Ring Slippage and Dissociation of Pentamethylcyclopentadienyl Ligand in an (η5-Cp*)Ir Complex with a κ3-O,C,O Tridentate Calix[4]arene Ligand under Mild Conditions

The first examples of kappa(3)-O,C,O tridentate calix[4]arene transition-metal complexes [Cp*M(p-(t)Bucalix[4]arene-(2-)-kappa(3)-O,C,O)] (M = Ir, Rh) that are stable both in the solid state and in solution were synthesized. The reaction of the Ir complex with 2 equiv of xylyl isocyanide afforded the (eta(1) -Cp*)Ir(CNXy)(2) complex in which the Cp* ligand is slipped from an eta(5) s to an eta(1) fashion, although ring slippage of an eta(5)-Cp* ligand is very uncommon in comparison with that of Cp. The reaction of the (eta(1)-Cp*)Ir complex with additional 1 equiv of isocyanide resulted in the liberation of the Cp* ligand as Cp*H, which was confirmed by H-1 NMR. This study provides the first observation of stepwise dissociation of a Cp* ligand from group 4-10 transition-metals via eta(1) coordination. This unique phenomenon seems to be facilitated by flexible coordination of an OH group in the C-metalated calix[4]arene ligand.