Reaction of 1,1',3,3'-tetra-tert-butyl-5,5'-dihydropentafulvalene (1) with methyllithium and subsequent treatment with an excess of tetracarbonylnickel leads to the isomeric, paramagnetic complexes (eta-5: eta-5-(t)Bu4C10H4)(eta-2: eta-2-(t)Bu4C10H6(CO)2Ni2 (2a) and (eta-5: eta-2-(t)Bu4C10H5)2(CO)2Ni2 (2b). Treatment of 2a with Br2/P[C6H5]3, and with I2/P[C6H5]3, respectively, affords by elimination of 1 the compounds (eta-5: eta-5-(t)Bu4C10H4)(P[C6H5]3)2Ni2X2, with X = Br (3) and with X = I (4), respectively. By treatment of 2b with bromine the paramagnetic Ni(III)-species (eta-5-(t)Bu2C5H2)((t)Bu2C5H3)NiBr2 (5) is obtained. The solid state structure of 5 is discussed.