Long-Range Intramolecular Electronic Communication in a Trinuclear Ruthenium Tropolonate Complex

Jun Yoshida; Kyohei Kuwahara; Kota Suzuki; Hidetaka Yuge

doi:10.1021/acs.inorgchem.6b02249

Long-Range Intramolecular Electronic Communication in a Trinuclear Ruthenium Tropolonate Complex

Inorg Chem. 2017 Feb 20;56(4):1846-1856. doi: 10.1021/acs.inorgchem.6b02249. Epub 2017 Feb 3.

Authors

Jun Yoshida¹, Kyohei Kuwahara¹, Kota Suzuki¹, Hidetaka Yuge¹

Affiliation

¹ Department of Chemistry, School of Science, Kitasato University 1-15-1 Kitasato, Minami-ku, Sagamihara, Kanagawa 252-0373, Japan.

PMID: 28156109
DOI: 10.1021/acs.inorgchem.6b02249

Abstract

Dinuclear and trinuclear ruthenium complexes, [Ru(trop)₂(C₂trop)Ru(dppe)Cp] [2b; trop = tropolonato, C₂trop = ethynyltropolonato, dppe = 1,2-bis(diphenylphosphino)ethane] and [Ru(trop){(C₂trop)Ru(dppe)Cp}₂] (3), were synthesized, and their electronic and electrochemical properties were investigated in comparison with our previously reported complex [Ru(acac)₂(C₂trop)Ru(dppe)Cp] (2a). The electron-donating Ru^II(dppe)Cp unit and electron-accepting Ru^IIIO₆ unit are connected by C₂trop in these complexes. 2a incorporates acetylacetonate as an ancillary ligand, while 2b and 3 incorporate tropolonate as an ancillary ligand. Every complex, 2a, 2b, and 3, exhibits similar UV-vis-near-IR (NIR) absorption spectra, demonstrating the lack of explicit intramolecular electronic communication between the units at least in the neutral state. The weak NIR absorption in 2a further diminished upon electrochemical oxidation, indicating almost no electronic communication between the units. In contrast, 2b and 3 exhibit broad NIR absorptions upon oxidation. Additionally, 3 exhibits four stepwise redox couples in the electrochemical study, which are formally attributed to [Ru^II(trop)₃]^-/[Ru^III(trop)₃], two [Ru^II(dppe)Cp]/[Ru^III(dppe)Cp]⁺, and [Ru^III(trop)₃]/[Ru^IV(trop)₃]⁺ couples. Clear separation of the redox couples attributed to the two terminal [Ru(dppe)Cp] units demonstrates the thermodynamic stability of the intermediate oxidation states with respect to disproportionation. Further electrochemical studies using an electrolyte including perfluorinated weakly coordinating anions and density functional theory/time-dependent density functional theory calculations confirmed the effect of ancillary ligands, acetylacetonate and tropolonate. In the case of 2a, electronic delocalization over the whole complex, especially over the [Ru(acac)₂(trop)] unit, appears to be small. In contrast, the electronic communication between [Ru(dppe)Cp] and [Ru(trop)₃] units in 3 seems to be enhanced upon oxidation, resulting in the long-range intramolecular electronic communication.