Insights into Ruthenium(II/IV)-Catalyzed Distal C-H Oxygenation by Weak Coordination.

C-H hydroxylation of aryl acetamides and alkyl phenylacetyl esters was accomplished via challenging distal weak O-coordination by versatile ruthenium(II/IV) catalysis. The ruthenium(II)-catalyzed C-H oxygenation of aryl acetamides proceeded through C-H activation, ruthenium(II/IV) oxidation and reductive elimination, thus providing step-economical access to valuable phenols. The p-cymene-ruthenium(II/IV) manifold was established by detailed experimental and DFT-computational studies.

Aromatic Nanosandwich Obtained by σ-Dimerization of a Nanographenoid π-Radical.

A 139-π-electron nanographenoid radical was obtained by expanding the periphery of a naphthalimide-azacoronene hybrid with a methine bridge. The radical was isolated in the form of its σ-dimer, which was shown to possess a conformationally restricted two-layer structure both in the solid state and in solution. The dimer is cleaved into its parent radicals when exposed to ultraviolet or visible radiation in toluene solutions but is resistant to thermally induced dissociation. Under inert conditions, the radicals recombine quantitatively into the σ-dimer with observable kinetics, but they are oxidized into a ketone derivative in the presence of atmospheric oxygen. Combined structural, spectroscopic, and theoretical evidence shows that the σ-dimer contains a weak C(sp3)-C(sp3) bond, but is stabilized against thermal dissociation by a very strong dispersive interaction between the overlapping π surfaces.

π-Extended Polyaromatic Hydrocarbons by Sustainable Alkyne Annulations through Double C-H/N-H Activation.

The widespread applications of substituted diketopyrrolopyrroles (DPPs) call for the development of efficient methods for their modular assembly. Herein, we present a π-expansion strategy for polyaromatic hydrocarbons (PAHs) by C-H activation in a sustainable fashion. Thus, twofold C-H/N-H activations were accomplished by versatile ruthenium(II)carboxylate catalysis, providing step-economical access to diversely decorated fluorogenic DPPs that was merged with late-stage palladium-catalyzed C-H arylation on the thus-assembled DPP motif.

Cobalt-Catalyzed Hiyama-Type C-H Activation with Arylsiloxanes: Versatile Access to Highly ortho-Decorated Biaryls.

Versatile direct Hiyama-type C-H arylations of benzamides were accomplished with organosiloxanes by chelation-assisted cobalt catalysis. The C-H arylation featured broad substrate scope, including challenging C(sp3 )-H activation, the use of γ-valerolactone as biomass-derived solvent, and selectively provided the desired biaryls, even when being highly sterically hindered.

Heterocyclic Nanographenes and Other Polycyclic Heteroaromatic Compounds: Synthetic Routes, Properties, and Applications.

Two-dimensionally extended, polycyclic heteroaromatic molecules (heterocyclic nanographenes) are a highly versatile class of organic materials, applicable as functional chromophores and organic semiconductors. In this Review, we discuss the rich chemistry of large heteroaromatics, focusing on their synthesis, electronic properties, and applications in materials science. This Review summarizes the historical development and current state of the art in this rapidly expanding field of research, which has become one of the key exploration areas of modern heterocyclic chemistry.

Synthesis of a peripherally conjugated 5-6-7 nanographene.

A heteroaromatic nanographene containing a unique assembly of five-, six- and seven-membered rings is synthesized using oxidative coupling of an indole-containing precursor. Near-infrared absorption and emission properties of the nanographene core are enhanced by peripheral expansion and ring fusion at all oxidation levels. The dicationic state shows distinct aromaticity originating from a peripheral π-conjugated circuit. A partially coupled intermediate, trapped in the synthesis of the 5-6-7 nanographene, is explored as a reference system, showing an unexpected reduction of the optical band gap due to intramolecular charge transfer.

Expanded hexapyrrolohexaazacoronenes. Near-infrared absorbing chromophores with interrupted peripheral conjugation.

A family of azacoronenes containing up to two saturated bridges at the periphery was synthesized from substituted hexapyrrolylbenzenes using a two-step condensation-aromatization procedure. The introduction of peripheral bridges provides access to nonplanar, sterically crowded systems that display complex reactivity patterns, involving stereospecific aromatization of bridges and nucleophile additions. Despite the interrupted conjugation on the periphery, the new azacoronenes have easily accessible higher oxidation levels, and a quadruply charged species was chemically generated by reaction with SbCl5. These oxidized species show extensive π-electron conjugation and are efficient UV-vis-NIR absorbers, active up to ca. 2400 nm. Interruption of peripheral conjugation is shown to induce a tendency toward biradicaloid electron configurations in doubly oxidized species.

Synthesis of bis(phenanthropyrroles) via a tandem Scholl oxidation.

An electron-rich 3,4-diarylpyrrole is shown to undergo a tandem inter- and intramolecular Scholl oxidation, providing access to bis(phenanthropyrroles), a new class of bipyrrole derivatives with extended π conjugation. Intermolecular coupling of two pyrrole molecues is found to be the initial step of this reaction. Bis(phenanthropyrroles) are characterized by restricted rotation around the α-α bond and exhibit strong blue fluorescence and large Stokes shifts.