Diastereopure Fe(II) and Zn(II) complexes derived from a tridentate N,N',N-bis(methyl-L-prolinate)-substituted pyridine ligand

A series of mononuclear iron(II) and zinc(II) complexes of the new chiral Py(ProMe)(2) ligand (Py(ProMe)(2) = 2,6bis[[(S)-2-(methyloxycarbonyl)-1-pyrrolidinyl]methyl]pyridine) have been prepared. The molecular geometry in the solid state (X-ray crystal structures) of the complexes [FeCl2(Py(ProMe)(2))] (1), [ZnCl2(Py(ProMe)(2))] (2), [Fe(OTf)(2)(Py(ProMe)(2))] (3), [Fe(Py(ProMe)(2))(OH2)(2)](OTf)(2) (4), and [Zn(OTf)(Py(ProMe)(2))](OTf) (5) are reported. They all show a meridional NN'N coordination of the Py( ProMe) 2 ligand. The bis-chloride derivatives 1 and 2 represent neutral isostructural five-coordinated complexes with a distorted geometry around the metal center. Unusual sevencoordinate iron(II) complexes 3 and 4 having a pentagonal bipyramidal geometry were obtained using weakly coordinating triflate anions. The reaction of Zn(OTf) 2 with the Py(ProMe) 2 ligand afforded complex 5 with a distorted octahedral geometry around the zinc center. All complexes were formed as single diastereoisomers. In the case of complexes 3-5, the oxygen atoms of both carbonyl groups of the ligand are also coordinated to the metal. The stereochemistry of the coordinated tertiary amine donors in complexes 3-5 is of opposite configuration as in complexes 1 and 2 as a result of the planar penta-coordination of the ligand Py(ProMe)(2). Complexes 1, 2, and 5 have an overall Lambda-configuration at their metal center, while the Fe(II) ion in complexes 3 and 4 has the opposite Delta-configuration (crystal structures and CD measurements). The magnetic moments of iron complexes 1, 3, and 4 correspond to that of high-spin d(6) Fe(II) complexes. The solution structures of complexes 1-5 were characterized by means of UV-vis, IR, conductivity, and CD measurements and their electrochemical behavior. These studies showed that the coordination environment of 1 and 2 observed in the solid state is maintained in solution. In coordinating solvents, the triflate anion (3, 5) or water (4) co-ligands of complexes 3-5 are replaced by solvent molecules with retention of the original pentagonal bipyramidal and octahedral geometry, respectively.