RESUMO
Olefin metathesis is increasingly incorporated in polyfunctional industrial processes. The classical WO3/SiO2 olefin metathesis catalyst is combined to other catalysts in order to afford higher added-value chemicals. However, the combination of several reactions, not only in a single reactor, but also stemming from a single, multifunctional surface species is a desirable improvement regarding process issues. Well-defined surface organometallic tungsten species can be designed to implement targeted functionalities (carbene, hydride, alkyl, ). By tuning the metal's coordination sphere, it is possible to combine metathesis with several reactions, such as (de)hydrogenation, dimerization or isomerization. Novel, unconventional reactions for the production and upgrading of alkanes and alkenes have thus been uncovered. The reactivity of this library of supported catalysts is discussed based on the type of mediated transformations: monofunctional (alkene and alkyne metathesis), bifunctional (1-butene or 2-butenes to propylene), trifunctional (ethylene to propylene, alkane metathesis, ). Mechanistic considerations will be discussed to put these results in a wider perspective for future developments.
RESUMO
The first example of propylene production from 2-butene in promising yield is described by reacting trans-2-butene over tungsten hydrides precursor W-H/Al(2)O(3) at 150 °C and different pressures in a continuous flow reactor. The tungsten carbene-hydride active site operates as a "bi-functional catalyst" through the disfavoured 2-butene isomerisation on W-hydride and 2-butenes/1-butene cross-metathesis on W-carbene.
RESUMO
A well-defined, silica-supported tungsten oxo alkyl species prepared by the surface organometallic chemistry approach displays high and sustained activity in propene metathesis. Remarkably, its catalytic performances outpace those of the parent imido derivative, underlining the importance of the oxo ligand in the design of robust catalysts.