کد مقاله | کد نشریه | سال انتشار | مقاله انگلیسی | نسخه تمام متن |
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66472 | 48433 | 2011 | 7 صفحه PDF | دانلود رایگان |
![عکس صفحه اول مقاله: New chiral Schiff base–zinc complexes and their esterolytic catalytic activity New chiral Schiff base–zinc complexes and their esterolytic catalytic activity](/preview/png/66472.png)
A new series of chiral Zn–Schiff base (imine) complexes has been prepared from mono-N-sulfonyl derivatives of (1R,2R)-diaminocyclohexane, N-heterocyclic aldehydes, and zinc salts. The formation and characterization of the (L)ZnX2 complexes was established by NMR, IR and HRESI-MS. Spectroscopic and kinetic evidence indicates that these ligands may be bidentate or tridentate depending on conditions of the medium. The methanolysis of a chiral, racemic picolinate ester catalyzed by the Zn(II)–Schiff base complexes was studied kinetically. The rate constants were found to vary approximately a hundred-fold and in a complex way depending on the imine ligand and the Zn-counter anion, kobs = 5.0 × 10−6–4.8 × 10−4 M−1 s−1. A Job plot analysis of ternary complex formation of LZnX2 with two phosphonate transition state analogs suggests that two types of (imine)Zn(picolinate)X ternary complexes may be intermediates and that varying rate-limiting steps may be involved in the LZnX2-catalyzed methanolysis of picolinate esters.
A series of chiral Schiff base–zinc complexes derived from N-heterocyclic aldehydes and trans-cyclohexyldiamine N-sulfonamides are effective catalysts for the methanolysis of picolinate esters. Substantial differences in catalytic activity derive from the steric and electronic nature of the N-heterocycle and sulfonyl groups of the imine ligand and the anionic ligand X.Figure optionsDownload high-quality image (110 K)Download as PowerPoint slideHighlights
► New zinc–Schiff base complexes of cyclohexyldiamine-sulfonamides are prepared
► Their ester methanolyis activity for depends on the imine, counteranion and sulfonamide units
► The mechanism is probed via ligand deprotonation and TSA binding experiments.
Journal: Journal of Molecular Catalysis A: Chemical - Volume 339, Issues 1–2, 1 April 2011, Pages 72–78