Consequences of the One‐Electron Reduction and Photoexcitation of Unsymmetric Bis‐imidazolium Salts

Abstract

Coupling of uronium salts with in situ generated N-heterocyclic carbenes provides straightforward access to symmetrical [4](2+) and unsymmetrical bis-imidazolium salts [6](2+) and [9](2+) . As indicated by cyclic and square-wave voltammetry, [6](2+) and [9](2+) can be (irreversibly) reduced by one electron. The initially formed radicals [6](.+) and [9](.+) undergo further reactions, which were probed by EPR spectroscopy and density functional calculations. The final products of the two-electron reduction are the two carbenes. Upon irradiation with UV light both [6](2+) and [9](2+) emit at room temperature in solution but with dramatically different characteristics. The different fluorescence behavior is analyzed by emission spectroscopy and interpreted by using time-dependent density functional calculations as largely due to different excited-state dynamics of [6](2+) and [9](2+) . The geometries of both radicals [6](.+) and [9](.+) and excited states {[6](2+) }* and {[9](2+) }* are substantially different from those of the parent ground-state molecules.

Electron‐Deficient Imidazolium Substituted Cp Ligands and their Ru Complexes

“…Furthermore, we could remove the second so far unknown species 7 by extraction of the raw product 6 with dichloromethane. As it is known, di(imidazolium) salts can be formed under these conditions [25, 26] . We confirmed formation of 7 by independent synthesis and characterization (Supporting Information).…”

“…As it is known, di-(imidazolium) salts can be formed under these conditions. [25,26] Scheme3.Synthesis of the di(imidazolium)cyclopentadienylide 5 and H/D exchange of the Cp protons. We confirmed formation of 7 by independent synthesis and characterization (Supporting Information).…”

Aromaticity and sterics control whether a cationic olefin radical is resistant to disproportionation

“… 21,22 However, harnessing the exceptional electronic properties of NHC-derived electron-rich olefins for organic electronics remained challenging due to the undesired dissociation into the free carbenes (“Wanzlick's equilibrium”). 23–30 Whereas 8 is kinetically unstable towards dissociation, 31–33 10 stands in equilibrium with its monomers at room temperature. 34,35 …”

Crystal structure of 1,1',3,3'-tetraisopropyl-4,4',5,5'-tetramethyl-1H,1'H- [2,2'-biimidazole]-3,3'-diium difluoride tetrahydrate, C22H48F2N4O4

“…The F···H-O hydrogen bonds are near linear, and the F-O distances are short and reflect the very strong hydrogen bonds [F1···O1 = 224.4(9), 228.6(8)] [4][5][6]. The structure of the cation parallels that of the corresponding tetrafluoroborate salt reported by us a couple of years ago [7] (for a structural discussion see [8] and references cited therein). There are numerous structural reports on metal fluoride hydrates containing both coordinated water and fluoride ligands linked by hydrogen bonds, see e.g.…”