Metal- and Ligand-Centered Monoelectronic Oxidation of μ-Nitrido[((tetraphenylporphyrinato)manganese)(phthalocyaninatoiron)], [(TPP)Mn−N−FePc]. X-ray Crystal Structure of the Fe(IV)-Containing Species [(THF)(TPP)Mn−N−FePc(H₂O)](I₅)·2THF

Abstract

The reaction of mu-nitrido[((tetraphenylporphyrinato)manganese)(phthalocyaninatoiron)], [(TPP)Mn-N-FePc], with I(2) in THF develops with the formation of two different species, i.e., [(THF)(TPP)Mn-N-FePc(H(2)O)](I(5)).2THF (I) and [(TPP)Mn(IV)-N-Fe(III)Pc](I(3)) (II). On the basis of single-crystal X-ray work and Mössbauer, EPR, Raman, and magnetic susceptibility data, I, found to be isostructural with the corresponding Fe-Fe complex, is shown to contain a low-spin triatomic Mn(IV)=N=Fe(IV) system (metal-centered oxidation). Data at hand for II (Mössbauer, EPR, Raman) show, instead, that oxidation takes place at one of the two macrocycles, very likely TPP (ligand-centered oxidation). The same cationic fragment present in I, and containing the Mn(IV)=N=Fe(IV) bond system, is also obtained when (TPP)Mn-N-FePc is allowed to react in THF with (phen)SbCl(6) (molar ratio 1:1). There are indications that the use of (phen)SbCl(6) in excess (2:1 molar ratio), in benzene, probably determines further oxidation with the formation of a species showing the combined presence of the Mn(IV)-Fe(IV) couple and of a pi-cation radical.

Mid- to high-valent imido and nitrido complexes of iron

“…For instance, azide photolysis has provided nitride bridged diiron complexes in which the iron centers are supported by tetradentate macrocycles such as tetraphenylporphyrin, cyclam derivatives, and phthalocyanines, 16 [57][58][59][60]. A number of high-valent nitride bridged species have been reported, and valencetautomerism may be prevalent in some of these high-valent systems [61].…”

“…For example, in {(por)-Fe} 2 (l-N) and [{(por)Fe} 2 (l-N)] + the linear Fe-(l-N)-Fe arrangement leads to highly covalent p-bonding and a delocalized electronic description for the two iron centers [63]. There are also intriguing heterobimetallic nitride bridged systems (17) [7,59,64]. For instance [(tpp)Mn-NFePc] (where tpp = tetraphenylporphyrinato and Pc = phthalocyaninato) can be oxidized by one electron, removing an electron either from one of the macrocyclic ligands or from a metal center, to provide a strongly coupled and low-spin Mn IV @N@Fe IV system [59].…”

Bio‐organometallic Approaches to Nitrogen Fixation Chemistry

“…Holm and coworkers have recently begun to examine the coordination chemistry of iron nitrides to see if a nitride which bridges six iron centers can be obtained [96]. Literature precedent shows ample evidence for linear Fe-N-Fe bridges for octahedrally coordinated iron [97][98][99][100] and, more recently, a bent Fe-N-Fe bridge for pseudotetrahedral iron centers from our laboratory at Caltech (vide infra) [89, 3.3 Biomimetic Systems that Model Structure and Function 105 …”

µ-Nitrido Bridged Diiron Phthalocyanines: Old Complexes for New Catalytic Applications

“…Since then, this area has been largely developed due to the works by Ercolani's group. [3][4][5][6][7][8][9] Porphyrin and phthalocyanine macrocyclic ligands in homoleptic and heteroleptic arrangements have been used to accommodate M-N=M structural unit with the same and different transition metals in a variety of combinations. [10][11][12][13][14] µ-Nitrido dimers based on non-macrocyclic ligands have been also described.…”

“…Ercolani's group has also prepared and investigated different types of µ-nitrido bridged complexes including the systems with same metal but different ligands, (TPP) FeNFe(Pc), [6] and with different ligands and metals, (TPP) FeNRu(Pc) [7] and (TPP)MnNFe(Pc). [8,9] These compounds were synthesised using corresponding metalloporphyrin azido complex and iron phthalocyanine in the controlled conditions. From Mössbauer and EPR data it was concluded that the (TPP)FeNFe(Pc) complex underwent a rapid electronic exchange across the bridging nitrogen atom and both metal centres have intermediate oxidation state +3.5 in spite of asymmetric ligand environment.…”