The synthesis of Ar'CrCrAr' in 2005 gave a new momentum to the chemistry of multiple bonded metal-metal species and became a new impetus for the isolation of increasingly shorter metal-metal interactions. The terphenyl ligand (Ar') allows to protect the bimetallic unit against external interactions. In addition, it has no effects on the CrCr multiple bond although it has been shown that 6 interactions occur when chromium is replaced by cobalt or iron. The use of ligands based on nitrogen as coordinating element has been shown to be associated to a shortening of the metal-metal bond. The possibility of using the U2 unit as framework of a new kind of chemistry was also investigated.