Iron compounds containing a bridging oxo or sulfido moiety are ubiquitous in biological systems but iron compounds containing the heavier chalcogenides selenium and tellurium are much rarer. Here we show that treatment of the ferrous starting material [(^t^Bupyrpyrr₂)Fe(OEt₂)] (1-OEt₂) (^t^Bupyrpyrr₂ = 3,5-^tBu₂-bis(pyrrolyl)pyridine) with phosphine chalcogenide reagents E=PR₃ results in the neutral phosphine chalcogenide adducts [(^t^Bupyrpyrr₂)Fe(E=PR3)] (E = O, S, Se; R = Ph;E = Te; R = tBu) (1-E). However, treatment of the anionic starting material [K]₂[(^t^Bupyrpyrr₂)Fe₂(u-N₂)] (2-N₂) with the appropriate chalcogenide transfer reagents results in clean formation of isostructural ferrous bridging mono-chalcogenide ate complexes K₂[(^t^Bupyrpyrr₂)Fe₂(u-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 these bridging chalcogenide complexes were analyzed using a variety of spectroscopic techniques including ¹H NMR, UV-Vis, and Mössbauer spectroscopy. The spin-state and degree of communication between the ferrous ions was probed via SQUID magnetometry where it was found that all iron centers were high-spin (S = 2) Fe(II) with antiferromagnetic coupling between them. Magnetic studies established that antiferromagnetic coupling between the ferrous ions increases as the identity of the chalcogen is tunned from O to the heaviest congener Te. 2-N₂ could also be used to access the low valent compound (^t^Bupyrpyrr₂)Fe₂(N₂)₂(K(18-crown-6))₂ (3) capable of cleaving C-H and C-F bonds.

Lisa Pick

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