The Structure of the Peroxo Species in the TS-1 Catalyst as Investigated by Resonant Raman Spectroscopy** Silvia Bordiga,* Alessandro Damin, Francesca Bonino, Gabriele Ricchiardi, Carlo Lamberti, and Adriano Zecchina Ti-silicalite-1 (TS-1) [1] has exhibited a remarkably high efficiency and molecular selectivity in oxidation reactions with H 2 O 2 under mild conditions, such as for olefin epox- idation, phenol hydroxylation, cyclohexanone ammoxima- tion, and conversions of ammonia to hydroxylamine, secon- dary alcohols to ketones, and secondary amines to dialkylhy- droxylamines [2] (Figure 1). Because of its relevance in indus- trial applications, it has been one of the most studied materials in heterogeneous catalysis in recent years. [3±13] It has been shown that the active species is a Ti IV atom isomorphically inserted into the MFI-type framework. [1] TS-1 is characterized by an increase of the unit cell volume proportional to the Ti content [1,5,7,14] and by the presence of a ™fingerprint∫ IR absorption component [1,6b,8±10,13] centered at 960 cm 1 , the intensity of which grows proportionally with increased Ti content. This band is clearly visible in IR spectra appearing on the low-energy tail of the very strong absorption resulting from the n asym (Si-O-Si) modes that appear in the broad 1250±1030 cm 1 region. In addition to the component at COMMUNICATIONS 4734 ¹ 2002 WILEY-VCH Verlag GmbH&Co. KGaA, Weinheim 0044-8249/02/4124-4734 $ 20.00+.50/0 Angew. Chem. Int. Ed. 2002, 41, No. 24 [1] For example: a) C. F. Lochow, R. G. Miller, J. Org. Chem. 1976, 41, 3020±3022; b) H. Suzuki, H. Yashima, T. Hirose, M. Takahashi, Y. Moro-oka, T. Ikawa, Tetrahedron Lett. 1980, 21, 4927±4930; c) I. Matsuda, T. Kato, S. Sato, Y. Izumi, Tetrahedron Lett. 1986, 27 , 5747 ± 5750; d) A. Zoran, Y. Sasson, J. Blun, J. Org. 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Res. 2001, 34, 18±29; b) A. F¸rstner, Angew. Chem. 2000, 112, 3140±3172; Angew. Chem. Int. Ed. 2000, 39, 3012 ± 3043; c) R. H. Grubbs, S. Chang, Tetrahedron 1998, 54, 4413 ± 4450; d) S. K. Armstrong, J. Chem. Soc. Perkin Trans. 1 1998, 371 ± 388; e) M. Schuster, S. Blechert, Angew. Chem. 1997 , 109, 2124±2145; Angew. Chem. Int. Ed. Engl. 1997 , 36, 2036 ± 2056. [3] a) M. Arisawa, E. Takezawa, A. Nishida, M. Mori, M. Nakagawa, Synlett 1997 , 1179±1180; b) H. Uchida, Y. Torisawa, A. Nishida, M. Nakagawa, J. Synth. Org. Chem. Jpn. 1999, 57 , 1004±1015; c) M. Arisawa, C. Kato, H. Kaneko, A. Nishida, M. Nakagawa, J. Chem. Soc. Perkin Trans. 1 2000, 1873±1876; d) M. Arisawa, H. Kaneko, A. Nishida, K. Yamaguchi, M. Nakagawa, Synlett 2000, 841 ± 843; e) M. Arisawa, M. Takahashi, E. Takezawa, T. Yamaguchi, Y. Torisawa, A. Nishida, M. Nakagawa, Chem. Pharm. Bull. 2000, 48, 1593 ± 1596; f) M. Arisawa, C. Theeraladanon, A. Nishida, M. Nakagawa, Tetrahedron Lett. 2001, 42, 8029 ± 8033; g) M. Arisawa, H. Kaneko, A. Nishida, M. Nakagawa, J. Chem. Soc. Perkin Trans. 1 2002, 959 ± 964. [4] The tricyclohexylphosphane dihydroimidazolidene ruthenium catalyst (a) M. Scholl, T. M. Trnka, J. P. Morgan, R. H. Grubbs, Tetrahedron Lett. 1999, 40, 2247±2250; b) M. Scholl, S. Ding, C. W. Lee, R. H. Grubbs, Org. Lett. 1999, 1, 953 ± 956; c) A. K. Chatterjee, R. H. Grubbs, Org. Lett. 1999, 1, 1751 ± 1753) is an effective catalyst; A phosphane- free N-heterocyclic carbene complex (d) S. B. Garber, J. S. Kingsbury, B. L. Gray, A. H. Hoveyda, J. Am. Chem. Soc. 2000, 122, 8168 ± 8179; e) S. Gessler, S. Randl, S. Blechert, Tetrahedron Lett. 2000, 41, 9973 ± 9976) is also effective. The catalysts, [Cl 2 Ru(PCy 3 ) 2 ¼CHCH¼Ph] and [Cl 2 Ru(PCy 3 ) 2 ¼CHPh], were ineffective for this isomerization. [5] Grubbs and co-workers found that vinylic ethers were not reactive in cross-metathesis. He also reported the formation of a new Fischer carbene species prepared by the reaction of a ruthenium±alkylidene complex with ethyl vinyl ether. (a) A. K. Chatterjee, J. P. Morgan, M. Scholl, R. H. Grubbs, J. Am. Chem. Soc. 2000, 122, 3783 ± 3784; b) J. Louie, R. H. Grubbs, Organometallics 2002, 21, 2153 ± 2164). [6] a) The Chemistry of Heterocyclic Compounds, Indoles (Ed.: W. J. Houlihan), Wiley-International, Toronto, 1972 ; b) G. W. Gribble, J. Chem. Soc. Perkin Trans. 1 2000, 1045 ± 1075. [*] Prof. Dr. S. Bordiga, + A. Damin, F. Bonino, Dr. G. Ricchiardi, Dr. C. Lamberti, + Prof. Dr. A. Zecchina Dipartimento di Chimica IFM and INSTM Research Unit, Turin University Via P. Giuria 7, 10125 Torino (Italy) Fax: (þ 39)011-670-7855 E-mail: silvia.bordiga@unito.it [ þ ] also with INFM UdR di Torino Universit‡ (Italy) [**] This project has been supported by MURST (Cofin 2000, Area 03): ™Structure and reactivity of catalytic centers in zeolitic materials∫. We are indebted to R. Tagliapietra, M. Ricci, F. Rivetti, and G. SpanÚ for fruitful discussions. Figure 1. Schematic representation of the most relevant oxidation reac- tions catalyzed by TS-1.