Trifluoromethyl Fluorosulfonate (CF3OSO2F) and Trifluoromethoxy Sulfur Pentafluoride (CF3OSF5) - Two Gaseous Sulfur(VI) Compounds with Insulating Properties.

In this work, we analyzed trifluoromethyl fluorosulfonate (CF3OSO2F) and trifluoromethoxy sulfur pentafluoride (CF3OSF5) regarding their potential use as dielectrics by investigating some of their intrinsic and extrinsic properties. Both compounds show a higher breakdown voltage than SF6 with averaged relative breakdown voltages of 1.3±0.2 for CF3OSO2F and 1.4±0.2 for CF3OSF5 compared to SF6 with 1.0. Like the dielectric (CF3)2CFCN, both compounds decompose during the breakdown process. The decomposition products were analyzed by IR spectroscopy and GCIR methods. Furthermore, the molecular structures of both gaseous compounds CF3OSO2F and CF3OSF5 have been determined by in situ crystallization, and their physical properties were determined as well.

Gold Teflates Revisited: From the Lewis Superacid [Au(OTeF5 )3 ] to the Anion [Au(OTeF5 )4 ].

A new synthetic access to the Lewis acid [Au(OTeF5 )3 ] and the preparation of the related, unprecedented anion [Au(OTeF5 )4 ]- with inorganic or organic cations starting from commercially available and easy-to-handle gold chlorides are presented. In this first extensive study of the Lewis acidity of a transition-metal teflate complex by using different experimental and quantum chemical methods, [Au(OTeF5 )3 ] was classified as a Lewis superacid. The solid-state structure of the triphenylphosphine oxide adduct [Au(OPPh3 )(OTeF5 )3 ] was determined, representing the first structural characterization of an adduct of this highly reactive [Au(OTeF5 )3 ]. Therein, the coordination environment around the gold center slightly deviates from the typical square planar geometry. The [Au(OTeF5 )4 ]- anion shows a similar coordination motif.

Reactivity of [AuF3 (SIMes)]: Pathway to Unprecedented Structural Motifs.

We report on a comprehensive reactivity study starting from [AuF3 (SIMes)] to synthesize different motifs of monomeric gold(III) fluorides. A plethora of different ligands has been introduced in a mono-substitution yielding trans-[AuF2 X(SIMes)] including alkynido, cyanido, azido, and a set of perfluoroalkoxido complexes. The latter were better accomplished via use of perfluorinated carbonyl-bearing molecules, which is unprecedented in gold chemistry. In case of the cyanide and azide, triple substitution gave rise to the corresponding [AuX3 (SIMes)] complexes. Comparison of the chemical shift of the carbene carbon atom in the 13 C{1 H} NMR spectrum, the calculated SIMes affinity and the Au-C bond length in the solid state with related literature-known complexes yields a classification of trans-influences for a variety of ligands attached to the gold center. Therein, the mixed fluorido perfluoroalkoxido complexes have a similar SIMes affinity to AuF3 with a very low Gibbs energy of formation when using the perfluoro carbonyl route.

Insights on the Lewis Superacid Al(OTeF5 )3 : Solvent Adducts, Characterization and Properties.

Preparation and characterization of the dimeric Lewis superacid [Al(OTeF5 )3 ]2 and various solvent adducts is presented. The latter range from thermally stable adducts to highly reactive, weakly bound species. DFT calculations on the ligand affinity of these Lewis acids were performed in order to rank their remaining Lewis acidity. An experimental proof of the Lewis acidity is provided by the reaction of solvent-adducts of Al(OTeF5 )3 with [PPh4 ][SbF6 ] and OPEt3 , respectively. Furthermore, their reactivity towards chloride and pentafluoroorthotellurate salts as well as (CH3 )3 SiCl and (CH3 )3 SiF is shown. This includes the formation of the dianion [Al(OTeF5 )5 ]2- .

Borane Adducts of Aromatic Phosphorus Heterocycles: Synthesis, Crystallographic Characterization and Reactivity of a Phosphinine-B(C6 F5 )3 Lewis Pair.

A phosphinine-borane adduct of a Me3 Si-functionalized phosphinine and the Lewis acid B(C6 F5 )3 has been synthesized and characterized crystallographically for the first time. The reaction strongly depends on the nature of the substituents in the α-position of the phosphorus heterocycle. In contrast, the reaction of B2 H6 with various substituted phosphinines leads to an equilibrium between the starting materials and the phosphinine-borane adducts that is determined by the Lewis basicity of the phosphinine. The novel phosphinine borane adduct (6-B(C6 F5 )3 ) shows rapid and facile insertion and [4+2] cycloaddition reactivity towards phenylacetylene. A hitherto unknown dihydro-1-phosphabarrelene is formed with styrene. The reaction with an ester provides a new, facile and selective route to 1-R-phosphininium salts. These salts then undergo a [4+2] cycloaddition in the presence of Me3 Si-C≡CH and styrene to cleanly form unprecedented derivatives of 1-R-phosphabarrelenium salts.

2-(Dimethylamino)phosphinine: A Phosphorus-Containing Aniline Derivative.

The yet unknown 2-amino-substituted λ3 ,σ2 -phosphinines are phosphorus-containing aniline derivatives. Calculations show that the strong interaction of the π-donating NR2  group with the aromatic system results in a high π-density at the phosphorus atom. We could now synthesize 2-N(CH3 )2 -functionalized phosphinines, starting from a 3-N(CH3 )2 -substituted 2-pyrone and (CH3 )3 Si-C≡P. Their reaction with CuBr⋅S(CH3 )2 affords CuI  complexes with the first example of a neutral phosphinine acting as a rare bridging µ2 -P-4e donor-ligand between two CuI  centers. Our experimental and theoretical investigations show that 2-aminophosphinines are missing links in the series of known 2-donor-functionalized phosphinines.

Discoveries and Challenges en Route to Swinhoeisterol†A.

In this work, a full account of the authors' synthetic studies is reported that culminated in the first synthesis of 13(14→8),14(8→7)diabeo-steroid swinhoeisterol A as well as the related dankasterones A and B, 13(14→8)abeo-steroids, and periconiastone A, a 13(14→8)abeo-4,14-cyclo-steroid. Experiments are described in detail that provided further insight into the mechanism of the switchable radical framework reconstruction approach. By discussing failed strategies and tactics towards swinhoeisterol A, the successful route that also allowed an access to structurally closely related analogues, such as Δ22 -24-epi-swinhoeisterol A, is eventually presented.

Synthesis and Characterization of Poly(hydrogen halide) Halogenates (-I).

Herein, we report the synthesis and characterization of a variety of novel poly(hydrogen halide) halogenates (-I). The bifluoride ion, which is known to have the highest hydrogen bond energy of ≈160 kJ mol-1 , is the most famous among many examples of [X(HX)n ]- anions (X=F, Cl) known in the literature. In contrast, little is known about poly(hydrogen halide) halogenates containing two different halogens, ([X(HY)n ]- ). In this work we present the synthesis of anions of the type [X(HY)n ]- (X=Br, I, ClO4 ; Y=Cl, Br, CN) stabilized by the [PPh4 ]+ and [PPN]+ cation. The obtained compounds have been characterized by single-crystal X-ray diffraction, Raman spectroscopy and quantum-chemical calculations. In addition, the behavior of halide ions in hydrogen fluoride was investigated by using experimental and quantum-chemical methods in order to gain knowledge on the acidity of hydrogen halides in HF.

Friedel-Crafts Type Methylation with Dimethylhalonium Salts.

The dimethylchloronium salt [Me2 Cl][Al(OTeF5 )4 ] is used to methylate electron-deficient aromatic systems in Friedel-Crafts type reactions as shown by the synthesis of N-methylated cations, such as [MeNC5 F5 ]+ , [MeNC5 F4 I]+ , and [MeN3 C3 F3 ]+ . To gain a better understanding of such fundamental Friedel-Crafts reactions, the role of the dimethylchloronium cation has been evaluated by quantum-chemical calculations.

Trifluoromethylation of [AuF3 (SIMes)]: Preparation and Characterization of [Au(CF3 )x F3-x (SIMes)] (x=1-3) Complexes.

Trifluoromethylation of [AuF3 (SIMes)] with the Ruppert-Prakash reagent TMSCF3 in the presence of CsF yields the product series [Au(CF3 )x F3-x (SIMes)] (x=1-3). The degree of trifluoromethylation is solvent dependent and the ratio of the species can be controlled by varying the stoichiometry of the reaction, as evidenced from the 19 F NMR spectra of the corresponding reaction mixtures. The molecular structures in the solid state of trans-[Au(CF3 )F2 (SIMes)] and [Au(CF3 )3 (SIMes)] are presented, together with a selective route for the synthesis of the latter complex. Correlation of the calculated SIMes affinity with the carbene carbon chemical shift in the 13 C NMR spectrum reveals that trans-[Au(CF3 )F2 (SIMes)] and [Au(CF3 )3 (SIMes)] nicely follow the trend in Lewis acidities of related organo gold(III) complexes. Furthermore, a new correlation between the Au-Ccarbene bond length of the molecular structure in the solid state and the chemical shift of the carbene carbon in the 13 C NMR spectrum is presented.

Cobalt Corroles as Electrocatalysts for Water Oxidation: Strong Effect of Substituents on Catalytic Activity.

Two Co(III) complexes (1Py2 and 2Py2) of new corrole ligands H3L1 (5,15-bis(p-methylcarboxyphenyl)-10-(o-methylcarboxyphenyl)corrole) and H3L2 (5,15-bis(p-nitrophenyl)-10-(o-methylcarboxyphenyl)corrole) with two apical pyridine ligands have been synthesized and thoroughly characterized by cyclic voltammetry, UV-vis-NIR, and EPR spectroscopy, spectroelectrochemistry, single-crystal X-ray diffraction studies, and DFT methods. Complexes 1Py2 and 2Py2 possess much lower oxidation potentials than cobalt(III)-tris-pentafluorophenylcorrole (Co(tpfc)) and similar corroles containing pentafluorophenyl (C6F5) substituents, thus allowing access to high oxidation states of the former metallocorroles using mild chemical oxidants. The spectroscopic (UV-vis-NIR and EPR) and electronic properties of several oxidation states of these complexes have been determined by a combination of the mentioned methods. Complexes 1Py2 and 2Py2 undergo three oxidations within 1.3 V vs FcH+/FcH in MeCN, and we show that both complexes catalyze water oxidation in an MeCN/H2O mixture upon the third oxidation, with kobs (TOF) values of 1.86 s-1 at 1.29 V (1Py2) and 1.67 s-1 at 1.37 V (2Py2). These values are five times higher than previously reported TOF values for C6F5-substituted cobalt(III) corroles, a finding we ascribe to the additional charge in the corrole macrocycle due to the increased oxidation state. This work opens up new possibilities in the study of metallocorrole water oxidation catalysts, particularly by allowing spectroscopic probing of high-oxidation states and showing strong substituent-effects on catalytic activity of the corrole complexes.

Oxygen-Bridged Ga2 (Et)3 (OTeF5 )3 and the Weakly Coordinating Anions [Ga(Et)(OTeF5 )3 ]- and [Ga(OTeF5 )4 ].

Salts of the weakly coordinating anions [Ga(OTeF5 )4 ]- as well as [Ga(Et)(OTeF5 )3 ]- and the neutral Ga2 (Et)3 (OTeF5 )3 were synthesized and characterized by spectroscopic methods and single-crystal X-ray diffraction. Ga2 (Et)3 (OTeF5 )3 was formed by treating GaEt3 with pentafluoroorthotelluric acid (HOTeF5 ) and reacted with PPh4 Cl and CPh3 Cl to [PPh4 ][Ga(Et)(OTeF5 )3 ] and [CPh3 ][Ga(Et)(OTeF5 )3 ]. In contrast, Ag[Ga(OTeF5 )4 ] was prepared from AgOTeF5 and GaCl3 and was used as a versatile starting material for further reactions. Starting with Ag[Ga(OTeF5 )4 ] the substrates [PPh4 ][Ga(OTeF5 )4 ] and [CPh3 ][Ga(OTeF5 )4 ] were formed from PPh4 Cl and CPh3 Cl.

Perfluoro Alkyl Hypofluorites and Peroxides Revisited.

A more convenient synthesis of the perfluoro alkyl hypofluorite (F3 C)3 COF as well as the hitherto unknown (C2 F5 )(F3 C)2 COF compound is reported. Both hypofluorites can be prepared by use of the corresponding tertiary alcohols RF OH and elemental fluorine in the presence of CsF. An appropriate access to these highly reactive hypofluorites is crucial. The hypofluorites are then transferred into their corresponding perfluoro bisalkyl peroxides RF OORF [RF =(F3 C)3 C, (C2 F5 )(F3 C)2 C] by treatment with partially fluorinated silver wool. NMR, gas-phase infrared, and solid-state Raman spectra of the perfluoro bisalkyl peroxides are presented and their chemical properties are discussed.

Synthesis of (+)-Darwinolide, a Biofilm-Penetrating Anti-MRSA Agent.

Darwinolide, a recently identified marine natural product from the Antarctic sponge Dendrilla membranosa, was previously shown to exhibit promising activity against the biofilm phase of methicillin-resistant Staphylococcus aureus. Its challenging tetracyclic rearranged spongian diterpenoid structure links a trimethylcyclohexyl subunit to a seven-membered core with two fused tetrahydrofuran units. Herein, we describe the first synthesis of (+)-darwinolide, which features a convergent aldol fragment coupling, an Ireland-Claisen rearrangement, and an organocatalytic desymmetrization as the key steps. Our results provide a foundation for the development of novel antibiofilm-specific antibiotics.

From Polyhalides to Polypseudohalides: Chemistry Based on Cyanogen Bromide.

Pseudohalogens are defined as molecular entities that resemble the halogens in their chemistry. While our understanding of polyhalogen chemistry has increased over the last years, research on polypseudohalogen compounds is lacking. The pseudohalogen BrCN possesses a highly pronounced σ-hole at the bromine side of the molecule, inducing strong halogen bonding. This allows the synthesis and characterization of new polypseudohalogen anions, as shown by the single-crystal X-ray diffraction of [PNP][Br(BrCN)] and [PNP][Br(BrCN)3 ]. Both the nearly linear anion [Br(BrCN)]- and the distorted pyramidal anion [Br(BrCN)3 ]- were characterized by Raman spectroscopy and quantum-chemical calculations. The behavior of the polypseudohalogen compounds in solution and as room-temperature ionic liquids (RT-ILs) using the [NBu4 ]+ cation was studied by 13 C and 15 N NMR spectroscopy. These types of ILs are capable of dissolving elemental gold and offer themselves as promising compounds in metal recycling.

A Very Strong Methylation Agent: [Me2 Cl][Al(OTeF5 )4 ].

A new chloronium-containing salt, [Me2 Cl][Al(OTeF5 )4 ], was synthesized on multigram scale by means of a simple one-pot procedure. The isolated product can be handled at room temperature and used as a strong electrophilic methylation agent. This is demonstrated by the methylation of the very weak bases P(CF3 )3 , PF3 , MeI, and MeBr.

No Fear of Perfluorinated Peroxides: Syntheses and Solid-State Structures of Surprisingly Inert Perfluoroalkyl Peroxides.

We report on the solid-state structures of bis(nonafluoro-tert-butyl) peroxide [(F3 C)3 CO]2 and bis(undecafluoro-2-methyl-2-butyl) peroxide [(C2 F5 )(F3 C)2 CO]2 . These peroxides were prepared from the corresponding hypofluorites and fluorinated silver wool. The solid-state structures obtained after in situ crystallisation show unusual COOC dihedral angles of 180°, as well as elongated O-O bonds because of the bulky perfluorinated alkyl groups. The perfluorinated alkyl peroxides are insensitive to both impact (>40 J) and friction (>360 N), and resistant towards mineral acids (HX; X=F, Cl, Br) and elemental halogens (X2 ). Ferrocene is oxidized by [(F3 C)3 CO]2 to [FeIII Cp2 ][OC(CF3 )3 ].

Further Development of Weakly Coordinating Cations: Fluorinated Bis(triarylphosphoranylidene)iminium Salts.

So far unknown bis(triarylphosphoranylidene)iminium cations [PPN]+ with one fluorine atom in para ([PPN-1F ]+ ), two in meta ([PPN-2F ]+ ), or three in para and meta positions of the phenyl rings ([PPN-3F ]+ ) were obtained by a newly developed one-pot reaction. These halogenated [PPN]+ cations were characterized by IR and Raman spectroscopy in comparison with quantum-chemical calculations, ESI+ mass spectrometry, NMR spectroscopy, and single-crystal X-ray diffraction. To assess their quality as weakly coordinating cations and the associated ability to stabilize labile anions, the electrostatic potential and fluoride-ion affinity were calculated and compared with those of the unsubstituted and so far unknown perfluorinated [PPN-5F ]+ cations.

Closing the Gap: Structural Evidence for the Missing Hexabromide Dianion [Br6 ]2.

The formation and experimental characterization of the first hexabromide dianion is presented. This dianion fills the last remaining gap in the series of polybromides from the tribromide [Br3 ]- to the undecabromide [Br11 ]- . The experimental results are compared to quantum-chemical calculations. These calculations predict-based on electrostatic interactions-a T-structure for the hexabromide dianion, while halogen-halogen bonding favors the hockey-stick-like structure experimentally found in the crystal structure. The hexabromide is built of two tribromide moieties, one of which is highly asymmetric. The classification of this unique anion as hexabromide dianion is discussed. The counter ion [C5 H10 N2 Br]+ stabilizes the hexabromide dianion by additional σ-hole interactions. The compound is fully characterized by mass spectrometry, NMR-, IR and single crystal Raman spectroscopies as well as single-crystal X-ray diffraction.

Synthesis and Characterization of Nonclassical Interhalides Based on Bromine Monochloride.

Due to a more distinct σ-hole, BrCl is able to form stronger halogen bonds than those in polyhalogen anions based on Cl2 and Br2 . This stabilization allows the crystallographic characterization of a variety of new polyinterhalides, in which chloride functions as the central ion as shown by the molecular structures of [AsPh4 ][Cl(BrCl)3 ] and [CCl(NMe2 )2 ][Cl(BrCl)5 ]. Furthermore, the solid-state structure of an octahedrally coordinated nonclassical interhalide is reported for the first time. The tridecainterhalide monoanion [Cl(BrCl)6 ]- consists of a central chloride ion, which is coordinated by six BrCl molecules in a slightly distorted octahedral structure. All new compounds were characterized by single-crystal X-ray diffraction (XRD), NMR and Raman spectroscopy, as well as quantum-chemical calculations.