Catalytic C鈥揝 Cross-Coupling Reactions Employing Ni Complexes of Pyrrole-Based Pincer Ligands
详细信息 查看全文
- 作者：Gopaladasu T. Venkanna ; Hadi D. Arman ; Zachary J. Tonzetich
- 刊名：ACS Catalysis
- 出版年：2014
- 出版时间：September 5, 2014
- 年：2014
- 卷：4
- 期：9
- 页码：2941-2950
- 全文大小：504K
- ISSN：2155-5435
文摘
A series of catalytic C鈥揝 coupling reactions utilizing well-defined Ni(II) PNP pincer complexes as precatalysts are reported (PNP = anion of 2,5-bis[(dialkyl/aryl-phosphino)methyl]pyrrole, abbreviated as P2RPyr). Coupling reactions employing a variety of aryl iodides and thiols in the presence of base and DMF proceed in good to excellent yield at 80 掳C with low catalyst loadings. Aryl bromides were found to result in substantially lower yields, and aryl chlorides were found to be unreactive under the catalytic conditions. In an effort to further understand the reactivity of the nickel PNP precatalysts, complexes of Ni(II) containing amide, alkoxide, hydroxide, thiolate, and hydrosulfide ligands have been prepared and examined in stoichiometric reactions relevant to carbon-heteroatom coupling. Full characterization of each nickel complex is provided, including solid-state structures. The results of stoichiometric reactions implicate a reduced Ni(I) species as the active catalyst, which forms by reduction of the Ni(II) precatalyst in the presence of excess thiolate. The facility in forming Ni(I) species is invoked to rationalize the observed activity among different Ni PNP precatalysts.