Well-Defined Silica-Supported Calcium Reagents: Control of Schlenk Equilibrium by Grafting

Gauvin, Regis; Buch, Frank; Delevoye, Laurent; Harder, Sjoerd

Document type :

Article dans une revue scientifique: Article original

DOI :

10.1002/chem.200802512

PMID :

19288485

Permalink :

http://hdl.handle.net/20.500.12210/83706

Title :

Well-Defined Silica-Supported Calcium Reagents: Control of Schlenk Equilibrium by Grafting

Author(s) :

Gauvin, Regis [Auteur]

Unité de Catalyse et Chimie du Solide - UMR 8181 [UCCS]
Buch, Frank [Auteur]
Universität Duisburg-Essen = University of Duisburg-Essen [Essen]
Delevoye, Laurent [Auteur]

Unité de Catalyse et Chimie du Solide - UMR 8181 [UCCS]
Harder, Sjoerd [Auteur]
Universität Duisburg-Essen = University of Duisburg-Essen [Essen]

Journal title :

Chemistry - A European Journal

Abbreviated title :

Chem.-Eur. J.

Volume number :

Pages :

4382-4393

Publication date :

2009-04-15

ISSN :

0947-6539

English keyword(s) :

surface chemistry
supported catalysts
silica
heterogeneous catalysis
calcium

HAL domain(s) :

Chimie

English abstract : [en]

Bound to stay heteroleptic: Grafting of homoleptic benzyl and amide calcium reagents onto silica affords well-defined supported heteroleptic species, catalytically active in hydrosilylation, hydroamination, and styrene ...
Show more >Bound to stay heteroleptic: Grafting of homoleptic benzyl and amide calcium reagents onto silica affords well-defined supported heteroleptic species, catalytically active in hydrosilylation, hydroamination, and styrene polymerization. The fact that attempts to generate a molecular model were thwarted by the Schlenk equilibrium affording the homoleptic compound (see scheme) emphasizes the importance of immobilization as an approach for the syntheses of heteroleptic calcium complexes. image Calcium reagents Ca(α-Me3Si-2-Me2N-benzyl)2⋅2 thf (1) and Ca[N(SiMe3)2]2⋅2 thf (2) reacted with silica partially dehydroxylated at 700 °C to afford materials that bear (SiO)Ca(α-Me3Si-2-Me2N-benzyl)⋅1.6 thf (SiO2-1) and (SiO)Ca [N(SiMe3)2]⋅1.3 thf (SiO2-2) fragments, respectively. Due to the bulk of the supported complexes, the silanol groups are only partially metalated: 50 % in SiO2-1 and 70 % in SiO2-2. In the case of SiO2-2, a parallel SiMe3-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)3SiOH, 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.Show less >

Language :

Anglais

Audience :

Internationale

Popular science :

Non

Administrative institution(s) :

Université de Lille
CNRS
Centrale Lille
ENSCL
Univ. Artois

Collections :

Unité de Catalyse et Chimie du Solide (UCCS) - UMR 8181

Research team(s) :

RMN et matériaux inorganiques (RM2I)

Submission date :

2023-05-30T18:06:53Z
2024-04-26T09:25:59Z

Version	Link	Modification date
3	20.500.12210/83706*	2024-04-26T09:22:30Z
1	20.500.12210/83706.1	2023-05-30T18:06:53Z

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Well-Defined Silica-Supported Calcium ...

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