A chiral bimetallic Lewis acid, 2,2′-(1,2-phenylene)bis[(4R,5R)-4,5-diphenyl-1,3,2-ioxaborolane] (1a), has been synthesized. The exceptionally strong binding of 1a with benzylamine was demonstrated by titrations. The complex formation ratio of 1a : amine = 1 : 2 was determined by a Job plot. The binding constants, K1 and K2, were determined by non-linear curve fitting to be K1 << K2. The results can be explained in terms of an allosteric effect. The first amine molecule coordinates with one of the two boron atoms of 1a; at the same time, one NH proton interacts with one of the two oxygen atoms in the other dioxaborolane ring to form a hydrogen bond. As a result, the two dioxaborolane rings are conformationally fixed by two-point binding to provide a preferable binding site for the second amine molecule. Although only a small chiral recognition of 1-phenylethylamine has been obtained with 1a, the clear separation of the peaks of the amine provides the possibility to use 1a as an NMR chiral-shift reagent.
合成了手性双
金属
路易斯酸2,2'-(1,2-亚苯基)双[(4R,5R)-4,5
-二苯基-1,3,2-
碘杂
硼杂
硼烷](1a)。滴定证明了 1a 与
苄胺的异常强的结合。 1a:胺=1:2的复合物形成比例通过Job图确定。通过非线性曲线拟合确定结合常数K1和K2为K1<
乙胺手性识别,但胺峰的清晰分离提供了使用 1a 作为 NMR 手性位移试剂的可能性。