Summary Mononuclear metal-peroxo species are invoked as the key intermediates in metalloenzymatic or synthetic catalysis. However, either transience or sluggishness reactivity of synthetic analogs of metal-peroxo species impedes our understanding of oxygen activation mechanism. Herein, we designed and characterized a dioxygen-derived mononuclear osmium-peroxo complex, in which the peroxo ligand is stabilized by internally aromatic metallacycle. We demonstrate that the osmium-peroxo species shows catalytic activity toward promoterless alcohol dehydrogenations. Furthermore, computational studies provide a new mechanism for the osmium-peroxo-mediated alcohol oxidation, starting with the concerted double-hydrogen transfer and followed by the generation of osmium-oxo species. Interestingly, the internally aromatic metallacycle also plays a vital role in catalysis, which mediates the hydrogen transfer from osmium center to the distal oxygen atom of Os–OOH moiety, thus facilitating the Os–OOH→Os=O conversion. We expect that these insights will advance the development of aromatic metallacycle toward aerobic oxidation catalysis.

Metalla-chalcogenirenium | Density functional calculations | Metallacycles | P-block cations | AromaticityChalcogenirenium cations, featuring an unsaturated three-membered organic ring, are limited but known to be synthesizable from alkynes with bulky electron-donating groups. Metalla-chalcogenirenium compounds have been synthesized as stable compounds through the reactions of a cyclic metal-carbyne complex-metallapentalyne with PhSCl, PhSeCl or PhTeCl. As a result of the high strain in the three-membered metallacycles, the metalla-chalcogenirenium cations react readily with the base or chloride ions. These reactions furnish a series of unprecedented chalcogenirenium cations with intact M=C bonds. The intrinsic stabilization effect of aromaticity is further elucidated by density functional calculations.

Metallacyclopentadienes play an important role in transition-metal-catalyzed cyclotrimerization of alkynes. Isolation and characterization of these unique five-membered metallacycles could promote further understanding of related catalytic reactions. In this work, the first metallafulvenallene complexes were synthesized by the reaction of fused metallacyclopentadiene with terminal alkynes. Single-crystal X-ray diffraction and NMR spectroscopic studies on the metallafulvenallene complexes demonstrate that the bicyclic framework consists of a metallacyclopentadiene fused with a six-membered metallacycle, featuring an η1-vinylidene ligand. Deuterium labeling experiments were carried out to investigate the mechanism for the transformation of fused metallacyclopentadiene to fused metallafulvenallene. The UV–vis absorption spectra of these unique structures were measured.

A number of C- and S-shaped perylene diimide (PDI) heterohelicenes with high dipole moments were synthesized from simple perylene tetrabutylester (PTE). Taking advantage of the weak coordination ability of the sterically crowded peri ester groups in PTE, efficient Rh­(III)-catalyzed 2,8- and 2,11-bisiodinations of the perylene core were realized. The 2,8- and 2,11-diiodinated PTEs and PDIs represent key synthons for further ortho-π-extensions. In contrast to most helical π-skeletons that feature loose molecular packings, enantiomerically pure C-shaped PDI azahelicenes adopt unique spiral-stair-like π-stacking superstructures.