1.    X.-Y. Dou, J.-Q. Wang, Y. Du, E. Wang, L.-N. He*, Guanidium salt functionalized PEG: an effective and recyclable homogeneous catalyst for the synthesis of cyclic carbonates from CO₂ and epoxides under solvent-free conditions, Synlett, 2007, (19), 3058-3062.[link]

Abstract: A guanidinium bromide covalently bound to CO₂-philic polyethylene glycol is proved to be a highly effective homogeneous catalyst for the eco-friendly synthesis of cyclic carbonates from carbon dioxide and epoxides under mild conditions, which requires no additional organic solvents or co-catalyst. Notably, it has been found that there is a pronouncedly cooperative effect between the catalyst part and the support part. Moreover, the catalyst is able to be reused with retention of high catalytic activity and selectivity. This process looks promising as a strategy for homogeneous catalyst recycling.

2.     J.-S. Tian, C.-X. Miao, J.-Q. Wang, F. Cai, Y. Du, Y. Zhao and L.-N. He*, Efficient synthesis of dimethyl carbonate from methanol, propylene oxide and CO₂ catalyzed by recyclable inorganic base/phosphonium halide-functionalized polyethylene glycol, Green Chem., 2007, 9, 566-571.[link]

Abstract: The cycloaddition of propylene oxide and CO₂ to form propylene carbonate promoted by phosphonium salt convalently bound to polyethylene glycol (PEG), and the transesterification of propylene carbonate with methanol to DMC mediated by PEG-supported K₂CO₃, were separately investigated. Single supported catalyst (K₂CO₃/BrBu₃PPEG₆₀₀₀PBu₃Br) was shown to be active for DMC synthesis from propylene oxide, CO₂ and methanol under mild reaction conditions, even under low CO₂ pressure (2 bar). The catalyst was readily separated and reused without catalyst leaching detected by ³¹P NMR. Notably, excellent yield of DMC and complete conversion of propylene carbonate were reached under optimized reaction conditions. This procedure was also successfully applied to the synthesis of other dialkyl carbonates, and eliminates the requirement for toxic and wasteful feedstocks such as phosgene and carbon monoxide.

3.  J.-Q. Wang, F. Cai, E. Wang, L.-N. He*, Supercritical carbon dioxide and poly (ethylene glycol): an environmentally benign biphasic solvent system for aerobic oxidation of styrene, Green Chem., 2007, 9, 882-887.[link]

Abstract: Aerobic oxidation of styrene catalyzed by PdCl₂/CuCl can be smoothly performed in the supercritical carbon dioxide and poly (ethylene glycol) biphasic system. High conversion of styrene and yield of acetophenone were obtained in the presence of a relatively low catalyst loading. This environmentally benign biphasic catalytic system can be applied to the Wacker oxidation of various alkenes. Furthermore, the PdCl₂-mediated oxidation of styrene was preferentially converted into benzaldehyde using a biphasic scCO₂/PEG system. The PEG could effectively immobilize and stabilize the catalysts. The present biphasic system could facilitate products separation and catalyst recycling. The effects of the reaction parameters such as solvent and CO₂ pressure were also investigated in detail.

4.  Y. Zhao, J.-S. Tian, X.-H. Qi, Z.-N. Han, Y.-Y. Zhuang and L.-N. He*, Quaternary ammonium salt-functionalized chitosan: an easily recyclable catalyst for efficient synthesis of cyclic carbonates from epoxides and carbon dioxide, J. Mol. Catal. A: Chem., 2007, 271(1-2), 284-289.[link]

Abstract: A quaternary ammonium salt covalently bound to chitosan (a functionalized biopolymer) is reported as an efficient and recyclable single-component catalyst for the synthesis of propylene carbonate from propylene oxide and CO₂ without any organic solvent or co-catalyst. Notably, this environmental benign and cost-effective process has great potential to be applied in various continuous flow reactors in industry.

5.     J.-Q. Wang, X.-D. Yue, F. Cai, L.-N. He*, Solventless synthesis of cyclic carbonates from carbon dioxide and epoxides catalyzed by silica-supported ionic liquids under supercritical conditions, Catal. Commun., 2007, 8, 167-172.[link]

Abstract: Silica-supported quaternary ammonium salt proved to be a recyclable and efficient heterogeneous catalyst for the synthesis of cyclic carbonates from epoxides and CO₂ under supercritical conditions, which requires no additional organic solvents either for the reaction or for the separation of product; the work-up procedure is straightforward and the catalyst could be reused without obvious loss of catalytic activity and selectivity. Moreover, this organic solvent-free process presented here could show much potential application in industry due to its simplicity, easy product separation from reaction medium and catalyst recycling. It could be profitably applied to the development of fix-bed continuous flow reactors, avoiding the use of solvent to isolate the products.

6.   H. Tang, P. Gao, G. Zhao, Z. Zhou*, L.-N. He*, C. Tang, (1R,2R)-(-)-2Dimethylamino-1-(4-nitrophenyl)-1,3-propanediol/L-Proline Cocatalyzed Enantioselective Morita-Baylis-Hillman Reaction. Catal. Commun., 2007, 8, 1811-1814.[link]