Generation of triplet carbenes by oxidation of an allene compound

Carbodicarbenes and Striking Redox Transitions of their Conjugate Acids: Influence of NHC versus CAAC as Donor Substituents

Herein, a new type of carbodicarbene (CDC) comprising two different classes of carbenes is reported; NHC and CAAC as donor substituents and compare the molecular structure and coordination to Au(I)Cl to those of NHC-only and CAAC-only analogues. The conjugate acids of these three CDCs exhibit notable redox properties. Their reactions with [NO][SbF₆ ] were investigated. The reduction of the conjugate acid of CAAC-only based CDC with KC₈ results in the formation of hydrogen abstracted/eliminated products, which proceed through a neutral radical intermediate, detected by EPR spectroscopy. In contrast, the reduction of conjugate acids of NHC-only and NHC/CAAC based CDCs led to intermolecular reductive (reversible) carbon-carbon sigma bond formation. The resulting relatively elongated carbon-carbon sigma bonds were found to be readily oxidized. They were, thus, demonstrated to be potent reducing agents, underlining their potential utility as organic electron donors and n-dopants in organic semiconductor molecules.

Tuning effects for some cyclic aromatic carbenes bearing remote amino groups

Yamamoto and co-workers synthesized two cyclic aromatic carbenes with remote amino groups. Here we theoretically studied related compounds to explore tuning effects on the singlet-triplet splitting by variations of functional groups. For the Yamamoto compound, the lowest singlet state lies 15.7 kcal/mol below the lowest triplet. The singlet-triplet separation is reduced by ∼7 kcal/mol when the dimethylamino groups are replaced by H. In one set of carbenes, when X = O, we substitute S, Se, Te, SO, SeO, and TeO for X; the resulting ΔE(S-T) predictions are 9.9, 7.3, 3.9, 4.3, 2.3, and -0.1 kcal/mol, respectively. A different set of X fragments yields triplet electronic ground states with ΔE(S-T) values of -8.6 (X = BH), -6.8 (X = AlH), -7.2 (X = GaH), -7.5 (X = InH), and -7.0 kcal/mol (X = TlH). We also predicted ΔE(S-T) with N(CH3)2 replaced by PH2, AsH2, SbH2, BiH2, BH2, CH3, OH, and F. Of all the molecules considered, that with N(CH3)2 replaced with BH2 and X = BH most favors the triplet state, lying 13.7 kcal/mol below the singlet. Finally, we have relocated the N(CH3)2 and NH2 groups from the (3, 6) positions to the (4, 5), (2, 7), and (1, 8) terminal ring positions, with very interesting results.