Diruthenium Complexes with Bridging Diethynyl Polyaromatic Ligands: Synthesis, Spectroelectrochemistry, and Theoretical Calculations

Abstract

This work describes syntheses and electrochemical, spectroscopic, and bonding properties in a new series of dinuclear ruthenium(II) complexes bridged by polyaromatic (biphenyl, fluorene, phenanthrene, and pyrene) alkynyl ligands. Longitudinal expansion of the π-conjugated polyaromatic core of the bridging ligands caused a reduced potential difference between the anodic steps and reinforced their bridge-localized nature, as evidenced by UV/vis/near-IR and IR spectroelectrochemical data combined with DFT and TDDFT calculations. Importantly, the intricate multiple IR ν(CC) absorption bands for the singly oxidized states imply a thermal population of a range of conformers (rotamers) with distinct electronic character. This behavior was demonstrated with more accurate DFT calculations of selected nontruncated 1e − oxidized complexes in three different conformations. The combined experimental and theoretical data reveal that thermally populated rotamers featuring various mutual orientations of the ligated metal termini and the bridging diethynyl polyaromatic moieties have a significant impact on the electronic absorption and ν(CC) wavenumbers of the singly oxidized systems. ■ INTRODUCTIONSince the first report of the Creutz−Taube ion [(H 3 N) 5 Ru(μ-pyrazine)Ru(NH 3 ) 5 ] 5+ , there have been numerous experimental and theoretical attempts to elaborate the properties of related symmetrical diruthenium complexes due to the surprising stability of the Ru II Ru III mixed-valence states. 1 It has been well documented that diruthenium complexes with metal centers linked by π-conjugated bridges allow for facile electron transfer along the whole molecular framework. Accordingly, pertinent studies have concentrated on elaborately selecting the conjugated bridging ligands and tuning the electronic effect of the ancillary ligands to subtly modulate the intramolecular electron-transfer properties in mixed-valence complexes. 2,3 We have focused on dinuclear ruthenium complexes with a particular type of redox-active terminals, viz., (P,P′-dppe)(η 5 -C 5 Me 5 )Ru, which are interconnected by the conjugated bridge participating in the redox behavior. These complexes may become attractive candidates for molecular wires. 4 Furthermore, a range of studies in our laboratory as well as other literature reports have convincingly elucidated that the horizontal scaling of π-conjugated bridges results in poor solubility and chemical stability of the oxidized species and an attenuation of the electronic transport in a mixed-valence system; introducing aromatic rings such as benzene or a heterocycle in the spacer can constitute an attractive alternative to improve this instability and eventually to tune their physical or even chemical properties. 5 Therefore, a reasonable control of the length and appropriate extension of the conjugation in the bridging ligands can afford improved stability and allow for efficient tuning of the electron-transfer properties. 6 In addition, numerous studies have indicated that fluorene, phenanthrene, and pyrene ...

Ferrocenyl‐Pyrenes, Ferrocenyl‐9,10‐Phenanthrenediones, and Ferrocenyl‐9,10‐Dimethoxyphenanthrenes: Charge‐Transfer Studies and SWCNT Functionalization

“…They observed a redox separation of 80 (2,7‐bis(3,6‐di‐ tert ‐butyl‐9 H ‐carbazol‐9‐yl)pyrene) to 100 mV (2,7‐bis(carbazol‐9‐yl)pyrene), which is in good agreement with the results observed for 5 b and 7 b . The group of Rao and Liu investigated the redox splitting of 2,7‐((η 5 ‐C 5 Me 5 )(dppe)RuC≡C) 2 ‐pyrene, which showed a value of 120 mV …”

“…The Fc group in position 1 in 3 (30 mV vs. FcH/FcH + ) is more easily to oxidize than the Fc in position 2 in 7 a ( E °′=50 mV). However, the 1,6‐ and 2,7‐substitution patterns of pyrenes 5 b and 7 b have no significant influence on the redox potentials and the redox splitting as was reported for Fc 2 ‐naphthalenes, as well as 2,7‐bis(carbazol‐9‐yl)‐, 2,7‐bis(3,6‐di‐ tert ‐butyl‐9 H ‐carbazol‐9‐yl)‐, and 2,7‐((η 5 ‐C 5 Me 5 )(dppe)RuC≡C) 2 ‐pyrenes . In contrast, the Fc/Fc + redox potential of 10 and 12 differ as expected for electron‐withdrawing (C(=O)) or ‐donating (MeO) groups in positions 9 and 10 of the phenanthrene core.…”

Binuclear Ruthenium Complexes with Benzo[1,2‐b;4,5‐b′]dithiophene Analogues as Bridge Ligands: Syntheses, Characterization and Notable Difference on Electronic Coupling

“…Kaim, [14] Low, [8,15] Zhong, [16,17] Chen, [18] and Liu [19,20] groups have performed various experiments to characterize and investigate the electronic coupling of these systems by electrochemistry, spectroelectrochemistry and theoretical calculations. Kaim, [14] Low, [8,15] Zhong, [16,17] Chen, [18] and Liu [19,20] groups have performed various experiments to characterize and investigate the electronic coupling of these systems by electrochemistry, spectroelectrochemistry and theoretical calculations.…”

“…However, numerous studies have been conducted by Kaupp, Low and Liu et al, which have proven that similar broad NIR absorptions are composed of several sub-bands caused by different rotameric forms [19,21,[28][29][30]. However, numerous studies have been conducted by Kaupp, Low and Liu et al, which have proven that similar broad NIR absorptions are composed of several sub-bands caused by different rotameric forms [19,21,[28][29][30].…”

Elaborately Tuning Intramolecular Electron Transfer Through Varying Oligoacene Linkers in the Bis(diarylamino) Systems

“…Recently, mixed-valence (MV) compounds with two identical redox-active groups have attracted continuous attention because they are one of the most widely exploited model systems used to study intramolecular electron transfer processes and can provide important and broad prospects for constructing highly functionalized molecules with interesting electronic and photophysical properties essential for molecular devices12345. Accordingly, numerous studies have focused on elaborately screening rigid and π -conjugated bridging ligands linking two redox termini to subtly tune the intramolecular electron-transfer properties in MV systems678910.…”