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

The iron half-sandwich [Cp′Fe(μ-I)](2) (Cp′ = 1,2,4-(Me(3)C)(3)C(5)H(2), 1) reacts with the pseudohalides NCO(–), SCN(–), SeCN(–) and N(3)(–) to give [Cp′Fe(μ-NCO)](2) (2), [Cp′Fe(μ-S)](2) (3), [Cp′Fe(μ-Se(2))](2) (4) and [Cp′Fe(μ-N)](2) (5), respectively. Various spectroscopic techniques including X-ray diffraction, solid-state magnetic susceptibility studies and (57)Fe 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 H(2) (10 atm), but undergoes clean reactions with CO (5 bar) and XylNC (Xyl = 2,6-Me(2)C(6)H(3)) 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.