Indefinitely stable iron(IV) cage complexes formed in water by air oxidation

Abstract

In nature, iron, the fourth most abundant element of the Earth's crust, occurs in its stable forms either as the native metal or in its compounds in the +2 or +3 (low-valent) oxidation states. High-valent iron (+4, +5, +6) compounds are not formed spontaneously at ambient conditions, and the ones obtained synthetically appear to be unstable in polar organic solvents, especially aqueous solutions, and this is what limits their studies and use. Here we describe unprecedented iron(IV) hexahydrazide clathrochelate complexes that are assembled in alkaline aqueous media from iron(III) salts, oxalodihydrazide and formaldehyde in the course of a metal-templated reaction accompanied by air oxidation. The complexes can exist indefinitely at ambient conditions without any sign of decomposition in water, nonaqueous solutions and in the solid state. We anticipate that our findings may open a way to aqueous solution and polynuclear high-valent iron chemistry that remains underexplored and presents an important challenge.

Chronic toxicity of the Iron (IV) clathrochelate complexes for white rats

“…Останніми роками вивченню властивостей сполук Феруму (IV) присвячено багато праць (Gloves et al, 2006;England et al, 2014;Tomyn et al, 2017), оскільки рідкісний нетрадиційний ступінь окиснення +4 реалізується в каталітичних циклах багатьох ферумовмісних ферментів, але зовсім не досліджувалась біологічна активність речовин даного типу, зокрема, не висвітлено його вплив на організм свиней, фармакокінетику та фармакодинаміку. Перед проведенням таких експериментів обов'язковими є доклінічні дослідження на лабораторних тваринах (Kotsiumbas, 2006).…”

A Ferrocene‐Based Dicationic Iron(IV) Carbonyl Complex

“…[28] While the oxidation state + IV for non-biomimetic iron is rare, [29] it is even less common for complexes with carbonyl ligands,w hich are generally good ligands for metals in low oxidation states.H ence high-valent metal carbonyl complexes,s uch as [PtCl 5 (CO)] À , [30] [OsF 5 (CO] À , [31] and [OsCl 5 -(CO)] À , [32] are exceedingly rare and only [OsCl 5 (CO)] À is crystallographically characterized. [28] While the oxidation state + IV for non-biomimetic iron is rare, [29] it is even less common for complexes with carbonyl ligands,w hich are generally good ligands for metals in low oxidation states.H ence high-valent metal carbonyl complexes,s uch as [PtCl 5 (CO)] À , [30] [OsF 5 (CO] À , [31] and [OsCl 5 -(CO)] À , [32] are exceedingly rare and only [OsCl 5 (CO)] À is crystallographically characterized.…”

“…As expected, coordination of strongly p-acidic CO to [Cp* 2 Fe] 2+ results in as ignificantly smaller d of 0.42 mm s À1 for [Cp* 2 Fe(CO)](SbF 6 ) 2 compared to 0.59 mm s À1 for [Cp* 2 Fe](SbF 6 ) 2 .O verall, we conclude that the CO complex indeed qualifies as an Fe IV compound, although the concept of assigning formal oxidation states to transition metals is difficult for complexes with highly covalent metal-ligand bonds.H ence,a nother concept of assessing the electronic structure of iron carbonyl complexes has recently been reported by Wolczanski, offering an alternative interpretation based on ligand-centered oxidations. [28] While the oxidation state + IV for non-biomimetic iron is rare, [29] it is even less common for complexes with carbonyl ligands,w hich are generally good ligands for metals in low oxidation states.H ence high-valent metal carbonyl complexes,s uch as [PtCl 5 (CO)] À , [30] [OsF 5 (CO] À , [31] and [OsCl 5 -(CO)] À , [32] are exceedingly rare and only [OsCl 5 (CO)] À is crystallographically characterized. At ransient tetravalent [Rh(O) 2 CO] complex has been postulated on an Al 2 O 3 surface at low temperatures, [33] and the tetravalent Mo and Wc omplexes [M(O) 2 (CO) 4 ]h ave been detected by matrix spectroscopy.…”

Ein Ferrocen‐basierter dikationischer FeIV‐Carbonylkomplex

“…[28] Obwohl die Oxidationsstufe + IV fürn icht-biomimetische Eisenverbindungen schon selten ist, [29] ist diese sehr rar fürM etallcarbonylkomplexe,d aC Oi mA llgemeinen als guter Ligand fürniedrige Oxidationsstufen gilt. In diesem Zusammenhang ist ein alternatives Konzept von Wolczanski zur elektronischen Struktur von Eisencarbonylkomplexen zu erwähnen, welches ligandenzentrierte Oxidationen diskutiert.…”

“…In diesem Zusammenhang ist ein alternatives Konzept von Wolczanski zur elektronischen Struktur von Eisencarbonylkomplexen zu erwähnen, welches ligandenzentrierte Oxidationen diskutiert. [28] Obwohl die Oxidationsstufe + IV fürn icht-biomimetische Eisenverbindungen schon selten ist, [29] ist diese sehr rar fürM etallcarbonylkomplexe,d aC Oi mA llgemeinen als guter Ligand fürniedrige Oxidationsstufen gilt. So existieren nur wenige Beispiele fürh ochvalente Metallcarbonylkomplexe,w ie z.…”