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Porous Polymer for Heterogeneous Catalysis
Published in Inamuddin, Mohd Imran Ahamed, Rajender Boddula, Porous Polymer Science and Applications, 2022
Vivek Mishra, Simran Aggarwal, Shubham Pandey
Conventionally, the Suzuki–Miyaura crosscoupling reaction for the C–C bond formation is catalyzed by very expensive Pd. As compared to Pd, the first-row transition metal Ni is cheap, more reactive, and abundant, and therefore, Ni-based catalysts are a sustainable alternative to Pd for C–C bond formation. Also, the α-diimine-based metal catalyst has attracted chemists toward themselves as they are easy to synthesize, stable, and highly active as a catalyst. Combining the advantage of both, Dong et al.72 synthesized a Ni(II)-α-diimine-POP via Sonogashira coupling of Ni(II) α-diimine and 1,3,5-triethynylbenzene in solvothermal conditions. Initially, a Schiff-base condensation reaction was performed between 4-iodo-2,6-diisopropylbenzenamine and butane-2,3-dione, followed by metalation with DME(NiBr2), then coupled with 1,3,5-triethynylbenzene to form Ni(II)-α-diimine POP (Scheme 6.27).
Insertion or Ziegler–Natta Polymerization of Olefins
Published in Samir H. Chikkali, Metal-Catalyzed Polymerization, 2017
Samir H. Chikkali, Ketan Patel, Sandeep Netalkar
An important event in the search for new catalysts in the area olefin polymerization occurred when Brookhart and co-workers in 1995 synthesized a new class of Ni(II) and Pd(II) complexes stabilized by bulky α-diimine ligands (Schiff bases) (Figure 2.46).97 This finding represents one of the most important breakthroughs in the development of late transition metal catalysts for efficient olefin polymerization. In a ligand-centered catalyst design, Brookhart and coworkers discovered that α-diimine ligands stabilize Ni(II)/Pd(II) complexes. The ligands display a neutral coordination with the two imine-nitrogens donating their electron lone-pairs to the metal center and assuming cis-coordination. This neutral donor ligand was proven useful to stabilize the metal center by forming a five-membered chelate ring. In addition, the α-diimine ligands set also offers an opportunity to modify electronic and steric properties by introduction of substituents onto the aryl rings.97 In a typical Brookhart diimine complex, the ligand backbone consists of a bidentate diimine ligand with the possibility of variation at R1 or R2 positions, or the imine nitrogen’s donate their lone pair to the electrophilic metal center. The metal center displays square-planar geometry, with the cis-coordinating diimine ligand flanked by aryl substituents. The net charge on the metal complex is zero, whereas the oxidation state of the metal is +2, which is satisfied by the two anionic chlorides.
N-Heterocycles
Published in Navjeet Kaur, Metals and Non-Metals, 2020
Synthesis of diimine in (+)-(S,S)-configuration has been optimized with meso- as it has no potential in asymmetric catalysis. (S,S)-Diimine is synthesized in quantitative yields when enantioenriched (+)-(S,S)- aniline is condensed with glyoxal (Scheme 68). However, extensive optimization is required for the cyclization and purification of this product. Berthon-Gelloz et al. [145] modified the cyclization protocol using zinc chloride to coordinate the diimine in the reactive s-cis conformation which provided pure (S,S,S,S)-product in 87% yields after recrystallization [146].
Synergistic lanthanide extraction triggered by self-assembly of heterodinuclear Zn(II)/Ln(III) Schiff base/carboxylic acid complexes
Published in Solvent Extraction and Ion Exchange, 2021
Norman Kelly, Thomas Doert, Felix Hennersdorf, Karsten Gloe
The diimine ligands have been synthesized by the standard Schiff base condensation reaction[101]: To a solution of the diamine spacer (5.00 mmol) in methanol (20 mL) was added a methanol solution (10 mL) of 3-methoxysalicylaldehyde (10.00 mmol to give H2L1, H2L3, H2L5) or 3-ethoxysalicylaldehyde (10.00 mmol to give H2L2, H2L4, H2L6). The mixture was stirred for 48 h at room temperature. In case of H2L1 and H2L3 the solvent was removed under reduced pressure to give a yellow solid residue which was recrystallized from methanol. The solid was washed with methanol and diethyl ether and dried in vacuo. In case of the other ligands the mixture was directly filtrated and the precipitate was washed with methanol and diethyl ether and dried in vacuo.