Sylvie Choua

“Chain-Like” Trimetallic Ruthenium Complexes with C7 Carbon-Rich Bridges: Experimental and Theoretical Investigations of Electronic Communication Tuning in Five Distinct Oxidation States

In this work, we report the synthesis and the electronic properties of the unique highly conjugated molecular wires trans-[Cl-(dppe)(2)Ru=C=C=(Ph)C-CH=(CH(3))C-C[triple bond]C-(X)(2)Ru-C=C-C(CH(3))=CH-C(Ph)=C=C=Ru(dppe)(2)Cl](n+) (n = 2, X = dppe ([3a](OTf)(2)) and dppm ([3b](OTf)(2)) with three similar metal centers spanned by two odd-numbered unsaturated C(7) chains providing a 28 A long conjugated path and displaying five well-separated redox states (n = 0-4). Successive one-electron transfer steps were studied by means of cyclic voltammetry, EPR and UV-vis-NIR-IR spectroelectrochemistry. The electronic and physical properties of the different states were further rationalized with the help of DFT-based calculations. Upon one-electron reduction (n = 1), the single electron is delocalized over the two carbon chains through the central metal atom to an extent driven by the rotations within and between the chains. The second reduction (n = 0) involves the whole carbon-rich conjugated path of the molecule in a spin polarized scheme: one electron is delocalized over each chain, and the two electrons are antiferromagnetically coupled with a coupling on the order of kT. Interestingly, oxidation processes strongly involve both the metal atoms and the bridging ligands. The combined investigations reveal that the mono-oxidized system (n = 3) presents a spin density uniformly distributed between the metal atoms and the carbon atoms of the chains, whereas in the second oxidation state (n = 4) the compounds show a strong antiferromagnetic coupling on the order of 4 kT between the two single electrons localized in two distinct delocalized spin orbitals implying all the carbon atoms of the bridges and the three metal atoms. Thus, for the first time, electronic communication was fully evidenced and tuned in homonuclear trimetallic oligomeric carbon-rich systems in either an oxidation or a reduction process.

Diporphyrinylamines: Synthesis and Electrochemistry

The synthesis of three possible diporphyrinylamines is described. All compounds were obtained by using the Buchwald-Hartwig aromatic amination reaction. The electronic spectra of the three porphyrin dimers showed characteristic features found in highly delocalized systems. The first oxidation of these compounds took place on the connecting amine function.

Diarylethene-Containing Carbon-Rich Ruthenium Organometallics: Tuning of Electrochromism

The association of a dithienylethene (DTE) system with ruthenium carbon-rich systems allows reaching sophisticated and efficient light- and electro-triggered multifunctional switches R-[Ru]-C≡C-DTE-C≡C-[Ru]-R, featuring multicolor electrochromism and electrochemical cyclization at remarkably low voltage. The spin density on the DTE ligand and the energetic stabilization of the system upon oxidation could be manipulated to influence the closing event, owing to the noninnocent behavior of carbon-rich ligands in the redox processes. A combination of spectroscopic (UV-vis-NIR-IR and EPR) and electrochemical studies, with the help of quantum chemical calculations, demonstrates that one can control and get a deeper understanding of the electrochemical ring closure with a slight modification of ligands remote from the DTE unit. This electrochemical cyclization was established to occur in the second oxidized state (EEC mechanism), and the kinetic rate constant in solution was measured. Importantly, these complexes provide an unprecedented experimental means to directly probe the remarkable efficiency of electronic (spin) delocalization between two trans carbon-rich ligands through a metal atom, in full agreement with the theoretical predictions. In addition, when no cyclization occurs upon oxidation, we could achieve a redox-triggered magnetic switch.

Electronic communication in "chain-like" trimetallic ruthenium complexes with two C7 carbon-rich conjugated bridges.

This paper describes the synthesis and properties of the first homotrinuclear metal complexes with large carbon-rich ligands that provide unique extended conduits for electron mobility.

Redox and Luminescent Properties of Robust and Air-Stable N-Heterocyclic Carbene Group 4 Metal Complexes

Robust and air-stable homoleptic group 4 complexes of the type M(L)2 [1-3; M = Ti, Zr, Hf; L = dianionic bis(aryloxide) N-heterocyclic carbene (NHC) ligand] were readily synthesized from the NHC proligand 1,3-bis(3,5-di-tert-butyl-2-hydroxyphenyl)imidazolinium chloride (H3L,Cl) and appropriate group 4 precursors. As deduced from cyclic voltammetry studies, the homoleptic bis-adduct zirconium and hafnium complexes 2 and 3 can also be oxidized, with up to four one-electron-oxidation signals for the zirconium derivative 2 (three reversible signals). Electron paramagnetic resonance data for the one-electron oxidation of complexes 1-3 agree with the formation of ligand-centered species. Compounds 2 and 3 are luminescent upon excitation in the absorption band at 362 nm with emissions at 485 and 534 nm with good quantum yields (ϕ = 0.08 and 0.12) for 2 and 3, respectively. In contrast, the titanium complex 1 does not exhibit luminescent properties upon excitation in the absorption band at 310 and 395 nm. Complexes 2 and 3 constitute the first examples of emissive nonmetallocene group 4 metal complexes.

Corrigendum: Nickel(II) meso-Hydroxyporphyrin Complexes Revisited: Palladium-Catalysed Synthesis, Electronic Structures of Derived Oxy Radicals, and Oxidative Coupling to a Dioxoporphodimethene Dyad

We report the synthesis and characterisation of new examples of meso-hydroxynickel(II) porphyrins with 5,15-diphenyl and 10-phenyl-5,15-diphenyl/diaryl substitution. The OH group was introduced by using carbonate or hydroxide as nucleophile by using palladium/phosphine catalysis. The NiPor-OHs exist in solution in equilibrium with the corresponding oxy radicals NiPor-O. . The 15-phenyl group stabilises the radicals, so that the 1 H NMR spectra of {NiPor-OH} are extremely broad due to chemical exchange with the paramagnetic species. The radical concentration for the diphenylporphyrin analogue is only 1 %, and its NMR line-broadening was able to be studied by variable-temperature NMR spectroscopy. The EPR signals of NiPor-O. are consistent with somewhat delocalised porphyrinyloxy radicals, and the spin distributions calculated by using density functional theory match the EPR and NMR spectroscopic observations. Nickel(II) meso-hydroxy-10,20-diphenylporphyrin was oxidatively coupled to a dioxo-terminated porphodimethene dyad, the strongly red-shifted electronic spectrum of which was successfully modelled by using time-dependent DFT calculations.

Ruthenium Carbon-Rich Complexes as Redox Switchable Metal Coupling Units

With the help of EPR spectroscopy, we show that the diamagnetic [Ru(dppe)2(-C≡C-R)2] system sets up a magnetic coupling between two organic radicals R, i.e., two nitronyl nitroxide or two verdazyl units, which is stronger than that of related platinum organometallic systems. Surprisingly, further oxidation of the ruthenium redox-active metal coupling unit (MCU), which introduces an additional spin unit on the carbon-rich part, leads to the switching off of this interaction. On the contrary, in simpler complexes bearing only one of the organic radical ligands [C6H5-C≡C-Ru(dppe)2-C≡C-R], one-electron oxidation of the transition metal unit generates an interaction between the two spin carriers of comparable magnitude to that observed in the above corresponding neutral systems.

New metal phthalocyanines/metal simple hydroxide multilayers: experimental evidence of dipolar field-driven magnetic behavior.

A series of new hybrid multilayers has been synthesized by insertion-grafting of transition metal (Cu(II), Co(II), Ni(II), and Zn(II)) tetrasulfonato phthalocyanines between layers of Cu(II) and Co(II) simple hydroxides. The structural and spectroscopic investigations confirm the formation of new layered hybrid materials in which the phthalocyanines act as pillars between the inorganic layers. The magnetic investigations show that all copper hydroxide-based compounds behave similarly, presenting an overall antiferromagnetic behavior with no ordering down to 1.8 K. On the contrary, the cobalt hydroxide-based compounds present a ferrimagnetic ordering around 6 K, regardless of the nature of the metal phthalocyanine between the inorganic layers. The latter observation points to strictly dipolar interactions between the inorganic layers. The amplitude of the dipolar field has been evaluated from X-band and Q-band EPR spectroscopy investigation (Bdipolar ≈ 30 mT).

Inexpensive and Efficient Ullmann Methodology To Prepare Donor-Substituted Porphyrins

The preparation of porphyrins functionalized with one or two carbazoles (or phenoxazines) is described. The electron donors were introduced into one or two porphyrin meso positions by using the inexpensive Ullmann coupling procedure. Very good yields were obtained, and for two new compounds, the X-ray structures were solved. Preliminary electrochemical data coupled with electronic spectroscopy are also reported.

EPR and theoretical studies of the reduction product of the fulvenephosphaallene system

Fluoren-9-ylidenemethylene-(2,4,6-tri-tert-butyl-phenyl)phosphane (2), a new type of phosphaallene with the terminal carbone incorporated in a cyclopentadienyl ring, has been synthesized and its crystal structure has been determined. The 31 P and 13 C (central carbon) hyperfine tensors of the reduction compound of this phosphaallene have been measured on the EPR spectra recorded after electrochemical reduction of a solution of 2 in THF. Structures of the model molecules HPCCp (where Cp is a cyclopentadienyl ring), [HPCCp] − and [HPCHCp] have been optimized by DFT and the hyperfine couplings of the paramagnetic species have been calculated by DFT and SCI methods. The comparison between the experimental and the theoretical results shows that, in solution, the radical anion [2] − is readily protonated and that the EPR spectra are due to the phosphaallylic radical.