Chiral Recognition of Racemic Proline based on Chiral Macrocyclic Nickel(II) Complex: Synthesis and Crystal Structures

Two dinuclear carbonato-bridged nickel(II) complexes formulated as [Ni(rac-L)]2(µ-CO3)(H2O)(im)4(ClO4)2 (1) and [Ni(SS-L)]2(µ-CO3)(H2O)(im)4(ClO4)2 (2) (L = 5,5,7,12,12,14-hexamethyl-1,4,8,11-tetraazacyclotetradecane, im = imidazole) were isolated from the reactions of [Ni(rac-L)](ClO4)2 and [Ni(SS-L)](ClO4)2 with imidazole in the air, respectively, and a hydrocarbonato-coordinated nickel(II) complex formulated as [Ni(rac-L)](HCO3)(ClO4) (3) was reacted with obtained when [Ni(rac-L)](ClO4)2 reacted with l-cysteine under weakly basic conditions in the air. We found that the macrocyclic nickel(II) complexes can easily take up and fix atmospheric CO2 at room temperature. Single-crystal X-ray diffraction analyses revealed of all three complexes that the central Ni(II) atoms all have a six-coordinated distorted octahedral coordination geometry, and the carbonate anion bridges two Ni(II) atoms in a tridentate fashion to form dimers in complexes 1 and 2, and the hydrocarbonate coordinates with Ni(II) in a didentate fashion in complex 3. The monomers of {[Ni(RR-L)]2(µ-CO3)(H2O)}2+/{[Ni(SS-L)]2(µ-CO3)(H2O)}2+ are connected through hydrogen bonds to generate one-dimensional right- and left-handed helical chains in complex 1. The chiral nature of complex 2 has been confirmed by CD spectroscopy.

CO 2 fixation by macrocyclic nickel(II) complexes: synthesis and structures of helical chains constructed via hydrogen bonds involving imidazole

The selective hydrogenolysis of CO bonds is critical for the effective valorization of lignin. Herein, we synthesized a series of highly efficient NixCoyAl-T catalysts by a coprecipitation-calcination-reduction method and evaluated their catalytic hydrogenolysis performance towards the CO bonds of lignin-derived aryl ether, using isopropanol as the hydrogen donor source. The results revealed that the Ni0.5Co1.5Al-600 catalyst displayed superior activity and its catalytic performances were strongly influenced by the Ni/Co molar ratios and calcination temperatures. The enhanced dispersion of metal particles and the electron transfer from Ni to Co in Ni0.5Co1.5Al-600 catalyst facilitated the cleavage of CO bonds in lignin model compounds. Furthermore, the β-benzyl-H atom in 2-phenoxy-1-phenylethanol (PPE) also contributes to the cleavage of Caliphatic-O bonds. Under optimized reaction conditions (180 ℃, reaction time 2 h), PPE was completely converted over the Ni0.5Co1.5Al-600 catalyst, and the yield of ethylbenzene and cyclohexanol reached 95.91wt% and 85.73wt%, respectively. These findings demonstrate that the NixCoyAl-T catalytic system holds great promise for the production of valuable chemicals from lignin under mild conditions. 

Selective hydrogenolysis of C-O bonds in lignin model compounds and Kraft lignin over highly efficient NixCoyAl catalysts

The development of sustainable catalysts for the conversion of carbon dioxide into value-added chemicals is an effective way to alleviate environmental problems. This study examined the cyclic addition of epoxy propane (PO) and carbon dioxide to propylene carbonate (PC) in a microchannel using a range of imidazol-based deep eutectic ionic liquids (DEILs). By examining the effects of various operating circumstances, such as reaction temperature, operating pressure, residence time, and CO2 to PO molar ratio, the performance of the microreactor was evaluated. According to the findings, the residence time was drastically decreased, going from a few hours in a traditional stirring reactor to just over a minute in a microreactor. The yield of PC could reach 94.23%, and the space-time yield could reach 10.063 g/g/h at 80 °C, 1 MPa, and a residence time of 19 min, while they were 92.32% and 0.406 g/g/h, respectively, for 7 h in a traditional reactor under the same circumstances. It was 24.8 times higher in space-time yield for the microchannel. 

Fang Liu

Papers

CO 2 fixation by macrocyclic nickel(II) complexes: synthesis and structures of helical chains constructed via hydrogen bonds involving imidazole

Selective hydrogenolysis of C-O bonds in lignin model compounds and Kraft lignin over highly efficient NixCoyAl catalysts

Highly efficient synthesis of cyclic carbonate with CO2 under mild condition catalyzed by deep eutectic solvents in a microreactor