Vinylidene-acetylene isomerization energy

DFT calculations confirmed the similarities with the alkyne/vinylidene transformation but have revealed that additional parameters were essential to achieve the isomerization [8, 20-23]. The hydride ligand on the 14-electron fragment RuHC1L2 opens up a pathway for the transformation similar to that obtained for the acetylene to vinylidene isomerization. However, thermodynamics is not in favor of the carbene isomer for unsubstituted olefins and the tautomerization is observed only when a re electron donor group is present on the alkene. Finally the nature of the X ligand on the RuHXL2+q (X = Cl, q=0 X = CO, q=l) 14-electron complex alters the relative energy of the various intermediates and enables to stop the reaction on route to carbene. 

Zou, S.L. Bowman, J.M. A new ab initio potential energy surface describing acetylene/vinylidene isomerization. Chem. Phys. Lett. 2003, 368, 421-424. 

Field, R.W. Jacobson, M.P. Order out of chaos Local bends above the energy of the acetylene-vinylidene isomerization barrier. In Abstracts of papers of the American Chemical Society 217, 141-PHYS Part 2, Mar 21, 1999. 

Ab initio calculations of the potential energy surface of triplet oxygen-assisted isomerization of acetylene to vinylidene suggest that it cannot proceed in a unimolec-ular fashion." ... 

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