IRON(II) COMPLEXES WITH NOVEL PENTADENTATE LIGANDS VIA C-C BOND FORMATION BETWEEN VARIOUS NITRILES AND [2,4-BIS(2-PYRIDYLMETHYLIMINO)PENTANE]IRON(II) PERCHLORATE - SYNTHESIS AND STRUCTURES

The iron(II) complex of 2,4-bis(2-pyridylmethylimino)pentane (L-1), tr ans-[FeL1(MeCN)(2)][ClO4](2) . MeCN, was prepared by a template reacti on and isolated as pale red crystals. An acetonitrile solution of the complex exhibited a crossover from a low-to a high-spin form above 20 degrees C. With this complex as precursor, a series of iron(Ir) comple xes with novel pentadentate ligands, 3-(1-alkyl (or ryl)-methyl)-1-imi no-2,4-bis(2-pyridylmethylimine) (L-2), was prepared using various nit riles such as propionitrile, isobutyronitrile, benzyl cyanide, benzoni trile, 4-fluoro-, 3,4-difluoro-, and pentafluoro-benzonitrile, as well as acetonitrile, as solvents. On formation of L-2, the co-ordination mode of the L-1 part of the parent compound was converted from trans i nto cis-P with concomitant C-C bond formation between the central carb on atom of L-1 and the carbon atom of the various nitriles. The isolat ed triimine part in the pentadentate ligands occupies one of the trigo nal faces of the distorted octahedron. The resulting complex undergoes rapid intramolecular isomerization at or above room temperature. The crystal structures of the precursor and of three new iron(II) complexe s with pentadentate ligands have been determined.