Synthesis of new dipyridinylamine and dipyridinylmethane ligands and their coordination chemistry with Mg(II) and Zn(II)

Sterically hindered, symmetrically 2,20- substituted bispyridylamines 1a - c and methylenebispyridine 4 were prepared in a three-step procedure from commercially available 2,6-dibromopyridine, via a Cu-mediated alkylation followed by two consecutive Buchwald-Hartwig N-arylation reactions or two Negishi cross-coupling reactions, respectively, in the presence of Pd catalysts. Deprotonation of the NH and CH2 bridge of 1a and 4, respectively, enables the formation of Zn(II) and Mg(II) complexes, whose structures have been determined by single-crystal diffraction studies and/or NMR spectroscopy. A magnesium-isopropyl complex stabilized by a bispyridyldiiminate ligand derived from 4 is shown to be an active catalyst for the isotactic polymerization of methyl methacrylate.