Two Components in a Molecule:  Highly Efficient and Thermally Robust Catalytic System for CO₂/Epoxide Copolymerization

Abstract

Salicylaldehyde compound containing an ammonium salt unit, [2-(HO)-3-tBu-5-{Bu3N+(CH2)3Si(Me2)}C6H2C(O)H][BF4 -], is prepared from which a Salen-type ligand and its cobalt(III) complex, (Salen-1)CoX (1: Salen-1 = [trans-N,N‘-bis(3-tBu-5-(Bu3N+(CH2)3Si(Me2)-salicylidene)-1,2-cyclohexanediamine)]X2; X = 2,4-dinitrophenolate), is prepared. Complex 1 shows high activity for CO2/(propylene oxide) copolymerization even at a condition of high [propylene oxide]/[catalyst] ratio and high temperature up to 90 °C, at which conditions a typical binary system of [(Salen)CoX]/[PPNCl] does not yield any copolymer. A very high TOF (up to 3500 h-1) and TON (up to 14500) are achieved, which have never been attained with other catalytic systems. The high selectivity (>84%) for the formation of copolymer over cyclic carbonate and the high molecular weight of the obtained polymers (M n = 53000−95000) are the other merits of the catalyst.

Bifunctional Chiral Catalyst for the Synthesis of Chiral Cyclic Carbonates from Carbon Dioxide and Epoxides

“…To extend the scope of reaction, various substituted terminal epoxides were investigated with 2 Ab as the catalyst (Table 1, entries [14][15][16][17]. Epichlorohydrin and 1,2-epoxybutane were transformed into the corresponding chiral cyclic carbonates in moderate enantiomeric purity (Table 1, entries 14 and 15).…”

“…[4][5][6][7][8][9][12][13][14][15] Meanwhile, a quaternary ammonium group was recently introduced into the frame of the salen ligand, thus leading to a novel bifunctional catalyst in one molecule. [16,17] This type of compound would be a good class of catalyst for the kinetic resolution of racemic epoxides. Herein, we report a convenient route to chiral cyclic carbonates through the kinetic resolution of racemic epoxides with a new bifunctional chiral catalyst (Figure 1).…”

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

“…However, Co Schiff base complexes are not highly active at a high monomer/catalyst mole ratio in conjunction with a Lewis base or organic salt, which prevents them from becoming commercially viable. 19 Contrarily, one Co Schiff base complex showed a moderate catalytic activity at only high pressure. However, the complex was inactive at low CO 2 pressure.…”

“…20 The complex exhibited high selectivity for polycarbonate over cyclic carbonate. After this study, the quaternary ammonium salt unit was anchored by Lee et al, 19 and a Lewis base moiety was anchored to the Salen ligand by Wang and co-workers. 21 Compared with the binary catalyst systems composed of a Co Schiff base complex and a Lewis base or organic salt, the bifunctional Salen complexes displayed excellent activity and polycarbonate selectivity because the anchored units of aromatic rings had an important role in maintaining the thermal stability and high activity of the catalyst.…”

A Highly Active and Recyclable Catalytic System for CO2/Propylene Oxide Copolymerization

“…[6,7] These values, which were achieved with 2 in the copolymerization of CO 2 and propylene oxide, are still low enough to warrant further improvement, [7] because low activity means higher catalyst cost and higher levels of catalyst-derived metal residue in the resin.[8] This metal residue either colors the resin or causes toxicity. For the TON of 14 500 attained with 2, the residual cobalt level in the resin reached 40 ppm unless it was removed.…”