RAFT法制备负载型CBS催化剂及其在苯乙酮不对称还原中的应用

Synthesis of Supported CBS Catalyst by RAFT Polymerization and the Application in Asymmetric Reduction of Acetophenone

以苯乙烯(St)与自制的功能性苯乙烯(FSt)为单体,双硫代苯甲酸枯基酯(CDB)为链转移剂,偶氮二异丁腈(AIBN)为引发剂,通过可逆加成-断裂链转移(RAFT)聚合法合成了相对分子质量可控、窄分布的负载型CBS催化剂,并应用于苯乙酮的不对称还原中。利用红外光谱、高温凝胶色谱进行了表征。研究了FSt含量对催化剂前驱体相对分子质量(Mn)及其分布(PDI)的影响,以及RAFT法与传统自由基聚合法制备的催化剂催化效果的差异,并考察了CBS催化单元与二硫酯活性端基的相互影响。结果表明,随着FSt含量的增加,聚合物的Mn降低,其PDI先变大后保持在1.25左右;二硫酯活性端基不影响催化剂的活性;随着催化剂中FSt含量的增加,苯乙醇的对映体过量值(ee值)先迅速增大后维持在94%,产率达97.2%。

Supported CBS catalysts with controlled molecular weight and low polydispersity were successfully synthesized by reversible addition-fragmentation chain transfer（RAFT） polymerization, using cumyl dithiobenzoate （CDB） as RAFT agent, AIBN as initiator, styrene（St） and self-made functional styrene（FSt） as monomer. The CBS catalysts was used in the asymmetric reduction of acetophenone, and characterized by GPC and FT-IR. The influence of the FSt concentration on the molecular weight and the molecular weight distribution on the catalyst precursor was investigated. The difference between the catalysts by RAFT polymerization and the traditional free radical polymerization was studied. The interaction between the CBS catalytic unit and the active end groups of the dithioester was also investigated. The results show that, as increase of FSt content, the molecular weight of the polymer decreases, and the distribution of PDI becomes larger after about 1.25, the active end group of dithioate does not affect the activity of the catalyst. The ee value of phenylethyl alcohol firstly increases to 94% with the FSt concentration and the yield is up to 97.2 %.