18-冠-6与Eu(fod)3+在CCl4中的化学平衡及其配合物的结构

在室温下测定了CCl_4溶液中,18-冠-6的亚甲基、Eu(fod)的t—丁基质子的PMR化学位移与溶液组成的相互关系。提出了生成配合物RS,R_2S,R_2,R_3(S为18-冠-6,R为Eu(fod)_3)的模式。求得了平衡常数值(升/摩):K_1=RS]/(R]S])=2.O×10~5,K_2=R_2S]/(R]RS])=1.0×10~3,Q_1=R_2]/R]~2=4.2×10~2,Q_2=R_3]/(R_2]R])=4.0×10~1。并测得在配合物RS,R_2S中18-冠-6质子的平均化学位移分别为4.90,10.84(ppm,相对于纯18-冠-6); 在配合物R,R_2,R_3,RS,R_2中t-丁基质子平均化学位移分别为1.53,2.33,0.54,1.02,2.42(ppm,相对于TMS)。 根据配合物的化学位移值,并考虑分子及分子轨道的对称性、位阻等因素提出了配合物R_2,RS,R_2S的可能的结构模型。

CHEMICAL EQUILIBRIUM AND STRUCTURE OF COMPLEXES OF 18-CROWN-6 WITH SHIFT REAGENT Eu(FOD)3 IN CCl4

The chemical shifts of protons in 18-crown-6 and in t-butyl of Eu (fod)3 were measured as functions of composition in CCl4 at room temperature. In analyzing of results the formation of complex RS,R2S and also R2 ,R3 was assumed, where R is Eu(fod)3 and S is 18-crown-6. Comparison of the experimental PMR shift with the calculated ones leads to the following best values of equilibrium constants(1.mol-1): K1=RS]/(R]S]= 2.0xxxxxxxxxx105;K2 = R2S]/(R]RS]=1.0xxxxxxxxxxx103;=R2] /R]2=4.2xxxxxxxx102;Q2=R3]/(R2]R])=4.0xxxxxxxxx101. The PMR average shifts obtained in the same calculation for proton in 18-crown-6 are 4.9 for complex RS and 10.84 for complex R2S(ppm, relative to pure 18-crown-6), the average shifts for protons in t-butyl are 1.53, for R,2.33 for R2 ,0.54 for Rs ,1.02 for RS and 2.43 for R2S (ppm, relative to TMS). The possible structure of complexes R,R2 ,RS,R2S were suggestsd on the chemical shift of complexes and taking the symmetry of molecules and of molecular orbitals and also steric hindrances into account.