Toward understanding the structure–catalyst activity relationship of new indium MOFs as catalysts for solvent-free ketone cyanosilylation

Abstract

Four new indium metal–organic frameworks, MOFs, namely [In₂(hfipbb)₃(1,10-phen)₂]·2H₂O (InPF-12), [In₂(hfipbb)₃(2,2′-bipy)₂]·2H₂O (InPF-13), [In₂(hfipbb)₃(4,4′-bipy)] (InPF-14) and [In₄(OH)₄(hfipbb)₄(4,4′-bipy)] (InPF-15), (InPF = indium polymeric framework, hfipbb = hexafluoroisopropylidene bisbenzoate, phen = phenantroline, bipy = bipyridine), have been hydrothermally obtained and result in efficient Lewis acid catalysts in solvent-free cyanosilylation of carbonyl compounds. For acetophenone: (i) the coordination number and μ-OH groups presence seem to be decisive factors to obtain a better catalytic behavior and (ii) the presence of Lewis base moieties (CO groups not coordinated to indium cation), besides the Lewis acid sites, creates a two-component catalytic system, based on the “dual activation” phenomenon that makes InPF-15 the best catalyst in this type of reaction. It was also found that the use of this highly reactive, recyclable and environmentally benign catalyst allows the efficient synthesis of various trimethylsilyl cyanohydrins from a wide range of cyclic, aliphatic and aromatic ketones.