Structural evidence for monodentate binding of guanine to the dirhodium( ii , ii ) core in a manner akin to that of cisplatin
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The reaction of Rh2(OAc)4(bpy) (bpy = 2,2′-bipyridine) with 9-ethylguanine (9-EtGH) proceeds with substitution of two acetate ligands to produce [Rh2(OAc)2(bpy)(9-EtGH)(H2O)2(CH3SO4)][CH3SO4]·(H2O) (1), which has been structurally characterized. In compound 1, the equatorial sites of one rhodium center are occupied by a chelating bpy molecule and 9-EtGH is equatorially coordinated via N(7) to the other rhodium center. The interaction of the 9-EtGH base with the dirhodium core is further stabilized by an intramolecular hydrogen bond between the purine O(6) and the equatorial water molecule. The eight non-equivalent bpy proton resonances, as well as that of the purine H(8) (which shifts upfield upon coordination as compared to free 9-EtGH, due to bpy ring current effects), were assigned by means of 2D NMR spectroscopy. The pH titration curve of the H(8) proton reveals pH-independent behavior and a pKa value of 8.0 for N1–H deprotonation; both observations corroborate N(7) binding of the purine base to the dirhodium unit in solution. These findings indicate that, in the presence of a chelating agent that blocks one rhodium center, 9-EtGH binds to a single rhodium center in a monodentate fashion via N(7), instead of in a bridging fashion through the N(7) and O(6) sites as previously noted. © 2003 The Royal Society of Chemistry.
author list (cited authors)
Chifotides, H. T., Hess, J. S., Angeles-Boza, A. M., Galán-Mascarós, J. R., Sorasaenee, K., & Dunbar, K. R.