Effective and Reversible Carbon Dioxide Insertion into Cerium Pyrazolates. Issue 14 (30th January 2020)

• Record Type: Journal Article
• Authors: Bayer, Uwe; Werner, Daniel; Maichle‐Mössmer, Cäcilia; Anwander, Reiner
• Is Part Of: Angewandte Chemie international edition. Volume 59:Issue 14(2020)
• Page Start: 5830
• Page End: 5836
• Publication Date: 2020-01-30
• Subjects: carbon dioxide -- cerium -- cycloaddition -- epoxides -- pyrazolates; Chemistry -- Periodicals; 540
• DOI: 10.1002/anie.201916483
• Languages: English
• ISSNs: 1433-7851

Abstract

Abstract: The homoleptic pyrazolate complexes [Ce III 4 (Me2 pz)12 ] and [Ce IV (Me2 pz)4 ]2 quantitatively insert CO2 to give [Ce III 4 (Me2 pz⋅CO2 )12 ] and [Ce IV (Me2 pz⋅CO2 )4 ], respectively (Me2 pz=3, 5‐dimethylpyrazolato). This process is reversible for both complexes, as observed by in situ IR and NMR spectroscopy in solution and by TGA in the solid state. By adjusting the molar ratio, one molecule of CO2 per [Ce IV (Me2 pz)4 ] complex could be inserted to give trimetallic [Ce3 (Me2 pz)9 (Me2 pz⋅CO2 )3 (thf)]. Both the cerous and ceric insertion products catalyze the formation of cyclic carbonates from epoxides and CO2 under mild conditions. In the absence of epoxide, the ceric catalyst is prone to reduction by the co‐catalyst tetra‐ n ‐butylammonium bromide (TBAB). Abstract : CO2 sponges : Cerous and ceric pyrazolates have been demonstrated to insert carbon dioxide and afford the complexes [Ce III 4 (Me2 pz⋅CO2 )12 ] and [Ce IV (Me2 pz⋅CO2 )4 ]. The insertion is reversible and can be exploited for the catalytic formation of cyclic carbonates from epoxides. The potentially reducing behavior of tetra‐ n ‐butylammonium bromide (TBAB) as a co‐catalyst is also revealed.