Synthesis and Properties of Spiro-double Sila[7]helicene: The LUMO Spiro-conjugation.

A double helicene with a spiro-Si linker (4) was synthesized by four successive nucleophilic substitutions on SiCl4 . Its (P,P), (M,M) and (P,M) isomers were isolated and characterized by single crystal X-ray analysis. Due to the central spirosilabi[fluorene] moiety, the two helicene units in 4 are symmetrically and nearly perpendicularly arranged. (P,P)-4 and (M,M)-4 exhibit unique optical properties attributable to the LUMO spiro-conjugation between the two sila[7]helicene units.

Stepwise Reduction of Azapentabenzocorannulene.

Mono- and dianions of 2-tert-butyl-3a2 -azapentabenzo[bc,ef,hi,kl,no]corannulene (1 a) were synthesized by chemical reduction with sodium and cesium metals, and crystallized as the corresponding salts in the presence of 18-crown-6 ether. X-ray diffraction analysis of the sodium salt, [{Na+ (18-crown-6)(THF)2 }3 {Na+ (18-crown-6)(THF)}(1 a2- )2 ], revealed the presence of a naked dianion. In contrast, controlled reaction of 1 a with Cs allowed the isolation of singly and doubly reduced forms of 1 a, both forming π-complexes with cesium ions in the solid state. In [{Cs+ (18-crown-6)}(1 a- )]⋅THF, asymmetric binding of the Cs+ ion to the concave surface of 1 a- is observed, whereas in [{Cs+ (18-crown-6)}2 (1 a2- )], two Cs+ ions bind to both the concave and convex surfaces of the dianion. The present study provides the first successful isolation and characterization of the reduced products of heteroatom-containing buckybowl molecules.

Functionalization of Azapentabenzocorannulenes by Fivefold C-H Borylation and Cross-Coupling Arylation: Application to Columnar Liquid-Crystalline Materials.

Herein, the one-shot fivefold functionalization of azapentabenzocorannulenes by an iridium-catalyzed fivefold C-H borylation reaction that exhibits excellent regioselectivity is reported. The borylated product can be used as a versatile synthetic intermediate for further derivatization via Suzuki-Miyaura cross-coupling reactions. This fivefold borylation/arylation sequence was employed to synthesize liquid-crystalline azapentabenzocorannulenes with five 3,4,5-trialkoxyphenyl groups, which assemble into 1D hexagonal columnar structures over a wide temperature range. The present method expands the variety and utility of azapentabenzocorannulenes as promising π-conjugated cores.

A Hybrid of Corannulene and Azacorannulene: Synthesis of a Highly Curved Nitrogen-Containing Buckybowl.

A highly curved nitrogen-containing buckybowl, which can be considered as a corannulene/azacorannulene hybrid, was synthesized and characterized. This molecule has a polycyclic aromatic C40 N core, corresponding to a partial azafullerene structure C80-x Nx (x=1,2,3…), and exhibits interesting properties that arise from its large and highly curved π surface and the embedded nitrogen atom, which include association with C60 , a lower LUMO level relative to azapentabenzocorannulene, and the formation of a radical cationic species upon oxidation.

The Key RuV=O Intermediate of Site-Isolated Mononuclear Water Oxidation Catalyst Detected by in Situ X-ray Absorption Spectroscopy.

Improvement of the oxygen evolution reaction (OER) is a challenging step toward the development of sustainable energy technologies. Enhancing the OER rate and efficiency relies on understanding the water oxidation mechanism, which entails the characterization of the reaction intermediates. Very active Ru-bda type (bda is 2,2'-bipyridine-6,6'-dicarboxylate) molecular OER catalysts are proposed to operate via a transient 7-coordinate RuV═O intermediate, which so far has never been detected due to its high reactivity. Here we prepare and characterize a well-defined supported Ru(bda) catalyst on porous indium tin oxide (ITO) electrode. Site isolation of the catalyst molecules on the electrode surface allows trapping of the key 7-coordinate RuV═O intermediate at potentials above 1.34 V vs NHE at pH 1, which is characterized by electron paramagnetic resonance and in situ X-ray absorption spectroscopies. The in situ extended X-ray absorption fine structure analysis shows a Ru═O bond distance of 1.75 ± 0.02 Å, consistent with computational results. Electrochemical studies and density functional theory calculations suggest that the water nucleophilic attack on the surface-bound RuV═O intermediate (O-O bond formation) is the rate limiting step for OER catalysis at low pH.

Synthesis of Pyrrole-Fused Corannulenes: 1,3-Dipolar Cycloaddition of Azomethine Ylides to Corannulene.

In the long history of corannulene chemistry, the 1,3-dipolar cycloaddition to corannulene is unprecedented. Reported herein is the 1,3-dipolar cycloaddition of a polycyclic aromatic azomethine ylide to corannulene, a reaction which occurs exclusively at the rim bond of corannulene, from the convex side in an exo fashion. The cycloadducts were successfully converted, by successive oxidative dehydrogenation, into pyrrole-fused corannulenes, which exhibited pronounced solvatofluorochromism.

Benzene-Fused Azacorannulene Bearing an Internal Nitrogen Atom.

A novel nitrogen-doped corannulene derivative, 8-tert-butyl-6b(2) -azapentabenzo[bc,ef,hi,kl,no]corannulene, was synthesized by 1,3-dipolar cycloaddition of a polycyclic aromatic azomethine ylide with a diarylethyne and subsequent palladium-catalyzed intramolecular cyclization. This molecule represents the first example of a corannulene derivative bearing an internal heteroatom, and exhibits unique structural and physical properties caused by the introduction of the nitrogen atom and extended π-conjugation, as compared to the parent corannulene.