Reactions of 13‐Vertex Carboranes with Strong Bases: Synthesis and Structural Characterization of Carborane Monoanions with exo‐π Bonding

Abstract

Several monoanions of 13-vertex carboranes were prepared in high yields from the reactions of C,C'-linked 13-vertex carboranes with tBuOK or NaH in dry THF at room temperature. These monoanions were characterized by various spectroscopic methods, elemental analysis, and single-crystal X-ray diffraction. The results showed substantial double-bond character between the cage-carbon atom and the exo vicinal carbon atom, thus leading to charge delocalization into the cage. As a result, the atom-atom distances within the cage were elongated, with one broken C-B bond. However, the cage geometry of the monoanions remained very similar to that of their corresponding neutral 13-vertex closo-carboranes. These monoanions represent the first examples of 13-vertex carboranes with exo-π bonding to hypercarbon atoms.

Reaction of N-heterocyclic carbenes with 13-vertex closo-carboranes: synthesis and structural characterization of zwitterionic salts of 13-vertex nido-carboranes

“…The 1 H NMR spectrum of 13 displayed a triplet of the unique exo α-CH at 5.82 ppm with J = 4.8 Hz, indicative of the α-CH being split by its neighboring methylene unit. Accordingly, the 13 9 Elemental analyses also confirmed the composition of 13.…”

“…We wondered whether such a salt is an intermediate for the formation of the final products 1-12. To this end, 11 9 it is suggested that the deprotonation of α-methylene in 13-vertex carboranes proceeds instantly after mixing with NHC to afford the imidazolium salt of carborane anion that is slowly converted to the final product 1.…”

“…2 A number of 13-and 14-vertex carboranes as well as their metal complexes have been prepared and structurally characterized. [3][4][5][6][7][8][9][10][11][12][13] They share some chemical properties with 12-vertex carboranes, and on the other hand they have their own unique features. For example, 13-vertex carborane 1,2-(CH 2 ) 3 -1,2-C 2 B 11 H 11 can undergo single-electron reduction to afford a stable carborane radical anion with [2n + 3] framework electrons, 14 which accepts additional electrons to give 13vertex nido-carborane dianions.…”

Synthesis and structural characterization of 14-vertex germa-, stanna-, and plumba-carboranes

“…15 It reacted with 1.5 equiv. of GeCl 2 •dioxane in refluxing THF for 3 days to give a single product according to the 11 16…”

“…[2][3][4][5][6] They have shown some interesting properties. [7][8][9][10][11][12] For example, they can be reduced by group 1 metals to form the corresponding nido-carborane dianions that are good π-ligands for d-block transition metals. Accordingly, several 14-and 15-vertex metallacarboranes of d-block transition metals have been synthesized using polyhedral expansion methodology.…”