Intermediates in catalytic hydrogenation of 1,3-butadiene, propadiene and methylacetylene on MoS2 catalyst

Abstract

Hydrogenation of 1,3-butadiene with a mixture of H₂ and D₂ on a MoS₂ catalyst gave [²H₀]but-1-ene and [²H₂]but-1-ene in proportion to the partial pressures of H₂ and D₂, but little [²H₁]but-1-ene was formed. If hydrogenation of butadiene was performed with HD, 3-[²H₁]but-1-ene and 4-[²H₁]-but-1-ene were mainly formed. The ratio of 3-[²H₁] to 4-[²H₁] isomers was found to be in good agreement with the isotope effect for the reaction with H₂ and D₂. On the basis of these results, a s-butenyl intermediate (σ-allylic complex, CH₃—CH—CHCH₂) was derived for the hydro-genation of butadiene. The intermediates in the hydrogenation of propadiene as well as the conversion of methylacetylene to propene were deduced by the same procedures as was σ-allyl (CH₂—CHCH₂) for propadiene and n-propenyl (CHCH—CH₃) for methylacetylene. These-results indicate that the σ-allylic complexes formed on the active sites for the hydrogenation reaction do not undergo reversible interconversion to the corresponding π-allylic complexes. The selective 1,2-addition of a hydrogen molecule to the dienes and the other catalytic features of MoS₂ are explained well by the isolated active site having three degrees of coordinative unsaturation described by the ³M-site.