Geometrical conditions are analyzed in a study of metal complex substitution reaction mechanisms. By assuming SAF(dynamic) = SAF(static) for reaction substrates, gaps between reaction substrates, which are normally hard and inpenetrable, remaining almost non-neg. during the reaction, and an activation energy for bond migration around the unit sphere surface considerably lower than that needed in bond breaking, a dynamic cone packing approach is developed which describes quant. the relative positions and gaps between ligands during the reaction. The model can also be used to calculate the max. empty space for incoming ligands and for reaction intermediate. Reaction routes which leads to large neg. gaps between inert ligands simply imply high reaction barriers and they are thus unfavorable. Lewis base association and dissociation, metal-carbon s bond thermolysis, and CO insertion reaction are discussed briefly by using U(C5H5)3X (X = NCS-, Cl- and R-) as examples.4

Key words: REACTION MECHANISM, HALIDE, DYNAMIC MODELS, CYCLOPENTADIENE P, CHEMICAL REACTION, STERIC EFFECT, STEREOCHEMISTRY, METALLOCENES, MOLECULAR ORBITAL THEORY, POTENTIAL BARRIER