Electron Configuration of Ferric Ions in Low-Spin (Dicyano)(meso-tetraarylporphyrinato)iron(III) Complexes

Abstract

The electron configuration of a series of low-spin (dicyano){meso-tetrakis(2,4,6-trialkylphenyl)porphyrinato}iron(III) complexes, [Fe(R-TPP)(CN)2]- where R = Me, Et, or iPr, together with the parent [Fe(TPP)(CN)2]-, has been examined in dichloromethane−methanol solution by 1H NMR, 13C NMR, and EPR spectroscopies. While the ferric ion of [Fe(TPP)(CN)2]- has shown a common (d xy )2(d xz ,d yz )3 configuration, the ferric ions of the alkyl-substituted complexes [Fe(R-TPP)(CN)2]- have exhibited the preference of a less common (d xz ,d yz )4(d xy )1 configuration. Spectroscopic characteristics of the complexes in which ferric ions take the (d xz ,d yz )4(d xy )1 configuration are (i) axial type EPR spectra, (ii) downfield shifted pyrrole and meta signals in 1H NMR spectra, and (iii) downfield shifted meso-carbon signals in 13C NMR spectra. Occurrence of the less common (d xz ,d yz )4(d xy )1 configuration in [Fe(R-TPP)(CN)2]- has been ascribed to the electronic interaction between iron(dπ) and cyanide(pπ*) orbitals. The interaction stabilizes the dπ orbitals and induces (d xz ,d yz )4(d xy )1 configuration. Since the electron configuration of (dicyano){meso-tetrakis(2,6-dichlorophenyl)porphyrinato}iron(III), [Fe(Cl-TPP)(CN)2]-, which carries bulky electronegative chlorine atoms at the ortho positions, is presented as a common (d xy )2(d xz ,d yz )3, the less common (d xz ,d yz )4(d xy )1 configuration in [Fe(R-TPP)(CN)2]- can be ascribed, at least partially, to the electron-donating ability of the meso-aryl groups.

meso-Substituted Porphyrin with Benzo[1,2-b:4,5-b’]dithiophene Moieties

“…Spectral and analytical data have been already extensively reported in the literature. [9] Compound 1. The synthesis of this compound was previously reported elsewhere in the literature.…”

Hemoglobina extracelular gigante de Glossoscolex paulistus: um extraordinário sistema supramolecular hemoproteico

“…142 De qualquer maneira, a atribuição tanto do estado de coordenação como da natureza do ligante coordenado no sexto sítio de coordenação é um pré-requisito para tais estudos. 142 Em hemoproteínas, distorções assimétricas do macrociclo porfirínico são induzidas por ligantes axiais, [143][144][145] O fato da porfirina desenvolver diversas funções em biologia é uma clara evidência da influência do ambiente proteico sobre suas propriedades. 153 Segundo Marques e Brown, 153 um dos mais significativos desenvolvimentos na química das porfirinas nos últimos 20 anos consiste nos estudos focados na flexibilidade do anel porfirínico.…”

Proton NMR Study of Low‐Spin meso‐Unsubstituted β‐Substituted Alkyl Iron Porphyrins: Remarkable Influence of Peripheral Substitution on Spin Density

“…The assignment was then completed with the [a] OEP: octaethylporphyrin in CD 3 OD. [8] [b] TPP: tetraphenylporphyrin in CD 2 Cl 2 /CD 3 OD at 202 K. [21] [c] At 298 K. [23] [d] At 308 K.…”

“…The former studies generally indicated that the electronic ground state was (d xy ) 2 (d xz ,d yz ) 3 for these complexes. However, more recently, it was shown that the bis(cyanido) complexes of meso-substituted Fe III porphyrins having alkyl substituents of increasing size [17] and other iron(III) porphyrins having bulky substituents in the meso position [18][19][20][21] show a large shift in the pyrrole protons towards the diamagnetic region, which is indicative of a large contribution of the unusual (d xz d yz ) 4 2 ] appear at very high magnetic field (δ = -10 to -20 ppm). This large upfield shift of the β-pyrrole protons indicates the existence of large spin densities on the β-pyrrole carbons, which is induced by the interactions between porphyrin 3e g and iron d π orbitals.…”