Novel iron(ii) complexes with hexadentate nitrogen ligands obtained via intramolecular redox reactions (original) (raw)

2001, Journal of the Chemical Society, Dalton Transactions

Two novel complexes: [Fe(L 2Ј )][BPh 4 ] 2 , 1, and [Fe(L 3Ј )][BPh 4 ] 2 , 2, with the hexadentate nitrogen ligands, L nЈ = 1,9-bis(2Ј-pyridyl)-5-[(R-2Љ-pyridyl)methyl]-2,5,8-triazanon-1-ene, where R = ethoxy for L 2Ј and methoxy for L 3Ј , were obtained from the iron() complex of the pentadentate ligand, L 1 = 1,9-bis(2Ј-pyridyl)-2,5,8-triazanonane. Complexes 1 and 2 were also obtained by making the hexadentate ligands: 1,9-bis(2Ј-pyridyl)-5-[(ethoxy-2Јpyridyl)methyl]-2,5,8-triazanonane (L 2 ) and 1,9-bis(2Ј-pyridyl)-5-[(methoxy-2Љ-pyridyl)methyl]-2,5,8-triazanonane (L 3 ) react with Fe(), respectively. 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() species. Both preparative methods are examples of oxidative dehydrogenation of a Fe() polyamine complex, in which the thermodynamically and kinetically stable final product is a low spin Fe() imine complex. In the case of the first method an increase in the size and denticity of the starting ligand is observed. Fig. 1 Structures of the ligands. H p (B 4 ) 6.74 t(8) J m-p-o (7) 6.75 t(8) J m-p-o (7) H m (B 4 ) 6.89 t(16) J o-m-p (7) 6.90 dd(16) J m-o (8) J m-p (7) H3