ausblenden:
Schlagwörter:
Carbanions; Carbenes; Multiple Redox-States; N-Heterocycle; Radicals
Zusammenfassung:
Herein, the first stable anions K[SIPrBp] (4 a-K) and K[IPrBp] (4 b-K) (SIPrBp=BpC{N(Dipp)CH2}2, IPrBp=BpC{N(Dipp)CH}2; Bp=4-PhC6H4; Dipp=2,6-iPr2C6H3) derived from classical N-heterocyclic carbenes (NHCs) (i.e. SIPr and IPr) have been isolated as violet crystalline solids. 4 a-K and 4 b-K are prepared by KC8 reduction of the neutral radicals [SIPrBp] (3 a) and [IPrBp] (3 b), respectively. The radicals 3 a and 3 b as well as [Me-IPrBp] 3 c (Me-IPrBp=BpC{N(Dipp)CMe}2) are accessible as crystalline solids on treatment of the respective 1,3-imidazoli(ni)um bromides (SIPrBp)Br (2 a), (IPrBp)Br (2 b), and (Me−IPrBp)Br (2 c) with KC8. The cyclic voltammograms of 2 a–2 c exhibit two one-electron reversible redox processes in −0.5 to −2.5 V region that correspond to the radicals 3 a–3 c and the anions (4 a–4 c)−. Computational calculations suggest a closed-shell singlet ground state for (4 a–4 c)− with the singlet-triplet energy gap of 17–24 kcal mol−1.
