Reactions of an Osmium-Hexahydride Complex with Cytosine, Deoxycytidine, and Cytidine: The Importance of the Minor Tautomers

Complex OsH6(PiPr3)2 (1) deprotonates cytosine to give molecular hydrogen and the d4-trihydride derivative OsH3(cytosinate)­(PiPr3)2 (2), which in solution exists as a mixture of isomers containing κ2-N1,O (2a) and κ2-N3,O (2b) amino-oxo and κ2-N3,N4 (2c) imino-oxo tautomers. The major isomer 2b associates with the minor one 2c through N–H···N and N–H···O hydrogen bonds to form [2b·2c]2 dimers, which crystallize from saturated pentane solutions of 2. Complex 1 is also able to perform the double deprotonation of cytosine (cytosinate′) to afford the dinuclear derivative (PiPr3)2H3Os­(cytosinate′)­OsH3(PiPr3)2 (3), where the anion is coordinated κ2-N1,O and κ2-N3,N4 to two different OsH3(PiPr3)2 metal fragments. The deprotonation of deoxycytidine and cytidine leads to OsH3(deoxycytidinate)­(PiPr3)2 (4) and OsH3(cytidinate)­(PiPr3)2 (5), respectively, containing the anion κ2-N3,N4 coordinated. Dimer [2b·2c]2 and dinuclear complex 3 have been characterized by X-ray diffraction analysis.