Jean-Marie Basset

Catalytic Cleavage of the C-H and C-C Bonds of Alkanes by Surface Organometallic Chemistry: An EXAFS and IR Characterization of a Zr-H Catalyst

The catalytic cleavage under hydrogen of the C & singlebond;H and C & singlebond;C bonds of alkanes with conventional catalysts requires high temperatures. Room-temperature hydrogenolysis of simple alkanes is possible on a well-defined and well-characterized zirconium hydride supported on silica obtained by surface organometallic chemistry. The surface structure resulting from hydrogenolysis of (≡SiO)Zr(Np)3 (Np, neopentyl) was determined from the extended x-ray absorption fine structure (EXAFS) and 1H and 29Si solid-state nuclear magnetic resonance and infrared (IR) spectra. A mechanism for the formation of (≡SiO)3Zr-H and (≡SiO)2SiH2 and the resulting low-temperature hydrogenolysis of alkanes is proposed. The mechanism may have implications for the catalytic formation of methane, ethane, and lower alkanes in natural gas.

Catalytic Hydrogenolysis at Low Temperature and Pressure of Polyethylene and Polypropylene to Diesels or Lower Alkanes by a Zirconium Hydride Supported on Silica-Alumina: A Step Toward Polyolefin Degradation by the Microscopic Reverse of Ziegler–Natta Polymerization

Cleavage and polymerization with the same catalyst: The catalyst system named in the title, which cleaves polyethylene and polypropylene under a hydrogen atmosphere, is also capable of polymerizing ethylene or propylene. This shows the close relationship between olefin insertion and β-alkyl elimination [Eq. (a), (P)=polymer chain(P)].

SILICA-SUPPORTED TANTALUM CATALYSTS FOR ASYMMETRIC EPOXIDATIONS OF ALLYL ALCOHOLS

Tantalum good, titanium bad: This appears to be the case for silica-supported catalysts for the asymmetric epoxidation of allyl alcohols. Complexes such as [SiO-Ta(OEt)(4)] were prepared from silica and [Ta(=CHCMe(3))(CH(2)CMe(3))(3)], and in the presence of a tartrate and an alkyl hydroperoxide, these surface tantalum compounds lead to efficient and convenient catalysts for the asymmetric epoxidation of 2-propen-1-ol (R=H) and trans-2-hexen-1-ol (R=nPr; see reaction).

Observation of a H-agostic bond in a highly active rhenium-alkylidene olefin metathesis heterogeneous catalyst by two-dimensional solid-state NMR spectroscopy

Keywords: agostic interactions ; heterogeneous catalysis ; NMR spectroscopy ; rhenium Reference EPFL-ARTICLE-204447doi:10.1002/1521-3773(20021202)41:23 3.0.CO;2-OView record in Web of Science Record created on 2015-01-08, modified on 2017-12-03

Versatility of silica used as a ligand: effect of thermal treatments of silica on the nature of silica-supported alkyl tantalum species

Abstract The tris(neopentyl)neopentylidene tantalum complex reacts with the silanol groups of silica dehydroxylated at temperatures ranging from 300 to 700°C to form well-defined surface organometallic species. For a silica dehydroxylated at 300°C, the amount of available silanols allows the formation of species 3 linked by two covalent bonds to silica, while the dehydroxylation at 700°C leads to the formation of species 2 with only one covalent bond to silica. Dehydroxylation thus constitutes a way to control the hapticity of silica towards organometallic complexes.

Metathesis of Alkanes: Evidence for Degenerate Metathesis of Ethane over a Silica‐Supported Tantalum Hydride Prepared by Surface Organometallic Chemistry

The mutual exchange of methyl groups of ethane molecules is catalyzed by a silica-supported tantalum hydride surface complex (see the schematic representation of the transition states). This process, which resembles degenerate olefin metathesis, is five times faster than the productive alkane metathesis.

Asymmetric Epoxidation of Allylic Alcohols Catalyzed by (≡SiO)xTa(OEt)3-x(Dialkyl Tartrate Diolate): Influence of the Reaction Conditions

Silica-supported chiral tantalum alkoxides are active catalysts for the asymmetric epoxidation of propenol and trans hex-2-en-1ol. The influence of different parameters on their catalytic performance was followed: the impregnation duration by a tartrate (step in their preparation); the nature of the solvent (CH2Cl2, pentane, toluene) and of the oxidant (TBHP, CHP, H2O2); poisoning effects by water or t-butanol; the reaction temperature and the substrate concentration.

New optically active organotin compounds for heterogeneous bimetallic catalysis

Abstract Chiral tin(IV) derivatives with two or three chiral centers adjacent to the metal (−)-Ment2SnMe2, (−)-Ment2SnPh2, (−)-Ment3 SnCl, (−)-Ment3SnH; (−)-Ment  (1R, 2S, 5R)-1-chloro-5-methyl-2-isopropylcyclohexane, R2Sn[CH(Me)(n-Hex)]2 (R  Bu or Ph) have been prepared either by the coupling of methylmagnesium chloride with tin halides or by the reaction of lithium stannates with optically active (2-octyl)tosylate. The stereospecificity of both processes was remarkably high, leading to new optically pure organotin reagents which have been fully characterized.

New optically active organogermane compounds containing the adamantyl radical for heterogeneous bimetallic catalysis. Part II

Abstract Chiral organogermane(IV) derivatives H 3 GeAdCH 2 CO 2 (−)-menthyl, H 3 GeAdCH 2 CH 2 O(−)-bornyl and H 3 GeAdCH 2 CH 2 O 2 CCH 2 O(−)-menthyl (Ad=adamantyl) have been prepared in six steps from the 1-bromoadamantane. The new optically pure organogermane reagents which have been fully characterised have been used in the preparation of heterogeneous bimetallic catalysts.

Tantalkatalysatoren auf Kieselgel für die asymmetrische Epoxidierung von Allylalkoholen

Tantal erfolgversprechend – Titan erfolglos: Dies scheint fur auf Kieselgel als Tragermaterial fixierte Katalysatoren zu gelten, die fur die asymmetrische Epoxidierung von Allylalkoholen entwickelt wurden. Komplexe wie [SiO−Ta(OEt)4] wurden aus Kieselgel und [Ta(=CHCMe3)(CH2CMe3)3] synthetisiert. In Gegenwart eines Tartrats und eines Alkylhydroperoxids bilden diese Materialien, an deren Oberflache sich Tantalzentren befinden, effiziente und leicht handhabbare Katalysatoren fur die asymmetrische Epoxidierung von 2-Propen-1-ol (R=H) und trans-2-Hexen-1-ol (R=nPr; siehe Reaktionsgleichung).