Sandra Korn and William S. Sheldrick
The pH-dependent reaction of
[Ru(η6-C6H6)(D2O)
3]2+ with adenosine and guanosine 5′-mono-, -di-
and -tri-phosphates has been studied by 1H and
31P-{1H} NMR spectroscopy.
Diastereomeric
µ-1κN1:
2κ2
N6, N7 co-ordinated cyclic
trimers of the type
[{Ru(5′-AMP)(η6-C6H6)
}3] predominate for adenosine 5′-monophosphate
(5′-AMP2-) in the range pH* 3.30–9.18. An
X-ray structural analysis of the
RuSRuSRuS
diastereomer
[{Ru(5′-AMP)(η6-p-MeC6H
4Pri)}3]·7.5H2O
1b established a pronounced degree of conformational flexibility in the
sugar and phosphate residues. In contrast to
5′-AMP2-, cyclic trimers cannot be observed in
more strongly acid solution (pH* ⩽ 3.16) for the
equilibrium system
5′-ATP–(η6-C6H6)Ru
II (5′-ATP4- = adenosine
5′-triphosphate) and remain relatively minor species even at
neutral or higher pH* values. As confirmed by pronounced low-field
31P-{1H} NMR shifts of up to 7.8 and 8.6
ppm for the β- and γ-phosphorus atoms,
κ3N7, O(P
β), O(Pγ)
macrochelates provide the dominant metal species in acid solution.
Time-dependent NMR studies for
5′-ADP–(η6-C6H6)Ru
II (5′-ADP3- = 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′-AMP2-. Reaction
of guanosine 5′-monophosphate (5′-GMP2-)
with
[Ru(η6-C6H6)(D2O)
3]2+ afforded
κN7-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, κ3N7,
O(Pβ),
O(Pγ) macrochelates are observed for
the
5′-GTP–(η6-C6H6)Ru
II equilibrium system
(5′-GTP4- = guanosine
5′-triphosphate) in acid solution. Initial macrochelation in the
5′-GDP–(η6-C6H6)Ru
II system (5′-GDP3- = guanosine
5′-diphosphate) again leads to rapid cleavage of the terminal
β-phosphate function.