Syntheses, Structures and Redox Properties of New Macrocyclic Triazatriolefinic Pd~0 Complexes and Their Polypyrrole Modified Electrodes Application to Heterogeneous Catalytic Suzuki Cross-Coupling Reactions

摘要

New triolefinic macrocyclic ligands of the type (E,E,E)-1,6,11-tris(arenesulfonyl)-l,6,ll-triazacyclopentadeca-3,8,13-triene (aryl: a = ferrocenyl, b = 4-pyrrol-1-ylphenyl, c = 4-methyl-phenyl) and their Pd° complexes (laab, labb and 1bcc) have been prepared and characterized. Further structural characterization in the solid state has also been performed by means of X-ray diffraction analysis for the complex 1bcc. The redox properties of both the ligands and their Pd complexes have been studied using cyclic voltammetric and coulombim-etric techniques. In particular, complexes and ligands containing the pyrrole group do polymerize upon exposure to sufficiently positive potentials, on glassy carbon electrodes, generating highly stable modified electrodes. The new modified electrodes are efficient and selective heterogeneous catalysts for Suzuki cross-couplings, benefiting from simple removal of the catalyst from the reaction vessel. As an example, more than 2·10~5 metal cycles are achieved at 65 degC in the coupling of phenylboronic acid and cinnamyl bromide, lodoarenes and phenylboronic acid are also converted into biphenyls with relatively good conversions.