Simultaneous Presence of Open Metal Sites and Amine Groups on a 3D Dy(III)-Metal-Organic Framework Catalyst for Mild and Solvent-Free Conversion of CO2 to Cyclic Carbonates.

TLDR: In this article, a 3D metal-organic framework with micropores and free NH2 groups was proposed to promote the chemical fixation of CO2 to cyclic carbonates.

Abstract: Carbon dioxide (CO2) fixation to generate chemicals and fuels is of high current importance, especially toward finding mild and efficient strategies for catalytic CO2 transformation to value added products. Herein, we report a novel Lewis acid-base bifunctional amine-functionalized dysprosium(III) metal-organic framework [Dy3(data)3·2DMF]·DMF (2,5-data: 2,5-diamino-terephthalate), NH2-TMU-73. This compound was fully characterized and its crystal structure reveals a 3D metal-organic framework (MOF) with micropores and free NH2 groups capable of promoting the chemical fixation of CO2 to cyclic carbonates. NH2-TMU-73 is built from the Dy(III) centers and data2- blocks, which are arranged into an intricate underlying net with a rare type of xah topology. After activation, NH2-TMU-73 and its terephthalate-based analogue (TMU-73) were applied for CO2-to-epoxide coupling reactions to produce cyclic carbonates. Important features of this catalytic process concern high efficiency and activity in the absence of cocatalyst, use of solvent-free medium, atmospheric CO2 pressure, and ambient temperature conditions. Also, NH2-TMU-73 features high structural stability and can be recycled and reused in subsequent catalytic tests. An important role of free amino groups and open metal sites in the MOF catalyst was highlighted when suggesting a possible reaction mechanism.