Recently, enormous effort has been devoted to tackle the problematic emissions of CO₂ into the air. The frustrated Lewis pairs (FLPs) comprising of sterically hindered Lewis acid and base have attracted extensive attention catalytic potential for activating small molecules liking H₂, CO₂, etc, through the metal-free catalysis pathway. However, most reported FLPs are homogeneous catalysts, which are highly sensitive to moisture, as well as hard to be recycled, preventing their practical applications. Taken together, the rational design of FLPs-functional heterogeneous catalysts featuring high stability and catalytic activity is of sought after yet high challenge. Herein, Ma group reported a boron-functional MOCs constructed from boron-functional linkers and Zr nodes, for efficient CO₂ transformation. Ma and co-workers described that the boron-functional MOCs presented high catalytic activity towards the cyclization reaction of o-phenylenediamine with CO₂ using PhSiH₃ as the reduced agent through a FLP-mediated pathway. To gain deep insight into the catalysis mechanism, DFT calculation was performed to reveal the electronic structure of boron-functional linker, and followed the cyclization reaction process of o-phenylenediamine.
Specifically, we present a DFT/ with dsp3-BJ correction modeling for the catalytic cycle of the MOCs in the transformation of a variety of o-phenylenediamine into benzimidazole derivatives using CO₂ and Ph₂SiH₃. (See Figure 1). Quantum mechanical calculations were carried out in the catalytic cycle to estimate the efficiency using MOCs by analyzing all structure-activity dual of transition state and product in polarized continuum model (SMD) and in gas phase.
Indeed, the catalytic process needs 4 reaction intermediates as proposed by Ma et al. It seems that the formation of “frustrated Lewis pairs” contributes in the mechanism or the catalytic process. Feasible catalytic reaction process thermodynamically with Lower energy of transition states (TS) were observed. Besides, solvation effect impacts really the profile energy path as well as the dispersion correction. The calculated interaction energy for MOCs agrees very well with the experimental data. Further studies are underway to understand the role of boron-functional MOCs for the activation of CO₂ and to explore new applications.
Figure 1: Boron-functional MOCs catalyzed synthesis of benzimidazoles via cyclization of
o-phenylenediamines with CO₂ and PhSiH₃ proposed by Ma et al.

Hassan Rabaa

Prof, UNT-Tx and IbnTofail-Morocco

Appearances