New cationic complexes [Ni(η3-CH2C6H5)(PPh3)2]PF6 (3) and [Ni(η3-CH2C6H5)((+)-DIOP)]PF6 (4) were synthesized from the corresponding neutral compounds [Ni(η3-CH2C6H5)X(PR3)2] (X = Cl, Br), by metathetical halide abstraction with TIPF6. Complex 3 was characterized by X-ray crystallography and shown to have a distorted square-planar geometry with the benzylic group coordinated in a quasi-allylic fashion. Crystals are monoclinic, space group P21/n, a = 11.798(5), b = 19.251(2), c = 18.561(3) Å, β = 93.03°, V = 4208.6 Å3. Solution NMR studies showed benzyl fluxionality and phosphine lability in compound 3, but not in 4. The latter one is catalytically inactive towards styrene oligomerization, whereas 3 produces styrene oligomers (M¯n≈1000) with 67% isotactic content. Although [Ni(η3-CH2C6H5)CI(PCy3)] and trans[Ni(Cl)(H)(PCy3)2] are inactive, addition of TlPF6 induced catalytic activity with formation of highly isotactic (90%) styrene oligomers with similar M¯n and a different terminal group.