Metal–Cocatalyst Interaction Governs the Catalytic Activity of M^II-Porphyrazines for Chemical Fixation of CO₂

Abstract

Chemical fixation of CO 2 to produce cyclic carbonates can be a green and atomic efficient process. In this work, a series of porphyrazines (Pzs) containing electronwithdrawing groups and central M II ions (where M = Mg, Zn, Cu, and Co) were synthesized and investigated as catalysts for the cycloaddition of CO 2 to epoxides. Then, the efficiency of the Pzs was tested by varying cocatalyst type and concentration, epoxide, temperature, and pressure. Mg II Pz bearing trifluoromethyl groups (1) showed the best conversion, producing, selectively, 78% of propylene cyclic carbonate (PCC), indicating that a harder and stronger Lewis acid is more effective for epoxide activation. Moreover, cocatalyst variation showed a notable effect on the reaction yields. Spectrophotometric titrations, MALDI-TOF mass spectra, and theoretical calculations suggest poisoning of the catalyst when tetrabutylammonium chloride (TBAC) and large amounts of tetrabutylammonium bromide (TBAB) were used in the system. The same was not observed for tetrabutylammonium iodide (TBAI), indicating that the metal−cocatalyst interaction may govern the reaction rate. In addition, two rare examples of crystalline structures were obtained, proving the distorted square pyramidal geometry with water molecule as axial ligand. This is one of the first studies reporting Pzs as catalysts for the chemical fixation of CO 2 , and we believe that the intricate balance between cocatalyst concentration and conversion efficiency shown here may aid future studies in the area.

Single-component, metal-free, solvent-free HO-functionalized 1,2,3-triazole-based ionic liquid catalysts for efficient CO2 conversion

“…2), as it acts in two different steps of the catalytic cycle (Scheme 2): in epoxide ring-opening, where it requires good nucleophilicity to open the epoxide; and in the ring-closure step, when anions that produce good leaving groups can achieve better conversion. 36,37 Our data showed, as seen in Fig. 2, that with the same cation structure, iodide (72 h À1 ) achieved a higher TOF than bromide (58 h À1 ), acetate (53 h À1 ), and less-nucleophilic sulfate (1 h À1 ) or triflate (not active).…”

Recent Advancements in Metal‐catalysts Design for CO2/Epoxide Reactions

“…Recently, Milani and coworkers reported the behavior of various porphyrazines complexes bearing bivalent metal ions [Mg(II), Zn(II), Co(II), Cu(II)] ( 43 – 48 , Figure 12). [57] The initial screening shows a superior performance, with PO (3 MPa; 140 °C, 3 h), of the magnesium catalysts vis‐à‐vis the other metal centers with the highest TOF of 12893 h −1 observed for the complex 43 bearing the electron withdrawing −CF 3 groups.…”

Single-molecule magnet behaviour and catalytic properties of tetrahedral Co(ii) complexes bearing chloride and 1,2-disubstituted benzimidazole as ligands

“…Numerous homogeneous and heterogeneous catalysts have been developed for this purpose, such as ionic liquids, 12–14 organocatalysts and other metal-free catalysts, 15–17 metal oxides and hydroxides, 18–21 metal–organic frameworks, 22,23 and metal complexes. 24–27…”

“…Numerous homogeneous and heterogeneous catalysts have been developed for this purpose, such as ionic liquids, [12][13][14] organocatalysts and other metal-free catalysts, [15][16][17] metal oxides and hydroxides, [18][19][20][21] metal-organic frameworks, 22,23 and metal complexes. [24][25][26][27] Our group has reported an active zinc(II) compound bearing 1,2-disubstituted-benzimidazole ligands to catalyse the transformation of several epoxides to cyclic carbonates. 28 Based on these results, we envisaged the possibility of using analogous cobalt(II) complexes as efficient catalysts since the Lewis acidity associated with the structural and coordinative flexibility of the Co II ion could lead to attractive catalytic performances in this transformation.…”