Nucleophilic attack upon ethylene co-ordinated to mercury(II): a molecular-orbital study concerning the origin of the acceleration by HgII

Abstract

An ab initio molecular-orbital study has been carried out on the nucleophilic attack upon free C₂H₄, [Li(C₂H₄)]⁺, and [HgH(C₂H₄)]⁺. It is clearly shown that the nucleophilic attack is difficult in the first two systems but very easy in [HgH(C₂H₄)]⁺. An important factor in the metal-accelerated nucleophilic attack is the energy level of the metal acceptor orbital; because the acceptor orbital of HgH⁺ lies low in energy, the exchange repulsion between the nucleophile and the olefin decreases and the bonding interaction between the nucleophile and olefin increases, leading to the acceleration. Changes in geometry and electron distribution caused by the nucleophilic attack have been investigated in detail and are explained on the basis of orbital mixing.