Indacyclopentadienes and Aromatic Indacyclopentadienyl Dianions: Synthesis and Characterization.

A series of unprecedented metallacycles of indium, including indacyclopentadienes (2), spiro indacyclopentadienes (3), aromatic indacyclopentadienyl dianions with an In-Li bond (4), and aromatic indacyclopentadienyl dianions with an In-In bond (5), were synthesized and structurally characterized by single-crystal X-ray structural analysis for the first time. Both indacyclopentadienes 2 and 3 were synthesized by reaction of 1,4-dilithio-1,3-butadienes with InCl3 . Structural transformations between 2 and 3 were observed. Reduction of indacyclopentadienes 2 with an excess amount of lithium afforded aromatic indacyclopentadienyl dianions 4 with an In-Li bond or 5 with an In-In bond, respectively, depending on the substituents on the ring. The aromatic character of 4 and 5 was confirmed by both experimental measurements and theoretical analysis.