A Study On Highly Efficient Cross Coupling Reaction Of Terminal Alkynes By Pd-Cu Bimetallic Catalyst

With improvement of people's environmental awareness, green solvents in organic chemistry research is more and more abtracted, and the reports about green chemical reaction are constantly emerging. In this dissertation, the high efficiency cross-coupling reaction of terminal alkynes were studied by using catalyst of two transition metals and green supercritical carbon dioxide solvent. The conditions of cross-coupling reaction were optimized via screening catalysts and alkali additives, and investigating the effect of molar ratio of substrates, reaction temperature, pressure and time on yield. Under the optimized reaction conditions, substrate adaptability was researched, and the reaction mechanism was discussed, and a series of asymmetric 1,3-butadiyne compounds were preparated with high reaction yield.The main works in the dissertation are as follows :1. Screening catalysts of cross-coupling reactionThe screening catalysts such as CuCl₂·2H₂O, CuCl₂, PdCl₂, NiCl₂·6H₂O,Pd?NH₃?4Cl·HH₂O,,PdCl₂/CuCl₂·2H₂O, NiCl₂·6H₂O/CuCl₂·2H₂O, Pd?NH₃?4Cl₂·H₂O/NiCl₂·6H₂O, Pd?NH₃?4Cl₂·H₂O/CuCl₂·2H₂O for cross-coupling reaction of phenyl acetylene and 4-methoxylphenylacetylene ?1: 3? were carried outby using DBU as alkali additive in 5 h at 50? after that 2 MPa O2 and 9 MPa CO2 were pressurized into the stainless steel vessel at room temperature, respectively. The screening results show bimetallic catalyst Pd?NH₃?4Cl₂·H₂O/CUCl₂·2H₂O ?1: 1, 10 mol%? is best with 80% yield.Therefore, the catalyst Pd?NH₃?4Cl₂·H₂O/CuCl₂·2H₂O ?1: 1, 10 mol%? has been optimized for cross-coupling reaction of terminal alkynesin this dissertation.2. Screening alkali additive of cross-coupling reactionThe screening alkali additives such as NaOAc, K2CO3, CS2CO3, NEt3, Pyridine,TMEDA, TBD, DBU for cross-coupling reaction of phenylacetylene and 4-methoxylphenylacetylene ?1: 3? were accomplished by using Pd?NH₃?4Cl₂·H₂O/CuCl₂·2H₂O ?1: 1, 10 mol%? as catalyst in 5 h at 50? after that 2 MPa O2 and 9 MPa CO2 were pressurized into the stainless steel vesselat room temperature, respectively. The screening results show organic base TMEDA ?120 mol%? as alkali additives was best, and 92% yield of cross-coupling reaction products 1 -?4-methoxyphenyl?-4-phenyl-1,3-butadiyne reaction was obtained. Therefore, alkali additives TMEDA ?120 mol%? has been optimized for cross-coupling reaction of terminal alkynesin this dissertation.3. Optimization of cross coupling reaction conditionsThe reaction conditions such as substrate molar ratio,temperature, time, pressure of oxygen and carbon dioxide were inspected in catalytic reaction system of supercritical carbon dioxide as solvent via using Pd?NH₃?4Cl₂·OH₂O/CuCl₂·2H₂O ?1: 1,10 mol%? as catalyst and TMEDA ?120 mol%? as alkali additive. The optimized reaction conditions are1: 2 mole ratio of phenylacetylene and 4-methoxylphenylacetylene, 2 MPa O2, 9 MPa CO2,50? and 4 h. Under the optimized reaction conditions, the yield of products 1-?4-methoxyphenyl?-4-phenyl-1,3-butadiyne is 92% for the cross-coupling reaction. The catalytic reaction system of supercritical carbon dioxideas the solvent optimized in this dissertation is also suitable for the cross coupling reaction of terminal alkynes in organic solvents. Under optimized reaction conditions, the reaction yield could be reached to 82%by using dichloromethane as solvent.4. Substrate scope of the cross coupling reaction under optimized conditionsUnder the optimized reaction conditions, the substrate scope of terminal alkyne cross-coupling reaction was investigated. The results show that the substrate scope is wide in the optimized catalytic reaction system using supercritical carbon dioxide as the solvent,of which is suitable not only for liquid alkynes, and also for solid alkynes like ferroceneacetylene. Besides the terminal alkynes containing alkyl unit ?69%? and thienyl unit ?74%? with lower yields, the yields of other terminal alkynes are higher in the catalytic reaction system of supercritical carbon dioxide optimized in this dissertation, and the yields of cross coupling reaction can reach above 80% in the catalytic system.The catalytic reaction system of supercritical carbon dioxide optimized in this dissertation is not suited to pyridineacetylene and cyclopropylacetylene because of the effect of alkaline from pyridineacetylene and easy gasification of cyclopropylacetylene with lower boiling point.5. Deduction of cross-coupling reaction mechanismThe reaction mechanism of bimetallic palladium copper composite catalyst was superficially studied in this dissertation. The intermediates and the reaction mechanism of cross coupling reaction catalyzed by bimetallic catalyst and the phase change were studied using FTIR, NMR, free radical inhibitors, ammonium salt catalyst with copper complex anion and visual stainless steel vessel of supercritical carbon dioxide. Based on the literature and our research results, the mechanism of cross coupling reaction catalyzed by bimetallic palladium copper is deduced.6. Characterization of cross-coupling reaction productThe composition and molecular structure of the cross coupling reaction products for all experimental substrates were confirmed by FTIR, NMR and MS.