Structural Differences and Redox Properties of Unsymmetric Diiron PDIxCy Complexes

Abstract

We present two bimetallic iron complexes, [Fe 2 (PDIeCy)(OTf ) 4 ] (1) and [Fe 2 (PDIpCy)(THF)(OTf ) 4 ] (2) coordinated by an unsymmetric ligand. The new ligand, PDIeCy (PDI = pyridyldiimine; e = ethyl; Cy = cyclam), is a variant of the previously reported PDIpCy (p = propyl) ligand, featuring a shorter linker between the two metal coordination sites. The structural and electronic properties of 1 and 2, both in the solid and solution state, were analyzed by means of X-ray crystallography, and spectroscopic methods, including 19 F-NMR. The two ligand platforms yield markedly different diiron structures: the PDIeCy ligand permits formation of a bridged, μ-OTf complex, while the [a] 499 two iron centers of the PDIpCy-based 2 remain unconnected, directly, under all conditions examined. Both compounds contain electronically non-coupled high-spin (S = 2) ferrous centers, as established by Mössbauer spectroscopy and magnetic susceptibility studies. Cyclic voltammetry demonstrates the rich redox chemistry of the compounds, involving both ligand and metal-centered redox processes. Moreover, we synthesized the two-electron reduced [Fe 2 (PDIeCy)] 2+ form of 1, which contains the dianionic PDI 2ligand, and represents a two-electron charge localized complex.group, to support dinuclear complexes thereof (Scheme 1). [29] We reported the synthesis of non-coupled homo-and heterobimetallic Ni-and Zn-containing PDIpCy complexes. We now have focused our attention on diiron compounds. Iron offers Scheme 1. Synthesis of 1 and 2.