The reaction of tetrakisneopentyl titanium, TiNp 4 (1), with the surface of partially dehydroxylated Aerosil silica and MCM-41 and the reactivity of the resultant supported titanium alkyl product with water, alcohols, and oxygen are reported. Two methods of preparation have been investigated and compared for the grafting of TiNp 4: (i) reaction of the support with the vapor of the sublimed complex and (ii) impregnation of the support with a solution of die complex. The second method appeared to be more reliable for "larger scale" preparations. The surface species thus obtained were characterized by infrared spectroscopy, solid state NMR, XAFS, elemental analysis, and various test reactions. Whereas on an Aerosil silica partially dehydroxylated at 500 °C, SiO 2-(500), the surface complex is a monopodal titanium trisalkyl complex, ≡SiO-Ti[CH 2C(CH 3) 3] 3, 2a, a bipodal titanium bisalkyl complex, (≡SiO) 2Ti[CH 2C-(CH 3) 3] 2, 2b, is obtained as the major species (ca. 65%) with 2a on MCM-41 (500). The reason for this difference in behavior is discussed on the basis of the surface structure. The results obtained from hydrolysis confirmed the structure proposed for the supported alkyl complexes. For the reaction of the alkyl surface complexes with alcohols (MeOH, EtOH, tBuOH), the surface compounds obtained were characterized by the same techniques and by XPS and UV-vis. The results are consistent with the formation of monosiloxytrisalkoxy titanium complexes on SiO 2-(500), ≡SiO-Ti(OR) 3,3a OR, and of ≡SiO-Ti(O tBu) 3, 3a OtBu, and (≡SiO) 2Ti(O tBu) 2,3b OtBu, on MCM-41 (500), after reaction with tBuOH. The supported titanium alkyl, 2a, also reacts with oxygen, leading mainly to ≡SiO-Ti[OCH 2C(CH 3) 3] 3, probably via an unstable surface compound such as ≡SiO-Ti[OCH 2C(CH 3) 3] 2[OOCH 2C(CH 3) 3], resulting from the incorporation of two molecules of oxygen in 2a.
ASJC Scopus subject areas
- Physical and Theoretical Chemistry
- Organic Chemistry
- Inorganic Chemistry