Coordination Modes of 9‐Methyladenine in cis ‐Platinum( II ) Complexes with Dimethyl(phenyl)phosphanes as Ancillary Ligands − Synthesis and Characterization of cis ‐[PtL 2 (9‐MeAd) 2 ](NO 3 ) 2 , cis ‐[PtL 2 {9‐MeAd(−H)}] 3 (NO 3 ) 3 , and cis ‐[L 2 Pt{9‐MeAd(−H)}PtL 2 ](NO 3 ) 3

Treatment of 9‐methyladenine (9‐MeAd) with cis ‐[PtL 2 (NO 3 ) 2 ] ( 1 ) (L = PMe 2 Ph) in a 2:1 molar ratio generated the bis(adduct) cis ‐[PtL 2 (9‐MeAd) 2 ](NO 3 ) 2 ( 2 ), which was isolated and fully characterized by multinuclear ( 1 H, 31 P, 13 C, 195 Pt and 15 N) NMR analysis, which showed that the two nucleobases are selectively coordinated through the N1 atom. Small amounts of a mono(adduct) cis ‐[PtL 2 (S)(9‐MeAd)] 2+ ( 3 ) (S = solvent) and of a diplatinated species cis ‐[L 2 Pt(S){9‐MeAd(−H)}PtL 2 ] 3+ ( 4 ) are formed in DMSO solution when 9‐MeAd is present in smaller quantities than 1 . Complex 3 is platinated at N1, with a solvent molecule representing the fourth ligand around the metal center. Complex 4 contains an adenine molecule deprotonated and platinated at N1,N6,N7, with two cis ‐L 2 Pt units bonded to nitrogen atom N1 and to nitrogen atoms N6 and N7, respectively. With increasing relative concentration of the nucleobase, both complexes 3 and 4 progressively convert into the bis(adduct) 2 , the only species detectable in solution when the Ad/Pt molar ratio is 2:1. The trinuclear compound cis ‐[L 2 Pt{9‐MeAd(−H)}] 3 (NO 3 ) 3 ( 5 ) (L = PMe 2 Ph), containing an NH 2 ‐deprotonated nucleobase bridging the metal centers through the N1 and N6 atoms, is quantitatively formed when the dinuclear hydroxo complex cis ‐[Pt(μ‐OH)L 2 ] 2 (NO 3 ) 2 ( 6 ) reacts with 9‐MeAd in CH 3 CN solution. The isolated complex was fully characterized by multinuclear NMR spectroscopy and mass spectrometry. It appears to be stable in solution in CH 3 CN and chlorinated solvents, whereas in DMSO it partially converts into a new species, probably the dinuclear analog cis ‐[PtL 2 {9‐MeAd(−H)}] 2 (NO 3 ) 2 , in which the adenine maintains its coordination mode. At equilibrium the trinuclear/dinuclear species molar ratio is 20:1. Through the addition of a stoichiometric amount of nitrate 1 to a DMSO solution of 5 we were able to generate the diplatinated compound 4 in high yield. Complex 4 displays a new coordination mode for the adeninate ion, with N1 bonded to one platinum atom whereas N6 and N7 are chelated to a second one. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2003)