Influence of the phosphonate ligand on the structure of phosphonate-substituted titanium oxo clusters

Article abstract of DOI:10.1002/ejic.201300859

The reaction of titanium isopropoxide, Ti(OiPr)₄, with bis(trimethylsilyl) phosphonates has led to structures containingTi₃O units [= Ti₃(μ³-O)(μ²-OiPr) ₃(OiPr)₃(O₃PR)

Full text of DOI:10.1002/ejic.201300859

FULL PAPER
DOI:10.1002/ejic.201300859
Influence of the Phosphonate Ligand on the Structure of
Phosphonate-Substituted Titanium Oxo Clusters
Matthias Czakler,[a] Christine Artner,[a] and Ulrich Schubert*[a]
Keywords: Titanium / Alkoxides / Phosphorus / Hydrolysis / Cluster compounds
The reaction of titanium isopropoxide, Ti(OiPr)4, with bis(tri-
methylsilyl) phosphonates has led to structures contain-
ingTi3O units [= Ti3(μ3-O)(μ2-OiPr)3(OiPr)3(O3PR)3] as the ba- Ti(OiPr)4 was also treated with allylphosphonic acid to yield
clusters were formed in which two Ti4 cluster units are
bridged by isopropyl phosphonate ligands. For comparison,
sic structural motif. This unit can be capped by a single
Ti(OiPr)2L group (L = neutral ligand) through phosphonate
bridges (for R = xylyl), or sandwich-like structures can be
formed with two Ti3O units bonded to a central Ti atom (for
R = CH2CH2CH2Cl or benzyl). For R = allyl or ethyl, dimeric
a Ti4 cluster. The reaction of Ti(OiPr)4 with the bulky bis(tri-
methylsilyl) 2-naphthylmethyphosphonate did not yield an
oxo cluster but instead the phosphonate-substituted titanium
alkoxide Ti4(OiPr)8(O3PCH2naphthyl)4.
oxides, the water for hydrolysis being produced in situ
through esterification of the acid.[3]
Introduction
Phosphonates are often used as protecting ligands for ti-
Metal oxo clusters are of great interest as nanosized inor- tania nanoparticles[4] (leading to water-stable and function-
ganic building blocks for hybrid materials.[1] They can be alized nanoparticles with several applications) because of
easily processed, because they are molecular compounds. the stable Ti–O–P bonds. A few phosphonate- and phos-
When incorporated into organic polymers, some of the phinate-substituted oxo clusters have been obtained by the
properties of the polymers are improved in comparison with reaction of titanium alkoxides with some phosphonic or
the parent polymers.[2] A common route to titanium oxo phosphinic acids.[5–7] The formation of oxo groups in the
clusters is the addition of a carboxylic acid to titanium alk- clusters was attributed to residual moisture in the solvents
Scheme 1. Trimetylsilyl phosphonates used in this study.
or phosphonic acids[5–8] rather than to an esterification re-
action. The compounds obtained by reaction with phos-
[a] Institute of Materials Chemistry, Vienna University of
Technology,
phinates had similar structures to comparable carboxylate-
Getreidemarkt 9, 1060 Wien
substituted derivatives.[5,7]
E-mail: Ulrich.Schubert@tuwien.ac.at
http://www.imc.tuwien.ac.at/
In this article we first introduced polymerizable organic
groups into metal oxo clusters by using functionalized
phosphonate ligands for the preparation of class II hybrid
materials. We then extended this study to other phos-
phonate ligands to elucidate the influence of organic sub-
© 2013 The Authors. Published by Wiley-VCH Verlag GmbH &
Co. KGaA. This is an open access article under the terms of
the Creative Commons Attribution-NonCommercial License,
which permits use, distribution and reproduction in any me-
dium, provided the original work is properly cited and is not
used for commercial purposes.
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stituents on the structures of clusters. We mainly used the ligands (204 pm). The average Ti–O bond length of the μ2-
bis(trimethylsilyl) esters of phosphonic acids as the starting OiPr groups is 202 pm, and that of the terminal OiPr li-
compounds, which have rarely been employed. For example, gands is 180 pm.
trimethylsilyl esters of phosphonic acids[9] have previously
The 31P NMR spectrum shows two signals, and hence
been used for reactions with Ti(OiPr)4 instead of the parent the cluster has mirror symmetry in solution. Accordingly,
1
acids. Use of the esters provides better reproducibility and the H NMR spectrum shows four different OiPr signals,
easier handling compared with phosphonic acids them- and the 13C NMR spectrum six doublets for the phos-
selves.
The bis(trimethylsilyl) phosphonates (Scheme 1a–f) em-
phorus-coupled carbon atoms of the allyl group.
The drawback of using phosphonic acids is their low
ployed include compounds with different functionalities as solubility in organic solvents. Furthermore, reproducing the
well as different steric demands. Allylphosphonic acid was synthesis of crystalline 1 took several attempts. To over-
also used to compare its behavior with that of the esters.
come these problems, bis(trimethylsilyl) phosphonates were
used in the remainder of this work.
When TMS-allylPP was treated with Ti(OiPr)4 in a 1:2
ratio in isopropyl alcohol, the cluster [Ti8(μ3-O)2(μ2-OiPr)6-
(OiPr)8(O3P-allyl)6{O2P(OiPr)allyl}2] (2) was formed (Fig-
ure 2). Cluster 2 consists of two Ti4O units [= Ti4(μ3-O)2-
(μ2-OiPr)3(OiPr)4(O3P-allyl)3] as in 1, which are connected
by two mono(isopropyl esters) of allylphosphonate. The
“capping” titanium atom of each Ti4O unit is thus coordi-
nated to only one terminal OiPr ligand and the oxygen
atoms of two allylphosphonate ester groups (instead of two
terminal OiPr ligands and a dmso molecule in 1).
The bond lengths in 2 are similar to those in 1, with an
average Ti–O bond length of 197 pm for the phosphonate
groups. An exception is again the Ti–O bond trans to the
terminal OiPr ligand on the “capping” titanium atom
(204 pm). The bridging OiPr groups have an average Ti–O
bond length of 203 pm and the terminal OiPr groups an
average Ti–O bond length of 178 pm.
Results and Discussion
The phosphonate-substituted oxo clusters [Ti4(μ3-O)(μ2-
OiPr)3(OiPr)5(O3PR)3(dmso)] (R
= Ph, Me, tBu, 4-
NCC6H4) were obtained by Mehring et al.[6] by the reaction
of Ti(OiPr)4 with RP(O)(OH)2. The structure of this cluster
type consists of a symmetric Ti3(μ3-O)(μ2-OiPr)3(OiPr)3 tri-
angle in which three octahedrally coordinated Ti atoms are
bridged by a μ3-oxygen atom. The titanium atoms of the
triangle are additionally bridged by three μ2-OiPr ligands,
and each titanium atom is coordinated by a terminal OiPr
ligand. The fourth (“capping”) Ti atom is connected to this
triangular unit through the three phosphonate ligands. The
vacant coordination sites at the fourth titanium atom are
occupied by two terminal OiPr groups and one dmso mole-
cule; dmso was used as the solvent due to the low solubility
of phosphonic acids in organic solvents.
Cluster 2 was synthesized several times, and either tri-
We obtained cluster 1 with the same structure when allyl-
phosphonic acid was used (Figure 1). The average Ti–O dis-
tance of the phosphonate groups is 197 pm, with the excep-
tion of the Ti–O bond at Ti1 trans to the terminal OiPr
¯
clinic (space group P1, denoted as 2) or monoclinic crystals
(space group P21/n, denoted as 2b) were obtained. The mo-
lecular structures are the same in both cases, and the bond
lengths and angles are similar (only the values for 2 are
given in Figure 2), but the packing of the clusters is dif-
ferent. The clusters are parallel to each other in 2 and
aligned at an angle of 58.2° in 2b.
The most remarkable feature of 2 is the isopropyl phos-
phonate groups. The formation of an isopropyl phos-
phonate indicates that, similarly to the reactions of carbox-
ylic acids, esterification of the (noncoordinated or coordi-
nated) phosphonic acid could also be the source of the oxo
groups, especially because the ester/μ3-O ratio in 2 is 1:1.
The reactions of bis(trimethylsilyl) phosphonates with
alcohols leads to the corresponding phosphonic acid and
alkoxytrimethylsilane[10] in a fast reaction.[11] Use of the tri-
methylsilyl esters thus allows generation of the phosphonic
acid in situ, which may substitute some of the OiPr groups
of Ti(OiPr)4. The (coordinated or noncoordinated) phos-
phonic acid could then react with 2-propanol, possibly cata-
lyzed by Ti(OiPr)x moieties,[12] to produce water for con-
densation and the observed isopropyl monoester.
Figure 1. Molecular structure of [Ti4(μ3-O)(μ2-OiPr)3(OiPr)5(O3P-
allyl)3(dmso)] (1). Hydrogen atoms have been omitted for clarity.
Selected distances [pm] and angles [°]: Ti1–O21 208.7(3), Ti1–O13
195.5(4), Ti1–O19 181.7(4), Ti2–O3 193.3(4), Ti2–O11 197.1(4),
Ti2–O9 176.4(4), Ti2–O4 203.8(4), O13–P1 151.6(4); P1–O13–Ti1
163.9(2), O13–P1–O11 112.5(2), Ti2–O3–Ti3 105.14(16), O19–Ti1–
O13 90.62(15), O19–Ti1–O21 93.08(15), O3–Ti2–O11 88.34(14).
Crystals of 2 (or 2b) are soluble in common organic sol-
vents. Its NMR spectroscopic data, however, are ambigu-
ous. In the 31P NMR spectrum, five peaks are observed.
1
Interpretation of the H NMR spectroscopic data was lim-
ited due to the high number of chemically similar groups.
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Figure 2. Molecular structure of [Ti8(μ3-O)2(μ2-OiPr)6(OiPr)8(O3P-allyl)6{O2P(OiPr)allyl}2] (2). Hydrogen atoms have been omitted for
clarity. Selected distances [pm] and angles [°]: Ti1–O16 203.54(18), Ti1–O17 196.64(19), Ti1–O18 177.69(19), Ti2–O1 195.59(17), Ti2–O3
204.43(18), Ti2–O7 178.1(2), Ti3–O3 202.08(18), Ti3–O1 195.39(17), O17–P4 151.7(2), P4–O19A 150.2(4); O17–Ti1–O16 89.21(8), O18–
Ti1–O17 92.61(8), O19A–P4–O17 107.63(17), O7–Ti2–O3 98.22(9), O1–Ti2–O3 76.48(7), Ti3–O1–Ti2 105.32(8).
The integrals fitted well, but the multiplicities and signal
overlap led to very broad and indistinct signals. The 13C
NMR spectrum also shows five doublets for the allyl
groups, but signal overlap again made it difficult to eluci-
date the symmetry of 2.
The reaction of TMS-EtPP with Ti(OiPr)4 in isopropyl
alcohol resulted in [Ti8O2(OiPr)14(O3PEt)6{O2P(OiPr)Et}2]
(3), which is isostructural with cluster 2, and the bond
lengths and angles are the same within error limits. The 31
P
NMR spectroscopic data of 3 are in agreement with the
solid-state structure, and the 1H and 13C NMR spectra gen-
erally confirmed the structural data, with the same limita-
tions as already noted for 2.
In the chemistry of silica-based hybrid materials, chlo-
ropropyl-substituted alkoxysilane precursors play an impor-
tant role, because substitution of chlorine opens the door
to derivatives with other more complex functional groups.
With this in mind, TMS-ClPrPP was treated with
Figure 3. Molecular structure of [Ti7(μ3-O)2(μ2-OiPr)6(OiPr)6-
(O3PCH2CH2CH2Cl)6] (4). Hydrogen atoms have been omitted for
clarity. Selected distances [pm] and angles [°]: Ti1–O1 195.9(2),
Ti1–O14 198.1(2), Ti1–O2 202.3(2), Ti2–O1 196.3(2), Ti3–O13
Ti(OiPr)4 in isopropyl alcohol to yield [Ti7O2(OiPr)12- 192.6(2), Ti4–O1 195.8(2), Ti4–O12 198.7(2), Ti4–O15 177.4(3),
P1–O12 153.3(3), P1–O13 152.2(3), P1–O14 153.4(3); O1–Ti1–O14
88.24(10), O1–Ti1–O2 76.59(9), O14–Ti1–O2 87.43(10), O13–P1–
O12 112.00(14), O13–P1–O14 111.78(14), O12–P1–O14 111.55(14).
(O3PCH2CH2CH2Cl)6] (4) (Figure 3). The structure of 4 is
also based on Ti3O units [= Ti3(μ3-O)(μ2-OiPr)3(OiPr)3-
(O3P-R)3]. In contrast to 2 and 3, the two Ti3O units in 4
are connected by a single titanium atom, that is, a sandwich
structure is formed with Ti3 as the central atom and the which Cl is replaced by Br. This was also observed in the
Ti3O units as “ligands” (in this way of looking at the struc- spectra of the precursors. Because 1-bromo-3-chloroprop-
tures, 1 would be a half-sandwich structure). The bond ane was used for the preparation of ClPrPP, both halogens
lengths are similar to those in 1; the Ti–O distances of the can react with dimethyl phosphite, and therefore a small
phosphonate groups are 198 pm for the titanium atoms of amount of (3-bromopropyl)phosphonate was also formed.
the Ti3O units and 193 pm for the central Ti atom.
The presence of some bromine (replacing Cl) was also seen
The 31P NMR spectrum shows only one peak, which in- in the electron density map of the single-crystal measure-
dicates the high symmetry and stability of this cluster in ments.
1
solution. This is also evidenced in the H NMR spectrum,
The reaction of TMS-BzlPP with Ti(OiPr)4 yielded
in which only two different signals for the OiPr groups are Ti7O2(OiPr)12(O3PCH2C6H5)6 (5), which is isostructural to
observed. The 13C NMR spectrum confirms this observa- 4. Bond angles and distances of both compounds are very
tion, in which the coupling constant JPC is seen. Other similar. The benzyl groups in the center of the structure
smaller signals indicate the presence of a side-product in adopt a paddle-wheel-like arrangement.
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The previously described reactions indicate that the or- ates described in this article. The crystallization time of 7
ganic group of the phosphonate ligand has some (electronic was much shorter than for the other clusters reported in
or steric) influence on the structure of the formed clusters. this article. Compound 7 could therefore represent the
To shed light on this issue, phosphonate ligands with steri- structure of an initially formed substitution product, which
cally more demanding groups were included in this study. possibly crystallized more easily from the isopropyl alcohol
Furthermore, aromatic phosphonic acids are slightly more solution due to the apolarity of the naphthyl group and
acidic.
The reaction of TMS-XylPP and Ti(OiPr)4 led to the for-
thus escaped hydrolysis.
mation of [Ti4O(OiPr)8(O3P-xyl)3(iPrOH)] (6; Figure 4).
The structure is analogous to that of 1, the neutral ligand
at the “capping” titanium atom being isopropyl alcohol (in-
stead of dmso as in 1).
Figure 5. Molecular structure of [Ti4(μ2-OiPr)(OiPr)7(O3PMeNp)4-
(iPrOH)2·2iPrOH] (7). Hydrogen atoms have been omitted for clar-
ity. Selected distances [pm] and angles [°]: Ti3–O11 206.5(3), Ti3–
O10 177.4(3), Ti3–O13 209.9(3), Ti1–O1 201.7(3), Ti2–O1 232.1(3),
Ti2–O2 201.8(3), Ti1–O13 194.4(3), P1–O1 156.2(3), P1–O2
153.0(3), P1–O15 149.4(3), P2–O19 150.0(4), Ti4–O15 205.5(3),
Ti4–O16 189.9(4), Ti4–O23 201.2(4), Ti4–O22 176.5(3); P1–O1–Ti2
89.18(13), P1–O15–Ti4 156.8(2), P1–O2–Ti2 102.23(16), Ti1–O13–
Ti3 110.58(13), O2–Ti2–O1 66.38(11), O11–Ti3–O13 83.98(13),
O10–Ti3–O11 93.43(15), Ti1–O1–Ti2 128.60(14).
Figure 4. Molecular structure of [Ti4(μ3-O)(μ2-OiPr)3(OiPr)5-
(O3P-xyl)3(iPrOH)] (6). Hydrogen atoms have been omitted for
clarity. Selected distances [pm] and angles [°]: Ti1–O1 197.5(3),
Ti1–O15 196.3(3), Ti4–O12 177.6(3), Ti4–O15 194.8(3), Ti4–O10
196.5(3), Ti4–O13 202.6(3), O7–P1 150.3(3), O1–P1 154.2(3), O10–
P1 154.3(3), Ti3–O5 213.7(3), Ti3–O6 181.1(3), Ti3–O9 178.7(3),
Ti3–O7 201.1(3); Ti4–O15–Ti1 105.36(13), O12–Ti4–O13
101.73(13), O15–Ti4–O13 76.85(12), O7–P1–O10 113.57(17), P1–
O1–Ti1 124.52(17).
The appearance of only one signal in the 31P NMR spec-
The structure of 7 consists of four octahedrally coordi-
trum indicates that cluster 6 has C3 symmetry in solution. nated titanium atoms arranged in an irregular shape. In
1
This was confirmed by the H NMR spectrum in which contrast to all the other structures, in which all the phos-
only three different signals for the CH3 groups of OiPr and phonates bind in a 3.111 mode [w.xyz denotes the number
only one singlet for the CH3 of the xylyl group can be seen. of metal atoms to which the phosphonate ligand is coordi-
The proton of the coordinated isopropyl alcohol exchanges nated (w), and the number of metal atoms to which each
easily on the NMR timescale, because only averaged signals oxygen is coordinated (x,y,z)[13]], just one phosphonate in
of the isopropyl alcohol and the OiPr groups were ob- 7 coordinates in the 3.111 mode. The other phosphonates
served.
coordinate in the 4.211, 3.211, and 2.110 modes. As a result
The reaction of a phosphonate with an even bulkier sub- of the high connectivity of the phosphonates, there is only
stituent, namely TMS-NpMePP, resulted in the complex one bridging OiPr ligand.
[Ti4(μ2-OiPr)(OiPr)7(O3PMeNp)4] (7; Figure 5). In 7, two
The NMR measurements are in good agreement with the
of the OiPr ligands of Ti(OiPr)4 are substituted by one O3P- crystal structure. Four signals are detected in the 31P NMR
MeNp ligand [formal composition Ti(OiPr)2(O3PMeNp)], spectrum, with a shift difference of 8.80 ppm. The latter is
but no partial hydrolysis took place. This is in contrast to attributed to the different binding modes of the phos-
the reactions with the other bis(trimethylsilyl) phosphon- phonate ligands. Three doublets for the CH2 groups are de-
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tected in the 13C NMR spectrum, although four were ex-
pected. One of these doublets has a higher intensity, which
indicates signal overlap.
and distillation. Samples for NMR measurements were obtained
by washing the crystalline substances with iPrOH, drying and dis-
solving in the designated solvent.
[Ti4O(OiPr)8{O3P(allyl)}3(dmso)] (1): Allylphosphonic acid
(315 mg, 2.6 mmol) was dissolved in water-free dmso (3 mL) under
an inert gas, and Ti(OiPr)4 (1.5 mL, 5.2 mmol) was added slowly
under vigorous stirring. The suspension formed was stirred until a
clear solution was obtained. After 4 weeks, 0.6 g (62% yield) of
crystalline 1 was obtained. 1H NMR (C6D6, 250 MHz): δ = 1.48
(d, J = 6.15 Hz, 12 H, CHCH3), 1.49 (d, J = 6.18 Hz, 12 H,
CHCH3), 1.68 (d, J = 6.35 Hz, 12 H, CHCH3), 1.73 (d, J =
6.28 Hz, 12 H, CHCH3), 1.94 (s, 6 H, SCH3), 2.76 (dd, JH,H = 7.30,
JP-H = 21.6 Hz, 4 H, PCH2), 2.87 (dd, JH,H = 7.40, JP-H = 22.0 Hz,
2 H, PCH2), 4.74 (m, 6 H, CH=CH2), 5.22 (m, 11 H, CHCH3),
6.31 (m, 3 H, CH=CH2) ppm. 31P NMR (C6D6, 101.2 MHz): δ =
14.48, 16.01 ppm. 13C NMR (C6D6, 62.9 MHz): δ = 24.90 (s,
CHCH3), 24.97 (s, CHCH3), 25.13 (s, CHCH3), 25.19 (s, CHCH3),
34.16 (d, J = 150.3 Hz, PCH2), 34.85 (d, J = 151.4 Hz, PCH2),
39.34 (s, SCH3), 77.80 (s, CHCH3), 78.02 (s, CHCH3), 78.96 (s,
CHCH3), 79.53 (s, CHCH3), 116.76 (d, J = 14.7 Hz, CH=CH2),
117.49 (d, J = 15.1 Hz, CH=CH2), 131.86 (d, J = 11.3 Hz,
CH2=CH), 132.65 (d, J = 10.9 Hz, CH2=CH) ppm.
Conclusions
Trimethylsilyl esters of phosphonic acids are better pre-
cursors for the preparation of phosphonate-substituted tita-
nium oxo clusters due their better solubility, as stated in
earlier work.[7,9] This renders the reactions more reliable,
and crystals of good quality were obtained easily.
It was previously proposed that metal alkoxides may re-
act with P-O-SiMe3 in non-hydrolytic condensation pro-
cesses.[9] The results presented in this article indicate that
another possibility must also be considered. The reactions
of bis(trimethylsilyl) phosphonates with isopropyl alcohol
liberates phosphonic acid, which could substitute some of
the OiPr groups of Ti(OiPr)4. This latter reaction must be
fast, because otherwise the (sparingly soluble) acids would
precipitate. The formation of 7 indicates that the introduc-
tion of phosphonate ligands is not necessarily coupled to
the formation of oxo groups. The latter might be due to
the slow esterification of (coordinated or noncoordinated)
phosphonic acid, as it is the case with carboxylic acids. This
possibility is strongly supported by the presence of iso-
propyl phosphonate ligands in 2 and 3.
The synthesis of 1 and 2 shows that titanium alkoxo de-
rivatives with polymerizable organic groups can be prepared
in which the organic groups are linked to Ti through robust
phosphonate ligands. Owing to the presence of both or-
ganic double bonds and Ti-OR groups in 1, this derivative
appears to be suitable for the preparation of hybrid materi-
als, similar to alkoxysilanes (RO)3Si-RЈ with polymerizable
groups RЈ.
[Ti8O2(OiPr)12{O3P(allyl)}6{O2P(allyl)(OiPr)}2] (2): Bis(trimethyl)-
silyl allylphosphonate (200 mg, 0.8 mmol) was added in a ratio of
1:2 to Ti(OiPr)4 (464 μL, 1.6 mmol) in isopropyl alcohol (1 mL).
After 6 weeks, crystals of the cluster 2 or 2b were obtained in 30%
yield (70 mg). 1H NMR (C6D6, 250 MHz): δ = 1.36–1.50 (m, 48 H,
CHCH3), 1.62–1.80 (m, 48 H, CHCH3), 2.65–2.94 (m, 8 H, PCH2),
3.05–3.34 (m, 6 H, PCH2), 3.62–3.88 (m, 2 H, PCH2), 4.61–4.79
(m, 6 H, CHCH3), 5.11–538 (m, 24 H, CH=CH2, CHCH3), 5.50–
5.65 (d, 2 H, CH=CH2), 6.16–6.50 (m, 8 H, CH=CH2) ppm. 31P
NMR (C6D6, 101.2 MHz):
δ = 13.77, 13.99, 15.50, 15.69,
16.57 ppm. 13C NMR (C6D6, 62.9 MHz): δ = 23.89 (s, CHCH3),
24.06 (s, CHCH3), 24.73 (s, CHCH3), 24.84 (s, CHCH3), 25.11 (s,
CHCH3), 25.28 (s, CHCH3), 25.34 (s, CHCH3), 32.84 (d, J =
145.5 Hz, PCH2), 34.31 (d, J = 154.3 Hz, PCH2), 34.86 (d, J =
149.9 Hz, PCH2), 69.34 (s, CHCH3), 69.45 (s, CHCH3), 77.50 (s,
CHCH3), 77.72 (s, CHCH3), 77.79 (s, CHCH3), 78.07 (s, CHCH3),
78.53 (s, CHCH3), 78.69 (s, CHCH3), 79.03 (s, CHCH3), 79.26,
82.34 (s, CHCH3), 82.67 (s, CHCH3), 116.35 (d, J = 14.6 Hz,
CH=CH2), 116.68 (d, J = 15.3 Hz, CH=CH2), 116.88 (d, J =
15.3 Hz, CH=CH2), 116.99 (d, J = 15.3 Hz, CH=CH2), 117.34 (d,
J = 14.2 Hz, CH=CH2), 131.78 (d, J = 11.2 Hz, CH=CH2), 131.90
(d, J = 10.6 Hz, CH=CH2), 132.16 (d, J = 10.7 Hz, CH=CH2),
132.70 (d, J = 11.6 Hz, CH=CH2), 133.39 (d, J = 11.0 Hz,
CH=CH2) ppm.
From a structural point of view, it is interesting to note
that the structures of the phosphonate-substituted oxo clus-
ters are derived from a common motif, that is, Ti3(μ3-O)(μ2-
OiPr)3(OiPr)3(O3P-R)3. This Ti3O motif can be varied in a
variety of ways and thus appears to be a robust building
block.
Experimental Section
[Ti8(μ3-O)2(μ2-OiPr)6(OiPr)8(O3PCH2CH3)6{O2(OiPr)PCH2CH3}2]
(3): Ti(OiPr)4 (420 μL, 1.45 mmol) was diluted with iPrOH (3 mL),
and then bis(trimethylsilyl) ethylphosphonate (200 μL, 0.72 mmol)
was added quickly. The mixture was stirred for 5 min. Crystals of
3 were obtained after 4 weeks. Yield: 40 mg (45 %). 1H NMR
(CDCl3, 250 MHz): δ = 1.02–1.48 (m, 120 H, CH3), 1.48–2.18 (m,
16 H, CH2), 4.42–4.70 (m, 6 H, CH), 4.74–5.02 (m, 10 H, CH)
ppm. 31P NMR (CDCl3, 101.2 MHz): δ = 18.91, 19.01, 19.22,
19.58, 20.11, 20.37, 20.61, 24.12 ppm. 13C NMR (CD2Cl2,
62.90 MHz): δ = 7.23 (d, J = 51.3 Hz, CH2CH3), 19.98 (d, J =
155.2 Hz, CH2), 23.97 (s, CH2CH3), 24.26 (s, CHCH3), 24.52 (s,
CHCH3), 24.69 (s, CHCH3), 25.10 (s, CHCH3), 64.16 (s, CHCH3),
68.45 (s, CHCH3), 77.91 (s, CHCH3), 79.02 (s, CHCH3), 79.54 (s,
CHCH3) ppm.
General: Manipulations were carried out under an inert gas by
using standard Schlenk and glove-box techniques. Diethyl ethyl-
phosphonate, allyl bromide, 1-bromo-3-chloropropane, benzyl
bromide, 1-bromo-3,5-dimethylbenzene, 2-(bromomethyl)naphthal-
ene and triethyl phosphite were purchased from Sigma–Aldrich and
used as received. Diethyl 3,5-dimethylphenylphosphonate was pre-
pared by a procedure similar to that already reported.[14] The bis-
(trimethylsilyl) esters were prepared by adding bromotrimethylsil-
ane (3 mol) to a solution of the corresponding diethyl phosphonate
(1 mol) in CH2Cl2. The bis(trimethylsilyl) esters were obtained after
removing all volatiles in vacuo. All esters were characterized by 31
P
and 1H NMR measurements before use. Isopropyl alcohol was
dried by heating at reflux in the presence of sodium and distillation;
dmso was dried by heating in the presence at reflux of CaSO4 and
distillation followed by heating at reflux in the presence of CaH2
[Ti7(μ3-O)2(μ2-OiPr)6(OiPr)6(O3PCH2CH2CH2Cl)6] (4): Bis(tri-
methylsilyl) (3-chloropropyl)phosphonate (300 μL, 1.11 mmol) was
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diluted with iPrOH (2 mL), and then Ti(OiPr)4 (576 μL, 2 mmol)
was added quickly under an inert gas. After 14 weeks, small crystals
were obtained; for further growth, 0.5 mL of volatiles was distilled
off to yield crystals suitable for single-crystal XRD after a further
2 weeks. Yield: 100 mg (17%). 1H NMR (CD3Cl, 250 MHz): δ =
[Ti4(μ2-OiPr)(OiPr)7(O3PMeNp)4(iPrOH)2·2iPrOH] (7): Bis(tri-
methylsilyl) (2-naphthylmethyl)phosphonate (420 mg, 1.15 mmol)
was dissolved in iPrOH (2 mL), and Ti(OiPr)4 (665 μL, 2.3 mmol)
was added quickly. Crystals suitable for single-crystal XRD were
obtained after 1 d. Yield: 200 mg (40 %). 1H NMR (C6D6,
1.45 (d, 36 H, CHCH3), 1.63 [d, 36 H, CHCH3 (μ2-OiPr)], 1.91 (dt, 250 MHz): δ = 1.00–1.65 (m, 60 H, CH3), 3.20–3.90 (m, 8 H, CH2),
12 H, PCH2), 2.38 (m, 12 H, CH2CH2CH2), 3.84 (t, 12 H, CH2Cl), 4.00–4.60 (m, 6 H, CH), 5.00–5.60 (m, 6 H, CH), 7.20–8.20 (m, 28
4.68 (m, 6 H, CHCH3), 5.16 [m, 6 H, CHCH3 (μ2-OiPr)] ppm.
H, CCH) ppm. 31P NMR (C6D6, 101.2 MHz): δ = 12.82, 13.24,
31P NMR (CD3Cl, 101.2 MHz): δ = 18.76 ppm. 13C NMR (C6D6, 17.43, 21.62 ppm. 13C NMR (C6D6, 62.90 MHz): δ = 22.87, 23.60,
62.90 MHz): δ = 24.33 (J = 148 Hz, PCH2), 24.47 (CHCH3), 24.74
(CHCH3), 26.74 (J = 5 Hz, CH2), 46.33 (J = 13 Hz, CH2Cl), 78.46
23.90, 24.05, 24.29, 24.56, 24.79, 24.93, 25.47, 25.81, 26.17, 26.34
(all CH3), 35.77 (J = 143 Hz, CH2), 36.61 (J = 140 Hz, CH2), 37.01
(J = 143 Hz, CH2), 71.77 (CHCH3), 78.38 (CHCH3), 78.74
(CHCH3), 81.09 (CHCH3), 81.84 (CHCH3), 82.68 (CHCH3), 84.57
(CHCH3), 124.77, 124.91, 125.15, 125.61, 125.71, 127.59, 128.78,
129.09, 129.25, 129.59, 130.51, 132.49, 132.83, 132.98, 133.92,
134.33, 134.50 (arom. C-H or C from naphthyl) ppm.
1
(CHCH3), 79.78 (CHCH3) ppm. The H NMR spectrum shows a
small triplet at δ = 3.72 ppm, and the 31P NMR spectrum a small
signal at δ = 18.50 ppm for the bromo species.
[Ti7(μ3-O)2(μ2-OiPr)6(OiPr)6(O3PCH2C6H5)6] (5): Bis(trimethyl-
silyl) benzylphosphonate (200 μL, 0.64 mmol) was diluted with iP-
rOH (1 mL), and then Ti(OiPr)4 (370 μL, 1.28 mmol) was added
quickly. Crystals suitable for single-crystal XRD were obtained af-
ter 9 weeks. Yield: 150 mg (66%). 1H NMR (C6D6, 250 MHz): δ =
1.12–1.49 (m, 72 H, CHCH3), 3.13–3.96 (m, 12 H, PCH2), 4.45–
5.41 (m, 12 H, CHCH3), 7.21–8.08 [m, 30 H, CH (Ph)] ppm. 31P
NMR (CD2Cl2, 101.2 MHz): δ = 13.13, 13.573, 15.39, 15.73, 23.63,
24.28 ppm.
X-ray Structure Analyses: All measurements were performed at
100 K by using Mo-Kα (λ = 71.073 pm) radiation. Data were col-
lected with a Bruker AXS SMART APEX II four-circle dif-
fractometer with κ-geometry. Data were collected with φ- and ω-
scans and a 0.5° frame width. The data were corrected for polariza-
tion and Lorentzian effects, and an empirical absorption correction
(SADABS) was employed. The cell dimensions were refined by
[Ti4O(OiPr)8(O3P-xyl)3(iPrOH)] (6): Bis(trimethylsilyl) (3,5-di- using all unique reflections. SAINT PLUS software (Bruker Ana-
methylphenyl)phosphonate (100 mg, 0.3 mmol) was diluted with
iPrOH (1 mL), and then Ti(OiPr)4 (176 μL, 0.6 mmol) was added
quickly. Crystals suitable for single-crystal XRD were obtained af-
lytical X-ray Instruments, 2007) was used to integrate the frames.
The symmetry was then checked by using the PLATON program.
The X-ray crystal data are presented in Tables 1 and 2. The struc-
tures were solved by the Patterson method (SHELXS97),[15] and
1
ter 3 weeks. Yield: 100 mg (72%). H NMR (CD3Cl, 250 MHz): δ
= 1.17 (d, J = 6.1 Hz, 18 H, CHCH3), 1.40 (d, J = 6.2 Hz, 18 H, refinement was performed by the full-matrix least-squares method
CHCH3), 1.46 (d, J = 6.3 Hz, 18 H, CHCH3), 2.34 (s, 18 H, CCH3), based on F2 (SHELXL97) with anisotropic thermal parameters for
4.71 (m, 5 H, CHCH3), 5.06 (m, 4 H, CHCH3), 7.11 (s, 3 H, CCH), all non-hydrogen atoms. Hydrogen atoms were inserted in calcu-
7.53 (d, J = 13.9 Hz, CCH) ppm. 31P NMR (CD3Cl, 101.2 MHz): lated positions and refined riding on the corresponding atom, those
δ = 10.18 ppm. 13C NMR (C6D6, 62.90 MHz): δ = 21.10 (CCH3), bonded to oxygen atoms were identified in the electron density
24.79 (CHCH3), 24.93 (CHCH3), 78.12 (CHCH3), 78.83 (d), 129.47
map. The carbon atoms of the different OiPr ligands of 1, 2, 2b, 3,
(J = 10.7 Hz, CCH), 131.38 (J = 197 Hz, PC), 131.77 (CCH), 4, and 7 were disordered as well as the carbon atoms of the dif-
136.76 [J = 16 Hz, C(xyl)] ppm.
ferent phosphonates of 1, 2b, and 3. In 2 and 2b, the isopropyl ester
Table 1. Crystal data and structure refinement details for 1–3.
Compound
1
2
2b
3
Empirical formula
Mr
Crystal system
Space group
a [pm]
b [pm]
c [pm]
C70H155O38P6S2Ti8
2238.08
monoclinic
P21/c
3366.33(17)
1270.76(7)
2763.86(14)
90
114.257(2)
90
10779.4(10)
4
C72H152O40P8Ti8
2288.90
C72H152O40P8Ti8
2288.90
monoclinic
P21/n
1260.81(4)
1873.03(6)
2282.43(8)
90
93.6370(10)
90
5379.18
2
1.413
0.758
C32H76O20P4Ti4
1096.41
triclinic
triclinic
¯
¯
P1
P1
1192.63(4)
1315.97(4)
1888.04(8)
95.737(2)
1173.14(3)
1266.27(4)
1870.42(5)
90.5310(10)
95.6330(10)
114.4040(10)
2514.25(12)
2
α [°]
β [°]
93.920(2)
γ [°]
114.5600(10)
2661.77(17)
1
1.428
0.766
V [106 pm3]
Z
DX [Mgm–3]
1.379
0.762
1.448
0.807
μ [mm–1]
Crystal size [mm]
No. measured refl.
Independent refl.
Observed refl. [IϾ 2σ(I)]
θmax [°]
0.3ϫ 0.2ϫ 0.2
116818
32005
0.4ϫ 0.3ϫ 0.2
52732
19103
12969
32.64
0.0548, 0.1685, 1.019
19103/719
w = 1/[σ2(Fo2) +
(0.0861P)2 + 2.4222P]
1.619, –1.634
0.4ϫ 0.4ϫ 0.3
121493
18194
13342
31.75
0.6ϫ 0.5ϫ 0.4
99598
16665
13216
31.55
0.0601, 0.1840, 1.074
16665/820
w = 1/[σ2(Fo2) +
16463
30.56
R [F2 Ͼ 2σ(F)], wR(F2), S 0.0633, 0.1665, 0.939
0.0682, 0.1966, 1.098
18194/663
w = 1/[σ2(Fo2) +
Refl./param.
32005/1205
Weighting scheme[a]
w = 1/[σ2(Fo2) +
(0.0761P)2]
(0.0673P)2 + 17.5872P] (0.0863P)2 + 6.1747P]
δρmax,min [10–6 epm–3]
1.551, –1.760
2.329, –1.886
2.944, –1.597
2
2
[a] P = (Fo + 2Fc )/3.
Eur. J. Inorg. Chem. 2013, 5790–5796
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FULL PAPER
Table 2. Crystal data and structure refinement details for 4–7.
Compound
4
5
6
7
Empirical formula
Mr
Crystal system
Space group
a [pm]
b [pm]
c [pm]
C27H60Cl3O16P3Ti3.50
1007.66
monoclinic
P21/n
1474.51(4)
1506.18(4)
2021.22(6)
90
C78H126O32P6Ti7
2096.91
monoclinic
P21/n
1348.84(17)
1496.1(2)
2399.1(3)
90
C111H204O41P6Ti8
2763.76
monoclinic
P21/n
1416.99(12)
2272.53(18)
2227.81(17)
90
C77H113O23P4Ti4
1722.15
triclinic
¯
P1
1327.97(14)
1421.57(15)
2497.7(3)
α [°]
83.599(4)
β [°]
104.184(2)
90
4352.0(2)
4
1.538
0.978
98.141(4)
90
4792.4(11)
2
1.453
0.730
101.300(4)
90
7034.8(10)
2
1.305
0.571
74.598(4)
83.251(4)
4498.5(9)
2
1.270
0.479
γ [°]
V [106 pm3]
Z
DX [Mgm–3]
μ [mm–1]
Crystal size [mm]
No. measured refl.
Independent refl.
Observed refl. [IϾ 2σ(I)]
θmax [°]
0.3ϫ 0.2ϫ 0.2
113501
8719
0.2ϫ 0.2ϫ 0.1
62552
8294
5573
24.87
0.5ϫ 0.3ϫ 0.2
105744
12938
7468
25.41
0.0528, 0.1229, 1.000
12938/799
w = 1/[σ2(Fo2) +
0.6ϫ 0.5ϫ 0.4
116779
18623
12241
26.63
0.0715, 0.2450, 1.041
18623/1124
w = 1/[σ2(Fo2) +
(0.1379P)2 + 7.4926P]
1.539, –0.705
6723
26.24
R [F2 Ͼ 2σ(F)], wR(F2), S 0.0465, 0.1306, 1.049
0.0704, 0.2205, 1.035
8294/556
w = 1/[σ2(Fo2) +
Refl./parameters
8719/517
Weighting scheme[a]
w = 1/[σ2(Fo2) +
(0.0606P)2 + 11.9306P]
1.477, –0.690
(0.1079P)2 + 27.4456P] (0.0371P)2 + 10.814P]
δρmax,min [10–6 epm–3]
1.767, –1.104
0.662, –0.533
2
2
[a] P = (Fo + 2Fc )/3.
[5] G. Guerrero, M. Mehring, P. H. Mutin, F. Dahan, A. Vioux,
J. Chem. Soc., Dalton Trans. 1999, 61, 1537–1538.
[6] M. Mehring, G. Guerrero, F. Dahan, P. H. Mutin, A. Vioux,
Inorg. Chem. 2000, 39, 3325–3332.
[7] D. Chakraborty, V. Chandrasekhar, M. Bhattacharjee, R.
Krätzner, H. W. Roesky, M. Noltemeyer, H. Schmidt, Inorg.
Chem. 2000, 39, 23–26.
[8] M. G. Walawalkar, S. Horchler, S. Dietrich, D. Chakraborty,
H. W. Roesky, M. Schäfer, H.-G. Schmidt, G. M. Sheldrick, R.
Murugavel, Organometallics 1998, 17, 2865–2868; A. Pevec, In-
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and the allyl group were interchangeably disordered. The positions
of the disordered groups were refined with about 50% occupancy
each. CCDC-948341 (for 1), -948342 (for 2), -948343 (for 2b),
-948344 (for 3), -948345 (for 4), -948346 (for 5), -948347 (for 6)
and -948348 (for 7) contain the supplementary crystallographic
data for this paper. These data can be obtained free of charge
from The Cambridge Crystallographic Data Centre via
www.ccdc.cam.ac.uk/data_request/cif.
Acknowledgments
[9] G. Guerrero, P. H. Mutin, A. Vioux, Chem. Mater. 2000, 12,
1268–1272.
[10] C. E. McKenna, M. T. Higa, N. H. Cheung, M.-C. McKenna,
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[11] N. Moszner, F. Zeuner, U. K. Fischer, V. Rheinberger, Macro-
mol. Chem. Phys. 1999, 200, 1062–1067.
[12] D. Seebach, E. Hungerbühler, R. Naef, P. Schnurrenberger, B.
Weidmann, M. Züger, Synthesis 1982, 138–141.
[13] V. Chandrasekhar, T. Senapati, A. Dey, S. Hossain, Dalton
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[14] L. Deng, J. Diao, P. Chen, V. Pujari, Y. Yao, G. Cheng, D. C.
Crick, B. V. V. Prasad, Y. Song, J. Med. Chem. 2011, 54, 4721–
4734.
This work was supported by the Fonds zur Förderung der wissen-
schaftlichen Forschung (FWF), Austria (project P22536). The
X-ray measurements were carried out at the X-ray Center of the
Vienna University of Technology.
[1] U. Schubert, Chem. Mater. 2001, 13, 3487–3494; L. Rozes, N.
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[4] For example, see:W. Gao, L. Dickinson, C. Grozinger, F. G.
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Received: July 7, 2013
Published Online: October 2, 2013
Eur. J. Inorg. Chem. 2013, 5790–5796
5796
© 2013 The Authors. Published by Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim