W(CH3)6 was supported on the surface of SiO2-Al2O3 (500) and was extensively characterized. On silica-alumina solid-state NMR, elemental analysis and gas quantification clearly point out the formation of a mixture of mono-podal, [≡Si–O–WMe5] and bi-podal species, [(≡Si–O)2WMe4], with the migration of one methyl from W to Al. These complexes are transformed at 120 oC into three types of carbynic tungsten surface complexes; two are neutral [≡Si–O–W(≡CH)Me2], [(≡Si–O)2W(≡CH)Me] and one is cationic [≡Si–O–W(≡CH)Me]+[Al-Me]-. These complexes are efficient for metathesis of n-decane (TON=350). Comparison with already synthesized silica supported neutral bi-podal tungsten indicates that the high increase in activity is due to the cationic character of one of the grafted tungsten complexes. Metathesis of linear alkanes catalyzed by the well-defined precursor on silica [≡Si–O–WMe5] affords a wide distribution of linear alkanes from methane up to triacontane. Olefin metathesis using the same catalyst and under the same reaction conditions gives a very striking different distribution of linear α-olefins and internal olefins. This shows that olefin and alkane metathesis processes occur via very striking different pathways. The same catalyst was found also to be very active in the direct transformation of ethylene to propylene. The mechanism involves the single site dimerization of ethylene to propylene the isomerization of butene-1 to butene-2 and the cross metathesis of ethylene and butene-2. 1) N. Riache, E. Callens and J.M. Basset, Handbook of Metathesis, R.H. Grubbs, Editor, Wiley, Chapter 2, Vol.1, 2014. 2) Manoja K. Samantaray, Emmanuel Callens, Edy Abou-Hamad, Aaron J. Rossini, Cory M. Widdifield, Raju Dey, Lyndon Emsley, and Jean-Marie Basset, Journal of the American Chemical Society, Vol. 136, 1054-1061, 2014 3) Manoja K. Samantaray, Raju Dey, Edy Abou-Hamad, Ali Hamieh, and Jean-Marie Basset, ACS catalysis, Submitted 2014

Alkane and olefin metathesis with well-defined W(Me)6 supported on silica/silica-alumina catalysts

249th National Meeting (2015)

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