Synchronizing substrate activation rates in multicomponent reactions with metal-organic framework catalysts

Abstract

A study on the influence of the cation coordination number, number of Lewis acid centers, concurrent existence of Lewis base sites, and structure topology on the catalytic activity of six new indium MOFs, has been carried out for multicomponent reactions (MCRs). The new indium polymeric frameworks, namely [In(OH)(popha)(HO)]·3 HO (InPF-16), [In(popha)(2,2′-bipy)]·3 HO (InPF-17), [In(OH)(popha)(4,4′-bipy)]·4 HO (InPF-18), [In(popha)(4,4′-bipy)]·3 HO (InPF-19), [In(OH)(Hpopha)]·0.5 (1,7-phen) (InPF-20), and [In(popha)(1,10-phen)]·4 HO (InPF-21) (InPF=indium polymeric framework, Hpopha=5-(4-carboxy-2-nitrophenoxy)isophthalic acid, phen=phenanthroline, bipy=bipyridine), have been hydrothermally obtained by using both conventional heating (CH) and microwave (MW) procedures. These indium frameworks show efficient Lewis acid behavior for the solvent-free cyanosilylation of carbonyl compounds, the one pot Passerini 3-component (P-3CR) and the Ugi 4-component (U-4CR) reactions. In addition, InPF-17 was found to be a highly reactive, recyclable, and environmentally benign catalyst, which allows the efficient synthesis of α-aminoacyl amides. The relationship between the Lewis base/acid active site and the catalytic performance is explained by the 2D seven-coordinated indium framework of the catalyst InPF-17. This study is an attempt to highlight the main structural and synthetic factors that have to be taken into account when planning a new, effective MOF-based heterogeneous catalyst for multicomponent reactions.