Quasi-HKUST as Tandem Catalyst for Direct Imine Formation under Green Approach

: Copper based metal-organic framework (Cu 3 (BTC) 2 (H 2 O) 3 ] n ·nH 2 OMeOH (HKUST) has been submitted to under controlled conditions to thermolysis under air atmosphere at different temperatures ranging from 100 to 300 °C. This treatment produces the partial removal of ligands, as well as, the generation of structural defects and additional porosity in a controlled way. The resulting defective materials,The resulting defective materials denoted according to the literature as quasi MOFs, were subsequently employed as heterogeneous tandem catalysts in the one pot synthesis of N-benzylideneaniline from aniline and benzyl alcohol in open air as terminal oxidant at 70 °C under base-and dehydrating agent-free conditions. The Q-HKUST catalysts calcined at 240 °C and 260 °C (QH-240 and QH-260, respectively) was the most efficient in the series, can efficiently promotinge imine synthesis, in particular QH-240 within 1h by forming water as the only by-product. Data from Knoevenagel condensation of malononitrile shows that in QH-240 the distances of Cu ions in HKUST cavities are preserved, increasing the Knoevenagel activity, but a strong rearrangement takes place at 300 o C or above. The unsaturated copper active sites with simultaneous presence of micro-and mesopores in QH-240 tandem catalyst are responsible for this excellent catalytic performance. The effective parameters on catalytic activity of QH-240 including deligandation temperature, the amount of catalyst, the ratio of reactants, and reaction temperature as well as the stability and recyclability of the catalyst were also investigated. The possible mechanism used by QH-240 follows alcohol aerobic oxidation and subsequent anaerobic condensation of aldehyde intermediate with aniline.