α,α′-Diamino-p-quinodimethanes with Three Stable Oxidation States

Abstract

Herein, we report the rational design, synthesis, and characterization of α,α′-diamino-substituted-p-quinodimethanes, which are a group of partially substituted p-quinodimethanes. These exhibit two reversible one-electron redox steps and electrochromism in the ultraviolet, visible, and near-infrared regions. We were able to isolate the crystalline compounds of all three oxidation states: neutral, radical cation, and dication. The obtained results not only create the bridge between p-quinodimethane and α,α,α′,α′-tetrasubstituted-p-quinodimethane, but also demonstrate the straightforward modular approach for the synthesis of π-conjugated open-shell compounds.

A crystalline radical cation derived from Thiele’s hydrocarbon with redox range beyond 1 V

“…1 ) 28 – 31 but also other related structurally characterized radicals (Δ E = 0.20 − 0.59 V; Fig. 3b ) 10 , 12 , 34 , 38 , 39 , hinting at a pronounced degree of radical stability conferred by BN-substitution. Notably, 1 • + can also be viewed as a hybrid of the boryl-C 6 H 4 -carbene radical (Δ E = 0.20 V) 39 reported by Jana et al and the pyridyl-carbene radical cation (Δ E = 0.59 V) 12 reported by Hansmann et al — both of which exhibit much narrower redox ranges independently.…”

“…the neutral and dicationic forms. Most recently, Jana et al pushed this strategy further, reporting that symmetrical CH(NDippMe) disubstitution accesses a more stable radical cation with a redox range extended to 0.48 V 34 .…”

α,α′-Diamino-p-tetrafluoroquinodimethane: Stability of One- and Two-Electron Oxidized Species and Fixation of Molecular Oxygen

“…The C1−N1 bond length in 5 is 1.368(2) Å, which is shorter than that of its corresponding nonfluorinated analogue 5-H [1.376(2) Å]. 10 The C1−C2 bond length of 5 is 1.377(2) Å, which is longer than that of 5-H [1.366(2) Å] but shorter than that of Thiele's hydrocarbon [1.381(3) Å] 16 and CAAC-based Thiele's hydrocarbon [1.381(2) Å]. 8a The bond length alternation (BLA) of the central benzene ring of 5 is 0.099 Å, which is almost similar to those of 5-H (0.107 Å) and Thiele's hydrocarbon (0.103 Å) (Table 1).…”

“…This can be attributed to the presence of the F substituents in 5 that provide a steric hindrance and render the H–C–N and central–C 6 F 4 planes non-co-planar. The C1–N1 bond length in 5 is 1.368(2) Å, which is shorter than that of its corresponding nonfluorinated analogue 5-H [1.376(2) Å] . The C1–C2 bond length of 5 is 1.377(2) Å, which is longer than that of 5-H [1.366(2) Å] but shorter than that of Thiele’s hydrocarbon [1.381(3) Å] and CAAC-based Thiele’s hydrocarbon [1.381(2) Å] .…”

“…9 Very recently, we have reported α,α′-diamino-pquinodimethanes IV (Scheme 1) with three isolable oxidation states: neutral, radical cation, and dication. 10 Compound IV can be considered as a formally monosubstituted carbene 11 end-group-based p-quinodimethane derivative.…”