114635-47-1

Upstream product

• 51455-98-2 azido(tetraphenylporphyrinato)iron(III) 

Relevant academic research and scientific papers

Electron Paramagnetic Resonance Signature of Tetragonal Low Spin Iron(V)-Nitrido and-Oxo Complexes Derived from the Electronic Structure Analysis of Heme and Non-Heme Archetypes

Iron(V)-nitrido and-oxo complexes have been proposed as key intermediates in a diverse array of chemical transformations. Herein we present a detailed electronic-structure analysis of [FeV(N)(TPP)] (1, TPP2- = tetraphenylporphyrinato), and [FeV(N)(cyclam-ac)]+ (2, cyclam-ac = 1,4,8,11-tetraazacyclotetradecane-1-acetato) using electron paramagnetic resonance (EPR) and 57Fe M?ssbauer spectroscopy coupled with wave function based complete active-space self-consistent field (CASSCF) calculations. The findings were compared with all other well-characterized genuine iron(V)-nitrido and-oxo complexes, [FeV(N)(MePy2tacn)](PF6)2 (3, MePy2tacn = methyl-N′,N″-bis(2-picolyl)-1,4,7-triazacyclononane), [FeV(N){PhB(t-BuIm)3}]+ (4, PhB(tBuIm)3- = phenyltris(3-tert-butylimidazol-2-ylidene)borate), and [FeV(O)(TAML)]a' (5, TAML4- = tetraamido macrocyclic ligand). Our results revealed that complex 1 is an authenticated iron(V)-nitrido species and contrasts with its oxo congener, compound I, which contains a ferryl unit interacting with a porphyrin radical. More importantly, tetragonal iron(V)-nitrido and-oxo complexes 1-3 and 5 all possess an orbitally nearly doubly degenerate S = 1/2 ground state. Consequently, analogous near-axial EPR spectra with g|| a?1 ≤ 2 were measured for them, and their g|| and ga?1 values were found to obey a simple relation of ga?1 2 + (2-ga1)2 = 4. However, the bonding situation for trigonal iron(V)-nitrido complex 4 is completely different as evidenced by its distinct EPR spectrum with g|| a?1. Further in-depth analyses suggested that tetragonal low spin iron(V)-nitrido and-oxo complexes feature electronic structures akin to those found for complexes 1-3 and 5. Therefore, the characteristic EPR signals determined for 1-3 and 5 can be used as a spectroscopic marker to identify such highly reactive intermediates in catalytic processes.

Resonance Raman Spectra of Nitridoiron(V) Porphyrin Intermediates Produced by Laser Photolysis

Nitridoiron(V) porphyrins, NFeOEP (OEP, octaethylporphinato anion), NFeTPP (TPP, tetraphenylporphinato anion), and NFeTMP (TMP, tetramesitylporphinato anion), were produced by laser irradiation of thin films of the corresponding azido complexes at ca. 30 K.Formation of the nitrido complexes was detected by the appearance of the ν(FeN) (ν, stretching vibration) at 876 cm-1 for the OEP and TPP complexes and at 873 cm-1 for the TMP complex in resonance Raman (RR) spectra.These assignments were confirmed by observed frequency shifts due to (56)Fe/(54)Fe and (14)N/(15)N isotopic substitutions.Frequencies of structure-sensitive bands known for OEP and TPP complexes suggest the Fe(V) state for the nitrido complex and rule out the possibility of ?-cation-radical formation.Although the spin state cannot be determined definitively by vibrational spectroscopy, the relatively small FeN stretching force constant (5.07 mdyn/Angstroem) favors the high-spin (dxy)1(dxz)1(dyz)1 configuration that was found for isoelectronic oxomanganese(IV) porphyrins.In the case of the OEP complex, RR spectroscopy provides evidence for a reaction scheme in which NFeVOEP is first formed by laser photolysis of the N3FeIIIOEP complex due to low-power irradiation (1-60 mW in the 406.7-514.5-nm range) and subsequently converted to the μ-nitrido dimer (FeOEP)2N by local heating, which occured when high laser power (220 mW at 413.1 nm) was applied to the sample.This dimer exhibits the symmetric Fe-N-Fe stretching band at 438 cm-1, which shows expected shifts upon (56)Fe/(54)Fe and (14)N/(15)N substitutions.Formation of the μ-nitrido dimer is also confirmed by the positions of the structure-sensitive bands in the high-frequency region.The above reaction scheme resembles the autoxidation process of oxyiron porphyrins at low temperature which yields ferrylporphyrins as the intermediate and the μ-oxo dimer as the final product at room temperature.