Zeolite Activation of Organometallics: Anchoring and Decarbonylation Kinetics of Mo(CO)6 in Dehydrated Na56Y Zeolite
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- 作者：Anthony L. Fernandez ; Jianbin Hao ; Roberta L. Parkes ; Anthony J. Poë ; and Eduardo J. S. Vichi
- 刊名：Organometallics
- 出版年：2004
- 出版时间：May 24, 2004
- 年：2004
- 卷：23
- 期：11
- 页码：2715 - 2723
- 全文大小：131K
- 年卷期：v.23,no.11(May 24, 2004)
- ISSN：1520-6041
文摘
Quantitative temperature-dependent kinetic studies are reported of thermal reactions ofMo(CO)6 that has been newly encapsulated in the 
-cages of a Na56Y zeolite host. Understatic vacuum, Mo(CO)6 undergoes parallel anchoring and decarbonylation reactions, thelatter yielding (OC)3Mo-Na56Y directly and the former resulting in the development of acharacteristic six-band spectrum in the C-O stretching region. Kinetic and spectroscopicevidence was obtained for there being two different forms of (OC)3Mo-Na56Y. The activationparameters are unusual, with very low enthalpies and extremely negative entropies, viz.
H
ntities/thermod.gif"> = 40 ± 3 kJ mol-1 and Sntities/thermod.gif"> = -185 ± 9 J K-1 mol-1 for anchoring and decarbonylation.This contrasts with the typically high enthalpic and positive entropic factors reported forcorresponding CO dissociative reactions in xylene (Hntities/thermod.gif"> = 133 ± 6 kJ mol-1 and Sntities/thermod.gif"> = +28± 16 J K-1 mol-1) or even the quite unusual values Hntities/thermod.gif"> = 61 ± 5 kJ mol-1 and Sntities/thermod.gif"> = -139± 13 J K-1 mol-1 reported previously for 13CO exchange in Mo(CO)6-Na56Y. It is concludedthat the inner surface of Na56Y provides different activating environments for differentreactions, behaving as multidentate anionic "zeolate" nucleophiles, with varying numbersof O2- ions participating in highly ordered transition states. A common intermediate, withthree O2- ions participating in the anchoring and decarbonylation process, is proposed, onewith two O2- ions being proposed for the 13CO exchange reaction. The importance oftemperature-dependent time-resolved infrared spectroscopy in elucidating such intimatemechanistic details is emphasized.
-cages of a Na56Y zeolite host. Understatic vacuum, Mo(CO)6 undergoes parallel anchoring and decarbonylation reactions, thelatter yielding (OC)3Mo-Na56Y directly and the former resulting in the development of acharacteristic six-band spectrum in the C-O stretching region. Kinetic and spectroscopicevidence was obtained for there being two different forms of (OC)3Mo-Na56Y. The activationparameters are unusual, with very low enthalpies and extremely negative entropies, viz.Hntities/thermod.gif"> = 40 ± 3 kJ mol-1 and Sntities/thermod.gif"> = -185 ± 9 J K-1 mol-1 for anchoring and decarbonylation.This contrasts with the typically high enthalpic and positive entropic factors reported forcorresponding CO dissociative reactions in xylene (Hntities/thermod.gif"> = 133 ± 6 kJ mol-1 and Sntities/thermod.gif"> = +28± 16 J K-1 mol-1) or even the quite unusual values Hntities/thermod.gif"> = 61 ± 5 kJ mol-1 and Sntities/thermod.gif"> = -139± 13 J K-1 mol-1 reported previously for 13CO exchange in Mo(CO)6-Na56Y. It is concludedthat the inner surface of Na56Y provides different activating environments for differentreactions, behaving as multidentate anionic "zeolate" nucleophiles, with varying numbersof O2- ions participating in highly ordered transition states. A common intermediate, withthree O2- ions participating in the anchoring and decarbonylation process, is proposed, onewith two O2- ions being proposed for the 13CO exchange reaction. The importance oftemperature-dependent time-resolved infrared spectroscopy in elucidating such intimatemechanistic details is emphasized.