CPO-27-M as heterogeneous catalysts for aldehyde cyanosilylation and styrene oxidation

A series of isostructural 3D metal-organic frameworks of 2,5-dihydroxyterephthalate with different metal ions, CPO-27-M (or MOF-74-M, M = Co, Mg, Mn, Ni and Zn), have been studied as catalysts for cyanosilylation of aldehydes with trimethylsilylcyanide and oxidation of styrene with tert-butylhydroperoxide, and two mixed-metal Co-Mn MOFs also studied for cyanosilylation. All these MOFs are active in promoting cyanosilylation, but for styrene oxidation, only the Co and Mn MOFs are active while the others behave as initiators rather than catalysts. For both reactions, CPO-27-Mn exhibits the highest activity, and the catalytic processes are heterogeneous. Radical mechanisms were proposed for the styrene oxidation over CPO-27-Mn, which yields styrene oxide, benzaldehyde and a minor amount of phenylacetaldehyde. The cyanosilylation over CPO-27-Mn shows size selectivity towards aldehyde substrates, and the catalyst can be recycled without losing its structural integrity and catalytic activity. It is also recyclable for styrene oxidation, though the structure changes after the catalytic reaction.