Circular olefin copolymers made de novo from ethylene and α-olefins.

Ethylene/α-olefin copolymers are produced in huge scale and widely used, but their after-use disposal has caused plastic pollution problems. Their chemical inertness made chemical re/upcycling difficult. Ideally, PE materials should be made de novo to have a circular closed-loop lifecycle. However, synthesis of circular ethylene/α-olefin copolymers, including high-volume, linear low-density PE as well as high-value olefin elastomers and block copolymers, presents a particular challenge due to difficulties in introducing branches while simultaneously installing chemical recyclability and directly using industrial ethylene and α-olefin feedstocks. Here we show that coupling of industrial coordination copolymerization of ethylene and α-olefins with a designed functionalized chain-transfer agent, followed by modular assembly of the resulting AB telechelic polyolefin building blocks by polycondensation, affords a series of ester-linked PE-based copolymers. These new materials not only retain thermomechanical properties of PE-based materials but also exhibit full chemical circularity via simple transesterification and markedly enhanced adhesion to polar surfaces.

Unsaturated Alcohols as Chain-Transfer Agents in Olefin Polymerization: Synthesis of Aldehyde End-Capped Oligomers and Polymers.

Palladium diimine-catalyzed polymerization of olefins using unsaturated alcohols as chain-transfer agents has been demonstrated. The reaction affords aldehyde end-capped polymers whose molecular weight can be tuned by varying the ratio of olefin/chain-transfer agent. Notably, >95% efficient end capping with aldehyde can be achieved under optimized conditions. This end-capping procedure is a rare example of introducing a highly reactive and versatile terminal functionality in polyolefin chains using a functional group-tolerant late metal catalyst. The reactivity of these end-capped polymers is illustrated here via functionalization with dyes to yield colored, hydrocarbon-soluble polyolefin derivatives.

Enantioselective Ni-Al Bimetallic Catalyzed exo-Selective C-H Cyclization of Imidazoles with Alkenes.

A Ni-Al bimetallic catalyzed enantioselective C-H exo-selective cyclization of imidazoles with alkenes has been developed. A series of bi- or polycyclic imidazoles with ß-stereocenter were obtained in up to 98% yield and >99% ee. The bifunctional SPO ligand-promoted bimetallic catalysis proved to be critical to this challenging stereocontrol.

Brønsted Acid Enabled Nickel-Catalyzed Hydroalkenylation of Aldehydes with Styrene and its Derivatives.

A Brønsted acid enabled nickel-catalyzed hydroalkenylation of aldehydes and styrene derivatives has been developed. The Brønsted acid acts as a proton shuttle to transfer a proton from the alkene to the aldehyde, thereby leading to an economical and byproduct-free coupling. A series of synthetically useful allylic alcohols were obtained through one-step reactions from readily available styrene derivatives and aliphatic aldehydes in up to 88 % yield and with high linear selectivity.

Enantioselective Friedel-Crafts alkylation of pyrrole with chalcones catalyzed by a dinuclear zinc catalyst.

A highly enantioselective Friedel-Crafts (F-C) alkylation of pyrrole with a wide range of simple nonchelating chalcone derivatives catalyzed by a chiral (Zn2EtL)n (L = (S,S)-1) complex has been developed. The catalyst (Zn2EtL)n complex was prepared in situ by reacting the chiral ligand (S,S)-1 with 2 equiv of diethylzinc. A series of ß-pyrrole-substituted dihydrochalcones were usually formed mostly in excellent yields (up to 99%) and excellent enantioselectivity [up to 99% enantiomeric excess (ee)] by using 15 mol % catalyst loading under mild conditions. The absolute stereochemistry of the products was determined to be the S-configuration by X-ray crystallographic analysis of 13g. Meanwhile, a weak negative nonlinear effect was observed. On the basis of the experimental results and previous reports, a possible mechanism was proposed to explain the origin of the asymmetric induction.

L-Proline: an efficient N,O-bidentate ligand for copper-catalyzed aerobic oxidation of primary and secondary benzylic alcohols at room temperature.

A novel and highly practical copper-catalyzed aerobic alcohol oxidation system with L-proline as the ligand at room temperature has been developed. A wide range of primary and secondary benzylic alcohols tested have been smoothly transformed into corresponding aldehydes and ketones with high yields and selectivities.