Synthesis, characterization, and structure of [{PtMe3(9-MeA)}3] (9-MeAH=9-methyladenine):: A cyclic trimeric platinum(IV) complex with a nucleobase

Reaction of [{PtMe(3)l}(4)] with AgOAc in acetone results in formation of trimethylplatinum(IV) acetate (1) that reacts with 9-methyladenine (9-MeAH) in ratio 1:1 with its deprotonation yielding a trim ethyl (9-methyladeninato)platinum-(IV) complex (2) that was obtained from acetone/diethyl ether as [{PtMe3(9-MeA)}(3)].Me2CO (2a) and from chloroform/diethyl ether as [{PtMe3(9-MeA)}(3)].1.5Et(2)O.2H(2)O (2b). Single-crystal X-ray investigations revealed that 2a and 2b in the solid state form cyclic trimeric molecules in which three PtMe3 moieties are bridged by deprotonated 9-methyladenine ligands in mu-kappaN(1):kappa(2)N(6),N-7 coordination mode. The methyladeninato ligands include angles with the plane defined by the Pt-3 unit between 55.9(3)degrees and 66.6(3)degrees. Thus, the structures of the cyclic trimers resemble hollow truncated cones, Crystals of the acetone solvate 2a consist of stacks of unidirectional trimeric molecules the solvate acetone molecules lie between the trimers. In the crystals of complex 2b, the trimeric molecules are arranged head-to-head, and the cavity between is filled with four water molecules. Complex 2 was also fully characterized by H-1, C-13, and Pt-195 NMR spectroscopies. The existence of the cyclic trimeric structure of complex 2 in acetone solution was confirmed by ESI mass spectrometry exhibiting the protonated trimeric complex [{PtMe3-(9-MeA)}(3)H](+) [2 + H](+) (m/z 1165) as base peak. CID experiments of that parent ion showed as main fragmentation processes loss of two methyl ligands (probably as ethane) and cleavage of a methyladenine ligand.