Fusing Dicarbollide Ions with N‐Heterocyclic Carbenes

Abstract

Discovered by Hawthorne in 1965, dicarbollide ions are an intriguing class of nido-carboranes that mimic the behavior of the cyclopentadienyl anion. Herein, we show that it is possible to directly link the dicarbollide ion to an N-heterocyclic carbene (NHC) to form an isolable N-dicarbollide-substituted NHC dianion. This molecule can be accessed by the sequential double deprotonation of a mono-nido-carboranyl imidazolium zwitterion. As revealed by a single-crystal X-ray diffraction study, the first deprotonation leads to a monoanionic dicarbollide ion that adopts a bis(dicarbollide) structure in the solid state. Subsequent deprotonation of this monoanion leads to the first N-dicarbollide NHC, which was fully characterized by multinuclear NMR spectroscopy as well as single-crystal X-ray diffraction.

1,3‐Bis(tricyanoborane)imidazoline‐2‐ylidenate Anion—A Ditopic Dianionic N‐Heterocyclic Carbene Ligand

“…[7, 8c, 9] In 2014, anionic carboranyl units were introduced as substituents at the imidazole nitrogen atoms, [10] for example in the dianion V (Figure 1). [10a] The concept of using anionic boron clusters as substituents at NHCs via C cluster À N bonds was extended to other boron cages such as {nido-7,8-C 2 B 9 }, [11] and recently, halogenated {closo-1-CB 11 } cages have been attached as well. [12] To the best of our knowledge, no other dianionic NHCs are known.…”

Exceptionally Long C−C Single Bonds in Diamino‐o‐carborane as Induced by Negative Hyperconjugation

“…Previous density‐functional theory (DFT) computations indicated that 1,2‐(NH 2 ) 2 ‐ o ‐carboranes could have strikingly long C−C bonds . However, there are relatively few known species with direct o ‐carboranyl C−N bonds and no experimental report on the synthesis of 1,2‐(NH 2 ) 2 ‐ o ‐carborane . Herein, structural evidence for exceptionally long C−C bonds in 1,2‐diamino‐substituted o ‐carborane systems are reported in which the C−C distances are controlled by negative hyperconjugation between the lone pairs at nitrogen atoms (LP N ) and the antibonding orbitals of the C−C bond (σ* C−C ).…”

Expansion of the (BB)Ru metallacycle with coinage metal cations: formation of B–M–Ru–B (M = Cu, Ag, Au) dimetalacyclodiboryls

“… 35 – 37 Unusual electronic and steric properties of carboranes clusters led to their use in ligand design, catalysis, electrochemistry, polymer science, and photophysics. 38 – 53 …”