Solvent-free heterogeneous catalysis for cyanosilylation in a dynamic cobalt-MOF

Abstract

The butterfly-like tetranuclear cobalt cluster based 3D MOF [Me₂NH₂][Co₂(bptc)(μ₃-OH)(H₂O)₂] (1) underwent a reversible thermally triggered single-crystal-to-single-crystal transformation via Co–O_water weakened intermediate 1a to produce a partly dehydrated phase [Me₂NH₂][Co₂(bptc)(μ₃-OH)(H₂O)] (2), which was confirmed by single-crystal X-ray diffraction, powder X-ray diffraction, thermogravimetric analysis, and IR spectroscopy. During the dehydration course, the local coordination environment of one Co²⁺ ion was changed from the saturated octahedron to a coordinately unsaturated square-pyramid, accompanied by a crystal color change from red to purple. Compared with pristine hydrated 1, dehydrated 2 exhibits highly efficient and recyclable catalytic activity for cyanosilylation of carbonyl compounds with a low catalyst loading of 0.1 mol% Co at room temperature under solvent-free conditions, which due to the open Co²⁺ sites as catalytically activated sites played a significant role in the heterogeneous catalytic process.