Synthesis Of Dione-palladium(Ⅱ) Pincer Complexes And Theirs Catalytic Activity In Suzuki And Heck Coupling

Pincer complexes are widely used in organic synthesis and material science. We synthesized three kinds of OCO dicarbonyl ligands 7a-d, 11, 15a-f starting from benzene m-xylene, 5-But-1,3-dibenzoic acid, 1,3-dibenzoic acid and 5-nitro-1,3-dibenzoic acid. Treatment of these ligands with Pd（OAc）₂ in trifluoroacetic acid resulted in the corresponding pincer complexes Pd^Ⅱ-OCO-But（8a-d）, Pd^Ⅱ-OCO-H（12） and Pd^Ⅱ-OCO-NO₂（16a-b, 16e-f） pincer compounds, respectively. The Pd^Ⅱ-OCO pincers（8a-d, 12, 16a-b, 16e-f） and their precursors（7a-d, 11, 15a-f） were all fully characterized by elemental analysis, IR, ¹H NMR, ¹³C NMR spectroscopy. We also disscussed the influence of the electronic and spatial effect of substituent on the formation of the OCO palladium pincer complexes.The applications of OCO palladium pincer complexes as mentioned above in Suzuki and Heck coupling reactions were also studied. The impact of type of pincers（Z=But,H,NO₂） as well as substituent R on the catalytic activities in Suzuki and Heck coupling reactions were investigated. We also assessed different substituent of halo atoms. We optimized the reaction conditions and compared the properties of these three series pincers to find out the best catalyst in Suzuki and Heck coupling reactions. In Suzuki and Heck coupling reaction, when R were the same, there was little effect on the catalytic activities of different pincer complexes. Comparison of substituent effect on the Suzuki and Heck coupling reactions, we found that three series Pd^Ⅱ-OCO pincers with electron donating substituent were best. In the coupling reactions, the bromobenzenes were usually higher coupling yield than those of the chlorobenzenes, which was the same with the energy of C-X bond. A phenomenon was also observed that with the electron-donating groups groups of aryl halides improved lower catalytic yields than those bearing electron-withdrawing. 5-tert-butyl-1,3-bis（4’-methylbenzoyl） benzene palladium（Ⅱ） showed different ultraviolet absorption in different solvents, we comform that it can be used to distinguish solvents.