Hong Yan

Publications (3)9.87 Total impact

• Source

  Available from: Prinessa Chellan

  Dataset: Cyclometallated Pd(II) thiosemicarbazone complexes: new catalyst precursors for Suzuki-coupling reactions

  Hong Yan, Prinessa Chellan, Tingyi Li, Jincheng Mao, Kelly Chibale, Gregory S Smith
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  ABSTRACT: a b s t r a c t Four tridentate [C,N,S] thiosemicarbazone Pd(II) complexes were applied as catalyst precursors for the Suzuki–Miyaura coupling of a variety of aryl halides and aryl boronic acids. After screening various cat-alytic conditions, it was found that one dinuclear complex IV containing the bis(diphenylphosphino) fer-rocene spacer was able to efficiently catalyze these reactions with yields up to 99% irrespective of the type of aryl substituent on the substrate. Cross-coupling reactions are a set of palladium catalyzed reac-tions that are an essential synthetic tool. The most well-known and widely used cross-coupling reactions are the Heck, Stille, Suzu-ki, Negishi, and Buchwald–Hartwig cross-couplings. 1,2 These types of reactions have proven useful for the syntheses of polymers, 3,4 natural products, 5 agrochemicals, 6,7 and pharmaceuticals. 8,9 Thus, the search for a metal complex which can catalyze these types of reactions efficiently while maintaining high chemo-and regio-selectivities and recyclability is an ongoing process. In cross-coupling reactions, palladium(II) complexes are gener-ally used as catalyst precursors from which the active Pd(0) species is generated in situ. One disadvantage of the current catalyst sys-tems used is that the metal complex sometimes undergoes decom-position during the reaction leading to poor recyclability of the metal complex as well as impurities in the products making the process a costly one. 10 Thiosemicarbazones are widely known for their metal chelating abilities to a large variety of metals. 11 These compounds can be classified as hybrid ligands as they are capable of acting as bi-or multidentate ligands through several donor atoms. 12 Studies into the biological applications of thiosemicarbazone metal complexes are prolific. Research into their role in catalysis however, is still a relatively new area of interest. One of the earliest reports of their catalytic abilities was published in 1998 by Pelagatti and co-workers; they found that tridentate [N,N,S] thiosemicarbazone palladium(II) complexes were able to catalyze chemoselective homogenous hydrogenation reactions. 13 More recently, a cyclo-metallated ruthenium(II) thiosemicarbazone complex was used for the catalytic transfer hydrogenation of substituted ketones with high efficiency. 14 Moderate activities were also observed for the Suzuki–Miyaura coupling of aryl halides and phenylboronic acids using tridentate [S,N,O] Ni(II) thiosemicarbazones. 15 Tridentate pincer-type Pd(II) complexes are known to effi-ciently catalyze carbon–carbon coupling reactions. 16–19 Tridentate thiosemicarbazone Pd(II) complexes may exhibit a similar behav-ior. The thiosemicarbazone ligand occupies three of the four coor-dination sites available on the metal and this may restrict how the olefinic or organo-halide substrates coordinate with the metal thus influencing the selectivity of the catalyst. These complexes are also known to exhibit high thermal stability, both in the solid state and in solution, making them good candidates for high temperature homogenous catalysis. Within our group, we have investigated the synthesis and application of tridentate [O,N,S] Pd(II) thiosemi-carbazone complexes as anticancer and antimalarial agents. 20–22 To demonstrate the versatility of these complexes, we have also studied their catalytic activity as catalyst precursors for the Mizor-oki–Heck coupling reaction and have recently published some of our findings. 23 These promising results along with our previous re-search on various cross-coupling reactions 24 have prompted us to extend our catalytic studies of Pd(II) thiosemicarbazones to triden-tate [C,N,S] systems prepared by C–H activation of the thiosemicar-bazone aryl ortho-carbon. In this Letter we report the preliminary
• Article: Copper-catalyzed decarboxylative C(sp2)-C(sp3) coupling reactions via radical mechanism.

  Hailong Yang, Peng Sun, Yan Zhu, Hong Yan, Linhua Lu, Xiaoming Qu, Tingyi Li, Jincheng Mao
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  ABSTRACT: We have successfully developed an example of copper-catalyzed decarboxylative C(sp(2))-C(sp(3)) coupling reactions via C-H functionalization for the first time. It is noteworthy that our catalytic system is very stable, low-cost, palladium-free, ligand-free, and easily accessible.
  Chemical Communications 07/2012; 48(63):7847-9. · 6.17 Impact Factor
• Article: The ligand and base-free Pd-catalyzed oxidative Heck reaction of arylboronic acids and olefins.

  Peng Sun, Yan Zhu, Hailong Yang, Hong Yan, Linhua Lu, Xiang Zhang, Jincheng Mao
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  ABSTRACT: Highly effective Pd-catalyzed Heck-type oxidative couplings between arylboronic acids and terminal olefins were reported. It is noteworthy that such reactions could be carried out in the absence of the base and the ligand.
  Organic & Biomolecular Chemistry 05/2012; 10(23):4512-5. · 3.70 Impact Factor