Studies On The Pyrazolyl PCN-Palladium Pincer Complex Synthesis And Catalytic Application In Allylation Of Aldehydes

We have developed a facile, direct method based on the one pot phosphorylation/palladation reaction for the preparation of unsymmetrical PCN pincer palladium complexes. According to this method, two new PCN pincer palladium complexes 2a-2b were synthesized. The structure of the new compounds was characterized and applied to the allylation of aldehydes. The main contents are as follows:1. The synthesis of Unsymmetrical PCN pincer palladium complexesThe new compounds 1 were prepared from commercially available m-phthalaldehyde in four steps by reduction of aldehyde group, bromination and nucleophilic substitution with 3,5-dimethyl pyrazole. Then compound 1 reacted with diphenylchlorophosphine or ditertbutylchlorophosphine in the presence of triethylamine in refluxing toluene, followed by the addition of palladium chloride. Two new PCN pincer palladium complexes 2a-b were successfully isolated after purification. All the new compounds were characterized by elemental analysis, IR,1H NMR, 13C NMR,31P NMR and MS spectra. All the new compounds were characterized by elemental analysis, IR,1H NMR,13C NMR,31P NMR and MS (ESI) spectra. The molecular structures of 2b were further confirmed by single-crystal X-ray analysis. 2. The application of Unsymmetrical PCN pincer palladium compounds as catalysts in the Allylation of Aldehydes.The PCN pincer palladium compounds was used as the catalysts in the allylation of aldehydes. The catalysts, reaction temperature, solvent and other conditions were screened. Under nitrogen atmosphere, DMF as solvent,2.5 mol%catalyst 3,50℃for 24h were the optimal conditions,96.7%was obtained.