Cationic aqua complexes are prepared from a trans-chelating tridentate ligand, (R,R)-4,6-dibenzofurandiyl-2,2‘-bis(4-phenyloxazoline) (DBFOX/Ph), and various transition-metal(II) perchlorates. These complexes are effective catalysts in the Diels−Alder reactions of cyclopentadiene with 3-alkenoyl-2-oxazolidinone dienophiles and show excellent enantioselectivities. The active catalyst complex prepared from nickel(II) perchlorate hexahydrate has an octahedral structure with three aqua ligands, and it can be isolated and stored for months without loss of catalytic activity. Iron(II), cobalt(II), copper(II), and zinc(II) complexes are similarly active. The absolute configuration induced in the reaction can be readily predicted on the basis of the C 2-symmetric structure of the complexes as well as the simple structure of the substrate complex. The aqua complex prepared from Ni(II) or Zn(II) perchlorate results in highly effective chiral amplification in the Diels−Alder reaction. Use of the DBFOX/Ph ligand of a low enantio purity of 20% ee leads to a 96% ee for the endo cycloadduct. Two mechanisms for amplification are involved in this remarkable chiral amplification:  (1) precipitation of an S 4-symmetric meso 2:1 complex between DBFOX/Ph and Ni(II) ion and (2) associative formation of 1:1 heterochiral complexes by the aid of hydrogen bonds based on aqua ligands to produce stable meso oligomers.

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Perpendicularly magnetized layers are used widely for high-density information storage in magnetic hard disk drives and nonvolatile magnetic random access memories. Writing and erasing of information in these devices is implemented by magnetization switching in local magnetic fields or via intense pulses of electric current. Improvements in energy efficiency could be obtained when the reorientation of perpendicular magnetization is controlled by an electric field. Here, we report on reversible electric-field-driven out-of-plane to in-plane magnetization switching in Cu/Ni multilayers on ferroelectric BaTiO 3 at room temperature. Fully deterministic magnetic switching in this hybrid material system is based on efficient strain transfer from ferroelastic domains in BaTiO 3 and the high sensitivity of perpendicular magnetic anisotropy in Cu/Ni to electric-field-induced strain modulations. We also demonstrate that the magnetoelectric coupling effect can be used to realize 180°magnetization reversal if the out-of-plane symmetry of magnetic anisotropy is temporarily broken by a small magnetic field.

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