科研之友
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摘要
The palladium-catalyzed direct arylation of alkylated- furan, thiophene, and thiazole and benzoxazole heterocycles with electronically and sterically deactivated bromoarenes was selectively and efficiently promoted by ferrocenyl polyphosphanes. In this C-H bond activation reaction of heteroaromatics, the performances of polydentate di-, tri-, and tetraphosphane ligands were compared, showing that the triphosphane 1,1',2-tris(diphenylphosphino)-4-tert-butylferrocene 3 was the most effective for the coupling. The introduction of more electron-donating (iPr) or electron-withdrawing (furyl) groups on the phosphorus atoms did not improve the ligand performances. The coordination behavior of 3 towards palladium(II) and other group 10 metals, Ni(II) and Pt(II), was studied and the corresponding 1,2-P chelating phosphorus complexes were isolated in high yields and fully characterized by multinuclear (1)H, (13)C, (31)P NMR (3 center dot PdCl(2), 3 center dot PtCl(2)) and X-ray structures (3 center dot NiBr(2)). It was found that the triphosphane ligand 3 was able to accommodate bidentate chelating cis coordination to group 10 metals, and additionally a much rarely described bis monodentate trans configuration. The combination of these two modes of coordination in a multimetallic species was clearly evidenced for the first time for a ferrocenyl poly-phosphane. This versatility in bonding is a clear difference of 1 coordination potential of this catalytically more efficient triphosphane compared to analogous ferrocenyl di- or tetraphosphanes.
- 出版日期2010-3
