Nitrene-transfer reactions are powerful synthetic tools for the direct incorporation of nitrogen atoms into organic molecules. The discovery of novel nitrene-transfer reactions has been dominantly supported not only by improvements in transition-metal catalysts but also by the employment of novel precursors of nitrenoids. Since pioneering work involving the use of organic azides and iminoiodinanes as practical synthetic tools for nitrogen-containing compounds was reported, a new approach using various N-heterocycles containing strain energy or a weak bond has emerged. In this review, we briefly summarize the history of nitrene-transfer chemistry from the viewpoint of its precursors. In particular, the use of N-heterocycles such as 2H-azirines, 1,4,2-dioxazol-5-ones, 1,2,4-oxadiazol-5-ones, isoxazol-5(4H)-ones, and isoxazoles is comprehensively described, showing the recent remarkable progress in this chemistry.

Recent Progress on Cyclic Nitrenoid Precursors in Transition-Metal-Catalyzed Nitrene-Transfer Reactions

The field of multimetallic catalysis is rapidly developing and some multimetallic complexes catalyze organic transformations to yield the desired products in more efficient ways owing to the combined action of different metals in a cooperative fashion. This Concept article describes the recent advances of cooperative catalysis playing in multimetallic systems such as homo‐multimetallic complexes with short metal‐metal distances, homo‐multimetallic complexes with long metal‐metal distances, hetero‐multimetallic complexes and metallocene‐based multimetallic complexes with special attention towards redox‐switchable catalysis. Examples are illustrated in which the use of multimetallic complexes show clear enhancement of catalytic outcomes when compared with the sum of their corresponding mononuclear counterparts. Furthermore, several examples are discussed showing the effects of electronic communication in cooperative systems.

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Cooperative Effects in Multimetallic Complexes Applied in Catalysis

Metal‐Metal Cooperation in Dinucleating Complexes Involving Late Transition Metals Directed Towards Organic Catalysis

Tuning metal–metal interactions for cooperative small molecule activation

Oxidative nitrene transfer from azides to alkynes via Ti(ii)/Ti(iv) redox catalysis: Formal [2+2+1] synthesis of pyrroles

Azoarenes are valuable chromophores that have been extensively incorporated as photoswitchable elements in molecular machines and biologically active compounds. Here, we report a catalytic nitrene dimerization reaction that provides access to structurally and electronically diverse azoarenes. The reaction utilizes aryl azides as nitrene precursors and generates only gaseous N2 as a byproduct. By circumventing the use of a stoichiometric redox reagent, a broad range of organic functional groups are tolerated, and common byproducts of current methods are avoided. A catalyst featuring a Ni—Ni bond is found to be uniquely effective relative to those containing only a single Ni center. The mechanistic origins of this nuclearity effect are described.

Catalytic Azoarene Synthesis from Aryl Azides Enabled by a Dinuclear Ni Complex

Conjugated polymers containing main chain azoarene repeat units are synthesized by a dinickel catalyzed N=N coupling reaction of aromatic diazides. The polymerization exhibits broad substrate scope...

Catalytic Synthesis of Conjugated Azopolymers from Aromatic Diazides.

Catalytic C(sp2)–H Amination Reactions Using Dinickel Imides

Azoarenes function as molecular switches that can be triggered by external stimuli, such as heat, light, and electrochemical potential. Here, we show that a dinickel catalyst can induce cis/trans isomerization in azoarenes through a N═N bond rotation mechanism. Catalytic intermediates containing azoarenes bound in both the cis and trans forms are characterized. Solid-state structures reveal the importance of π-back-bonding interactions from the dinickel active site in lowering the N═N bond order and accelerating bond rotation. The scope of the catalytic isomerization includes high-performance acyclic, cyclic, and polymeric azoarene switches.

John M. Andjaba

Papers

Catalytic Azoarene Synthesis from Aryl Azides Enabled by a Dinuclear Ni Complex

Catalytic Synthesis of Conjugated Azopolymers from Aromatic Diazides.

Catalytic C(sp2)–H Amination Reactions Using Dinickel Imides

Dinickel-Catalyzed N═N Bond Rotation.

Black-to-Transmissive Dual Polymer Complementary Electrochromics with High Coloration Efficiency