Multistate Redox‐Active Metalated Triarylamines

Abstract

Abstracttrans‐[(η5‐C5H5)Fe(η5‐C5H4‐η1‐C≡C)Ru(C≡C‐4‐C6H4NPh2)(dppe)2] [4; dppe = 1,2‐bis(diphenylphosphanyl)ethane] and trans,trans,trans‐[{(η5‐C5H5)Fe(η5‐C5H4‐η1‐C≡C)Ru(dppe)2(C≡C‐4‐C6H4)}3N] (7) have been synthesized from trans‐[Ru(C≡C‐4‐C6H4NPh2)Cl(dppe)2] (3) and trans,trans,trans‐[{(dppe)2ClRu(C≡C‐4‐C6H4)}3N] (6), respectively, and the identities of trans‐[Ru(C=CH‐4‐C6H4NPh2)Cl(dppe)2][PF6] (2, precursor to 3), 3, and 4 have been confirmed crystallographically. Chemical oxidation of 4 and 7 afforded the isolable mixed‐valence species 4[PF6] and 7[PF6]3. The CV of 4 reveals sequential loss of three electrons in fully reversible oxidation steps, whereas the CV of 7 shows five reversible redox waves; in contrast, oxidation of the precursor amines HC≡C‐4‐C6H4NPh2 and (HC≡C‐4‐C6H4)3N are irreversible processes. All oxidation processes afford reversible changes in the linear optical properties. Complementary time‐dependent density functional theory (TD‐DFT) studies suggest that the initial oxidation process for 4 and 7 is iron‐centered and is followed by one (for 4) or three (for 7) ruthenium‐centered oxidations. The final reversible oxidation is assigned by TD‐DFT as delocalized along the metalla‐ethynylarylamine moiety. The intense optical changes consequent on reversible oxidation, together with their charge‐transfer character, suggest that 4 and 7 have potential as nonlinear as well as linear optical multistate switches.