Arene complexes lanthanoid

Unfortunately almost all other information on the nature and structure of lanthanoid arene complexes is based on indirect data. The exception is the recently obtained unusual complex with Yb-naphthalene-V grouping [68] and the mixed cyclopenta-dienyl/naphthalene complex of lutetium [69]. Their properties and X-ray data are discussed below. 

Liu, Y., Zhang, H. Y., Bai, X. P., Wada, T., and Inoue, Y. (2000) Molecular design of crown ethers. 21. Synthesis of novel double-armed benzo-15-crown-5 lariats and their complexation thermodynamics with light lanthanoid nitrates in acetonitrile, J. Org. Chem. 65, 7105-7109 see also Danil de Namor, A. F. D., Chahine, S., Jafou, O., and Baron, K. (2003) Solution thermodynamics of lanthanide-cryptand 222 complexation processes, J. Coord. Chem 56, 1245-1255 Israeli, Y., Bonal, C., Detellier, C., Morel, J. P., and Morel-Desrosiers, N. (2002) Complexation of the La(III) cation by p-sulfonatocalix[4]arene - A La-139 NMR study, Canad. J. Chem. 80, 163-168. 

It seems to be rather strange that arene lanthanoid complexes remained unknown for a long time even so the energy of Ln-benzene bond is over 50 kcal/mol [57]. 

In addition to compounds considered above, there is a quite different variant of the arrangement of arene-lanthanoid complexes the compounds in which the arene loses its aromaticity and in which the nature of ligand - metal interaction approximates the a kind of bonding. Such a type of bond has been found in the mixed cyclopenta-dienyl/naphthalene complex of lutetium obtained via CpLuCl2 [69] ... 

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