Facility: D04B-XAFS1 beamline. Publication: NOTESTEIN, J. M.; ANDRINI, L. R.; KALCHENKO, V. I.; REQUEJO, F. G.; KATZ, A.; IGLESIA, E. Journal of the American Chemical Society, v. 129, n. 5, p. 1122-1131, 2007. NOTESTEIN, J. M.; SOLOVYOV, A.; ANDRINI, L. R.; REQUEJO, F. G.; KATZ, A.; IGLESIA, E. Journal of the American Chemical Society, v. 129, n. 50, p. 15585-15595, 2007. Funding: Argentine PICT-ANPCYT # 06-17492. U.S. DOE Office of Basic Energy Sciences (DE-FG02-05ER15696). CIAM collaborative research agreement (NSF-CNPq-CONICET). Catalytic consequences of the structural environment and electronics of Ti in grafted Ti-calixarenes 8 that has already been applied successfully to unravel different Ti-catalyst structures, 9-11 to quantitatively probe the local coordination and electronics of grafted Ti-calixarenes. In Ti K-edge XANES, the intensity of the pre-edge feature provides a direct measure of available Ti 3d orbitals. 12, * The presence of intense XANES pre-edge features has been empirically related to the presence of 4-coordinate species and to highly active oxidation catalysts, 3,13 but a more complete analysis of the structural requirements for * An increase in the number of 3d electrons, which is determined by the number and identity of coordinating ligands, decreases the Lewis acidity. Highly dispersed Ti centers on or within vSiO 2 frameworks are active catalysts for selective oxidation and other molecular rearrangements catalyzed by Lewis acids, 1-4 because the resulting 4-coordinate Ti centers are electron-deficient and can expand their coordination to bind oxidants or substrates and to activate oxidants toward attack by electron-rich substrates. These Ti centers have been widely studied since the first reports of TS-1 5 and MCM41-grafted Cp 2 TiCl 2 6 materials as prototypical Ti-SiO 2 catalysts. Previous studies by UV-visible, 7 infrared or Raman 8 spectroscopies have sought to develop routes for the synthesis of isolated Ti centers and to probe the structural and electronic features of isolated Ti sites. In our studies, we chose Ti K-edge X-ray absorption spectroscopy a powerful method Justin M. Notestein 1 , Leandro R. Andrini 2 , Vitaly I. Kalchenko 3 , Félix G. Requejo 2 , Alexander Katz 1 , Enrique Iglesia 1 1 Department of Chemical Engineering, University of California at Berkeley, Berkeley, California, USA 2 Departamento de Física, Facultad de Ciencias Exactas, Universidad Nacional de La Plata and IFLP-INIFTA (CONICET), La Plata, Argentina 3 Institute of Organic Chemistry, National Academy of Sciences of Ukraine, Murmanskaya Str., Ukraine Calixarene-metal complexes provide the opportunity for fundamental studies to correlate basic characteristics and properties of molecules and atomic species. In particular because grafted Ti-calixarenes provide Ti centers with varying electron density and coordination but maintain accessible sites (active centers) with uniform structures and unrestricted access to reactants, they allow for a systematic approach to relating oxidation reactivity to Ti 3d occupancy, a descriptor of Lewis acid strength, and Ti coordination. Thus, the relationship between activity, geometry and concepts of electronics in catalysis can be revisited and clarified due to the well-defined nature of these Ti sites, allied to the chemical and local sensitivity of X-ray absorption techniques.