原位合成手性镍配合物中的阻转异构及磁性研究

Atropisomerism and Magnetic Properties of an in situ Synthesized Chiral Nickel Complex

阻转异构体是一类特殊的手性化合物.利用轴手性配体制得的具有阻转异构行为的配合物在不对称催化等领域有广泛的应用.相比之下,通过原位反应由非手性底物制备这类手性配合物的报道较少,而利用非轴手性化合物原位组装得到非轴手性阻转异构体的报道则更加罕见.乙腈是一种廉价易得的基本化工原料,在金属离子存在下活化乙腈分子是向有机分子中引入氰甲基的一种有效手段.本文利用乙腈分子进攻2-二吡啶基酮获得了一例含有氰甲基官能团的配体dpkMeCN-H[dpkMeCN=cyanomethyl-di(pyridin-2-yl)methanol].在Ni^(II)和K^(I)的配位作用下,该体系发生原位组装生成了一对阻转异构体.磁性拟合结果表明镍离子之间主要为铁磁耦合,且它们由于八面体畸变产生一定的零场分裂,使手性镍配合物产生磁各向异性.

Atropisomers refer to a subclass of chiral compounds that cannot be superposed with its mirror image.For a long time,chiral complexes play an important role in the fields of medicine,dyes,materials and natural products.Metal complexes as atropisomers have widespread applications in asymmetric catalysis.In contrast,fewer examples are known as obtaining atropisomers from achiral substrate,while it is even rarer to use non-axial-chirality ligand to achieve atropisomers.In general,acetonitrile is reactive inert and difficult to break the C—H bond in acetonitrile,so it is usually not a good nucleophilic reagent precursor.Activation of acetonitrile molecules assisting with transition-metal ions is an effective approach for introducing cyanomethyl groups.Herein we demonstrate a pair of atropisomers obtained through in⁃situ assembly under the coordination of Ni^(II) and K^(I),where the non-axial-chirality ligand dpkMeCN-H[dpkMeCN=cyanomethyl-di(pyridin-2-yl)methanol]containing a cyanomethyl group was introduced by the reaction with acetonitrile.From the magnetic measurements and analysis,the ferromagnetic coupling between two Ni^(Ⅱ)ions was revealed.Accompanied with zero-field splitting from the distorted octahedral NiⅡions,magnetic anisotropy was preserved for the chiral nickel complexes.