Carbon Extrusion/Cluster Contraction: Synthesis of the Fluorinated Cyano‐closo‐Undecaborate K₂[3‐NC‐closo‐B₁₁F₁₀]

Abstract

Releasing carbon: Deprotonation of the amino group of the [1‐H2N‐closo‐CB11F11]− anion results in a transformation of the carba‐closo‐dodecaborate cluster into a closo‐undecaborate dianion. The rearrangement is accompanied by loss of a fluoride anion, and the CN fragment is converted into a cyano ligand (see scheme).

Stepwise Introduction of Cyano Groups into nido‐ and closo‐Undecaborate Clusters

“…The B−B distances of [2‐NC‐ closo ‐B 11 H 10 ] 2− are close to those of the parent dianion [ closo ‐B 11 H 11 ] 2− ( 1 ) . Larger differences are found for d (B−B) of [2‐NC‐ closo ‐B 11 F 10 ] 2− , especially for B1–B4/B5/B6/B7, which are much longer for the fluorinated dianion (Table ).…”

“…[f] C s symmetry. [g] K + salt . [h] [Et 4 N] + salt; the dianions [2,3‐(NC) 2 ‐ closo ‐B 11 H 9 ] 2− and [2,6‐(NC) 2 ‐ closo ‐B 11 H 9 ] 2− are disordered.…”

“…Important reactions of the [ closo ‐B 11 H 11 ] 2− anion are halogenations to give [ closo ‐B 11 Hal 11 ] 2− (Hal=Cl, Br, I) . Only a few { closo ‐B 11 } clusters with a functional group attached to the B atoms have been reported so far, for example, [4‐Me 2 S‐ closo ‐B 11 H 10 ] − [30] and [3‐NC‐ closo ‐B 11 F 10 ] 2− …”

Reaction of 13‐Vertex Carboranes with Nucleophiles: Unprecedented Cage‐Carbon Extrusion and Formation of Monocarba‐closo‐dodecaborate Anions

“…However, the resonance of B2 in 3 overlaps with other cage B peaks, and is hardly resolved. [13] The other is the conversion of [7-R-m-(9,10-HR'C)-7-nido-CB 10 H 11 ] À to [1-R-6-CH 2 R'-1-closo-CB 9 H 8 ] À , in which cage-carbon extrusion is suggested to proceed after removal of one BH vertex. The 31 P NMR spectrum of 3 exhibits one sharp peak at d = 32.7 ppm, supportive of a tertiary phosphonium salt.…”

“…[10] Single-crystal X-ray analyses confirm the molecular structures of 2, 3, and 5, as shown in Figures 1-3, respectively. [16,17] Although the reasons are not yet clear, comparison of the 13 that of 84 ppm in the corresponding 12-vertex carborane 1,2-(CH 2 ) 3 -1,2-C 2 B 10 H 10 offers some insight into the charge density of the cage carbon atoms. [12] Cage-carbon extrusion from carborane clusters is very rare but not unknown.…”