Claude Lapinte

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.

Photochromic Organometallics with a Dithienylethene (DTE) Bridge, [YCCDTECCY] (Y={MCp*(dppe)}): Photoswitchable Molecular Wire (M=Fe) versus Dual Photo‐ and Electrochromism (M=Ru)

Dinuclear acetylide-type complexes bridged by a photochromic dithienylethene unit (DTE), [Y-C[triple bond]C-DTE-C[triple bond]C-Y] 1 (Y={MCp*(dppe)}; Cp*=pentamethylcyclopentadienyl, M=Fe (1(Fe)), Ru (1(Ru))), have been prepared, and their wirelike and switching behavior, as well as their oxidation chemistry has been investigated. The DTE complexes 1 exhibit photochromic behavior in a manner similar to organic DTE derivatives; UV irradiation causes ring closure of the open isomer 1O to form the closed isomer 1C and visible-light irradiation of the resultant 1C causes reverse ring opening to regenerate 1O. But the performance is dependent on the metals. With respect to the interconversion rates and the 1C content at the photostationary state under UV irradiation, the ruthenium complex 1(Ru) is superior to the iron analogue 1(Fe). The wirelike performance is associated with the photochromic processes, and the efficient switching performance has been verified for 1(Fe) as characterized by the V(ab) values [V(ab) is the electronic coupling derived from intervalence charge-transfer (IVCT) bands: V(ab)(1(Fe)C; ON)=0.047 eV versus V(ab)(1(Fe)O; OFF)=0 eV], and are also supported by the large switching factor (SF=K(C)(C; ON)/K(C)(O; OFF)=39; K(C)=comproportionation constant). SF for 1(Ru) is determined to be 4.2. The remarkable switching behavior arises from the different pi-conjugated systems in the two isomeric forms, that is, cross-conjugated (1O) and fully conjugated pi-systems (1C). It was also found that, in contrast to the reversible redox behavior of the iron complex 1(Fe), the ruthenium complex 1(Ru)O undergoes oxidative ring closure to form the dicationic species of the closed isomer 1(Ru)C(2+) and, thus, the ruthenium system 1(Ru) shows dual photo- and electrochromism. The distinct oxidation behavior of 1(Fe) and 1(Ru) can be ascribed to the spin distribution on the diradical intermediates 1(Fe)O(2+) and 1(Ru)O(2+), as supported by DFT calculations.

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).

Redox-active organometallics: magnetic and electronic couplings through carbon-silicon hybrid molecular connectors.

Treatment of the triflate complex Cp*(dppe)FeOTf [12; Cp* = eta(5)-C(5)(CH(3))(5), dppe = 1,2-bis(diphenylphosphino)ethane, OTf = CF(3)SO(3)] with an excess of HC[triple bond]C-(Si(CH(3))(2))(x)-C[triple bond]CH (x = 2-4) in diethyl ether provides the binuclear bis(vinylidene) derivatives [Cp*(dppe)Fe=C=CH(Si(CH(3))(2))(x)CH=C=Fe(dppe)Cp*][OTf](2) (x = 2, 13; x = 3, 14; x = 4, 15), which were isolated as ochre solids and rapidly characterized by FT-IR, (1)H, (31)P, and (13)C NMR spectroscopies. The complexes 13-15 were reacted with potassium tert-butoxide to afford the bis(alkynediyl) complexes [Cp*(dppe)Fe-C[triple bond]C(Si(CH(3))(2))(x)C[triple bond]C-Fe(dppe)Cp*] (x = 2, 1; x = 3, 2; x = 4, 3), which were isolated as orange powders in yields ranging from 76 to 91%. The IR, cyclic voltammetry, and UV-vis data obtained for 1-3 and the X-ray crystal structures determined for 1 and 3 reveal the importance of the sigma-pi conjugation (hyperconjugation) between the Si-Si sigma bond and the adjacent C[triple bond]C pi-symmetric orbitals in the description of the electronic structure of the ground state of these complexes. When reacted at low temperature with 2 equiv of [(C(5)H(5))(2)Fe]X or AgX [X = BPh(4), B(3,5-(CF(3))(2)C(6)H(3))(4))], compounds 1-3 provide 1[X](2), 2[X](2), and 3[X](2), which can be isolated and stored below -20 degrees C. EPR spectroscopy and magnetization measurements established that the superexchange interaction propagates through the Si-Si bonds (J = -0.97(2) cm(-1) for 3[X](2)). UV-vis-near-IR spectra were obtained with an optically transparent thin-layer electrosynthetic (OTTLE) cell for 1-3[OTf](n) (n = 0-2). A band with a maximum that increases from 6400 cm(-1) (1[OTf]) to 8500 cm(-1) (3[OTf]) observed for the mixed-valence species was ascribed to intervalence charge transfer evidencing photodriven electron transfer through the carbon-silicon hybrid connectors with H(ab) parameters ranging from 64 to 285 cm(-1).

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 C4 bridged mixed-valence iron(II)–iron(III) complex delocalized on the infrared timescale

The first 35-electron acetylide bridged diiron complex [{Fe(η5-C5Me5)(dppe)}2(µ-C4)]PF6, 3PF6[dppe = ethylenebis(diphenylphosphine)] and the 36- and 34-electron bis-iron(II) and bis-iron(III) homologous derivatives are synthesized and it is established that the FeII–FeIII complex is the first non-trapped mixed-valence compound with two half-sandwich monomeric units joined by a C4 bridge.

Through-Bond versus Through-Space Coupling in Mixed-Valence Molecules: Observation of Electron Localization at the Single-Molecule Scale

Scanning tunneling microscopy (STM) is used to study two dinuclear organometallic molecules, meta-Fe2 and para-Fe2, which have identical molecular formulas but differ in the geometry in which the metal centers are linked through a central phenyl ring. Both molecules show symmetric electron density when imaged with STM under ultrahigh-vacuum conditions at 77 K. Chemical oxidation of these molecules results in mixed-valence species, and STM images of mixed-valence meta-Fe2 show pronounced asymmetry in electronic state density, despite the structural symmetry of the molecule. In contrast, images of mixed-valence para-Fe2 show that the electronic state density remains symmetric. Images are compared to constrained density functional (CDFT) calculations and are consistent with full localization of charge for meta-Fe2 on to a single metal center, as compared with charge delocalization over both metal centers for para-Fe2. The conclusion is that electronic coupling between the two metal centers occurs through the bonds of the organic linker, and through-space coupling is less important. In addition, the observation that mixed-valence para-Fe2 is delocalized shows that electron localization in meta-Fe2 is not determined by interactions with the Au(111) substrate or the position of neighboring solvent molecules or counterion species.

Investigation of the iron–carbon bonding for alkyl, alkynyl, carbene, vinylidene, and allenylidene complexes using 57Fe Mössbauer spectroscopy

Abstract The synthesis of the iron allenylidene [Cp*(dppe)Fe(CCC(OCH3)CH3)][BPh4] (7) was achieved in one step, from the reaction of the Cp*(dppe)FeCl (8) with 1 equiv. of Me3–Si–CC–CCH. By working in methanol and in the presence of NaBPh4, the complex 7 was isolated in 85% yield as a dark green powder. Comparison of the Mossbauer parameters of a series of 16 compounds having the same Cp*(dppe)Fe backbone and a end-bound hydrocarbon ligand shows that it is possible to identify both the oxidation state of the metal (FeII vs. FeIII) and the metal–carbon bonding (single vs. double bond) of the terminal hydrocarbon ligands using Mossbauer spectroscopy.

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.