Unusual Dinitrogen Binding and Electron Storage in Dinuclear Iron Complexes

Abstract

A rare example of a dinuclear iron core with a non-linearly bridged dinitrogen ligand is reported in this work. One-electron reduction of [( tBupyrr2py)­Fe­(OEt2)] (1) ( tBupyrr2py2– = 2,6-bis­((3,5-di-tert-butyl)­pyrrol-2-yl)­pyridine) with KC8 yields the complex [K]2­[( tBupyrr2py)­Fe]2­(μ2-η1:η1-N2) (2), where the unusual cis-divacant octahedral coordination geometry about each iron and the η5-cation-π coordination of two potassium ions with four pyrrolyl units of the ligand cause distortion of the bridging end-on μ-N2 about the FeN2Fe core. Attempts to generate a Et2O-free version of 1 resulted instead in a dinuclear helical dimer, [( tBupyrr2py)­Fe]2 (3), via bridging of the pyridine moieties of the ligand. Reduction of 3 by two electrons under N2 does not break up the dimer, nor does it result in formation of 2 but instead formation of the ate-complex [K­(OEt2)]2­[( tBupyrr2py)­Fe]2 (4). Reduction of 1 by two electrons and in the presence of crown-ether forms the tetraanionic N2 complex [K2]­[K­(18-crown-6)]2­( tBupyrr2py)­Fe]2­(μ2-η1:η1-N2) (5), also having a distorted FeN2Fe moiety akin to 2. Complex 2 is thermally unstable and loses N2, disproportionating to Fe nanoparticles among other products. A combination of single-crystal X-ray diffraction studies, solution and solid-state magnetic studies, and 57Fe Mössbauer spectroscopy has been applied to characterize complexes 2–5, whereas DFT studies have been used to help explain the bonding and electronic structure in these unique diiron-N2 complexes 2 and 5.

Effects of 2,6‐Dichlorophenyl Substituents on the Coordination Chemistry of Pyridine Dipyrrolide Iron Complexes

“…In addition to imido formation upon exposure to organic azides, the Fe II starting material ( tBu PDP tBu )Fe(OEt 2 ) can engage in small molecule activation while retaining cis ‐divacant octahedral geometries in the corresponding products. This is exemplified by its reaction with elemental sulfur [10] and formation of a dinuclear bridging dinitrogen complex upon reduction with KC 8 [11] . Similar cis ‐divacant octahedral geometries were established in cobalt chemistry for ( tBu PDP tBu )Co(OEt 2 ) and the isolable organic azide adduct ( tBu PDP tBu )Co(N 3 1 Ad) [12] .…”

Dinitrogen Coordination to a High‐Spin Diiron(I/II) Species

“…This complex also displays the cis ‐ μ ‐1,2 coordination mode, which remains rare in diiron chemistry with only two other examples reported (Figure 1). Notably, prior examples were obtained for highly‐reduced compounds or using strong‐field ligands contrasting the ligand field imposed here [8, 9] …”

Nickel(II) carbonyl, ammonia, and acetonitrile complexes supported by a pyridine dipyrrolide pincer ligand

“…1). The pyridine dipyrrolide is a particularly attractive ligand framework, as several examples of pyridine dipyrrolide pincers with different substituents on the ligand backbone (e.g., Me, t-Bu, Ph, Mes) are known and have already been successfully used with both early and late transition-metal ions such as Ti (Zhang et al, 2016), Zr (Zhang et al, 2016(Zhang et al, , 2020, Cr (Gowda et al, 2018), Mo (Gowda et al, 2018), Fe (Sorsche et al, 2020;Hakey et al, 2019), Co (Grant et al, 2016), Pt (Komine et al, 2014), Pd (Yadav et al, 2018) and Zn (Komine et al, 2014) to form well-defined metal complexes.…”