Phosphonate Modified Titanium Alkoxides: Intermediates in the Sol-Gel Processing of Novel Titania / Phosphonate Inorgani
- PDF / 270,534 Bytes
- 6 Pages / 612 x 792 pts (letter) Page_size
- 106 Downloads / 197 Views
Phosphonate Modified Titanium Alkoxides: Intermediates in the Sol-Gel Processing of Novel Titania / Phosphonate Inorganic-Organic Hybrids P. Hubert Mutin, Michael Mehring1, Gilles Guerrero and André Vioux UMRCNRS 5637, Université de Montpellier 2, Pl. E. Bataillon 34095 Montpellier Cedex 5, France 1 Universität Dortmund, Otto Hahn Str. 6 44227 Dortmund, Germany ABSTRACT We are currently developing a 2-step sol-gel route to metal oxide / phosphonate hybrid materials, based on the non-hydrolytic condensation of a metal alkoxide with a phosphonic acid, followed by hydrolysis / condensation of the remaining alkoxy groups. Several molecular intermediates in this process were obtained by reaction of Ti(OiPr)4 with phosphonic acids RPO3H2 (R = Me, Ph, tBu): [Ti4(OiPr)2(tBuPO3)]4 (1),[Ti4(µ3-O)(OiPr)5(µOiPr)3(PhPO3)3]·DMSO (2), [Ti4(µ3-O)(OiPr)5(µ-OiPr)3(MePO3)3]·DMSO (3), [Ti4(µ3O)(OiPr)5(µ-OiPr)3(tBuPO3)3]·DMSO (4), which were characterized by single crystal X-ray structure analysis and/or NMR spectroscopy. These compounds give information on the sol-gel chemistry in our process and are structural models for the final hybrid materials. In all cases the non-hydrolytic condensation is complete, and the phosphoryl oxygen is coordinated to a titanium atom. In addition, these clusters are soluble in common organic solvents and contain hydrolyzable alkoxy groups, which make them potential building blocks in the sol gel process. Accordingly, the use of cluster 2 as a single source precursor was investigated. INTRODUCTION
Because of the lack of stability of metal-carbon bonds toward hydrolysis, coupling molecules are needed to bind covalently an organic group to a transition metal oxide network. We recently proposed to use organophosphorus acids as coupling molecules: indeed, both P-C and M-O-P bonds are quite stable towards hydrolysis[1]. In addition, M-O-P bonds are easily accessible by nonhydrolytic condensation between M-OR and P-OH functions, which have been used to prepare layered metal phosphates[2] and phosphonates[3], as well as molecular metal phosphates[4]. We are currently exploring the homogeneous incorporation of phosphonate and phosphinate units into transition metal oxide networks, via a 2-step sol-gel process [5]. The first step involves the non-hydrolytic condensation of a metal alkoxide with a phosphonic acid, the second step corresponds to the hydrolysis / condensation of the remaining alkoxy groups (figure 1). The aim of this work was to study the alkoxophosphonate intermediate species formed after the first nonhydrolytic step and after partial hydrolysis in the system Ti(OiPr)4 / RPO3H2 (R = Me, tBu, Ph), in order to gain information on the sol-gel chemistry in this system. In addition, to date the only crystallographically characterized molecular titanium phosphonates are the alkoxoanion [Ti2(OMe)6(O3PPh)2][nBu4N]2 [6] and the partially hydrolyzed [(Cp*TiO3PR)4(µO)2] (R = Me, Ph) and [(Cp*Ti)3(tBuPO3)2(tBuPO2(OH))(µ-O)2] [7].
CC2.4.1 Downloaded from https://www.cambridge.org/core. Rice University, on 18 M
Data Loading...
