1,3‐Diethynyl‐5‐(X)‐benzene‐Bridged [Cp*(dppe)Fe]n+ Units: Effect of Substituents on the Metal‐Metal Interactions

Abstract

AbstractThe new complexes [1,3‐{Cp*(dppe)Fe−C≡C‐}2‐5‐(X)‐(C6H3)] (X=CH3, [m‐1 b]; X=C(O)OCH3, [m‐1 c]; X=C≡C−4−C6H4−C(O)OCH3, [m‐1 d]; X=C≡C−4−C6H4‐NO2, [m‐1 e]) were prepared by reaction of the iron chloride Cp*(dppe)FeCl (4) and the proligands 3 b–e obtained by a cross coupling reaction between the suitable aryl dibromides and trimethylsylilacethylene. After purification the complexes [m‐1 b–e] were isolated in yields ranging from 14 to 37 % and characterized by elemental analysis, high‐resolution, ESI‐mass spectra, multinuclear NMR, cyclic voltammetry, and IR spectroscopy. The complexes [m‐1 b], [m‐1 d], and [m‐1 e] were also characterized by XRD analyses on single crystals. The doubly oxidized complexes [m‐1 b–e](PF6)2 were prepared (in ca. 64–87 % yields) by treatment of a CH2Cl2 solution of the corresponding neutral complexes [m‐1 b–e] with two equiv. of [(C5H5)2Fe](PF6). The mixed‐valence complexes (MV) [m‐1 b–e](PF6) were obtained by comproportionation between one equiv. of [m‐1 b–e] and one equiv. of [m‐1 b–e](PF6)2. CV, IR and NIR data led to the conclusion that the MV [m‐1 b–e](PF6) complexes are weakly coupled Class II MV derivatives and the distribution of the charge between the alkynyl iron centers and the phenyl ring might be tuned by the X‐substituents in a limited extend.