Synthesis, characterization, and reactivity of [Li(N6,N9-Me2Ade(-H))]: a structurally characterized lithiated adenine

The reaction of N6,N9-dimethyladenine (N6,N9-Me2Ade, 1) with methyllithium in aprotic solvents such as tetrahydrofuran and pyridine resulted in the formation of the lithiated adenine Li(N6,N9-Me2Ade-H)] (2) that was isolated as highly air and moisture sensitive tetrahydrofuran (2.(1/4)THF) and pyridine (2.py) adducts in excellent yields (>90%). The identities of 2.(1/4)THF and 2.py were confirmed by 1H and 13C NMR spectroscopy. In crystals of 2.(3/2)py, the dimethyladeninato ligand exhibited a chelating and bridging coordination mode (kappa2N6,N7:kappaN3) resulting in a 1-D polymeric chain-like structure in which the tetrahedral coordination sphere of the lithium atoms was completed by a pyridine molecule. Reactions of 2.(1/4)THF with electrophiles such as MeI, Me3SiCl, and Me3SnCl resulted in high yields (88-98%) of the formation of the adenine deriatives N6,N6,N9-Me3Ade-H (3), N6-(SiMe3)-N6,N9-Me2Ade(-H) (4), and N6-(SnMe3)-N6,N9-Me2Ade-H (5), respectively. Compounds 3-5 were characterized by 1H, 13C, 29Si (4), and 119Sn (5) NMR spectroscopy and MS investigations, and the stannylated derivative 5 also was characterized by single-crystal diffraction analysis exhibiting a mononuclear structure. The reaction of the stannylated adenine 5 with n-BuLi in n-hexane proceeded in the sense of a tin-lithium transmetalation reaction yielding the solvent-free lithium adeninate Li(N6,N9-Me2Ade-H)] (2) in 90% yield.