Diruthenium(III,III) Bis(alkynyl) Compounds with Donor/Acceptor-Substituted geminal-Diethynylethene Ligands

Diruthenium(ii)-capped oligothienylethynyl bridged highly soluble organometallic wires exhibiting long-range electronic coupling

Organometallic molecular wires with π-conjugation along their molecular backbones are of considerable interest for application in molecular-scale electronics. In this regard, thienylethynyl-based π-conjugated oligomers of three, five and seven thienylethynyl units with -C[triple bond, length as m-dash]C-H termini have been successfully synthesized through stepwise Pd(0)/Cu(i)-catalyzed Sonogashira coupling. The corresponding highly soluble diruthenium(ii) diacetylide complexes (O1-Ru2, O3-Ru2, O5-Ru2 and O7-Ru2, respectively) have been prepared by the reaction of cis-Ru(dppe)2Cl2 and NaPF6 in DCM with the corresponding rigid rod-like thienylethynyl oligomers with one, three, five and seven thienylethynyl π-conjugated segments containing alkynyl termini (O1, O3, O5 and O7). These Ru(ii)-Cl capped diacetylide complexes have been further functionalized by incorporating a phenylacetynyl moiety to afford [Ru(ii)-C[triple bond, length as m-dash]C-Ph]-capped diacetylide organometallic wires (O1-Ru2-Ph, O3-Ru2-Ph, O5-Ru2-Ph and O7-Ru2-Ph). The photophysical properties of the highly soluble thienylethynyl-based oligomers and Ru(ii)-organometallic wires have been explored to understand their electronic properties. Electrochemical studies of the binuclear ruthenium(ii)-alkynyl complexes showed highly interesting results, revealing long-range electrochemical communication between the two remote Ru(ii) termini connected even with five and seven thienylethynyl units. DFT computational studies further support the long range electrochemical communication between the redox active metal termini through heavy participation of the thienylethynyl bridge in the corresponding mono-oxidized mixed valence species of the organometallic wire-like complexes.

Mixed valency in ligand-bridged diruthenium frameworks: divergences and perspectives

Emerging fundamental issues involving intramolecular electron transfer at the mixed valent diruthenium frameworks and its application prospects have been highlighted.

Filling a Gap: Electrochemical Property Comparison of the Completed Compound Series [Mo2(DArF)n(O2C-Fc)4-n] (DArF = N,N'-Diarylformamidinate; O2C-Fc = Ferrocenecarboxylate)

The reaction of cis-[Mo2(O2C-Fc)2(NCCH3)4][BF4]2 (cis-1) with two electronically different N,N'-diarylformamidinate (DArF) ligands (DArF = N,N'-bis(p-trifluoromethylphenyl)formamidinate (DTfmpF), N,N'-bis(p-anisyl)formamidinate (DAniF)) results in the isolation of the tris- and monosubstituted complexes [Mo2(DTfmpF)3(O2C-Fc)] (2a) and [Mo2(DAniF)(O2C-Fc)3] (2b). These complexes complete the series of [Mo2(DArF)n(O2C-Fc)4-n] (n = 4-0) type compounds, thus allowing for a comprehensive study. On the basis of the oxidation potential E1/2([Mo2](4+)/[Mo2](5+)) of all Mo2 complexes, ligand basicity is found to decrease in the order DAniF(-) > DTfmpF(-) > Fc-CO2(-) ≫ CH3CN. In addition, no direct electronic interaction between the trans-positioned Fc units in complex 2b is detected, which is attributed to the full overlap of all Fc oxidation processes. Furthermore, the low-energy absorption bands of compounds 2a,b are located at different positions in their respective UV-vis spectra.

Sustainable metal alkynyl chemistry: 3d metals and polyaza macrocyclic ligands

This article describes the recent development of sustainable metal-alkynyl chemistry based on the combination of 3d metals and polyaza macrocycles.

Syntheses, characterization and electrochemical and spectroscopic properties of ruthenium–iron complexes of 2,3,5,6-tetrakis(2-pyridyl)pyrazine and ferrocene-acetylide ligands

A mixed-valence Ru^IIFe^III complex displays 0.50 V of redox potential difference induced by Ru⋯Fe interactions across the Ru–CC–Fc backbone and moderate IVCT band centered at 1247 nm.

Synthesis and Electronic Structure of Ru2(Xap)4(Y-gem-DEE) Type Compounds: Effect of Cross-Conjugation

Reported in this Article are the preparation and characterization of a series of new Ru2(II,III) compounds bearing one cross-conjugated σ-geminal-diethynylethene ligand (gem-DEE), namely, Ru2(Xap)4(Y-gem-DEE) (Xap = N,N'-anilinopyridinate (ap) or 2-(3,5-dimethoxy)anilinopyridinate (DiMeOap), and Y = Si(i)Pr3 (1) or H (2)) and [Ru2(ap)4]2(μ-gem-DEE) (3). Compounds 1-3 were characterized by spectroscopic and voltammetric techniques as well as the single crystal X-ray diffraction study of 2a. The X-ray structural data of 2a and the spectroscopic/voltammetric data of compounds 1 and 2 indicate that the gem-DEE ligands are similar to simple alkynyls in their effects on the molecular and electronic structures of the Ru2(Xap)4 moiety. Similar to the previously studied [Ru2(ap)4]2(μ-C2n) type compounds, dimer 3 exhibits pairwise 1e(-) oxidations and reductions, albeit the potential splits within the pair (ΔE1/2) are significantly smaller than those of [Ru2(ap)4]2(μ-C4). The electronic absorption spectra of the reduced and oxidized derivatives of 1a and 3 were determined using spectroelectrochemistry methods. No discernible intervalence charge transfer transition (IVCT) was detected in the near-IR spectrum for either 3(-) or 3(+), suggesting that the Ru2-Ru2 coupling in these mixed-valence states is weak. DFT calculations on a model compound of 3 yielded six singly occupied molecular orbitals (SOMOs), which have Ru2 contributions similar to those previously calculated for the [Ru2(ap)4]2(μ-C2n) type compounds. Among six SOMOs, SOMO-2 is the only one containing substantial dπ-π(gem-DEE) character across the entire Ru2-μ-gem-DEE-Ru2 linkage, which explains the weakened Ru2-Ru2 coupling.

Rational synthesis and characterization of dimolybdenum(II) compounds bearing ferrocenyl-containing ligands toward modulation of electronic coupling

Three novel cis-to-trans-converted dimolybdenum(II) complexes, trans-[Mo2(O2C-Fc)2(DPPX)2][BF4]2 {2a-2c; DPPX = DPPA [N,N-bis(diphenylphosphino)amine], DPPM [1,1-bis(diphenylphosphino)methane], and DPPE [1,2-bis(diphenylphosphino)ethane], respectively}, were synthesized through the insertion of bulky diphosphine ligands, which force a permanent trans arrangement, as evidenced by X-ray crystallography and density functional theory calculations. All compounds were characterized by means of NMR, UV-vis, and IR spectroscopy as well as thermogravimetry-mass spectrometry measurements. Interestingly, uncommon UV-vis transitions and oxidation sequences were observed compared to previously reported ones. As verified by electrochemical measurements, all synthesized complexes show two separate one-electron-redox processes assigned to subsequent oxidations of the two redox-active ferrocenecarboxylate ligands, with a split of ca. 70 mV. This behavior reveals electronic interaction between the two equatorially trans-positioned ferrocenyl units. The presented work provides new insights into the rational synthesis of electronically coupled trans-coordinated Mo2 systems, paving the way toward the design of linear multicenter redox-active oligomers.

Conformation-determined through-bond versus through-space electronic communication in mixed-valence systems with a cross-conjugated urea bridge

Bis-triarylamine 2 and cyclometalated diruthenium 6(PF6)2 with a linear trans,trans-urea bridge have been prepared, together with the bis-triarylamine 3 and cyclometalated diruthenium 8(PF6)2 with a folded cis,cis-N,N-dimethylurea bridge. The linear or folded conformations of these molecules are supported by single-crystal X-ray structures of 2, 3, and other related compounds. These compounds display two consecutive anodic redox waves (N(·+/0) or Ru(III/II) processes) with a potential separation of 110-170 mV. This suggests that an efficient electronic coupling is present between two redox termini through the cross-conjugated urea bridge. The degree of electronic coupling has been investigated by using spectroelectrochemical measurements. Distinct intervalence charge-transfer (IVCT) transitions have been observed for mixed-valent (MV) compounds with a linear conformation. The IVCT transitions can also be identified for the folded MV compounds, albeit with a much weaker intensity. DFT results support that the electronic communication occurs by a through-bond and through-space pathway for the linear and folded compounds, respectively. The IVCT transitions of the MV compounds have been reproduced by TDDFT calculations. For the purpose of comparison, a bistriarylamine and a diruthenium complex with an imidazolidin-2-one bridge and a urea-containing mono-triarylamine and monoruthenium complex have been synthesized and studied.

Electronic tuning of Mo2(thioamidate)4 complexes through π-system substituents and cis/trans isomerism

We report an exploration of the coordination chemistry of a systematic series of cyclic thioamidate ligands with the quadruply-bonded Mo2(4+) core. In addition to the S and N donor atoms that bind to Mo, the ligands utilized in this study have an additional O or S atom in conjugation with the thioamidate π system. The preparation of four new Mo2 complexes is described, and these compounds are characterized by X-ray crystallography, NMR and UV-vis spectroscopy, electrochemistry, and DFT calculations. These complexes provide a means to interrogate the electronics of Mo2(thioamidate)4 systems. Notably, we describe the first two examples of Mo2(thioamidate)4 complexes in their cis-2,2-regioisomer. By varying the π-system substituent and regioisomerism of these compounds, the electronics of the dimolybdenum core is shown to be altered with varying degrees of effect. Cyclic voltammetry results show that changing the π-system substituent from O to S results in an increase in the Mo2(4+/5+) oxidation potential by 170 mV. Changing the arrangement of ligands around the dimolybdenum core from trans-2,2 to cis-2,2 slightly weakens the metal-ligand bonds, raising the oxidation potential by a more modest 30-100 mV. MO diagrams of each compound derived from DFT calculations support these conclusions as well; the identity of the π-system substituent alters the δ-δ* (HOMO-LUMO) gap by up to 0.4 eV, whereas regioisomerism yields smaller changes in the electronic structure.