A DFT study on the mechanism of the gas phase reaction of ground-state Y (4d15s2,2D) with 2-butyne

The reaction of ground-state Y with 2-butyne has been investigated in detail using B3LYP method. Four pathways for elimination of H2 were identified. Two isomers, Y(HCCC)CH3 and Y(H2CCCCH2) were assigned to the observed product, YC4H4. The calculated PESs suggest that the concerted H2-elimination leading to Y(H2CCCCH2) + H2 product is the most favorable pathway. For the elimination of CH3, combining the results of this work with our previous study on Y + propyne reaction, a general mechanism for the reactions of Y with 2-alkynes bearing RCCCH3 structure was established: Y + RCCCH3 → π-complex → TS(H-migration) → HY(CH2CC)R → TS (CC insertion) → (CH2)HYCCR → TS(H-migration) → H3CYCCR → CH3 + YC2R. Such mechanism was found to be always energetically more favorable than the direct sp-sp3 CC bond insertion mechanism. Further, such mechanism can also be applied to the elimination of CH4 and it can be described as: Y + CH3CCCH3 → π-complex → TS (H-migration) → HY(H2CCC)CH3 → TS(CC insertion) → (H2CCC)HYCH3 → TS(H-migration) → CH4 + YC3H2.