Syntheses, Structures, and Properties of Some Piano-Stool Iron Acetylides Bearing a Functional Anthracenyl Group

The present study reports the isolation and the structural (X-ray), electrochemical (CV), and spectroscopic (IR, Mössbauer, ESR, UV–vis−NIR) characterization of the new complexes [(η²-dppe)(η⁵-C₅Me₅)Fe(−CC-9,10-ant-X)]ⁿ⁺ n[Y] (dppe = 1,2-bis(diphenylphosphino)ethane; ant = anthracene; n = 0, 1; 3a ⁿY, X = H; 3b ⁿY, X = Br; 3c ⁿY, X = CN; 3d, X = CCSiⁱPr₃; 3e, X = CCH; Y = PF₆, TCNE, TCNQ). It was shown that anthracene acts as a better transmitter than phenyl. The electron density on the Fe(III) nucleus depends on the distance between the metal center and the counteranion. The bulky (η²-dppe)(η⁵-C₅Me₅)Fe moiety is big enough to push the anthracene rings further apart and disrupts π−π stacking except in the case of 3c[TCNE] for which stacking is observed both between the TCNE anion and the (C₅Me₅) ligand and between anthracene fragments. The Fe(II) complexes display MLCT transitions in the 550–650 nm range while LMCT transitions can be observed in the 600–850 nm spectral range for the Fe(III) complexes. The Fe(II) and Fe(III) complexes exhibit weak luminescence property derived from the alkynyl anthracene units. Both Fe(II) and Fe(III) moieties can quench the ligand-centered emission by two different mechanisms.