Synthesis and Characterization of [Cu(NHC)<sub>2</sub>]X Complexes: Catalytic and Mechanistic Studies of Hydrosilylation Reactions
作者:Silvia Díez-González、Edwin D. Stevens、Natalie M. Scott、Jeffrey L. Petersen、Steven P. Nolan
DOI:10.1002/chem.200701013
日期:2008.1
when compared with related [Cu(NHC)]-based systems, these cationic complexes proved to be more efficient under similar reaction conditions. The activation step of [Cu(NHC)2]X precatalysts towards hydrosilylation was investigated by means of 1H NMR spectroscopy. Notably, it was shown that one of the N,N'-bis(2,6-diisopropylphenyl)imidazol-2-ylidene (IPr) ligands in [Cu(IPr)2]BF4 is displaced by tBuO(-)
据报道,从容易获得的材料中以高收率制备了两个系列的[Cu(NHC)2] X络合物(NHC = N-杂环卡宾,X = PF6或BF4)。这些配合物已经在光谱和结构上进行了表征。检查了这些阳离子双-NHC络合物在酮的氢化硅烷化中的活性,并且配体和抗衡离子均显示出对催化性能的显着影响。此外,当与相关的基于[Cu(NHC)]的系统进行比较时,这些阳离子配合物在相似的反应条件下被证明是更有效的。通过1H NMR光谱研究了[Cu(NHC)2] X预催化剂向氢化硅烷化的活化步骤。值得注意的是,它表明N,N'-bis(2 [Cu(IPr)2] BF4中的6-二异丙基苯基)咪唑-2-亚烷基(IPr)配体在NaOtBu存在下被tBuO(-)取代,生成中性[Cu(IPr)(OtBu)]。已知该醇铜是NHC-铜氢化物的直接前体,NHC-铜氢化物是该转化中的实际活性物质。此外,已经根据反应过程中形成的物质合理化了试剂的装载量和抗衡离子的作用。