Dendritic lanthanide complexes and the effect of Lewis-acid encapsulation

The synthesis of complexes using terbium(III) ions and dendritic branches based on L-lysine building blocks is reported. These complexes are bound via predominantly electrostatic lanthanide–carboxylate interactions, and were characterised using a range of approaches. The ability of these Lewis-acidic complexes and terbium acetate to influence the regiochemical outcome of a Diels–Alder reaction was investigated, but they were found to have minimal effect. Interestingly, however, non-dendritic terbium(III) acetate was observed to remain bound to the product of the reaction, broadening its NMR spectrum, whilst the dendritic terbium complexes did not interact in this way. This indicates that the Lewis-acidic centre in the more highly functionalised dendritic derivatives may be inaccessible, either sterically or electronically, both to substrates and products of organic transformations.