Solid-State ^49/47Ti NMR of Titanium-Based MCM-41 Hybrid Materials

Abstract

Titanium solid-state NMR spectroscopy data for a series of organic-inorganic titanium MCM-41 based materials have been collected. These materials have been synthesized by first modifying the mesoporous silica MCM-41 in one step with a mixture of silanes: a triazine propyl triethoxysilane acting as functional linker and methyltrimethoxysilane or hexamethyldisilizane as capped agents to mask the remaining silanol groups. Second, the appropiate titanium precursor Ti(OPr(i))(4), [{Ti(OPr(i))(3)(OMent)}(2)] (OMent = 1R,2S,5R-(-)-menthoxo), Ti(OPr(i))(4), or [Ti(eta(5)-C(5)HMe(4))Cl(3)], has been immobilized by reaction with the modified MCM-41. Finally, after Ti(OPr(i))(4) immobilization onto the organomodified support the reaction with the chiral (+)-diethyl-l-tartrate was accomplished. The materials without functional linker have been also prepared by reaction in one step of the capped agent and the titanium precursor with the mesoporous silica. Relevant correlations of titanium NMR resonance chemical shifts and line widths can be inferred depending on different factors. The immobilization procedure used to prepare titanium-based MCM-41 hybrid materials and the choice of the silylating reagents employed to mask the silanol groups present on the silica surfaces produce significant differences in the Ti NMR spectra. Furthermore, depending on the electronic and sterical influence of the substituents directly attached to the titanium center, chemical shifts and line widths are modified providing novel information about titanium structure.

Spies Within Metal-Organic Frameworks: Investigating Metal Centers Using Solid-State NMR

“…Applications of Ti-based MOFs and Ti-functionalized MOFs are diverse and include sensors, epoxidation catalysis, and hydrogen storage − sometimes by using isotopically enriched reagents. To our best of our knowledge, there has not yet been a 47/49 Ti SSNMR study of Ti-based MOFs, and 47/49 Ti NMR tensor parameters should provide valuable information regarding the local environment of Ti cations within the MOF MIL-125(Ti).…”

Heterogenization of [Ti(η5-C5HMe4)Cl3] on to MCM-41 and organomodified MCM-41 to form epoxidation catalyst

“…Taking into account the experimental evidences, as the titanium content values obtain by AAS, the presence of tether and capped ligands confirm by NMR and FT-IR analysis, and capped agent loading values obtained by elemental analysis; as well as, the titanium environment [33], the proposed structures for the four different titanium materials are shown in Fig. 7.…”

Synthesis and photocatalytic applications of nano-sized zinc-doped mesoporous titanium oxide

“…The same pattern was observed for TD sample spectrum, however, an increase in the intensity and width of the peaks has been recorded. This broadening and increase in the intensity of the peaks implies less titanium quantity in the surface [38] which is due to a decrease in the crystallinity of the material, probably due to zinc doping.…”