Catalytic homologation of olefins to higher and lower olefins: a metathesis related reaction

With Fe/SiO₂, Ru/SiO₂ and Os/SiO₂, any acyclic olefin (e.g. ethylene, propylene or isobutene) homologates at 200 - 300°C to yield higher and lower olefins with the simultaneous formation of methane. The reaction is catalytic when H₂ is present. The main features of such reactions are reported, i.e. conversions, turnover numbers, product distribution, effect of contact time on the selectivity for α-olefins and branched olefins. The results are compared with those obtained in Fischer-Tropsch syntheses. It is shown that the mode of C-C bond formation for the hydrocondensation of CO or olefin homologation is the same. Two possible mechanisms are discussed to account for the data. These mechanisms assume either the insertion of a carbene into a metal-alkyl bond or the attack of a carbene on a coordinated olefin.