Adamantane structure, exchangeability

Cyclization of organoaluminums proceeds via intermolecular and intramolecular exchange. The bis-hydroalumination product of McjAlC CH, (Me2Al)3CMe, can lose Me3Al leading to a sublimable compound with the composition Me5AlgC4Me4 and an adamantane-like structure ... 

The problems encountered in structural analysis are well illustrated with the adducts formed between R(fod)3 and adamantane-l-carbonitrile (fig. 2), a highly structured ligand. Raber et al. (1981) reported a procedure for the evaluation of the structure of the Eu(fod)3 adduct using LIS data. Best fit of the LIS data was obtained with a Eu-N bond distance of 2.1 A. However, using H and spin-lattice relaxation rates induced by Gd(fod)3, Peters et al. (1982) determined a Gd-N bond distance of 2.6 A, which is more in line with values expected for R +-N bond distances. Peters suggested that the values of the bound shifts obtained for the europium adduct were inaccurate due to the presence of complex equilibria involving the mono and bis adducts, and free substrate, all in fast exchange on the NMR time scale. 

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