From experimental data it is known that the phosphorus activation by nickel complexes depends on the ligand nature. The σ-donor ligands influence the electronic charge transfer to the P4 molecule and the values of the Ni-P and P-P distances. The type of attachment (η1 or η2) of P4 molecule to nickel complex is also important, because in the η2 case the activation is more profound. The electronic factors governing these processes are usually unknown. For this reason, in this work the electronic structure of the nickel complexes [Ni(L)P4]q (q=0, 2; L=bipy, phen, PPh3, triphos) has been studied. The investigations were carried out by ab initio MO LCAO method in the RHF or ROHF approximation, taking into consideration the interaction configuration and using GAMESS program. In all the cases the Ni+2L/NiL and Ni+2LP4/NiLP4 reduction processes are energetically convenient (in according with experimental results). The energies profits in the Ni+2LP4/NiLP4 reduction are 0.4283 atomic units of energy (a.u.e.) for L= bipy, 0.3786 a.u.e. (L= phen), 0.2034 (L= PPh3) and 0.1244 (L= triphos).figureFrom the electronic structure calculation it follows that for L= triphos or PPh3 the η1-attachment of P4 molecule to nickel complex is convenient, but in the cases of L=bipy or phen the η2-attachment is energetically preferable leading to the more strong activation of P4 than the η1-bounding. The total charge on P4 molecule is lower in the case of η2-attachment and the P-P distances of the coordinated edge to nickel become longer. The dependence of total energy changes ΔE at the reduction of above compounds in function on the reduction experimental potentials φ (Yu.G.Budnikova, private communication) is linear (see Figure).