pH-Dependent competition between κ2N7,O( P) macrochelation and µ-N1,N 7 oligomer formation for (η6-arene)RuII complexes of adenosine and guanosine 5′-mono-, -di- and -tri-phosphates

Abstract

The pH-dependent reaction of [Ru(η ⁶ -C ₆ H ₆ )(D ₂ O) ₃ ] ²⁺ with adenosine and guanosine 5′-mono-, -di- and -tri-phosphates has been studied by ¹ H and ³¹ P-{ ¹ H} NMR spectroscopy. Diastereomeric µ-1κN ¹ :2κ ² N ⁶ , N ⁷ co-ordinated cyclic trimers of the type [{Ru(5′-AMP)(η ⁶ -C ₆ H ₆ ) } ₃ ] predominate for adenosine 5′-monophosphate (5′-AMP ^2- ) in the range pH* 3.30–9.18. An X-ray structural analysis of the Ru _S Ru _S Ru _S diastereomer [{Ru(5′-AMP)(η ⁶ -p-MeC ₆ H ₄ Pr ⁱ )} 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* ⩽ 3.16) for the equilibrium system 5′-ATP–(η ⁶ -C ₆ H ₆ )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-field ³¹ P-{ ¹ H} NMR shifts of up to 7.8 and 8.6 ppm for the β- and γ-phosphorus atoms, κ ³ N ⁷ , O(P _β ), O(P _γ ) macrochelates provide the dominant metal species in acid solution. Time-dependent NMR studies for 5′-ADP–(η ⁶ -C ₆ H ₆ )Ru ^II (5′-ADP ^3- = adenosine 5′-diphosphate) indicated that initial macrochelation of this nucleotide is followed by cleavage of the β-phosphate group and formation of cyclic trimers of 5′-AMP ^2- . Reaction of guanosine 5′-monophosphate (5′-GMP ^2- ) with [Ru(η ⁶ -C ₆ H ₆ )(D ₂ O) ₃ ] ²⁺ afforded κN 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, κ ³ N ⁷ , O(P _β ), O(P _γ ) macrochelates are observed for the 5′-GTP–(η ⁶ -C ₆ H ₆ )Ru ^II equilibrium system (5′-GTP ^4- = guanosine 5′-triphosphate) in acid solution. Initial macrochelation in the 5′-GDP–(η ⁶ -C ₆ H ₆ )Ru ^II system (5′-GDP ^3- = guanosine 5′-diphosphate) again leads to rapid cleavage of the terminal β-phosphate function.