C₄ Cumulene and the Corresponding Air‐Stable Radical Cation and Dication

Abstract

A neutral C 4 cumulene 1 that includes a cyclic alkyl(amino) carbene (cAAC), its air-stable radical cation 1C + , and dication 1 2+ have been synthesized. The redox property of 1C + was studied by cyclic voltammetry. EPR and theoretical calculations show that the unpaired electron in 1C + is mainly delocalized over the central C 4 backbone. The commercially available CBr 4 is utilized as a source of dicarbon in the cumulene synthesis.

How to Bend a Cumulene

“…These ligands are stronger π acceptors than NHCs . Moreover, the syntheses of [3]cumulenes with CAACs as terminal groups have been successful, contrary to NHCs . The PESs of CAAC [2 n ]cumulenes are also shallower than those of the odd cumulenes, but the two sets are more similar than in the case of the NHC cumulenes (Figure b).…”

“…For example, they can be used as molecular wires as their conductivity is significantly better than the other possible form of linear carbon chains, polyynes . Strong σ donors as end‐capping groups of the cumulene chain give their radical species a remarkable stability, with some of these radicals stable even to air . Cumulenes have been known for around 100 years, however, [3]cumulenes that have strong σ donors as terminal groups, such as N‐heterocyclic or cyclic (alkyl)(amino) carbenes (NHCs or CAACs, respectively), have only recently been studied .…”

“…Strong σ donors as end‐capping groups of the cumulene chain give their radical species a remarkable stability, with some of these radicals stable even to air . Cumulenes have been known for around 100 years, however, [3]cumulenes that have strong σ donors as terminal groups, such as N‐heterocyclic or cyclic (alkyl)(amino) carbenes (NHCs or CAACs, respectively), have only recently been studied . As discussed above, these types of terminal groups significantly change the properties of the carbon chain with respect to the classical [3]cumulenes and allenes.…”

Diborabutatriene: An Electron‐Deficient Cumulene

“…[15] While the CAAC ligands in this neutral compound are expectedly co-planar, when twice-oxidized to a dication (3 2+ ), which is isoelectronic with 2, the ligands remain essentially eclipsed rather than adopting a staggered conformation. [15] While the CAAC ligands in this neutral compound are expectedly co-planar, when twice-oxidized to a dication (3 2+ ), which is isoelectronic with 2, the ligands remain essentially eclipsed rather than adopting a staggered conformation.…”

Diborabutatrien: ein elektronenarmes Cumulen

“…4.07 ) ist die sterische Abstoßung in 2 geringer. [15] Das UV/Vis-Spektrum von 2 zeigt eine intensive Bande bei 382 nm (Abbildung 3). Eine zeitabhängige (TD-)DFTAnalyse sagt ein solches Spektrum als Überlagerung von drei Übergängen bei l = 353, 366 und 380 nm voraus.…”