Sethuraman Muthuramalingam, M. Velusamy, Swati Singh Rajputa
Feb 3, 2023
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Chemistry, an Asian journal
Abstract
Fixation of atmospheric CO2 into value-added products is a promising methodology. A series of novel nickel(II) complexes of the type [Ni(L)(CH3CN)2](BPh4)21 - 5, where L= N,N-bis(2-pyridylmethyl)-N',N'-dimethylpropane-1,3-diamine (L1), N,N-dimethyl-N'-(2-(pyridin-2-yl)ethyl)-N'-(pyridin-2-ylmethyl) propane-1,3-diamine (L2), N,N-bis((4-methoxy-3,5-dimethylpyridin-2-ylmethyl)-N',N'-dimethylpropane-1,3-diamine (L3), N-(2-(dimethylamino) benzyl)-N',N'-dimethyl-N-(pyridin-2-ylmethyl) propane-1,3-diamine (L4) and N,N-bis(2-(dimethylamino)benzyl)-N',N'-dimethylpropane-1,3-diamine (L5) have been synthesized and characterized as the catalysts for the conversion of atmospheric CO2 into organic cyclic carbonates. The single-crystal X-ray structure of 2 was determined and exhibited distorted octahedral coordination geometry with cis-α configuration. The complexes were employed as a catalyst for the conversion of CO2 and epoxides into five-membered cyclic carbonates under 1 atmospheric (atm) pressure at room temperature in the presence of Bu4NBr. The catalyst containing electron-releasing -Me and -OMe groups afforded the maximum yield of cyclic carbonates, 34% (TON, 680) under 1 atm air. It was drastically enhanced to 89% (TON, 1780) under pure CO2 gas at 1 atm. It is the highest catalytic efficiency known for CO2 fixation using nickel-based catalysts at room temperature and 1 atm pressure. The catalytic efficiency is strongly influenced by the electronic and steric factors of the ligands. Furthermore, all the catalysts can convert a wide range of epoxides (ten examples) into corresponding cyclic carbonate with excellent selectivity (>99%) under this mild condition.