Bonding and Electronic Properties of Linear Diethynyl Oligothienoacene-Bridged Diruthenium Complexes and Their Oxidized Forms

Abstract

A series of five diruthenium diethynyl complexes based on α,β-fused oligothienoacenes in the core of the bridging ligands [{Ru(dppe)Cp*}(μ-C≡C-L-C≡C)] [dppe = 1,2-bis(diphenylphosphino)ethane, Cp* = η-CMe; L = thieno[3,2-b]thiophene (4), thieno[2,3-b]thiophene (5), 3,4-dimethylthieno[2,3-b]thiophene (6), dithieno[3,2-b:2',3'-d]thiophene (7), and thieno[3,2-b]thieno[2',3':4,5]thieno[2,3-d]thiophene (8)] have been synthesized and fully characterized electrochemically and spectroscopically. Elongation of the redox noninnocent oligothienoacene bridge core causes a smaller potential difference between the initial two anodic steps, not seen for free dialkyl oligothienoacenes, and increased positive charge delocalization over the conjugated bridge backbone. The highest occupied molecular orbital of the parent complexes resides predominantly on the oligothienoacene core, with strong participation of the ethynyl linkers and slightly smaller contribution from the metallic termini. This bonding character makes the initial one-electron oxidation symmetrical, as revealed by combined voltammetric and spectroscopic (IR, UV-vis-near-IR, and electron paramagnetic resonance) methods as well as density functional theory (DFT) and time-dependent DFT calculations of truncated and selected nontruncated models of the studied series. The remarkable gradual appearance of two C≡C stretching absorptions in the IR spectra of the monocationic diethynyl complexes is ascribed to increasing vibronic coupling of the IR-forbidden ν(C≡C) mode of the oxidized -[C≡C-core-C≡C]- bridge with a low-lying π-π*(intrabridge)/metal-to-ligand charge-transfer electronic transition in the near-to-mid-IR spectral region.

Role of Substituents at 3‐position of Thienylethynyl Spacer on Electronic Properties in Diruthenium(II) Organometallic Wire‐like Complexes

“…The integral ratio of aromatic protons are in accordance with the integral ratio of alkyl CH 2 protons, unambiguously indicating the successful insertion of [-Ru(II)(dppe)] unit to the thienylethynyl spacers (4 a-4 g). 13 C{ 1 H} NMR of the complexes (5 a, 5 c and 5 d) shows a characteristic signal of RuÀ C�C bond at 126.9 ppm, whereas for 5 b and 5 f, the signals are observed at 127.2 and 127.1 ppm respectively. However, low solubility in common organic solvents restricted the resolution of 13 C{ 1 H} NMR spectrum of complex 5 g. 31 P{ 1 H} NMR spectra shows a sharp singlet resonance in the region of 49.4-49.1 ppm for the eight phosphorus nuclei of dppe moiety, indicating the trans geometry around the Ru(II) centres.…”

“…1 H NMR (600 MHz, CDCl 3 ,) δ (ppm): 7.40-7.27 (m, 30H, Ph of dppe), 7.21-7.11 (m, 11H, Ph of dppe), 7.08-7.0 (m, 40H + 2H, Ph of dppe + CH of thienyl), 2.65-2.56 (m, 16H, CH 2 of dppe). 13 C{ 1 H} NMR (150 MHz, CDCl 3 ,) δ (ppm): 135. 1, 134.7, 134.5, 134.1, 134.0, 130.3, 129.6, 129.3, 129.1, 129.0, 128.9, 128.5, 127.6, 127.3, 127.2, 127.1, 127.0, 126.9 (RuÀ C�CÀ ), 30.9 (quint.…”

“…[12] The efficient tuning of the electron transfer properties can be modulated with appropriate extension of the conjugation in the thienylethynyl bridging spacers. However, the degree of the electron transfer processes can be perturbed to different extents, depending on several key factors such as the degree of conjugation, [13] nature of electron-rich/ deficient groups on the bridging moiety [14] and different metal precursors. [15] Therefore, the electronic properties of the organometallic wire-like complexes can be tuned by controlling these parameters and by judicious designing.…”

Electronic Properties of Oxidized Cyclometalated Diiridium Complexes: Spin Delocalization Controlled by the Mutual Position of the Iridium Centers

“…A wide range of bridged diruthenium(II) complexes belonging to the latter family have been thoroughly explored owing to their facile accessibility and high stability. The ruthenium centers in a major part of the these Ru(BL)Ru complexes are linked to conjugated bridging ligands (BL) through ethynyl or vinyl groups . The related cyclometalated ruthenium(II) complexes are less frequently reported, despite embedding the metal center into the π‐conjugated system, which is conducive to increased conjugation between the metal centers and the carbometalated ligands .…”

Ruthenium Carbon-Rich Group as a Redox-Switchable Metal Coupling Unit in Linear Trinuclear Complexes

“…For this purpose, transitionmetal acetylide are attractive redox active building blocks. [5][6][7][8][9][10][11] They present fast and discrete interfacial electron transfers, [12][13][14][15][16] and allowed modulation of different features such as NLO, [17][18][19] luminescent, [20][21][22] or other optical properties, 10,[23][24][25][26][27] as well as magnetism 23,[28][29][30][31] and conductivity. [32][33][34][35][36][37][38][39][40][41][42][43][44][45][46] Among all studied systems, ruthenium acetylides with a trans ditopic structure are particularly well suited owing to their unique ability to operate as a connector allowing electron flow to occur through different elements in multi-component systems.…”