First-row transition metal complexes of a novel pentadentate amine/imine ligand containing a hexahydropyrimidine core

2-Methyl-2-(pyridin-2-yl)propane-1,3-diamine and formaldehyde are condensed to prepare the hexahydropyrimidine derivative, which is subsequently reacted with two equivalents of 2-vinylpyridine, to produce a novel, potentially pentadentate amine/imine ligand. Full NMR spectroscopic details are reported. The ligand, hexahydro-5-methyl-5-(pyridin-2-yl)-1,3-bis[2-(pyridin-2-yl)ethyl]pyrimidine, acts as a pentadentate in a series of first-row transition metal complexes (M = Ni²⁺, Fe²⁺, Zn²⁺, Cu²⁺) but is tridentate towards Mn²⁺, in the corresponding dibromido complex. Single-crystal X-ray structure analyses reveal the metal ions to be hexacoordinate in the case of M = Ni²⁺, Fe²⁺, with and additional aqua or halido (Br⁻, Cl⁻) ligand, or pentacoordinate (M = Zn²⁺, Cu²⁺, Mn²⁺). Ferric complexes were not obtained, neither from complexation experiments employing iron(III), nor from oxidations using the iron(II) complex, and hydrogen peroxide or iodosylbenzene. In the case of the latter reactions, mass spectrometric data indicate oxidation of the hexahydropyrimidine core, with concomitant decomplexation of the ligand.