Detailed structural investigation of the grafting of [Ta(=CHtBu)(CH 2tBu)3] and [Cp*TaMe4] on silica partially dehydroxylated at 700 °C and the activity of the grafted complexes toward alkane metathesis

Erwan Le Roux, Mathieu Chabanas, Anne Baudouin, Aimery De Mallmann, Christophe Copéret*, E. Alessandra Quadrelli, Jean Thivolle-Cazat, Jean-Marie Maurice Basset, Wayne Lukens, Anne Lesage, Lyndon Emsley, Glenn J. Sunley

*Corresponding author for this work

Research output: Contribution to journalArticlepeer-review

117 Scopus citations

Abstract

The reaction of [Ta(=CHtBu)(CH2tBu)3] or [Cp*Ta(CH3)4] with a silica partially dehydroxylated at 700 °C gives the corresponding monosiloxy surface complexes [(≡SiO)Ta(=CHtBu)(CH2tBu)2] and [(≡SiO) Ta(CH3)3Cp*] by eliminating a σ-bonded ligand as the corresponding alkane (H-CH2tBu or H-CH3). 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 [(≡SiO)Ta(=CHtBu)(CH2tBu)2(≡SiOSi≡)] (1a′) and [(≡SiO)Ta(CH3)3 Cp*(≡SiOSi≡)] (2a′). In the case of [(≡SiO)Ta(=CHtBu) (CH2tBu)2(≡SiOSi≡)], 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 (JC-H = 80 Hz), which was measured by J-resolved 2D solid-state NMR spectroscopy. The product selectivity in propane metathesis in the presence of [(≡SiO)Ta(=CHtBu)- (CH2tBU)2(≡SiOSi≡)] (1a′) as a catalyst precursor and the inactivity of the surface complex [(≡SiO)Ta-(CH 3)3CP*(≡SiOSi≡)] (2a′) show that the active site is required to be highly electrophilic and probably involves a metallacyclobutane intermediate.

Original languageEnglish (US)
Pages (from-to)13391-13399
Number of pages9
JournalJournal of the American Chemical Society
Volume126
Issue number41
DOIs
StatePublished - Oct 20 2004

ASJC Scopus subject areas

  • Catalysis
  • Chemistry(all)
  • Biochemistry
  • Colloid and Surface Chemistry

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