Dinuclear Nickel Complexes Using Hexadentate Benzothiazole-Based Diamine-Bisphenolate Ligands: Highly Active Catalysts for Copolymerization of Carbon Dioxide with Epoxides

Abstract

We reported for the first time the utilization of hexadentate benzothiazole-based diamine-bisphenolate ligands to synthesize structurally well-characterized dinickel dicarboxylate complexes and studied their catalysis for copolymerization of carbon dioxide with epoxides. Dinickel carboxylate complexes having a 1,3-diamine-bridged backbone were demonstrated to be high-performance catalysts for alternating copolymerization of CO 2 and cyclohexene oxide (CHO) with high product selectivity. Particularly, acetate-supported nickel complex 2 enabled us to promote such CO 2 -copolymerization of this kind with a maximum turnover frequency of up to 2600 h −1 and gave good molecular weight controllability under high-pressure conditions. It is worth noting that bimetallic Ni catalyst 2 was also capable of mediating the catalytic CO 2 -polymerization of alicyclic epoxides at atmospheric pressure. Kinetic investigations of CO 2 /CHO copolymerization by 2 allowed us to determine the rate equation of −d[CHO]/dt = k p [2] 1 [CHO] 1 , and such catalysis exhibited a first-order dependence on both dinickel complex and CHO concentrations.

Bimetallic nickel complexes containing imidazole-based phenolate ligands as efficient catalysts for the copolymerization of carbon dioxide with epoxides

“…However, Ni complex 10 bearing 2,4,6-trinitrophenolate coligands was inactive in the same CO 2 -copolymerization, possibly due to the poor initiating group for TNP moieties. These results agree with the previous observations of nickel complex-mediated CO 2 /CHO copolymerization by a benzothiazole-based salan-type catalyst system, 36 in which dinickel complex 1 containing the methyl N -substituted salan-type ligand scaffold and acetate as coligands was the most efficient. Given the impressive performance in CO 2 -copolymerization of CHO by 1 , the same complex was selected to investigate the detailed catalytic characteristics including the temperature effect and controllability of the obtained molecular weight.…”

“…As displayed in Scheme S1(b), † the methyl or ethyl N-substituted proligand (L 1 -H 2 or L 2 -H 2 ) could be directly prepared by utilizing the one-pot Mannich condensation of triphenylimidazole-derived phenol and paraformaldehyde with N,N′-dimethylethylenediamine or N,N′-diethylethylenediamine based on a modified procedure from the literature. 32,36 The structures of these imidazole-containing diamine-bisphenol ligand precursors were fully determined by NMR spectroscopy and elemental analysis. Scheme 1 illustrates the synthetic pathways for a series of bimetallic nickel complexes coordinated on imidazole-containing phenolate ligands of this type.…”

“…Among these ligand scaffolds, several different N-involving heterocyclic moieties, such as benzotriazole, pyrazolyl and benzothiazole groups, were successfully bonded to diaminebisphenolates, as exhibited by types A-C in Chart 1, and the corresponding dinickel complexes could be synthesized to evaluate their catalytic performances for the ROCOP of CHO with CO 2 . [34][35][36] Upon comparing the catalysis outcomes for the same copolymerization, the bis(benzoate) dinickel complex coordinated on a benzotriazole-based 1,3-diamine-bisphenolate ligand was demonstrated to display the highest catalytic activity under optimized conditions among these binickel catalysts. 37 These results also suggested that the N-heterocyclic motif in the ancillary ligand may have significant effects on the catalytic efficiency during the CO 2 /epoxide ROCOP.…”

Bimetallic Nickel Complexes as Effective and Versatile Catalysts for Copolymerization of Epoxides with Carbon Dioxide or Phthalic Anhydride: Catalysis and Kinetics

“…Based on the above kinetic investigations, the reaction rate of such CO 2 copolymerization could be presented as −d[CHO]/d t = k p [ 3 ] 1 [CO 2 ] 0 [CHO] 1 , which followed the first-order dependence on both dinickel catalyst and CHO concentrations as well as the zero order on CO 2 . These results agree well with previous outcomes for nickel complex-catalyzed CO 2 /CHO copolymerization by nitrogen-heterocycle containing salan-type derivatives. ,, …”

“…These results agree well with previous outcomes for nickel complex-catalyzed CO 2 /CHO copolymerization by nitrogen-heterocycle containing salan-type derivatives. 32,37,41 Based on structural analyses of dinickel complexes, kinetics data, and polymer characterization by MALDI-TOF mass spectrometry and the earlier reported literature, 19,32 a plausible copolymerization mechanism mediated by complex 3 was proposed as illustrated in Scheme 3. Except for the dissociation of THF from complex 3 and ring-opening of CHO by the nucleophilic iodide group, the catalytic behaviors of CO 2 /CHO copolymerization by 3 may be similar to the previous mechanistic studies for the same polymerization catalysis utilizing a dinuclear nickel benzoate complex incorporating the same ancillary ligand.…”