LIGAND AND SUBSTITUENT EFFECTS IN METHANE ACTIVATION BY MERCURY(II) COMPLEXES

This paper reports a computational study of methane activation by the HgN and HgF bonds of the Hg-II complexes FHgNZ (where NZ is NH2, NO2, N-3, NC, NCO, NCS, NO, NS, N2H). The present study probes the thermody namic and kinetic effects of activating ligand (L-a) modification for a given spectator ligand (L-s) and vice versa. The wide range of calcu lated kinetic and thermodynamic values indicates a degree of sensitivi ty in methane activation by Hg-II complexes to the ligand environment. The trends show that [2(sigma) + 2(sigma)] activation of of a methane C-H bond by Hg-II complexes is thermodynamically favored by a more ba sic activating ligand and a less basic spectator ligand. The lowest me thane activation barriers are observed for an activating ligand with v ariable denticity (i.e. NO2) that can provide extra stabilization for the methane activation transition state versus the ground state. The i mplications of the results for experimental Hg-II methane conversion c atalysts are discussed. (C) 1998 Elsevier Science B.V.