Phosphoniumsalze mit Hydrogendihalogenidanionen HCl2−, HBr2− Hl2− oder HBrCl−

Phosphonium Salts with Hydrogen Dihalide Anions HCl₂^?, HBr₂^?, HI₂^?, or HBrCl^? Phosphonium hydrogen dihalides [R₃PR′][XHY] (X = Y = Cl, Br, I; X = Br, Y = Cl) resp. [R₃PH]HBr₂ are obtained as extremely hydrolyzable crystals by reaction of phosphonium halides or tertiary phosphanes with hydrogen halide. According to IR spectroscopic results the solid compounds mostly contain anions [XHX]^? with symmetric hydrogen bonds. In solution ¹H NMR measurements show a slight (X = Cl, Br) or considerable (X = I) dissociation according to HX₂^? ? X^? + HX. On heating the solid compounds decompose with formation of hydrogen halide and [R₃PR′]X or [R₃PH]X. In this process the hydrogen bromidechlorides [R₃PR′][BrHCl] exclusively eliminate HCl. NMR studies (¹H und ³¹P) with solutions containing [R₃PH]HBr₂ (R = phenyl, 1-naphtyl) or HBr and Ph₃P in varying molar ratios show that a fast proton exchange between the competing Lewis bases R₃P and Br^? exists.     

Retention of the Zn−Zn bond in [Ge9Zn−ZnGe9]6− and Formation of [(Ge9Zn)−(Ge9)−(ZnGe9)]8− and Polymeric [−(Ge9Zn)2−−]

Reactions of Zn^I₂L₂ (where L=[HC(PPh₂NPh)]⁻) with solutions of the Zintl phase K₄Ge₉ in liquid ammonia lead to retention of the Zn−Zn bond and formation of the anion [(η⁴‐Ge₉)Zn−Zn(η⁴‐Ge₉)]⁶⁻, representing the first complex with a Zn−Zn unit carrying two cluster entities. The trimeric anion [(η⁴‐Ge₉)Zn{μ₂(η¹:η¹Ge₉)}Zn(η⁴‐Ge₉)]⁸⁻ forms as a side product, indicating that oxidation reactions also take place. The reaction of Zn₂Cp*₂ (Cp*=1,2,3,4,5‐pentamethylcyclopentadienyl) with K₄Ge₉ in ethylenediamine yielded the linear polymeric unit {[Zn[μ₂(η⁴:η¹Ge₉)]}²⁻ with the first head‐to‐tail arrangement of ten‐atom closo ‐clusters. All anions were obtained and structurally characterized as [A (2.2.2‐crypt)]⁺ salts (A =K, Rb). Copious computational analyses at a DFT‐PBE0/def2‐TZVPP/PCM level of theory confirm the experimental structures and support the stability of the two hypothetical ten vertex cluster fragments closo ‐[Ge₉Zn]²⁻ and (paramagnetic) [Ge₉Zn]³⁻.     

Negative-ion-negative-ion neutralization-reionization (−NR−)

There are four neutralization-reionization processes which can be studied. In the first two, gaseous cations are collisionally reduced and the resulting fast neutrals are either oxidized by collisional electron removal (NR) or reduced further by collisional electron attachment (NR^?). In the third and fourth processes, gaseous anions are collisionally oxidized and the resulting fast neutrals are either oxidized further by collisional electron removal (^?NR) or reduced by collisional electron attachment (^?NR^?). These four processes are illustrated briefly using the interrelated species [SF₅]⁺ and [SF₅]^?. Negative-ion-negative-ion neutralization-reionization (^?NR^?) processes are illustrated for [CH₃O]^?, [C₂H₅O]^?, [CO₃]^? and [HCO₃]^? and compared with ^?NR processes. In addition, collisional electron attachment ionization of fast neutrals formed in unimolecular fragmentation of cations is illustrated. The ^?NR^? studies of [CO₃]^? and [HCO₃]^? show that both CO₃ and HCO₃ are stable neutral species with lifetimes greater than 0.7 μs.     

Concise Syntheses of bis‐Strychnos Alkaloids (−)‐Sungucine, (−)‐Isosungucine,and (−)‐Strychnogucine B from (−)‐Strychnine

The first chemical syntheses of complex, bis‐Strychnos alkaloids (?)‐sungucine ( 1 ), (?)‐isosungucine ( 2 ), and (?)‐strychnogucine B ( 3 ) from (?)‐strychnine ( 4 ) is reported. Key steps included (1) the Polonovski–Potier activation of strychnine N‐oxide; (2) a biomimetic Mannich coupling to forge the signature C23?C5′ bond that joins two monoterpene indole monomers; and (3) a sequential HBr/NaBH₃CN‐mediated reduction to fashion the ethylidene moieties in 1 – 3 . DFT calculations were employed to rationalize the regiochemical course of reactions involving strychnine congeners.     

Total Syntheses of (−)‐Conidiogenone B, (−)‐Conidiogenone,and (−)‐Conidiogenol

Cyclopianes are novel diterpenes featuring a highly strained 6/5/5/5 tetracyclic core embedded with 6–8 consecutive stereocenters. The concise total syntheses of (?)‐conidiogenone B, (?)‐conidiogenone, and (?)‐conidiogenol have been accomplished in 14–17 steps. The present work features a HAT‐mediated alkene–nitrile cyclization to access the cis‐biquinane, a Nicholas/Pauson–Khand reaction to construct the linear triquinane, and a Danheiser annulation to afford the congested angular triquinane skeleton.     

Total Syntheses of (−)‐Isoschizogamine and (−)‐2‐Hydroxyisoschizogamine

Total syntheses of (?)‐isoschizogamine and (?)‐2‐hydroxyisoschizogamine are described. The synthesis employs two asymmetric Michael additions to establish chiral centers at C7 and the quaternary carbon C20. Regioselective reduction of the methylthioiminium cation rather than the enamine generates an isoschizogamine‐type pentacyclic skeleton. Acidic hydrolysis of the isoschizogamine‐type intermediate in the absence of oxygen provides natural (?)‐isoschizogamine. Conducting the reaction in the presence of oxygen leads to a multistep oxidative hydrolysis cascade that affords unnatural (?)‐2‐hydroxyisoschizogamine.     

(PhTe)3−: The Anionic Tellurium Analogue of I3−

The missing link between solid-state tellurium chemistry and polyhalide ions is provided by the synthesis of the almost linear (PhTe)₃⁻ ion, whose structure is shown. Tritelluride units are a recurring motif in the solid state and are related to the structures of polyhalides.