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

Complex OsH6(PiPr3)2 (1) reacts with 1-methylthymine and 1-methyluracil to give OsH3(PiPr3)2(nucleobase’) (2, 3) containing the deprotonated nucleobases (nucleobase’) κ2-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(PiPr3)2(nucleoside’) (4–7) with the deprotonated nucleoside (nucleoside’) κ2-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(PiPr3)2 (8) in the presence of Et3N affords dinuclear species OsH3(PiPr3)2(nucleobase’)-(ribose)­(PiPr3)2H2Os (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(PiPr3)2}2(nucleobase’’) (11, 12) with the nucleobase skeleton (nucleobase’’) κ2-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(PiPr3)2(nucleobase’’’) (13, 14; nucleobase’’’ = monodeprotonated thymine or uracil). The X-ray structures of complexes 6, 11, and 14 are also reported.