Jean Thivolle-Cazat

“Hydro‐metathesis” of Olefins: A Catalytic Reaction Using a Bifunctional Single‐Site Tantalum Hydride Catalyst Supported on Fibrous Silica (KCC‐1) Nanospheres

We thank ESCPE-Lyon, the CNRS, and the KAUST for financial and logistic support and Anne Baudouin for NMR spectra acquisition.

Non-Oxidative Coupling Reaction of Methane to Ethane and Hydrogen Catalyzed by the Silica-Supported Tantalum Hydride: (≡SiO)2Ta−H

Silica-supported tantalum hydride, (SiO)2Ta-H (1), proves to be the first single-site catalyst for the direct non-oxidative coupling transformation of methane into ethane and hydrogen at moderate temperatures, with a high selectivity (>98%). The reaction likely involves the tantalum-methyl-methylidene species as a key intermediate, where the methyl ligand can migrate onto the tantalum-methylidene affording the tantalum-ethyl.

σ‐Bond Metathesis of Alkanes on a Silica‐Supported Tantalum(V) Alkyl Alkylidene Complex: First Evidence for Alkane Cross‐Metathesis

C-C activation of unactivated alkanes on a silica-supported neopentyl neopentylidene TaV complex [Eq. (1)] affords the alkane cross-metathesis products tBuCH2 R and an alkane-metathesis catalyst. Since the activity and product distributions are similar to those obtained with a silica-supported TaIII hydride, these results are a first step in understanding alkane σ-bond metathesis on metal hydrides.

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.

Molecular Insight Into Surface Organometallic Chemistry Through the Combined Use of 2D HETCOR Solid‐State NMR Spectroscopy and Silsesquioxane Analogues

Reference EPFL-ARTICLE-204460doi:10.1002/1521-3773(20011203)40:23 3.0.CO;2-XView record in Web of Science Record created on 2015-01-08, modified on 2017-12-03

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.

Oxide supported surface organometallic complexes as a new generation of catalysts for carbon–carbon bond activation

Abstract This paper reviews recent applications of well-defined silica-supported hydrides of the group 4 and 5 transition metals in the field of carbon–carbon and carbon–hydrogen bonds activation of alkanes. The synthesis and characterization of the zirconium and tantalum hydrides is presented. (SiO) 3 M–H complexes (M=Ti 1 , Zr 2 , Hf 3 ) are obtained by hydrogen treatment at c.a. 150°C of Si–O–MNp 3 (Np=CH 2 C(CH 3 ) 3 ). These three surface complexes are formally 8 electrons species and are consequently very electrophilic. (SiO) 2 Ta–H 4 is obtained by hydrogen treatment at c.a. 150°C of (Si–O) x Ta(CHC(CH 3 ) 3 )(CH 2 C(CH 3 ) 3 ) 3− x ( x =1,2) and is also highly electrophilic. Examples of applications of these hydrides in the field of the activation of alkanes at moderate temperatures are then given. The complexes 1 – 3 can achieve the hydrogenolysis of alkanes at low temperature. With 1 a simultaneous reaction of skeletal isomerization occurs. With 2 and 3 the mechanism of C–C bond cleavage passes through an elementary step of β-alkyl transfer. The mechanism of hydroisomerization observed with 1 passes also by an elementary step of β-alkyl transfer but in this case the β-H elimination–olefin reinsertion occurs quite rapidly so that a skeletal isomerization also occurs. Complexes of type 2 or 3 were found to catalyze under olefin pressure the olefin polymerization, and under hydrogen pressure, the polyolefin hydrogenolysis. Here the equilibrium between the olefin insertion into a metal–alkyl and the β-alkyl transfer is shown to occur with the same catalyst in agreement with the concept of microreversibility. A new catalytic reaction, called “alkane metathesis” has been discovered with complex 4 . By this reaction alkanes are catalytically transformed into higher and lower alkanes. The mechanism by which this reaction occurs is not fully understood. The products distribution, especially with labeled alkanes is explained by a concerted mechanism by which a Ta–C bond and a C–C bond of the alkane can be cleaved and reformed simultaneously via a kind of four centered σ-bond metathesis which has no precedent in classical organometallic chemistry.

Palladium-catalyzed carbon—carbon bond formation from (η6-chloroarene)Cr(CO)3 complexes an example of bimetallic activation in homogeneous catalysis

Abstract The effect of the coordination of a tricarbonylchromium moiety to the aromatic ring of aryl chlorides in the activation toward oxidative addition of the CCl bond to zerovalent palladium complexes is described. It presents an overview of catalytic reactions and fundamental investigations with the aim to rationalizing the role of the Cr(CO) 3 moiety on some of the elementary steps of these reactions. This topic is divided according to the nature of the catalytic reactions involving the tricarbonyl (chloroarene) chromium complexes. Firstly, the results obtained during the cross-coupling reaction with nucleophilic reagents (copper acetylides, organostannanes) and the catalytic Heck olefination reaction are presented. Then, several carbonylation processes, such as hydrocarbonylation into aldehydes, mono- and double carbonylation into amides and α-oxo-amides, and finally alkoxycarbonylation into esters, are discussed. Particular attention is given to the catalytic and stoichiometric aspects of this last reaction.

Structure–Reactivity Relationship in Alkane Metathesis Using Well‐Defined Silica‐Supported Alkene Metathesis Catalyst Precursors

Alkane metathesis can be performed by using well-defined silica-supported alkene metathesis catalyst precursors as long as the coordination sphere of the metal centre contains both alkyl and alkylidene groups, such as in [([triple chemical bond]SiO)Mo([triple chemical bond]NAr)(=CHtBu)(CH2tBu)]. This system transforms mainly linear alkanes, from propane to hexane, into their lower and higher homologues. Mechanistic studies clearly show that alkene metathesis is a key step of this reaction and also suggest that this system is a single-site single-component system, namely, alkenes are formed and transformed on one site, which is in contrast to that observed with a mixture of catalysts.

Bi-metallic activation in homogeneous catalysis: palladium-catalysed carbonylation of tricarbonyl(chloroarene)chromium complexes to the corresponding aldehydes, esters, amides, and α-oxo amides

Tricarbonyl(chloroarene)chromium complexes undergo palladium-catalysed carbonylation to give aromatic aldehydes, esters, amides, and α-oxo amides.