Supramolecular architectures based on p-cymene/ruthenium complexes functionalized with nucleobases

Abstract

The nucleophilic attack of a series of nucleobase derivatives on the [(η⁶-p-cymene)RuCl(μ-Cl)]₂ dinuclear entity has yielded four mononuclear complexes with the general formula [Ru(η⁶-p-cymene)(L)Cl₂], in which L stands for cytosine (1), 2-thiouracil (2), hypoxanthine (3) and 5-aminouracil (4). Furthermore, the sieving of chlorido from compound 1, assisted by a mild base, has prompted the formation of a tetranuclear ruthenium cationic complex which crystallizes as [(η⁶-p-cymene)₄Ru₄(μ-cytosinato-κN1:κN3,O2)₄](CF₃SO₃)₄ (compound 5). The crystal structure analysis of compounds 1–4 reveals that the supramolecular packing is dominated by the self-assembly capabilities provided by the stabilized nucleobase-tautomer, which is at the same time dependent on the Ru/nucleobase coordination mode. In this regard, the assembly of the complex units is conducted through base-pairing interactions, and is also assisted by means of nucleobase/chloride hydrogen bonding. The stability of these monomeric entities in water and phosphate buffered solution is analysed by means of ¹H- and ³¹P-NMR. The tetranuclear entity of compound 5 presents an available hydrogen-donor set (exocyclic amino group) but it lacks any available acceptor atom, which prevents the nucleobase mediated self-assembly of the complex units. Consequently, a doubly interpenetrated supramolecular network is woven by the hydrogen bonding between the triflate (CF₃SO₃⁻) anions and complex cationic entities.