pH-dependent competition between kappa(2)N-7,O(P) macrochelation and mu-N-1,N-7 oligomer formation for (eta(6)-arene)Ru-II complexes of adenosine and guanosine 5'-mono-, -di- and -tri-phosphates

The pH-dependent reaction of [Ru(eta(6)-C6H6)(D2O)(3)](2+) with adenosine and guanosine 5'-mono-, -di- and -tri-phosphates has been studied by H-1 and P-31-{H-1} NMR spectroscopy. Diastereomeric mu-1 kappa N-1:2 kappa(2)N(6), N-7 co-ordinated cyclic trimers of the type [{Ru(5'-AMP)(eta(6)-C6H6)}(3)] predominate for adenosine 5'-monophosphate (5'-AMP(2-)) in the range pH* 3.30-9.18. An X-ray structural analysis of the RuSRuSRuS diastereomer [{Ru(5'-AMP)(eta(6)-p-MeC6H4Pr1)}(3)] .7.5H(2)O 1b established a pronounced degree of conformational flexibility in the sugar and phosphate residues. In contrast to 5'-AMP(2)-, cyclic trimers cannot be observed in more strongly acid solution (pH* less than or equal to 3.16) for the equilibrium system 5'-ATP-(eta(6)-C6H6)Ru-II (5'-ATP(4-) = adenosine 5'-triphosphate) and remain relatively minor species even at neutral or higher pH* values. As confirmed by pronounced low-held P-31-{H-1} NMR shifts of up to 7.8 and 8.6 ppm for the beta- and gamma-phosphorus atoms, kappa(3)N(7), O(P-beta), O(P-gamma) macrochelates provide the dominant metal species in acid solution. Time-dependent NMR studies for 5'-ADP-(eta(6)-C6H6)Ru-II (5'-ADP(3-) = adenosine 5'-diphosphate) indicated that initial macrochelation of this nucleotide is followed by cleavage of the beta-phosphate group and formation of cyclic trimers of 5'-AMP(2-). Reaction of guanosine 5'-monophosphate (5'-GMP(2-)) with [Ru(eta(6)-C6H6)(D2O)(3)](2+) afforded kappa N-7-co-ordinated 1:1 and 2:1 complexes in the range pH* 3.69-8.38. In addition to analogous 1:1 and 2:1 species, kappa(3)N(7), O(P-beta), O(P-gamma) macrochelates are observed for the 5'-GTP-(eta(6)-C6H6)Ru-II equilibrium system (5'-GTP(4-) = guanosine 5'-triphosphate) in,acid solution. Initial macrochelation in the 5'-GDP-(eta(6)-C6H6)Ru-II system (5'-GDP(3-) = guanosine 5'-diphosphate) again leads to rapid cleavage of the terminal beta-phosphate function.