Oxidative Dehydrogenation Coupling Reaction Catalyzed By Nickel

Oxidative coupling can directly construct C-X（X=C,N,O,P,etc.）bonds,which is an important method in modern organic synthesis.However,most of the current catalytic systems used in oxidative coupling reactions require expensive metals or complex ligands,which limits their application to a certain extent.In this paper,cheap and available nickel is used as the catalytic active center for the oxidative coupling reaction.Based on the adjustable acid-base and physical and chemical properties of the hydrotalcite-like compounds,a series of high-efficiency,low-cost,easy-to-separate,environmentally friendly nickel-containing hydrotalcites have been prepared by adjusting its composition and programmed roasting method,which can efficiently catalyze oxidative coupling reactions.（1）In the oxidative coupling reaction of N-aryltetrahydroisoquinoline and nitromethane,we first screened different nickel salt catalysts and found that NiCl₂ exhibited the highest catalytic performance.The reaction conditions were optimized:0.5 mmol of N-aryltetrahydroisoquinoline,3mmol of nitromethane,5%of NiCl₂,2 mL of 1,4-dioxane,20%of sodium bicarbonate,80℃,oxygen atmosphere,18 h.Under the optimized conditions,the conversion of N-phenyltetrahydroisoquinoline reached>99%with a selectivity of 92%.The catalytic system has good substrate tolerance.（2）A series of NiGa-based hydrotalcite catalysts were designed and prepared,and their catalytic performance was studied in the model reaction of N,N-dimethyl-p-toluidine and malononitrile.The optimal conditions were as follows:0.5 mmol of N,N-dimethyl-p-toluidine,1 mmol of malononitrile,3mL of acetonitrile,0.2 g of Ni₃Ga-LDO,8 equivalents of TBHP,80℃,12 h.Under the optimized conditions,the conversion and selectivity were>99%and 86%,respectively.The catalyst has good stability and reusability in the cyanation of N,N-dimethyl-p-toluidine and malononitrile.XRD characterization results showed that the structure of the catalyst remained basically unchanged after recycle.In reactions using different N-methylaniline derivatives as substrates,this catalytic system showed good adaptability.Finally,the possible action path of the catalyst in the cyanation reaction was also explored.（3）On the basis of the above research,we further applied nickel-containing hydrotalcite catalysis to the oxidative coupling reaction of isochroman and aniline.The catalyst could accelerate the coupling reaction between isochroman and primary amine under relatively mild conditions.Under the optimized reaction conditions:the isochroman 0.5 mmol,aniline 1mmol,1,1,2,2-tetrachloroethane 2 mL,Ni₃Ga-LDO 0.2 g,TBHP 4equivalents,80℃,24 h,the conversion reached 86%with a 77%selectivity of N-phenylisochroman-1-amine.Stability studies showed that Ni₃Ga-LDO catalyst has good structural stability and reusability in the oxidative coupling reaction of isochroman and aniline.When different aniline derivatives were used as raw materials,the Ni₃Ga-LDO catalyst showed good substrate applicability.