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 κ3-O,C,O tridentate calix[4]arene transition-metal complexes [Cp*M(p-tBucalix[4]arene(2−)-κ3-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 (η1-Cp*)Ir(CNXy)2 complex in which the Cp* ligand is slipped from an η5 to an η1 fashion, although ring slippage of an η5-Cp* ligand is very uncommon in comparison with that of Cp. The reaction of the (η1-Cp*)Ir complex with additional 1 equiv of isocyanide resulted in the liberation of the Cp* ligand as Cp*H, which was confirmed by 1H NMR. This study provides the first observation of stepwise dissociation of a Cp* ligand from group 4–10 transition-metals via η1 coordination. This unique phenomenon seems to be facilitated by flexible coordination of an OH group in the C-metalated calix[4]arene ligand.