The synthesis and characterization of the first heterobinuclear tetraphosphorus complexes 3a and 3b with a [Si(mu,eta(2:2)-P-4)-Ni] core are reported. The latter result from conversion of the silylene-activated P-4 ligand LSiP4 (1; L =CH[(C=CH2)CMe][N-(2,6-(Pr2C6H3)-Pr-i)](2)) with the beta-diketiminatonickel(I) complexes [(L'Ni)(2)center dot toluene] (L' =CH[CMeN(2,6-iPr(2)C(6)H(3))](2)) and [(L '' Ni)(2)center dot toluene] (L '' =CH[CMeN(2,6-Et2C6H3)](2)), respectively. Unexpectedly, the complexes 3a and 3b feature a [Si(mu,eta(2:2)-P-4)Ni] core with nickel(I) centers as shown by X-ray diffraction analysis, electron paramagnetic resonance, and magnetic measurements. The latter prove that the products are paramagnetic both in the solid state and in solution because of the presence of tetrahedral nickel(I) sites.