Reactivity of a Bis(amidinato)iron(II) Complex [Fe(MesC(NPri)2)2] toward Some Oxidizing Reagents

Isostructural bridging diferrous chalcogenide cores [FeII(μ-E)FeII] (E = O, S, Se, Te) with decreasing antiferromagnetic coupling down the chalcogenide series

Iron compounds containing a bridging oxo or sulfido moiety are ubiquitous in biological systems, but substitution with the heavier chalcogenides selenium and tellurium, however, is much rarer, with only a few examples reported to date. Here we show that treatment of the ferrous starting material [(^tBupyrpyrr₂)Fe(OEt₂)] (1-OEt₂) (^tBupyrpyrr₂ = 3,5-^tBu₂-bis(pyrrolyl)pyridine) with phosphine chalcogenide reagents E = PR₃ results in the neutral phosphine chalcogenide adduct series [(^tBupyrpyrr₂)Fe(EPR₃)] (E = O, S, Se; R = Ph; E = Te; R = ^tBu) (1-E) without any electron transfer, whereas treatment of the anionic starting material [K]₂[(^tBupyrpyrr₂)Fe₂(μ-N₂)] (2-N₂) with the appropriate chalcogenide transfer source yields cleanly the isostructural ferrous bridging mono-chalcogenide ate complexes [K]₂[(^tBupyrpyrr₂)Fe₂(μ-E)] (2-E) (E = O, S, Se, and Te) having significant deviation in the Fe-E-Fe bridge from linear in the case of E = O to more acute for the heaviest chalcogenide. All bridging chalcogenide complexes were analyzed using a variety of spectroscopic techniques, including ¹H NMR, UV-Vis electronic absorbtion, and ⁵⁷Fe Mössbauer. The spin-state and degree of communication between the two ferrous ions were probed via SQUID magnetometry, where it was found that all iron centers were high-spin (S = 2) Fe^II, with magnetic exchange coupling between the Fe^II ions. Magnetic studies established that antiferromagnetic coupling between the ferrous ions decreases as the identity of the chalcogen is tuned from O to the heaviest congener Te.

Redox-Controlled and Reversible N-N Bond Forming and Splitting with an IronIV Terminal Imido Ligand

Oxidation of the low-spin Fe^IV imido complex [{(^tBupyrr)₂py}Fe═NAd] (1) ((^tBupyrr)₂py^2- = 2,6-bis(3,5-di-tert-butyl-pyrrolyl)pyridine, Ad = 1-adamantyl) with AgOAc or AgNO₃ promotes reductive N-N bond coupling of the former imido nitrogen with a pyrrole nitrogen to form the respective ferric hydrazido-like pincer complexes [{(^tBupyrrNAd)(^tBupyrr)py}Fe(κ²-X)] (X = OAc^-, 2^OAc; NO₃^-, 2^NO₃). Reduction of 2^OAc with KC₈ cleaves the N-N bond to reform the Fe^IV imido ligand in 1, whereas acid-mediated demetalation of 2^OAc or 2^NO₃ yields the free hydrazine ligand [(^tBupyrrNHAd)(^tBupyrrH)py] (3), the latter of which can be used as a direct entry to the iron imido complex when treated with [Fe{N(SiMe₃)₂}₂]. In addition to characterizing these Fe systems, we show how this nitrene transfer strategy can be expanded to Co for the one-step synthesis of Co{(^tBu-NHAdpyrr)(^tBupyrr)py}] (4) ((^tBu-NHAdpyrr)(^tBupyrr)py^2- = 2-(3-tBu-5-(1-adamantylmethyl-2-methylpropane-2-yl)-pyrrol-2-yl)-6-(3,5-tBu₂-pyrrol-2-yl)-pyridine).

A dianionic C3-symmetric scorpionate: synthesis and coordination chemistry

Introducing charges into ligand systems fine-tunes their electronic properties and influences the solubility of their metal complexes. Herein, we present a synthesis of a dianionic, C3-symmetric ligand combining three anionic N-donors tethered to a positively charged phosphonium center. The tris-skatylmethylphosphonium (TSMP) ligand, isolated in the form of its dipotassium salt TSMPK2, is the first dianionic homoscorpionate capable of metal exchange. The potassium cations in TSMPK2 are exchangeable for other metals, which results in rich coordination chemistry. Thus, the ligand displays a bridging μ2:κ2:κ1 coordination mode with trigonal planar Cu(i) centers in the tetrameric complex [(TSMP)Cu]44-. The κ3 mode is accessed upon addition of 1 equiv. of P(OEt)3 per Cu(i) to yield the tetrahedral monomeric complex [(TSMP)CuP(OEt)3]-. Both Fe(ii) and Ni(ii) in pyridine give octahedral high-spin κ3 complexes with composition (TSMP)M(Py)3 (M = Fe, Ni). Displacement of three pyridine ligands in (TSMP)Fe(Py)3 for a second equivalent of TSMP gives a high-spin pseudotetrahedral 2 : 1 complex [(TSMP)2Fe]2- with the ligands in κ2 coordination mode. The reduction in coordination number is likely due to electrostatic repulsion of the negatively-charged indolides as well as their weaker π-accepting character as compared to pyridine.

Reactivity of an All-Ferrous Iron-Nitrogen Heterocubane under Reductive and Oxidative Conditions

The reactivity of the all-ferrous FeN heterocubane [Fe4 (Ntrop)4 ] (1) with i) Brønsted acids, ii) σ-donors, iii) σ-donors/π-acceptors, and iv) one-electron oxidants has been investigated (trop = 5H-dibenzo[a,d]cyclo-hepten-5-yl). 1 showed self-re-assembling after reactions with i) and proved surprisingly inert in reactions with ii) and iii), with the exception of CO. Reductive and oxidative cluster degradation was observed in reactions with CO and TEMPO, respectively. These reactions yielded new cluster compounds, namely a trinuclear bis(μ3 -imido) 48 electron complex in the former case and a tetranuclear all ferric μ-oxo-μ-imido species in the latter case. Characterization techniques include NMR and in situ IR spectroscopy, single crystal X-ray analysis, Mössbauer spectroscopy, cyclic voltammetry, magnetic susceptibility measurements, and DFT calculations.