Reactivity studies on [Cp′Fe(μ-I)]2: nitrido-, sulfido- and diselenide iron complexes derived from pseudohalide activation

Abstract

The iron half-sandwich [Cp′Fe(μ-I)]₂ (Cp′ = 1,2,4-(Me₃C)₃C₅H₂, 1) reacts with the pseudohalides NCO⁻, SCN⁻, SeCN⁻ and N₃⁻ to give [Cp′Fe(μ-NCO)]₂ (2), [Cp′Fe(μ-S)]₂ (3), [Cp′Fe(μ-Se₂)]₂ (4) and [Cp′Fe(μ-N)]₂ (5), respectively. Various spectroscopic techniques including X-ray diffraction, solid-state magnetic susceptibility studies and ⁵⁷Fe Mössbauer spectroscopy were employed in the characterization of these species. Mössbauer spectroscopy shows a decreasing isomer shift with increasing formal oxidation state, ranging from Fe(II) to Fe(IV), in complexes 1 to 5. The sulfido-bridged dimer 3 exhibits strong antiferromagnetic coupling between the Fe(III) centers. This leads to temperature-independent paramagnetism (TIP) at low temperature, from which the energy gap between the ground and the excited state can be estimated to be 2J = ca. 700 cm⁻¹. The iron(IV) nitrido complex [Cp′Fe(μ-N)]₂ (5) shows no reactivity towards H₂ (10 atm), but undergoes clean reactions with CO (5 bar) and XylNC (Xyl = 2,6-Me₂C₆H₃) to form the diamagnetic isocyanate and carbodiimide complexes [Cp′Fe(CO)₂(NCO)] (7) and [Cp′Fe(CNXyl)₂(NCNXyl)] (8), respectively. All compounds were fully characterized, and density functional theory (DFT) computations provide useful insights into their formation and the electronic structures of complexes 3 and 5.