Detailed structural characterization of the grafting of [Ta(=CHtBu)(CH2tBu)3] and [Cp*TaMe4] on silica partially dehydroxylated at 700 C and the activity of the grafted complexes toward alkane metathesis

Journal Article · Mon Aug 30 04:00:00 EDT 2004 · Journal of the American Chemical Society

DOI:https://doi.org/10.1021/ja046486r· OSTI ID:840583

Le Roux, Erwan ^[1]; Chabanas, Mathieu; Baudouin, Anne; de Mallmann, Aimery; Coperet, Christophe; Quadrelli, E Allesandra; Thivolle-Cazat, Jean; Basset, Jean-Marie; Lukens, Wayne; Lesage, Anne; Emsley, Lyndon; Sunley, Glenn J

---

1. LBNL Library

The reaction of [Ta({double_bond}CHtBu)(CH{sub 2}tBu){sub 3}] or [Cp*Ta(CH{sub 3}){sub 4}] with a silica partially dehydroxylated at 700 C gives the corresponding monosiloxy surface complexes [({triple_bond}SiO)Ta({double_bond}CHtBu)(CH{sub 2}tBu){sub 2}] and [({triple_bond}SiO)Ta(CH{sub 3}){sub 3}Cp*] by eliminating a {sigma}-bonded ligand as the corresponding alkane (H-CH{sub 2}tBu or H-CH{sub 3}). EXAFS data show that an adjacent siloxane bridge of the surface plays the role of an extra surface ligand, which most likely stabilizes these complexes as in [({triple_bond}SiO)Ta({double_bond}CHtBu)(CH{sub 2}tBu){sub 2}({triple_bond}SiOSi{triple_bond})] (1a') and [({triple_bond}SiO)Ta(CH{sub 3}){sub 3}Cp*({triple_bond}SiOSi{triple_bond})] (2a'). In the case of [({triple_bond}SiO)Ta({double_bond}CHtBu)(CH{sub 2}tBu){sub 2}({triple_bond}SiOSi{triple_bond})], the structure is further stabilized by an additional interaction: a C-H agostic bond as evidenced by the small J coupling constant for the carbenic C-H (H{sub C-H} = 80 Hz), which was measured by J-resolved 2D solid-state NMR spectroscopy. The product selectivity in propane metathesis in the presence of [({triple_bond}SiO)Ta({double_bond}CHtBu)-(CH{sub 2}tBu){sub 2}({triple_bond}SiOSi{triple_bond})] (1a') as a catalyst precursor and the inactivity of the surface complex [({triple_bond}SiO)Ta-(CH{sub 3}){sub 3}Cp*({triple_bond}SiOSi{triple_bond})] (2a') show that the active site is required to be highly electrophilic and probably involves a metallacyclobutane intermediate.

• Research Organization: Ernest Orlando Lawrence Berkeley National Laboratory, Berkeley, CA (US)
• Sponsoring Organization: USDOE Director. Office of Science. Office of Basic Energy Sciences; BP Chemicals Ldt, Centre National de la Recherche Scientifique, L'ENS de Lyon, Ecole Superieure de Chimie Physique Electronique de Lyon (US)
• DOE Contract Number: AC03-76SF00098
• OSTI ID: 840583
• Report Number(s): LBNL--56217
• Journal Information: Journal of the American Chemical Society, Journal Name: Journal of the American Chemical Society Journal Issue: 41 Vol. 126
• Country of Publication: United States
• Language: English

Related Subjects

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CHEMISTRY
ALKANES
CATALYSTS
COUPLING CONSTANTS
PRECURSOR
PROPANE
SILICA
SILOXANES
SPECTROSCOPY