 8.19 (s, 1H, N@CH),
7.56 (s, 1H, aryl), 7.14 (d, J = 8.2 Hz, 1H, aryl), 7.09 (d, J = 7.9 Hz,
1H, aryl), 6.94 (d, J = 7.9 Hz, 1H, aryl), 6.89 (d, J = 8.2 Hz, 1H, aryl),
6.85 (s, 1H, aryl), 5.32 (m, 1H, OCH), 4.80 (m, 1H, OCH), 2.74 (m,
4H, CH2), 2.44 (m, 2H, CH2), 2.30 (m, 2H, CH2), 1.65 (s, 9H, CH3),
1.59 (d, J = 6.1 Hz, 3H, CH3), 1.55 (d, J = 6.1 Hz, 3H, CH3), 1.46 (m,
8H, CH2), 1.29 (d, J = 6.1 Hz, 3H, CH3), 1.19 (s, 9H, C(CH3)3), 1.08
ature [72]. IR (KBr, cmꢀ1):
m 2962 (s), 1598 (s), 1460 (s), 1422 (s),
1260 (s), 1091 (s), 1020 (s), 870 (s), 799 (s). Anal. Calc. for C54H34-
N2O4Ti: C, 78.83; H, 4.17; N, 3.40. Found: C, 78.85; H, 4.16; N,
3.34%. Yellow crystals 14ꢁC7H8ꢁDME suitable for X-ray structural
analysis were grown from a solvent mixture of toluene and DME
(10:1).
2.12. Preparation of (L2)Ti(OiPr)2 (15)
This compound was prepared as yellow crystals from the reac-
tion of 2H2 (0.45 g, 1.0 mmol) with Ti(OiPr)4 (0.28 g, 1.0 mmol) in
toluene (20 mL) and recrystallization from a toluene solution by
a similar procedure as in the synthesis of 14. Yield: 0.40 g (65%).
M.p.: 140–142 °C (dec.). 1H NMR (C6D6): d 7.92 (s, 1H, CH@N),
7.79 (m, 2H, aryl), 7.64 (d, J = 10.2 Hz, 1H, aryl), 7.58 (m, 2H, aryl),
7.47 (d, J = 8.8 Hz, 1H, aryl), 7.41 (d, J = 8.4 Hz, 1H, aryl), 7.29 (d,
J = 7.5 Hz, 1H, aryl), 7.25 (t, J = 7.5 Hz, 1H, aryl), 7.10 (t, J = 7.2 Hz,
1H, aryl), 7.04 (m, 2H, aryl), 6.98 (t, J = 7.4 Hz, 1H, aryl), 6.49 (t,
J = 7.6 Hz, 1H, aryl), 6.42 (d, J = 6.5 Hz, 1H, aryl), 5.27 (m, 1H,
OCH), 4.74 (m, 1H, OCH), 1.61 (s, 9H, CH3), 1.58 (d, J = 6.0 Hz, 3H,
CH3), 1.56 (d, J = 6.0 Hz, 3H, CH3), 1.30 (d, J = 6.0 Hz, 3H, CH3),
(d, J = 6.1 Hz, 3H, CH3). IR (KBr, cmꢀ1):
m 2960 (s), 2922 (s), 1556
(s), 1469 (s), 1258 (s), 1113 (s), 1018 (s), 988 (s), 810 (s). Anal. Calc.
for C41H55NO4Ti: C, 73.09; H, 8.23; N, 2.08. Found: C, 73.15; H,
8.25; N, 2.04%.
2.16. Preparation of (L5)Ti(OiPr)2ꢁ(L5)2Ti (20ꢁ21)
This compound was prepared as yellow crystals from the reac-
tion of 5H2 (0.32 g, 1.0 mmol) with Ti(OiPr)4 (0.28 g, 1.0 mmol) in
toluene (20 mL) and recrystallization from a toluene solution by
a similar procedure as in the synthesis of 17ꢁ18. Yield: 0.24 g
(63%). M.p.: 185–187 °C (dec.). 20: 1H NMR (C6D6): d 7.99 (s, 1H,
N@CH), 7.10 (m, 1H, aryl), 7.06 (m, 1H, aryl), 7.02 (m, 1H, aryl),
6.94 (m, 3H, aryl), 6.75 (m, 1H, aryl), 6.66 (m, 3H, aryl), 5.29 (m,
1H, OCH), 4.80 (m, 1H, OCH), 2.16 (s, 3H, CH3), 2.12 (s, 3H, CH3),
1.62 (br s, 6H, CH3), 1.16 (br s, 6H, CH3). 21: 1H NMR (C6D6): d
7.85 (s, 2H, N@CH), 7.41 (m, 2H, aryl), 7.00 (m, 4H, aryl), 6.88 (m,
4H, aryl), 6.80 (m, 4H, aryl), 6.62 (m, 4H, aryl), 6.51 (m, 2H, aryl),
1.27 (d, J = 6.0 Hz, 3H, CH3). IR (KBr, cmꢀ1):
m 2962 (s), 1606 (m),
1586 (m), 1548 (m), 1455 (m), 1260 (s), 1090 (s), 1018 (s), 799
(s). Anal. Calc. for C37H39NO4Ti: C, 72.90; H, 6.45; N, 2.30. Found:
C, 72.85; H, 6.46; N, 2.34%.
2.13. Preparation of (L2)2Ti (16)
2.25 (s, 6H, CH3), 1.91 (s, 6H, CH3). IR (KBr, cmꢀ1):
m 2962 (s),
A benzene solution (2 mL) of 15 (61 mg, 0.1 mmol) was warmed
up to 60 °C and kept for one hour at this temperature. Yellow crys-
tals, which were identified as (L2)2Ti (16) by X-ray diffraction anal-
ysis, were isolated in 92% yield (43 mg) after this solution was
stood at room temperature for one day. M.p.: 266–268 °C (dec.).
1H NMR (C6D6): d 8.51 (s, 2H, CH@N), 8.12 (m, 2H, aryl), 7.63 (m,
2H, aryl), 7.38 (m, 4H, aryl), 7.08 (m, 10H, aryl), 6.81 (m, 6H, aryl),
6.70 (m, 2H, aryl), 6.48 (m, 2H, aryl), 6.28 (m, 2H, aryl), 1.42 (s, 18H,
1604 (m), 1439 (m), 1260 (s), 1091 (s), 1019 (s), 798 (s). Anal. Calc.
for C69H65N3O8Ti2: C, 71.44; H, 5.65; N, 3.62. Found: C, 71.45; H,
5.56; N, 3.64%. The 1H NMR spectrum of the mixture 20ꢁ21 could
not be assigned unambiguously, but according to the analogous
complexes 15 and 16, their CH@N groups were assigned, which
showed that the ratio of 20/21 is 1:1.
2.17. Preparation of (L5)2Ti (21)
CH3). IR (KBr, cmꢀ1):
m 2959 (s), 1603 (m), 1584 (m), 1541 (m),
1449 (m), 1408 (m), 1260 (s), 1089 (s), 1019 (s), 798 (s). Anal. Calc.
for C62H50N2O4Ti: C, 79.65; H, 5.39; N, 3.00. Found: C, 79.55; H,
5.46; N, 2.94%.
A benzene solution (2 mL) of mixture 20ꢁ21 (232 mg, 0.2 mmol)
was warmed up to 60 °C and kept for one hour at this temperature.
Yellow microcrystals were isolated in 90% yield (183 mg) after this
solution was kept at room temperature for two days. M.p.: 280–
282 °C (dec.). 1H NMR (C6D6): d 7.85 (s, 2H, N@CH), 7.41 (m, 2H,
aryl), 7.00 (m, 4H, aryl), 6.88 (m, 4H, aryl), 6.80 (m, 4H, aryl),
6.62 (m, 4H, aryl), 6.51 (m, 2H, aryl), 2.25 (s, 6H, CH3), 1.91 (s,
2.14. Preparation of (L3)Ti(OiPr)2ꢁ(L3)2Ti (17ꢁ18)
A toluene solution (10 mL) of 3H2 (0.40 g, 1.0 mmol) was slowly
added to a toluene solution (10 mL) of Ti(OiPr)4 (0.28 g, 1.0 mmol)
6H, CH3). IR (KBr, cmꢀ1):
m 2964 (s), 1607 (s), 1544 (s), 1430 (s),

144
L. Chen et al. / Inorganica Chimica Acta 402 (2013) 140–155
1376 (s), 1260 (s), 1093 (s), 1019 (s), 796 (s). Anal. Calc. for C42H34-
N2O4Ti: C, 74.34; H, 5.05; N, 4.13. Found: C, 74.35; H, 5.09; N,
4.04%.
800 (s). Anal. Calc. for C38H56N2O4Ti: C, 69.92; H, 8.65; N, 4.29.
Found: C, 69.90; H, 8.66; N, 4.34%.
2.22. Preparation of (L8)Ti(OiPr)2 (26)
2.18. Preparation of (L6)Ti(OiPr)2 (22)
This compound was prepared as yellow microcrystals from the
reaction of 8H2 (0.42 g, 1.0 mmol) with Ti(OiPr)4 (0.28 g, 1.0 mmol)
in toluene (20 mL) and recrystallization from a toluene solution by
a similar procedure as in the synthesis of 14. Yield: 0.40 g (68%).
M.p.: 155–157 °C (dec.). 1H NMR (C6D6): d 7.64 (s, 2H, N@CH),
7.22 (d, J = 6.4 Hz, 2H, aryl), 7.05 (t, J = 7.2 Hz, 4H, aryl), 6.90 (d,
J = 4.8 Hz, 2H, aryl), 6.81 (d, J = 6.8 Hz, 2H, aryl), 6.62 (d,
J = 6.4 Hz, 2H, aryl), 6.43 (m, 2H, aryl), 4.96 (m, 2H, OCH), 1.79 (s,
6H, CH3), 1.29 (br s, 6H, CH3), 1.22 (br s, 6H, CH3). IR (KBr, cmꢀ1):
This compound was prepared as yellow microcrystals from the
reaction of 6H2 (0.43 g, 1.0 mmol) with Ti(OiPr)4 (0.28 g, 1.0 mmol)
in toluene (20 mL) and recrystallization from a toluene solution by
a similar procedure as in the synthesis of 14. Yield: 0.44 g (74%).
M.p.: 180–182 °C (dec.). 1H NMR (C6D6): d 8.00 (s, 1H, N@CH),
7.56 (d, J = 2.0 Hz, 1H, aryl), 7.12 (s, 1H, aryl), 7.06 (m, 2H, aryl),
6.98 (t, J = 7.6 Hz, 1H, aryl), 6.84 (d, J = 7.2 Hz, 1H, aryl), 6.75 (s,
1H, aryl), 6.62 (d, J = 7.2 Hz, 1H, aryl), 5.34 (m, 1H, OCH), 4.88 (m,
1H, OCH), 2.17 (s, 3H, CH3), 2.13 (s, 3H, CH3), 1.70 (s, 9H, CH3),
1.64 (d, J = 6.2 Hz, 3H, CH3), 1.61 (d, J = 6.2 Hz, 3H, CH3), 1.27 (s,
9H, CH3), 1.22 (d, J = 6.00 Hz, 3H, CH3), 1.13 (d, J = 6.00 Hz, 3H,
m
2961 (s), 1607 (s), 1535 (m), 1442 (s), 1260 (vs), 1089 (s), 1017
(s), 798 (s). Anal. Calc. for C34H36N2O4Ti: C, 69.86; H, 6.21; N,
4.79. Found: C, 69.84; H, 6.26; N, 4.74%.
CH3). IR (KBr, cmꢀ1):
m 2956 (s), 1560 (m), 1445 (s), 1260 (s),
1098 (s), 1016 (s), 801 (s). Anal. Calc. for C35H47NO4Ti: C, 70.82;
H, 7.98; N, 2.36. Found: C, 70.85; H, 7.92; N, 2.34%.
2.23. Preparation of (L9)Ti(OiPr)2 (27)
This compound was prepared as yellow microcrystals from the
reaction of 9H2 (0.53 g, 1.0 mmol) with Ti(OiPr)4 (0.28 g, 1.0 mmol)
in toluene (20 mL) and recrystallization from a toluene solution by
a similar procedure as in the synthesis of 14. Yield: 0.58 g (83%).
M.p.: 140–142 °C (dec.). 1H NMR (C6D6): d 7.64 (s, 2H, N@CH),
7.30 (d, J = 6.4 Hz, 2H, aryl), 7.18 (d, J = 7.6 Hz, 2H, aryl), 6.92 (t,
J = 8.0 Hz, 2H, aryl), 6.75 (d, J = 7.2 Hz, 2H, aryl), 6.58 (d,
J = 7.2 Hz, 2H, aryl), 6.49 (t, J = 7.6 Hz, 2H, aryl), 4.67 (m, 2H,
OCH), 1.80 (s, 6H, CH3), 1.71 (s, 18H, CH3), 1.12 (d, J = 6.0 Hz, 6H,
2.19. Preparation of (L7)2Ti(OiPr)2 (23)
This compound was prepared as yellow crystals from the reac-
tion of 7H (0.37 g, 1.0 mmol) with Ti(OiPr)4 (0.14 g, 0.5 mmol) in
toluene (20 mL) and recrystallization from a toluene solution by
a similar procedure as in the synthesis of 14. Yield: 0.27 g (61%).
M.p.: 125–127 °C (dec.). 1H NMR (C6D6): d 8.68 (s, 1H, N@CH),
8.55 (s, 1H, N@CH), 7.84 (m, 8H, aryl), 7.57 (m, 6H, aryl), 7.45 (m,
6H, aryl), 7.21 (m, 6H, aryl), 6.82 (m, 4H, aryl), 6.70 (m, 2H, aryl),
5.45 (m, 1H, OCH), 4.67 (m, 1H, OCH), 1.36 (br s, 6H, CH3), 1.16
(d, J = 6.0 Hz, 3H, CH3), 1.06 (d, J = 6.0 Hz, 3H, CH3). IR (KBr,
CH3), 1.08 (d, J = 6.4 Hz, 6H, CH3). IR (KBr, cmꢀ1):
m 2970 (s), 1605
(s), 1544 (s), 1403 (s), 1298 (s), 1260 (s), 1089 (s), 1008 (s), 795
(s). Anal. Calc. for C42H52N2O4Ti: C, 72.40; H, 7.52; N, 4.02. Found:
C, 72.35; H, 7.46; N, 4.04%.
cmꢀ1):
m 2961 (s), 1612 (m), 1451 (m), 1260 (s), 1090 (s), 1017
(s), 799 (s). Anal. Calc. for C58H48N4O4Ti: C, 76.31; H, 5.30; N,
6.14. Found: C, 76.29; H, 5.36; N, 6.12%.
2.24. Preparation of (L10)Ti(OiPr)2 (28)
2.20. Preparation of (L7)3Ti(OiPr) (24)
This compound was prepared as yellow microcrystals from the
reaction of 10H2 (0.64 g, 1.0 mmol) with Ti(OiPr)4 (0.28 g,
1.0 mmol) in toluene (20 mL) and recrystallization from a toluene
solution by a similar procedure as in the synthesis of 14. Yield:
0.63 g (78%). M.p.: 175–177 °C (dec.). 1H NMR (C6D6): d 7.70 (s,
2H, N@CH), 7.23 (d, J = 7.6 Hz, 2H, aryl), 7.18 (d, J = 7.6 Hz, 2H, aryl),
6.96 (m, 2H, aryl), 6.85 (m, 2H, aryl), 6.53 (m, 2H, aryl), 4.66 (m, 2H,
OCH), 1.80 (s, 6H, CH3), 1.78 (s, 18H, CH3), 1.17 (s, 18H, CH3), 1.10
This compound was prepared as yellow crystals from the reac-
tion of 7H (0.56 g, 1.5 mmol) with Ti(OiPr)4 (0.14 g, 0.5 mmol) in
toluene (20 mL) and recrystallization from a toluene solution by
a similar procedure as in the synthesis of 14. Yield: 0.39 g (63%).
M.p.: 110–112 °C (dec.). 1H NMR (C6D6): d 8.64 (s, 1H, N@CH),
8.51 (s, 1H, N@CH), 8.42 (s, 1H, N@CH), 7.84 (m, 12H, aryl), 7.60
(m, 11H, aryl), 7.11 (m, 14H, aryl), 6.93 (m, 4H, aryl), 6.74 (m,
4H, aryl), 6.46 (m, 3H, aryl), 5.47 (m, 1H, OCH), 1.27 (br s, 3H,
(d, J = 6.0 Hz, 6H, CH3), 1.05 (d, J = 6.0 Hz, 6H, CH3). IR (KBr, cmꢀ1):
m
CH3), 1.17 (br s, 3H, CH3). IR (KBr, cmꢀ1):
1581 (m), 1260 (s), 1093 (s), 1019 (s), 799 (s). Anal. Calc. for C81H58-
N6O4Ti: C, 79.27; H, 4.76; N, 6.85. Found: C, 79.25; H, 4.76; N,
6.84%.
m 2962 (s), 1607 (m),
2964 (s), 1533 (s), 1430 (s), 1387 (s), 1260 (s), 1097 (s), 1016 (s),
799 (s). Anal. Calc. for C50H68N2O4Ti: C, 74.24; H, 8.47; N, 3.46.
Found: C, 74.25; H, 8.46; N, 3.34%.
2.25. Preparation of (L11)Ti(OiPr)2 (29)
2.21. Preparation of (L12)Ti(OiPr)3 (25)
This compound was prepared as yellow crystals from the reac-
tion of 11H2 (0.60 g, 1.0 mmol) with Ti(OiPr)4 (0.28 g, 1.0 mmol) in
toluene (20 mL) and recrystallization from a toluene solution by a
similar procedure as in the synthesis of 14. Yield: 0.48 g (62%).
M.p.: 96–98 °C (dec.). 1H NMR (C6D6): d 7.98 (s, 2H, N@CH), 7.80
(d, J = 7.6 Hz, 2H, aryl), 7.73 (d, J = 8.0 Hz, 2H, aryl), 7.70 (m, 4H,
aryl), 7.22 (d, J = 7.2 Hz, 2H, aryl), 6.89 (t, J = 7.6 Hz, 2H, aryl),
6.82 (d, J = 8.4 Hz, 2H, aryl), 6.73 (d, J = 7.2 Hz, 2H, aryl), 6.61 (t,
J = 7.6 Hz, 2H, aryl), 4.96 (m, 2H, OCH), 1.72 (s, 18H, CH3), 1.14
(d, J = 6.0 Hz, 6H, CH3), 1.09 (d, J = 6.0 Hz, 6H, CH3). IR (KBr,
This compound was prepared as yellow microcrystals from the
reaction of 12H (0.43 g, 1.0 mmol) with Ti(OiPr)4 (0.28 g, 1.0 mmol)
in toluene (20 mL) and recrystallization from a toluene solution by
a similar procedure as in the synthesis of 14. Yield: 0.44 g (67%).
M.p.: 116–118 °C (dec.). 1H NMR (C6D6): d 8.01 (d, J = 8.0 Hz, 1H,
aryl), 7.90 (s, 1H, N@CH), 7.55 (d, J = 2.8 Hz, 1H, aryl), 7.27 (t,
J = 7.6 Hz, 1H, aryl), 7.04 (d, J = 7.2 Hz, 1H, aryl), 6.74 (t, J = 7.6 Hz,
1H, aryl), 6.71 (d, J = 2.4 Hz, 1H, aryl), 6.47 (d, J = 7.6 Hz, 1H, aryl),
6.16 (d, J = 8.4 Hz, 1H, aryl), 4.94 (m, 3H, OCH), 3.93 (s, 2H, NH2),
2.0 (s, 3H, CH3), 1.89 (s, 3H, CH3), 1.67 (s, 9H, CH3), 1.26 (s, 9H,
cmꢀ1):
m 2959 (s), 1604 (m), 1547 (m), 1454 (m), 1384 (s), 1260
(s), 1087 (s), 1016 (s), 799 (s). Anal. Calc. for C48H52N2O4Ti: C,
74.99; H, 6.82; N, 3.64. Found: C, 74.95; H, 6.86; N, 3.62%.
CH3), 1.24 (s, 9H, CH3), 1.21 (s, 9H, CH3). IR (KBr, cmꢀ1):
(m), 2952 (s), 1601 (m), 1355 (s), 1261 (s), 1094 (s), 1019 (s),
m
3455

L. Chen et al. / Inorganica Chimica Acta 402 (2013) 140–155
145
Table 1
Crystal data and experimental parameters for compounds 14–19.
Compound
14ꢁC7H8ꢁDME
65H52N2O6Ti
15
16
17ꢁ18
19
Formula
C
C74H78N2O8Ti2
1219.18
monoclinic
P21
11.732(3)
20.372(5)
13.555(3)
90
C62H50N2O4Ti
934.94
C87H89N3O8Ti2
1400.41
monoclinic
P21
13.272(1)
18.675(2)
15.438(2)
90
C41H55NO4Ti
673.76
orthorhombic
P212121
10.021(2)
10.796(2)
34.202(5)
90
Formula weight
Crystal system
Space group
a (Å)
b (Å)
c (Å)
1004.99
orthorhombic
P212121
11.451(1)
15.465(1)
28.495(2)
90
orthorhombic
P212121
13.487(1)
18.250(2)
26.636(2)
90
a
(°)
b (°)
90
90
5046.0(7)
4
1.323
95.24(1)
90
3226.1(13)
2
90
90
107.91(1)
90
3640.9(6)
2
90
90
c
(°)
V (Å3)
6556.1(10)
4
0.947
3700.1(11)
4
1.209
Z
Dcalc (g/cm3)
1.255
1.277
Size (mm)
F(000)
0.35 ꢂ 0.26 ꢂ 0.22
0.26 ꢂ 0.24 ꢂ 0.20
0.32 ꢂ 0.28 ꢂ 0.24
0.35 ꢂ 0.28 ꢂ 0.23
0.34 ꢂ 0.18 ꢂ 0.16
2104
1288
1960
1480
1448
2h range (°)
3.88–50.50
25550
9127 (0.0611)
7646
3.48–55.80
32252
14935 (0.0301)
12707
3.06–55.74
48341
15524 (0.0381)
14499
3.54–50.50
18511
12619 (0.0379)
10715
5.16–144.90
30605
7042 (0.0461)
6375
No. of reflections collected
No. of unique reflections (Rint
No. of observed reflections
)
Absorbed corrections (Tmax, Tmin
R
)
0.95, 0.92
0.045
0.94, 0.92
0.041
0.96, 0.95
0.048
0.94, 0.91
0.055
0.71, 0.51
0.030
Rw
0.095
0.086
0.141
0.124
0.070
wR2 (all data)
Goodness-of-fit
0.101
1.02
0.088
1.02
0.145
1.12
0.133
1.06
0.071
1.01
Flack
v
ꢀ0.01(2)
ꢀ0.01(1)
0.05(2)
ꢀ0.01(2)
0.01(1)
Table 2
Crystal data and experimental parameters for compounds 20ꢁ21, 23, 24 and 29.
Compound
20ꢁ21
69H65N3O8Ti
1160.04
monoclinic
P21
12.960(1)
12.081(1)
19.156(2)
90
23ꢁTHF
24
29
Formula
C
C58H48N4O4Ti
912.90
hexagonal
P65
25.644(1)
25.644(1)
14.326(1)
90
C81H58N6O4Ti
1227.23
orthorhombic
P212121
14.426(4)
17.398(4)
34.210(8)
90
C48H52N2O4Ti
768.82
orthorhombic
C2221
18.434(3)
18.468(3)
24.873(4)
90
Formula weight
Crystal system
Space group
a (Å)
b (Å)
c (Å)
a
(°)
b (°)
91.36(1)
90
2998.3(4)
2
90
120
8158.3(5)
6
1.115
90
90
8586(4)
4
0.949
90
90
8468(3)
8
1.206
c
(°)
V (Å3)
Z
Dcalc (g/cm3)
1.285
Size (mm)
F(000)
0.43 ꢂ 0.20 ꢂ 0.13
0.40 ꢂ 0.20 ꢂ 0.20
0.24 ꢂ 0.22 ꢂ 0.20
0.30 ꢂ 0.28 ꢂ 0.22
1216
2868
2560
3264
2h range (deg)
3.84–55.20
18075
12757 (0.0499)
9274
3.66–50.00
40525
9548 (0.0564)
6177
2.62–55.74
69473
20430 (0.0992)
13858
4.42–50.50
20,867
7631 (0.0333)
7399
No. of reflections collected
No. of unique reflections [R(int)
No. of observed reflections
]
Absorbed corrections (Tmax, Tmin
R
)
0.96, 0.87
0.064
0.96, 0.92
0.062
0.97, 0.96
0.069
0.95, 0.93
0.029
Rw
0.117
0.171
0.145
0.064
wR2 (all data)
Goodness-of-fit
0.132
1.03
0.188
1.12
0.157
1.01
0.065
1.09
Flack
v
ꢀ0.03(2)
ꢀ0.02(3)
0.07(2)
0.01(2)
2.26. General procedure for asymmetric hydrophosphonylation of
aromatic aldehydes
tone/n-hexane 1:5–1:1). Enantiomeric excesses were determined
by HPLC analysis using a Chiralcel AS-H or AD-H or OD-H column.
In a nitrogen-filled glove box, titanium complex (0.05 mmol)
was dissolved in toluene or THF (1.0 mL). Aldehyde (0.5 mmol)
and dimethyl phosphite (0.65 mmol) were added successively into
the solution at 20 °C. After the solution was stirred at this temper-
ature for 48 h, solvent was removed. CH2Cl2 (10 mL) and 2 M
NaHCO3 (10 mL) were added and stirred for 0.5 h, then extracted
with CH2Cl2 (10 mL ꢂ 3). The combined organic layers were
washed with brine (20 mL) and dried with anhydrous Na2SO4, then
filtered. The solvent was removed, and the resulting residue was
further purified by flash column chromatography on silica gel (ace-
2.26.1. Dimethyl hydroxyl (phenyl) methylphosphonate [25]
HPLC (AS-H, 254 nm, hexane/2-propanol = 80:20, 0.8 mL/min):
tR = 11.0 and 13.0 min. 1H NMR (CDCl3): d 7.48 (m, 2H, Ph), 7.35
(m, 3H, Ph), 5.05 (d, J = 10.8 Hz, 1H, CH), 3.70 (d, J = 10.4 Hz, 3H,
CH3), 3.66 (d, J = 10.4 Hz, 3H, CH3); the proton of the OH group
was not observed.
2.26.2. Dimethyl hydroxyl (4-chlorophenyl) methylphosphonate [25]
HPLC (AS-H, 254 nm, hexane/2-propanol = 80:20, 0.8 mL/min):
tR = 14.6 and 17.9 min. 1H NMR (CDCl3): d 7.42 (d, J = 8.4 Hz, 2H,

146
L. Chen et al. / Inorganica Chimica Acta 402 (2013) 140–155
Table 3
Selected bond distances (Å) and bond angles (ꢀ) for compounds 14–21, 23, 24 and 29.
Compound 14
Ti(1)–O(1)
Ti(1)–O(3)
Ti(1)–N(1)
1.863(2)
1.867(2)
2.238(2)
96.22(9)
94.70(9)
161.09(8)
85.31(8)
79.85(8)
170.55(9)
85.72(9)
88.13(8)
Ti(1)–O(2)
Ti(1)–O(4)
Ti(1)–N(2)
1.890(2)
1.880(2)
2.219(2)
102.46(8)
93.82(8)
98.84(8)
171.93(8)
87.23(8)
84.54(8)
80.10(8)
O(1)–Ti(1)–O(2)
O(1)–Ti(1)–O(4)
O(2)–Ti(1)–O(4)
O(1)–Ti(1)–N(1)
O(2)–Ti(1)–N(1)
O(3)–Ti(1)–N(1)
O(4)–Ti(1)–N(1)
N(2)–Ti(1)–N(1)
O(1)–Ti(1)–O(3)
O(2)–Ti(1)–O(3)
O(3)–Ti(1)–O(4)
O(1)–Ti(1)–N(2)
O(2)–Ti(1)–N(2)
O(3)–Ti(1)–N(2)
O(4)–Ti(1)–N(2)
torsion (aryl–aryl)
58.5(3), 64.0(3)
Compound 15
Ti(1)–O(1)
Ti(1)–O(3)
1.889(2)
1.775(2)
2.211(2)
96.68(7)
93.64(7)
100.85(8)
80.58(7)
86.28(7)
Ti(1)–O(2)
Ti(1)–O(4)
1.879(2)
1.792(2)
129.17(7)
114.98(7)
111.55(7)
83.10(6)
172.15(8)
68.0(2)
Ti(1)–N(1)
O(1)–Ti(1)–O(2)
O(1)–Ti(1)–O(4)
O(2)–Ti(1)–O(4)
O(1)–Ti(1)–N(1)
O(3)–Ti(1)–N(1)
Torsion (aryl–aryl)
O(1)–Ti(1)–O(3)
O(2)–Ti(1)–O(3)
O(3)–Ti(1)–O(4)
O(2)–Ti(1)–N(1)
O(4)–Ti(1)-N(1)
Compound 16
Ti(1)–O(1)
Ti(1)–O(3)
1.865(2)
1.858(2)
2.220(2)
96.34(7)
94.83(7)
162.34(7)
86.03(7)
79.30(7)
167.48(7)
87.89(7)
85.46(7)
Ti(1)–O(2)
Ti(1)–O(4)
Ti(1)–N(2)
1.893(2)
1.901(2)
2.230(2)
104.61(7)
92.77(7)
97.60(7)
169.57(7)
88.00(7)
84.59(7)
78.85(7)
Ti(1)–N(1)
O(1)–Ti(1)–O(2)
O(1)–Ti(1)–O(4)
O(2)–Ti(1)–O(4)
O(1)–Ti(1)–N(1)
O(2)–Ti(1)–N(1)
O(3)–Ti(1)–N(1)
O(4)–Ti(1)–N(1)
N(1)–Ti(1)–N(2)
O(1)–Ti(1)–O(3)
O(2)–Ti(1)–O(3)
O(3)–Ti(1)–O(4)
O(1)–Ti(1)–N(2)
O(2)–Ti(1)–N(2)
O(3)–Ti(1)–N(2)
O(4)–Ti(1)–N(2)
Torsion (aryl–aryl)
59.3(2), 64.4(2)
Compound 17ꢁ18
Ti(1)–O(1)
1.857(3)
Ti(1)–O(2)
1.918(3)
Ti(1)–O(3)
1.853(3)
Ti(1)–O(4)
1.943(3)
Ti(1)–N(1)
2.197(3)
Ti(1)–N(2)
2.188(3)
Ti(2)–O(5)
1.865(3)
Ti(2)–O(6)
1.859(3)
Ti(2)–O(7)
1.766(3)
Ti(2)–O(8)
1.811(3)
Ti(2)–N(3)
2.294(3)
O(1)–Ti(1)–O(2)
O(1)–Ti(1)–O(4)
O(2)–Ti(1)–O(4)
O(1)–Ti(1)–N(1)
O(2)–Ti(1)–N(1)
O(3)–Ti(1)–N(1)
O(4)–Ti(1)–N(1)
N(1)–Ti(1)–N(2)
O(5)–Ti(2)–O(7)
O(6)–Ti(2)–O(7)
O(7)–Ti(2)–O(8)
O(6)–Ti(2)–N(3)
O(8)–Ti(2)–N(3)
163.37(11)
88.88(11)
83.93(11)
84.69(11)
81.49(11)
95.90(12)
97.92(11)
177.99(12)
111.36(15)
114.32(16)
102.05(17)
81.57(12)
172.85(15)
O(1)–Ti(1)–O(3)
O(2)–Ti(1)–O(3)
O(3)–Ti(1)–O(4)
O(1)–Ti(1)–N(2)
O(2)–Ti(1)–N(2)
O(3)–Ti(1)–N(2)
O(4)–Ti(1)–N(2)
O(5)–Ti(2)–O(6)
O(5)-Ti(2)–O(7)
O(6)–Ti(2)-O(8)
O(5)–Ti(2)-N(3)
O(7)–Ti(2)–N(3)
torsion (aryl–aryl)
98.77(11)
91.84(11)
164.76(11)
97.19(11)
96.54(12)
84.52(11)
81.45(11)
129.51(14)
95.26(14)
95.27(15)
82.00(12)
85.11(14)
17: 63.2(4)18: 64.4(4), 68.4(4)
Compound 19
Ti(1)–O(1)
Ti(1)–O(3)
1.864(1)
1.801(1)
2.269(1)
113.05(6)
117.70(6)
99.97(7)
79.04(5)
175.28(6)
Ti(1)–O(2)
Ti(1)–O(4)
1.882(1)
1.783(1)
124.07(6)
96.76(6)
96.25(6)
85.67(6)
82.71(6)
71.0(2)
Ti(1)–N(1)
O(1)–Ti(1)–O(2)
O(1)–Ti(1)–O(4)
O(2)–Ti(1)–O(4)
O(1)–Ti(1)–N(1)
O(3)–Ti(1)–N(1)
torsion (aryl–aryl)
O(1)–Ti(1)–O(3)
O(2)–Ti(1)–O(3)
O(3)–Ti(1)–O(4)
O(2)–Ti(1)–N(1)
O(4)–Ti(1)–N(1)
Compound 20ꢁ21
Ti(1)–O(1)
Ti(1)–O(3)
Ti(1)–N(1)
Ti(2)–O(5)
Ti(2)–O(7)
Ti(2)–N(3)
O(1)–Ti(1)–O(3)
O(2)–Ti(1)–O(3)
O(3)–Ti(1)–O(4)
O(1)–Ti(1)–N(2)
1.846(3)
1.879(3)
2.230(3)
1.895(4)
1.777(3)
2.246(4)
93.99(11)
159.17(11)
99.84(12)
173.72(12)
Ti(1)–O(2)
Ti(1)–O(4)
Ti(1)–N(2)
Ti(2)–O(6)
1.900(3)
1.852(3)
2.251(3)
1.865(3)
1.787(3)
98.71(12)
99.86(11)
94.20(11)
86.06(11)
79.49(11)
Ti(2)–O(8)
O(1)–Ti(1)–O(2)
O(1)–Ti(1)–O(4)
O(2)–Ti(1)–O(4)
O(1)–Ti(1)–N(1)
O(2)–Ti(1)–N(1)

L. Chen et al. / Inorganica Chimica Acta 402 (2013) 140–155
147
O(2)–Ti(1)–N(2)
O(3)–Ti(1)–N(2)
O(4)–Ti(1)–N(2)
O(5)–Ti(2)–O(6)
O(5)–Ti(2)–O(8)
O(6)–Ti(2)–O(8)
O(5)–Ti(2)–N(3)
O(7)–Ti(2)–N(3)
torsion (aryl–aryl)
86.40(11)
80.09(11)
83.32(11)
132.65(14)
92.73(18)
96.93(16)
80.90(15)
86.51(13)
O(3)–Ti(1)–N(1)
O(4)–Ti(1)–N(1)
N(1)–Ti(1)–N(2)
O(5)–Ti(2)–O(7)
O(6)–Ti(2)–O(7)
O(7)–Ti(2)–O(8)
O(6)–Ti(2)–N(3)
O(8)–Ti(2)–N(3)
85.01(12)
172.00(12)
91.32(11)
110.93(16)
112.12(15)
101.84(16)
82.93(13)
170.95(17)
20: 60.7(4)21: 64.1(4), 58.0(4)
Compound 23
Ti(1)–O(1)
1.952(3)
Ti(1)–O(2)
1.892(3)
Ti(1)–O(3)
1.824(3)
Ti(1)–O(4)
1.790(3)
Ti(1)–N(1)
2.298(3)
Ti(1)–N(2)
2.270(3)
O(1)–Ti(1)–O(2)
O(1)-Ti(1)–O(4)
O(2)–Ti(1)–O(4)
O(1)–Ti(1)-N(1)
O(2)–Ti(1)–N(1)
O(3)–Ti(1)–N(1)
O(4)–Ti(1)–N(1)
N(1)–Ti(1)–N(2)
159.83(13)
91.47(14)
98.09(13)
88.19(12)
78.88(12)
86.75(13)
168.33(14)
70.31(12)
O(1)–Ti(1)–O(3)
O(2)–Ti(1)–O(3)
O(3)–Ti(1)–O(4)
O(1)–Ti(1)–N(2)
O(2)–Ti(1)-N(2)
O(3)–Ti(1)–N(2)
O(4)–Ti(1)–N(2)
torsion (aryl–aryl)
96.52(13)
98.11(14)
104.88(14)
74.92(12)
86.10(12)
155.50(14)
98.34(14)
62.3(4), 69.2(4)
Compound 24
Ti(1)–O(1)
1.907(2)
Ti(1)–O(2)
1.856(2)
Ti(1)–O(3)
1.909(2)
Ti(1)–O(4)
1.768(2)
Ti(1)–N(1)
2.255(3)
Ti(1)–N(2)
2.280(3)
O(1)–Ti(1)–O(2)
O(1)–Ti(1)–O(4)
O(2)–Ti(1)–O(4)
O(1)–Ti(1)–N(1)
O(2)–Ti(1)–N(1)
O(3)–Ti(1)–N(1)
O(4)–Ti(1)–N(1)
N(1)–Ti(1)–N(2)
97.81(10)
94.25(11)
104.39(10)
76.99(10)
156.31(10)
83.74(10)
99.07(10)
70.09(10)
O(1)–Ti(1)–O(3)
O(2)–Ti(1)–O(3)
O(3)–Ti(1)–O(4)
O(1)–Ti(1)–N(2)
O(2)–Ti(1)–N(2)
O(3)–Ti(1)–N(2)
O(4)–Ti(1)–N(2)
torsion (aryl–aryl)
160.10(9)
97.88(10)
93.63(10)
85.67(10)
86.58(10)
83.13(10)
168.92(11)
63.9(3), 83.2(3), 87.6(3)
Compound 29
Ti(1)–O(1)
Ti(1)–O(3)
1.931(2)
1.778(2)
2.277(2)
165.35(7)
93.69(8)
94.60(8)
80.15(8)
88.49(7)
90.75(7)
162.96(8)
73.49(7)
Ti(1)–O(2)
Ti(1)–O(4)
Ti(1)–N(2)
1.945(2)
1.777(2)
2.269(2)
94.72(8)
94.66(8)
105.65(8)
88.94(8)
78.91(8)
162.99(7)
90.64(7)
65.3(2)
Ti(1)–N(1)
O(1)–Ti(1)–O(2)
O(1)–Ti(1)–O(4)
O(2)–Ti(1)–O(4)
O(1)–Ti(1)–N(1)
O(2)-Ti(1)–N(1)
O(3)–Ti(1)–N(1)
O(4)–Ti(1)–N(1)
N(1)–Ti(1)–N(2)
O(1)–Ti(1)–O(3)
O(2)–Ti(1)–O(3)
O(3)–Ti(1)–O(4)
O(1)–Ti(1)–N(2)
O(2)–Ti(1)–N(2)
O(3)–Ti(1)–N(2)
O(4)–Ti(1)–N(2)
torsion (aryl–aryl)
Ph), 7.35 (d, J = 8.4 Hz, 2H, Ph), 5.04 (d, J = 10.8 Hz, 1H, CH), 3.73 (d,
J = 6.0 Hz, 3H, CH3), 3.70 (d, J = 6.0 Hz, 3H, CH3), 2.03 (br s, 1H, OH).
2.26.6. Dimethyl hydroxyl (2-fluorophenyl) methylphosphonate [73]
HPLC (AS-H, 210 nm, hexane/2-propanol = 3:1, 0.5 mL/min):
tR = 18.1 and 25.0 min. 1H NMR (CDCl3): d 7.68 (t, J = 7.5 Hz, 1H,
Ph), 7.30 (m, 1H, Ph), 7.20 (t, J = 7.5 Hz, 1H, Ph), 7.05 (t, J = 9 Hz,
1H, Ph), 5.43 (d, J = 11.2 Hz, 1H, CH), 4.53 (br s, 1H, OH), 3.80 (d,
J = 10.6 Hz, 3H, CH3), 3.67 (d, J = 10.6 Hz, 3H, CH3).
2.26.3. Dimethyl hydroxyl (4-nitrophenyl) methylphosphonate [25]
HPLC (AS-H, 254 nm, hexane/2-propanol = 80:20, 0.8 mL/min):
tR = 25.4 and 29.9 min. 1H NMR (CDCl3): d 8.25 (d, J = 8.5 Hz, 2H,
Ph), 7.68 (d, J = 7.0 Hz, 2H, Ph), 5.21 (d, J = 12.2 Hz, 1H, CH), 3.76
(t, J = 10.3 Hz, 6H, CH3), 1.64 (br s, 1H, OH).
2.26.7. Dimethyl hydroxyl (p-tolyl) methylphosphonate [73]
HPLC (AS-H, 210 nm, hexane/2-propanol = 5:1, 1.0 mL/min):
tR = 14.2 and 18.4 min. 1H NMR (CDCl3): d 7.37 (d, J = 6.4 Hz, 2H,
Ph), 7.19 (d, J = 7.9 Hz, 2H, Ph), 5.01 (d, J = 10.4 Hz, 1H, CH), 3.72
(d, J = 10.4 Hz, 3H, CH3), 3.67 (d, J = 10.3 Hz, 3H, CH3), 2.57 (br s,
1H, OH), 2.35 (s, 3H, CH3).
2.26.4. Dimethyl hydroxyl (4-methoxyphenyl) methylphosphonate
[25]
HPLC (AS-H, 254 nm, hexane/2-propanol = 80:20, 0.8 mL/min):
tR = 25.9 and 39.9 min. 1H NMR (CDCl3): d 7.41 (d, J = 8.8 Hz, 2H,
Ph), 7.23 (d, J = 8.8 Hz, 2H, Ph), 4.99 (d, J = 10.0 Hz, 1H, CH), 3.81
(s, 3H, CH3), 3.72 (d, J = 10.4 Hz, 3H, CH3), 3.66 (d, J = 10.4 Hz, 3H,
CH3), 3.22 (br s, 1H, OH) .
2.26.8. Dimethyl hydroxyl (2-methoxyphenyl) methylphosphonate
[31]
2.26.5. Dimethyl hydroxyl (o-tolyl) methylphosphonate [73]
HPLC (AS-H, 210 nm, hexane/2-propanol = 5:1, 0.5 mL/min):
tR = 21.5 and 31.9 min. 1H NMR (CDCl3): d 7.64 (d, J = 7.6 Hz, 1H,
Ph), 7.23 (m, 2H, Ph), 7.16 (m, 1H, Ph), 5.29 (d, J = 10.8 Hz, 1H,
CH), 3.71 (d, J = 10.4 Hz, 3H, CH3), 3.64 (d, J = 10.4 Hz, 3H, CH3),
3.21 (br s, 1H, OH), 2.38 (s, 3H, CH3).
HPLC (AD-H, 215 nm, hexane/2-propanol = 90:10, 1.0 mL/min):
tR = 15.6 and 16.6 min. 1H NMR (CDCl3): d 7.50 (d, J = 7.6 Hz, 1H,
Ph), 7.30 (t, J = 8.0 Hz, 1H, Ph), 7.00 (t, J = 7.5 Hz, 1H, Ph), 6.91 (d,
J = 8.3 Hz, 1H, Ph), 5.4 (d, J = 12.1 Hz, 1H, CH), 3.87 (s, 3H, CH3),
3.78 (d, J = 10.4 Hz, 3H, CH3), 3.62 (d, J = 10.4 Hz, 3H, CH3), 3.14
(br s, 1H, OH).

148
L. Chen et al. / Inorganica Chimica Acta 402 (2013) 140–155
2.26.9. Dimethyl hydroxy (2-chlorophenyl) methylphosphonate [31]
HPLC (AD-H, 215 nm, hexane/2-propanol = 90:10, 1.0 mL/min):
tR = 9.7 and 10.7 min. 1H NMR (CDCl3): d 7.74 (d, J = 7.7 Hz, 1H, Ph),
7.36 (m, 2H, Ph), 7.28 (m, 1H, aryl), 5.60 (d, J = 11.8 Hz, 1H, CH),
3.80 (d, J = 10.4 Hz, 3H, CH3), 3.67 (d, J = 10.4 Hz, 3H, CH3); the pro-
ton of the OH group was not observed.
tent with their C1-symmetric structures. Their IR spectra exhibit
peaks corresponding to aromatic stretches in addition to O–H
stretches at about 3420 cmꢀ1, and strong C@N stretches at about
1617 cmꢀ1
.
3.2. Synthesis and characterization of titanium complexes with C1-
symmetric ligands
2.26.10. Dimethyl hydroxyl (3-chlorophenyl) methylphosphonate [31]
HPLC (OD-H, 215 nm, hexane/2-propanol = 90:10, 1.0 mL/min):
tR = 11.0 and 14.1 min. 1H NMR (CDCl3): d 7.51 (s, 1H, Ph), 7.36 (d,
J = 4.7 Hz, 1H, Ph), 7.30 (d, J = 4.9 Hz, 2H, Ph), 5.04 (d, J = 4.8 Hz, 1H,
CH), 3.74 (d, J = 6.4 Hz, 3H, CH3), 3.72 (d, J = 6.4 Hz, 3H, CH3); the
proton of the OH group was not observed.
Titanium complexes can be efficiently prepared via alcohol
elimination reaction between Ti(OiPr)4 and protic reagents. For
example, treatment of Ti(OiPr)4 with 1 equiv of 1H2 in toluene
gives the bis-ligated titanium complex (L1)2Ti (14) in 70% yield
(Scheme 1), and no mono-ligated complex (L1)Ti(OiPr)2 (13) was
isolated. However, under similar reaction conditions, treatment
of Ti(OiPr)4 with 1 equiv of 2H2, 3H2 or 4H2 gives, after recrystalli-
2.26.11. Dimethyl hydroxyl (4-fluorophenyl) methylphosphonate [31]
HPLC (OD-H, 215 nm, hexane/2-propanol = 90:10, 1.0 mL/min):
tR = 11.7 and 14.5 min. 1H NMR (CDCl3): d 7.46 (m, 2H, Ph), 7.08 (t,
J = 8.6 Hz, 2H, Ph), 5.04 (d, J = 10.3 Hz, 1H, CH), 3.71 (t, J = 10.5 Hz,
6H, CH3), 2.26 (br s, 1H, OH).
zation from
a toluene solution, the mono-ligated complex
(L2)Ti(OiPr)2 (15), a mixture of mono-ligated complex (L3)Ti(OiPr)2
(17) and bis-ligated complex (L3)2Ti (18), and mono-ligated
complex (L4)Ti(OiPr)2 (19), respectively, in good yields
2.26.12. Dimethyl hydroxyl (naphthalene-1-yl)methylphosphonate
[31]
HPLC (OD-H, 254 nm, hexane/2-propanol = 90:10, 1.0 mL/min):
tR = 20.0 and 26.5 min. 1H NMR (CDCl3): d 8.08 (d, J = 8.2 Hz, 1H,
aryl), 7.88 (m, 3H, aryl), 7.55 (m, 3H, aryl), 5.90 (d, J = 11.3 Hz,
1H, CH), 3.71 (d, J = 10.4 Hz, 3H, CH3), 3.54 (d, J = 10.4 Hz, 3H,
CH3), 2.54 (br s, 1H, OH).
O
NH2
OH
O
N
N
O
Ti
O
OH
O
2.27. X-ray crystallography
14
H
r.t.
C7H8
Single-crystal X-ray diffraction measurements were carried out
on a Rigaku Saturn CCD or on a Bruker SMART CCD diffractometer
-0.5 Ti(OiPr)4
C7H8/m.s.
using graphite monochromated Mo K
a radiation (k = 0.71073 Å)
or Cu K radiation (k = 1.54187 Å). An empirical absorption correc-
a
O
tion was applied using the SADABS program [74]. All structures were
solved by direct methods and refined by full-matrix least squares
on F2 using the SHELXL-97 program package [75]. All hydrogen atoms
were geometrically fixed using the riding model. The crystal data
and experimental data for complexes 14–21, 23, 24 and 29 are
summarized in Tables 1 and 2. Selected bond lengths and angles
are listed in Table 3.
Ti(OiPr)4
C7H8
N
N
O
Ti
O
O
OH
HO
1H2
13
Scheme 1. Synthesis of complex 14.
3. Results and discussion
CMe3
3.1. Synthesis and characterization of ligands
Condensation of (R)-2-amino-20-hydroxy-1,10-binaphthyl, (R)-5,50,
6,60,7,70,8,80-octahydro-2-amino-20-hydroxy-1,10-binaphthyl,(R)-2-
amino-20-hydroxy-6,60-dimethyl-1,10-biphenyl, (R)-2,20-diamino-6,
60-dimethyl-1,10-biphenyl or (R)-2,20-diamino-1,10-binaphthyl
with 1 or 2 equiv of salicylaldehyde, 3-tert-butylsalicylaldehyde,
3,5-di-tert-butylsalicylaldehyde or pyridine-2-carboxaldehyde in
toluene in the presence of molecular sieves at 70 °C gives, the
C1-symmetric Schiff-base ligands 1H2–7H (Schemes 1–7), and C2-
symmetric Schiff-base ligands 8H2–11H2 (Schemes 8–11), respec-
tively, in good yields. These Schiff base ligands are stable in dry
air atmosphere, but they degrade in the presence of moisture.
For example, treatment of 11H2 with a drop of H2O in toluene at
60 °C for one hour leads to the isolation of the C1-symmetric
Schiff-base ligand 12H in 95% yield (Scheme 11). Compounds 1H2
–12H are very soluble in CH2Cl2, CHCl3, toluene and benzene, but
only slightly soluble in n-hexane. The new ligands 3H2, 4H2 and
12H have been fully characterized by various spectroscopic tech-
niques and elemental analyses. Their 1H NMR spectra indicate that
they are unsymmetrical on the NMR timescale, which are consis-
O
NH2
OH
O
N
N
O
Ti
O
OH
O
Me3C
16
Me3C
H
60 C
C6H6
-0.5 Ti(OiPr)4
C7H8/m.s.
N
CMe3
O
Ti(OiPr)4
C7H8
N
O
Ti
O
OH
HO
O
CMe3
2H2
15
Scheme 2. Synthesis of complexes 15 and 16.

L. Chen et al. / Inorganica Chimica Acta 402 (2013) 140–155
149
(-
OH
O
S-
c-
h-
e-
Me3C
CMe3
H
N
O
NH2
OH
NH2
OH
O
N
OH
N
O
HO
6H2
Ti(OiPr)4
CMe3
Ti
CMe3
C7H8/m.s.
O
OH
O
C7H8
18
H
Me3C
r.t.
C7H8
-0.5 Ti(OiPr)4
C7H8/m.s.
CMe3
O
O
N
O
Ti(OiPr)4
C7H8
Ti
N
O
N
O
Ti
O
O
OH
O
HO
22
3H2
17
Scheme 6. Synthesis of complex 22.
Scheme 3. Synthesis of complexes 17 and 18.
OH
O
Me3C
H
CMe3
NH2
OH
N
OH
CMe3
C7H8/m.s.
HO
CMe3
N
N
N
4H2
O
C7H8
O
Ti(OiPr)4
Me3C
O
N
N
Ti
O
N
CMe3
N
O
Ti
N
O
O
24
O
1/3 Ti(OiPr)4
C7H8
19
O
Scheme 4. Synthesis of complex 19.
H
N
NH2
OH
N
OH
C7H8/m.s.
7H
O
NH2
OH
C7H8
O
N
N
O
1/2Ti(OiPr)4
Ti
O
N
OH
O
O
21
O
N
H
N
O
Ti
60
C
-0.5 Ti(OiPr)4
C6H6
O
C7H8/m.s.
N
N
23
O
Ti(OiPr)4
C7H8
Scheme 7. Synthesis of complexes 23 and 24.
N
O
Ti
O
O
OH
HO
mes 2–4). The observed reactivity differences are most likely due
to the different steric demand of these ligands. A similar result is
also observed between ligand 5H2 and 6H2, in which 5H2 gives a
mixture of mono-ligated complex (L5)Ti(OiPr)2 (20) and bis-ligated
complex (L5)2Ti (21) (Scheme 5), while 6H2 gives the mono-ligated
5H2
20
Scheme 5. Synthesis of complexes 20 and 21.

150
L. Chen et al. / Inorganica Chimica Acta 402 (2013) 140–155
OH
O
CMe3
HO
Me3C
HO
H
2
NH2
NH2
N
N
N
CMe3
CMe3
C7H8/m.s.
O
Ti(OiPr2)4
C7H8
N
O
Ti
O
NH2
HO
O
N
12H
H2
Ti(OiPr2)4
8H2
C7H8
H2O
25
OH
O
Me3C
Me3C
2
H
N
O
Ti
HO
CMe3
CMe3
O
O
NH2
NH2
CMe3
C7H8/m.s.
N
N
O
N
HO
26
Ti(OiPr2)4
Me3C
10H2
C7H8
Scheme 8. Synthesis of complex 26.
CMe3
Me3C
HO
OH
O
Me3C
2
N
CMe3
H
O
NH2
N
N
O
O
Ti
NH2
C7H8/m.s.
O
N
CMe3
HO
Ti(OiPr2)4
Me3C
9H2
C7H8
28
CMe3
Scheme 10. Synthesis of complexes 25 and 28.
N
N
CMe3
O
O
O
O
Me3C
HO
OH
O
Ti
Me3C
2
H
CMe3
NH2
N
N
NH2
C7H8/m.s.
27
Scheme 9. Synthesis of complex 27.
HO
complex (L6)Ti(OiPr)2 (22) (Scheme 6). The mono-ligated titanium
alkoxides can be converted to the bis-ligated complex via ligand
redistribution reaction. For example, treatment of mono-ligated
complex (L2)Ti(OiPr)2 (15) or (L5)Ti(OiPr)2 (20) at 60 °C gives the
bis-ligated complexes (L2)2Ti (16) and (L5)2Ti (21), respectively,
in good yields (Schemes 2 and 5). Reaction of Ti(OiPr)4 with 2 or
3 equiv of ligand 7H gives the bis-ligated complex (L7)2Ti(OiPr)2
(23) and the tris-ligated complex (L7)3Ti(OiPr) (24), respectively,
in good yields (Scheme 7), presumably because of the flexibility
of the ligand 7. Under similar reaction conditions, treatment of
ligand 12H with 1 equiv of Ti(OiPr)4 gives a mono-ligated complex
(L12)Ti(OiPr)3 (25) in 67% yield (Scheme 10).
These complexes are stable in dry nitrogen atmosphere, while
they are very sensitive to moisture. They are soluble in organic sol-
vents such as THF, DME, pyridine, toluene, and benzene, and only
slightly soluble in n-hexane. They have been characterized by var-
ious spectroscopic techniques, and elemental analyses. The 1H
NMR spectra support that the ratio of isopropoxyl group OiPr and
Ti(OiPr2)4
Me3C
11H2
C7H8
N
CMe3
O
O
O
O
Ti
N
CMe3
29
Scheme 11. Synthesis of complex 29.
ligand anion is 2:1 for complexes 15 and 19, 1:1 for 23, 1:3 for
24, and 3:1 for 25, respectively. The solid-state structures of com-

L. Chen et al. / Inorganica Chimica Acta 402 (2013) 140–155
151
plexes 14–21, 23 and 24 have further been confirmed by X-ray dif-
fraction analyses.
The single-crystal X-ray diffraction analyses show that there is
one molecule (L3)Ti(OiPr)2 (17) and one molecule (L3)2Ti (18),
one molecule (L5)Ti(OiPr)2 (20) and one molecule (L5)2Ti (21), in
the lattice. In each molecule (L1)2Ti (14), (L2)2Ti (16), (L3)2Ti
(18), and (L5)2Ti (21), the Ti4+ ion is six coordinate and
r-bound
to four oxygen atoms and two nitrogen atoms from the two ligands
1, 2, 3 and 5, respectively, in a distorted-octahedral geometry
(Figs. 2–5), in which the two nitrogen atoms in 14, 16 and 21 adopt
a cis configuration while those of 18 are situated in trans configu-
ration, presumably because of the steric effect of the ligand. The
average distance of Ti–OAr is 1.875(2) Å for 14, 1.879(2) Å for 16,
1.893(3) Å for 18, and 1.869(3) Å for 21, respectively, and the aver-
age distance of Ti–N is 2.229(2) Å for 14, 2.225(2) Å for 16, 2.241(3
) Å for 18, and 2.241(3) Å for 21, respectively. These crystal data are
comparable to those found in rac-(L1)2Ti and (S)-(L1)2Ti [72]. The
twisting between the biaryl rings of torsion angles are 58.5(3)°
and 64.0(3)° for 14, 59.3(2)° and 64.4(2)° for 16, 64.4(4)° and
68.4(4)° for 18, and 64.1(4)° and 58.0(4)° for 21, respectively.
The single-crystal X-ray diffraction analyses show that in each
molecule (L2)Ti(OiPr)2 (15), (L3)Ti(OiPr)2 (17), (L4)Ti(OiPr)2 (19),
Fig. 4. Molecular structure of 18 in the co-crystallized complexes 17ꢁ18 (thermal
ellipsoids drawn at the 35% probability level).
and (L5)Ti(OiPr)2 (20), the Ti4+ ion is five coordinate and
r-bound
to two oxygen atoms from two isopropoxyl groups (OiPr) and
two oxygen atoms and one nitrogen atom from the one ligand 2,
3,
4 and 5, respectively, in a distorted-trigonal–bipyramidal
Fig. 2. Molecular structure of 14 (thermal ellipsoids drawn at the 35% probability
level).
Fig. 5. Molecular structure of 21 in the co-crystallized complexes 20ꢁ21 (thermal
ellipsoids drawn at the 35% probability level).
Fig. 3. Molecular structure of 16 (thermal ellipsoids drawn at the 35% probability
Fig. 6. Molecular structure of 15 (thermal ellipsoids drawn at the 35% probability
level).
level).

152
L. Chen et al. / Inorganica Chimica Acta 402 (2013) 140–155
geometry (Figs. 6–9), in which the nitrogen atom and one isoprop-
oxyl group (OiPr) are situated on the axial position. The average
distance of Ti–OAr is 1.884(2) Å for 15, 1.862(3) Å for 17, 1.873(1
) Å for 19, and 1.880(4) Å for 20, respectively, which are slightly
longer than the average distance of Ti–OiPr in 15 (1.784(2) Å), 17
(1.789(3) Å), 19 (1.792(1) Å), and 20 (1.782(3) Å). The distance of
Ti–N is 2.211(2) Å for 15, 2.294(3) Å for 17, 2.269(1) Å for 19, and
2.246(4 ) Å for 20 respectively. The biaryl rings are twisted by
68.0(2)° for 15, 63.2(4)° for 17, 71.0(2)° for 19, and 60.7(4)° for
20, respectively. These structural data are comparable to those
found in 14, 16, 18 and 21 (Table 3).
The molecular structure of 23 shows that the Ti4+ ion is six coor-
dinate and
r-bound to two oxygen atoms from two isopropoxyl
groups (OiPr) and two oxygen atoms and two nitrogen atoms from
Fig. 7. Molecular structure of 17 in the co-crystallized complexes 17ꢁ18 (thermal
ellipsoids drawn at the 35% probability level).
Fig. 10. Molecular structure of 23 (thermal ellipsoids drawn at the 35% probability
level).
Fig. 8. Molecular structure of 19 (thermal ellipsoids drawn at the 35% probability
level).
Fig. 9. Molecular structure of 20 in the co-crystallized complexes 20ꢁ21 (thermal
Fig. 11. Molecular structure of 24 (thermal ellipsoids drawn at the 35% probability
level).
ellipsoids drawn at the 35% probability level).

L. Chen et al. / Inorganica Chimica Acta 402 (2013) 140–155
153
the two ligands 7 in a distorted-octahedral geometry (Fig. 10), in
which the two nitrogen atoms (N(1) and N(2)) are situated in cis
configuration and the other nitrogen atoms (N(3) and N(4)) are
not coordinated to the Ti4+ ion. The average distance of Ti–OAr is
1.922(3) Å, which is slightly longer than that of Ti–OiPr (1.807(3
) Å). The average distance of Ti–N is 2.284(3) Å. These structural
data are comparable to those found in complexes 14–21 (Table
3). The torsion angles between the binaphthyl rings are 62.3(4)°
and 69.2(4)°, which are close to those found in 14, 15 and 16 (Table
3).
The molecular structure of 24 shows that the Ti4+ ion is six coor-
dinate and
r-bound to one oxygen atom from one isopropoxyl
group (OiPr) and three oxygen atoms from the three ligands 7
and two nitrogen atoms from one pyridinylmethylimido group of
one ligand 7 in a distorted-octahedral geometry (Fig. 11), in which
the two nitrogen atoms (N(1) and N(2)) are situated in cis
configuration and the other two pyridinylmethylimido groups of
the other two ligands 7 are not coordinated to the Ti4+ ion. The
average distance of Ti–OAr is 1.891(2) Å, which is slightly longer
than the distance of Ti–OiPr (1.768(2) Å). The average distance of
Ti–N is 2.268(3) Å. The twisting between the binaphthyl rings of
torsion angles are 63.9(3)°, 83.2(3)° and 87.6(3)°. These structural
data are comparable to those found in complex 23.
Fig. 12. Molecular structure of 29 (thermal ellipsoids drawn at the 35% probability
level).
3.3. Synthesis and characterization of titanium complexes with C2-
symmetric ligands
of Ti(OiPr)4 with 1 equiv of 8H2, 9H2, 10H2 or 11H2 in toluene gives,
after recrystallization from a toluene solution, the mono-ligated
complex (L8)2Ti(OiPr)2 (26), (L9)2Ti(OiPr)2 (27), (L10)2Ti(OiPr)2
Simultaneously, we have also prepared a series of chiral tita-
nium complexes with C2-symmetric ligands 8H2–11H2. Treatment
Table 4
Enantioselective hydrophosphonylation of aromatic aldehydes catalyzed by titanium complexes.a
OH
O
P
OMe
O
titanium complex
+
Ar * P(OMe)2
O
OMe
H
Ar
H
Entry
Complex
Ar
Solvent
Temp. (°C)
Yieldb (%)
ee (%)c
1
2
3
4
5
6
7
8
14
15
16
19
21
22
23
24
25
26
27
28
29
21
21
21
21
21
21
21
21
21
21
21
21
21
21
21
21
Ph
Ph
Ph
Ph
Ph
Ph
Ph
Ph
Ph
Ph
Ph
Ph
Ph
Ph
Ph
Ph
Ph
Ph
toluene
toluene
toluene
toluene
toluene
toluene
toluene
toluene
toluene
toluene
toluene
toluene
toluene
CH2Cl2
Et2O
THF
THF
THF
THF
THF
THF
THF
THF
20
20
20
20
20
20
20
20
20
20
20
20
20
20
20
20
10
0
20
20
20
20
20
20
20
20
20
20
20
90
95
90
96
88
96
91
84
90
90
85
90
87
90
91
94
78
42
91
86
82
88
87
89
95
90
95
86
84
20
7.6
22
7.2
27
7.7
18
6.3
5.0
5.3
6.7
5.9
7.8
30
24
45
47
49
48
53
47
56
66
61
40
45
41
42
44
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
1-naphthyl
2-CH3C6H4
2-FC6H4
2-MeOC6H4
2-ClC6H4
3-ClC6H4
4-ClC6H4
4-FC6H4
4-NO2C6H4
4-MeOC6H4
4-CH3C6H4
THF
THF
THF
THF
THF
THF
a
b
c
All reactions were carried on a 0.5 mmol scale with 10 mol% of complex and 1.3 equiv of dimethyl phosphate, solvent 1.0 mL, time 48 h.
Isolated yields.
Enantiomeric excess was determined by chiral HPLC.

154
L. Chen et al. / Inorganica Chimica Acta 402 (2013) 140–155
(28) and (L11)2Ti(OiPr)2 (29), respectively, in good yields (Schemes
8–11). These complexes are stable in dry nitrogen atmosphere,
while they are sensitive to moisture. They are soluble in organic
solvents such as THF, DME, pyridine, toluene, and benzene, and
only slightly soluble in n-hexane. They have been characterized
by various spectroscopic techniques and elemental analyses. Their
1H NMR spectra indicate that the complexes are symmetrical on
the NMR timescale, and support that the ratio of isopropoxyl group
OiPr and ligand anion 8, 9, 10 or 11 is 2:1. The solid-state structure
of complex 29 has been further confirmed by X-ray diffraction
analysis.
bis-ligated titanium complex (L1)2Ti (14), while under similar
reaction conditions the more bulky ligands 2H2, 4H2, and 6H2 form
the mono-ligated titanium complexes (L2)Ti(OiPr)2 (15), (L4)Ti(Oi-
Pr)2 (19), and (L6)Ti(OiPr)2 (22), respectively. Overall the
bis-ligated complex titanium complexes are more effective chiral
catalysts for the enantioselective hydrophosphonylation reaction
than the C1 and C2-symmetric mono-ligated titanium complexes,
e.g., the bis-ligated complex 14 shows an increased enantioselec-
tivity in the hydrophosphonylation reaction, and a moderate ee va-
lue (up to 20%) has been obtained, while the mono-ligated C1-
symmetric complex 15 and C2-symmetric complex 29 do not.
Although our ligand set using peripheral biaryl-based NO2 or
N2O2-ligand in multidentate systems does not provide a suitable
coordination sphere to achieve a significant enantioselectivity
(ee > 90%) for hydrophosphonylation, the present results should
significantly expand the range of possibilities in designing catalysts
not only for hydrophosphonylation but also for many other reac-
tions [76–85]. Further optimization of the ligand architecture to
improve the enantiomeric excess for this transformation and the
exploration of these catalysts toward other types of transforma-
tions are still underway.
The molecular structure of 29 shows that the Ti4+ ion is six coor-
dinate and
r-bound to two oxygen atoms from two isopropoxyl
groups (OiPr) and two oxygen atoms and two nitrogen atoms from
the one ligand 11 in a distorted-octahedral geometry (Fig. 12), in
which the two nitrogen atoms are situated in cis configuration.
The average distance of Ti–OAr is 1.938(2) Å, which is slightly long-
er than that of Ti–OiPr (1.778(2) Å). The average distance of Ti–N is
2.273(2) Å. The twisting between the binaphthyl rings of torsion
angle is 65.3(2)°. These structural data are comparable to those
found in complexes 14 and 15 (Table 3).
3.4. Asymmetric hydrophosphonylation of aldehydes
Acknowledgements
To examine the catalytic potential of these complexes toward
the asymmetric reactions, hydrophosphonylation of aromatic alde-
hydes with dimethyl phosphite have been tested under the condi-
tions given in Table 4.
This work was supported by the National Natural Science Foun-
dation of China (Grant Nos. 21074013, 21172022, 21272026),
the Program for New Century Excellent Talents in University
(NCET-10-0253), the Fundamental Research Funds for the Central
Universities, and Beijing Municipal Commission of Education.
The titanium complexes 14–16, 19, and 21–29 are efficient cat-
alysts for hydrophosphonylation of aromatic aldehydes with di-
methyl phosphate in toluene, however, the enantiomeric excess
is low (Table 4, entries 1–13). The bis-ligated complex 21 shows
the highest enantioselectivity for this transformation, but only a
moderate ee value (27%) has been obtained (Table 4, entry 5).
When C2-symmetric ligands 8–11 are used, the different enanti-
oselectivity between the bis-ligated C2-symmetric complexes and
mono-ligated C2-symmetric complexes is observed (Table 4, en-
tries 1, 3, 5, 10–13), but rather poor enantioselectivities (only up
to 7.8% ee) mediated by complexes 26–29 have been obtained. Sol-
vent has a notable effect on the enantioselectivity (Table 4, entries
5, 14–16), and a moderate enantioselectivity (45% ee) has been ob-
tained in THF. The enantioselectivity can be slightly improved by
lowering the temperature but the rate decreases (Table 4, entries
16–18). When various aromatic aldehydes are used (Table 4, en-
tries 19–29), the steric hindrance has a noticeable effect on the
enantioselectivity, and 2-chlorobenzaldehyde gives the best
enantioselectivity with 66% ee (Table 4, entry 23), but the elec-
tronic effect on the enantioselectivity is not noticed. The titanium
complexes 14–16, 19, and 21–29 can promote the asymmetric
hydrophosphonylation of aromatic aldehydes, however, these
complexes showed either no activity or rather poor activity for
hydrophosphonylation of aliphatic aldehydes or ketones such as
valeraldehyde and acetophenone, in which racemic products with
low conversions (<5%) were detected under similar reaction condi-
tions, presumably because of the electronic effect of the substrates.
Appendix A. Supplementary material
CCDC 922365, 922366, 922367, 922368, 922369, 922370,
922373, 922374, and 922379 contains the supplementary crystal-
lographic data for 14, 15, 16, 17ꢁ18, 19, 20ꢁ21, 23, 24, and 29. These
data can be obtained free of charge from The Cambridge
Crystallographic Data Centre via www.ccdc.cam.ac.uk/data_re-
quest/cif. Supplementary data associated with this article can be
found, in the online version, at http://dx.doi.org/10.1016/
j.ica.2013.04.008.
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