Ligand Rearrangement in Cyclononatetraenyl Complexes of the Early Lanthanides

Three new lanthanide complexes of the general form [Ln(Cnt)(CntInd)] (Ln = Ce, Pr, and Nd; Cnt = cyclononatetraenyl; and CntInd = cyclononatetraenyl-dihydroindene) have been synthesized from the corresponding LnI₃salt and several equivalents of the KCnt ligand. A novel C–C coupling has been observed between one Cnt^–moiety and one dihydroindene moiety, originating from the collapse of a Cnt unit. The observed CntInd ligand is dianionic, harboring one more electron than a typical Cnt ligand. The complexes are characterized by X-ray diffraction,¹H NMR, and UV–visible studies. The novel complexes are formed instead of the [Ln(Cnt)₃] (Ln = Ce, Pr, and Nd), which are only reported with late lanthanide ions, while lanthanum did not form one or the other complex.