Moritz Malischewski

Isolation and structural and electronic characterization of salts of the decamethylferrocene dication

Charging up the iron in ferrocene salts Ferrocene is the archetype of the sandwich compounds, so called because a metal atom is inserted between two carbon rings. The elucidation of ferrocenes structure was pivotal to the development of organometallic chemistry during the mid-20th century. The ease with which the iron in the center of the molecule can toggle between the +2 and +3 oxidation states has made the compound a common electrochemical standard. Malischewski et al. report the synthesis and isolation of ferrocene salts with iron in the +4 state, which they characterize crystallographically and spectroscopically. Science, this issue p. 678 An archetypal organometallic compound has been isolated in a higher oxidation state. Ferrocene and its decamethyl derivative [Cp*2Fe] are the most common standards for nonaqueous electrochemical investigations because of their well-defined and only mildly solvent-dependent reversible Fe(II)/Fe(III) redox couple. Higher oxidation states have only rarely been studied. We report the isolation and crystallographic and spectroscopic characterization of surprisingly stable Fe(IV) salts of the [Cp*2Fe]2+ dication, produced by oxidation of [Cp*2Fe] with AsF5, SbF5, or ReF6 in neat sulfur dioxide as well as [XeF](Sb2F11) in neat hydrogen fluoride. The Sb2F11– salt exhibits a metallocene with the expected mutually parallel arrangements of the Cp* rings, whereas the As2F11–, AsF6–, SbF6–, and ReF6– salts manifest tilt angles ranging from 4° to 17°. Both 57Fe Mössbauer spectroscopy and superconducting quantum interference device magnetization studies reveal identical d-orbital splitting with an S = 1, 3E ground state based on the 3d electronic configuration e2g3a1g1 of all [Cp*2Fe]2+ salts.

Crystal Structure Determination of the Pentagonal-Pyramidal Hexamethylbenzene Dication C6(CH3)6 2+

In contrast to the well-known 2-norbornyl cation, the structure of which was a matter of long debate until its pentacoordinated nature was recently proven by an X-ray structure, the pentagonal-pyramidal dication of hexamethylbenzene has received considerably less attention. This species was first prepared by Hogeveen in 1973 at low temperatures in magic acid (HSO3 F/SbF5 ), for which he proposed a non-classical structure (containing a hexacoordinated carbon) based on NMR spectroscopy and reactivity studies, but no X-ray crystal structure has been reported. C6 (CH3 )62+ can be obtained through the dissolution of hexamethyl Dewar benzene epoxide in HSO3 F/SbF5 and crystallized as the SbF6- salt upon addition of excess anhydrous hydrogen fluoride. The crystal structure of C6 (CH3 )62+ (SbF6- )2 ⋅HSO3 F confirms the pentagonal pyramidal structure of the dication. The apical carbon is bound to one methyl group (distance 1.479(3) Å) and to the five basal carbon atoms (distances 1.694(2)-1.715(3) Å).

Trip2C6H3SeF: The First Isolated Selenenyl Fluoride

Joining the stable: The first examples of the highly instable selenenyl fluorides RSeF are prepared from the reaction on the tin selenide RSeSnMe(3) with XeF(2). Through the use of extremely large protecting groups (m-terphenyl ligands) which stabilizes the RSeF units against disproportionation, the compounds could be isolated and characterized by NMR spectroscopy and single-crystal structure analysis (see structure).

Jahn-Teller Effect in the B12F12 Radical Anion and Energetic Preference of an Octahedral B6(BF2)6 Cluster Structure over an Icosahedral Structure for the Elusive Neutral B12F12.

The B12F12(-) radical anion was generated by oxidation of [CoCp2(+)]2B12F12(2-) with AsF5 in SO2. In the crystal structure of [CoCp2(+)]B12F12(-), the anion displays a lowered symmetry (D2h) instead of an Ih-symmetric dianion as a result of Jahn-Teller distortion. Moreover, shortening of the B-F bonds and subtle changes of the B-B bonds are observed. DFT calculations show that, for the unknown neutral B12F12, unprecedented structural isomers [e.g., octahedral B6(BF2)6] are energetically favored instead of an icosahedral structure. The structures and energetics are compared with those of the analogous chlorine compounds.

Protonation of Ferrocene - Low-Temperature X-Ray Diffraction Study of [Cp2FeH](PF6) Reveals an Iron-Bound Hydrido Ligand

Ferrocene, Cp2 Fe, is quantitatively protonated in a mixture of liquid HF/PF5 to yield [Cp2 FeH](PF6 ), which was characterized by 1 H/13 C NMR and 57 Fe Mössbauer spectroscopy as well as single-crystal X-ray diffraction analysis. X-ray diffraction analysis at 100 K revealed a disordered, iron-coordinated hydrido ligand, which was unambiguously located by aspherical atom refinement at 100 K, and by analyzing the non-disordered crystal structure at 30 K, revealing a non-agostic structure.

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.

Crystal structure of bis-(fluoro-sulfato-κO)xenon(II), Xe(SO3F)2.

The Xe atom in Xe(SO3F)2 is linearly bonded to two O atoms of the fluorosulfate unit.

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.