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 aN-picolyl-ImPy salt (10) having a picolyl group at N atom on ImPy. Nickel(II) complexes such as py-ImPyNi(II)Cl-2(7,8a-8e) andN-picolyl-ImPyNi(II)Cl-2(12) were synthesized via transmetalation protocol from silver(I) complexes, py-ImPyAgCl (5,6a-6e) andN-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 didN-picolyl-ImPy ligand. py-ImPyNi(II)Cl(2)complexes (8a-8e) withtert-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).