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

摘要

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.