“…Interestingly, the very broad absorption band of 1 2+ (range: 400 – 700 nm) arising from the charge transfer from the NHB ligand to the central pyridyl ring, stretches across the visible region. This is in contrast to dications derived from wholly carbon systems which are typically restricted to absorptions in the UV region 6 – 13 , and hints at potential applications of all three states of this organoboron redox system in visible light photoredox catalysis. Fig.…”
Section: Resultsmentioning
confidence: 82%
“…Organic molecules that can reversibly access three stable redox states have received considerable recent attention 5 – 14 , reflecting applications as super-electron donors 15 , photo-/electro-catalysts 16 , redox switches 17 , or in redox-flow batteries etc 18 . However, such systems are rarely isolated, due to the redox instability of the intervening radical species 13 . Thiele’s hydrocarbon, which can gain aromaticity upon successive one-electron oxidations, presents itself as a privileged platform for such applications.…”
Section: Introductionmentioning
confidence: 99%
“…Importantly, the diverse library of available carbenes also allows for modular tuning of the CPh 2 termini 32 . That said, recently reported analogues based on N-heterocyclic carbenes (NHCs) by Ghadwal et al, cyclic (alkyl)(amino)carbenes (CAACs) and acyclic diaminocarbenes (ADCs) by Jana et al are characterized either by two single-electron transfer events at potentials which are very close (Δ E < 0.25 V) 28 , 29 , or by a single two-electron redox wave 30 , 31 , alluding to the instability of the respective mixed-valence radical cations towards disproportionation 13 , 33 . As such, these systems are typically limited to only two stable redox states, viz.…”
Thiele’s hydrocarbon occupies a central role as an open-shell platform for new organic materials, however little is known about its redox behaviour. While recent synthetic approaches involving symmetrical carbene substitution of the CPh2 termini yield isolable neutral/dicationic analogues, the intervening radical cations are much more difficult to isolate, due to narrow compatible redox ranges (typically < 0.25 V). Here we show that a hybrid BN/carbene approach allows access to an unsymmetrical analogue of Thiele’s hydrocarbon 1, and that this strategy confers markedly enhanced stability on the radical cation. 1•+ is stable across an exceptionally wide redox range (> 1 V), permitting its isolation in crystalline form. Further single-electron oxidation affords borenium dication 12+, thereby establishing an organoboron redox system fully characterized in all three redox states. We perceive that this strategy can be extended to other transient organic radicals to widen their redox stability window and facilitate their isolation.
“…Interestingly, the very broad absorption band of 1 2+ (range: 400 – 700 nm) arising from the charge transfer from the NHB ligand to the central pyridyl ring, stretches across the visible region. This is in contrast to dications derived from wholly carbon systems which are typically restricted to absorptions in the UV region 6 – 13 , and hints at potential applications of all three states of this organoboron redox system in visible light photoredox catalysis. Fig.…”
Section: Resultsmentioning
confidence: 82%
“…Organic molecules that can reversibly access three stable redox states have received considerable recent attention 5 – 14 , reflecting applications as super-electron donors 15 , photo-/electro-catalysts 16 , redox switches 17 , or in redox-flow batteries etc 18 . However, such systems are rarely isolated, due to the redox instability of the intervening radical species 13 . Thiele’s hydrocarbon, which can gain aromaticity upon successive one-electron oxidations, presents itself as a privileged platform for such applications.…”
Section: Introductionmentioning
confidence: 99%
“…Importantly, the diverse library of available carbenes also allows for modular tuning of the CPh 2 termini 32 . That said, recently reported analogues based on N-heterocyclic carbenes (NHCs) by Ghadwal et al, cyclic (alkyl)(amino)carbenes (CAACs) and acyclic diaminocarbenes (ADCs) by Jana et al are characterized either by two single-electron transfer events at potentials which are very close (Δ E < 0.25 V) 28 , 29 , or by a single two-electron redox wave 30 , 31 , alluding to the instability of the respective mixed-valence radical cations towards disproportionation 13 , 33 . As such, these systems are typically limited to only two stable redox states, viz.…”
Thiele’s hydrocarbon occupies a central role as an open-shell platform for new organic materials, however little is known about its redox behaviour. While recent synthetic approaches involving symmetrical carbene substitution of the CPh2 termini yield isolable neutral/dicationic analogues, the intervening radical cations are much more difficult to isolate, due to narrow compatible redox ranges (typically < 0.25 V). Here we show that a hybrid BN/carbene approach allows access to an unsymmetrical analogue of Thiele’s hydrocarbon 1, and that this strategy confers markedly enhanced stability on the radical cation. 1•+ is stable across an exceptionally wide redox range (> 1 V), permitting its isolation in crystalline form. Further single-electron oxidation affords borenium dication 12+, thereby establishing an organoboron redox system fully characterized in all three redox states. We perceive that this strategy can be extended to other transient organic radicals to widen their redox stability window and facilitate their isolation.
“…The aforementioned redox-potentials also have similarities to tetrakis(dimethylamino)ethylene (TDAE) 22 as well as to certain electron-rich olefins derived from carbenes. 23 However, we believe that a better comparison of H 4 4 (BF 4 ) 4 is with TCNE ( E 1/2 (1.Red) = −0.23 V and E 1/2 (2.Red) = −0.95 V vs. HFc/HFc + in MeCN), 20 as the tetracationic compound reported here is expected to act as an electron acceptor like TCNE, and not as electron donors like TDAE or the electron-rich olefins. As expected, the tetrasilver( i ) complex 3 (BF 4 ) 4 is not very robust towards redox processes.…”
Unusual and unexpected chemical transformations often provide access to completely new types of functional molecules. We report here the synthesis of a methylene-bridged bis-triazolium salt designed as a precursor for...
“…1 This is arguably due to the presence of three stable redox states. [2][3][4] Thereby, the radical cations 5,6 show peculiar photo-chemical and conductive properties. [7][8][9][10] In their neutral, reduced redox state, they are of use as organic redox agents.…”
The dissociation mechanism of electron rich olefins into their parent carbenes has been a controversial topic since Wanzlick’s pioneering work. Herein, we present a combined synthetic and computational study on...
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