Hybrid Silica Gels Containing 1,3-Butadiyne Bridging Units. Thermal and Chemical Reactivity of the Organic Fragment Robert J. P. Corriu,* Joe ¨l J. E. Moreau,* ,† Philippe Thepot, and Michel Wong Chi Man Pre ´ curseurs Organome ´ talliques de Mate ´ riaux, CNRS UMR44, Case Courrier 007, De ´ partement de Chimie Organique Fine, Universite ´ de Montpellier II, Sciences et Techniques du Languedoc, 34095 Montpellier Ce ´ dex 05, France Received June 14, 1995. Revised Manuscript Received August 2, 1995 X Silica gel containing diyne units have been obtained from molecular organosilicon precursors and the properties associated to the very reactive unsaturated organic moieties have been explored. The sol-gel polymerization of 1,4-bis(trimethoxysilyl)-1,3-butadiyne ((MeO) 3 SiCtCCtCSi(OMe) 3 ) quantitatively led to a silsesquioxane network, [O 1.5 - SiCtCCtCSiO 1.5 ] n , consisting of siloxanes chains with bridging diyne units. The derived xerogels were characterized by IR and 13 C and 29 Si CP MAS NMR spectroscopies. The major environment of the Si atom corresponded to a T 2 CSi(OR)(OSi) 2 substructure, and only minor Si-C bond cleavage occurred during the sol-gel condensation. The chemical reactivity of the hybrid organic-inorganic gel was studied and used as a tool for the study of the organization of the solid induced by the organic moieties. Upon heating, in the solid state, the diyne fragments undergo a polyaddition to give an ene-yne structure. The polymeri- zation, observed in the solid state, suggests favorable arrangements of the organic fragments within the amorphous solid. The resulting composite material consists in a network made of interpenetrating ene-yne and siloxane polymers. On the other hand, the organic diyne fragments in the hybrid gel have been removed, leaving silica behind, in two ways: (i) The thermal oxidation in air led to microporous silicas with N 2 BET surface areas in the range 300-350 m 2 g -1 . (ii) Interestingly, the smooth Si-C bond cleavage by MeOH catalyzed by NH 4 F gave highly porous silica with N 2 BET surface areas up to 950 m 2 g -1 . The latter elimination of the organic moiety under mild reaction conditions is of particular interest since it gives rise to silica with a surface area significantly higher than that produced upon thermal oxidation and higher than that of the originating hybrid precursor. Introduction The sol-gel process, which offered unique possibilities for the elaboration of inorganic solids, 1 also recently proved to be of great interest for the preparation of hybrid organic-inorganic materials. The hydrolysis and polycondensation of substituted alkoxysilanes RSi- (OR′) 3 containing a nonhydrolyzable Si-C bond gave rise to a variety of silsesquioxanes 2 (eq 1). Materials with unique properties and applications can be produced upon changing the nature of the organic substituent. Di- or polysilylated organic molecules were shown to give an easy versatile access to amorphous microporous hybrid materials (eq 2). In an approach to control the morphology of the resulting solid at the molecular level, organic fragments with various structural features were introduced. 3,4 This can be also used for inserting functional organic group in a silicate network to produce hybrid gels with interesting reactivity. Silica gels with electroactive properties were for example obtained from molecular precursors containing thiophene oligomers. 5 We decided to investigate the properties of gels containing diacetylene units: (O 1.5 SiCtCCtCSiO 1.5 ). Such molecularly defined hybrid silicate diyne network should be prepared easily from organosilicon precursor. Moreover the solid material should exhibit a high reactivity in two ways: (i) Polymerization of the highly reactive diyne frag- ment: diacetylene molecules are known to polymerize † Present address: Laboratoire de Chimie Organome ´tallique, ENS Chimie Montpellier, 8 rue de l’Ecole Normale, 34053 Montpellier Cedex 01, France. X Abstract published in Advance ACS Abstracts, November 1, 1995. (1) (a) Brinker, C. J.; Scherer, G. W. Sol-Gel Science; Academic Press: London, 1990, and references therein. (b) Hench, L. L.; West, J. K. Chem. Rev. 1990, 90, 33. (2) (a) Schmidt, H. K. Mater. Res. Soc. Symp. Proc. 1984, 32, 327. (b) Schmidt, H. K. Inorganic and Organometallic Polymers; ACS Symp. Ser. No. 360; American Chemical Society: Washington, DC, 1988; p 333. (c) Schmidt, H. K. Mater. Res. Soc. Symp. Proc. 1990, 180, 961 and references therein. (d) Brown, J. F., Jr.; Vogt, L. H.; Prescott, P. I. J. Am. Chem. Soc. 1964, 86, 1120. (e) Brown, J. F., Jr. J. Am. Chem. Soc. 1965, 87, 4317. (f) Slinyakova, I. B.; Kurennaya, L. I. Vysokomol. Soedin. Ser. B 1972, 14, 889; Chem. Abstr. 1973, 78, 136829v. (3) (a) Shea, K. J.; Loy, D. A.; Webster, O. W. Chem. Mater. 1989, 1, 574. (b) Shea, K. J.; Loy, D. A.; Webster, O. W. J. Am. Chem. Soc. 1992, 114, 6700 and references therein. (4) Corriu, R. J. P.; Moreau, J. J. E.; The ´pot, Ph.; Wong Chi Man, M. Chem. Mater. 1992, 4, 1217. (5) Corriu, R. J. P.; Moreau, J. J. E.; The ´pot, Ph.; Wong Chi Man, M.; Chorro, C.; Le ´re-Porte, J.-P.; Sauvajol, J.-L. Chem. Mater. 1994, 6, 640. nRSi(OR′) 3 9 8 H 2 O 9 8 -R′OH [RSiO 1.5 ] n (1) n(RO) 3 SiXSi(OR) 3 9 8 H 2 O f [O 1.5 SiXSiO 1.5 ] n (2) 100 Chem. Mater. 1996, 8, 100-106 0897-4756/96/2808-0100$12.00/0 © 1996 American Chemical Society