Molecular precursor complexes for the reaction between methane and a systematically selected set of second-row transition metal complexes are studied using methods of high accuracy. Comparisons are made to previous detailed studies of the transition states and product complexes of the oxidative addition reaction. The electronic structure requirements for a strongly bound precursor and for a low barrier for the oxidative addition are compared and found to be quite different. A ground or a low-lying singlet state is required for the formation of a strongly bound precursor. A ground or a low-lying triplet state is required for a low reaction barrier. The barrier counted from the precursor is thus to a large extent determined by the reactant singlet-triplet splitting. Comparisons are made to experimentally derived results for RhCp(CO). The levels of accuracy needed for the energy evaluation and for the geometry optimization are tested. It is found that for the precursors the inclusion of van der Waals attraction is needed in the geometry optimization.