A thiourea-functionalized metal-organic macrocycle for the catalysis of Michael additions and prominent size-selective effect was written by Yang, Lu;Zhao, Liang;Zhou, Zhen;He, Cheng;Sun, Hui;Duan, Chunying. And the article was included in Dalton Transactions in 2017.Reference of 1190-39-2 This article mentions the following:
A discrete tetranuclear thiourea-based metal-organic macrocycle (MOM) with a large size was constructed by a well-designed organic ligands 1-(2-pyridylmethyleneamino)-3-[4-[4-[(2-pyridylmethyleneamino)carbamothioylamino]phenyl]sulfonylphenyl]thiourea (SPT) and 1-(2-pyridylmethyleneamino)-3-[3-[(2-pyridylmethyleneamino)carbamothioylamino]phenyl]thiourea (PDT) with nickel(II) ions via self-assembly. Incorporation of thiourea groups as hydrogen-bond donors into a metal-organic complex system led to a new approach for synthesis of functionalized heterogeneous catalysts, as this not only introduced coordination sites serving as chelators, but also overcomes the issues of self-association via intermol. H-bonding, often occurring in homogeneous systems. The packing structure of this material formed a confined environment suitable for the access of substrate mols. dragged by the strong hydrogen-bond interactions from the thiourea groups, thus achieving a high catalytic performance in Michael additions of β-nitrostyrenes to nitroalkanes I [R = C6H5, 4-ClC6H4, 4-MeC6H4, etc.], with remarkable yields and size-selectivity in heterogeneous phase. Moreover, a comparison of the IR spectrum of Ni-SPT with the spectra of di-Me malonate- and β-nitrostyrene-impregnated Ni-SPT indicated that both substrate mols., β-nitrostyrene and di-Me malonate, were able to access the cavity of the trimeric subunit. In the experiment, the researchers used many compounds, for example, malonic acid dibutyl ester (cas: 1190-39-2Reference of 1190-39-2).
malonic acid dibutyl ester (cas: 1190-39-2) belongs to esters. Carboxylic acid esters of low molecular weight are colourless, volatile liquids with pleasant odours, slightly soluble in water. Esters contain a carbonyl center, which gives rise to 120° C–C–O and O–C–O angles. Unlike amides, esters are structurally flexible functional groups because rotation about the C–O–C bonds has a low barrier. Their flexibility and low polarity is manifested in their physical properties; they tend to be less rigid (lower melting point) and more volatile (lower boiling point) than the corresponding amides. Reference of 1190-39-2
Referemce:
Ester – Wikipedia,
Ester – an overview | ScienceDirect Topics