α-Diimine Ni-Catalyzed Ethylene Polymerizations: On the Role of Nickel(I) Intermediates

Nickel(II) complexes with bidentate N,N-α-diimine ligands constitute a broad class of promising catalysts for the synthesis of branched polyethylenes via ethylene homopolymerization. Despite extensive studies devoted to the rational design of new Ni(II) α-diimines with desired catalytic properties, the polymerization mechanism has not been fully rationalized. In contrast to the well-characterized cationic Ni(II) active sites of ethylene polymerization and their precursors, the structure and role of Ni(I) species in the polymerization process continues to be a “black box”. This perspective discusses recent advances in the understanding of the nature and role of monovalent nickel complexes formed in Ni(II) α-diimine-based ethylene polymerization catalyst systems.

Ruthenium(III) Based Diimine Complexes; Synthesis, Characterization, PXRD Study and Catalytic Hydrogenation of Cyclohexene

This study deals with preparation and characterization of a group of RuIII-chelates contains tetradentate diimine ligands. These quadridentate ligands are derived from 2-OH-1-naphthaldehyde and a number of aliphatic diamines where the number of methylene groups between the two azomethine nitrogen donors varied from two to six are the components of quadridentate ligands. The pure isolated compounds were subjected to several physicochemical investigations to assign their structures. Spectral and magnetic measurements suggested a distorted octahedral arrangement of the six coordinate diimine ruthenium(III) complexes. The structural optimization for one of the current RuIII-complexes was determined based on the processing of powder X-ray diffraction (PXRD) data by the computer program Expo 2014 PXRD. As well DFT calculations were applied to optimize the geometry in the case of complexes 1. The newly synthesized ruthenium(III) diimines were tested as catalysts for hydrogenation of cyclohexene. The effect of the catalyst structure and the type of catalysis as well as the nature and amount of the solvent used on the catalytic performance of the current catalysts were studied. Catalytic experiments reported that the ongoing ruthenium(III) complexes are promising precatalysts that have successfully catalyzed hydrogenation of cyclohexene by hydrogen gas under moderate process conditions. The results obtained allowed to establish a mechanism for the studied catalytic hydrogenation reactions.

One-Pot Synthesis and Characterization of Biomimetic Copper(I) Complexes

A modular one-pot synthesis yielding tetracoordinated-N,N,N,N-copper(I) complexes bearing imine and diimine ligands was developed. Copper aids the condensation of a pyridine or imidazole carbaldehyde with a biphenyl amine and even stabilizes labile ligands. Tetradentate and bidentate ligands were formed, the latter forming homoleptic CuL2 complexes. The identity and purity of the compounds were assessed by NMR, elemental analysis and mass spectrometry. The interconversion of different species in solution was studied by variable temperature NMR. The complexes aim to mimic the histidine copper brace of lytic polysaccharide monooxygenases (LPMOs) and bond lengths obtained from XAS and single crystal XRD for the complexes were compared to reported photoreduced LPMOs.