• sintesi
• metatesi di olefine
• catalizzatori
• caratterizzazione analitica

Yves Chauvin, Robert H. Grubbs and Richard R. Schrock won the Nobel Prize for chemistry in 2005 “for the development of metathesis method in organic synthesis”. Yves Chauvin proposed a mechanism for the olefin metathesis, research activity of R. Schrock instead, was dedicated to synthesize different kind of catalysts for this reaction, he studied complexes known as metal alkylidens (M=CHR). Focusing on Shrock-type catalysts with the general formula [M(E)(=CHR)(X)(Y)] (M = Mo, W), is worth to note that latest studies on the reaction mechanism, highlighted some characteristics which improves their activity. The dissymmetry at the metal centre, in particular, the different electron donation ability of the X and Y ligands (one weaker and one stronger σ-donor ligand) and strong trans-influence of E ligand, affords very good results in increasing the activity of the species. Add to this, recently, in order to improve also the prevention of the deactivation of the catalyst, these metal alkylidenes have been supported on silica partially dehydroxylated. And they displayed activities which in most cases, surpassed their molecular precursors. The group in which this Thesis has been performed focused the work on silica-supported tungsten oxo alkylidene bearing phenolate ligands (X,Y). Is worthy to report the case of [(≡SiO)W(=O)(=CHtBu)(OHMT)2] and [(≡SiO)W(=O)(=CHtBu)(dAdPO)2] (OHMT = 2,6-dimesitylphenoxide, dAdPO = 2,6-diadamantyl-4-methylphenoxide). For this Thesis work we decided to investigate the reactivity of [W(=O)(=CHtBu)(SHMT)2] thiolate analogues to [(≡SiO)W(=O)(=CHtBu)(OHMT)2] (OHMT = 2,6-dimesitylphenoxide).While the molecular precursor shows no significant catalytic activity, the grafted analogue is an efficient catalyst for alkene metathesis of internal olefin. The surface complex [(≡SiO)W(=O)(=CHtBu)(SHMT)] showed unprecedented activity in metathesis of terminal olefins. Desymmetrization of the ligand set of tungsten oxo alkylidene catalysts has proven effective for generating efficient 1-alkene metathesis catalysts.