1,4‐Diethynylbenzene‐Bridged [Cp*(dppe)Fe]n+ Units: Effect of 2,5‐Ethynyl Groups on the Chemical and Electronic Properties

The bis(ironvinylidene) complex [1,4-{Cp*(dppe)Fe=C=CH}(2)-2,5-(C equivalent to CH)(2)-C6H2](PF6)(2) ([2-2H](PF6)(2)) was prepared from 1,2,4,5-tetraethynylbenzene and two equiv. of Cp*(dppe)FeCl in 87 % yield. The reaction is very selective and [2-2H](PF6)(2) is the unique organoiron species to be formed. Deprotonation of [2-2H](PF6)(2) provided the target complex 2 (66 % yield) and subsequent oxidation gave the monocationic and dicationic complexes 2(PF6) and 2(PF6)(2). The new complexes were characterized by ESI-mass spectrometry, IR, multinuclear NMR, ESR and Mossbauer spectroscopy, and XRD analyses on single crystals for [2-2H](PF6)(2) and 2(PF6)(2). The magnetic properties of 2(PF6)(2) were investigated by VT H-1 NMR. The data were analyzed with the support of quantum chemistry calculations. The terminal ethynyl groups on the aromatic ring of the bridge modify the population of the bridge-oxidized state, weaken the electronic communication (H-ab approximate to 601 cm(-1)) and strengthen magnetic coupling interactions (J = -530 cm(-1)) compared to the unsubstituted species (H-ab = 1700 cm(-1) and J = -340 cm(-1), respectively).