Reactivity of Tetraneopentylhafnium, Hf(CH2tBu)4, with Silica Surfaces
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- 作者：Gé ; raldine Tosin ; Catherine C. Santini ; Mostafa Taoufik ; Aimery De Mallmann ; and Jean-Marie Basset
- 刊名：Organometallics
- 出版年：2006
- 出版时间：July 3, 2006
- 年：2006
- 卷：25
- 期：14
- 页码：3324 - 3335
- 全文大小：349K
- 年卷期：v.25,no.14(July 3, 2006)
- ISSN：1520-6041
文摘
The reaction of Hf(CH2tBu)4 with a silica surface treated at 800 
C affords a unique surfaceorganometallic species in only one surface environment, (
SiO)Hf(CH2tBu)3 (1-SiO2-(800)). In contrast,with SiO2-(500) two surface species, (SiO)Hf(CH2tBu)3 (1-SiO2-(500)) and (SiO)2Hf(CH2tBu)2 (2-SiO2-(500)), in a molar ratio of 70:30 are obtained. Thermal treatment of 1-SiO2-(800) at increasingtemperatures leads to the successive evolution of neopentane, isobutene, and isobutane as well as severalalkanes varying from C1 to C5. Polyisobutenes are also formed on the surface. The mechanism by whichsuch decomposition occurs suggests a succession of 
hars/gamma.gif" BORDER=0 >-H eliminations with formation of neopentanefollowed by hars/beta2.gif" BORDER=0 ALIGN="middle">-methyl transfer and formation of isobutene and [Hf]-Me. This isobutene is reinsertedinto [Hf]-Me with formation of isopentene and [Hf]-H. A comparison of the analytical data of 1-SiO2-(800)and (SiO)Zr(CH2tBu)3 indicated the hafnium complex exhibits in EXAFS shorter Hf-C and Hf-Obonds and a larger Hf-Chars/alpha.gif" BORDER=0>-Chars/beta2.gif" BORDER=0 ALIGN="middle"> angle and in 2D J-resolved NMR spectra a lower 1J(Chars/alpha.gif" BORDER=0>-H) value. Thesedifferences underlined a larger steric hindrance in the coordination sphere of the Hf metal. The thermalstability of 1-SiO2-(800) was monitored by infrared spectroscopy, in batch and continuous flow reactors,and proved that 1-SiO2-(800) was more stable than (SiO)Zr(CH2tBu)3 and more active in alkanehydrogenolysis.
C affords a unique surfaceorganometallic species in only one surface environment, (SiO)Hf(CH2tBu)3 (1-SiO2-(800)). In contrast,with SiO2-(500) two surface species, (SiO)Hf(CH2tBu)3 (1-SiO2-(500)) and (SiO)2Hf(CH2tBu)2 (2-SiO2-(500)), in a molar ratio of 70:30 are obtained. Thermal treatment of 1-SiO2-(800) at increasingtemperatures leads to the successive evolution of neopentane, isobutene, and isobutane as well as severalalkanes varying from C1 to C5. Polyisobutenes are also formed on the surface. The mechanism by whichsuch decomposition occurs suggests a succession of hars/gamma.gif" BORDER=0 >-H eliminations with formation of neopentanefollowed by hars/beta2.gif" BORDER=0 ALIGN="middle">-methyl transfer and formation of isobutene and [Hf]-Me. This isobutene is reinsertedinto [Hf]-Me with formation of isopentene and [Hf]-H. A comparison of the analytical data of 1-SiO2-(800)and (SiO)Zr(CH2tBu)3 indicated the hafnium complex exhibits in EXAFS shorter Hf-C and Hf-Obonds and a larger Hf-Chars/alpha.gif" BORDER=0>-Chars/beta2.gif" BORDER=0 ALIGN="middle"> angle and in 2D J-resolved NMR spectra a lower 1J(Chars/alpha.gif" BORDER=0>-H) value. Thesedifferences underlined a larger steric hindrance in the coordination sphere of the Hf metal. The thermalstability of 1-SiO2-(800) was monitored by infrared spectroscopy, in batch and continuous flow reactors,and proved that 1-SiO2-(800) was more stable than (SiO)Zr(CH2tBu)3 and more active in alkanehydrogenolysis.