Synthesis and Electrochemistry of Schiff Base Cobalt(III) Complexes and Their Catalytic Activity for Copolymerization of Epoxide and Carbon Dioxide

Abstract

A series of cobalt complexes with N,N,O,O‐tetradentate Schiff base ligands were prepared. All the complexes were characterized by spectroscopy and electrochemical methods. An X‐ray crystal structure analysis revealed that L1‐CoIII‐dnp was monomeric with a six‐coordinated central cobalt(III) atom in the solid state. The complexes were employed as catalysts for the alternating copolymerization of CO2 and racemic propylene oxide. End group analysis of the resulting polymer provided strong evidence for a monomer insertion mechanism for the propagation step. The catalytic activity was interpreted using the redox potential of cobalt(II/III) for the L‐CoIII‐dnp complexes, which offered a measure of the bond strength, or the degree of inertness of the axial ligand, to promote or suppress the monomer insertion.magnified image

Alternating copolymerization of CO2 with propylene oxide and terpolymerization with aliphatic epoxides by bifunctional cobalt Salen complex

“…Numerous attempts to isolate complex 1 in some solvents proved to be unsuccessful. Compared with the structures of N,N'-bis(3,5-di-tertbutylsalicylidene)-1,2-cyclohexanediamine Co III 2,4-dinitrophenoxy (complex 2) and 2,2-dimethyl-1,3-propylene bis(3,5-di-tert-butylsalicylideneimino) Co III 2,4-dinitrophenolate, 26,27 complex 1 should be a stable six-coordinated central Co octahedron (Figure 1). Simple Salen Co III X complexes alone have proven to be inactive under low CO 2 pressure or at elevated temperature, where they are reduced to Co II derivatives.…”

“…Methylene chloride, hexane and chloroform were distilled from CaH 2 under argon. N,N¢-[2,2¢-bis(nitrilomethylidyne)]bis [a-methyl-4-(morpholin-1-ylmethyl)-6-tert-butyl phenolato]-1,2-cyclohexanediamine 24,25 and N,N¢-[2,2¢-bis(nitrilomethylidyne)]bis[a-methyl-4-(morpholin-1-ylmethyl)-6-tert-butyl phenolato]-1,2-cyclohexanediamino [26][27][28][29] Co II were prepared according to methods reported in the literature.…”

ESIPT reaction of potential bioactive heterocyclic Schiff base: Atomic visualization coupled with in vitro spectroscopy

“…The intramolecular electron transfer and proton transfer reactions of Schiff bases containing nitrogen, sulphur and/or oxygen have been extensively investigated over few decades owing to their rich photochemical and photophysical properties which enables them to find wide range of important applications [17][18][19][20]. Heterocyclic Schiff base like benzothiazole, benzoxazoles and benzimidazole which are also medicinally important compounds as they comprise bioactive scaffold of many drugs [8].…”

Alternating copolymerization of carbon dioxide and cyclohexene oxide catalyzed by salen CoIII(acetate) complexes

“…As shown in Fig. 2, the structure is indeed a six-coordinate octahedral as the structure of the salen Co III (2,4-dinitrophenoxy) [35, 36]. X-ray diffraction data showed that the crystal was analogous monomeric structures.…”

“…Coates and coworkers [34] reported that a five-coordinated cobalt complex is pseudo square-pyramidal with Co located slightly above the plane of the salen ligand in the direction of the axial ligand. Recently, we reported the X-ray crystal structure of the salen Co III (2,4-dinitrophenoxy) is six coordinated [35, 36]. As far as we are aware, the crystal structure of the cobalt Schiff base complexes with axial acetate ligand has not been reported.…”