Nickel(II) Complexes of Tripodal Ligands as Catalysts for Fixation of Atmospheric CO₂ as Organic Carbonates

Abstract

The 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)2 1–5, 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 have been used as a catalyst for converting 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 electronic and steric factors of the ligands strongly influence the catalytic efficiency. 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.

%VBur index and steric maps: from predictive catalysis to machine learning

“…75 And in 2023 nickel(II) complexes of tripodal ligands could fixate at atmospheric CO 2 pressure, and the best catalyst was fully characterized by steric maps. 76 Another solution by means of calculations was the reduction of the kinetic cost defined by the rate determining step (rds) by means of finding out alternative catalytic systems with several examples, monitoring the substituents on the phosphine to achieve milder conditions in a palladium-catalysed benzosilole formation from aryloxyethynyl silanes and towards milder conditions by predictive catalysis via steric hindrance in the pincer-Ru-catalysed hydrogenation of thioesters. 77 On the other hand, in some cases, the proposed modifications turned out to be almost sterile, for example the modification of a pincer ligand bound to ruthenium for N 2 O fixation.…”