Hafnocene Puts N₂ And CO₂ To Work

If chemists could take N₂ and CO₂ out of the air and convert them into value-added chemicals, they would really have something. Wesley H. Bernskoetter, Emil Lobkovsky, and Paul J. Chirik of Cornell University have opened a door to that possibility by preparing a substituted hydrazine from N₂ and CO₂ in a reaction mediated by hafnocene, a hafnium bis(cyclopentadienyl) complex (Angew. Chem. Int. Ed., DOI: 10.1002/anie.200604099). Chirik's group has previously shown that hafnocene and zirconocene can preferentially bind N₂ side-on (rather than end-on) between two of the metallocene molecules, an orientation that sets up N₂ for further reaction (Dalton Trans. 2007, 16). For hafnocene, they now report that reacting the hafnocene-N₂ complex with CO₂ leads to insertion of CO₂ into the Hf-N bonds (shown). Addition of Me₃SiI (Me = methyl) liberates the N₂-CO₂ core by forming the substituted dicarboxyl hydrazine (Me₃Si)₂N-N(CO₂SiMe₃)₂ mixed with iodinated hafnocene, which can be recycled.