Molecular Insight Into Surface Organometallic Chemistry Through the Combined Use of 2D HETCOR Solid-State NMR Spectroscopy and Silsesquioxane Analogues

✍ Scribed by Mathieu Chabanas; Elsje Alessandra Quadrelli; Bernard Fenet; Christophe Copéret; Jean Thivolle-Cazat; Jean-Marie Basset; Anne Lesage; Lyndon Emsley

• Publisher: John Wiley and Sons
• Year: 2001
• Tongue: English
• Weight: 100 KB
• Volume: 40
• Category: Article
• ISSN: 0044-8249
• DOI: 10.1002/1521-3773(20011203)40:23<4493::aid-anie4493>3.0.co;2-x

✦ Synopsis

The structural characterization of heterogeneous catalysts remains difficult. In the late eighties, Feher and later others showed that polyhedral oligomeric silsesquioxanes (POSS) can be used to model the surface structure of partially dehydroxylated silica and therefore infer information about the coordination sphere of metal complexes directly supported on oxides such as silica. [1] This approach can also provide mechanistic insights on surface chemistry processes. However, no direct comparison between these models and their related surface complexes has been reported.

We have recently shown that the reaction of tris(neopentyl)neopentylidene tantalum, [Ta( CHtBu)(CH 2 tBu) 3 ] (1) with SiO 2-(500) gives a mixture of mono-[SiO-Ta(CHtBu)-(CH 2 tBu) 2 ] and bisgrafted surface complexes [(SiO) 2 Ta(CHtBu)(CH 2 tBu)], [2a] while its reaction with a SiO 2-(700) provides the monografted species [SiO-Ta-(CHtBu)(CH 2 tBu) 2 ] (2 s ) as the sole surface species. The characterization was based on elemental analysis, the evolution of neopentane during grafting of 1, and solvolysis of 2 s as well as infrared (IR) spectroscopy. [2b] We report here the use of high-resolution solid-state onedimensional (1D) and two-dimensional (2D) NMR spectroscopy to study 2 s and the use of high-resolution solution-state 1D and 2D NMR spectroscopy of its molecular analogue [(c-C 5 H 9 ) 7 Si 7 O 12 SiÀOÀTa(CHtBu)(CH 2 tBu) 2 ] (2 m ) to define the structure of 2 s at a molecular level and to investigate the reaction pathway leading to the grafted species.