Jian-Long Xia

Experimental and Theoretical Studies of Charge Delocalization in Biruthenium–Alkynyl Complexes Bridged by Thiophenes

A series of binuclear ruthenium-alkynyl complexes that are bridged by thiophene groups (thiophene, bithiophene, and terthiophene) have been synthesized. All of these complexes have been well-characterized by NMR spectroscopy, X-ray diffraction, and elemental analysis. The electronic properties of these complexes have been examined by using cyclic voltammetry, UV/Vis/NIR and IR spectroscopy, electron paramagnetic resonance (EPR) spectroscopy, and density functional theory (DFT) calculations. Electrochemical results showed that the potential difference (ΔE) and comproportionation constant (Kc) decreased with increasing size of the thiophene bridging unit. The UV/Vis/NIR spectra and TDDFT calculations of the monocations indicated that the NIR transitions displayed aromatic bridging character. EPR studies of the mono-oxidized radical species further demonstrated that the unpaired electron/hole was delocalized over both metals and the bridging ligand and established significant participation in the ligand oxidation.

Bridge-localized HOMO-binding character of divinylanthracene-bridged dinuclear ruthenium carbonyl complexes: spectroscopic, spectroelectrochemical, and computational studies.

The electronic properties of four divinylanthracene-bridged diruthenium carbonyl complexes [{RuCl(CO)(PMe3)3}2(μ-CH=CHArCH=CH)] (Ar=9,10-anthracene (1), 1,5-anthracene (2), 2,6-anthracene (3), 1,8-anthracene (4)) obtained by molecular spectroscopic methods (IR, UV/Vis/near-IR, and EPR spectroscopy) and DFT calculations are reported. IR spectroelectrochemical studies have revealed that these complexes are first oxidized at the noninnocent bridging ligand, which is in line with the very small ν(C≡O) wavenumber shift that accompanies this process and also supported by DFT calculations. Because of poor conjugation in complex 1, except oxidized 1(+), the electronic absorption spectra of complexes 2(+), 3(+), and 4(+) all display the characteristic near-IR band envelopes that have been deconvoluted into three Gaussian sub-bands. Two of the sub-bands belong mainly to metal-to-ligand charge-transfer (MLCT) transitions according to results from time-dependent DFT calculations. EPR spectroscopy of chemically generated 1(+)-4(+) proves largely ligand-centered spin density, again in accordance with IR spectra and DFT calculations results.

Substituted diethynyldithia[3.3]paracyclophanes—synthetically more accessible new building blocks for molecular scaffolding

A series of dialkyne building blocks based on the dithia[3.3]paracyclophane unit have been synthesized in good yields. The electronic properties of these novel dialkynes can be tuned through a transannular substitution effect. These synthetically more accessible diethynyldithia[3.3]paracyclophanes are promising candidates for the building of relatively carbon rich molecular scaffolds.