Aldiminium Cations as Countercations to Discrete Main Group Fluoroanions

The reactions of group 14 tetrafluorides (SiF4, GeF4, and SnF4) and group 15 pentafluorides (PF5, AsF5, and SbF5) with the CAAC-based trifluoride reagent [MeCAACH][F(HF)2] led to the isolation of salts containing discrete 5- or 6-coordinated fluoroanions. The syntheses of [MeCAACH][SiF5], [MeCAACH][GeF5], [MeCAACH][(THF)SnF5], and the structurally related [MeCAACH][(dioxane)SnF5], [MeCAACH][PF6], [MeCAACH][AsF6], and [MeCAACH][SbF6] are effective, selective and in high yield. All compounds were characterized by X-ray single-crystal structure analysis, NMR and Raman spectroscopy. It is worth noting that the synthesized [MeCAACH][GeF5] is a rare example of a structurally characterized compound with discrete [GeF5]- anion, while [MeCAACH][(THF)SnF5] and [MeCAACH][(dioxane)SnF5] represent the first compounds with discrete octahedrally coordinated tin fluoride anions with incorporated solvent molecules. Finally, the aldiminium-based cation [MeCAACH]+ proved to be suitable for the stabilization of rare discrete main group fluoride anions.

Heavy silylchalcogenido lanthanates synthesis Ph4P[Cp3La-ESiMe3] (E = S, Se, and Te) via fluoride-induced demethylation of dimethylcarbonate to Ph4P[OCO2Me] key intermediate

We report a new high-yield synthesis of so far not accessible tetraphenylphosphonium methylcarbonate Ph₄P[OCO₂Me] via solvothermal fluoride-induced demethylation and MeF elimination at Me₂CO₃ (DMC) by Ph₄P-F, structurally characterized as λ⁵-fluorophosphoran by XRD. The synthetic value of Ph₄P[OCO₂Me] key compound for preparing nearly all kinds of other Ph₄P[anion] salts with perfectly crystallizing (not symmetry frustrated) cation is demonstrated by examples beyond ionic liquid research: a complete set of silylchalcogenide salts Ph₄P[ESiMe₃] (E = S, Se, and Te) including the first example of a structurally characterized non-coordinating, naked [Te-SiMe₃]^- anion is presented. With this set of soft Lewis bases and metal organic Lewis acids [Cp₃La] at hand, a comprehensive series of crystalline 1 : 1 lanthanate complexes Ph₄P[Cp₃La-ESiMe₃] has been prepared. Their structural features and trends such as complexation induced Si-E bond elongation and a pronounced trend in La-E-Si bond angle contraction with E = S < Se < Te are discussed. Heteronuclear ¹H, ¹³C, ²⁹Si, and ¹³⁹La NMR studies provide a set of ¹³⁹La NMR shifts for homologs of heavy chalcogen-lanthanum complexes.

Phosphorus-Containing Superbases: Recent Progress in the Chemistry of Electron-Abundant Phosphines and Phosphazenes

The renaissance of Brønsted superbases is primarily based on their pronounced capacity for a large variety of chemical transformations under mild reaction conditions. Four major set screws are available for the selective tuning of the basicity: the nature of the basic center (N, P, …), the degree of electron donation by substituents to the central atom, the possibility of charge delocalization, and the energy gain by hydrogen bonding. Within the past decades, a plethora of neutral electron-rich phosphine and phosphazene bases have appeared in the literature. Their outstanding properties and advantages over inorganic or charged bases have now made them indispensable as auxiliary bases in deprotonation processes. Herein, an update of the chemistry of basic phosphines and phosphazenes is given. In addition, due to widespread interest, their use in catalysis or as ligands in coordination chemistry is highlighted.

Phosphangulene: A Molecule for All Chemists

Phosphangulene (1) is a hexacyclic triarylphosphine with a distinctive conical shape and other features that allow the compound to be viewed from diverse perspectives and to be embraced by chemists from different parts of the field as a molecule worthy of special attention. In recent work, phosphangulene and its derivatives have proven to be effective tools for probing general principles that govern molecular organization in solids. The phosphangulene family is particularly well-suited for these studies because systematic structural changes in the compounds are easy to introduce. In crystals of phosphangulene itself, molecules are stacked efficiently like hats, giving rise to an R3m structure that is polar and pyroelectric. Simple conversion of the compound into phosphangulene oxide (7a) or other chalcogenides blocks effective stacking and forces crystallization to produce alternative structures that have many suboptimal intermolecular interactions and vary little in energy as their geometries are altered. This leads to high levels of polymorphism, and phosphangulene oxide (7a) belongs to the elite set of compounds known to exist in five or more forms characterized by single-crystal X-ray diffraction. For similar reasons, phosphangulene chalcogenides form crystals with complex unit cells in which multiple inequivalent molecules are needed to optimize packing, and the compounds are also predisposed to form solvates and mixed crystals containing other molecules. For example, crystallization of a 1:1 mixture of phosphangulene and oxide 7a yielded needles composed of pure phosphangulene along with crystals of the oxide containing substantial amounts of phosphangulene. Phosphangulene has one known polymorph, and its crystallization rejects the oxide. In contrast, the oxide is highly polymorphic, and its crystallization is prone to errors in which molecules in the lattice are replaced by other compounds. Packing in crystals of the oxide appears to be so ineffective that the orientation and even the identity of the molecular components can be varied without imposing severe energetic penalties.Because substituted members of the phosphangulene family have awkward curved shapes that cannot be packed efficiently, they have emerged as highly effective partners for cocrystallizing fullerenes and for using concave-convex interactions to control how fullerenes can be organized in materials. This can be achieved without eliminating fullerene-fullerene contacts of the type needed to ensure conductivity. In addition, phosphangulene has created unlimited opportunities for making complex structures with large curved aromatic surfaces based on a new strategy in which the central atom of phosphorus is used to form covalent bonds with other elements or to introduce coordinative interactions with metals. In these ways, recent work has put phosphangulene in the spotlight as a compound of unusually broad interest and shown that it can appropriately be called a molecule for all chemists.

Temperature- and solvate-dependent disorder in the crystal structure of [PNP]+[HSO4]−

Metathesis reactions of [PNP]Cl ([PNP]+ ≡ bis(triphenyl-λ 5-phosphanylidene)ammonium) with Na2[SO4] or K[HSO4] in water yield [PNP]2[SO4] and [PNP][HSO4], respectively, as colorless solids. Reactions under basic conditions lead to a partial decomposition of the weakly coordinating [PNP]+ cation. N-Diphenylphosphine-triphenylphosphazene, triphenylphosphinimine, and benzene were identified as decomposition products by NMR spectroscopy. The compounds [PNP]2[SO4] and [PNP][HSO4] were characterized by multinuclear NMR and vibrational spectroscopy. [PNP][HSO4] could be crystallized from acetonitrile-diethyl ether giving single crystals with and without additional acetonitrile solvate molecules. The [HSO4]− anions form dimers in the solid state in both structures, which are held together by O–H⋯O hydrogen bonds. At T = 127 K the [HSO4]− anions in the crystal structure of solvate free [PNP][HSO4] are ordered, while at T = 300 K and in the structure containing additional acetonitrile solvate molecules a disorder of the [HSO4]− anions over two positions is observed, for the latter even at 150 K.

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-1^F ]⁺ ), two in meta ([PPN-2^F ]⁺ ), or three in para and meta positions of the phenyl rings ([PPN-3^F ]⁺ ) 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-5^F ]⁺ cations.

Theoretical and Synthetic Study on the Existence, Structures, and Bonding of the Halide-Bridged [B2X7](-) (X = F, Cl, Br, I) Anions

While hydrogen bridging is very common in boron chemistry, halogen bridging is rather rare. The simplest halogen-bridged boron compounds are the [B2X7](-) anions (X = F, Cl, Br, I), of which only [B2F7](-) has been reported to exist experimentally. In this paper a detailed theoretical and synthetic study on the [B2X7](-) anions is presented. The structures of [B2X7](-) anions have been calculated at the MP2/def2-TZVPP level of theory, and their local minima have been shown to be of C2 symmetry in all cases. The bonding situation varies significantly between the different anions. While in [B2F7](-) the bonding is mainly governed by electrostatics, the charge is almost equally distributed over all atoms in [B2I7](-) and additional weak iodine···iodine interactions are observed. This was shown by an atoms in molecules (AIM) analysis. The thermodynamic stability of the [B2X7](-) anions was estimated in all phases (gas, solution, and solid state) based on quantum-chemical calculations and estimations of the lattice enthalpies using a volume-based approach. In the gas phase the formation of [B2X7](-) anions from [BX4](-) and BX3 is favored in accord with the high Lewis acidity of the BX3 molecules. In solution and in the solid state only [B2F7](-) is stable against dissociation. The other three anions are borderline cases, which might be detectable under favorable conditions. However, experimental attempts to identify [B2X7](-) (X = Cl, Br, I) anions in solution by (11)B NMR spectroscopy and to prepare stable [PNP][B2X7] salts failed.

Bifunctional ligands in combination with phosphines and Lewis acidic phospheniums for the carbonylative Sonogashira reaction

Bifunctional ligands (L1–L4) in combination with Lewis acidic phosphenium(v) and phosphine have been developed for the carbonylative Sonogashira reaction.