Synthesis And Application Of Porous Polymer NHC-Pd Catalyst

Homogenous Palladium catalysts are widely applied in Suzuki-Miyaura coupling reactions because of its efficient catalytic properties. But they suffer from the terrible recoverability, which severely restricts the further development of homogenous Pallddium catalysts. Porous materials provide selective reactant molecules reacting chanel, and its larger surface area can bring more catalytic sites to the catalyst. N-heterocyclic carbenes (NHCs) palladium catalyst in combination with porous materials ensure the comparable catalytic performance to the homogeneous Palladium catalysts, while achieving recycling.1,3,5-triphenyl benzene and adamantane are chosed as core skeletal structures to support NHC-Pd main-chain organometallic polymers named 2-5a and 3-6 respectively.2-5a and 3-6 are used as heterogeneous catalysts to catalysize Suzuki-Miyaura coupling reaction. We can realize the recovering and recycling of catalysts by centrifugation easily in this paper. Details are as follows:First of all,1,3,5-tris (4-iodophenyl) benzene 2-2 was obtained by condensation of three molecules of original material 4-iodo-acetophenone followed by Ullman reaction and quaternized to give quaternary ammonium salt 2-4a, then reacted with Pd(OAc)2 to produce organometallic polymer catalyst 2-5a which was applied to Suzuki-Miyaura coupling reaction. The reaction of Bromoanisole and Phenylboronic acid was chosen as template reaction to optimize conditions, in terms of solvent, temperature, base, amount of catalyst, the reaction gas atmosphere and TBAB additives, Sequentially. The condition of 70 ℃, EtOH, K2CO3,10 mol%of Pd catalyst in air atmosphere was tested as optimum condition. The Suzuki-Miyaura reactions of representative 14 substrates were chosen to test the application of catalyst 2-5a with 37%-98% yield under optimum condition, the catalytic effect was slight lower with 2 cycles.Secondly, We synthesized orgaometallic polymer catalyst 3-6 through the rational route. 1-bromo-adamantane reacted with anhydrous benzene to give the product 1,3,5,7-tetraphenyladamantane 3-2 by Fridel-Crafts alkylation at first. 1,3,5,7-tetrakis(4-(imidazol-1-yl)phenyl)adamantane 3-3 was obtained by the oxidation reaction of 3-2 with [Bis(trifluoroacetoxy)iodo]benzene and reacted imidazole by Ullman reaction, quaternization reaction, coordination reaction with Pd(OAc)2, sequentially. The effect of solvents on the catalyst morphology and effect of morphology on the catalytic properties were also explored.Optimum condition was conducted in accordance with the above process, it is 50℃, H2O/EtOH(v/v,2:1), K2CO3,10 mol% of Pd catalyst in air atmosphere. With the optimum condition, we test the catalyst suitability of different types of substituents with 19 substrates, such as electronic effect, spatial Effects and reactivity with chemical group of -CN,-CH3,-OCH3,-COCH3,-CF3, et al. The yields were 40%-99%, the catalytic effect was slight lower after 4 cycles in Suzuki-Miyaura reaction with 94% yield.Thirdly, every figure of 1H NMR,13C NMR and IR of products consistents with the corresponding structure of matter. The thermal stability, and morphology of catalyst 2-5a and 3-6 were characterized by TGA, SEM, TEM respectively. Two catalysts had good thermal stability, they can be stable at> 300 ℃ and the small particles are irregular, amorphous. The data of XPS shows that Pd(Ⅱ) is present in the catalyst.In summary, two catalysts synthesized can effectively catalyze Suzuki-Miyaura coupling reaction, while the recovery of catalyst can be realised, and good results were achieved, all of the desired design goals were matched.