Organomagnesia: Reversibly High Carbon Dioxide Uptake by Magnesium Pyrazolates

Abstract

Abstract 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(pztBu,tBu)2]2 inserts CO2 instantly and quantitatively forming the tetrameric complex [Mg(CO2·pztBu,tBu)2]4 and monomeric donor‐stabilized [Mg(CO2·pztBu,tBu)2(thf)2]. Complexes of the type [Mgx(pzR,R)2x(HpzR,R)y]n (R = iPr, tBu) engage in similar insertion reactions involving dissociation of the carbamic acid HOOCpzR,R. Even solid polymeric derivatives [Mg(pzR,R)2]n (R = Me, H) react instantaneously and exhaustively with CO2, the resulting [Mg(CO2·pz)2]m featuring a CO2 capacity of 35.7 wt% (8.2 mmol g−1). All described magnesium pyrazolates display completely reversible CO2 uptake in solution and in the solid state, respectively, as monitored via VT 1H NMR and in situ FTIR spectroscopy as well as thermogravimetric analysis. Fluorinated [Mg2(pzCF3,CF3)4(thf)3] does not yield any isolable CO2 insertion product but exhibits the highest activity in the catalytic transformation of epoxides and CO2 to cyclic carbonates.

Keywords

• carbon dioxide
• catalysis
• epoxides
• magnesium
• pyrazolates