Organomagnesia: Reversibly High Carbon Dioxide Uptake by Magnesium Pyrazolates.

A series of new pyrazolate and mixed pyrazolate/pyrazole magnesium complexes is described and their reactivity toward carbon dioxide is examined. The dimeric complex [Mg(pz )] inserts CO instantly and quantitatively forming the tetrameric complex [Mg(CO·pz )] and monomeric donor-stabilized [Mg(CO·pz )(thf)]. Complexes of the type [Mg(pz) (Hpz)] (R = iPr, tBu) engage in similar insertion reactions involving dissociation of the carbamic acid HOOCpz. Even solid polymeric derivatives [Mg(pz)] (R = Me, H) react instantaneously and exhaustively with CO, the resulting [Mg(CO·pz)] featuring a CO capacity of 35.7 wt% (8.2 mmol g). All described magnesium pyrazolates display completely reversible CO uptake in solution and in the solid state, respectively, as monitored via VT H NMR and in situ FTIR spectroscopy as well as thermogravimetric analysis. Fluorinated [Mg(pz)(thf)] does not yield any isolable CO insertion product but exhibits the highest activity in the catalytic transformation of epoxides and CO to cyclic carbonates.