γ-Selective C(sp3)–H amination via controlled migratory hydroamination

Remote functionalization of alkenes via chain walking has generally been limited to C(sp3)–H bonds α and β to polar-functional units, while γ-C(sp3)–H functionalization through controlled alkene transposition is a longstanding challenge. Herein, we describe NiH-catalyzed migratory formal hydroamination of alkenyl amides achieved via chelation-assisted control, whereby various amino groups are installed at the γ-position of aliphatic chains. By tuning olefin isomerization and migratory hydroamination through ligand and directing group optimization, γ-selective amination can be achieved via stabilization of a 6-membered nickellacycle by an 8-aminoquinoline directing group and subsequent interception by an aminating reagent. A range of amines can be installed at the γ-C(sp3)–H bond of unactivated alkenes with varying alkyl chain lengths, enabling late-stage access to value-added γ-aminated products. Moreover, by employing picolinamide-coupled alkene substrates, this approach is further extended to δ-selective amination. The chain-walking mechanism and pathway selectivity are investigated by experimental and computational methods.

Nickel-Hydride Catalyzed Remote Hydroarylation of Olefins

Metal hydride-catalyzed remote hydrofunctionalization has attracted extensive attention in the past decade, as it provides a complementary approach for selective functionalization of remote C(sp3)–H bonds. Recently, a wide variety of olefinic remote hydrofunctionalizationation reactions have been realized through the synergistic combination of NiH-catalyzed chain-walking and Ni-catalyzed cross-coupling. In this personal account we discuss our recent achievement in the remote hydroarylation of olefins as well as our recent achievement in asymmetric hydroarylation.

Advances in the synthesis of polyolefin elastomers with “chain-walking” catalysts and electron spin resonance research of related catalytic systems

: In recent years, polyolefin elastomers play an increasingly important role in industry. The late transition metal complex catalysts, especially α-diimine Ni(II) and α-diimine Pd(II) complex catalysts, are popular “chain-walking” catalysts. They can prepare polyolefin with various structures, ranging from linear configuration to highly branched configuration. Combining the “chain-walking” characteristic with different polymerization strategies, polyolefins with good elasticity can be obtained. Among them, olefin copolymer is a common way to produce polyolefin elastomers. For instance, strictly defined diblock or triblock copolymers with excellent elastic properties were synthesized by adding ethylene and αolefin in sequence. As well as the incorporation of polar monomers may lead to some unexpected improvement. Chain shuttling polymerization can generate multiblock copolymers in one pot due to the interaction of the catalysts with chain shuttling agent. Furthermore, when regarding ethylene as the sole feedstock, owing to the “oscillation” of the ligands of the asymmetric catalysts, polymers with stereo-block structures can be generated. Generally, the elasticity of these polyolefins mainly comes from the alternately crystalline-amorphous block structures, which is closely related to the characteristic of the catalytic system. To improve performance of the catalysts and develop excellent polyolefin elastomers, research on the catalytic mechanism is of great significance. Electron spin resonance (ESR), as a precise method to detect unpaired electron, can be applied to study transition metal active center. Therefore, the progress on the exploration of the valence and the proposed configuration of catalyst active center in the catalytic process by ESR is also reviewed.

Propylene Homopolymerization and Copolymerization with Ethylene by Acenaphthene-Based α-Diimine Nickel Complexes to Access EPR-Like Elastomers

Benefiting from the unique chain walking characteristic of late transition metal complexes, branched EPR-like elastomers bearing distinct differences compared to traditional linear EPRs are reported herein. Firstly, a series of...

Chain-walking reactions of transition metals for remote C–H bond functionalization of olefinic substrates

Transition metal-assisted remote C–H bond activation at the non-classical reaction sites of various olefinic substrates with the aid of a chain-walking process is depicted in this feature article.