Frédéric Paul

Organometallic molecular wires and other nanoscale-sized devices: An approach using the organoiron (dppe)Cp*Fe building block

Abstract In this paper, the potential that organometallic architectures consisting of two transition metal centers linked by an organic unsaturated spacer present for the study and development of new molecular wires is discussed. After a bibliographical survey of representative existing molecules, emphasis is set on the decisive role of the terminal organometallic capping groups. In this connection, the very rich redox chemistry of the (dppe)Cp*Fe unit in mononuclear complexes is subsequently developed. Finally, the syntheses and studies of diverse organometallic molecular wire models realized in our group and incorporating this fragment are presented and conclusions on the present state of the art are drawn. A review with 352 references.

Catalytic synthesis of isocyanates or carbamates from nitroaromatics using Group VIII transition metal catalysts

Abstract In order to produce various isocyanates, catalyzed carbonylations of nitroaromatic compounds constitute a set of very appealing reactions for industry. These environmentally benign reactions present many advantages over the traditional phosgene route actually used for isocyanate production. Group VIII metal complexes constitute currently the most interesting catalysts for these transformations and this review focuses on the academic research conducted in this field. After a brief introduction, some general data about the ‘direct’ and ‘indirect’ carbonylation processes is given and the most active catalytic systems developed for both transformations are described. Then, the mechanistic data available for specific catalytic systems are presented and the reaction schemes of these reactions thoroughly analyzed. Finally, industrial perspectives regarding reductive carbonylation reactions are briefly discussed before concluding. A review with 390 references.

Electron‐Rich Iron/Ruthenium Arylalkynyl Complexes for Third‐Order Nonlinear Optics: Redox‐Switching between Three States

The new [(η(2)-dppe)(η(5)-C(5)Me(5))Fe(C≡C-1,4-C(6)H(4)C≡C)Ru(η(2) -dppe)(2) C≡C(C(6)H(5))] complex (3-H) and its hexanuclear relative [{(η(2)-dppe)(η(5)-C(5) Me(5))Fe(C≡C-1,4-C(6)H(4)-C≡C)Ru(η(2)-dppe)(2)(C≡C-1,4-C(6)H(4)C≡C)(3)(1,3,5-C(6)H(3))] (4) have been synthesized and characterized. The linear and cubic nonlinear optical properties of these compounds in their various redox states have been studied along with those of the analogous complexes [(η(2)-dppe)(η(5)-C(5)Me(5))Fe(C≡C-1,4-C(6)H(4)C≡C)Ru(η(2)-dppe)(2)R][PF(6)](n) (n=0-2; R=Cl, 2-Cl; R=C≡C(4-C(6)H(4)NO(2)),3-NO(2)). We show that molecules exhibiting large third-order nonlinearities can be obtained by assembling such dinuclear Fe/Ru units around a central 1,3,5-substituted C(6)H(3) core. These data are discussed with a particular emphasis on the large changes in their nonlinear (third-order) optical properties brought about by oxidation. Experimental and computational (DFT) evidence for the electronic structures of these compounds in their various redox states is presented using 3-H(n+) as a prototypical model. Single crystals of this complex in its mono-oxidized state (3-H[PF(6)]) provide the first structural data for such carbon-rich Fe(III) /Ru(II) heteronuclear mixed-valent (MV) systems. Although experimental evidence for the structure of the dioxidized states was more difficult to obtain, the theoretical study reveals that 3-H(2+) can be considered to have a biradical structure with two independent spins. The low-lying absorptions that appear in the near-infrared (NIR) range for all these compounds following oxidation correspond to intervalence charge-transfer (IVCT) bands for the mono-oxidized states and to ligand-to-metal charge-transfer (LMCT) transitions for the dioxidized states. These play a crucial role in the strong optical modulation achieved. The possibility of accessing additional states with distinct linear or nonlinear optical properties is also briefly discussed.

3,5-Bis(ethynyl)pyridine and 2,6-bis(ethynyl)pyridine spanning two Fe(Cp*)(dppe) units: role of the nitrogen atom on the electronic and magnetic couplings.

The role of the nitrogen atom on the electronic and magnetic couplings of the mono-oxidized and bi-oxidized pyridine-containing complex models [2,6-{Cp(dpe)Fe-C≡C-}(2)(NC(5)H(3))](n+) and [3,5-{Cp(dpe)Fe-C≡C-}(2)(NC(5)H(3))](n+) is theoretically tackled with the aid of density-functional theory (DFT) and multireference configuration interaction (MR-CI) calculations. Results are analyzed and compared to those obtained for the reference complex [1,3-{Cp*(dppe)Fe-C≡C-)}(2)(C(6)H(4))](n+). The mono-oxidized species show an interesting behavior at the borderline between spin localization and delocalization and one through-bond communication path among the two involving the central ring, is favored. Investigation of the spin state of the dicationic complexes indicates ferromagnetic coupling, which can differ in magnitude from one complex to the other. Very importantly, electronic and magnetic properties of these species strongly depend not only upon the location of the nitrogen atom in the ring versus that of the organometallic end-groups but also upon the architectural arrangement of one terminus, with respect to the other and/or vis-à-vis the central ring. To help validate the theoretical results, the related families of compounds [1,3-{Cp*(dppe)Fe-C≡C-)}(2)(C(6)H(4))](n+), [2,6-{Cp*(dppe)Fe-C≡C-}(2)(NC(5)H(3))](n+), [3,5-{Cp*(dppe)Fe-C≡C-}(2)(NC(5)H(3))](n+) (n = 0-2) were experimentally synthesized and characterized. Electrochemical, spectroscopic (infrared (IR), Mössbauer), electronic (near-infrared (NIR)), and magnetic properties (electron paramagnetic resonance (EPR), superconducting quantum interference device (SQUID)) are discussed and interpreted in the light of the theoretical data. The set of data obtained allows for many strong conclusions to be drawn. A N atom in the long branch increases the ferromagnetic interaction between the two Fe(III) spin carriers (J > 500 cm(-1)), whereas, when placed in the short branch, it dramatically reduces the magnetic exchange in the di-oxidized species (J = 2.14(5) cm(-1)). In the mixed-valence compounds, when the N atom is positioned on the long branch, the intermediate excited state is higher in energy than the different ground-state conformers and the relaxation process provides exclusively the Fe(II)/Fe(III) localized system (H(ab) ≠ 0). Positioning the N atom on the short branch modifies the energy profile and the diabatic mediating state lies just above the reactant and product diabatic states. Consequently, the LMCT transition becomes less energetic than the MMCT transition. Here, the direct coupling does not occur (H(ab) = 0) and only the coupling through the bridge (c) and the reactant (a) and product (b) diabatic states is operating (H(ac) = H(bc) ≠ 0).

Chemistry of the 1,3,5,7-octatetraynediyl carbon rod end-capped by two electron-rich (η5-C5Me5)(η2-dppe)Fe groups

Abstract The synthesis of the organoiron complex [(η5-C5Me5)(η2-dppe)FeCCCCCCCCFe(η2-dppe)(η5-C5Me5)] (2, dppe=1,2-bis(diphenylphosphino)ethane) is reported with its full spectroscopic characterizations (1H-, 31P-, and 13C-NMR, IR, Raman, UV–vis and 57Fe Mossbauer). The X-ray analysis of 2 shows that the molecule adopts a geometry very close to the anti conformation in the solid state. The shortening of the FeC bond distance associated with the increase in the number of carbon atoms suggests some cumulenic contribution to the description of the electronic structure of the all-carbon bridge. The 13C-NMR, 57Fe Mossbauer data and theoretical calculations confirm this trend and indicate that the cumulenic contribution is significant in the vicinity of the metal center but vanishes in the middle of the carbon rod. Vibrational spectroscopy carried out on the single crystals of [(η5-C5Me5)(η2-dppe)FeCCCCFe(η2-dppe)(η5-C5Me5)] (1) and 2 and on solutions of these compounds indicates that the CC bond stretching mode is not very sensitive to the relative orientation of the terminal endgroups. The electronic structure of the titled compound has been investigated using density functional theory. The geometrical changes occurring upon elongation of the carbon chain were nicely reproduced and interpreted. Time-dependant density functional theory calculations have been performed to rationalize the optical spectra.

First synthesis and spectroscopic characterization of isolated butatrienylidene complexes of transition metals

Abstract The complex Cp*Fe(dippe)Fe(CCCC)Fe(CO)2Cp* (3b, dippe=1,2-bis(diisopropylphosphino)ethane, Cp*=pentamethylcyclopentadienyl) was prepared by activation of the terminal butadiyne Cp*(CO)2FeCCCCH (2) with the chloro iron complex Cp*(dippe)FeCl (1b) in the presence of KPF6 and KOBut. Treatment of Cp*(P2)Fe((CCCC)Fe(CO)2Cp* (3a, P2=dppe, dppe=1,2-bis(diphenylphosphinoethane); 3b, P2=dippe) with HBF4 · Et2O produced the secondary iron butatrienylidene complexes [Cp*(P2)Fe{CCCC(H)Fe(CO)2Cp*}][BF4] (4a, P2=dppe, 75%; 4b, P2=dippe, 93%). The slightly more stable tertiary butatrienylidene iron derivatives [Cp*(P2)Fe{CCCC(CH3)Fe(CO)2Cp*}][OSO2CF3] (5a, P2=dppe, 22%; 5b, P2=dippe, 75%) were made by reacting the precursor complexes 3a–b with methyl triflate under similar conditions. All the compounds 4a–b and 5a–b are almost stable in solution at 20°C. They are light and air sensitive, even in solid state. The solid samples can be stored under argon for few days in the dark at 5°C. The complexes 4a–b and 5a–b were characterized by multinuclear NMR, IR, UV–vis, and Mossbauer spectroscopies, mass spectrometry and cyclic voltammetry. Their electronic structures are discussed in connection with the spectroscopic data.

Versatile reactions of a para-bromophenylacetylide iron(II) derivative and X-ray structure of the fluoro analogue. Synthesis of new redox-active organoiron(II) synthons

The synthesis of the new (η 2 -dppe)(η 5 -C 5 Me 5 )FeCC1,3-(C 6 H 4 X) ( m -2a / 2b ; X=F/Br) and (η 2 -dppe)(η 5 -C 5 Me 5 )FeCC1,4-(C 6 H 4 I) ( 2c ) complexes, as well as the solid-state structure of the known (η 2 -dppe)(η 5 -C 5 Me 5 )FeCC1,4-(C 6 H 4 F) ( 2a ) complex are described. The catalytic coupling reactions of the bromo complexes with various alkynes were next investigated. Starting from the known (η 2 -dppe)(η 5 -C 5 Me 5 )FeCC1,4-(C 6 H 4 Br) complex ( 2b ), the synthesis of the (η 2 -dppe)(η 5 -C 5 Me 5 )FeCC1,4-(C 6 H 4 )CCH complex ( 6d ) and of the corresponding silyl-protected precursors (η 2 -dppe)(η 5 -C 5 Me 5 )FeCC1,4-(C 6 H 4 )CCSiR 3 ( 6b / 6c ; R= i Pr/Me) are reported. By use of lithiumbromine exchange reactions on 2b , the silyl- ( 7a ; E=Si; R=Me) and tin- ( 7b – 7d ; E=Sn; R=Me, Bu, Ph) substituted analogues (η 2 -dppe)(η 5 -C 5 Me 5 )FeCC1,4-(C 6 H 4 )ER 3 are also isolated. The spectroscopic and electrochemical characterisations of all these new Fe(II)/Fe(III) redox-active building blocks are presented and the electronic substituent parameters for the “(η 2 -dppe)(η 5 -C 5 Me 5 )FeCC” group are determined by means of 19 F-NMR.

Triaryl-1,3,5-triazinane-2,4,6-triones (isocyanurates) peripherally functionalized by donor groups: synthesis and study of their linear and nonlinear optical properties.

The linear optical (LO) and nonlinear optical (NLO) properties of a series of isocyanurates functionalized by donor arms at the periphery are reported herein. These octupolar derivatives were obtained in a straightforward way from commercial isocyanate derivatives and were fully characterized. Although several of these compounds are known, those that exhibited the largest NLO activities are all new compounds. In terms of second-order activity, several of these derivatives exhibit remarkable activity/transparency tradeoffs. In terms of third-order activity, the longer derivatives with the stronger donor groups (X = NH(2), NMe(2), or NPh(2)) were shown to possess significant two-photon absorption cross sections. These strongly luminescent derivatives exhibit two-photon absorption cross sections up to 410 GM. DFT computations were also conducted to unravel their electronic structures and to rationalize their NLO properties. To our knowledge, the present study is the first concerned with the nonlinear optical properties of these original cyclotrimers.

New pyridyl-functionalized organoiron alkynyl complexes. Easy access to polymetallic architectures featuring an electroactive site by simple co-ordination reactions

Abstract The functionalized complexes 3a – d [(dppe)Cp*Fe(CCL)] (L=4-Py, 3-Py, 2-Py) were isolated with good yields from the alkynyl complex 1 [(dppe)Cp*Fe(CCH)] (dppe=1,2-bis(diphenylphosphino)ethane) from the corresponding bromopyridines using a Sonogashira-coupling reaction. These redox active compounds are stable under two redox states and react as usual pyridyl ligands towards methyl iodide or (THF)W(CO) 5 . They allow easy access to the corresponding pyridinium salt 4a or to the dimetallic iron–tungsten complex 5a .

Iron Alkynyl Helicenes: Redox-Triggered Chiroptical Tuning in the IR and Near-IR Spectral Regions and Suitable for Telecommunications Applications.

The combination of a bis-alkynyl-helicene moiety with two iron centers leads to novel electroactive species displaying unprecedented redox-triggered chiroptical switching. Upon oxidation, strong changes of vibrational modes (either local or extended coupled modes) are detected by vibrational circular dichroism and Raman optical activity. Remarkably, the sign of the optical rotation at 1.54 µm (that is, at wavelengths typically used for telecommunications) changes upon oxidation while the topology and stereochemistry of the helicene remain unchanged.