Reductive Degradation of nido‐1‐CB₈H₁₂ into Smaller‐Cage Carborane Systems via New Monocarbaboranes [arachno‐5‐CB₈H₁₃]⁻ and closo‐2‐CB₆H₈

Abstract

Treatment of the nido-1-CB8H12 (1) carborane with NaBH4 in THF at ambient temperature led to the isolation of the stable [arachno-5-CB8H13]- (2(-)), which was isolated as Na+[5-CB8H13]-.1.5 THF and PPh4 +[5-CB8H13]- in almost quantitative yield. Compound 2(-) underwent a boron-degradation reaction with concentrated hydrochloric acid to afford the arachno-4-CB7H13 (3) carborane in 70 % yield, whereas reaction between 2(-) and excess phenyl acetylene in refluxing THF gave the [closo-2-CB6H7]- (4-) in 66 % yield. Protonation of the Cs+4(-) salt with concentrated H2SO4 or CF3COOH in CH2Cl2 afforded a new, highly volatile 2-CB6H8 (4) carborane in 95 % yield, the deprotonation of which with Et3N in CH2Cl2 leads quantitatively to Et3NH+[2-CB6H7](-) (Et3NH+4(-)). Both compounds 4- and 4 can be deboronated through treatment with concentrated hydrochloric acid in CH2Cl2 to yield the carbahexaborane nido-2-CB5H9 (5) in 60 % yield. New compounds 2-, 3, and 4 were structurally characterised by the ab initio/GIAO/MP2/NMR method. The method gave superior results to those carried out using GIAO-HF when relating the calculated 11B NMR chemical shifts to experimental data.

Synthesis and Electrochemistry of Cyclopentadienyl Ferratricarbollides Substituted by Me and Ph Groups on the Cage Carbon Atoms

“…NMR spectroscopic and mass spectrometric instrumentation and techniques were essentially the same as those in other recent publications from our laboratories. [14] Electrochemical measurements were carried out with a computer-controlled multipurpose potentiostat µAUTOLAB III (Eco Chemie, Netherlands) at room temperature equipped with a standard Metrohm three-electrode cell with a rotating platinum disc electrode (AUTOLAB RDE, 3 mm diameter) as the working electrode, a platinum sheet auxiliary electrode and a saturated calomel reference electrode (SCE), which was separated from the analyzed solution by a salt bridge. The analyzed compounds were dissolved in dichloromethane (Fluka, absolute, declared H 2 O content Յ 0.005 %) to give a solution containing approximately 5 ϫ 10 -4  analyte and 0.1  Bu 4 N[PF 6 ] (Fluka, purissimum for electrochemistry) as the supporting electrolyte.…”

Boron

“…Subsequent deboronation, protonation, and the reaction of acetylene with [arachno-5-CB 8 H 13 ] À is described. 28 The reactions of the arachno-4,6-C 2 B 7 H 13 carborane with the secondary and primary amines, Me 2 NH Á BH 3 and t BuNH 2 Á BH 3 , in ionic liquid media has been shown to result in both boron-insertion into the cage at a position across the two cage-carbons and additional hydrogen-elimination via the reaction of an hydridic B-H with an N-H group to produce the 6-(RR 0 N)-nido-5,7-C 2 B 8 H 11 carboranes. Computational characterisations indicate that the aminenitrogen atoms form unique exopolyhedral dative BQN double bonds with a cage-boron.…”

“…122 Triple decker complexes have also been synthesised by the reaction of the unusual pentylene analogue, K 2 [MeC(BPh) 2 N 2 (BPh 2 )CMe] with [{Cp*RuCl} 4 ] to form (25), the molecular structure of which has been reported. 123 Fluoride abstraction from a BODIPY dye produces the well defined borenium ion which can be converted to a borenium hydride (26) via treatment with DIBAL-H. 124 In an elegant series of synthetic and computational experiments Liu and co-workers have synthesised and structurally characterised the 1,2-azaborine compounds (27)(28)(29)(30)(31), shown below, enabling a direct comparison of delocalised bonds in the ''pre-aromatic'' BN-heterocycles against the fully delocalized azaborine (31). 125 The structurally related B-N heterocycle 2-phenyl-1,2-azaboratabenzene has also been investigated as a potential transition metal ligand.…”

Synthese von 3‐DBU‐closo‐2‐CB6H6 und [3‐Cl‐closo‐2‐CB6H6]– – eine erste einfache Synthese für [CB6]‐closo‐Cluster

“…2008 wurde schließlich eine Synthese publiziert, in der eine Ausbeute von 66 % angegeben wird. Die Protonierung des genannten Anions durch konzentrierte H 2 SO 4 oder CF 3 COOH führt zu der ungeladenen Spezies 2‐CB 6 H 8 , welche jedoch äußerst flüchtig und luftempfindlich ist 7. Alle hier genannten Synthesen sind mehrstufig, verlaufen über nido ‐1‐CB 8 H 12 als Intermediat und gehen von Decaboran aus 7.…”

“…Die Protonierung des genannten Anions durch konzentrierte H 2 SO 4 oder CF 3 COOH führt zu der ungeladenen Spezies 2‐CB 6 H 8 , welche jedoch äußerst flüchtig und luftempfindlich ist 7. Alle hier genannten Synthesen sind mehrstufig, verlaufen über nido ‐1‐CB 8 H 12 als Intermediat und gehen von Decaboran aus 7. Ein Gemisch (2:3) aus [2‐Ph‐ closo ‐2‐CB 6 H 6 ] – 8 und [1‐Ph‐ closo ‐1‐CB 6 H 6 ] – 8 wurde ausgehend von [4‐Ph‐ arachno ‐4‐CB 8 H 13 ] 12 mit einer Gesamtausbeute von 82 % synthetisiert.…”