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Keywords:

  • Titanium;
  • Alkoxides;
  • Phosphorus;
  • Hydrolysis;
  • Cluster compounds

Abstract

  1. Top of page
  2. Abstract
  3. Introduction
  4. Results and Discussion
  5. Conclusions
  6. Experimental Section
  7. Acknowledgements

The reaction of titanium isopropoxide, Ti(OiPr)4, with bis(trimethylsilyl) phosphonates has led to structures containingTi3O units [= Ti33-O)(μ2-OiPr)3(OiPr)3(O3PR)3] as the basic 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 clusters were formed in which two Ti4 cluster units are bridged by isopropyl phosphonate ligands. For comparison, Ti(OiPr)4 was also treated with allylphosphonic acid to yield a Ti4 cluster. The reaction of Ti(OiPr)4 with the bulky bis(trimethylsilyl) 2-naphthylmethyphosphonate did not yield an oxo cluster but instead the phosphonate-substituted titanium alkoxide Ti4(OiPr)8(O3PCH2naphthyl)4.


Introduction

  1. Top of page
  2. Abstract
  3. Introduction
  4. Results and Discussion
  5. Conclusions
  6. Experimental Section
  7. Acknowledgements

Metal oxo clusters are of great interest as nanosized inorganic building blocks for hybrid materials.1 They can be easily processed, because they are molecular compounds. When incorporated into organic polymers, some of the properties of the polymers are improved in comparison with the parent polymers.2 A common route to titanium oxo clusters is the addition of a carboxylic acid to titanium alkoxides, the water for hydrolysis being produced in situ through esterification of the acid.3

Phosphonates are often used as protecting ligands for titania nanoparticles4 (leading to water-stable and functionalized nanoparticles with several applications) because of the stable Ti–O–P bonds. A few phosphonate- and phosphinate-substituted oxo clusters have been obtained by the reaction of titanium alkoxides with some phosphonic or phosphinic acids.57 The formation of oxo groups in the clusters was attributed to residual moisture in the solvents or phosphonic acids58 rather than to an esterification reaction. The compounds obtained by reaction with phosphinates had similar structures to comparable carboxylate-substituted derivatives.5,7

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 phosphonate ligands to elucidate the influence of organic substituents on the structures of clusters. We mainly used the bis(trimethylsilyl) esters of phosphonic acids as the starting compounds, which have rarely been employed. For example, trimethylsilyl esters of phosphonic acids9 have previously been used for reactions with Ti(OiPr)4 instead of the parent acids. Use of the esters provides better reproducibility and easier handling compared with phosphonic acids themselves.

The bis(trimethylsilyl) phosphonates (Scheme 1a–f) employed include compounds with different functionalities as well as different steric demands. Allylphosphonic acid was also used to compare its behavior with that of the esters.

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Scheme 1. Trimetylsilyl phosphonates used in this study.

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Results and Discussion

  1. Top of page
  2. Abstract
  3. Introduction
  4. Results and Discussion
  5. Conclusions
  6. Experimental Section
  7. Acknowledgements

The phosphonate-substituted oxo clusters [Ti43-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 Ti33-O)(μ2-OiPr)3(OiPr)3 triangle 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 molecule; dmso was used as the solvent due to the low solubility of phosphonic acids in organic solvents.

We obtained cluster 1 with the same structure when allylphosphonic acid was used (Figure 1). The average Ti–O distance of the phosphonate groups is 197 pm, with the exception of the Ti–O bond at Ti1 trans to the terminal OiPr ligands (204 pm). The average Ti–O bond length of the μ2-OiPr groups is 202 pm, and that of the terminal OiPr ligands is 180 pm.

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Figure 1. Molecular structure of [Ti43-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).

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The 31P NMR spectrum shows two signals, and hence the cluster has mirror symmetry in solution. Accordingly, the 1H NMR spectrum shows four different OiPr signals, and the 13C NMR spectrum six doublets for the phosphorus-coupled carbon atoms of the allyl group.

The drawback of using phosphonic acids is their low solubility in organic solvents. Furthermore, reproducing the synthesis of crystalline 1 took several attempts. To overcome 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 [Ti83-O)22-OiPr)6(OiPr)8(O3P-allyl)6{O2P(OiPr)allyl}2] (2) was formed (Figure 2). Cluster 2 consists of two Ti4O units [= Ti43-O)22-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 coordinated 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).

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Figure 2. Molecular structure of [Ti83-O)22-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).

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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.

Cluster 2 was synthesized several times, and either triclinic (space group Pequation image, denoted as 2) or monoclinic crystals (space group P21/n, denoted as 2b) were obtained. The molecular 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 different. 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 phosphonate groups. The formation of an isopropyl phosphonate indicates that, similarly to the reactions of carboxylic acids, esterification of the (noncoordinated or coordinated) 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 alkoxytrimethylsilane10 in a fast reaction.11 Use of the trimethylsilyl 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) phosphonic acid could then react with 2-propanol, possibly catalyzed by Ti(OiPr)x moieties,12 to produce water for condensation and the observed isopropyl monoester.

Crystals of 2 (or 2b) are soluble in common organic solvents. Its NMR spectroscopic data, however, are ambiguous. In the 31P NMR spectrum, five peaks are observed. Interpretation of the 1H NMR spectroscopic data was limited due to the high number of chemically similar groups. 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 elucidate 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 31P NMR spectroscopic data of 3 are in agreement with the solid-state structure, and the 1H and 13C NMR spectra generally confirmed the structural data, with the same limitations as already noted for 2.

In the chemistry of silica-based hybrid materials, chloropropyl-substituted alkoxysilane precursors play an important 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 Ti(OiPr)4 in isopropyl alcohol to yield [Ti7O2(OiPr)12(O3PCH2CH2CH2Cl)6] (4) (Figure 3). The structure of 4 is also based on Ti3O units [= Ti33-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 Ti3O units as “ligands” (in this way of looking at the structures, 1 would be a half-sandwich structure). The bond lengths are similar to those in 1; the Ti–O distances of the phosphonate groups are 198 pm for the titanium atoms of the Ti3O units and 193 pm for the central Ti atom.

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Figure 3. Molecular structure of [Ti73-O)22-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 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).

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The 31P NMR spectrum shows only one peak, which indicates the high symmetry and stability of this cluster in solution. This is also evidenced in the 1H NMR spectrum, in which only two different signals for the OiPr groups are observed. The 13C NMR spectrum confirms this observation, in which the coupling constant JPC is seen. Other smaller signals indicate the presence of a side-product in which Cl is replaced by Br. This was also observed in the spectra of the precursors. Because 1-bromo-3-chloropropane was used for the preparation of ClPrPP, both halogens can react with dimethyl phosphite, and therefore a small amount of (3-bromopropyl)phosphonate was also formed. The presence of some bromine (replacing Cl) was also seen in the electron density map of the single-crystal measurements.

The reaction of TMS-BzlPP with Ti(OiPr)4 yielded Ti7O2(OiPr)12(O3PCH2C6H5)6 (5), which is isostructural to 4. Bond angles and distances of both compounds are very similar. The benzyl groups in the center of the structure adopt a paddle-wheel-like arrangement.

The previously described reactions indicate that the organic group of the phosphonate ligand has some (electronic or steric) influence on the structure of the formed clusters. To shed light on this issue, phosphonate ligands with sterically more demanding groups were included in this study. Furthermore, aromatic phosphonic acids are slightly more acidic.

The reaction of TMS-XylPP and Ti(OiPr)4 led to the formation 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 (instead of dmso as in 1).

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Figure 4. Molecular structure of [Ti43-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).

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The appearance of only one signal in the 31P NMR spectrum indicates that cluster 6 has C3 symmetry in solution. This was confirmed by the 1H NMR spectrum in which only three different signals for the CH3 groups of OiPr and only one singlet for the CH3 of the xylyl group can be seen. The proton of the coordinated isopropyl alcohol exchanges easily on the NMR timescale, because only averaged signals of the isopropyl alcohol and the OiPr groups were observed.

The reaction of a phosphonate with an even bulkier substituent, namely TMS-NpMePP, resulted in the complex [Ti42-OiPr)(OiPr)7(O3PMeNp)4] (7; Figure 5). In 7, two of the OiPr ligands of Ti(OiPr)4 are substituted by one O3PMeNp ligand [formal composition Ti(OiPr)2(O3PMeNp)], but no partial hydrolysis took place. This is in contrast to the reactions with the other bis(trimethylsilyl) phosphonates described in this article. The crystallization time of 7 was much shorter than for the other clusters reported in this article. Compound 7 could therefore represent the structure of an initially formed substitution product, which possibly crystallized more easily from the isopropyl alcohol solution due to the apolarity of the naphthyl group and thus escaped hydrolysis.

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Figure 5. Molecular structure of [Ti42-OiPr)(OiPr)7(O3PMeNp)4(iPrOH)2·2iPrOH] (7). Hydrogen atoms have been omitted for clarity. 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).

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The structure of 7 consists of four octahedrally coordinated titanium atoms arranged in an irregular shape. In contrast to all the other structures, in which all the phosphonates bind in a 3.111 mode [w.xyz denotes the number of metal atoms to which the phosphonate ligand is coordinated (w), and the number of metal atoms to which each oxygen is coordinated (x,y,z)13], just one phosphonate in 7 coordinates in the 3.111 mode. The other phosphonates coordinate in the 4.211, 3.211, and 2.110 modes. As a result of the high connectivity of the phosphonates, there is only one bridging OiPr ligand.

The NMR measurements are in good agreement with the crystal structure. Four signals are detected in the 31P NMR spectrum, with a shift difference of 8.80 ppm. The latter is attributed to the different binding modes of the phosphonate ligands. Three doublets for the CH2 groups are detected in the 13C NMR spectrum, although four were expected. One of these doublets has a higher intensity, which indicates signal overlap.

Conclusions

  1. Top of page
  2. Abstract
  3. Introduction
  4. Results and Discussion
  5. Conclusions
  6. Experimental Section
  7. Acknowledgements

Trimethylsilyl esters of phosphonic acids are better precursors for the preparation of phosphonate-substituted titanium 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 react with P-O-SiMe3 in non-hydrolytic condensation processes.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 introduction 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 isopropyl phosphonate ligands in 2 and 3.

The synthesis of 1 and 2 shows that titanium alkoxo derivatives 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 organic double bonds and Ti-OR groups in 1, this derivative appears to be suitable for the preparation of hybrid materials, similar to alkoxysilanes (RO)3Si-R′ with polymerizable groups R′.

From a structural point of view, it is interesting to note that the structures of the phosphonate-substituted oxo clusters are derived from a common motif, that is, Ti33-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

  1. Top of page
  2. Abstract
  3. Introduction
  4. Results and Discussion
  5. Conclusions
  6. Experimental Section
  7. Acknowledgements

General: Manipulations were carried out under an inert gas by using standard Schlenk and glove-box techniques. Diethyl ethylphosphonate, allyl bromide, 1-bromo-3-chloropropane, benzyl bromide, 1-bromo-3,5-dimethylbenzene, 2-(bromomethyl)naphthalene and triethyl phosphite were purchased from Sigma–Aldrich and used as received. Diethyl 3,5-dimethylphenylphosphonate was prepared by a procedure similar to that already reported.14 The bis(trimethylsilyl) esters were prepared by adding bromotrimethylsilane (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 31P 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 and distillation. Samples for NMR measurements were obtained by washing the crystalline substances with iPrOH, drying and dissolving 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.

[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.

[Ti83-O)22-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.

[Ti73-O)22-OiPr)6(OiPr)6(O3PCH2CH2CH2Cl)6] (4): Bis(trimethylsilyl) (3-chloropropyl)phosphonate (300 μL, 1.11 mmol) was 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 = 1.45 (d, 36 H, CHCH3), 1.63 [d, 36 H, CHCH32-OiPr)], 1.91 (dt, 12 H, PCH2), 2.38 (m, 12 H, CH2CH2CH2), 3.84 (t, 12 H, CH2Cl), 4.68 (m, 6 H, CHCH3), 5.16 [m, 6 H, CHCH32-OiPr)] ppm. 31P NMR (CD3Cl, 101.2 MHz): δ = 18.76 ppm. 13C NMR (C6D6, 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 (CHCH3), 79.78 (CHCH3) ppm. The 1H 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.

[Ti73-O)22-OiPr)6(OiPr)6(O3PCH2C6H5)6] (5): Bis(trimethylsilyl) benzylphosphonate (200 μL, 0.64 mmol) was diluted with iPrOH (1 mL), and then Ti(OiPr)4 (370 μL, 1.28 mmol) was added quickly. Crystals suitable for single-crystal XRD were obtained after 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.

[Ti4O(OiPr)8(O3P-xyl)3(iPrOH)] (6): Bis(trimethylsilyl) (3,5-dimethylphenyl)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 after 3 weeks. Yield: 100 mg (72 %). 1H NMR (CD3Cl, 250 MHz): δ = 1.17 (d, J = 6.1 Hz, 18 H, CHCH3), 1.40 (d, J = 6.2 Hz, 18 H, CHCH3), 1.46 (d, J = 6.3 Hz, 18 H, CHCH3), 2.34 (s, 18 H, CCH3), 4.71 (m, 5 H, CHCH3), 5.06 (m, 4 H, CHCH3), 7.11 (s, 3 H, CCH), 7.53 (d, J = 13.9 Hz, CCH) ppm. 31P NMR (CD3Cl, 101.2 MHz): δ = 10.18 ppm. 13C NMR (C6D6, 62.90 MHz): δ = 21.10 (CCH3), 24.79 (CHCH3), 24.93 (CHCH3), 78.12 (CHCH3), 78.83 (d), 129.47 (J = 10.7 Hz, CCH), 131.38 (J = 197 Hz, PC), 131.77 (CCH), 136.76 [J = 16 Hz, C(xyl)] ppm.

[Ti42-OiPr)(OiPr)7(O3PMeNp)4(iPrOH)2·2iPrOH] (7): Bis(trimethylsilyl) (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, 250 MHz): δ = 1.00–1.65 (m, 60 H, CH3), 3.20–3.90 (m, 8 H, CH2), 4.00–4.60 (m, 6 H, CH), 5.00–5.60 (m, 6 H, CH), 7.20–8.20 (m, 28 H, CCH) ppm. 31P NMR (C6D6, 101.2 MHz): δ = 12.82, 13.24, 17.43, 21.62 ppm. 13C NMR (C6D6, 62.90 MHz): δ = 22.87, 23.60, 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.

X-ray Structure Analyses: All measurements were performed at 100 K by using Mo-Kα (λ = 71.073 pm) radiation. Data were collected with a Bruker AXS SMART APEX II four-circle diffractometer with κ-geometry. Data were collected with φ- and ω-scans and a 0.5° frame width. The data were corrected for polarization and Lorentzian effects, and an empirical absorption correction (SADABS) was employed. The cell dimensions were refined by using all unique reflections. SAINT PLUS software (Bruker Analytical 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 structures were solved by the Patterson method (SHELXS97),15 and refinement was performed by the full-matrix least-squares method based on F2 (SHELXL97) with anisotropic thermal parameters for all non-hydrogen atoms. Hydrogen atoms were inserted in calculated positions and refined riding on the corresponding atom, those bonded to oxygen atoms were identified in the electron density map. The carbon atoms of the different OiPr ligands of 1, 2, 2b, 3, 4, and 7 were disordered as well as the carbon atoms of the different phosphonates of 1, 2b, and 3. In 2 and 2b, the isopropyl ester and the allyl group were interchangeably disordered. The positions of the disordered groups were refined with about 50 % occupancy each. CCDC-948341 (for 1), -CCDC-948342 (for 2), -CCDC-948343 (for 2b), -CCDC-948344 (for 3), -CCDC-948345 (for 4), -CCDC-948346 (for 5), -CCDC-948347 (for 6) and -CCDC-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.

Table 1. Crystal data and structure refinement details for 13.
Compound122b3
  • [a]

    P = (Fo2 + 2Fc2)/3.

Empirical formulaC70H155O38P6S2Ti8C72H152O40P8Ti8C72H152O40P8Ti8C32H76O20P4Ti4
Mr2238.082288.902288.901096.41
Crystal systemmonoclinictriclinicmonoclinictriclinic
Space groupP21/cPequation imageP21/nPequation image
a [pm]3366.33(17)1192.63(4)1260.81(4)1173.14(3)
b [pm]1270.76(7)1315.97(4)1873.03(6)1266.27(4)
c [pm]2763.86(14)1888.04(8)2282.43(8)1870.42(5)
α [°]9095.737(2)9090.5310(10)
β [°]114.257(2)93.920(2)93.6370(10)95.6330(10)
γ [°]90114.5600(10)90114.4040(10)
V [106 pm3]10779.4(10)2661.77(17)5379.182514.25(12)
Z4122
DX [Mg m–3]1.3791.4281.4131.448
μ [mm–1]0.7620.7660.7580.807
Crystal size [mm]0.3 × 0.2 × 0.20.4 × 0.3 × 0.20.4 × 0.4 × 0.30.6 × 0.5 × 0.4
No. measured refl.1168185273212149399598
Independent refl.32005191031819416665
Observed refl. [I > 2σ(I)]16463129691334213216
θmax [°]30.5632.6431.7531.55
R [F2 > 2σ(F)], wR(F2), S0.0633, 0.1665, 0.9390.0548, 0.1685, 1.0190.0682, 0.1966, 1.0980.0601, 0.1840, 1.074
Refl./param.32005/120519103/71918194/66316665/820
Weighting scheme[a]w = 1/[σ2(Fo2) + (0.0761P)2]w = 1/[σ2(Fo2) + (0.0861P)2 + 2.4222P]w = 1/[σ2(Fo2) + (0.0673P)2 + 17.5872P]w = 1/[σ2(Fo2) + (0.0863P)2 + 6.1747P]
δρmax,min [10–6 e pm–3]1.551, –1.7601.619, –1.6342.329, –1.8862.944, –1.597
Table 2. Crystal data and structure refinement details for 47.
Compound4567
  • [a]

    P = (Fo2 + 2Fc2)/3.

Empirical formulaC27H60Cl3O16P3Ti3.50C78H126O32P6Ti7C111H204O41P6Ti8C77H113O23P4Ti4
Mr1007.662096.912763.761722.15
Crystal systemmonoclinicmonoclinicmonoclinictriclinic
Space groupP21/nP21/nP21/nPequation image
a [pm]1474.51(4)1348.84(17)1416.99(12)1327.97(14)
b [pm]1506.18(4)1496.1(2)2272.53(18)1421.57(15)
c [pm]2021.22(6)2399.1(3)2227.81(17)2497.7(3)
α [°]90909083.599(4)
β [°]104.184(2)98.141(4)101.300(4)74.598(4)
γ [°]90909083.251(4)
V [106 pm3]4352.0(2)4792.4(11)7034.8(10)4498.5(9)
Z4222
DX [Mg m–3]1.5381.4531.3051.270
μ [mm–1]0.9780.7300.5710.479
Crystal size [mm]0.3 × 0.2 × 0.20.2 × 0.2 × 0.10.5 × 0.3 × 0.20.6 × 0.5 × 0.4
No. measured refl.11350162552105744116779
Independent refl.871982941293818623
Observed refl. [I > 2σ(I)]67235573746812241
θmax [°]26.2424.8725.4126.63
R [F2 > 2σ(F)], wR(F2), S0.0465, 0.1306, 1.0490.0704, 0.2205, 1.0350.0528, 0.1229, 1.0000.0715, 0.2450, 1.041
Refl./parameters8719/5178294/55612938/79918623/1124
Weighting scheme[a]w = 1/[σ2(Fo2) + (0.0606P)2 + 11.9306P]w = 1/[σ2(Fo2) + (0.1079P)2 + 27.4456P]w = 1/[σ2(Fo2) + (0.0371P)2 + 10.814P]w = 1/[σ2(Fo2) + (0.1379P)2 + 7.4926P]
δρmax,min [10–6 e pm–3]1.477, –0.6901.767, –1.1040.662, –0.5331.539, –0.705

Acknowledgements

  1. Top of page
  2. Abstract
  3. Introduction
  4. Results and Discussion
  5. Conclusions
  6. Experimental Section
  7. Acknowledgements

This work was supported by the Fonds zur Förderung der wissenschaftlichen Forschung (FWF), Austria (project P22536). The X-ray measurements were carried out at the X-ray Center of the Vienna University of Technology.