Reactive half-metallocenium ionic liquids that undergo solventless ligand exchange.

The piano-stool half-metallocenium cations [Fe(C(5)R(5))(CO)(2)L](+) (C(5)R(5) = C(5)H(5), C(5)Me(5), C(5)Me(4)Et; L = 1-pentene, nBuCN, MeCN, Me(2)S, NH(3), NMe(3), pyridine) provide ionic liquids (ILs) with the bis(trifluoromethanesulfonyl)imide (Tf(2)N) anion without introducing long alkyl chains. Their melting points are affected by molecular symmetry, and their thermal stabilities reflect the strength of the metal-ligand bonding. These are reactive liquids that show solventless ligand exchange reactions by gas absorption. The direction of the ligand-exchange reaction is correlated with the stabilities. Based on the variation of the melting points, these ILs undergo transformations between the liquid and solid phases associated with the reaction.