Theoretical Study of the Products of Acetylene Addition to HgCl₂

Abstract

The ab initio MP2 method is used with the LANL2DZ basis to calculate the mercury chloride π,π-complex with two acetylene molecules (1) and various isomeric forms of mercury di(β)-vinyl chloride σ-complexes (2): cis-cis (2A), cis-trans (2B), and trans-trans (2C). The π,π-complex is the most stable form of all those considered; the difference between 1 and 2A is 24.9 kcal/mole. A relation between the total energies (kcal/mole) for isomeric forms 2 is established to be 2A (0) < 2B (0.98) < 2C (1.58). Complex 1 is shown to be transformed into 2A via the intermediate formation of 3, which is a hybrid form of the complex (π,σ-complex of mercury chloride with two acetylene molecules). The structures of the transition states for the transformations of 1 into 3 (structure 4) and of 3 into 2A (structure 5) and the corresponding transition activation energies are determined. The interaction of 2A, 2B, and 2C with the Cl^- anion as a model nucleophile is considered. It is shown that the resulting anions (6A, 6B, 6C) have a planar structure with the relative stability increasing in the series 6A<6B<6C.