Extended Quinolizinium-Fused Corannulene Derivatives: Synthesis and Properties

Abstract

Reported here is the design and synthesis of a novel class of extended quinolizinium-fused corannulene derivatives with curved geometry. These intriguing molecules were synthesized through a rationally designed synthetic strategy, utilizing double Skraup–Doebner–Von Miller quinoline synthesis and a rhodium-catalyzed C–H activation/annulation (CHAA) as the key steps. Single-crystal X-ray analysis revealed a bowl depth of 1.28–1.50 Å and a unique “windmill-like” shape packing of 12a(2PF 6 – ) due to the curvature and incorporation of two aminium ions. All of the newly reported curved salts exhibit green to orange fluorescence with enhanced quantum yields (Φf = 9–13%) and improved dispersibility compared to the pristine corannulene (Φf = 1%). The reduced optical energy gap and lower energy frontier orbital found by doping extended corannulene systems with nitrogen cations was investigated by UV–vis, fluorescence, and theoretical calculations. Electrochemical measurements reveal a greater electron-accepting behavior compared with that of their pyridine analogues. The successful synthesis, isolation, and evaluation of these curved salts provide a fresh perspective and opportunity for the design of cationic nitrogen-doped curved aromatic hydrocarbon-based materials.

C–H activation-enabled synthesis of a piperazine-embedded azadibenzo[a,g]corannulene analogue

“…), 20 have been established as valuable methods for synthesizing non-planar carbocycles, 21 heterocycles, 22 and various natural products. 23 Based on our continuous research interests in Pd-catalyzed C-H activation cyclization reactions, 17,18 and with precursor 7a ready, we initiated the screening of reaction conditions. Fortunately, the piperazine-embedded azadibenzo[a,g]corannulene analogue 5 was successfully obtained by the treatment of 7a with excess K 2 CO 3 , Pd(OAc) 2 , and PCy 3 HBF 4 in dry DMA under N 2 atmosphere at 130 °C for 24 hours, although with an unexpected by-product 17, as shown in Scheme 2. a Anhydrous solvents were used.…”

“…Our recent research interests in transition metal catalyzed C-H direct functionalization 17 have also been focusing on the construction of key C-C bond on curved aromatic systems via C-H activation strategies. 18 Herein, we report the design, synthesis, and X-ray crystallographic analysis of the first piperazine-embedded azadibenzo [a,g]corannulene analogue 5 in which two carbon atoms on the flank-spoke intersection of a corannulene skeleton have been replaced with nitrogen atoms. A 4-step bottom-up synthesis from commercially available compounds, including S N Ar substitution and a Pd-catalyzed intramolecular C-H activation arylation as key steps, is developed.…”