9-METHYLADENINE COMPLEXES OF PLATINUM(II) STABILIZED BY TRIMETHYLPHOSPHINE - USE OF N-15 NUCLEAR-MAGNETIC-RESONANCE SPECTROSCOPY TO ASSIGN THE COORDINATION SITE

The new 9-methyladenine (made) complexes cis-[Pt(PMe(3))(2)(made)(2)][ NO3](2) and cis-[{Pt(PMe(3))(2)(made - H)}(2)][NO3](2) have been prepa red and characterized. They are formed by treating stoichiometric amou nts of the nucleobase with an aqueous solution of cis-[Pt(PMe(3))(2)(N O3)(2)] at autogenous and neutral pH, respectively. A detailed multinu clear (H-1, P-31, Pt-195, C-13 and N-15 at natural abundance) NMR inve stigation in (CD3)(2)SO indicated that in the mononuclear complex the adenine ligands are N(1)-co-ordinated and that rotation around the met al-nitrogen bonds is slow on the NMR time-scale leading to the presenc e of two conformers with a relative abundance of ca. 2 : 1. In the din uclear complex the NH2-deprotonated adenine acts as a bridging ligand through the N(1) and N(6) atoms. The sites of metal binding are clearl y evidenced in the N-15 NMR spectra by the remarkable shifts shown by the co-ordinated nitrogens (60 ppm upfield for the endocyclic atom and 25 ppm downfield for the exocyclic one, with respect to the unco-ordi nated nucleobase) and their coupling with the P-31 nucleus of the liga nd in mutual trans position ((2)J(NP) ca. 60 Hz).