Complexation or Coupling
Complexation is the process where by two species join together to form a single species.

The joining process may proceed via LUMO/HOMO Lewis acid/Lewis base, SOMO/SOMO radical/radical or steric Guest/Host types of interaction.

Complexation processes are bimolecular in the formation direction and unimolecular in the decomplexation direction.

For more information look in the Chemogenesis webbook sections on complexation, radical chemistry, addition reactions, Lewis acid/base interaction matrix. and pericyclic reaction chemistry.