Asymmetric Catalysis by Layred Smectites Multi-Modified with Sugars

在DMF/H_2O中，将[Rh(Chito-OP)(COD)]~+(Rh-Chito~(++))(Chito-OP=壳聚糖亚磷酸)插层到氢氧化钠(NAHT)中，制备了Hectorite负载的Rh-Chito^+/NAHT(Rh-Chito-OP)-壳聚糖配合物(Rh-Chito-OP)。Rh-Chito^+/NAHT的空隙(d_&lt；001&gt；-0.96 nm)为1.06 nm，表明Rh-Chito^+在层间形成2/1螺旋结构，而不是8/5螺旋结构。2衣康酸二甲酯和香茅醛的加氢反应：衣康酸二甲酯的主要加氢产物是(R)-甲基琥珀酸二甲酯。在加氢过程中生成少量的偏二甲酸二甲酯作为异构化产物。催化活性明显依赖于反应溶剂。在甲醇中，反应没有进行。与Rh-Chito^+(均相络合物)相比，杂化Rh催化剂具有更高的不对称选择性。当乙醇/DMF(30：1)为反应溶剂时，选择性最高(16.7%e.e(R))。层间螺旋结构的可控构象可能是Rh-Chito^+/NaHT型催化剂具有较高的不对称选择性的原因。香茅醛加氢反应具有化学选择性。Rh-Chito^+/NAHT和Rh-Chito+主要是香茅醛的氢化C=O基团。这种催化行为明显不同于以氢化C=C键为主的[Rh(PPh_3)_2(Cd)]PF_6。

Hectorite-supported rhodium (I) -chitosan complex (Rh-Chito^+/NaHT) was prepared by the intercalation of [Rh (Chito-OP) (COD) ] ^+ (Rh-Chito^+) (Chito-OP=chitosan phosphite) into sodium hectorites (NaHT) in DMF/H_2O.Asymmetric hydrogenation of alpha, beta-unsaturated carboxylates such as itaconates containing various chain lengths of alcohol groups and chemoselective hydrogenation of citronellal were studied on the intercalation compound.1 Characterization : XRD measurement showed that the basal spacing of Rh-Chito^+/NaHT was 2.02nm. The clearance space (d_<001>-0.96nm) of Rh-Chito^+/NaHT was 1.06nm which suggested that 2/1 helical structure of Rh-Chito^+ was formed in the interlayr rather than 8/5 helical structure. TEM and FT-IR measurement confirm the formation of monolayr of the rhodium complex in the interlayr of hectorite.2 Hydrogenation of itaconates and citronellal : The main hydrogenation product for dimethyl itaconates was dimethyl (R) -methylsuccinate. Small amount of dimethyl mesaconate was formed as an isomerization product during the hydrogenation. Catalytic activity remarkably depended on the reaction solvents. In MeOH,the reaction did not proceed. Asymmetric selectivity of the hetrogenized Rh catalyst was higher than that of Rh-Chito^+ (homogeneous complex). Highest selectivity (16.7% e.e (R) ) was obtained when EtOH/DMF (30 : 1) was used as a reaction solvent. Probably the controlled conformation of helical structure in the interlayr contributes the higher asymmetric selectivity for Rh-Chito^+/NaHT.Chemoselectivity was observed for the hydrogenation of citronellal. Rh-Chito^+/NaHT and Rh-Chito+ predominantly hydrogenated C=O group of citronellal. This catalytic behavior is remarkably different from [Rh (PPh_3) _2 (CCD) ] PF_6 which predominantly hydrogenated C=C bond.