Imine or Enamine? Insights and Predictive Guidelines from the Electronic Effect of Substituents in H-Bonded Salicylimines
作者:R. Fernando Martínez、Esther Matamoros、Pedro Cintas、Juan C. Palacios
DOI:10.1021/acs.joc.0c00130
日期:2020.5.1
Imine and enamine bonds decorate the skeleton of numerous reagents, catalysts, and organic materials. However, it is difficult to isolate at will a single tautomer, as dynamic equilibria occur easily, even in the solid state, and are sensitive to electronic and steric effect, including π-conjugation and H-bonding. Here, using as model Schiff bases generated from salicylaldehydes and TRIS in a set of
Syntheses, structure, redox and catalytic epoxidation properties of dioxomolybdenum(VI) complexes with Schiff base ligands derived from tris(hydroxymethyl)amino methane
Five kinds of dioxomolybdenum(VI) complexes with Schiff base ligands derived from tris(hydroxymethyl)amino methane are prepared and structurally characterized by X-ray crystallography, which reveals that these complexes adopt a distorted octahedral six-coordinate configuration formed by the tridentate Schiff base ligand, one coordinating water and two binding oxygen atoms. These complexes show good catalytic activities and selectivity in the epoxidation of cyclohexene with t-butylhydroperoxide, especially for complex 4, which could give a nearly 100% of epoxidation conversion and selectivity. Introduction of the electron-withdrawing group to the salicylidene ring of complex strongly increases the effectiveness of a catalyst, but decreases the redox stability of a complex. (C) 2007 Elsevier B.V. All rights reserved.