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‡

Abstract

The iron(II) complex of 2,4-bis(2-pyridylmethylimino)pentane (L¹), trans-[FeL¹(MeCN)₂][ClO₄]₂·MeCN, was prepared by a template reaction 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 °C. With this complex as precursor, a series of iron(II) complexes with novel pentadentate ligands, 3-(1-alkyl (or aryl)-methyl)-1-imino-2,4-bis(2-pyridylmethylimine) (L²), was prepared using various nitriles such as propionitrile, isobutyronitrile, benzyl cyanide, benzonitrile, 4-fluoro-, 3,4-difluoro-, and pentafluoro-benzonitrile, as well as acetonitrile, as solvents. On formation of L², the co-ordination mode of the L¹ part of the parent compound was converted from trans into cis-β with concomitant C–C bond formation between the central carbon atom of L¹ and the carbon atom of the various nitriles. The isolated triimine part in the pentadentate ligands occupies one of the trigonal 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) complexes with pentadentate ligands have been determined.