M. Taoufik

Dinitrogen Dissociation on an Isolated Surface Tantalum Atom

Both industrial and biochemical ammonia syntheses are thought to rely on the cooperation of multiple metals in breaking the strong triple bond of dinitrogen. Such multimetallic cooperation for dinitrogen cleavage is also the general rule for dinitrogen reductive cleavage with molecular systems and surfaces. We have observed cleavage of dinitrogen at 250°C and atmospheric pressure by dihydrogen on isolated silica surface–supported tantalum(III) and tantalum(V) hydride centers [(≡Si-O)2TaIII-H] and [(≡Si-O)2TaVH3], leading to the TaV amido imido product [(≡SiO)2Ta(=NH)(NH2)]: We assigned the product structure based on extensive characterization by infrared and solid-state nuclear magnetic resonance spectroscopy, isotopic labeling studies, and supporting data from x-ray absorption and theoretical simulations. Reaction intermediates revealed by in situ monitoring of the reaction with infrared spectroscopy support a mechanism highly distinct from those previously observed in enzymatic, organometallic, and heterogeneous N2 activating systems.

Catalytic properties of silica-supported tantalum and tungsten hydrides in the cleavage and formation of C-C bonds of alkanes

Heterogeneous catalysts are widely used in industrial applications; they are often easily prepared at a low cost and can be conveniently separated from the reaction medium. However it is always difficult to define and control the active site and then to determine the various elementary steps of a catalytic reaction. On the contrary, homogeneous catalysis has been based on the rules of molecular organometallic chemistry, which affords a better understanding of what are the active species and the elementary steps of a process. Surface Organometallic Chemistry (SOMC) is aimed at the preparation of a new type of heterogeneous catalysts for which the concepts and the rules of molecular organometallic chemistry could be transposed. The reaction of molecular complexes with functional groups of a surface affords the formation of highly reactive well-defined supported organometallic species, usually unprecedented in solution.

Surface Organometallic Chemistry of Tantalum: Application to the Metathesis of Alkanes Catalyzed by a Tantalum Hydride Supported on Silica

Heterogeneous catalysts are widely used in industry because they can usually be conveniently separated from the reaction medium. From a fundamental point of view, it is always difficult to define and control the real coordination sphere and then to determine the various elementary steps of a catalytic reaction. On the contrary, homogeneous catalysis has been developed on the rules of Molecular Organometallic Chemistry, which affords a better understanding of what are the active species and the elementary steps of a process. Surface Organometallic Chemistry (SOMC) is aimed at the preparation of highly reactive well-defined supported organometallic species which would obey the concepts and the rules of Molecular Organometallic Chemistry. The formation of such supported organometallic species usually involves the reaction of molecular complexes with functional groups of a surface. Surface Organometallic Chemistry found application in the field of the activation and valorisation of alkanes which has been the subject of numerous studies during the last two decades [1,2]. The transformation of alkanes may involve the activation of C-H or CC bonds or both [3-5]. Among the various modes of C-H bond activation of alkanes, the use of highly electrophilic organometallic complexes of early