Cu(II) Metal-Organic Framework as a Recyclable Heterogeneous Catalyst for Substituted Pyridine Synthesis from Cyclic Ketones with Propargylamine.

The creation of efficient and stable metal-organic framework (MOF) catalysts with coordinatively unsaturated metal sites is critical in modern organic synthesis. Herein, we reported one new Cu(II)-MOF with the chemical formula of {[Cu(L)(H2O)]·2DMA·H2O}∞ (1) (H2L = 4,4'-((4R,5R)-4,5-diphenylimidazolidine-1,3-diyl)dibenzoic acid) for the annulation of cyclic ketones with propargylamine. Compound 1 possesses a 2-fold interpenetrating 3D kagome net with one channel opening of about 20 Å in diameter. Framework 1' exhibits high permanent porosity (778 m2/g, BET) and efficient recyclable catalytic activity for the annulation of cyclic ketones with propargylamine in a one-pot tandem reaction, affording a series of substituted pyridines in a good yield. X-ray photoelectron spectroscopy analysis indicates that Cu(II) is reduced to active Cu(I) species in the reaction system, while Cu(I) species selectively activate the triple bond to promote the annulation. The successful preparation of the heterogeneous Cu(II)-MOF presents new opportunities for developing highly active Cu catalysts for the annulation or other transformations mediated by Cu.