Synthesis and Characterization of Tetra(pyridyl)cyclo­butadiene Iron Complexes [Cp*Fe(C4py4)]– (py = 3‐pyridyl and 4‐pyridyl, Cp* = C5Me5)

Abstract

AbstractThe tetra(pyridyl)cyclobutadiene complexes [K([18{crown‐6){Cp*FeC4(3‐py)4}] (2) (3‐py = 3‐pyridyl) and [K([18{crown‐6){Cp*FeC4(4‐py)4}] (3) (4‐py = 4‐pyridyl) were synthesized by reacting two equivalents of bis(3‐pyridyl)acetylene and bis(4‐pyridyl)acetylene with the naphthalene complex [K([18{crown‐6){Cp*Fe(η4‐C10H8)}]. Compounds 2 and 3 were fully characterized by X‐ray crystallography, 1H and 13C{1H} NMR spectroscopy, UV/Vis spectroscopy, and elemental analysis. They display similar sandwich structures with an η5‐coordinated Cp* unit and an η4‐coordinated cyclobutadiene moiety. In the solid state, compounds 2 and 3 form distinct polymeric chain structures due to the interaction of the pyridyl nitrogen atoms with the potassium cations. Cyclic voltammetry measurements indicate that the [Cp*FeC4py4]– anions (py = 3‐py or 4‐py) undergo a reversible one electron oxidation to neutral [Cp*FeC4py4] complexes. A second quasi‐reversible redox event is attributed to the oxidation these products to unstable [Cp*FeC4py4]+ cations. The properties of 2 and 3 are compared with those of the previously reported 2‐pyridyl complex [K([18{crown‐6){Cp*FeC4(2‐py)4}] (1) [Dalton Trans. 2014, 43, 4247–4250].