Zwitterionic mixed-valence (MV) complexes offer a compelling strategy for designing charge-neutral molecular components for quantum-dot cellular automata (QCA). In this work, organometallic zwitterions 1a and 1b featuring two [Cp*(dppe)Fe] redox centers linked by a meta-phenylene ethynylene bridge and an internal carboxylate were generated and characterized. A comprehensive investigation combining cyclic voltammetry, IR, and vis-NIR spectroscopies unambiguously establishes that both 1a and 1b behave as charge-localized Robin-Day class-II MV systems. This crucial finding demonstrates that the covalently tethered counterion does not significantly alter the weak electronic communication inherent to the meta-substituted bridge. To rationalize these experimental results, density functional theory (DFT) calculations were performed. It is shown that while simplified gas-phase models inadequately predict a delocalized state, calculations incorporating a polarizable continuum model (PCM-CH2Cl2) successfully reproduce the experimentally observed charge localization. The agreement between the experimental data and the solvated theoretical model provides robust validation for the class-II description and confirms this zwitterionic design as a viable approach for creating charge-neutral molecular wires.

The new complexes [1,3-{Cp*(dppe)Fe-C equivalent to C-}(2)-5-(X)-(C6H3)] (X=CH3, [m-1 b]; X=C(O)OCH3, [m-1 c]; X=C equivalent to C-4-C6H4-C(O)OCH3, [m-1 d]; X=C equivalent to C-4-C6H4-NO2, [m-1 e]) were prepared by reaction of the iron chloride Cp*(dppe)FeCl (4) and the proligands 3 b-e obtained by a cross coupling reaction between the suitable aryl dibromides and trimethylsylilacethylene. After purification the complexes [m-1 b-e] were isolated in yields ranging from 14 to 37 % and characterized by elemental analysis, high-resolution, ESI-mass spectra, multinuclear NMR, cyclic voltammetry, and IR spectroscopy. The complexes [m-1 b], [m-1 d], and [m-1 e] were also characterized by XRD analyses on single crystals. The doubly oxidized complexes [m-1 b-e](PF6)(2) were prepared (in ca. 64-87 % yields) by treatment of a CH2Cl2 solution of the corresponding neutral complexes [m-1 b-e] with two equiv. of [(C5H5)(2)Fe](PF6). The mixed-valence complexes (MV) [m-1 b-e](PF6) were obtained by comproportionation between one equiv. of [m-1 b-e] and one equiv. of [m-1 b-e](PF6)(2). CV, IR and NIR data led to the conclusion that the MV [m-1 b-e](PF6) complexes are weakly coupled Class II MV derivatives and the distribution of the charge between the alkynyl iron centers and the phenyl ring might be tuned by the X-substituents in a limited extend.

The bis(ironvinylidene) complex [1,4-{Cp*(dppe)Fe=C=CH}(2)-2,5-(C equivalent to CH)(2)-C6H2](PF6)(2) ([2-2H](PF6)(2)) was prepared from 1,2,4,5-tetraethynylbenzene and two equiv. of Cp*(dppe)FeCl in 87 % yield. The reaction is very selective and [2-2H](PF6)(2) is the unique organoiron species to be formed. Deprotonation of [2-2H](PF6)(2) provided the target complex 2 (66 % yield) and subsequent oxidation gave the monocationic and dicationic complexes 2(PF6) and 2(PF6)(2). The new complexes were characterized by ESI-mass spectrometry, IR, multinuclear NMR, ESR and Mossbauer spectroscopy, and XRD analyses on single crystals for [2-2H](PF6)(2) and 2(PF6)(2). The magnetic properties of 2(PF6)(2) were investigated by VT H-1 NMR. The data were analyzed with the support of quantum chemistry calculations. The terminal ethynyl groups on the aromatic ring of the bridge modify the population of the bridge-oxidized state, weaken the electronic communication (H-ab approximate to 601 cm(-1)) and strengthen magnetic coupling interactions (J = -530 cm(-1)) compared to the unsubstituted species (H-ab = 1700 cm(-1) and J = -340 cm(-1), respectively).

the unprecedented tetrairon dication [{Cp*(dppe)FeC≡C-} 4 -μ-(1,2,4,5-C 6 H 2 )](PF 6 ) 2 ( 1 ) was obtained through a sequence of three reactions from 1,2,4,5-tetraethynylbenzene, Cp*(dppe)FeCl (Cp* = C 5 Me 5 , dppe = 1,2-bis(diphenylphosphino)-ethane), KOBu t , and ferrocenium hexafluorophosphate. The cyclic voltammogram of the target molecule isolated in 77% yield, exhibits four well separated and reversible redox events showing that 1 is thermodynamically stable with respect to disproportionation ( K c > 10 6 ). The tetranuclear dication 1 was characterized by XRD on single crystal, IR and NMR spectroscopies and Mössbauer spectrometry. The experimental data show that 1 behaves as a class II mixed-valence complex with the positive charges preferentially disposed on antipodal positions. This new molecule can be regarded as a potential molecular prototype of quantum-dot cellular automata.

Treatment of the iron hydride [Cp*(dppe)FeH] (1) with methyl triflate (CH3OSO2CF3) yielded the iron triflate adduct [Cp*(dppe)FeOSO2CF3] (4, 85 %). In the solid state, the triflate is coordinated at the iron center as shown by XRD (d(Fe-O) = 2.118(4) angstrom) and IR spectroscopy (nu(SO) = 1305 cm(-1)). In solution, 4 is in equilibrium with the 16-electron species [Cp*(dppe)Fe]OSO2CF3 (5(OSO2CF3)), 4/5(OSO2CF3) = 2:1). The CV of 4 displays two waves (E-1 = -0.74 V, E-2 = 0.24 V vs. SCE) assigned to the [Cp*(dppe)Fe(I)]/[Cp*(dppe)Fe(II)](+) and [Cp*(dppe)Fe(II)](+)/[Cp*(dppe)Fe(III)](2+) redox couples. Reduction of 4 with Cp2Co provided the complex [Cp*(dppe)Fe(I)] (6, 95 %) and oxidation of 6 with [Cp2Fe]PF6 gave [Cp*(dppe)Fe]PF6 (5(PF6), 98 %). XRD established the pseudo-trigonal bipyramidal geometry for the five-coordinated cation 5(+). The reactivity of 5(PF6) and 6 toward small molecules (CH2Cl2, H2O, CO, H-2, N-2) is reported.

The binuclear iron complexes [Cp*(PMe3)(CO)Fe-C(OCH3)=CH-CH=C(OCH3)-Fe(PMe3)(CO)Cp*] (1meso and 1dl) were prepared by double deprotonation of their known parents [Cp*(PMe3)(CO)Fe=C(OCH3)CH2-CH2-C(OCH3)=Fe(PMe3)-(CO)Cp*](PF6)(2) (Smeso and 5dl) and were isolated in good yield (90%). These complexes were characterized by ESI-mass spectrometry, IR and multinuclear NMR spectroscopy, and cyclic voltammetry. The singly and doubly oxidized forms lmeso(PF6)(n) and 1dl(PF6)(n) (n = 1, 2) were prepared by oxidation of the parent neutral complexes with 1 and 2 equiv of ferrocenium salt (93-100% yield). The related complex [Cp*(dppe)-Fe-C(OCH3)=CH-CH=C(OCH3)-Fe(dppe)Cp*](PF6) (2(PF6)) was obtained by reduction of the known dicationic derivative [Cp*(dppe)Fe-C(OCH3)=CH-CH=C(OCH3)-Fe(dppe)Cp*RPF6) (2-(PF6)(2)) with 1 equiv of cobaltocene (100% yield). Multinuclear NMR spectroscopy allowed us to establish the diiron(II) conjugated mu-bis(carbene) structure for lmeso(PF6)(2) and 1dl(PF6)(2). In the case of the meso derivative, H-1 NMR revealed the presence of E and Z isomers in a 4:1 ratio, confirming the presence of a C=C double bond in the middle of the bridge. The three radicals 1meso(PF6), 1dl(PF6), and 2(PF6), which are thermally stable, were analyzed by IR, MOssbauer, ESR, UV-vis, and NIR spectroscopy. Experimental data, discussed with the support of quantum chemistry calculations performed at the DFT level of theory, indicate that these radical cations exhibit characteristics of oxidation on the butadienediyl bridge rather than on the metal centers.

Related Article: Simon Guckel, Josef B. G. Gluyas, Sarah El-Tarhuni, Alexandre N. Sobolev, Mark W. Whiteley, Jean-Francois Halet, Claude Lapinte, Martin Kaupp, Paul J. Low|2018|Organometallics|37|1432|doi:10.1021/acs.organomet.8b00099

The complexes FcCH=C{1,4-C C-C6H4-C CM(dppe)Cp*}(2) (Fc = ferrocenyl (FeCp(eta-C5H4-); M = Fe (1), Ru (2)) were prepared from FcCH=C{1,4-C C-C6H4-C=C SiMe3}(2) (3) via a desilylation/metalation protocol in good (2; 65%) to excellent (1; 97%) yield. The iron compound 1 could also be prepared in a stepwise fashion by desilylation of 3 to give FcCH=C{1,4-C C-C6H4-C CH}(2) (4), reaction with FeCl(dppe)Cp* to give the vinylidene complex FcCH=C{1,4-C=C-C6H4-CH=C=Fe(dppe)Cp*}(2)] (PF6)(2) (5(PF6)(2); 65%), and deprotonation. The cyclic voltammograms of 1 and 2 are characterized by an initial oxidation wave resulting from the overlap of two closely spaced oxidation processes, the potentials of which are sensitive to the identity of M, and a subsequent, one-electron-oxidation wave. Thus, while the dications I2+ and 2(2+) could be prepared by oxidation with 2 equiv of ferrocenium hexafluorophosphate and isolated as the PF6- salts 1(PF6)(2) and 2(PF6)(2) at low temperature, the monocations 1(+) and 2(+) could only be detected and studied as comproportionated mixtures of 1, 1 (PF6), 1(PF6)(2) and 2, 2(PF6), 2(PF6)(2). A combination of EPR spectroscopy, IR and NIR spectroelectrochemistry, and DFT quantum chemical calculations reveal subtle distinctions in the electronic structures of 1(PF6) and 2(PF6) (n = 0-2). The HOMOs of 1 and 2 are more heavily distributed over the metal-diethynylbenzene arm trans to the ferrocenyl moiety. While one-electron oxidation of 1 gives 1(PF6), in which the spin density is similarly distributed along the branch of the molecule trans to the ferrocenyl group, the spin density in 2(PF6) is more extensively, but not fully, delocalized. Further analysis of the ESR, NIR, and IR spectra reveals that charges are essentially localized in 1(PF6) and 1(PF6)(2) on the IR time scale, but ground-state exchange between the Fe(dppe)Cp* moieties can take place via the ferrocenyl moiety on the slower ESR time scale. For 2(PF6) and 2(PF6)(2), optical charge transfer processes between the ferrocenyl moiety and the organometallic branches can also be observed, consistent with the increased coupling between the Ru(dppe)Cp* and Fc moieties that are linked by a linear conjugation pathway through the bridging-ligand backbone.

The electronic structures of the prototypical bimetallic buta-1,3-diyn-1,4-diyl-bridged radical cation complexes [{M(dppe)Cp'}(2)(mu-C CC C)](+) (M= Fe, Cp' = Cp* (1a), Cp (1b); M = Ru, Cp' = Cp* (2a), Cp (2b)) have been (re)investigated using a combination of UV-vis-NIR and IR spectroelectrochemistry, and quantum chemical calculations based on both dispersion-corrected global (BLYP35-D3) and local (Lh-SsirPW92-D3) hybrid functionals. Following analysis of new and existing data, including the IR-active v(C C) bands, the iron compounds [1](+) are reclassified as valence-trapped (Robin and Day Class II) mixed-valence complexes, in contrast to the ruthenium complexes [2](+), which are delocalized (Robin and Day Class III) systems. All members of the series exist as a thermally populated distribution of conformers in solution, and the overlapping spectroscopic profiles make the accurate extraction of the parameters necessary for the analysis of [1](+) and [2](+) within the framework of the Marcus-Hush model extremely challenging. Analysis of the spin-density distributions from a range of conformational minima provides an alternative representation of the degree of charge localization, and a comparison between members of the series is presented.

Treatment of the triflate complex [Cp*(dppe)FeOTf] {5; Cp*=eta(5)-C-5(CH3)(5), dppe=1,2-bis(diphenylphosphanyl) ethane, OTf=CF3SO3} with an excess of HC=C-[Si(CH3)(2)](2)-1,4-C6H4X (6a-e) in a mixture of THF and triethylamine (NEt3) provides the new complexes {1a: X=H; 1b: X=CH3; 1c: X= N(CH3)(2); 1d: X=CF3; 1e: X=Br}, which were isolated in 64 to 81 % yields as orange powders. The cyclic voltammetry, and multinuclear NMR, IR, and UV/Vis spectroscopic data obtained for 1a-e, as well as the X-ray crystal structures determined for 1a, 1c, and 1e, reveal the importance of the sigma-pi conjugation (hyperconjugation) between the Si-Si sigma-bond and the vicinal C=C pi-orbitals in the description of the electronic structure of the ground state of these complexes. When compounds 1a-e are reacted with [(C5H5)(2)Fe](PF6) (1 equiv.) at 20 degrees C, they provide [1a-e](PF6), which partially decompose in solution during the reaction process. They were isolated as mixtures with the mononuclear [Cp*(dppe) Fe=C=CH2](PF6) (7) and binuclear [Cp*(dppe) Fe=C=CH-CH=C=Fe(dppe) Cp*](PF6)(2) (8) vinylidenes. Reduction of these mixtures with cobaltocene affords the parent neutral compounds 1a-e in analytically pure forms. The iron(III) complexes were characterized by IR and Mssbauer spectroscopy, which clearly showed that the iron(III) nucleus sensed the electronic effect of the X substituents.

An entry from the Cambridge Structural Database, the world’s repository for small molecule crystal structures. The entry contains experimental data from a crystal diffraction study. The deposited dataset for this entry is freely available from the CCDC and typically includes 3D coordinates, cell parameters, space group, experimental conditions and quality measures.

The dinuclear iron complexes [Cp*(dppe)Fe-C C C4H2S-(C C)(x)-C4H2S-C C-Fe(dppe)Cp*] (2, x = 1; 3 x = 2) and [Cp*(dppe)Fe-C C-C4H2S-C C-C C-Fe(dppe) Cp*] (4) were prepared in one -pot procedures from known organometallic precursors. Compound 2 was obtained from Cp,*(dppe)Fe-C C-C4H2S-C C-C4H2S-C CH (6) and Cp*(dppe)FeCl (5) in 74% yield. Its relative 3, isolated in 84%, resulted from the oxidative coupling of Cp*(dppe)Fe-C C-C4H2S-C CH (7) in the presence of Cu(OAc)(2) and 1,8-diazabicyclo[5.4.0]-undec-7-ene (DBU). Complex 4 was obtained from the bridging ligand 2,5-bis(trimethylsilylbutadiynyl)thiophene (8) and two equiv of 5. The new complexes were characterized by ESI-mass spectrometry, IR, multi-nuclear NMR, cyclic voltammetry, and Mossbauer spectroscopy. Complex 3 was also analyzed by X-ray diffraction on a single crystal. The data are consistent with a sizable metal metal interaction across the 14- and 16 -carbon atoms of the bridges. The singly and doubly oxidized forms 2(PF6)(n) and 3(PF6)(n) (n = 1, 2) were obtained by oxidation of the corresponding 18 -electron iron(II) precursors with 1 and 2 equivs of ferrocenium salt, while 4 decomposed very quickly upon oxidation. The thermally stable salts 2(PF6)(n) and 3(PF6)(n) (n = 1, 2) were subjected to analyses by ESI-mass spectrometry, IR, Mossbauer, ESR, UV-vis, and NIR spectroscopies. The radical cations 2(PF6) and 3(PF6) belong to Class II of the mixed-valence Robin and Day classification with quite sizable electronic coupling parameters for large metal-metal separation (2(PF6), H-ab = 262 cm(-1), d(FeFe) = 17.7 angstrom; 3(PF6), H-ab = 203 cm(-1), d(FeFe) = 19.7 angstrom). Paramagnetic H-1 NMR spectroscopy was also performed on the dicationic salts to measure the magnetic exchange between the distant spin carriers (2(PF6)(2), Delta G(ST) = -120 cm(-1)). The data were analyzed with the support of quantum chemistry calculations at the DFT level of theory.

The binuclear Complex [{Cp*(dppe)Fe-C C-}(2)-mu-(1,2-C6H4)] (o-1) was prepared via the bis(vinylidene) [{(Cp*(dppe)-Fe = C = CH-}(2)-mu-(1,2-C6H4)](PF6)(2) (o-1H(2)(Pr-6)(2)) good yield. The new complex was characterized by ESI-mass spectrometry, IR, multinuclear NMR, and Mossbauer spectroscopies, X-ray diffraction on a single crystal, and cyclic voltammetry. The data are consistent with a strong steric interaction between the vicinal organoiron centers responsible for the very long time of reaction for the preparation of o-1. The singly and doubly oxidized forms o-1 (PF6) and o-1(PF6)(2), were prepared. by oxidation of o-1 with 1 and 2 equiv of ferrocenium salt. These salts were Characterized by high-resolution ESI-Mass spectra, XRD analyses on single crystals, and IR, Mossbauer, ESR, UV-vis, and NIR spectroscopies. In addition, the magnetic properties of compound o-1(PF6)(2) were investigated by H-1 and P-31 NMR. The data were analyzed with the support of quantum chemistry calculations at the DFT level of theory. The radical cation o-1(PF6) belongs to class JIB of the mixed-valence classification (H-ab < 1500 cm(-1)). The narrowness of the IVCT bands is explained by the steric hindrance, which limits the number of conformers. The singlet/triplet states ratio is independent of the temperature for the doubly oxidized complex o-1(PF6)(2).

The binuclear complexes Cp*(dppe)FeC CC CC CM(dppe)Cp* (6, M = Fe; 8, M = Ru) were obtained in good yield by treatment of the iron chloro complex Cp*(dppe)Fe-Cl (5) in the presence of KF with the bis(silylated) hexatriyne Me3SiC CC CC CSiMe3 and the ruthenium complex Cp*(dppe)RuC CC CC CSiMe3 (7), respectively. The oxidized species 6(PF6)(n) (n = 1, 2) and 8(PF6) were obtained in ca. 80% yield by treatment of the parent neutral compounds with 1 or 2 equiv of [Cp2Fe](PF6) in THF or dichloromethane at -78 degrees C. The CV of these compounds show three reversible waves with a separation larger than 0.5 V. The salts 6(PF6)(n) (n = 1, 2), and 8(PF6) were characterized by XRD. Quantum chemistry calculations performed at the DFT level on the oxidized species show a strong contribution of the -C-6- spacer to the delocalization of the spin density. IR spectra analyzed with the support of TD-DFT calculations are consistent with the delocalization of the odd electron on the fast IR time scale for the two mixed-valence complexes 6(PF6) and 8(PF6). Combined ESR measurements on rigid glass and on single crystal samples clearly establish that the electronic properties of MV species and particularly their magnetic anisotropies depend on the conformation of the molecules. In the case of the doubly oxidized species 6(PF6)(2), which carries two unpaired electrons, it is shown that the singlet vs triplet ground states can be inverted by the rotation of one metal end with respect to the other around the all-carbon chain axis. Very strong NIR bands are found for the symmetric 6(PF6) and nonsymmetric 8(PF6) MV (mixed-valence) derivatives allowing the determination of very large electronic couplings (H-ab = 3070 and 4025 cm(-1), respectively).

Treatment of[Cp*(dppe)Fe C C-1-naphthyl] (3) with [CpRu(NCCH3)(3)](PF6) (2(PF6)) in CH2Cl2 provides the heterobinudear complex [Cp*(dppe)Fe-C C-1-(eta(6)-C10H7)RuCp](PF6) in 80% isolated yield (Cp = eta(5)-C5H5, Cp* = eta(5)-C5Me5, dppe = 1,2-bis(diphenylphosphino)ethane). Complexation of the CpRu+ arenophile fragment specifically takes place onto either the substituted naphthyl ring A or on the unsubstituted ring B, providing isomers 1A(PF6) and 1B(PF6) in a 70/30 ratio. Under the same conditions, complexation of the cationic vinylidene 3H(PF6) or the iron(III) complex 3(PF6) affords 1A(PF6) and 1B(PF6) in a 30/70 ratio upon deprotonation of the dicationic vinylidenes 1AH(PF6)(2) and 1BH(PF6)(2) and monoelectronic reduction of the dicationic acetylides 1A(PF6)(2) and 1B(PF6)(2), respectively. The new compounds were characterized by NMR, IR, cyclic voltammetry, and UV-vis methods. The X-ray crystal structures show that the (eta(6)-arene)Ru distances lengthen according to the following sequence of compounds: 1B(PF6), 1B(PF6)(2), and 1A(PF6). It is found that the isomerization of 1A(PF6) into 1B(PF6) can be achieved at 20 degrees C upon activation of the (e-arene)Ru bond by one-electron oxidation of the remote iron center and assistance from a coordinating solvent molecule. The experimental data have been analyzed with the support of theoretical calculations performed at the density functional theory (DFT) level. It is proposed that the reaction pathway involves a transition state in which the CpRu+ entity is eta(3)-coordinated to the naphthyl rings in an exocyclic manner in a position opposite to the alkynyl iron moiety. Theoretical results also reflect the ability of the transition state to accommodate coordinating solvent molecules such as acetonitrile to lower the activation energy barrier of the haptotropic rearrangement.

The binuclear complexes {Cp*(dppe)M}2{μ-C≡CC[═C(CN)2]C[═C(CN)2]C≡C} (2Fe, M = Fe; 2Ru, M = Ru) and {Cp*(dppe)Fe}{C≡CC[═C(CN)2]C[═C(CN)2]C≡C}{Ru(dppe)Cp*} (2FeRu) were obtained by treatment of the binuclear precursors Cp*(dppe)M-C≡CC≡CC≡C-M′(dppe)Cp* (M = M′ = Fe, 1Fe; M = M′ = Ru, 1Ru; M = Fe, M′ = Ru, 1FeRu) with TCNE in CH2Cl2 at 20 °C. Complexes 2Fe and 2FeRu were isolated as deep purple powders (82% and 87% yields, respectively), and 2Ru was isolated as a brown-yellow solid (55%). The paramagnetic salt [2FeRu][C3(CN)5] was also isolated in 51% yield. The structural and electronic properties of the new compounds were investigated by 1H, 13C, and 31P NMR, XRD analysis, cyclic voltammetry, IR and UV–vis, EPR, and NIR spectroscopies. The experimental data clearly show that the insertion of the central −C≡C– triple bond of [M]–C6–[M] into tetracyanoethene (TCNE) dramatically decreases the electronic interaction between the metal termini. NIR spectroscopy of the salt [2FeRu][C3(CN)5] demonstrated that the c...

The organic precursor bis(trimethylsilylethynyl)TTFMe2 (3, TTF = tetrathiafulvalene) was prepared as a 1:1 mixture of the cis and trans isomers. Pure samples of 3-cis and 3-trans were obtained by crystallization and identified by XRD analysis. The treatment of pure 3-trans and a 1:1 mixture of 3-cis/trans with (i) potassium carbonate, (ii) the iron complex Cp*(dppe)FeCl [5, Cp* = eta(5)-C5Me5, dppe = 1,2-bis(diphenylphosphanyl)ethane] in the presence of KPF6, and (iii) tBuOK provided Cp*(dppe)Fe-C C-TTFMe2-C C-Fe(dppe) Cp* as the pure geometric isomer 6-trans (85%) and as the 60:40 mixture 6-cis/ trans (63%), respectively. The oxidation of 6-trans with [(C5H5)(2)Fe]PF6 gave [6-trans][PF6](n) (n = 1-3). Visible, IR, near-IR (NIR), and electron paramagnetic resonance (EPR) spectroscopy together with DFT data show that [6-trans][PF6] is a class II mixed-valence complex (H-ab = 85 cm(-1)) in which the spin distribution depends on the conformation of the molecule. Intramolecular electron transfer occurs through single-step tunneling and a multistep hoping mechanism. The triplet state is thermally accessible for [6-trans][PF6](2).