Dinickel-Catalyzed N═N Bond Rotation.

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.

Catalytic Synthesis of Conjugated Azopolymers from Aromatic Diazides.

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 and is compatible with heterocycles commonly featured in high performance organic materials, including carbazole, thiophene, propylenedioxythiophene (ProDOT), diketopyrrolopyrrole (DPP), and isoindigo. Copolymerizations can be carried out using monomer mixtures, and monoazide chain stoppers can be used to install well-defined end groups. Azopolymers possess unique properties owing to the functionality of the azo linkages. For example, protonation at nitrogen results in LUMO lowering and red-shifted absorption bands. Additionally, N=N bonds possess low-lying π* levels, allowing azopolymers to be reversibly reduced under mild conditions.

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

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.

Cp*Co(IPr): synthesis and reactivity of an unsaturated Co(i) complex.

Synthesis of coordinatively unsaturated Cp*Co(IPr) (2), is accomplished by addition of free N-heterocyclic carbene IPr to [(Cp*Co)2-µ-(η(4):η(4)-toluene)] (1). Stoichiometric reactivity is consistent with a 16 electron species, as 2 undergoes ligand addition/NHC displacement and reversible reaction with dihydrogen. Cp*Co(IPr) represents an elusive example of a stable Cp*CoL fragment.