lithium was found to react with Ni(II) and Co(II) salts to form noVel complexes in which the Ni or Co central metal atom is bonded to two nickelafluorenyl ligands. The crystal and molecular structures of the products were determined by single-crystal X-ray analysis.Recently there has been considerable interest in the aromatic properties of cyclic π-systems containing heteroatoms, mainly because of their potential ability to act as multielectron ligands. A well-known preparation of metal-cyclopentadienyl complexes involves the reaction of an appropriate cyclopentadienyllithium complex with with a metal salt. 1 Such reactions also can be carried out with heterocyclopentadienyllithium complexes. 2 Although the synthesis of heterofluorenyl-alkali-metal complexes containing main-group elements 3 and transition metals (zirconium) 4 have been reported, they were not employed in the formation of the compounds in which the metal atom is bonded to the heterocyclic ring.Recently we have reported the synthesis of (9-nickelafluorenyl)lithium complexes, 5 novel metallafluorenyl-alkali-metal compounds that contain a transition metal in the five-membered metallacyclic ring.We report here the reactions between metal bromides or acetylacetonates of nickel and cobalt and the (9-nickelafluore-nyl)lithium species 1, in which acetylacetonate or bromide ligands are displaced by the 9-nickelafluorenyl group to form complexes in which the nickel or cobalt atom is bonded to two 9-nickelafluorenyl ligands in a sandwich-type complex.