We show that tinchlorides, SnCl2 and FeCl3 complexes to the imines groups of a spherical polyphenyl-azomethine dendrimer in a stepwise fashion according to an electron gradient, with complexation in a more peripheral generation proceeding only after complexation in generations closer to the core has been completed.The metal-assembly in a discrete molecule can be converted to a size-regulated metal cluster with a size smaller than 1 nm as a molecular reactor.