N-H and N-C Bond Activation of Pyrimidinic Nucleobases and Nucleosides Promoted by an Osmium Polyhydride

Complex OsH6((PPr3)-Pr-i)(2) (1) reacts with 1-methylthymine and 1-methyluracil to give OsH3((PPr3)-Pr-i)(2)(nucleobase') (2, 3) containing the deprotonated nucleobases (nucleobase') kappa(2)-N,O coordinated by the nitrogen atom at position 3 and the oxygen bonded to the carbon atom of the ring at position 4. Similarly, the reactions of 1 with thymidine, 5-methyluridine, deoxyuridine, and uridine lead to OsH3((PPr3)-Pr-i)(2)(nucleoside') (4-7) with the deprotonated nucleoside (nucleoside') kappa(2)-N,O coordinated by the nitrogen atom at position 3 and the oxygen bonded to the carbon atom at position. 4 of the nucleobases. Treatment of complexes 5 and 7, containing nucleosides derived from ribose, with OsH2Cl2((PPr3)-Pr-i)(2) (8) in the presence of Et3N affords dinuclear species OsH3((PPr3)-Pr-i)(2)(nucleobase')-(ribose)((PPr3)-Pr-i)(2)H2Os (9, 10) formed by two different metal fragments. Complex 1 also promotes the cleavage of the N-C bond of 2-7 to give the dinuclear species {OsH3((PPr3)-Pr-i)(2)}(2)(nucleobase") (11, 12) with the nucleobase skeleton (nucleobase") kappa(2)-N,O coordinated to both metal fragments. These compounds can be also prepared by reaction of 1 with 0.5 equiv of thymine and uracil. The use of 1:1 hexahydride:nucleobase molar ratios gives rise to the preferred formation of the mononuclear complexes OsH3((PPr3)-Pr-i)(2)(nucleobase"') (13, 14; nucleobase"' = monodeprotonated thymine or uracil). The X-ray structures of complexes 6, 11, and 14 are also reported.