Formation of the Oxanickelacyclopentene Complex from Nickel(0), Carbon Dioxide, and Alkyne. An <i>ab initio</i> MO/SD-CI Study. Part II. Reactivity and Regioselectivity of Hydroxyacetylene

Abstract

Abstract The formation reaction of oxanickelacyclopentene from [Ni(PH3)], hydroxyacetylene (a model of ethoxyacetylene), and carbon dioxide was investigated by the ab initio MO/SD-CI method. Of the two possible products of oxanickelacyclopentene and , the former was yielded with a lower activation energy (Ea) of 27 kcal mol−1 and a higher exothermicity (Eexo) of 31 kcal mol−1 than the latter (Ea = 38 kcal mol−1 and Eexo = 25 kcal mol−1). This result is consistent with the regioselectivity experimentally observed in the Ni(0)-catalyzed 2-pyrone synthesis from ethoxyacetylene and carbon dioxide. The regioselectivity of this reaction and the reactivity of hydroxyacetylene are discussed in terms of the energy level and the shape of the hydroxyacetylene π* orbital.