Synthesis and structural characterization of stable coinage metal (Cu, Ag, Au) cyclopentadienyl complexes.

The electron withdrawing and oxidatively stable perfluorinated Cp* ligand [C5(CF3)5]- allowed for the isolation of rare and unusually stable coinage metal complexes [M(C5(CF3)5)(PtBu3)] (M = Cu, Ag, Au), representing the first complete and structurally comparable series of group 11 Cp coordination compounds. Full characterization and structure analysis revealed distinct and partly unknown coordination motifs with hapticities ranging from η1, η3/η1 and η3/η2 for gold, silver and copper, respectively. Quantum-chemical studies using DFT methods confirm these findings and connect them to the unique electronic structure of the given ligand system.

Substitution Lability of the Perfluorinated Cp* Ligand in [Rh(COD)(C5(CF3)5)] Towards Triphenylpnictogens EPh3 (E=N, P, As, Sb, Bi).

Triphenylpnictogens EPh3 (E=N, P, As, Sb, Bi) are able to displace the perfluorinated Cp* ligand in [Rh(COD)(C5(CF3)5)] (COD=1,5-cyclooctadiene) in up to quantitative yield. The resulting ionic products contain [C5(CF3)5]- as uncoordinated counter anion. The cations feature [Rh(COD)]+ fragments, coordinated by one (N, Bi), two (P, As) or three (Sb) triphenylpnictogen moieties. Whereas coordination via the pnictogen is observed for P, As and Sb, π-coordination of the aryl rings is observed for N and Bi.

The synthesis and characterization of an iron(VII) nitrido complex.

Complexes of iron in high oxidation states are captivating research subjects due to their pivotal role as active intermediates in numerous catalytic processes. Structural and spectroscopic studies of well-defined model complexes often provide evidence of these intermediates. In addition to the fundamental molecular and electronic structure insights gained by these complexes, their reactivity also affects our understanding of catalytic reaction mechanisms for small molecule and bond-activation chemistry. Here, we report the synthesis, structural and spectroscopic characterization of a stable, octahedral Fe(VI) nitrido complex and an authenticated, unique Fe(VII) species, prepared by one-electron oxidation. The super-oxidized Fe(VII) nitride rearranges to an Fe(V) imide through an intramolecular amination mechanism and ligand exchange, which is characterized spectroscopically and computationally. This enables combined reactivity and stability studies on a single molecular system of a rare high-valent complex redox pair. Quantum chemical calculations complement the spectroscopic parameters and provide evidence for a diamagnetic (S = 0) d 2 Fe(VI) and a genuine S = 1/2, d 1 Fe(VII) configuration of these super-oxidized nitrido complexes.

Structural characterization and reactivity of a room-temperature-stable, antiaromatic cyclopentadienyl cation salt.

The singlet states of cyclopentadienyl (Cp) cations are considered as true prototypes of an antiaromatic system. Unfortunately, their high intrinsic reactivity inhibited their isolation in the solid state as a salt, and controlled reactions are also scarce. Here we present the synthesis and solid state structure of the room-temperature-stable Cp cation salt [Cp(C6F5)5]+[Sb3F16]-. Although the aromatic triplet state of the [Cp(C6F5)5]+ cation is energetically favoured in the gas phase according to quantum chemical calculations, coordination of the cation by either [Sb3F16]- or C6F6 in the crystal lattice stabilizes the antiaromatic singlet state, which is present in the solid state. The calculated hydride and fluoride ion affinities of the [Cp(C6F5)5]+ cation are higher than those of the perfluorinated tritylium cation [C(C6F5)3]+. Reactions of [Cp(C6F5)5]+[Sb3F16]- with CO, which probably yields the corresponding carbonyl complex, and of radical Cp(C6F5)5∙ with selected model substrates (Cp2Fe, (Ph3C∙)2 and Cp*Al) are also presented.

Coordination of Tetracyanoquinodimethane-Derivatives with Tris(pentafluorophenyl)borane Provides Stronger p-Dopants with Enhanced Stability.

Strong molecular dopants for organic semiconductors that are stable against diffusion are in demand, enhancing the performance of organic optoelectronic devices. The conventionally used p-dopants based on 7,7,8,8-tetracyanoquinodimethane (TCNQ) and its derivatives "FxTCN(N)Q", such as 2,3,4,6-tetrafluoro-7,7,8,8-tetracyanoquinodimethane (F4TCNQ) and 1,3,4,5,7,8-hexafluorotetracyano-naphthoquinodimethane (F6TCNNQ), feature limited oxidation strength, especially for modern polymer semiconductors with high ionization energy (IE). These small molecular dopants also exhibit pronounced diffusion in the polymer hosts. Here, we demonstrate a facile approach to increase the oxidation strength of FxTCN(N)Q by coordination with four tris(pentafluorophenyl)borane (BCF) molecules using a single-step solution mixing process, resulting in bulky dopant complexes "FxTCN(N)Q-4(BCF)". Using a series of polymer semiconductors with IE up to 5.9 eV, we show by optical absorption spectroscopy of solutions and thin films that the efficiency of doping using FxTCN(N)Q-4(BCF) is significantly higher compared to that using FxTCN(N)Q or BCF alone. Electrical transport measurements with the prototypical poly(3-hexylthiophene-2,5-diyl) (P3HT) confirm the higher doping efficiency of F4TCNQ-4(BCF) compared to F4TCNQ. Additionally, the bulkier structure of F4TCNQ-4(BCF) is shown to result in higher stability against drift in P3HT under an applied electric field as compared to F4TCNQ. The simple approach of solution-mixing of readily accessible molecules thus offers access to enhanced molecular p-dopants for the community.

Structural Characterization and Bonding Analysis of [Hg{Fe(CO)5}2]2+ [SbF6]-2.

The non-classical carbonyl complex [Hg{Fe(CO)5}2]2+ [SbF6]-2 is prepared by reaction of Hg(SbF6)2 and excess Fe(CO)5 in anhydrous HF. The single-crystal X-ray structure reveals a linear Fe-Hg-Fe moiety as well as an eclipsed conformation of the eight basal CO ligands. Interestingly, the Hg-Fe bond length of 2.5745(7) Å is relatively similar to the corresponding Hg-Fe bonds in literature-known [Hg{Fe(CO)4}2]2- dianions (2.52-2.55 Å), which intrigued us to analyze the bonding situation in both the dications and dianions with the energy decomposition analysis with natural orbitals for chemical valence (EDA-NOCV) method. Both species are best described as Hg(0) compounds, which are also confirmed by the shape of the HOMO-4 and HOMO-5 of the dication and dianion, respectively, in which the electron pair is located mainly at the Hg. Furthermore, for the dication and the dianion, the σ back-donation from Hg into the [Fe(CO)5]22+ or the [Fe(CO)4]22- fragment is the most dominant orbital interaction and surprisingly these interaction energies are also very similar even in absolute values. The fact that both iron-based fragments are missing two electrons explains their prominent σ-acceptor properties.

Persilylation of ferrocene: the ultimate discipline in sterically overcrowded metal complexes.

We report the preparation and structural characterization of the first persilylated metallocene via the metalation of decabromoferrocene. Although Grignard conditions turned out to be insufficient due to the steric and electronic effects of silyl groups causing a decreased nucleophilicity of the metalated intermediates, stepwise lithium-halogen exchange yields complex mixtures of polysilylated compounds FeC10DMSnH10-n (n = 10, 9, 8) including the targeted decasilylated ferrocene. These mixtures were successfully separated allowing a systematic study of silylation effects on ferrocene by XRD, CV, NMR and UV/vis spectroscopy supported by DFT calculations. The findings were used to develop a high-yielding and simple preparation method to generate a tenfold substituted overcrowded ferrocene, FeC10DMS8Me2.

Substitution lability of the perfluorinated Cp* ligand in Rh(I) complexes.

Several cationic rhodium(I) complexes [Rh(COD)L2][C5(CF3)5] have been synthesized through substitution of the weakly bound [C5(CF3)5]- ligand from [Rh(COD)(C5(CF3)5)], further emphasizing its unique reactivity. Besides acetonitrile, pyridine derivatives with varying degrees of fluorination have been employed as ligands in order to investigate the influence of fluorination upon the binding affinity towards the resulting [Rh(COD)]+ fragment and the limit as to which the [C5(CF3)5]- ligand can be displaced. Furthermore, the newly synthesized compounds represent rare examples of rhodium complexes containing fluorinated pyridines as ligands.

A decacationic ferrocene-based metallostar.

Decacationic metallostars have been prepared by the reaction of permercurated ferrocene FeC10(HgO2CCF3)10 with superacidic (C5F5NH)(SbF6) (pK a = -11 estimated in H2O) in multigram scale. In the resulting compound, [FeC10Hg10(NC5F5) n ][SbF6]10, the labile pentafluoropyridine ligands are readily displaced by acetonitrile (MeCN) or tetrahydrothiophene (THT). In the X-ray structure of [FeC10Hg10(THT)10][SbF6]10·24 MeCN no cation-anion contacts between mercury and fluorine were observed. Moreover, cyclic voltammetry measurements of [FeC10(Hg(MeCN))10]10+ and [FeC10(Hg(THT))10]10+ revealed a (quasi)reversible one-electron oxidation of Fe(ii) to Fe(iii). From the reaction of [FeC10(Hg(MeCN))10]10+ with MoF6 as oxidant the ferrocenium cation [FeC10(Hg(MeCN))10]11+ was obtained and characterized via single crystal XRD. These electrophilic metallostars are promising potential building blocks for the synthesis of dendritic architectures containing a robust, tenfold functionalized ferrocene core.

Introducing the Perfluorinated Cp* Ligand into Coordination Chemistry.

The reaction of AgBF4 and [Rh(COD)Cl]2 (COD=1,5-cyclooctadiene) in presence of [NEt4 ][C5 (CF3 )5 ] afforded the fluorocarbon soluble complex [Rh(COD)(C5 (CF3 )5 )] by salt metathesis. This complex represents the first example for a successful coordination of the weakly basic [C5 (CF3 )5 ]- ligand, since its first synthesis in 1980. In addition to [Rh(COD)(C5 (CF3 )5 )] also the byproduct [Rh(COD)(C5 (CF3 )4 H)] was isolated and fully characterized. Accompanying DFT studies showed that the interaction energy of the [C5 (CF3 )5 ]- ligand towards the 12-electron fragment [Rh(COD)]+ is ≈70 kcal mol-1 lower in comparison to [C5 (CH3 )5 ]- due to reduced electrostatic interactions and weaker π-donor properties of the ligand. The quantitative but reversible substitution of the [C5 (CF3 )5 ]- ligand by toluene, converting it into a weakly coordinating anion, experimentally proved the extraordinary weak bonding interaction.

Increasing the oxidation power of TCNQ by coordination of B(C6F5)3.

The oxidation power of the cyanocarbon TCNQ (tetracyano-quinodimethane) can be significantly increased to approximately E = +0.9 V vs. Cp2Fe by coordination of up to four equivalents of the strong fluorinated Lewis acid B(C6F5)3, resulting in a highly reactive but easy-to-use oxidation system. Thianthrene and tris(4-bromophenyl)amine were oxidized to the corresponding radical cations. Dianionic [TCNQ·4 B(C6F5)3]2- was formed upon reduction with two equivalents of ferrocene or decamethylcobaltocene. [TCNQ·4 B(C6F5)3]- and [TCNQ·4 B(C6F5)3]2- are rare cases of redox-active weakly-coordinating anions.

The Tris(pentafluorophenyl)methylium Cation: Isolation and Reactivity.

Herein, we present two different routes for the synthesis of the perfluorinated trityl cation, which allowed the handling of the free, uncoordinated species in organic solvents for the first time. The usage of the weakly coordinating anion [Al(OTeF5 )4 ]- and its derivatives allows the characterization of this species by NMR spectroscopy and most importantly by single-crystal X-ray diffraction. The high hydride ion affinity of the cation is shown by hydrogen abstraction from isobutane. Furthermore, cyclic voltammetry reveals its oxidative potential which is supported by the reaction with tris(4-bromophenyl)amine, giving rise to the formation of the ammoniumyl radical cation, also known as "magic blue".

Eightfold Electrophilic Methylation of Octacyanotungstate [W(CN)8]4-/3-: Preparation of Homoleptic, Eight-Coordinate Methyl Isocyanide Complexes [W(CNMe)8]4+/5.

Homoleptic eightfold coordinated methyl isocyanide complexes of W(IV) and W(V) have been prepared for the first time. The reaction of [NBu4]4[W(CN)8] with methyl triflate (MeOTf) gives [W(CNMe)8][OTf]4. The even stronger methylating mixture of methyl fluoride (MeF) and arsenic pentafluoride (AsF5) in liquid sulfur dioxide (SO2) is able to fully alkylate both [NBu4]4[W(CN)8] and [NBu4]3[W(CN)8]. The paramagnetic octakis(methyl isocyanide)tungsten(V) complex [W(CNMe)8][AsF6]5 is thermally highly unstable above -30 °C. All compounds have been characterized via single-crystal X-ray diffraction and IR, Raman, and NMR or EPR spectroscopy.

Tenfold Metalation of Ferrocene: Synthesis, Structures, and Metallophilic Interactions in FeC10 (HgX)10.

The permercuration of ferrocene was achieved by reacting ferrocene with 10 equivalents of mercury(II) butyrate Hg(O2 CC3 H7 )2 in a facile one-pot reaction in multi-gram scale and high yields. The butyrate groups in FeC10 (HgX)10 (X=O2 CC3 H7 ) can be exchanged by treatment with trifluoro- or trichloroacetic acid (X=O2 CCF3 , O2 CCCl3 ). Substitution of the trifluoroacetate groups by halides (X=Cl, F) proceeds easily in aqueous THF. The completeness of metalation was confirmed by NMR and vibrational spectroscopy, mass spectrometry, as well as elemental analysis. Additionally, the first crystal structures of permetallated metallocenes are presented: FeC10 (HgX)10 (X=Cl, O2 CCF3 , O2 CCCl3 ).

The [2+2] cycloaddition product of perhalogenated cyclopentadienyl cations: structural characterization of salts of the [C10Cl10]2+ and [C10Br10]2+ dications.

Instead of monomeric cyclopentadienyl cations, the low-temperature reaction of hexachloro- and hexabromocyclo-pentadiene (C5Cl6 and C5Br6) with powerful Lewis acids SbF5 and AsF5 in SO2ClF yields salts of perhalogenated dications [C10Cl10][Sb3F16]2 and [C10Br10][As2F11]2 which are characterized via single crystal X-ray diffraction and NMR spectroscopy. Additionally, this reactivity is rationalized by quantum-chemical calculations.

Isolation and Structural Characterization of Eightfold Protonated Octacyanometalates [M(CNH)8 ]4+ (M=MoIV , WIV ) from Superacids.

Octacyanometalates K4 [Mo(CN)8 ] and K4 [W(CN)8 ] are completely protonated in superacidic mixtures of anhydrous hydrogen fluoride and antimony pentafluoride. The resulting hydrogen isocyanide complexes [Mo(CNH)8 ]4+ [SbF6 ]- 4 and [W(CNH)8 ]4+ [SbF6 ]- 4 are the first examples of eight-coordinate homoleptic metal complexes containing hydrogen isocyanide (CNH) ligands. The complexes were crystallographically characterized, revealing hydrogen-bonded networks with short N⋅⋅⋅H⋅⋅⋅F contacts. Low-temperature NMR measurements in HF confirmed rapid proton exchange even at -40 °C. Upon protonation, ν(C≡N) increases of about 50 cm-1 which is in agreement with DFT calculations.

Crystal structure of [K(18-crown-6)]+ 2[Pt(CN)4]2.

In the title compound, di-µ-cyanato-1:2κ2 N:C;2:3κ2 C:N-di-cyanato-2κ2 C-bis-(1,4,7,10,13,16-hexa-oxa-cyclo-octa-deca-ne)-1κ6 O;3κ6 O-1,3-dipotassium(I)-2-platinum(II), [K2Pt(CN)4(C12H24O6)2] or [K(18-crown-6)]2·[Pt(CN)4], two trans-orientated cyano groups of the square-planar [Pt(CN)4]2- dianion (Pt site symmetry ) bind to one potassium ion each, which are additionally coordinated by the six O atoms of 18-crown-6. No Pt⋯Pt inter-actions occur in the crystal, but very weak Pt⋯H contacts (2.79 Å) are observed.

Structural characterization of potassium salts of the decamethylmanganocene anion Cp*2Mn.

For the first time the crystal structure of a permethylated metallocene anion has been obtained. The 17 valence electron complex decamethylmanganocene Cp*2Mn is reduced by molten potassium in THF to its extremely air-sensitive anion [Cp*2Mn]-. The potassium salt [K(THF)2]+[Cp*2Mn]- crystallizes upon cooling from hot THF and forms infinite polymeric chains exhibiting strong KC contacts. In the presence of 18-crown-6 the polymeric structure is broken up. Crystals of [K(18-crown-6)(THF)2]+[Cp*2Mn]- were obtained upon slow cooling from THF to -80 °C displaying well separated cations and anions.

A Ferrocene-Based Dicationic Iron(IV) Carbonyl Complex.

The 16-valence electron species [Cp*2 Fe]2+ (Cp*=η-C5 Me5 ), formally featuring a tetravalent iron ion, quantitatively binds CO in HF solution to form the stable, diamagnetic carbonyl species [Cp*2 Fe(CO)]2+ . This dication forms salts in the presence of AsF6 - and SbF6 - that were crystallographically characterized. The molecular structure in crystals of [Cp*2 Fe(CO)](AsF6 )2 displays cyclopentadienyl rings that are clearly not parallel and an equatorially bound η1 -CO ligand. The formal oxidation state +IV of iron was investigated by 57 Fe Mössbauer spectroscopy and is supported by DFT computational analysis. A detailed spectroscopic characterization of the hitherto unprecedented high-valent iron carbonyl compounds is reported.

Isolation and Characterization of a Non-Rigid Hexamethylbenzene-SO2+ Complex.

During our studies towards the preparation of the pentagonal-pyramidal hexamethylbenzene dication C6 (CH3 )62+ , we isolated the unprecedented dicationic species C6 (CH3 )6 SO2+  (AsF6- )2 from the reaction of hexamethylbenzene with a mixture of anhydrous HF, AsF5 , and liquid SO2 . This compound can be understood as a complex of unknown SO2+ with hexamethylbenzene. Herein, we report on its synthesis, molecular structure, and spectroscopic characterization.