pH-Dependent competition between κ2N 7,O( P) macrochelation and μ-N 1,N  7 oligomer formation for (η6-arene)RuII complexes of adenosine and guanosine 5′-mono-, -di- and -tri-phosphates

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.