Strukturänderungen bei der Reduktion von 9‐(Diphenylmethyliden)fluoren mit Natrium‐Metall zu Schichten (R₂O)Na^⊕‐verknüpfter Kohlenwasserstoff‐Dianionen

Structural Changes on Reduction of 9‐(Diphenylmethylidene)fluorene by Sodium Metal to Sheets of (R₂O)Na⊕‐ Connected Hydrocarbon Dianions The single‐crystal structure of 9‐(diphenylmethylidene)fluorene (monoclinic, space group P2₁/n, Z = 4) proves a CC bond length of 135 pm and a twisting of the two Ph rings out of the methylidene‐fluorene plane by 70° and 83°. Its reduction in Et₂O solution by a Na mirror under Ar yields dark green crystals with a metallic luster. Their structure, determined in a N₂ flow cooled to 223 K (monoclinic, space group C2/c, Z = 4), reveals sheets of hydrocarbon dianions, connected by sodium(diethylether) links. The Na centers are sixfold coordinated as half‐sandwiches to the fluorene benzo rings and threefold allylic to the Ph rings. In the dianion of 9‐(diphenyl‐methylidene)fluorene, the central CC bond is stretched by 13 pm to 148 pm length, and the two molecular cyanine‐like halves are twisted by 51° relative to each other. Both the contact‐ion multiple structures as well as the structural changes on twofold reduction are discussed by way of comparison with literature examples and based on semiempirical calculations.