Redox-promoted associative assembly of metal-organic materials

Ligand-enabled oxidation of gold(i) complexes with o-quinones

Chelating P^P and hemilabile P^N ligands were found to trigger the oxidation of Au(i) complexes by o-benzoquinones. The ensuing Au(iii) catecholate complexes have been characterized by NMR spectroscopy, single crystal X-ray diffraction and X-ray absorption spectroscopy. They adopt tetracoordinate square-planar structures. Reactivity studies substantiate the reversibility of the transformation. In particular, the addition of competing ligands such as chloride and alkenes gives back Au(i) complexes with concomitant release of the o-quinone. DFT calculations provide insight about the structure and relative stability of the Au(i) o-quinone and Au(iii) catecholate forms, and shed light on the 2-electron transfer from gold to the o-quinone.

Chelating P^P and hemilabile P^N ligands were found to trigger the oxidation of Au(i) complexes by o-benzoquinones.

Ball-Milling-Enabled Reactivity of Manganese Metal*

Efforts to generate organomanganese reagents under ball-milling conditions have led to the serendipitous discovery that manganese metal can mediate the reductive dimerization of arylidene malonates. The newly uncovered process has been optimized and its mechanism explored using CV measurements, radical trapping experiments, EPR spectroscopy, and solution control reactions. This unique reactivity can also be translated to solution whereupon pre-milling of the manganese is required.

Alternative Technologies That Facilitate Access to Discrete Metal Complexes

Organometallic complexes: these two words jump to the mind of the chemist and are directly associated with their utility in catalysis or as a pharmaceutical. Nevertheless, to be able to use them, it is necessary to synthesize them, and it is not always a small matter. Typically, synthesis is via solution chemistry, using a round-bottom flask and a magnetic or mechanical stirrer. This review takes stock of alternative technologies currently available in laboratories that facilitate the synthesis of such complexes. We highlight five such technologies: mechanochemistry, also known as solvent-free chemistry, uses a mortar and pestle or a ball mill; microwave activation can drastically reduce reaction times; ultrasonic activation promotes chemical reactions because of cavitation phenomena; photochemistry, which uses light radiation to initiate reactions; and continuous flow chemistry, which is increasingly used to simplify scale-up. While facilitating the synthesis of organometallic compounds, these enabling technologies also allow access to compounds that cannot be obtained in any other way. This shows how the paradigm is changing and evolving toward new technologies, without necessarily abandoning the round-bottom flask. A bright future is ahead of the organometallic chemist, thanks to these novel technologies.

Ball size or ball mass – what matters in organic mechanochemical synthesis?

The effects of milling ball mass, size and material are isolated for a model mechanochemical co-crystallisation.

Selectivity in the Aerobic Dearomatization of Phenols: Total Synthesis of Dehydronornuciferine by Chemo- and Regioselective Oxidation

We describe a selective aerobic oxidation of meta-biaryl phenols that enables rapid access to functionalized phenanthrenes. Aerobic oxidations attract interest due to their efficiency, but remain underutilized in complex molecule settings due to challenges of selectivity. We discuss these issues in the context of Cu catalysis, and highlight the advantages of confining oxygen activation and substrate oxidation to the catalyst's inner-coordination sphere. This gives rise to predictable selectivity that we use for a concise synthesis of the aporphine dehydronornuciferine.

A chlorine-free protocol for processing germanium

Replacing molecular chlorine and hydrochloric acid with less energy- and risk-intensive reagents would markedly improve the environmental impact of metal manufacturing at a time when demand for metals is rapidly increasing. We describe a recyclable quinone/catechol redox platform that provides an innovative replacement for elemental chlorine and hydrochloric acid in the conversion of either germanium metal or germanium dioxide to a germanium tetrachloride substitute. Germanium is classified as a "critical" element based on its high dispersion in the environment, growing demand, and lack of suitable substitutes. Our approach replaces the oxidizing capacity of chlorine with molecular oxygen and replaces germanium tetrachloride with an air- and moisture-stable Ge(IV)-catecholate that is kinetically competent for conversion to high-purity germanes.

A Catalyst-Controlled Aerobic Coupling of ortho-Quinones and Phenols Applied to the Synthesis of Aryl Ethers

ortho-Quinones are underutilized six-carbon-atom building blocks. We herein describe an approach for controlling their reactivity with copper that gives rise to a catalytic aerobic cross-coupling with phenols. The resulting aryl ethers are generated in high yield across a broad substrate scope under mild conditions. This method represents a unique example where the covalent modification of an ortho-quinone is catalyzed by a transition metal, creating new opportunities for their utilization in synthesis.