Construction of C-C bonds via photoreductive coupling of ketones and aldehydes in the metal-organic-framework MFM-300(Cr)

Tian Luo,Zheng Yan,Eric J L Mcinnes,Yinlin Chen,Sihai Yang,Chengcheng Liu,Jie An,Alena M Sheveleva,Joseph H Carter,Martin Schröder,Chiu C Tang,Xue Han,Lili Li,Floriana Tuna

doi:10.1038/s41467-021-23302-w

Abstract

Construction of C-C bonds via reductive coupling of aldehydes and ketones is hindered by the highly negative reduction potential of these carbonyl substrates, particularly ketones, and this renders the formation of ketyl radicals extremely endergonic. Here, we report the efficient activation of carbonyl compounds by the formation of specific host-guest interactions in a hydroxyl-decorated porous photocatalyst. MFM-300(Cr) exhibits a band gap of 1.75 eV and shows excellent catalytic activity and stability towards the photoreductive coupling of 30 different aldehydes and ketones to the corresponding 1,2-diols at room temperature. Synchrotron X-ray diffraction and electron paramagnetic resonance spectroscopy confirm the generation of ketyl radicals via confinement within MFM-300(Cr). This protocol removes simultaneously the need for a precious metal-based photocatalyst or for amine-based sacrificial agents for the photochemical synthesis.

Highlights

Construction of C-C bonds via reductive coupling of aldehydes and ketones is hindered by the highly negative reduction potential of these carbonyl substrates, ketones, and this renders the formation of ketyl radicals extremely endergonic
The confined adsorption and activation of carbonyl substrates via the formation of strong host–guest hydrogen bonds promote their conversion into ketyl radicals within the Metal-organic framework (MOF) pores, which has been studied by synchrotron X
The purity of bulk material has been confirmed by powder X-ray diffraction (PXRD) and thermogravimetric analysis (TGA) (Supplementary Figs. 1 and 2)

Summary

Introduction

Construction of C-C bonds via reductive coupling of aldehydes and ketones is hindered by the highly negative reduction potential of these carbonyl substrates, ketones, and this renders the formation of ketyl radicals extremely endergonic. Reductive coupling of aldehydes and ketones offers a promising route to the synthesis of 1,2-diols, which are important structural motifs in a broad range of natural products[3], pharmaceuticals[4], protease inhibitor[5], peptidomimetics[6] and polymers[7], and are widely used as chiral ligands and auxiliaries in organic reactions[8] This is a very challenging photochemical process owing to the highly negative reduction potential of carbonyl compounds, for ketones [e.g., acetophenone: E1/2red = −1.79 V vs normalised hydrogen electrode (NHE)9] and to date, success has only been achieved in exceptional cases[9,10,11,12,13,14].

Methods

Results

Conclusion