New Five- and Six-Coordinate Imidazole and Imidazolate Complexes of Ferric Tetraphenylporphyrine

Article abstract of DOI:10.1021/ja00373a042

The synthesis of several new imidazole and imidazolate complexes of ferric tetraphenylporphyrine (TPP) are reported.The following coplexes have been made with L = imidazole (ImH) or 4-methylimidazole (4MeImH) and L^- = imidazolate (Im^-) or 4-methylimidazolate (4MeIm^-): FeTPP(L)(L^-), -2>^-, and (SbF6).Addition of Im^- to FeTPPCl resulted in the formation first of the imidazolate-bridged complex <(FeTPP)2(Im)>⁺ and then of ^-.Similar addition of 4MeIm^- to FeTPPCl resulted in the formation first of the high-spin mononuclear complex FeTPP(4MeIm) and then of ^-.The affinity of (SbF6) for a second 4MeImH was found to be very high, with K >/= 10⁷ M^-1 in toluene, 25 deg C.By contrast, 4MeImH was found preferentially to hydrogen bond to Fe(TPP)(4MeIm), with K ca. 5 * 10⁴ M^-1 in THF, 25 deg C.Coordination of 4MeImH was only observed at high concentration of ligand (K ca. 50 +/- 10 M^-1).The monoimidazole complex (SbF6) was concluded to be high spin after a comparison of the visible spectral properties of a large number of ferric TPP complexes.