Reversible coordination of N₂ and H₂ to a homoleptic S = ¹/₂ Fe(I) diphosphine complex in solution and the solid state

The synthesis and characterisation of the S = ¹/₂ Fe(I) complex [Fe(depe)₂]⁺[BAr^F₄]⁻ ([1]⁺[BAr^F₄]⁻), and the facile reversible binding of N₂ and H₂ in both solution and the solid state to form the adducts [1·N₂]⁺ and [1·H₂]⁺, are reported. Coordination of N₂ in THF is thermodynamically favourable under ambient conditions (1 atm; ΔG₂₉₈ = −4.9(1) kcal mol⁻¹), while heterogenous binding is more favourable for H₂ than N₂ by a factor of ∼300. [1·H₂]⁺[BAr^F₄]⁻ represents a rare example of a well-defined, open-shell, non-classical dihydrogen complex, as corroborated by ESR spectroscopy. The rapid exchange between N₂ and H₂ coordination under ambient conditions is unique for a paramagnetic Fe complex.