Dihalogenometal(II) complexes with bidentate phosphane ligands of the general type [M{Ph₂P(CH₂)_nPPh₂}X₂] with n = 2 to 5, X = Cl or Br and M = Co, Ni or Pd have been utilized as catalysts for the vinyl/addition polymerization of norbornene. These complexes can be activated with the Lewis-acids methylalumoxane (MAO) or tris(pentafluorophenyl)borane, B(C₆F₅)₃ in combination with triethylaluminium (AlEt₃). The nickel(II) and palladium(II) complexes show very high polymerization activities up to 10⁷ g_polymer mol_metal⁻¹ h⁻¹. Yet, the complexes Pd(dppe)Cl₂ (5, 1.9 × 10⁷ g_polymer mol_Pd⁻¹ h⁻¹) and Pd(dppp)Cl₂ (6, 3.0 × 10³ g_polymer mol_Pd⁻¹ h⁻¹) demonstrated that small changes in the ligand structure could have great effects on the polymerization activity [dppe = 1,2-bis(diphenylphosphino)ethane, Ph₂P(CH₂)₂PPh₂; dppp = 1,3-bis(diphenylphosphino)propane, Ph₂P(CH₂)₃PPh₂]. The activation process of the pre-catalysts 5 and 6 in combination with B(C₆F₅)₃/AlEt₃ was followed by multinuclear (¹H, ¹⁹F, and ³¹P) NMR investigations and by reaction with B(C₆F₅)₃ and Ag[closo-1-CB₁₁H₁₂]. The reaction of B(C₆F₅)₃ and AlEt₃ leads to an aryl/alkyl group exchange resulting in the formation of AlEt_3 − n(C₆F₅)_n and B(C₆F₅)_3 − nEt_n with Al(C₆F₅)₃ and BEt₃ as main products for an about equimolar ratio. AlEt_3 − n(C₆F₅)_n will then react with the pre-catalysts and abstract the chloride atoms to form [M{Ph₂P(CH₂)_nPPh₂}]²⁺ as the active species for the polymerization. The higher polymerization activity of 5/B(C₆F₅)₃/AlEt₃ compared to 6/B(C₆F₅)₃/AlEt₃ can be explained by a ligand redistribution reaction of unstable [Pd^II(dppe)]²⁺ to give inactive and isolable [Pd^II(dppe)₂]²⁺ and highly active, “naked” Pd²⁺ cations together with the lower coordinating ability of the anionic adduct [Cl–Al(C₆F₅)₃]⁻ in comparison to [Cl–B(C₆F₅)₃]⁻. The Lewis-acid Al(C₆F₅)₃ is much more activating than B(C₆F₅)₃. The [Pd(dppe)₂]²⁺ cation from the ligand redistribution was isolated in the (X-ray) structurally elucidated compounds [Pd^II(dppe)₂][ClB(C₆F₅)₃]₂·4CH₂Cl₂ and [Pd^II(dppe)₂][CB₁₁H₁₁Cl]₂·3CH₂Cl₂. The stable [Pd(dppp)]²⁺ cation from 6 could be crystallized as [Pd^II(dppp)(CB₁₁H₁₂)][CB₁₁H₁₂] (CB₁₁H₁₂ = mono-anionic carborane [closo-1-CB₁₁H₁₂]⁻).