Anion variation on a cobalt(iii) complex of salen-type ligand tethered by four quaternary ammonium salts for CO2/epoxide copolymerization

Abstract

Anion exchange of BF(4)(-) occurs by stirring a cobalt(III) complex of salen-type ligand tethered by four quaternary ammonium BF(4)(-) salts over a slurry of NaX in CH(2)Cl(2), affording a complex containing four X's per cobalt (X = 2,4,5-trichlorophenolate, 6; X = 4-nitrophenolate, 10; X = 2,4-dichlorophenolate, 12). The (1)H and (13)C NMR spectra are in agreement with an unusual imine uncoordinated structure. The two salen-phenoxys and the two X's persistently coordinate with cobalt(III) to form a square planar cobaltate complex while the other two X's scramble through coordination and decoordination to the axial sites of the square plane. Another form of the complex (X = 2,4,5-trichlorophenolate, 14; X = 4-nitrophenolate, 15; X = 2,4-dichlorophenolate, 16) is also prepared, in which the scrambling two X's in 6, 10, or 12 are replaced with the corresponding [X...H...X](-) homoconjugate. These complexes, which adopt an unusual imine uncoordinated structure, are excellent catalysts for CO(2)/propylene oxide copolymerization (turnover frequency (TOF), 8300-16,000 h(-1)). In all cases, the complex containing the homoconjugate [X...H...X](-) shows higher activity than the corresponding phenol-free complex. Among the prepared complexes, 4-nitrophenol-4-nitrophenolate homoconjugate complex 15 showed the best performance (TOF, 16,000 h(-1); selectivity, 98%; M(n), 273,000), allowing for replacement of the explosive 2,4-dinitrophenolate complex.

What's new with CO2? Recent advances in its copolymerization with oxiranes

“…17 Later improvements involved exchanging the 2,4-dinitrophenoxides for 2,4-dichlorophenoxides or 4-nitrophenoxides for increased laboratory safety. 19 Similarly great activity has been found utilizing the asymmetric (salen)CoX complexes 3 and 4 synthesized by Lu et al, featuring an appended bulky amine or quaternary ammonium salt at the 3-position of one phenyl ring, respectively (Fig. 4).…”

Thermal and weathering degradation of poly(propylene carbonate)

“…Preparation of 1 and polymerization were carried out through the reported method and conditions [6,13].…”

“…Binding situates both components in proximity regardless of low catalyst concentration or high polymerization temperature, consequently resulting in high turnover number (TON) and turnover frequency (TOF). Later, we found that complex 1 adopts an unusual binding mode, where the imine-nitrogens on the Salen-type ligand do not coordinate but, instead, the counter anions of the tethered quaternary ammonium units coordinate with cobalt [12,13]. Complex 1 displays a high TON of up to 16,000 and TOF of 16000 h À1 .…”

Cyclohexene oxide/carbon dioxide copolymerization by chromium(iii) amino-bis(phenolato) complexes and MALDI-TOF MS analysis of the polycarbonates

“…6 Also, CO 2 can be considered a renewable resource, 7 so its utilization is preferred over dwindling fossil fuels that are still the main basis for commercial polycarbonate synthesis. For example, complexes with Zn, [10][11][12] Al, 13 Co, [14][15][16][17][18][19][20][21] Fe, [22][23] Mg, 24 and Cr [25][26][27][28][29][30][31][32][33][34][35][36][37][38][39][40][41][42] have proven to be active in CO 2 /epoxide copolymerization. 9 Recently, a large number of complexes have been developed as active catalyst precursors for the copolymerization of CO 2 and epoxides.…”