cis‐1,4‐Selective Copolymerization of Ethylene and Butadiene: A Compromise between Two Mechanisms

Introducing ethylene units into polybutadiene backbones is an approach to synthesize advanced rubber materials, which has been a research challenge because of distinct polymerization mechanisms of the two monomers. To date, only trans ‐1,4‐ and 1,2‐regulated copolymers have been obtained. Herein, we reported the unprecedented cis ‐1,4 selective copolymerization of ethylene and butadiene by using the thiophene‐fused cyclopentadienyl‐ligated scandium complexes. The effects of the sterics and electronics of the catalytic precursors as well as the monomer loading mode on the activity and selectivity as well as the sequence lengths were investigated, and the mechanism was elucidated. Thus a novel ethylene‐based rubber material possessing a high molecular weight, 80 % cis ‐1,4 regularity and a T _g=−94 °C without an obvious melting point owing to short polyethylene sequences even at its content up to 45 mol %, was isolated. This new rubber material exhibited excellent anti‐flowing performance and strong tensile strength.     

Ruthenium‐Catalyzed para‐Selective C−H Alkylation of Aniline Derivatives

The para ‐selective C−H alkylation of aniline derivatives furnished with a pyrimidine auxiliary is herein reported. This reaction is proposed to take place via an N−H‐activated cyclometalate formed in situ. Experimental and DFT mechanistic studies elucidate a dual role of the ruthenium catalyst. Here the ruthenium catalyst can undergo cyclometalation by N−H metalation (as opposed to C−H metalation in meta ‐selective processes) and form a redox active ruthenium species, to enable site‐selective radical addition at the para position.     

A General and Highly Selective Cobalt‐Catalyzed Hydrogenation of N‐Heteroarenes under Mild Reaction Conditions

Herein, a general and efficient method for the homogeneous cobalt‐catalyzed hydrogenation of N‐heterocycles, under mild reaction conditions, is reported. Key to success is the use of the tetradentate ligand tris(2‐(diphenylphosphino)phenyl)phosphine). This non‐noble metal catalyst system allows the selective hydrogenation of heteroarenes in the presence of a broad range of other sensitive reducible groups.