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在手性配体及其催化剂设计中,立体效应是主要考虑因素,而电子效应研究得很少.最近我们设计合成了一类具有手性螺二氢茚骨架结构的单磷配体SIPHOS,该配体在铑催化的烯烃氢化反应中取得了很高的对映选择性.在此基础上,我们从光学的7,7'-二羟基-1,1'-螺二氢茚(SPINOL)出发,合成了系列4,4'-取代的螺环二酚及相应的单磷配体,并以铑催化的烯烃氢化反应为模型,系统地研究了骨架上的取代基电子效应对配体性能的影响.研究表明,由于取代基距离配位中心的磷原子较远,其电子效应对配体的催化性能影响不大.接下来,我们合成了磷原子上直接连有苯环的磷酸酯类配体,其取代基的电子效应通过苯环能够有效地传递到磷原子上,进而影响配体的催化性能.实验表明,该类配体在铑催化的α-和β-脱氢氨基酸酯的不对称氢化反应中,表现出明显的电子效应,即配体苯环上有推电子基时,催化剂的活性和对映选择性有很大的提高. 相似文献
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The dependences of soft magnetic properties and microstructures of the
sputtered FeCo (=FeFeCo薄膜 溅射条件 软磁性 高饱和磁化强度 FeCo film, sputtering conditions, high saturation magnetization,
soft magnetic properties 2005-10-26 3/7/2006 12:00:00 AM The dependences of soft magnetic properties and microstructures of the sputtered FeCo (=Fe65Co35) films on Co underlayer thickness tCo, FeCo thickness tFeCo, substrate temperature Ts and taxget-substrate spacing dT-s are studied. FeCo single layer generally shows a high coercivity with no obvious magnetic anisotropy. Excellent soft magnetic properties with saturation magnetization μ0Ms of 2.35 T and hard axis coercivity Hch of 0.25 kA/m in FeCo films can be achieved by introducing a Co underlayer. It is shown that sandwiching a Co underlayer causes a change in orientation and reduction in grain size from 70 nm to about 10 nm in the FeCo layer. The magnetic softness can be explained by the Hoffmann's ripple theory due to the effect of grain size. The magnetic anisotropy can be controlled by changing dT-S, and a maximum of 14.3 kA/m for anisotropic field Hk is obtained with dT-S=18.0 cm. 相似文献
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