Octavinyloctasilsesquioxane: Synthesis and Derivatives

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Octavinyloctasilsesquioxane is among the most versatile and widely studied polyhedral oligomeric silsesquioxane (POSS) platforms in hybrid materials chemistry. Its eight peripheral vinyl groups, arranged symmetrically about the cubic silsesquioxane core, consistent with the T8 cage classification, provide an exceptionally rich surface for chemical functionalization through reactions characteristic of terminal alkenes, enabling the rational synthesis of dendrimers, polymer networks, glycoclusters, and metal-coordinating ligands.

Synthesis and Historical Development

Octavinyloctasilsesquioxane was first prepared in 1978 by K. A. Andrianov and co-workers through the hydrolytic polycondensation of vinyltrichlorosilane, albeit with a yield of less than 10%.1 Subsequent efforts by numerous research groups sought to improve the synthetic methodology.2,3,4 In 1997, P. G. Harrison and C. Hall reported the preparation of (CH2=CHSiO1.5)8 in 30% yield through the hydrolysis of CH2=CHSiCl3 in ethanol.5 The use of an ion-exchange resin as a catalyst for the hydrolysis and condensation of CH2=CHSiCl3 further improved the reaction yield to 40%.6 A substantially higher yield of 80% was subsequently achieved by employing CH2=CHSi(OEt)3 as the silicon precursor in the presence of tetramethylammonium hydroxide as a phase-transfer catalyst.7

Functionalization via Alkene Reactivity

The chemical versatility of octavinyloctasilsesquioxane derives directly from the reactivity of its eight terminal vinyl groups toward a broad range of transformations applicable to alkene substrates. Thiol-ene functionalization with reagents such as thiophenol or cyclohexanethiol can be accomplished using azobisisobutyronitrile (AIBN) as a radical initiator or through irradiation with ultraviolet light, affording thioether-functionalized POSS derivatives bearing sulfur-containing peripheral arms.8,9,10,11 Radical addition of phosphines and phosphonates, including diethylphosphine or diethyl phosphate, to the vinyl periphery produces phosphorus-substituted silsesquioxanes that have been employed as coordinating ligands for transition metals, most notably rhodium.12 Oxidation of the vinyl groups with meta-chloroperoxybenzoic acid (m-CPBA) converts the terminal alkenes to epoxide moieties, and the resulting epoxy-functionalized silsesquioxane is capable of undergoing Lewis acid-initiated ring-opening polymerization to yield organic-inorganic hybrid composite materials.

Octavinyloctasilsesquioxane reactivity scheme showing thiol-ene, phosphination, hydrosilylation, and epoxidation

Figure 1. Selected functionalization reactions of octavinyloctasilsesquioxane. AIBN: azobisisobutyronitrile; m-CPBA: meta-chloroperoxybenzoic acid.

Dendrimer Synthesis via Hydrosilylation

Platinum-catalyzed hydrosilylation of octavinyloctasilsesquioxane with di- and trichlorosilanes produces chlorosilyl-functionalized silsesquioxane building blocks suitable for the construction of dendrimeric architectures, an approach related to the solid-state polymerization of functionalized POSS monomers. Subsequent treatment of the chlorosilyl-functionalized intermediate with an appropriate Grignard reagent affords a POSS-based dendrimer bearing 24 terminal vinyl groups per cubic silsesquioxane core, representing a significant increase in peripheral functionality relative to the parent compound. This stepwise approach to POSS-cored dendrimers illustrates the capacity of the octavinyl scaffold to serve as a platform for the hierarchical construction of well-defined macromolecular structures with precisely controlled peripheral chemistry.12

POSS-based dendrimer bearing 24 terminal vinyl groups synthesized from octavinyloctasilsesquioxane

Figure 2. Synthesis of a POSS-cored dendrimer bearing 24 terminal vinyl groups via platinum-catalyzed hydrosilylation and Grignard functionalization of octavinyloctasilsesquioxane.

References

(1) Andrianov, K. A.; Petrovnin, N. M.; Vasil’eva, T. V.; Skhlover, V. E.; D’yanchenko, B. I. Hydrolytic Polycondensation of Higher Alkyltriethoxysilanes. Zh Obshch Khim 1978, 48, 2692–2695.

(2) Voronkov, M. G.; Martynova, T. N.; Mirskov, R. G.; Belyi, V. I. Octavinylsilsesquioxane. Russian Journal of Organic Chemistry 1979, 49, 1522–1525.

(3) Kovrigin, V. M.; Lavrent’ev, V. I. Chromatographic-Mass-Spectroscopic Study of the Mechanism of Formation of Pervinyloctasilsesquioxane in Polycondensation of Vinyltrichlorosilane in Butanol. Russian Journal of Organic Chemistry 1989, 59, 377–383.

(4) Bonhomme, C.; Tolédano, P.; Maquet, J.; Livage, J.; Bonhomme-Coury, L. Studies of Octameric Vinylsilasesquioxane by Carbon-13 and Silicon-29 Cross Polarization Magic Angle Spinning and Inversion Recovery Crosspolarization Nuclear Magnetic Resonance Spectroscopy. J. Chem. Soc., Dalton Trans. 1997, 9, 1617–1626.

(5) Harrison, P. G.; Hall, C. Preparation and Characterization of Octasilsesquioxane Cage Monomers. Main Group Metal Chemistry 1997, 20, 515–529.

(6) Dare, E. O.; Liu, L.-K.; Peng, J. Modified Procedure for Improved Synthesis of Some Octameric Silsesquioxanes via Hydrolytic Polycondensation in the Presence of Amberlite Ion-Exchange Resins. Dalton Trans. 2006, 30, 3668–3671.

(7) Gao, J.; Wang, S.; Zhang, X.; Run, M. Synthesis of Cage Octa(Vinyl)Silsesquioxane. Youjigui Cailiao 2005, 19, 5–7.

(8) König, H. J.; Marsmann, H. C.; Letzel, M. C. Thioether Functionalized Octasilsesquioxanes. In Organosilicon Chemistry V; Auner, N., Weis, J., Eds.; Wiley-VCH Verlag GmbH, 2003; pp 425–428.

(9) Gao, Y.; Eguchi, A.; Kakehi, K.; Lee, Y. C. Efficient Preparation of Glycoclusters from Silsesquioxanes. Org. Lett. 2004, 6, 3457–3460.

(10) Lücke, S.; Stoppek-Langner, K.; Kuchinke, J.; Krebs, B. Octakis-(Dimethylphosphanoethyl)-Octasilsesquioxane: Synthesis, Characterization and Reactivity. Journal of Organometallic Chemistry 1999, 584, 11–15.

(11) Piorecka, K.; Radzikowska, E.; Kurjata, J.; Rozga-Wijas, K.; Stanczyk, W. A.; Wielgus, E. Synthesis of the First POSS Cage-Anthracycline Conjugates via Amide Bonds. New J. Chem. 2016, 40, 5997–6000.

(12) Ropartz, L.; Morris, R. E.; Schwarz, G. P.; Foster, D. F.; Cole-Hamilton, D. J. Dendrimer-Bound Tertiary Phosphines for Alkene Hydroformylation. Inorganic Chemistry Communications 2000, 3, 714–717.

Full CitationBonhomme, C.; Toledano, P.; Maquet, J.; Livage, J.; Bonhomme-Coury, L. "Studies of Octameric Vinylsilasesquioxane by Carbon-13 and Silicon-29 Cross Polarization Magic Angle Spinning and Inversion Recovery Cross Polarization Nuclear Magnetic Resonance Spectroscopy." Journal of the Chemical Society, Dalton Transactions, 1997, 1617-1626.
DOI: 10.1039/a700700k
Full text: Dalton Transactions → RSC Publishing

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