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Selective regulation of Lewis acid–base sites in metal–organic framework catalysts is an effective strategy to turn-on/off the catalytic activity for different CO₂ reactions.

Abstract

Regulating Lewis acid–base sites in catalysts to investigate their influence in the chemical fixation of CO₂ is significant but challenging. A metal–organic framework (MOF) with open metal Co sites, {(NH₂Me₂)[Co₃(μ ₃-OH)(BTB)₂(H₂O)]⋅9 H₂O⋅5 DMF} _n (1), was obtained and the results of the catalytic investigation show that 1 can catalyze cycloaddition of CO₂ and aziridines to give 99 % yield. The efficiency of the cyclization of CO₂ with propargyl amines is only 32 %. To improve the catalytic ability of 1, ligand XN with Lewis base sites was introduced into 1 and coordinated with the open Co sites, resulting in a decrease of the Lewis acid sites and an increase in the Lewis base sites in a related MOF 2 ({(NH₂Me₂)[Co₃(μ ₃-OH)(NHMe₂)(BTB)₂(XN)]⋅8 H₂O⋅4 DMF} _n ). Selective regulation of the type of active centers causes the yield of oxazolidinones to be enhanced by about 2.4 times, suggesting that this strategy can turn on/off the catalytic activity for different reactions. The catalytic results from 2 treated with acid solution support this conclusion. This work illuminates a MOF-construction strategy that produces efficient catalysts for CO₂ conversion.