A σ‐Donor with a Planar Six‐π‐Electron B₂N₂C₂ Framework: Anionic N‐Heterocyclic Carbene or Heterocyclic Terphenyl Anion?

Abstract

NB! The anionic ligand 2 was synthesized through deprotonation of a planar, formally zwitterionic diazadiborine precursor, isolated as a lithium salt, and structurally characterized. According to experimental evidence and theoretical calculations, 2 can be considered as an intermediate between two classical classes of ligands: N‐heterocyclic carbenes 1 and terphenyls 3.

Heterocarbenoids of germanium and tin and their polyhedral oxidation products: The case for thermodynamic product control in Group 14 chalcogenides

“…Although these molecules were first reported in the 1960s [5][6][7], they have only recently become the focus of intense research interests because of their outstanding ligand properties [8][9][10][11]. Thus, heterocarbenes are successful ligands in a wide range of catalytic reactions, such as Heck and Suzuki couplings [12][13][14], olefin metathesis [15][16][17][18], and C-H bond activation [19], to name a few.…”

Synthesis and Reactivity of Cationic Triruthenium Clusters Derived from 2‐Methyl‐ and 4‐Methylpyrimidines: From Conventional Cyclometalated Ligands to Novel Types of N‐Heterocyclic Carbenes

“…Concerning pyrimidylidenes, it should be noted that metal complexes with NHCs formally arising from monodeprotonation at the C 2 carbon atom of N 1 ,N 3 ‐dialkylated pyrimidines remain unknown, although a theoretical work has suggested their feasibility,11 and, apart from the palladium(II) complexes mentioned in the above paragraph8, 10 and the cluster complexes depicted in Scheme ,7 only a few other unsaturated NHCs related to pyrimidylidenes have been reported, namely, a diazadiborine NHC ligand described by Roesler and coworkers,12 and some NHCs based on a pyrimidine‐4,6‐dione core reported by the Lavigne et al 1314…”

N‐Heterocyclic Carbenes with Neutral Tethers

“…The result is a zwitterionic six -membered betaine that can be deprotonated to an anionic NHC ligand and coordinated to transition metals (see Figure 3. The concept was previously applied to N, P and S ligands [ 231 , 232 ] and has a carbene precursor in Roesler ' s backbone boron substituted NHC ligands [ 233 ]; the latter has not been coordinated to transition metals yet. The concept was previously applied to N, P and S ligands [ 231 , 232 ] and has a carbene precursor in Roesler ' s backbone boron substituted NHC ligands [ 233 ]; the latter has not been coordinated to transition metals yet.…”