Synthesis and Reactivity of Reduced α-Diimine Nickel Complexes Relevant to Acrylic Acid Synthesis

Challenges and recent advancements in the transformation of CO2 into carboxylic acids: straightforward assembly with homogeneous 3d metals

Transformation of carbon dioxide (CO2) into valuable organic carboxylic acids is essential for maintaining sustainability. In this review, such CO2 thermo-, photo- and electrochemical transformations under 3d-transition metal catalysis are described from 2017 until 2022.

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-Catalyzed Dehydrogenation Through an Intermolecular Hydrogen Atom Transfer Mechanism

The direct dehydrogenation of alkanes is among the most efficient ways to access valuable alkene products. Although several catalysts have been designed to promote this transformation, they have unfortunately found limited applications in fine chemical synthesis. Here, we report a conceptually novel strategy for the catalytic, intermolecular dehydrogenation of alkanes using a ruthenium catalyst. The combination of a redox-active ligand and a sterically hindered aryl radical intermediate has unleashed this novel strategy. Importantly, mechanistic investigations have been performed to provide a conceptual framework for the further development of this new catalytic dehydrogenation system.

Pyridine-Chelated Imidazo[1,5-a]Pyridine N-Heterocyclic Carbene Nickel(II) Complexes for Acrylate Synthesis from Ethylene and CO2

Nickel(II) dichloride complexes with a pyridine-chelated imidazo[1,5-a]pyridin-3-ylidene py-ImPy ligand were developed as novel catalyst precursors for acrylate synthesis reaction from ethylene and carbon dioxide (CO2), a highly promising sustainable process in terms of carbon capture and utilization (CCU). Two types of ImPy salts were prepared as new C,N-bidentate ligand precursors; py-ImPy salts (3, 4a–4e) having a pyridine group at C(5) on ImPy and a N-picolyl-ImPy salt (10) having a picolyl group at N atom on ImPy. Nickel(II) complexes such as py-ImPyNi(II)Cl2 (7, 8a–8e) and N-picolyl-ImPyNi(II)Cl2 (12) were synthesized via transmetalation protocol from silver(I) complexes, py-ImPyAgCl (5, 6a–6e) and N-picolyl-ImPyAgCl (11). X-ray diffraction analysis of nickel(II) complexes (7, 8b, 12) showed a monomeric distorted tetrahedral geometry and a six-membered chelate ring structure. py-ImPy ligands formed a more planar six-membered chelate with the nickel center than did N-picolyl-ImPy ligand. py-ImPyNi(II)Cl2 complexes (8a–8e) with tert-butyl substituents exhibited noticeable catalytic activity in acrylate synthesis from ethylene and CO2 (up to 108% acrylate). Interestingly, the use of additional additives including monodentate phosphines increased catalytic activity up to 845% acrylate (TON 8).

Syntheses and characterizations of iron complexes of bulky o-phenylenediamide ligand

We report the reactivity of the iron complexes of a bulky phenylenediamide ligand.

Synthesis of CO2-based polycarbonate-g-polystyrene copolymers via NMRP

The synthesis of CO₂-based APC-graft-polystyrene copolymers via NMRP.

Insertion of CO2 Mediated by a (Xantphos)NiI -Alkyl Species

The incorporation of CO₂ into organometallic and organic molecules represents a sustainable way to prepare carboxylates. The mechanism of reductive carboxylation of alkyl halides has been proposed to proceed through the reduction of Ni^II to Ni^I by either Zn or Mn, followed by CO₂ insertion into Ni^I -alkyl species. No experimental evidence has been previously established to support the two proposed steps. Demonstrated herein is that the direct reduction of (tBu-Xantphos)Ni^II Br₂ by Zn affords Ni^I species. (tBu-Xantphos)Ni^I -Me and (tBu-Xantphos)Ni^I -Et complexes undergo fast insertion of CO₂ at 22 °C. The substantially faster rate, relative to that of Ni^II complexes, serves as the long-sought-after experimental support for the proposed mechanisms of Ni-catalyzed carboxylation reactions.

Ni(i)–Ni(iii) cycle in Buchwald–Hartwig amination of aryl bromide mediated by NHC-ligated Ni(i) complexes

NHC-ligated Ni(i) intermediates in Buchwald–Hartwig amination of aryl halides were isolated and determined. The presence of a Ni(iii) intermediate was also indicated at low temperature.

Nickel-catalyzed intermolecular carboiodination of alkynes with aryl iodides

Odd-valent nickel-catalyzed intermolecular carboiodination of alkynes with aryl iodides to form highly substituted and functionalized alkenyl iodides has been developed.