The synthesis of metallic nanoparticles (MNP) with excessive floor space and managed form is of paramount significance to extend their catalytic efficiency. The detailed rising technique of NP is usually unknown and understanding the particular steps would pave the best way for a rational synthesis of the specified MNP. Right here we reap the benefits of the stabilization properties exerted by the tetragonal prismatic supramolecular nanocapsule 8·(BArF)8 to develop an artificial methodology for sub-nanometric RuNP (0.6–0.7 nm). The catalytic properties of those sub-nanometric nanoparticles had been examined on the hydrogenation of styrene, acquiring wonderful selectivity for the hydrogenation of the alkene moiety. As well as, the encapsulation of [Ru5] clusters contained in the nanocapsule is strikingly noticed in a lot of the experimental circumstances, as ascertained by HR-MS. Furthermore, an intensive DFT examine enlightens the character of the [Ru5] clusters as tb-Ru5H2(η6-PhH)2(η6-pyz)3 (2) trapped by two arene moieties of the clip, or as tb-Ru5H2(η1-pyz)6(η6-pyz)3 (3) trapped between the 2 Zn–porphyrin items of the nanocapsule. Each choices fulfill the Wade-Mingos counting guidelines, i.e. 72 CVEs for the closo tb. The trapped [Ru5] metallic clusters are proposed to be the first-grown seeds of subsequent formation of the subnanometric RuNP. Furthermore, the double function of the nanocapsule in stabilising ∼0.7 nm NPs and in addition in internet hosting ultra-small Ru clusters, is unprecedented and will pave the best way in direction of the synthesis of ultra-small metallic clusters for catalytic functions.