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Unusual Coordination of the Rare Neutral Imine Tautomer of 9‐Methyladenine Chelating in the N 6, N 7‐Mode to Ruthenium(II) Complexes
Author(s) -
Hotze Anna C. G.,
Broekhuisen Marjolein E. T.,
Velders Aldrik H.,
van der Schilden Karlijn,
Haasnoot Jaap G.,
Reedijk Jan
Publication year - 2002
Publication title -
european journal of inorganic chemistry
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.667
H-Index - 136
eISSN - 1099-0682
pISSN - 1434-1948
DOI - 10.1002/1099-0682(20022)2002:2<369::aid-ejic369>3.0.co;2-h
Subject(s) - tautomer , chemistry , ruthenium , protonation , imine , denticity , chelation , crystallography , stereochemistry , resonance (particle physics) , nuclear magnetic resonance spectroscopy , ion , crystal structure , inorganic chemistry , organic chemistry , catalysis , physics , particle physics
Abstract The coordination of the DNA model base 9‐methyladenine (9‐MeAde) to both complexes cis ‐[Ru(bpy) 2 Cl 2 ] and α‐[Ru(azpy) 2 (NO 3 ) 2 ] is reported. Structural characterisation using 2D NMR techniques and variable‐temperature NMR studies between 25 and −55 °C show that in the compounds α‐[Ru(azpy) 2 (9‐MeAde)](PF 6 ) 2 ( 1 ) and cis ‐[Ru(bpy) 2 (9‐MeAde)](PF 6 ) 2 ( 2 ), 9‐MeAde is coordinated to the ruthenium ion in a chelating mode via its N7 and exocyclic N6 atoms. The NMR spectroscopic data unambiguously prove the occurrence of the rare imine tautomer of 9‐MeAde in these complexes, which is clearly stabilised by the bidentate coordination of 9‐MeAde in both complexes. Variable‐temperature NMR spectra and 2D COSY data show that the H2 resonance of 9‐MeAde in 1 and 2 appears as a doublet at low temperatures and shows a COSY cross peak to the NH1 resonance of 9‐MeAde, which confirms the protonation at the N1 site. This protonated N1 site, together with an observed p K a of ca. 6.5 of compound 1 is in agreement with the presence of the imine tautomeric form of 9‐MeAde. As the binding mode of 9‐MeAde to both cis ‐[Ru(bpy) 2 ] and α‐[Ru(azpy) 2 ] moieties is the same, this binding mode does not explain the earlier observed difference in cytotoxicity between cis ‐[Ru(bpy) 2 Cl 2 ] and α‐[Ru(azpy) 2 Cl 2 ].