Complexation of Titanium Alkoxides with - Springer Link

Journal of Inorganic and Organometallic Polymers, Vol. 13, No. 1, March 2003 (© 2003)

Complexation of Titanium Alkoxides with Cis-2-butene-1,4-diol and Hydrolysis of Their Products Asgar Kayan 1 Received July 18, 2002; revised November 8, 2002 Reaction of Ti(OEt)4 and Ti(OBu n )4 with cis-2-butene-1,4-diol (B.diol-2H) in 1:1 molar ratio was studied at room temperature using the sol-gel process. 13 C{ 1 H}- and 1 H-NMR data showed that all the B.diol-2H completely reacted with both titanium alkoxides. Each of the products was hydrolyzed by water. The new hydrolyzed products were characterized by 13C- and 1 H-NMR spectroscopy and Karl–Fischer Titration. Thermogravimetric and differential thermal analyses (TGA-DTA) of the hydrolyzed-products were also studied. KEY WORDS: Sol-gel; titanium alkoxides; cis-2-butene-1,4-diol; hydrolysis of metal alkoxides.

INTRODUCTION Metal alkoxides and their organic derivatives have been used in the synthesis of glasses, ceramics and organic-inorganic hybrid materials [1–3]. The complexing of metal alkoxides with appropriate organic acids, diketones or glycols influences the functionality of the precursors and controls the degree of polycondensation of the reaction products [4–6]. The first group of complexing ligands that contains unsaturated bonds for metal alkoxides complexes are organic acids such as acrylic and methacrylic acid (McOH) [4, 7]. The second group of complexing organic compounds contains unsaturated bonds and involves b-ketoesters such as allyl acetoacetate [6, 8] and methacryloxyethyl acetoacetate [6, 9]. When organic acids or b-ketoesters are added to the metal alkoxide solution,

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Department of Chemistry, Kocaeli University, Ízmit, Turkey. E-mail: [email protected] 29 1053-0495/03/0300-0029/0 © 2003 Plenum Publishing Corporation

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some of the alkoxy groups in the starting material are replaced with the chelated organic groups [e.g., Eq. (1)]. Zr(OPr n )4 +2McOH |||Q [Zr(OPr n )2 (OMc)2 ]n − 2Pr nOH

(1)

In hydrolysis reactions of organic-modified metal alkoxide complexes, only the alkoxide group undergoes substitution while chelated organic groups remain bonded to the metal [Eq. (2)] [4, 5, 10, 11]. This observation is a result of chelate bond formation and steric hindrance effects [6, 8, 10, 12]. The other complexing organic compounds include glycols +H O

2 [Zr(OPr n )2 (OMc)2 ]n |||Q [ZrO(OMc)2 ]n − 2Pr nOH

(2)

[Equation (3)]. The reaction between glycols and metal alkoxides results in the formation of glycolates complexes (G:alkyl or G:alkylene) [13–16]. Furthermore, addition of cis-2-butene-1,4-diol to Ti(OPr i )4 in a 1:1 stoichiometry produces [Ti4 (OPr i )8 (m,g 2-OCH 2 CH=CHCH 2 O)2 -(m3 ,g 2OCH 2 CH=CHCH 2 O)2 ] or simply [Ti(OPr i )2 (OCH 2 CH=CHCH 2 O)]n [17]. OH M(OR)4 +nG

|Q (RO)4 − 2n M OH

R

O G O

S

+2nROH)n

(3)

n

In order to explore further this chemistry, we undertook a study of the reactions of the metal alkoxides, Ti(OEt)4 and Ti(OBu n )4 , with the chelated alcohol cis-2-butene-1,4-diol (B.diol-2H). The hydrolytic stability of the ligand on the metal alkoxide complexes was also investigated.

EXPERIMENTAL Methods and Materials 13

C- and 1 H-NMR spectra were recorded on a Bruker AC200 spectrometer. The amount of water in the hydrolysates was determined by Karl–Fischer (KF) titration using a Mettler DL 18. Thermogravimetric analysis (TGA) and differential thermal analysis (DTA) measurements were carried out on a Bahr-Thermoanalyse Type STA 501 thermal analyzer. The chemicals, Ti(OEt)4 (92%), Ti(OBu n )4 (90.6%), B.diol-2H (95%) and ethyl methyl ketone were used in the experiments without further purification.

Complexation of Titanium Alkoxides with Cis-2-butene-1,4-diol

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Preparation of [Ti(OEt)2 (B.diol)]n (1) Ti(OEt)4 (3.7 mmol) in methyl ethyl ketone (15 ml) was stirred for 10 minutes. B.diol-2H (3.7 mmol) was added to the solution. The mixture was stirred for two hours at room temperature. The solvent and liberated ethanol were removed from the gel under vacuum at about 60°C. 13C{ 1 H}NMR (in CDCl3 ), “ ppm (assignment): 19.10 (CH 3 , OEt); 64.03 (Ti-OCH 2 b b CH=); 71.36 (OCH 2 , OEt); 131.32 (Ti-OCH 2 -CH=). 1 H-NMR (in b b CDCl3 ), “ ppm (multiplicity, assignment): 1.2 (t, CH 3 , OEt); 4.4 (m, CH 2 , OEt); 4.93 (brs, CH 2 , from Ti-OCH 2 -CH=); 5.83 (brs, CH, from Ti-OCH 2 CH=). Hydrolysis of [Ti(OEt)2 (B.diol)]n (2) The hydrolysis of the [Ti(OEt)2 (B.diol)]n complex was carried out with a water/methyl ethyl ketone solution at room temperature for 30 min. The hydrolysis ratios of H 2 O/Ti(OEt)4 for these experiments were 2:1, 3:1, and 4:1. The amount of unreacted water was determined by KF-titrations [18]. The consumed water was found to be 1.79 mol (4H 2 O/Ti ethoxide) by subtracting unreacted water from the added water. Only transparent solutions were examined by 13C- and 1 H-NMR spectroscopy. These solutions included hydrolyzed product, released ethanol, and dissociated B.diol2H as shown in Fig. 1. The intensity ratio of CH 2 protons of dissociated B.diol-2H to CH 2 protons of B.diol that is bonded to the titanium

H

H C

HOH2C

C CH 2OH

+Ti(OEt)2 -EtOH

[ Ti(OEt)0.9 (OH)1 .28(OCH2 CH=CHCH2 O) ]n +4H2O

-1.1EtOH -0.6B.diol-2H

[ Ti(OEt)0.9 (OH)1 .28(B.diol)0 .4(O) 0 .51 ]n Fig. 1. Scheme for the complexation of Ti(OEt)4 with B.diol-2H and the hydrolysis of the complex.

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(product) indicated that 0.6 mol of B.diol-2H dissociated from starting complex 1. 1 H-NMR (in CDCl3 ), “ ppm (multiplicity, assignment): 1.2 (t, CH 3 , Ti-OEt, EtOH); 3.64 (m, CH 2 , EtOH); 3.91 (s, OH, from TiOH, EtOH and B.diol-2H); 4.14 (brs, CH 2 , B.diol-2H); 4.26 (brs, CH 2 , TiOEt); 4.88 (brs, CH 2 , Ti-OCH 2 CH=); 5.69 (m, CH, Ti-OCH 2 CH=, B.diol-2H). 13 C{ 1 H}-NMR (in CDCl3 ), “ ppm (assignment): 18.04 (CH 3 , EtOH); 57.73 b (HO-CH 2 -CH=, B.diol-2H); 64.10 (CH 2 , EtOH); 130.7 (HO-CH 2 -CH=, b b b 13 B.diol-2H). The same data were obtained for the C- and 1 H-NMR spectra using ethanol as a solvent.

TGA-DTA of Hydrolyzed-Product of [Ti(OEt)2 (B.diol)]n After the hydrolyzed product was dried under vacuum at 60°C, the product (50 mg) was used for TGA and DTA measurements. The thermograms are shown in Fig. 2. The TGA of the hydrolyzed product resulted in a weight loss of 50.7% up to 800°C. It is assumed that all the organic groups are removed at this temperature. In other words, hydrolyzed product contained 49.3% TiO2 , (or 29.6% Ti). Two exothermic peaks in DTA of the hydrolyzed product appear at 215 and 510°C and are attributed to the removal of the organic groups.

Fig. 2. TGA and DTA curves of the hydrolyzed product of [Ti(OEt)2 (B.diol)]n .


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Preparation of [Ti(OBu n)2 (B.diol)]n (3) A preparative procedure for 3, which was analogous to the above for 1, was performed [Eq. (4)]. 13C{ 1 H}-NMR (in CDCl3 ), “ ppm (assignment): 14.01 ( 4CH3, OBu n=); 19.18 ( 3CH 2 , OBu n ); 35.19 ( 2CH 2 , OBu n ); 62.84 b b b (Ti-OCH 2 -CH=); 75.79 ( 1CH 2 , OBu n ); 131.4 (Ti-OCH 2 -CH=); (Fig. 3). b b b 1 H-NMR (in CDCl3 ), “ ppm (multiplicity, assignment): 1.0 (t, 4CH 3 , n 3 n 1 2 OBu ); 1.3–1.6 (m, CH 2 CH 2 , OBu ); 4.25 (m, CH 2 , OBu n ); 4.90 (brs,

Fig. 3.

C-NMR spectra of Ti(OBu n )4 (1), B.diol-2H (2), and [Ti(OBu n )2 (B.diol)]n (3).

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CH 2 , from Ti-OCH 2 -CH=); 5.83 (brs, CH, from Ti-OCH 2 -CH=). ( 4CH 3 3 CH 2 - 2CH 2 - 1CH 2 -OTi). Ti(OBu n )4 +B.diol-2H |||Q [Ti(OBu n )2 (B.diol)]n − 2Bu nOH

(4)

Hydrolysis of [Ti(OBu n )2 (B.diol)]n (4) A preparative procedure for 4, which was analogous to the above for 1, was performed. 1 H-NMR (in CDCl3 ), “ ppm (multiplicity, assignment): 0.92 (t, 4CH 3 , TiOBu n and Bu n OH); 1.27–1.60 (m, 3CH 2 2CH 2 , b TiOBu n and Bu n OH); 3.57 (m, 1CH 2 , Bu n OH); 3.97 (s, OH, from TiOH, Bu n OH and B.diol-2H); 4.14 (brs, CH 2 , B.diol-2H); 4.48 (brs, CH 2 , TiOBu n ); 5.05 (brs, CH 2 , TiOCH 2 CH=); 5.69 (t, CH, TiOCH 2 CH=, and B.diol-2H); (Fig. 4). 13C{ 1 H}-NMR (in CDCl3 ), “ ppm (assignment): 13.95 ( 4CH 3 , Bu n OH); 19.13 ( 3CH 2 , Bu n OH); 34.85 ( 2CH 2 , Bu n OH); 57.70 (HOb b b CH 2 -CH=, B.diol-2H); 62.13 ( 1CH 2 , Bu n OH); 130.8 (HO-CH 2 -CH=, b b b B.diol-2H). ( 4CH 3 - 3CH 2 - 2CH 2 - 1CH 2 -OH, from hydrolysis of complex 3).

Fig. 4.

1

H-NMR spectrum of the hydrolyzed product of [Ti(OBu n )2 (B.diol)]n .


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Table I. Karl–Fischer Titration of the Hydrolysis of [Ti(OBu n )2 (B.diol)]n Added water/Ti(OBu n )4 , mole

Consumed water, mole

2/1 3/1 4/1

1.30 1.38 1.42

The consumed water was found to be 1.42 mole (4H 2 O/Ti butoxides) by KF titration (Table I). The amount of dissociated B.diol-2H from the starting complex 3 was found to be approximately 0.6 mole from the 1 H-NMR data [Eq. (5)]. +4H2 O |||Q [Ti(OBu n )0.9 (OH)0.54 (B.diol)0.4 (O)0.88 ]n [Ti(OBu n )2 (B.diol)]n || − 1.1Bu nOH − 0.6B.diol-2H (5)

TGA-DTA of the Hydrolyzed Product of [Ti(OBu n )2 (B.diol)]n After the hydrolyzed product of [Ti(OBu n )2 (B.diol)]n was dried at 60°C, TGA and DTA measurements were obtained. The TGA of the hydrolyzed product showed a weight loss of 56.2% up to 800°C. By the time that temperature is reached, all the organic groups are removed. The hydrolyzed product, therefore, contained 43.8% TiO2 (or 263% Ti). As shown in Fig. 5, the DTA of the hydrolyzed product included two exothermic peaks at 208 and 516°C, which is consistent with the removal of the organic groups.

Fig. 5. TGA-DTA curves of the hydrolyzed product of [Ti(OBu n )2 (B.diol)]n .

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RESULTS AND DISCUSSION The 13C{ 1 H}-NMR spectrum of uncoordinated cis-2-butene-1,4-diol exhibits two peaks at 57.66 (HO-CH 2 -CH=) and 130.6 ppm (HO-CH 2 b CH=). When cis-2-butene-1,4-diol is coordinated to Ti(OEt)4 , the CH 2 and b CH carbons of organic ligand are shifted to 64.0 and 131.3 ppm, respectively. The 1 H-NMR spectrum of the uncoordinated B.diol-2H also shows three peaks at 3.00, 4.20, and 5.73 ppm, which are characteristic of hydroxyl, CH 2 and CH protons, respectively. Upon addition of cis-2butene-1,4-diol to titanium ethoxide, the CH 2 protons of the diol are shifted downfield to 4.93 ppm. Furthermore, the signal for the OH proton in the 1 H-NMR spectrum is absent. Lack of an OH proton signal indicates that the B.diol is quantitatively coordinated to titanium. Characteristic 1 H- and 13C-NMR data were obtained for complex 3. For example, the 1 H-NMR spectrum 3 is consistent with that of [Ti(OEt)2 (B.diol)]n . Hence, the presence of the -OCH 2 CH=CHCH 2 Oligand is evident by the appearance of a broad singlet at 4.90 ppm for the CH 2 protons and at 5.83 ppm for the CH proton. It is proposed, therefore, that cis-2-butene-1,4-diolate is bonded to the titanium alkoxide as a chelating bridge ligand, as suggested by Hubert–Pfalzgraf [17]. For instance, [Ti(OPr i )2 (B.diol)]4 was determined to be an open-shell, tetranuclear polyhedron and, therefore, n should be 4. The hydrolysis reactions for compounds 1 and 3 were investigated by 13 C- and 1 H-NMR spectroscopy and Karl–Fischer titration. The unsaturated organic ligand; i.e., cis-2-butene-1,4-diolate, in compounds 1 and 3 is stable toward hydrolysis for a several hours in a 1:4 Ti-alkoxide/H 2 O ratio. 1 H- and 13C-NMR spectra of the hydrolyzed product were taken without removal of the dissociated B.diol-2H and the released alkoxides. Thus, the 1 H-NMR spectra of the transparent solutions of hydrolyzed products 2 and 4 in CDCl3 show that almost 60% of the cis-2-butene-1,4diol are dissociated from the starting complexes 1 and 3. The CH 2 protons of the dissociated B.diol-2H from compounds 2 and 4 appear at 4.14 ppm (see Fig. 4 for compound 4). The 1 H-NMR spectra of the hydrolyzed compounds of 2 and 4 show CH 2 proton signals for the B.diol at 4.88 and 5.05 ppm, respectively. These signals are evidence for the formation of both 2 and 4. The 1 H-NMR spectra of both 2 and 4 exhibited an OH signal for Ti-OH, CH 3 CH 2 OH, and HOCH 2 CH=CHCH 2 OH at 3.91 ppm. The shift in this signal suggests that the OH protons of ethanol and B.diol-2H are weakly bonded to titanium in the mixture. In contrast, the 13C-NMR spectra of hydrolyzed products 2 and 4 indicate that ethanol and B.diol-2H are dissociated from titanium. Because the data collection for 13C-NMR spectra took a long time, the hydrolyzed product decomposed to titanium


Fig. 6.

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C-NMR spectrum of the hydrolyzed product of [Ti(OBu n )2 (B.diol)]n .

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hydroxides, ethanol and cis-2-buten-1,4-diol in the presence of water (i.e., 4:1 H 2 O/Ti). The 13C-NMR spectrum of the hydrolyzed product of [Ti(OBu n )2 (B.diol)]n (Fig. 6) reveals two characteristic peaks for the dissociated cis-2-butene-1,4-diol at 57.70 (OCH 2 ) and 130.8 (CH=) ppm, respectively. The Karl–Fischer titration measurement indicates that [Ti(OEt)2 (B.diol)]n and [Ti(OBu n )2 (B.diol)]n consume 1.79 and 1.42 moles H 2 O, respectively. If both the Karl–Fischer titrations and the NMR spectroscopy results are considered, the formula of hydrolyzed products is [Ti(OEt)0.9 (OH)1.28 (B.diol)0.4 (O)0.51 ]n (2) and [Ti(OBu n )0.9 (OH)0.54 (B.diol)0.4 (O)0.88 ]n (4). The oxo ligand stems from a condensation reaction between the alkoxyl and hydroxyl groups bonded to titanium. The calculated percentage Ti for

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Kayan

complexes 2 and 4 is 31.35 and 27.95%, respectively. These values are very close to thermogravimetric analysis result, which gives 29.59% Ti for 2 and 26.25% Ti for 4. CONCLUSION In summary, inorganic-organic hybrid compounds 1 and 3 were synthesized by the sol-gel process and characterized by 13C{ 1 H}- and 1 H-NMR spectroscopy. These compounds can be used as a source of titania to obtain low density, microcellular, doped organic materials [17]. Compounds 1 and 3 contain a double bond, which is suitable for addition and polymerization reactions. The hydrolysis of 1 and 3 was also studied. The hydrolysis products, 2 and 4, were characterized by 13C{ 1 H}- and 1 H-NMR spectroscopy and Karl–Fischer titration. Both compounds were stable for several hours in water. ACKNOWLEDGMENTS The author thanks Inonu University where the Karl–Fischer titration measurements were carried out, and the Institut fur neue Materialien (INM) in Saarbruken, Germany, for providing the 13C- and 1 H-NMR spectra and the TGA-DTA measurements. REFERENCES 1. C. J. Brinker, D. E. Clark, and D. R. Ulrich, Better Ceramics Through Chemistry (Elsevier, New York, 1984). 2. L. C. Klein, ed., Sol-Gel Technology for Thin Films, Fibers, Preforms, Electronics, and Specialty Shapes (Noyes Publications, Park Ridge, New Jersey, 1988). 3. R. C. Mehrotra, in Chemistry, Spectroscopy and Aplications of Sol-Gel Glasses, R. Reisfeld and C. K. Jorgensen, eds. (Springer-Verlag, Berlin, 1992). 4. U. Schubert, E. Arpac, W. Glaubitt, A. Helmerich, and C. Chau, Chem. Mater. 4, 291 (1992). 5. D. Hoebbel, T. Reinert, K. Endres, H. Schmidt, A. Kayan, and E. Arpac, Proc. First Europ. Workshop on Hybrid Organic-Inorganic Materials, Bierville, France (1993), pp. 319–323. 6. C. Sanchez and M. In, J. Non-Cryst. Solids 147/148, 1 (1992). 7. H. Sayilkan and E. Arpac, Turkish J. Chem. 17, 92 (1993). 8. C. Sanchez and F. Ribot, New J. Chem. 18, 1007 (1994). 9. M. In, C. Gerardin, J. Lambard, and C. Sanchez, J. Sol-Gel Sci. Technol. 5, 101 (1995). 10. D. Hoebbel, T. Reinert, H. Schmidt, and E. Arpac, J. Sol-Gel Sci. Technol. 10, 115 (1997). 11. S. Sener, H. Sayilkan, and E. Sener, Bull. Chem. Soc. Jpn. 73, 1419 (2000). 12. R. Nass and H. Schmidt, J. Non-Cryst. Solids 121, 329 (1990). 13. D. C. Bradley, R. C. Mehrotra, and D. P. Gaur, Metal Alkoxides (Academic Press, London, 1978).


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C. Guizard, N. Cygankiewicz, A. Larbot, and L. Cot, J. Non-Cryst. Solids 82, 86 (1986). M. Gugliclmi and G. Carturan, J. Non-Cryst. Solids 100, 16 (1988). J. Zhao, W. Fan, D. Wu, and Y. Sun, J. Non-Cryst. Solids 261, 15 (2000). N. Miele-Pajot, L. G. Hubert-Pfalzgraf, R. Papiernik, J. Vaissermann, and R. Collier, J. Mater. Chem. 9, 3027 (1999). 18. E. Scholz, Karl–Fischer Titration (Springer-Verlag, Berlin, 1984).

14. 15. 16. 17.