| Summary: | 碩士 === 國立中正大學 === 化學暨生物化學研究所 === 102 === We have successfully synthesized palladium(II) N-heterocyclic carbene (NHC) complexes, [Pd(PPh3)2(Dmim)Cl][PF6] (6), Pd(pyridine)(Dmim)Cl2 (7) and Pd(CN)Cl2 (8) in quantitative yields, where Dmim is 1-decyl-3-methylimidazolium and (C^N) is 3-decyl-1-picolylimidazolin-2-ylidene. A solution of (Dmim)HPF6 (2) in THF was treated with Pd(PPh3)Cl2 at reflux for 4 hr to give NHC-complex, [Pd(PPh3)2(Dmim)Cl][PF6] (6) as white solid. Whereas a solution of (Dmim)HPF6 (2) in pyridine was treated with PdCl2 at 60 oC for 6 hour to afford Pd(pyridine)(Dmim)Cl2 (7) as yellow solid. Similary, a solution of 3-decyl-1-picolylimidazolin-2-ylidene bromide (4) in CH2Cl2 was treated with Ag2O at ambient temperature to afford transfer agent [AgBr(CN)] (5). The complex Pd(CN)Cl2 (8) can be synthesized as yellow solid by the direct reaction of Pd(CH3CN)2Cl2 with [AgBr(CN)] (5). All the complexes 6, 7 and 8 were characterized by NMR, MS and IR spectroscopies. It was found that only the strcucture of Pd(CN)Cl2 (8) is a CN bidentate complex, and both 6 and 7 were 4-coordinated Pd supported by monodentate NHC ligand.
Palladium has been known to exbihit extremely effective catalytic activity, diversity and selectivity than other transition metals. In the current study, we have demonstrated that all three N-heterocyclic carbene-Pd complexes 6, 7 and 8 exhibited excellent catalytic reactivity towards a series Heck-, Strecker-, Stille coupling and N-vinylation of various sulfonamides reactions. For example, only with a catalyst loading of as little as 0.25 mol% 6-catalyzed Heck arylation reactions could be completed in 15 min to give high yields of desired products. All three Pd complexes were also studied for the stereoselectivity in Heck reaction of electron rich olefin. It was found that 7 and 8 are better in control the stereoselectivity by varying the solvent of polarity. In Strecker reactions, with a catalyst loading of 3 mol% of 6, 7 and 8 under solventless conditions can afford high yields of products in 10 min. In Stille reactions, with a catalyst loading of 2 mol% of 6, 7 and 8 at 55 oC for 5 hr gave desired products in high yields (42 – 99 %). In addition, Stille reaction can be further accelerated under microwave irradiation conditions. Finally, in N-vinylation reaction of various sulfonamides, with a catalyst loading of 2 mol% of 6, 7 and 8 at 65 oC afforded products in good yields (64 - 99 %).
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