Synthesis, characterization and properties of titanium phosphonate clusters

Article abstract of DOI:10.1016/j.poly.2018.02.030

Titanium phosphonate clusters were synthesized by the reactions of titanium tetraisopropoxide (Ti(OiPr)₄) with arylphosphonic acids (ArPO₃H₂, Ar = Ph, 1-Nap, 4-MeOPh, 4-FPh, 4-ClPh, 4-BrPh, and 4-BrBn) and H₂O in tetrahydrofuran (THF) at room temperature. [Ti₄(μ₃-O)(OiPr)₅(μ-OiPr)₃(O₃PAr)₃]·solv (Ar = Ph (1), 1-Nap (2), 4-MeOPh (3), 4-FPh (4), 4-ClPh (5); solv = thf for 1 and 2 or 2-propanol for 3–5) were isolated as new Ti₄P₃-type clusters, while Ti₇(μ₃-O)₂(OiPr)₆(μ-OiPr)₆(O₃PBnBr)₆ (6) was isolated as a Ti₇P₆-type cluster. A co-crystal of Ti₄P₃- (7a) and Ti₇P₆-type (7b) clusters were obtained when 4-BrPhPO₃H₂ was used, and [Ti(OiPr)(acac)(O₃PPh)]₄ (8), a new cage cluster, was obtained when Ti(acac)₂(OiPr)₂ (Hacac = acetylacetone) was reacted with PhPO₃H₂.

Full text of DOI:10.1016/j.poly.2018.02.030

Accepted Manuscript
Synthesis, characterization and properties of titanium phosphonate clusters
Ryohei Hayami, Takuya Sagawa, Satoru Tsukada, Kazuki Yamamoto, Takahiro
Gunji
PII:
S0277-5387(18)30129-3
https://doi.org/10.1016/j.poly.2018.02.030
POLY 13070
DOI:
Reference:
To appear in:
Polyhedron
Received Date:
Accepted Date:
17 January 2018
27 February 2018
Please cite this article as: R. Hayami, T. Sagawa, S. Tsukada, K. Yamamoto, T. Gunji, Synthesis, characterization
and properties of titanium phosphonate clusters, Polyhedron (2018), doi: https://doi.org/10.1016/j.poly.2018.02.030
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Synthesis, characterization and properties of titanium phosphonate clusters
a
a
b
a
a
Ryohei Hayami , Takuya Sagawa , Satoru Tsukada , Kazuki Yamamoto , Takahiro Gunji *
a
Department of Pure and Applied Chemistry, Faculty of Science and Technology, Tokyo University
of Science, 2641 Yamazaki, Noda, Chiba 278-8510, Japan.
gunji@rs.noda.tus.ac.jp
b
Advanced Materials Laboratory, Advanced Automotive Research Collaborative Laboratory,
Graduate School of Engineering, Hiroshima University, 1-4-1 Kagamiyama, Higashi-Hiroshima City,
Hiroshima 739-8527, Japan.
Abstract
Titanium phosphonate clusters were synthesized by the reactions of titanium tetraisopropoxide
(
Ti(OiPr)
4
) with arylphosphonic acids (ArPO
3
H
2
, Ar = Ph, 1-Nap, 4-MeOPh, 4-FPh, 4-ClPh, 4-BrPh,
tetrahydrofuran (THF) at room temperature.
]·solv (Ar = Ph (1), 1-Nap (2), 4-MeOPh (3), 4-FPh (4), 4-ClPh
-type clusters, while
-type cluster. A co-crystal of Ti
-type (7b) clusters were obtained when 4-BrPhPO was used, and
PPh)] (8), a new cage cluster, was obtained when Ti(acac) (OiPr) (Hacac =
and
4-BrBn)
and
H
2
O
in
[
(
4
Ti (
3
-O)(OiPr)
5
(-OiPr)
3
(O
PAr)
3 3
4 3
5); solv = thf for 1 and 2 or 2-propanol for 3–5) were isolated as new Ti P
Ti
7 3
( -O)
2
(OiPr)
6
(-OiPr)
6
(O
3
PBnBr)
6
(6) was isolated as a Ti
7
P
6
4 3
P -
(
[
7a) and Ti
7
P
6
3 2
H
Ti(OiPr)(acac)(O
3
4
2
2
3 2
acetylacetone) was reacted with PhPO H .
Keywords: Titanium/ Phosphorus/ Cluster compound/ Titanium alkoxide
Introduction
Titanium-oxo clusters, which are composed of titanoxane (Ti–O–Ti) bonds, are used as nano
building blocks of organic–inorganic hybrid materials [1–4]. For instance, Sanchez [5,6] and
Schubert [7,8] synthesized organic–inorganic hybrid materials by the radical co-polymerization of
polymerizable functional clusters and organic monomers such as styrene or hydroxyethyl
methacrylate; these materials exhibited improved thermal stabilities and increased surface areas
compared to the corresponding pure organic polymers. However, the syntheses of these clusters have
some problems, such as the necessity for hydrothermal syntheses [9,10] and long reaction times
[
8,9,11], and lower stabilities [12,13].
Titanium phosphonate clusters, which are composed of titanoxane (Ti–O–Ti) and
phosphatitanoxane (Ti–O–P) bonds, have been the focus of recent research into new nano building
blocks because the Ti–O–P bond is more stable to hydrolysis; reactivities toward hydrolysis have
been reported to follow the order: Ti–O–Ti ≤ Ti–O–P < (Ti–acetylacetonate) < Ti–OOCR << Ti–OR,
and Ti–O–P < Ti–O–Si [14–16]. Moreover, P–C bonds exhibit very high chemical and thermal
stabilities. Titanium phosphonate clusters are classified into three types on the basis of the
substituents on the titanium atoms, namely (i) non-functional-type, (ii) alkoxy-type and (iii)

carboxy-alkoxy-type. Non-functional-type clusters, namely [(Cp*TiO
Me, Ph,) and [(Cp*Ti) (O PtBu) (tBuPO H)(-O) ], were first prepared by Roesky et al. [17]
through the reactions of Cp*TiX (X = Me, Cl) with RPO (R = Me, Ph, or tBu), while Mehring
and Mutin et al. first reported the preparation of the [Ti -O)(OiPr) (-OiPr) (O PR) ]·DMSO
alkoxy-type clusters through the reactions of Ti(OiPr) with RPO (R = Me, tBu, Ph and
-cyanophenyl) in DMSO [18,19]; Schubert [20] and Coppens [21] reported other alkoxy-type
clusters. We previously reported the synthesis of organic–inorganic hybrid materials containing the
Ti ( -O)(OiPr) (-OiPr) (O PPh) ]·THF cluster (1), which exhibited improved thermal and
3
PR)
4
(-O)
2 5 5
] (Cp* = C Me , R
=
3
3
2
3
2
3
3 2
H
(
4 3
5
3
3
3
4
3 2
H
4
[
4
3
5
3
3
3
mechanical properties, and refractive indices, compared with pure organic polymers [22,23].
Carboxy-alkoxy-type clusters bearing alkoxyl groups and carboxyl groups on the titanium atoms
were reported by Schubert [24,25] and Zhang [26–31]. In particular, Zhang reported that the
bandgap energy is dependent on the carboxyl-group substituent [26]. In recent years,
acetylacetonato-alkoxy-type clusters have been reported as a new classification type by Murugavel
et al. [32].
Although P–C and Ti–O–P bonds are very stable, almost all titanium phosphonate clusters are
composed of non-functional organic phosphonato groups; clusters bearing functional organic
phosphonato groups are known only for halopropyl, vinyl, allyl and 4-cyanophenyl moieties
[
19,20,24,25]. In particular, the aromatic phosphonato group has only been reported for the
4-cyanophenyl moiety.
Herein, we report the syntheses of new alkoxy-type titanium phosphonate clusters (1-8, Scheme 1)
4 3 2
prepared by reacting Ti(OiPr) with ArPO H (Ar = Ph, 1-Nap, 4-MeOPh, 4-FPh, 4-ClPh, 4-BrBn
and 4-BrPh) in THF for several days to weeks. In particular, clusters 3-7 have functional aromatic
phosphonato groups that have been applied to many organic reactions, such as cross-coupling
reactions. Moreover, the new acetylacetonato-alkoxy-type cage titanium phosphonate cluster 8 was
2 2 3 2
synthesized by the reaction of Ti(acac) (OiPr) with PhPO H in THF.
Materials and methods
Reagents
All reactions were carried out under an argon atmosphere or in a glovebox. Solvents were purified
using standard procedures [33] and stored over activated 3Å molecular sieves. Ti(OiPr)
acetylacetone (Hacac), nickel dibromide (NiBr ) and triethyl phosphite (P(OEt) ) were purchased
from Wako Pure Chemical Industries Ltd., Tokyo, Japan. 4-Bromoanisole, 1-bromonaphthalene,
-bromo-4-fluorobenzene, 1-bromo-4-chlorobenzene, 4-bromobenzyl bromide and
phenylphosphonic acid (PhPO ) were purchased from Tokyo Chemical Industry Co., Ltd., Tokyo,
Japan. Bromo(trimethyl)silane (Me SiBr) was purchased from Sigma-Aldrich Japan K. K, Tokyo,
Japan. Ti(OiPr) was purified by distillation (70.0-71.6 °C/1 mmHg) before use. Silica-gel column
4
,
2
3
1
3 2
H
3
4
chromatography was performed using Wako gel C-200 (spherical, neutral, 75–150 m) purchased
from Wako Pure Chemical Industries Ltd., Tokyo, Japan.
The arylphosphonate esters were prepared by the Michaelis-Arbuzov reactions of the haloaryl
compounds with P(OEt)
3
, catalyzed by NiBr
2
[34,35]. The arylphosphonic acids were prepared by
SiBr and methanol [36,37]. The preparation
the alcoholysis of the aryl phosphonate esters with Me
3

methods and results are provided in the Supporting Information. In addition, all the arylphosphonic
acids were dried at 60 °C in vacuo for 6 h. Titanium bis(acetylacetonate) diisopropoxide
(
(
Ti(acac)
2 2
(OiPr) ) was prepared according to the literature [38] and purified by distillation
133-134 °C / 3 mmHg).
Measurements
All nuclear magnetic resonance (NMR) spectra were recorded on a JEOL JNM-ECP500
1
13
19
31
spectrometer ( H at 500.16 MHz, C at 125.77 MHz, F at 470.62 MHz and P at 202.46 MHz) at
1
13
1
approx. 23 °C. The H and C{ H} NMR spectra were recorded using tetramethylsilane as the
1
9
1
31
1
internal standard. The F{ H} and P{ H} NMR spectra were recorded using trifluoroacetic acid
3
1
and 85% phosphoric acid as external standards, respectively. When a reaction was followed by
NMR spectroscopy, the reaction solution was transferred into an NMR tube and a capillary
containing H PO dissolved in D O was used as the external standard and to lock the signal. Fourier
P
3
4
2
transform infrared (FT-IR) spectra were recorded on a JASCO FT/IR-6100 spectrometer with
attenuated total reflectance (ATR, ZnSe prism, JASCO ATR PRO 0450-S). Elemental analyses were
performed using an Perkin Elmer 2400II elemental analyzer. Thermogravimetric-differential thermal
analysis (TG-DTA) studies were performed using a NETZCH JAPAN TG-DTA 2000SE instrument;
samples were heated to 1000 °C at a rate of 10 °C/min under a flow of air. Thermogravimetry mass
spectrometry (TG-MS) was performed using a Bruker TG-DTA 2000SA/MS 9610 instrument. The
2 3
sample was heated to 500 °C at a rate of 10 °C/min under a 100 mL/min flow of He. -Al O was
used as the reference for both thermal analysis methods. UV-Vis absorption spectra were recorded on
a JASCO V-670 UV-VIS-NIR spectrophotometer. X-ray photoelectron spectroscopy (XPS) was
performed using a Shimadzu KRATOS Nova instrument with monochromatic Al K radiation (15
kV, 150 W) as the X-ray source; spectra were referenced against the C(1s) peak at 284.6 eV. Crystal
data were collected using a Bruker AXS SMART APEX CCD X-ray diffractometer equipped with a
monochromatic Mo K radiation source (0.7107 Å). Empirical absorption corrections using
equivalent reflections and Lorentzian polarization corrections were performed using the SADABS
program [39]. All data were collected using the SMART and Bruker SAINTPLUS (Version 6.45)
software packages. Structures were solved using the SHELXS-97 program [40] and refined against
2
F using SHELXL-97 [41].
The deposition numbers are: CCDC-1487366 (for 1), 1553150 (for 2), 1553154 (for 3), 1553153
(
for 4), 1553152 (for 5), 1553149 (for 6), 1553151 (for 7) and 1561995 (for 8). Copies of the data
are available free of charge at http://www.ccdc.cam.ac.uk/conts/retrieving.html (or from the
Cambridge Crystallographic Data Centre, 12 Union Road, Cambridge, CB2 1EZ, UK; Fax: +44
1223 336033; e-mail: deposit@ccdc.cam.ac.uk).
Synthesis
General procedures for the synthesis of the titanium phosphonate clusters
Method A: A solution of ArPO
Ti(OiPr) (2 equiv.). A white precipitate was quickly formed. After stirring until the precipitate
disappeared, 0.33 equiv. of H O in THF (H O:THF = 1:99 v/v) was added, followed by stirring
3 2 4
H (1 equiv.) in THF (150 vol% based on Ti(OiPr) ) was added to
4
2
2

overnight. The solution was concentrated until a white precipitation appeared, after which the
mixture was heated to dissolve the precipitate. After the colorless solution was left standing for
several days at room temperature, colorless block single-crystals were obtained. The crystals were
collected by filtration, washed with THF and dried under reduced pressure to afford the titanium
phosphonate cluster.
1
[
Ti
4
3
(
3
-O)(OiPr)
5
(-OiPr)
3
(O
3
PPh)
3
]·thf (1): 58% yield. H NMR (500 MHz, CDCl
3
) , ppm: 1.06
),
3
(
d, JH–H = 5.5 Hz, 12H, terminal OCH(CH
3
)
2
), 1.37 (d, JH–H = 6.0 Hz, 18H, terminal OCH(CH
3
)
2
3
1
.44 (d, JH–H = 6.0 Hz, 18H, bridged OCH(CH
3
)
2
), 1.75–1.81 (m, 6H, THF), 3.79–3.82 (m, 6H,
3
THF), 4.69 (sept, JH–H = 6.0 Hz, 3H, terminal OCH(CH
3
)
2
), 4.92 (br s, 2H, terminal OCH(CH
3
)
2
),
3
3
5
.04 (sept, JH–H = 6.0 Hz, 3H, bridged OCH(CH
3
)
2
), 7.30–7.39 (m, 9 H, Ar), 7.88 (ddd, JH–H = 7.5
3
13
1
Hz, JP–H = 12.0 Hz, 6H, Ar). C{ H} NMR (126 MHz, CDCl
3
) , ppm: 24.51, 24.83, 25.36, 68.84,
2
4
3
7
9
8.45, 79.14, 79.40, 127.31 (d, JP–C = 14.4 Hz, Ar), 129.72 (d, JP–C = 2.9 Hz, Ar), 131.05 (d, JP–C
=
1
31
1
.6 Hz, Ar), 134.44 (d, JP–C = 203.9 Hz, Ar). P{ H} NMR (202 MHz, CDCl ) , ppm: 7.8, 9.1.
3
–
1
FT-IR (ATR/cm ): 3059, 2969, 2929, 2863, 1460, 1439, 1375, 1362, 1328, 1193, 1158, 1130, 1112,
093, 1066, 1044, 997, 987, 976, 949, 891, 849, 834, 755, 719, 697, 614, 595, 578, 560. Ceramic
yield: 42.7% (calcd. for Ti 16, 43.0%).
1
4 3
P O
1
[
Ti
4
(
3
-O)(OiPr)
5
(-OiPr)
3
(O
3
PNap)
3
]·thf (2): 22% yield. H NMR (500 MHz, CDCl
3
) , ppm:
), 1.41 (d,
3
0
.82 (br s, 12H, terminal OCH(CH
3
)
2
), 1.39 (d, JH–H = 6.5 Hz, 18H, terminal OCH(CH
3
)
2
3
J
3 2
H–H = 6.0 Hz, 18H, bridged OCH(CH ) ), 1.72–1.78 (m, 12H, THF), 3.69–3.72 (m, 12H, THF),
3
4
.44 (br s, 2H, terminal OCH(CH
3
)
2
), 4.69 (sept, JH–H = 6.5 Hz, 3H, terminal OCH(CH
3
)
2
), 5.05
3
3
(
sept, JH–H = 6.0Hz, 3H, bridged OCH(CH
3
)
2
), 7.48–7.53 (m, 6H, Ar), 7.64 (dd, JH–H = 7.0, 8.5 Hz,
3
3
3
3
H, Ar), 7.85 (d, JH–H = 8.5 Hz, 3H, Ar), 7.90 (d, JH–H = 8.0 Hz, 3H, Ar), 8.26 (dd, JH–H = 7.0 Hz,
3
3
13
1
J
3
P–H = 16.0 Hz, 3H, Ar), 9.20 (d, JH–H = 9.0 Hz, 3H, Ar). C{ H} NMR (126 MHz, CDCl ) ,
ppm: 24.50, 24.71, 24.88, 25.06, 25.42, 68.39, 78.66, 79.05, 79.38, 124.45 (d, JC–P = 16.4 Hz, Ar),
1
1
25.55 (d, JC–P = 39.4 Hz, Ar), 126.26 (d, JC–P = 301.3 Hz, Ar), 127.8, 129.47 (d, JC–P = 4.8 Hz, Ar),
30.61 (d, JC–P = 3.9 Hz, Ar), 130.70 (d, JC–P = 7.7 Hz, Ar), 131.73 (d, JC–P = 199.6 Hz, Ar), 133.38
31
1
(
d, JC–P = 11.4 Hz, Ar), 133.49 (d, JC–P = 12.6 Hz, Ar). P{ H} NMR (202 MHz, CDCl
3
) , ppm: 8.3.
FT-IR (ATR/cm ): 3059, 3038, 2968, 2929, 2965, 1507, 1459, 1375, 1362, 1333, 1192, 1112, 1096,
071, 1033, 999, 948, 850, 832, 798, 774, 734, 676, 614, 590, 567. Ceramic yield: 36.5% (calcd. for
Ti 16, 35.7%).
–
1
1
4 3
P O
Method B: A solution of ArPO
2 equiv.). A white precipitate was quickly formed. The mixture was stirred until the precipitate
disappeared, after which 0.33 equiv. of H O in THF (H O:THF = 1:99 v/v) was added, followed by
3 2 4 4
H in THF (150 vol% based on Ti(OiPr) ) was added to Ti(OiPr)
(
2
2
stirring overnight. After concentrating, the residue was dissolved in THF at room temperature. The
solution was covered with iPrOH. Colorless single crystals precipitated from the solution over a
period of several days to weeks. The crystals were collected by filtration, washed with iPrOH and
dried under reduced pressure to afford the titanium phosphonate cluster.

1
[
Ti
4
(
3
-O)(OiPr)
5
(-OiPr)
3
(O
3
PPhOMe)
3
]·iPrOH (3): 59% yield. H NMR (500 MHz, CDCl
3
) ,
),
), 1.43 (d, JH–H = 6.0 Hz, 18H, bridged
3
ppm: 1.10 (d, JH–H = 6.0 Hz, 24H, crystal solvent and coordinated iPrOH, and terminal OCH(CH
3
)
2
3
3
1
.33 (d, JH–H = 6.0 Hz, 18H, terminal OCH(CH
3
)
2
OCH(CH
3
)
2
), 3.67 (s, 2H, OH), 3.77 (s, 9H, OCH
3
), 4.47 (br s, 4H, solvent and terminal
3
3
OCH(CH
3
)
2
), 4.66 (sept, JH–H = 6.0 Hz, 3H, terminal OCH(CH
3
)
2
), 5.00 (sept, JH–H = 6.0 Hz, 3H,
3
4
3
bridged OCH(CH
3
)
2
), 6.84 (dd, JH–H = 8.5 Hz, JP–H = 2.5 Hz, 6H, Ar), 7.81 (dd, JH–H = 8.5 Hz,
3
13
1
J
P–H = 13.5 Hz, 6H, Ar). C{ H} NMR (126 MHz, CDCl
3
) , ppm: 24.55, 24.82, 24.86, 54.92,
2
1
3
7
1
8.24, 79.18, 112.71 (d, JP–C = 16.4 Hz, Ar), 126.22 (d, JP–C = 210.5 Hz, Ar), 132.91 (d, JP–C
=
4
31
1
0.6 Hz, Ar), 160.74 (d, JP–C = 3.8 Hz, Ar). P{ H} NMR (202 MHz, CDCl
3
) , ppm: 8.6, 9.6.
–
1
FT-IR (ATR/cm ): 3482, 2970, 2931, 2863, 2838, 1601, 1573, 1505, 1463, 1442, 1375, 1362, 1326,
1
6
320, 1293, 1253, 1197, 1158, 1135, 1105, 1092, 1081, 1034, 993, 977, 944, 850, 826, 812, 801, 683,
61, 613, 591, 553. Ceramic yield: 39.4% (calcd. for Ti
4
P
3
O
16, 39.8%).
1
[
Ti
4
(
3
-O)(OiPr)
5
(-OiPr)
3
(O
3
PPhF)
3
]·iPrOH (4): 12% yield. H NMR (500 MHz, CDCl
3
) ,
3
3
ppm: 1.09 (d, JH–H = 6.0 Hz, 24H, solvent, coordinated and terminal OCH(CH
3
)
2
), 1.33 (d, JH–H
=
3
6
2
3
.5 Hz, 18H, terminal OCH(CH
3
)
2
), 1.42 (d, JH–H = 6.0 Hz, 18H, bridged OCH(CH
3
3
)
2
), 3.43 (br s,
H, OH), 4.42 (br s, 4H, solvent, coordinated and terminal OCH(CH
3
)
2
), 4.66 (sept, JH–H = 6.5 Hz,
3
H, terminal OCH(CH
3
)
2
), 5.01 (sept, JH–H = 6.0 Hz, 3H, bridged OCH(CH
3
)
2
), 7.01 (ddd (like-td),
13
1
J = 3.5 Hz, 9.5 Hz, 6H, Ar), 7.86 (ddd, J = 6.0 Hz, 8.0 Hz, 13.0 Hz, 6H, Ar). C{ H} NMR (126
MHz, CDCl ) , ppm: 24.59, 24.79, 24.87, 78.54, 78.77, 79.59, 79.76, 114.48 (dd, J = 16.4, 82.2 Hz,
Ar), 130.32 (dd, J = 3.8, 207.6 Hz, Ar), 133.51 (dd, J = 8.6, 10.6 Hz, Ar), 163.99 (dd, J = 3.9, 249.0
3
31
1
19
1
Hz, Ar). P{ H} NMR (202 MHz, CDCl
3
) , ppm: 7.0, 8.3. F{ H} NMR (471 MHz, CDCl
3
) ,
ppm: −109.96, −110.16. FT-IR (ATR/cm ): 3068, 2971, 2930, 2865, 1595, 1499, 1464, 1377, 1362,
327, 1224, 1195, 1159, 1131, 1110, 1088, 1042, 998, 977, 950, 881, 853, 831, 683, 605. Ceramic
yield: 41.7% (calcd. for Ti 16, 42.8%).
–
1
1
4 3
P O
1
[
Ti
4
(
3
-O)(OiPr)
5
(-OiPr)
3
(O
3
PPhCl)
3
]·iPrOH (5): 13% yield. H NMR (500 MHz, CDCl
3
) ,
3
3
ppm: 1.08 (d, JH–H = 5.5 Hz, 24H, solvent, coordinated and terminal OCH(CH
3
)
2
), 1.33 (d, JH–H
=
3
6
2
.0 Hz, 18H, terminal OCH(CH
3
)
2
), 1.41 (d, JH–H = 6.0 Hz, 18H, bridged OCH(CH
3
)
2
), 3.68 (br s,
3
H, OH), 4.39 (br s, 4H, solvent and terminal OCH(CH
)
3 2
), 4.65 (sept, JH–H = 6.0 Hz, 3H, terminal
3
4
3
OCH(CH
3
)
2
), 5.00 (sept, JH–H = 6.0 Hz, 3H, bridged OCH(CH
3
)
2
), 7.31 (dd, JP–H = 3.0 Hz, JH–H
=
3
3
13
1
8
.5 Hz, 6H, Ar), 7.80 (dd, JH–H = 8.5 Hz, JP–H = 13.0 Hz, 6H, Ar). C{ H} NMR (126 MHz,
2
CDCl
3
) , ppm: 24.56, 24.72, 24.78, 24.86, 78.68, 79.63, 79.74, 127.64 (d, JC–P = 15.4 Hz, Ar),
3
1
4
1
32.63 (d, JC–P = 10.6 Hz, Ar), 133.29 (d, JC–P = 205.8 Hz, Ar), 135.88 (d, JC–P = 4.8 Hz, Ar).
31
1
–1
P{ H} NMR (202 MHz, CDCl
3
) , ppm: 6.6, 7.7. FT-IR (ATR/cm ): 3481, 3065, 2974, 2932,
2
8
862, 1584, 1563, 1481, 1463, 1449, 1377, 1362, 1327, 1202, 1135, 1114, 1086, 1060, 988, 948, 852,
4 3
35, 821, 753, 596, 560. Ceramic yield: 38.4% (calcd. for Ti P O16, 39.4 %).
1
Ti
7
(
3
-O)
2
(OiPr)
6
(-OiPr)
6
(O
3
PBnBr)
6
(6): 40% yield. H NMR (500 MHz, CDCl
3
) , ppm: 1.36
),
), 4.94 (sept,
3
3
(
d, JH–H = 6.0 Hz, 36H, terminal OCH(CH
3
)
2
), 1.38 (d, JH–H = 6.5 Hz, 36H, bridged OCH(CH
3
)
2
2
3
2.57 (d, JP–H = 23.5 Hz, 12H, CH
2
), 4.69 (sept, JH–H = 6.0 Hz, 6H, terminal OCH(CH
3
)
2

3
3
3
4
J
J
H–H = 6.5 Hz, 6H, bridged OCH(CH
3
)
2
), 7.19 (dd, JH–H = 8.5 Hz, JP–H = 2.0 Hz, 12H, Ar), 7.34 (d,
13
1
1
H–H = 8.5 Hz, 12H, Ar). C{ H} NMR (126 MHz, CDCl
3
) , ppm: 24.23, 24.99, 34.14 (d, JP–C
=
4
5
1
50.1 Hz, CH
2
), 78.66, 79.79, 119.51 (d, JP–C = 3.9 Hz, Ar), 131.25 (d, JP–C = 2.9 Hz, Ar), 132.11
3
2
31
1
(
d, JP–C = 6.7 Hz, Ar), 132.66 (d, JP–C = 8.6 Hz, Ar). P{ H} NMR (202 MHz, CDCl
3
) , ppm:
–
1
1
4.1. FT-IR (ATR/cm ): 3065, 2973, 2929, 2865, 1487, 1462, 1447, 1410, 1376, 1363, 1328, 1253,
1161, 1129, 1092, 1046, 1027, 1002, 987, 947, 854, 830, 762, 704, 644, 606, 591, 563. Ceramic
yield: 37.4% (calcd. for Ti 29, 37.3%).
7 6
P O
2
([Ti
4
(
3
-O)(OiPr)
5
(-OiPr)
3
(O
3
PPhBr)
3
]·iPrOH)·(Ti
7
(
3
-O)
2
(OiPr)
6
6 3 6
(-OiPr) (O PPhBr) ) (7):
1
59% yield. H NMR (500 MHz, CDCl
3
) , ppm: 1.17 (br s, 36H, solvent, coordinated and terminal
3
3
OCH(CH
3
)
2
), 1.29 (d, JH–H = 6.0 Hz, 18H, terminal OCH(CH
3
)
2
), 1.31 (d, JH–H = 6.0 Hz, 18H,
3
3
bridged OCH(CH
3
)
2
), 1.32 (d, JH–H = 6.5 Hz, 18H, terminal OCH(CH
3
)
2
), 1.40 (d, JH–H = 6.5 Hz,
1
8H, bridged OCH(CH
3
)
2
3
), 1.78 (br s, 4H, OH), 4.22 (br s, 6H, solvent, coordinated and terminal
3
OCH(CH
3
)
2
), 4.63 (sept, JH–H = 6.0 Hz, 3H, terminal OCH(CH
3
)
2
), 4.64 (sept, JH–H = 6.0 Hz, 3H,
3
3
bridged OCH(CH
3
)
2
), 4.91 (sept, JH–H = 6.5 Hz, 3H, terminal OCH(CH
3
)
2
), 4.99 (sept, JH–H = 6.5
4
3
4
Hz, 3H, bridged OCH(CH
3
)
2
), 7.24 (dd, JP–H = 3.5 Hz, JH–H = 8.5 Hz, 6H, Ar), 7.47 (dd, JP–H = 3.0
3
3
3
3
Hz, JH–H = 8.0 Hz, 6H, Ar), 7.56 (dd, JH–H = 8.5 Hz, JP–H = 13.0 Hz, 6H, Ar), 7.72 (dd, JH–H = 8.0
3
13
1
Hz, JP–H = 13.0 Hz, 6H, Ar). C{ H} NMR (126 MHz, CDCl
3
) , ppm: 24.59, 24.64, 24.84, 24.87,
4
4
2
78.67, 78.89, 79.79, 79.90, 124.49 (d, JC–P = 3.9 Hz), 124.69 (d, JC–P = 4.8 Hz), 130.63 (d, JC–P
=
2
3
3
15.3 Hz), 130.67 (d, JC–P = 15.3 Hz), 132.93 (d, JC–P = 10.5 Hz), 133.01 (d, JC–P = 10.5 Hz),
1
1
31
1
133.11 (d, JC–P = 204.1 Hz), 133.34 (d, JC–P = 203.3 Hz). P{ H} NMR (202 MHz, CDCl
3
) ,
-
1
ppm: 6.8, 9.0. The underlined data are assigned to the Ti
7
P
6
-type cluster. FT-IR (ATR/cm ): 2972,
2
5
901, 1579, 1477, 1449, 1377, 1209, 1160, 1134, 1065, 1056, 983, 944, 852, 831, 816, 739, 618,
95.
Synthesis of [Ti(acac)(OiPr)(O
A solution of PhPO (1.01 g, 6.4 mmol) in THF (5 mL) was added to a solution of
Ti(acac) (OiPr) (4.64 g, 12.7 mol) in THF (7 mL), and the resultant solution was stirred at room
3 4
PPh)] (8)
3 2
H
2
2
temperature for 1 day. The red solution that formed was allowed to stand and pale-yellow crystals of
compound 1 grew from the solution over 3 days (1.34 g, 58 %).
Cluster 8: Elemental analysis: calcd. for C56
H
76
3
O
24
P
4
Ti
4
C 46.43, H 5.29. Found C 46.41, H 5.26.
1
3
H NMR (500 MHz / CDCl
3
) , ppm: 1.06 (d, JH–H = 5.0 Hz, 12H), 1.16 (d, JH–H = 6.0 Hz, 12H),
1
.69 (s, 12H), 1.76 (s, 12H), 1.80–1.83 (m, 4H, THF), 3.72 (br-s, 4H, THF), 4.51 (s, 4H), 4.80–4.82
3
2
(
m, 4H), 7.22–7.24 (m, 8H), 7.32–7.35 (m, 4H), 7.90 (dd, JH–H = 7.5 Hz, JP–H = 13.5 Hz, 8H).
3
1
1
2
C{ H} NMR (126 MHz / CDCl
3
) , ppm: 24.07, 24.46, 81.95, 102.48, 127.16 (d, JC–P = 15.4 Hz),
4
3
1
1
29.11 (d, JC–P= 2.9 Hz), 130.78 (d, JC–P = 9.6 Hz), 135.50 (d, JC–P = 204.8 Hz), 188.23, 188.82.
3
1
1
P{ H} NMR (202 MHz / CDCl
3
) , ppm: −1.53. Only the main NMR spectral data are reported.
-
1
FT-IR (ATR/ cm ): 3052, 2970, 2925, 2867, 1585, 1524, 1437, 1358, 1283, 1173, 1155, 1137, 1104,
050, 992, 984, 930, 852, 772, 751, 720, 696, 667, 655, 618, 609, 601, 570. Ceramic yield: 40.3 %
calcd. for Ti 18 41.7 %).
1
(
4 4
P O

Stability testing of cluster 1
A 50 mg sample of cluster 1 was dissolved in 5 mL of toluene in an argon atmosphere. A part of the
3 4 2
solution was transferred into an NMR tube and a capillary containing H PO dissolved in D O, and
the NMR tube was capped with a septum and stored under an air atmosphere.
Results and discussion
Syntheses
The titanium phosphonate clusters were synthesized by the reaction of 2 equiv. of Ti(OiPr)
equiv. of arylphosphonic acid with 0.3 equiv. of water in THF. When the arylphosphonic acid
solution was added to the Ti(OiPr) solution, an exothermic reaction ensued with the immediate
4
and 1
4
formation of a white precipitate. After stirring for several hours, the precipitate dissolved to give a
colorless solution. This solution was evaporated until a white precipitation appeared, after which it
was dissolved by heating and then cooling; single crystals of 1 and 2 were obtained as Ti
THF-adduct clusters after several days (Method A, above). Single crystals of 3-5 were formed as
Ti -type iPrOH-adduct clusters over a period of several days to a week by the liquid-liquid
diffusion method using THF/iPrOH as the solvent. Cluster 6 was isolated as a Ti -type cluster,
-type (7b) clusters
4 3
P -type
4 3
P
7 6
P
4 3 7 6
while 7 was obtained as a co-crystallized mixture of two Ti P - (7a) and one Ti P
over several weeks (Method B, above).
The new cage cluster 8 was also synthesized by the reaction of Ti(acac)
THF; 8 was obtained as pale-yellow crystals over 3 days.
2 2 3 2
(OiPr) with PhPO H in
Ti(OiPr) X + ArPO H
2
2
3
2
X = OiPr
X = OiPr
X = acac
Ar = Ph
H O
H O
2
2
Ar = Ph (1), 1-Nap (2),
Ar = 4-BrBn (6),
4-BrPh (7)
4
4
4
-MeOPh (3),
-FPh (4), 4-ClPh (5),
-BrPh (7)
Ar = 4-BrBn (6),
-BrPh (7b)
4
Cluster 8
solv. = thf (for 1, 2)
iPrOH (for 3−5, 7a)
Ti P -type
7
6
Ti P -type
4
3
Scheme 1. Syntheses of clusters 1-8.

The solubilities of the clusters are listed in Table 1. All the clusters readily dissolved in CH
CHCl and THF. Moreover, clusters 4 and 5 are very soluble in organic solvents, such as hexane,
toluene, dichloromethane, chloroform, THF and iPrOH, facilitated by the low electron densities of
2 2
Cl ,
3
31
the aromatic groups or the polarities of the molecules. The P NMR spectrum of the mixture, after
the reaction of Ti(OiPr) , ClPhPO and water in THF, showed a strong signal at δ 5.9 ppm that is
assigned to cluster 5 (Fig. S1). Therefore, cluster 5 is contained in the reaction mixture as the main
product, but the isolated yields were very low due to its high solubility. When the Ti -type
iPrOH-adduct clusters were dissolved in THF, these clusters transformed into Ti -type THF-adduct
clusters, while the Ti -type THF-adduct clusters also transformed into the Ti -type iPrOH-adduct
clusters upon the addition of iPrOH.
4
3 2
H
4 3
P
4 3
P
4
P
3
4 3
P
a)
Table 1. Solubilities of the clusters 1-8 in organic solvents .
Solubility
Cluster
Hexane
−−
−−
−−
+
Toluene
++
+
CH Cl
2 2
CHCl
++
++
+
3
THF
+
iPrOH
b)
1
2
3
4
5
6
7
8
++
++
+
−−
b)
+
−−
c)
−
++
−
+
c)
++
++
−
++
++
++
++
++
++
++
++
++
++
++
c)
+
++
+
−−
++
−−
++
−−
−
c)
++
−−
++
++
−−
a) Solubility was estimated from the volume of solvent required to dissolve 10 mg of the cluster at r.t.:
+; < 1 mL, +; 1–5 mL, −; 5–10 mL, − −; 10 mL <.
+
b) Exchanged to iPrOH-adduct.
c) Exchanged to THF-adduct.
Structures
a)
(
(b)
:
:
:
:
:
C
O
P
Ti
Br
4 3 7 6
Fig. 1. ORTEP drawings of (a) Ti P -type cluster 2 and (b) Ti P -type cluster 6, with thermal ellipsoids at the 50%
probability level. Hydrogen atoms and crystal solvents are omitted for clarity. Color code: white, C; red, O; orange, P;
light green, Ti; brown, Br.

The structures of the clusters were determined by single crystal X-ray structure analyses. Ti
clusters 1-5 contain four titanium atoms with octahedral geometries, coordinated to three aryl
phosphonato groups, five terminal isopropoxy groups, three bridged isopropoxy groups, one  -O
atom and one solvent adduct (THF or iPrOH), as shown in Fig. 1a. The Ti–O and P–O bond lengths
and angles in all the Ti -type clusters were comparable to those previously reported for
PR) ]·DMSO (R = allyl, Ph) Ti -type clusters [18–20].
The framework of cluster 6 (Ti -type cluster) was composed of two [Ti ( -O)(OiPr)
Ti O) units, six 4-BrBnPO groups and one centered Ti atom (Fig. 1b). Furthermore, this structure is
-symmetric around the axis through a titanium atom in the Ti -type cluster and has a degree of
symmetry. It should be noted that the core structure of cluster 6 is the same as that of
Ti ( -O) (OiPr) (-OiPr) (O PR) (R = Bn and C Cl) [20].
A co-crystal containing two Ti -type (7a) and one Ti -type (7b) clusters in the unit cell was
obtained for cluster 7. We note that the compounds prepared by the reaction of Ti(OiPr) with
-iodophenyl or 4-toluenylphosphonic acids exhibited similar NMR spectra to that of cluster 7, but
4 3
P -type
3
4 3
P
[
(
Ti
4
(
3
-O)(OiPr)
5
(-OiPr)
3
(O
3
3
4 3
P
7
P
6
3
3
3 3
(-OiPr) ]
3
3
C
2
4 3
P
7
3
2
6
6
3
6
3 6
H
4
P
3
7 6
P
4
4
these compounds could not be isolated. Therefore, the structures of the titanium phosphonate
clusters are influenced by the steric hindrance of the aromatic groups on the phosphorus atoms and
depended especially on the size of the substituent in the para-position or the flexibilities of the
organic groups.
Clusters 3-7 are potentially useful in organic functional groups transformations, such as
cross-coupling reactions, the Michaelis-Arbuzov reaction and the Mizoroki-Heck reaction, as they
are similar to para-octaiodophenylsilsesquioxane [42], and for the hydrolysis of methoxyphenyl
groups to phenols [43].
Fig. 2 reveals that cluster 8 has a distorted-cubic framework and is composed of only Ti–O–P bonds,
2 3 4
in a similar manner to [Ti(OiPr) (O PtBu)] [19], rather than a combination of Ti–O–Ti and Ti–O–P
bonds [32]. Cluster 8 is composed of four titanium atoms, four phenylphosphonato groups, four
O2
(a)
(b)
Ti1
O4
O3
P2
O1
P1
Fig. 2. ORTEP drawings of (a) the molecular structure of cluster 8 and (b) its core structure, with thermal ellipsoids at
the 50% probability level. Hydrogen atoms are omitted for clarity. Color codes: light grey, C; red, O; orange, P; light
green, Ti.

isopropoxy groups and four chelating acetylacetonato groups. The vertices are arranged through the
titanium and phosphorus atoms. Each titanium atom is bound to one isopropoxy group, one chelating
acetylacetonato group, has two Ti–O–P bonds and exhibits an octahedral coordination. Key distances
are: Ti1–O1, 1.976(4) Å; Ti1–O2, 1.764(4) Å; Ti1–O3, 1.990(4) Å; P1–O1, 1.499(4) Å, which are
similar to those in [(Cp*TiO
Ti(acac) (OiPr) [45]. The oxygen atoms in the main backbone subtend angles of 163.9(2)°
Ti1–O1–P1) for the isopropoxy groups and 135.6(2)° (Ti1–O4–P2) for the acetylacetonato groups.
3
PPh)
4
(-O)
2 4 3
] [17], Ti ( -O)
2
(-OiPr)
2 8 2
(OiPr) (acac) [44] and
2
2
(
Spectral analyses and properties of clusters 1-8, and the stability of cluster 1
Clusters 1-7 exhibited signals assigned to the methyl moieties of the isopropoxy groups (δ 1.0–2.0
1
ppm) in their H NMR spectra. These signals were observed to have different chemical shifts for
cluster 1 (Ti
4
P
3
-type THF adduct), cluster 3 (Ti
4
3 7 6
P -type iPrOH adduct), cluster 6 (Ti P -type) and
Terminal OiPr
on Ti O units
3
Bridged OiPr
Terminal OiPr
on Ti O units
3
Coordinating THF
Cluster 1
Terminal OiPr
on Ti O units
Terminal OiPr
and coordinating iPrOH
3
Bridged OiPr
on Ti O units
3
Cluster 3
Cluster 6
Terminal OiPr
on Ti O units
Bridged OiPr
on Ti O units
3
3
7b
7a
7a
7a
Clusters 7
2
1.9
1.8
1.7
1.6
1.5
1.4
1.3
1.2
1.1
1
Chemical shift (ppm)
1
Fig. 3. H NMR spectra of clusters 1, 3, 6 and 7 in CDCl
3
in the δ 1.0-2.0 ppm region.
cluster 7 (co-crystal of one Ti
The spectrum of 1 exhibited three doublets for the isopropoxy groups (namely bridged isopropoxy
groups and terminal isopropoxy groups on the Ti O units, and other terminal isopropoxy groups) and
7 6 4 3
P - and two Ti P -type clusters in the unit cell), as shown in Fig. 3.
3
a multiplet assigned to molecular THF at around δ 1.8 ppm, while the spectrum of 3 showed only
three doublets for the isopropoxy groups. The signals observed for isopropyl alcohol have the same
chemical shifts as those of the terminal isopropoxy groups, which indicates a relatively facile ligand
exchange [19,20]. In contrast, cluster 6 exhibited only two doublets for the isopropoxy groups in its
1
H NMR spectrum, which suggests a highly symmetrical structure in solution, while 7 showed three

doublets assigned to a Ti
Furthermore, the doublet corresponding to the terminal isopropoxy groups of the Ti
7 6
Ti -type and the doublet corresponding to the bridged isopropoxy group in the Ti P
4
P
3
-type cluster and two signals assigned to a Ti
7
P
6
-type cluster.
O units in the
-type cluster,
- and Ti -type
3
4
P
3
overlapped at around 1.3 ppm. These results indicate that the structures of the Ti
4
P
3
7 6
P
1
clusters can be distinguished by H NMR spectroscopy.
1
The H NMR spectrum of cluster 8 is very complicated due to the unsymmetrical arrangements of
its isopropoxy and acetylacetonato groups; therefore, only the strong signals will be discussed. This
1
H NMR spectrum exhibited two isopropoxy doublets at δ 1.08 and 1.17 ppm, corresponding to the
3
axial and equatorial positions. Two signals assigned to the CH groups of the acetylacetonato groups
were observed at δ 1.71 and 1.78 ppm. A singlet corresponding to the CH unit of the acetylacetonato
group was observed at δ 4.53 ppm. Multiplets corresponding to the CH units of the isopropoxy
groups were observed at δ 4.81-4.92 ppm, while signals derived from the phenyl groups are
multiplets at δ 7.24-7.27 and 7.34-7.36 ppm for the m- and p-CH units, respectively. A doublet of
doublets, assigned to the o-CH group of the phenyl moiety, was observed at δ 7.90 ppm. Other NMR
spectra data are provided in the Materials and Methods section and the Supporting Information.
–
1
The FT-IR spectra of all the clusters exhibited C–C absorption bands at around 1158 and 1130 cm ,
assigned to the iso-branching vibrations [46,47] of the isopropoxy groups, asymmetric P–O bands at
–
1
–1
around 1070 cm and Ti–O bands at around 600 cm . No absorption bands assigned to P=O (usually
–
1
–1
observed at around 1143 cm ) [48] or P–OH (around 920 and 1020 cm ) [49,50] were observed.
The FT-IR spectral data are provided in the Materials and Methods section, Figs. S2 and S3, and
Table S1.
2
1
0
.5
(
a)
2
1
0
.5
Cluster 6
(
b)
Cluster 6
2
2
.5
1
Cluster 4
Cluster 1
.5
1
Cluster 8
.5
0
3
39 nm
Cluster 1
2
50
300
350
400
420
2
20
270
320
370
Wavelength (nm)
Cluster 4
.5
0
Cluster 8
339 nm
2
20
300
320
400
420
500
600
620
700
800
2
20
520
720
Wavelength (nm)
2 2
Fig. 4. UV-Vis spectra of clusters 1, 4, 6 and 8 concentrated in 15 M CH Cl (a) region 220-800 nm and (b)
region 220-420 nm.

The thermal properties of the clusters were measured by TG-DTA under a flow of air (Figs.
S4-S11); the thermal stabilities were found to decrease in the order: Ti > cluster 8 > Ti -type
clusters. The thermal stabilities of the Ti -type clusters were the lowest because the coordinated
solvents easily dissociate upon heating, even under a flow of nitrogen, as shown in Fig. S14. TG-MS
7
P
6
4 3
P
4 3
P
(
(
gas chromatographic elution at 153 °C) confirmed the presence of THF and propene in cluster 1
Fig. S15).
2 2
The UV-Vis spectra of clusters 1-7 in CH Cl exhibited bands assigned to the aromatic →*
transitions, as shown in Fig. S16. The UV-Vis spectra of clusters 1, 4 and 6 are given in Fig. 4. The
absorption edge values were almost identical, despite the differences in the aromatic groups and the
structures of clusters 1-7. Density functional theory (DFT) calculations on 1 reveal that the HOMO
and LUMO are located on the phenyl groups and Ti
3
O units respectively (Fig. S17). The UV-Vis and
DFT results suggest that intramolecular electron transfers from the aromatic groups to the Ti
3
O unit
might occur. The UV-Vis spectrum of cluster 8 exhibits three bands at 227, 257 and 339 nm (Figs. 4
and S16). The band at 227 nm is assigned to the →* transition of the phenyl group and is of a
similar absorption wavelength to that of cluster 1. The two bands at 257 and 339 nm are assigned to

→* transitions that appear to be between the acetylacetonato groups and titanium atoms [51,52];
→* transition splits are well known to occur during -electron bonding in complexes of transition

metals and the acetylacetonate ligand [51-54].
31
The stability of cluster 1 was evaluated by P NMR spectroscopy, the results of which are
31
displayed in Fig. 5. When 1 was dissolved in toluene and stored in air, its P NMR spectrum was
observed to change over time; it first exhibited a strong signal at δ 7.76 ppm, assigned to cluster 1,
and a small signal at δ 7.04 ppm (Fig. 5a). After 2 days, the intensity of the signal at δ 7.04 ppm had
increased (Fig. 5b), and after 3 days, the intensities of these two signals had reversed; moreover, a
new signal at δ 7.81 ppm appeared, as shown in Fig. 5c. After 7 days, the signal assigned to cluster 1
31
had completely disappeared, with many small signals appearing (Fig. 5d). After 10 days, the
P
7.76 ppm
7.04 ppm
(a)
(b)
7.81 ppm
(c)
7.43 ppm
(d)
(e)
2
5
20
15
10
5
0
Chemical shift ( ppm)
31
Fig. 5. P NMR spectra of cluster 1 dissolved in toluene in air after (a) 1 d, (b) 2 d, (c) 3 d,
(
d) 7 d, and (e) 10 d.

NMR spectrum had become very complex (Fig. 5e). Moreover, gelation was observed after 20 days.
Hence, cluster 1 is converted into other compounds in toluene in an aerobic atmosphere. The TG-MS
study revealed that molecular THF coordinated to the titanium atom easily dissociates. On the other
3
1
hand, when 1 was dissolved in toluene and maintained under argon, the P NMR spectrum exhibited
only two signals, at δ 7.76 and 7.05 ppm, even after 14 days. Hence, in air, cluster 1 is transformed
31
into another compound associated with the signal observed at δ 7.05 ppm. Furthermore, the
P
NMR spectrum of a solution of 1 in THF exhibited a single signal at δ 6.86 ppm, even after 14 days
in air (Fig. S18). The above results indicate that cluster 1 decomposes through hydrolysis in toluene
in the presence of atmospheric moisture to form polymeric materials and eventually a gel.
We note that cluster 1 is transformed to another compound, whose structure is unknown, by the
reaction with Hacac because of the high coordination ability of Hacac (see supporting information).
Conclusion
We have synthesized some new titanium phosphonate clusters by the reaction of Ti(OiPr)
ArPO with water in THF at room temperature. Clusters 1-5 (Ar = Ph (1), 1-Nap (2), 4-MeOPh
3), 4-FPh (4), 4-ClPh (5)) were formed as Ti -type clusters, while 6 (4-BrBn) was formed as a
Ti -type cluster. Furthermore, cluster 7, prepared from 4-BrPhPO , was isolated as a co-crystal
of one Ti - and two Ti -type clusters, while cluster 8 was synthesized by the reaction of
Ti(acac) (OiPr) with PhPO in THF, and was isolated as new cage cluster. The structures of all
4
and
3 2
H
(
4 3
P
7
P
6
3 2
H
P
7 6
4 3
P
2
2
3 2
H
the clusters were determined by single crystal X-ray analyses and NMR spectroscopy. The
solubilities and structures were found to depend on the electron densities and steric hindrance of the
phosphonate groups, respectively. The thermal stability was found to increase in order: Ti
> Ti -type clusters. The values of the absorption edges of the UV-Vis spectra of clusters 1-7 were
almost identical. The stability of cluster 1, dissolved in toluene and stored in air, was evaluated by
4 3
P -type >
8
7 6
P
31
P NMR spectroscopy.

Table 2. Crystallographic data of clusters 1–4.
cluster
CCDC
1
2
3
4
1487366
1553150
1553154
1553153
2
85 19 3 4
(C58H O P Ti )•
Empirical formula
C
46
H
79
O
19
P Ti
3 4
C
48
H
85
O
22
P Ti •C
3 4 3
H
8
O
45 76 3 19 3 4 3 8
C H F O P Ti •C H O
5
4 8
(C H O)
Formula weight
Space group
Crystal system
a (Å)
1220.6
3101.83
1358.65
1322.55
P2 /n
monoclinic
Pꢀ
C2/c
Pꢀ
1
triclinic
monoclinic
43.803(2)
13.5328(7)
25.3259(13)
90
triclinic
12.3418(11)
13.7751(12)
20.2975(17)
90.957(1)
105.730(1)
114.034(1)
2
11.6333(8)
14.3838(10)
20.5084(15)
21.9232(16)
90
b (Å)
13.5869(10)
21.5514(15)
96.333(1)
95.381(1)
101.244(1)
2
c (Å)



(°)
(°)
(°)
Z
91.257(1)
90
102.055(1)
90
4
4
Temp. (K)
103
103
103
103
F (000)
1280
6544
1432
2660
3
V (Å )
3001.7(5)
1.35
15009.0(13)
1.373
3297.3(4)
1.369
6324.5(8)
1.389
3
d (g/cm )
-
1

(mm )
0.657
0.545
0.610
0.635
Reflection collected
18539
42752
19114
36276
12948
0.0244
0.0412
0.1135
1.037
Independent reflections
12981
15443
13177
(
R
int
)
0.0524
0.0529
0.0723
0.1730
0.985
0.0235
0.0458
0.1223
1.050
R
1
(I > 2(I))
0.0707
wR
2
(all data)
GOF
0.2199
1.062

Table 3. Crystallographic data of clusters 5–8.
cluster
CCDC
5
6
7
8
1553152
1553149
1553151
1561995
2
(C45
H
75Br
3
O
O
19
32
P
3
Ti
4
7
)•
Empirical formula
C
45
H
76Cl
3
O
19
P Ti •C
3 4 3
H
8
O
C
78
H
120Br
6
O
32
P Ti
6 7
58 80 25 4 4
C H O P Ti
(
C
72
H
108Br
6
P
6
Ti
)
Formula weight
Space group
Crystal system
a (Å)
1371.90
P2 /n
2570.06
P2 /n
5374.18
1492.58
P2 /c
Pꢁꢀ
1
1
1
monoclinic
11.7895(8)
43.445(3)
12.9670(9)
90
monoclinic
17.588(8)
16.353(7)
18.710(8)
90
trigonal
monoclinic
22.197(8)
19.262(7)
16.587(6)
90
19.1548(8)
19.1548(8)
b (Å)
c (Å)
18.1136(15)
90



(°)
(°)
(°)
Z
104.091(1)
90
100.213(7)
90
90
107.782(6)
90
120
4
2
1
4
Temp. (K)
103
103
103
103
F (000)
2864
2580
2736
3104
3
V (Å )
6441.8(8)
1.415
5296(4)
1.612
5755.6(8)
1.551
2.731
32891
7845
6753(4)
1.468
3
d (g/cm )
-
1

(mm )
0.743
2.925
0.628
Reflection collected
37554
13400
0.0503
0.0604
0.1508
1.058
28788
10739
0.0898
0.0560
0.1528
0.970
32812
13130
0.0419
0.0677
0.1932
1.083
Independent reflections
(
R
int
)
0.0497
0.0741
0.2475
1.039
R (I > 2(I))
1
wR
2
(all data)
GOF
Acknowledgement
This work was supported by a Grant-in-Aid for Scientific Research on Innovative Areas “New
Polymeric Materials Based on Element-Blocks (No.2401)” (24102008A02) of the Ministry of
Education, Culture, Sports, Science and Technology, Japan. This was supported by JSPS KAKENHI
Grant Number JP16K17951. The activities of the Advanced Automotive Research Collaborative
Laboratory at Hiroshima University are supported by the Mazda Motor Corporation, Japan. Makoto
Tadokoro and Yuji Ohtake are greatly acknowledged for their assistance with the TG-MS analyses.
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Graphical abstract
4
Titanium phosphonate clusters were synthesized by the reaction of Ti(OiPr) and arylphosphonic
acids with water. These clusters were formed as Ti
steric hindrance of the phosphonato group. Moreover, a new cage cluster was synthesized by the
reaction of Ti(acac) (OiPr) with phenylphosphonic acid.
4 3 7 6
P -type or Ti P -type clusters depending on the
2
2