Jean-Pierre Launay

Long-distance intervalence electron transfer

Long-distance intervalence electron transfer can be monitored by the quantitative study of intervalence transitions in series of binuclear mixed-valence metal complexes, with metal–metal distances reaching 25 A. This allows the determination of the electronic coupling Vab, and its rate of decay with distance. Comparisons are made between several series of compounds, and also with organic mixed-valence systems. The decay is exponential with a coefficient varying in a relatively narrow range (0.08 to 0.12 A−1). Applications for molecular switching are discussed.

Long-range coupling in a mixed-valence diruthenium complexes containing bis-terpyridine ligands of various lengths as bridges

Dinuclear ruthenium(II) complexes have been prepared which contain back-to-back bis-terpyridine ligands of various lengths (Ru ⋯ Ru distances between 7 and 20 A) as bridges; significant electronic coupling is observed in mixed-valence states, even for the system with the longest separation.

Stepwise syntheses of mono- and di-nuclear ruthenium tpphz complexes [(bpy)2Ru(tpphz)]2– and [(bpy)2Ru(tpphz)Ru(bpy)2]4+{tpphz = tetrapyrido[3,2-a: 2′,3′-c: 3″,2″-h: 2″,3‴-j]phenazine}

The complex [(bpy)2Ru(tpphz)]2+(tpphz = tetrapyridophenazine), is obtained by reaction of [(bpy)2Ru(phendione)]2+with 5,6-diamino-1,10-phenanthroline; upon reaction with [(bpy)2Ru(Me2CO)2]2+, the fully conjugated dimer [(bpy)2Ru(tpphz)Ru(bpy)2]4+ is obtained.

Design and synthesis of the active part of a potential molecular motor

The design and synthesis of a ruthenium complex are described, together with its physico-chemical properties, showing its potential to work as a single molecule rotary motor.

Synthesis and Reactivity of [Penta(4‐halogenophenyl)cyclopentadienyl][hydrotris(indazolyl)borato]ruthenium(II) Complexes: Rotation‐Induced Fosbury Flop in an Organometallic Molecular Turnstile

The preparation of ruthenium(II) complexes coordinated to a penta(4-halogeno)phenylcyclopentadienyl ligand and to the hydrotris(indazolyl)borate ligand are detailed. Our strategy involves first the coordination of the penta(4-bromo)phenylcyclopentadienyl ligand by reaction with the ruthenium-carbonyl cluster followed by the coordination of the tripodal ligand. The pentabrominated precursor was successfully converted to the pentaiodinated derivative by using the Klapars-Buchwald methodology, applied for the first time on organometallic substrates. Cross-coupling reactions were performed on both pentabromo and pentaiodo complexes to introduce in a single step the five peripheric ferrocenyl fragments required to obtain a potential molecular motor. The two ligands present in the ruthenium complexes undergo a correlated rotation that was established both experimentally by NMR experiments and an X-ray diffraction study, and theoretically by DFT calculations. The potential-energy curve obtained by DFT revealed the energy barrier of the gearing mechanism to be only 4.5 kcal mol(-1). These sterically highly constrained complexes can be regarded as organometallic molecular turnstiles.

Synthesis of triester-functionalized molecular motors incorporating bis-acetylide trans-platinum insulating fragments

Bis-ferrocene compounds linked either by two triple bonds (1,4-di(ferrocenyl)butadiyne 1), or by the triple bond–platinum–triple bond sequence (trans-bis(ferrocenylethynyl)bis(triethylphosphine)platinum(II), 2) have been synthesized. The electronic coupling between the ferrocene groups has been estimated from the intensity of the intervalence transition in the electrochemically generated mixed valence complexes. Upon insertion of a platinum fragment a weak attenuation was observed, with the Vab parameter decreasing from 0.036 eV for 1 to 0.025 eV for 2. A theoretical study has also been performed, using a combination of DFT for geometry optimization and Extended Huckel Theory for the estimation of the electronic coupling. It was found that the electronic coupling decreases from 0.090 eV for 1 to 0.022 eV for a model of 2. In a second part of this work, we describe the synthesis of two molecular motors incorporating the ligand hydrotris[6-(ethoxycarbonyl)indazol-1-yl]borate which exhibits three pendant ester groups dedicated to be anchored onto an oxide surface. This stator is connected through a ruthenium centre to a pentasubstituted cyclopentadienyl rotor bearing ferrocene terminal electroactive groups, linked either by a phenylethynyl spacer (complex 4) or a spacer containing bis-acetylide trans-platinum insulating fragments (complex 8).

(Bipyridine)(terpyridine)(4-iodophenylcyanamide)ruthenium(II) complex: crystallography, electronic absorption spectroscopy, cyclic voltammetry and EPR measurements

Abstract The complex [Ru(bpy)(tpy)(Ipcyd)] + (where bpy: 2,2′-bipyridine, tpy: 2,2′:6′,2′′-terpyridine and Ipcyd: 4-iodophenylcyanamide anion) has been synthesized. An extensive characterization was carried out using IR, 1 H and 13 C NMR, ES-MS, UV–Vis, electrochemistry, EPR and X-ray single crystal diffraction analysis. Cyclic voltammogram shows an irreversible anodic peak around 0.7 V/ECS, the shape of the wave is typical of an electrochemical-chemical (EC) mechanism with an half-life time in the order of seconds for the generated species. Oxidation of the title compound has been investigated in order to explore its ability as a magnetic probe for further electronic studies on dinuclear complexes. The EPR spectrum at 100 K of the monooxidized species displays g ⊥ =2.00 and g ∣∣ =1.96 attributed to the presence of a radical coming from the phenylcyanamide oxidation, in relative good agreement with EH and ZINDO calculations.

Towards molecular switching: Photophysical properties of N,N′-bis(4-cyanophenyl)piperazine, a bridging TICT molecule

Abstract The properties of N,N′-bis(4-cyanophenyl)piperazine are described. This molecule has been devised to exhibit bridging properties, together with the possibility of giving twisted internal charge transfer (TICT) states following irradiation. The crystal structure shows that the molecule is almost planar in the ground state. Photochemical excitation on the charge transfer band at 300 nm gives rise to a luminescence which is very sensitive to the solvent polarity. In butanol, the dual luminescence characteristic of TICT is observed, which is attributed to the twisting motion of the acceptor(s) part of the molecule with respect to the donor. Transient absorption measurements have been also performed, which characterize the triplet state. A comparison with dimethylaminobenzonitrile is made.

Electron transfer through 2,7,9,10-tetraazaphenanthrene : a quantum interference effect ?

Abstract Intramolecular electron transfer has been detected in a binuclear complex of ruthenium using 2,7,9,10-tetraazaphenanthrene as bridging ligand. From the characteristics of the intervalence transition, the effective coupling V ab between ruthenium sites has been determined. It is found to be lower than in the corresponding complex with 4,4′-bipyridine, despite the fact that 2,7,9,10-tetraazaphenanthrene presents addition connections. Molecular orbital calculations confirm this effect. The analysis of these differences is performed in terms of “interference” effects between the different branches connecting the metal atoms.

One-pot palladium-catalysed synthesis of molecular wires

Abstract The one-pot desilylation of TMS-protected alcynes and cross-coupling with a brominated complex allows the use of sensitive diynes and provides an easy access to models of molecular wires.