Novel iron(II) complexes with hexadentate nitrogen ligands obtained via intramolecular redox reactions

Two novel complexes: [Fe(L-2')][BPh4](2), 1, and [Fe(L-3')][BPh4](2), 2, wi th the hexadentate nitrogen ligands, L-n' = 1,9-bis(2'-pyridyl)-5-[(R-2"-py ridyl) methyl]-2,5,8-triazanon-1-ene, where R = ethoxy for L-2' and methoxy for L-3', were obtained from the iron() complex of the pentadentate ligand , L-1 = 1,9-bis(2'-pyridyl)-2,5,8-triazanonane. Complexes 1 and 2 were also obtained by making the hexadentate ligands: 1,9-bis(2'-pyridyl)-5-[(ethoxy -2'-pyridyl) methyl]-2,5,8-triazanonane (L-2) and 1,9-bis(2'-pyridyl)-5-[( methoxy-2'-pyridyl) methyl]- 2,5,8-triazanonane (L-3) react with Fe(III), r espectively. The structures of complexes 1 and 2 were characterized by COSY , HMBC, HMQC and NOESY NMR studies, and both structures were also confirmed by X-ray analysis. In both cases, the geometry around iron is a distorted octahedron. Since 1 and 2 are diamagnetic at 298 K they are low-spin iron(I I) species. Both preparative methods are examples of oxidative dehydrogenat ion of a Fe() polyamine complex, in which the thermodynamically and kinetic ally stable final product is a low spin Fe(II) imine complex. In the case o f the rst method an increase in the size and denticity of the starting liga nd is observed.