Binuclear Double-Stranded Helicates and Their Catalytic Applications in Desymmetrization of Mesodiols.

The ligand L1 of 4-methyl-2,6-diformylphenol and L2 of 4- tert-butyl-2,6-diformylphenol are synthesized through Schiff base condensation with rac-, ( R)-(+), or ( S)-(-)-1,1'-binaphthyl-2,2'-diamine (BNDA). As a result, the racemic L1rac, L2rac, and enantiopure L1RR, L1SS, L2RR, and L2SS ligands are obtained incorporating Cu(II) and Zn(II) salts by a simple one-pot metal template method. The series of dinuclear complexes of [M2LX2] (here, M = Cu2+, Zn2+; X = acetate ion, chloride ion; L = L1RR, L1SS, L1rac, L2RR, L2SS, L2rac) formulas are obtained in common. Among them, the single crystal X-ray structures for [Zn2L1rac(OAc)2] and [Zn2L1SSCl2] complexes are obtained. The detailed crystal structure and the chiroptical studies performed on these complexes dictates a self-sorting behavior in their self-assembly process and illustrate a chirality transfer from the ligand to the metal center on the complexes. The enantiopure dinuclear complexes [M2LRRX2] and [M2LSSX2] generate enantiopure ΛΛ and ΔΔ isomers, respectively, but the racemic complexes produce only homochiral ΛΛ and ΔΔ assemblies. The detailed studies based on UFLC (Ultra Fast Liquid Chromatography), CD, and single crystal X-ray structure together show the absence of heterochiral ΛΔ mesocate. All these complexes are adapted as catalysts for desymmetrization of various mesodiols, and the enantiopure complexes are found to give efficient enantioselectivity in desymmetrization of mesodiols with benzoyl chloride to monobenzoylated ester providing 98% yield and 92% ee.

D-A-D Structured Bis-acylhydrazone Exhibiting Aggregation-Induced Emission, Mechanochromic Luminescence, and Al(III) Detection.

A readily accessible D-A-D triad molecule 1 was synthesized through acylhydrazone bond formation using carefully chosen building blocks. The molecule 1 exhibits emission through charge-coupled proton transfer and enhanced emission induced through aggregation and mechanochromic luminescence. Further, it detects Al(III) selectively among other cations in an efficient manner.

Enantiomeric Resolution of Asymmetric-Carbon-Free Binuclear Double-Stranded Cobalt(III) Helicates and Their Application as Catalysts in Asymmetric Reactions.

A series of double-stranded binuclear helicates [Co2(H1)2]4+, [Co2(H2)2]4+, and [Co2(H3)2]4+, derived from monodeprotonated bis-pyridyl hydrazine-based ligands of H21, H22, and H23 with one, two, and three -CH2 spacers, were obtained. These asymmetric-carbon-free racemic helicates were separated into their ΔΔ and ΛΛ enantiomers. The resolved helicates were examined for the first time as enantioselective catalysts in asymmetric benzoylation and nitroaldol reactions.