کد مقاله کد نشریه سال انتشار مقاله انگلیسی نسخه تمام متن
1311608 975334 2008 7 صفحه PDF دانلود رایگان
عنوان انگلیسی مقاله ISI
Effect of silica type and grafting method on the reactivity of tetraneopentylchromium(IV) towards and on silica
موضوعات مرتبط
مهندسی و علوم پایه شیمی شیمی معدنی
پیش نمایش صفحه اول مقاله
Effect of silica type and grafting method on the reactivity of tetraneopentylchromium(IV) towards and on silica
چکیده انگلیسی

The grafting of tetraneopentylchromium(IV) onto the surface hydroxyls of silica has been investigated by varying both the method of deposition and the nature of the silica support. Reaction of the volatile organometallic with the silica surface in vacuo is compared with reaction in solution. A faster reaction but a lower ultimate Cr loading was obtained using the solution deposition technique. The reactions of the organometallic compound with Aerosil 200, a fumed silica often used to model catalyst supports, and Sylopol 952, a silica gel used as a carrier for chromium-based ethylene polymerization catalysts, are compared. After thermal pretreatment at 200 °C, grafting on both supports yields bis(neopentyl)chromium(IV) fragments regardless of the grafting method used, suggesting that a paired arrangement of the surface hydroxyl groups exists on both types of silicas. The higher Cr loading achieved on the silica gel is attributed to its higher surface area. Thermally-induced neopentane elimination from the grafted bis(neopentyl)chromium(IV) fragments occurs at the same rate and with the same stoichiometry for both Aerosil- and Sylopol-supported materials. Consequently, interactions of the grafted organometallic fragments with nearby siloxanes appear to be unimportant in the early stages of the transformation of bis(alkyl)chromium(IV) to the alkylidene.

Grafting of Cr(CH2C(CH3)3)4 onto silicas of different origin (fumed versus gel), prepared as powders or as self-supporting disks, results in the same bis(neopentyl)chromium(IV) fragment that undergoes α-H elimination to neopentylidenechromium(IV). However, much less Cr is fixed on the silica when the grafting occurs from solution compared to the vapor phase.Figure optionsDownload as PowerPoint slide

ناشر
Database: Elsevier - ScienceDirect (ساینس دایرکت)
Journal: Inorganica Chimica Acta - Volume 361, Issue 11, 27 July 2008, Pages 3315–3321
نویسندگان
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