Synthesis, Characterization, and Catalytic Study of Amine-Bridged Bis(phenolato) Co(II) and Co(II/III)-M(I) Complexes (M = K or Na)

Abstract

Co(II) complexes 1−3 bearing amine-bridged bis(phenolato) complexes have been synthesized through reactions of bis(phenols) with CoCl 2 or Co(OAc) 2 . Oxidation of the Co(II) complex with air resulted in partial oxidation, generating mixed valence Co(II/III) complexes 4 and 5. In addition, due to the presence of alkali compounds (KOAc and NaOMe), 4 and 5 formed as Co-alkali metal heterometallic complexes, which are the first example of mixed valence Co(II/III)-M(I) (M = K or Na) complexes. Complexes 1−5 showed good activity in the cycloaddition of epoxides and CO 2 under atmospheric pressure, generating cyclic carbonates in 40−99% yields. Co(II/III)-Na(I) complex 5 performed better in reactions of bulkier substrates, underlining the enhanced activity of mixed valence Co-alkali metal heterometallic complexes. On the contrary, complex 5 showed limited activity in copolymerization of epoxide and CO 2 .

Synthesis of Heterometallic Rare Earth(III)–Cobalt(II) Complexes and Their Application in Alternating Copolymerization of Cyclohexene Oxide and Carbon Dioxide

“…We recently reported synthesis of Co(II) bis(phenolate) complexes through reaction of bis(phenols) with Co(II) precursors. [ 26 ] However, the attempt to prepare a Co(II) complex with tris(phenolate) ligand under similar conditions failed (Scheme 1). No reaction of H 3 L and Co(OAc) 2 occurred in heated THF in the presence or absence of NEt 3 , while with KOH an ill‐defined mixture was obtained.…”

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

“…Amino‐bridged bis(phenolato) Co(II) complexes 32 – 34 were reported by Yao and coworkers (Figure 9). [52] Furthermore by addition of alkali compounds (KOAc, NaOMe) they observed the formation of multinuclear herometallic species with mixed valence Co(II/III) and M(I) (M=Na or K) 35 due to the oxidation of Co(II) by air. In the presence of TBAI all these complexes are active in the cycloaddition of CO 2 to ECH (0.1 MPa; 45–75 °C, 24 h).…”

Cycloaddition of di-substituted epoxides and CO2under ambient conditions catalysed by rare-earth poly(phenolate) complexes

“…A large number of catalysts have been developed to catalyse the cycloaddition reaction, including transition metals (e.g., Cr, [15][16][17] Fe, [18][19][20][21] Co, [22][23][24][25][26][27] and Zn [28][29][30][31][32][33] ), main group metals (e.g., Mg, [34][35][36] Al, [37][38][39][40][41][42] Ca [43][44][45][46] ), rare-earth metal catalysts [47][48][49][50][51][52][53][54][55][56][57] and organocatalysts. 5,[58][59][60][61][62][63]…”

“…A large number of catalysts have been developed to catalyse the cycloaddition reaction, including transition metals ( e.g. , Cr, 15–17 Fe, 18–21 Co, 22–27 and Zn 28–33 ), main group metals ( e.g. , Mg, 34–36 Al, 37–42 Ca 43–46 ), rare-earth metal catalysts 47–57 and organocatalysts.…”