Studies On The Structure And Catalytic Properties Of Polymer Immobilized L-proline And Carbonylcobalt Catalysts

L-proline and carbonylcobalt catalystshave been widely used as homogenous catalysts for Aldol and carbonylation reactions. To research and develop the recyclable L-proline and carbonylcobalt catalysts are of great theoretical and practical significances. In this work, the preparation and catalytic properties of Z-proline and carbonylcobalt catalysts immobilized by polymers for Aldol reactions and alkoxy-carbonylation of ethylene oxide have been studied, respectively. The polymer immobilized L-proline and carbonylcobalt catalysts have been evaluated by micro-reactor tests for Aldol reactions of aldehyde and ketone and alkoxy-carbonylation of ethylene oxide and characterized by using physico-chemical methods. Our experimental results have shown that these novel hetergenous catalysts not only exhibit unique catalytic activities and seletivities for the reaction studied, but also present excellent recyclabilities. The main results are summarized as follows:1. The preparation of polymer immobilized L-proline catalyst by copolymerization of O-acryloyl-trans-4-hydroxy-L-proline hydrochloride (AHP) with N-isopropylacrylamide (NIPAM) can easily adjust the L-proline content in polymer catalyst. It has been shown that the polymer L-proline catalyst exhibits higher stereoselectivity than AHP monomer catalyst with similar catalytic activity for Aldol reaction of p-nitrobenzaldehyde with cyclohexanone. Besides, the polymer L-proline catalyst is easier to be separated from the reaction system than the AHP monomer catalyst. After ten recycles, the stereoselectivity to Aldol reaction product remains almost unchanged with p-nitrobenzaldehyde conversion higher than 96 mol%, indicating the excellent recyclability of polymer catalyst.2. A novel polymer immobilizated carbonylcobalt catalyst[Co2(CO)6]P4VP through N→Co coordination bond has been prepared by solvothermal method using poly (4-vinylpyridine) (P4VP) and Co2(CO)8 as starting materials. The polymer catalyst exhibited better catalytic properties for alkoxy-carbonylation of ethylene oxide (EO) in terms of EO conversion (85.8 mol%) and methyl 3-hydroxypropanoate (3-MHP) selectivity (79.6 mol%) and higher stability than those of Co2(CO)8. Especially, the [Co2(CO)6]P4VP catalyst can be easily separated and reused 5 times with only slight decrease in EO conversion and 3-MHP selectivity. It has been proposed that pyridine fragments in the polymer catalysts act not only as promoters to enhance the catalytic activity and selectivity for alkoxy-carbonylation of ethylene oxide but also as stabilizers to increase the reusability of carbonylcobalt species through N→Co coordination bonds.3. K[Co(CO)4] catalyst can be prepared by KBH4 reduction method under mild conditions, and the optimum preparation conditions are 1.0 g CoCl2, n(CoCl2):n(KBH4)=1:3,20 mL THF, Pco=4 MPa, T=20 ℃ and t=2 h.The prepared K[Co(CO)4] catalyst exhibits 70.0 mol% EO conversion and 94.5 mol% 3-MHP selectivity for alkoxy-carbonylation of ethylene oxide. The polymer immobilized carbonylcobalt catalyst K[Co(CO)3P4VP] has been prepared by using K[Co(CO)4] and P4VP as precursors. After five recycles,3-MHP selectivity over the K[Co(CO)3P4VP] catalyst was still higher than40.0 mol%, while EO conversion decreased obviously, indicating that the recyclability of K[Co(CO)3P4VP] is lower than that of [Co2(CO)6]P4VP catalyst.