Metathese des olefines avec les precurseurs zerovalents du tungstene W(CO)₅L (L = CO, PPh₃, P(n-C₄H₉)₃) associes a AlX₃ (X = Cl, Br); une etude de spectroscopie IR et RMN ³¹P

Interaction in solution between W(CO)₅L (L = CO, PPh₅, P(n-C₄H₉)₃) and AlX₃ (X = Cl, Br) has been studied in order to obtain some insight into the coordination sphere of the resulting catalyst for metathesis. When L is sufficiently basic (L = PPh₃, P(n-C₄H₉)₃) there is formation of an addition compound L(CO)₄WCO AlBr₃ detected by infrared and ³¹P NMR spectroscopy. The result of this adduct formation is a strong decrease of electron density on the tungsten followed by the easy dissociation of the ligand L as detected by infrared and ³¹P NMR spectroscopy. Coordinatively unsaturated tungsten is thus obtained and is relatively stable in solution. The free phosphine is complexed to the excess Lewis acid. This coordinatively unsaturated tungsten favors ligand interchange (formation of W(CO)₆) as well as oxidation of zerovalent tungsten to divalent tungsten W(CO)₄x₂ (X = Cl, Br). The results are compared with those already published with other catalytic systems derived from hexavalent or zerovalent complexes of tungsten.