Template reaction

[1] An early example is the dialkylation of a nickel dithiolate:[2] The corresponding alkylation in the absence of a metal ion would yield polymers.

[4] The condensation of formaldehyde, ammonia, and tris(ethylenediamine)cobalt(III) to give a clathrochelate complex is one example.

In a general sense, transition metal-based catalysis can be viewed as template reactions: Reactants coordinate to adjacent sites on the metal ion and, owing to their adjacency, the two reactants interconnect (insert or couple) either directly or via the action of another reagent.

In the area of homogeneous catalysis, the cyclo-oligomerization of acetylene to cyclooctatetraene at a nickel(II) centre reflects the templating effect of the nickel, where it is supposed that four acetylene molecules occupy four sites around the metal and react simultaneously to give the product.

For example, if a competing ligand such as triphenylphosphine were added to occupy one coordination site, then only three molecules of acetylene could bind, and these come together to form benzene (see Reppe chemistry).