Fusing N‐Heterocyclic Carbenes with Carborane Anions

Abstract

Here we describe the fusion of two families of unusual carbon-containing molecules that readily disregard the tendency of carbon to form four chemical bonds, namely Nheterocyclic carbenes (NHCs) and carborane anions. Deprotonation of an anionic imidazolium salt with lithium diisopropylamide at room temperature leads to a mixture of lithium complexes of C-2 and C-5 dianionic NHC constitutional isomers as well as a trianionic (C-2, C-5) adduct. Judicious choice of the base and reaction conditions allows the selective formation of all three stable polyanionic carbenes. In solution, the so-called abnormal C-5 NHC lithium complex slowly isomerizes to the normal C-2 NHC, and the process can be proton-catalyzed by the addition of the anionic imidazolium salt. These results indicate that the combination of two unusual forms of carbon atoms can lead to unexpected chemical behavior, and that this strategy paves the way for the development of a broad new generation of NHC ligands for catalysis.

Iridium-catalysed regioselective borylation of carboranes via direct B–H activation

“…Icosahedral carboranes are carbon–boron molecular clusters, sharing many features with benzene such as aromaticity, high thermal and chemical stability 1 2 . On the other hand, carboranes have their own unique characteristics such as spherical geometry and hydrophobic molecular surface 1 2 , which make them attractive building blocks for boron neutron capture therapy agents in medicine 3 4 5 6 , functional units in supramolecular design/materials 7 8 9 10 11 12 13 14 15 16 17 and versatile ligands in coordination/organometallic chemistry 18 19 20 21 22 23 . These research activities have drawn growing interests in the selective functionalization of carboranes 1 2 24 25 26 .…”

N‐Heterocyclic Carbenes with a Nido‐C2B9 Carborane Backbone

“…As for modifying the carbene ligands with carboranyl groups, Lavallo and co‐workers designed the carboranyl groups ( closo ‐CB 11 or nido ‐C 2 B 9 clusters) substituted imidazolium salts and obtained various NHCs by deprotonation using different bases [ 10 ] (Figure 2, I , II ). Willans's group tethered carborane and NHC in one ligand and got its versatile transition metal complexes [ 11 ] (Figure 2, III ).…”

Silver(I) Clusters Stabilized by the Carba‐closo‐dodecaboranylethynyl Ligand with O‐Donor Coligands and Template Ions

“…[7] More often, the {closo-1-CB 11 } cluster is bonded to a functional group that binds to the metal. Phosphanes, [9] nitriles, [10] N-heterocyclic carbenes, [11] and alkynes [12][13][14][15][16][17][18] with carba-closo-dodecaboranyl groups are recent examples for such derivatives.…”