Well-defined silica-supported calcium reagents: Control of schlenk equilibrium by grafting

Gauvin RM, Buch F, Delevoye L, Harder S (2009)

Publication Type: Journal article, Original article

Publication year: 2009

Journal

Chemistry - A European Journal Wiley-VCH Verlag

Original Authors: Gauvin R.M., Buch F., Delevoye L., Harder S.

Publisher: Wiley-VCH Verlag

Book Volume: 15

Pages Range: 4382-4393

Journal Issue: 17

DOI: 10.1002/chem.200802512

Abstract

Calcium reagents Ca(α-Me Si-2-Me N-benzyl) ·2thf (1) and Ca[N(SiMe ) ] ·2thf (2) reacted with silica partially dehydroxylated at 700 °C to afford materials that bear (≡ SiO)Ca(α-Me Si-2-Me N-benzyl)·1.6thf (SiO -l) and (≡SiO)Ca [N-(SiMe ) ]·1.3thf (SiO -2) fragments, respectively. Due to the bulk of the supported complexes, the silanol groups are only partially metalated: 50% in SiO -l and 70% in SiO -2. In the case of SiO -2, a parallel SiMe -capping side reaction affords in fine a silanol-free surface. The materials were characterized by IR spectroscopy, 1D and 2D solid-state high-field NMR spectroscopy, and elemental analysis. Reaction of 2 with one equivalent of the bulky silanol (tBuO) SiOH, a silica-surface mimic, afforded the homoleptic bis-silyloxide calcium derivative through ligand exchange (Schlenk equilibrium), and a derivative was isolated and structurally characterized. Preliminary studies have shown that both grafted benzyl and amide derivatives are active in olefin hydrosilylation, intramolecular hydroamination, and styrene polymerization, with evidence showing that catalysis occurs through supported species. In styrene polymerization, a marked influence of the surface acting as a ligand on the stereoselectivity of the reaction was observed, as syndiotactic-rich polystyrene (88% of r diads) was obtained. These results illustrate that grafting of calcium benzyl or amide compounds on a silica surface is a new concept to prevent ligand exchange through the Schlenk equilibrium. Heteroleptic calcium complexes that cannot be synthesized as stable molecular species in solution can be obtained as silica-supported species which have been shown to be catalytically active. © 2009 Wiley-VCH Verlag GmbH & Co. KGaA.

Authors with CRIS profile

Sjoerd Harder Lehrstuhl für Anorganische und Metallorganische Chemie

Involved external institutions

Chimie ParisTech / École nationale supérieure de chimie de Paris (ENSCP) FR France (FR) Universität Duisburg-Essen (UDE) DE Germany (DE)

How to cite

APA:

Gauvin, R.M., Buch, F., Delevoye, L., & Harder, S. (2009). Well-defined silica-supported calcium reagents: Control of schlenk equilibrium by grafting. Chemistry - A European Journal, 15(17), 4382-4393. https://doi.org/10.1002/chem.200802512

MLA:

Gauvin, Regis M., et al. "Well-defined silica-supported calcium reagents: Control of schlenk equilibrium by grafting." Chemistry - A European Journal 15.17 (2009): 4382-4393.

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