Manipulation and Assessment of Charge and Spin Delocalization in Mixed-Valent Triarylamine–Vinylruthenium Conjugates

Abstract

Triarylamine-vinylruthenium conjugates (4-RC6H4)2N{C6H4-4-CH═CHRu(CO)Cl(PiPr3)2}, with R = CHO (1-CHO), C(═O)Me (1-Ac), COOMe (1-E), and Me (1-Me), have been prepared and investigated in their neutral, mono- and dioxidized states by cyclic voltammetry, IR, and UV/vis/near-infrared spectroelectrochemistry, electron paramagnetic resonance spectroscopy, and quantum-chemical calculations. Electron-withdrawing substituents at the triarylamine moiety shift the charge and spin density toward the more electron-rich vinylruthenium site in comparison to the 4-OMe-substituted triarylamine-vinylruthenium conjugate 1-OMe. A more asymmetric charge distribution changes the intense vibrationally structured intervalence charge-transfer (IVCT) band of completely delocalized, mixed-valent (MV) 1-OMe+ to a weaker, highly asymmetric, nonsolvatochromic band with significantly smaller bandwidth at the low-energy side. The temperature dependence of the IVCT band of the formyl derivative 1-CHO+ proves that vibrational coupling of the IVCT transition to a symmetrical vibration is the underlying reason for band skewing. All of our results indicate that the MV radical cations remain electronically strongly coupled despite an increasingly stronger bias of the highest occupied molecular orbital to the vinylruthenium entity. Moreover, the dications of these complexes were found to be paramagnetic, which makes them rare examples of compounds that combine strong electronic coupling in the cationic MV state with paramagnetism of the dications.